Abstracts
The objective of this study was to evaluate the influence of enriched environment on spatial memory acquisition in mice of three different age groups. Weanling, young, and young adult female Swiss mice were housed in a standard control or enriched environment for 50 days, and their spatial memory was tested with the Morris Water Maze. We did not observe an experimental effect for spatial memory acquisition, and there was neither an effect of time of analysis nor an interaction between experimental group and time of analysis. Regarding effects of experimental group and training day in relation to latency in finding the hidden platform, we did find an effect in the experimental young adult mice group (p = 0.027), but there was no interaction between these factors in all three groups. Based on these findings environmental enrichment did not enhance spatial memory acquisition in female Swiss mice in the tested age groups.
mice; memory; spatial behavior; hippocampus
O objetivo deste estudo foi avaliar a influência do ambiente enriquecido na aquisição da memória espacial de camundongos em três diferentes faixas etárias. Camundongos fêmeas Swiss recém-desmamados, jovens e adultos jovens foram alojados em ambiente controle ou em ambiente enriquecido durante 50 dias, e sua memória espacial foi testada por meio do Labirinto Aquático de Morris. Não houve efeito do grupo experimental na aquisição de memória espacial, do momento de análise, tampouco da interação entre o grupo experimental e o momento de análise. Quanto aos efeitos do grupo experimental e do dia de treino em relação à latência para encontrar a plataforma escondida, houve efeito do grupo experimental apenas para o grupo experimental adulto jovem (p = 0,027), com menor latência do grupo controle, porém sem interação entre esses fatores para todos os grupos. O enriquecimento ambiental não interferiu na aquisição de memória espacial de camundongos fêmeas Swiss nas faixas etárias analisadas.
camundongos; memória; comportamento espacial; hipocampo
The increase in life expectancy has been influenced by strategies to minimize aging’s
effects on memory by means of animal models such as mice. Enriched environment (EE)
rearing is one of those strategies; in this paradigm, mice live in conditions that
facilitate sensorial, visual, cognitive, and motor stimulation11 .Nithianantharajah J, Hannan AJ. Enriched environments,
experience-dependent plasticity and disorders of the nervous system. Nat Rev
Neurosci. 2006;7(9):697-709. http://dx.doi.org/10.1038/nrn1970
https://doi.org/10.1038/nrn1970...
. Cognitive stimuli including spatial complexity,
novelty, and physical activity affect brain plasticity. In turn, brain plasticity
promotes hippocampal neurogenesis22 .Kempermann G, Faber K, Ehninger D, Babu H, Leal-Galicia P, Garthe A
et al. Why and how physical activity promotes experience-induced brain
plasticity. Front Neurosci. 2010;4:189.
http://dx.doi.org/10.3389/fnins.2010.00189
https://doi.org/10.3389/fnins.2010.00189...
and
consequently positively influences spatial memory, a hippocampal-dependent process that
decreases with aging33 .Heo S, Prakash RS, Voss MW, Erickson KI, Ouyang C, Sutton BP et al.
Resting hippocampal blood flow, spatial memory and aging. Brain Res.
2010;1315:119-27.
http://dx.doi.org/10.1016/j.brainres.2009.12.020
https://doi.org/10.1016/j.brainres.2009....
,44 .Foster TC, DeFazio RA, Bizon JL. Characterizing cognitive aging of
spatial and contextual memory in animal models. Front Aging Neurosci. 2012;4:12.
http://dx.doi.org/10.3389/fnagi.2012.00012
https://doi.org/10.3389/fnagi.2012.00012...
. However, EE can also produce negative
results or no effect, depending on the resources used for enrichment, variables studied,
animal strain used, and environmental enrichment duration55 .Tsai PP, Pachowsky U, Stelzer HD, Hackbarth H. Impact of
environmental enrichment in mice. 1: effect of housing conditions on body
weight, organ weights and haematology in different strains. Lab Anim.
2002;36(4):411-9. http://dx.doi.org/10.1258/002367702320389071
https://doi.org/10.1258/0023677023203890...
.
Some studies have evaluated the effects of environmental enrichment on spatial memory by
using different age groups of mice in the same research66 .Frick KM, Stearns NA, Pan JY, Berger-Sweeney J. Effects of
environmental enrichment on spatial memory and neurochemistry in middle-aged
mice. Learn Mem. 2003;10(3):187-98.
http://dx.doi.org/10.1101/lm.50703
https://doi.org/10.1101/lm.50703...
,77 .Harburger LL, Lambert TJ, Frick KM. Age-dependent effects of
environmental enrichment on spatial reference memory in male mice. Behav Brain
Res. 2007;185(1):43-8.
http://dx.doi.org/10.1016/j.bbr.2007.07.009
https://doi.org/10.1016/j.bbr.2007.07.00...
,88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
,99 .Gresack JE, Kerr KM, Frick KM. Life-long environmental enrichment
differentially affects the mnemonic response to estrogen in young, middle-aged,
and aged female mice. Neurobiol Learn Mem. 2007;88(4):393-408.
http://dx.doi.org/10.1016/j.nlm.2007.07.015
https://doi.org/10.1016/j.nlm.2007.07.01...
,1010 .Diniz DG, Foro CA, Rego CMD, Gloria DA, Oliveira FR, Paes JM et al.
Environmental impoverishment and aging alter object recognition, spatial
learning, and dentate gyrus astrocytes. Eur J Neurosci. 2010;32(3):509-19.
http://dx.doi.org/10.1111/j.1460-9568.2010.07296.x
https://doi.org/10.1111/j.1460-9568.2010...
, with housing periods similar to that used here66 .Frick KM, Stearns NA, Pan JY, Berger-Sweeney J. Effects of
environmental enrichment on spatial memory and neurochemistry in middle-aged
mice. Learn Mem. 2003;10(3):187-98.
http://dx.doi.org/10.1101/lm.50703
https://doi.org/10.1101/lm.50703...
,77 .Harburger LL, Lambert TJ, Frick KM. Age-dependent effects of
environmental enrichment on spatial reference memory in male mice. Behav Brain
Res. 2007;185(1):43-8.
http://dx.doi.org/10.1016/j.bbr.2007.07.009
https://doi.org/10.1016/j.bbr.2007.07.00...
,88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
. However, the majority of these studies have only evaluated
mice from young ages to middle age and senescence, when memory impairment has already
started. Improvements in spatial memory were only observed in middle-aged66 .Frick KM, Stearns NA, Pan JY, Berger-Sweeney J. Effects of
environmental enrichment on spatial memory and neurochemistry in middle-aged
mice. Learn Mem. 2003;10(3):187-98.
http://dx.doi.org/10.1101/lm.50703
https://doi.org/10.1101/lm.50703...
,88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
and aged mice77 .Harburger LL, Lambert TJ, Frick KM. Age-dependent effects of
environmental enrichment on spatial reference memory in male mice. Behav Brain
Res. 2007;185(1):43-8.
http://dx.doi.org/10.1016/j.bbr.2007.07.009
https://doi.org/10.1016/j.bbr.2007.07.00...
in those studies. In this research, we opted to submit
weanling, young, and young adult female mice to EE with the intention of evaluating
whether EE influences spatial memory acquisition prior to the onset of memory impairment
and determining if there is an interaction between EE and the age during EE.
METHOD
Animals
Forty-seven female Swiss mice from three different age groups: weanling (21 days), young (3 months) and young adult (7 months) were used. These animals were supplied by the Central Vivarium of the Universidade Federal de Mato Grosso do Sul, and the study was conducted there. The animals were randomly housed in a standard control environment (CE) or EE, as follows: weanling CE (n = 8), weanling EE (n = 8), young CE (n = 8), young EE (n = 8), young adult CE (n = 7), and young adult EE (n = 8). The CE and EE groups were both housed for 50 days. This research was approved by the Animal Use Ethics Committee of the Universidade Federal de Mato Grosso do Sul (protocol nº 336/2011).
Procedures
EE and CE
The CE consisted of a standard rodent box (31 cm wide, 39 cm long, and 18 cm
high) lined with shavings, and food and water were available ad
libitum. The EE was an ample metallic cage with two levels (60
cm wide, 81 cm long, and 46 cm high) containing two sets of stairs for
second-level access (where water and food were available ad
libitum)1010 .Diniz DG, Foro CA, Rego CMD, Gloria DA, Oliveira FR, Paes JM et al.
Environmental impoverishment and aging alter object recognition, spatial
learning, and dentate gyrus astrocytes. Eur J Neurosci. 2010;32(3):509-19.
http://dx.doi.org/10.1111/j.1460-9568.2010.07296.x
https://doi.org/10.1111/j.1460-9568.2010...
,1111 .Santos AF. Influência do enriquecimento ambiental na aquisição,
retenção e evocação da memória espacial em duas linhagens de camundongos
[dissertação]. Campo Grande: Universidade Católica Dom Bosco;
2009., three catwalks, one running wheel, and one
trampoline. The lower level was lined with shavings.
The cage was also supplied with toys commercially available for children,
tunnels, and nesting material (paper). The toys and nesting materials were
changed two times per week during cage cleaning1111 .Santos AF. Influência do enriquecimento ambiental na aquisição,
retenção e evocação da memória espacial em duas linhagens de camundongos
[dissertação]. Campo Grande: Universidade Católica Dom Bosco;
2009.,1212 .Kulesskaya N, Rauvala H, Voikar V. Evaluation of social and
physical enrichment in modulation of behavioural phenotype in C57BL/6J female
mice. PLoS ONE. 2011;6(9):e24755.
http://dx.doi.org/10.1371/journal.pone.0024755
https://doi.org/10.1371/journal.pone.002...
. Approximately 10 to 15 different objects
were placed, along with 4 paper sheets or crumbled pieces of nesting
material in every change. The light cycle was controlled under a 12-hour
light/dark cycle, and the temperature was maintained at 21 ± 3ºC.
Morris water maze
The Morris Water Maze (MWM)1313 .Morris R. Spatial localization does not require the presence of
local cues. Learn Motiv. 1981;12:239-60.
http://dx.doi.org/10.1016/0023-9690(81)90020-5
https://doi.org/10.1016/0023-9690(81)900...
was a black polyethylene circular tank adapted for
mouse dimensions (101 cm diameter and 53 cm high) that was filled with room
temperature water (21 ± 3ºC) before training sessions. This tank was
virtually subdivided into four quadrants. A black platform was attached in
one of the quadrants (11 cm diameter and 19.5 cm high), with the superior
part located ~1 cm below the water surface (hidden from the mouse’s view),
and its location remained the same during all training days and final
tests1111 .Santos AF. Influência do enriquecimento ambiental na aquisição,
retenção e evocação da memória espacial em duas linhagens de camundongos
[dissertação]. Campo Grande: Universidade Católica Dom Bosco;
2009.. The platform
had a rough surface that allowed the mice to easily climb onto it once its
presence was detected. On the internal walls of the tank, above the water
and on all four quadrants, images were fixed to serve as spatial reference
points.
Spatial memory task
To test spatial memory in the MWM, we used an adapted protocol comprised of
three training trials per day over 5 consecutive days, with an inter-trial
interval of 30 seconds1111 .Santos AF. Influência do enriquecimento ambiental na aquisição,
retenção e evocação da memória espacial em duas linhagens de camundongos
[dissertação]. Campo Grande: Universidade Católica Dom Bosco;
2009.,1414 .Rossato JI, Bevilaqua LRM, Medina JH, Izquierdo I, Cammarota M.
Retrieval induces hippocampal-dependent reconsolidation of spatial memory. Learn
Mem. 2006;13(4):431-40. http://dx.doi.org/10.1101/lm.315206
https://doi.org/10.1101/lm.315206...
. The training trial was performed beginning on
the 40th day of housing. The final spatial memory test, performed
to verify acquisition of spatial memory after training, was on the
50th day of housing, 4 days after training trials had
finished. It was conducted in three series with an inter-series interval of
30 seconds1111 .Santos AF. Influência do enriquecimento ambiental na aquisição,
retenção e evocação da memória espacial em duas linhagens de camundongos
[dissertação]. Campo Grande: Universidade Católica Dom Bosco;
2009..
During the training trials and final test, mice were individually placed in
one of three randomly chosen quadrants (except the hidden platform one),
facing the border of the tank. Each mouse had 90 seconds to find the hidden
platform in each training trial and in each series of the final test. If the
mouse could not find it, it was manually placed on the platform by the
examiner, where it stayed for 30 seconds1010 .Diniz DG, Foro CA, Rego CMD, Gloria DA, Oliveira FR, Paes JM et al.
Environmental impoverishment and aging alter object recognition, spatial
learning, and dentate gyrus astrocytes. Eur J Neurosci. 2010;32(3):509-19.
http://dx.doi.org/10.1111/j.1460-9568.2010.07296.x
https://doi.org/10.1111/j.1460-9568.2010...
,1111 .Santos AF. Influência do enriquecimento ambiental na aquisição,
retenção e evocação da memória espacial em duas linhagens de camundongos
[dissertação]. Campo Grande: Universidade Católica Dom Bosco;
2009.. Afterward, the animal was placed into a
standard rodent box, where it rested for 30 seconds, and then returned to
the tank, if it had not yet completed the third trial/series. The task was
considered complete when animals found and climbed onto the platform. The
training trials and test series were conducted by two examiners; one placed
and removed the animals from the tank, and the other measured the latency
period to find the hidden platform and recorded the data. The latency period
to find the hidden platform was measured by a digital chronometer1111 .Santos AF. Influência do enriquecimento ambiental na aquisição,
retenção e evocação da memória espacial em duas linhagens de camundongos
[dissertação]. Campo Grande: Universidade Católica Dom Bosco;
2009. in each training trial
and test series. Immediately after completing the three training trials, the
animals were removed from the platform, dried with a cloth towel, and warmed
by an incandescent lamp placed over a standard rodent box, before they were
returned to their respective cages. All training and tests were performed
during the light phase of the light/dark period. The animals were euthanized
after they completed the final spatial memory task.
Statistical analysis
Evaluations of the experimental group effect, animal’s age effect, and the interaction between these factors in relation to the latency period to find the hidden platform in the MWM and on the final test were performed by means of two-way variance analysis (ANOVA). Evaluations of the experimental group effect, training day effect, and the interaction between these factors in relation to the latency period to find the hidden platform in the MWM were performed by means of two-way repeated measure ANOVA and Tukey’s post-hoc testing between groups. We used SigmaStat software (version 3.5), considering a significance level of 5%. All data are presented as mean ± standard error of mean.
RESULTS
There was no experimental group effect regarding the latency period to find the MWM hidden platform on the final test day. That is, independent of animal age, there was no difference between the CE and EE groups (p = 0.471). There was also no effect concerning the age animals were housed (p = 0.341) and there was no interaction between these variables (p = 0.590, Figure 1 and Table 1).
Latency period to find the hidden platform for the control and enriched environments between weanling, young, and young adult mice on the day of the memory test after 4 days of training. The columns and bars represent the means and standard errors of means.
For weanling animals, there was no experimental group effect (p = 0.481) or training day effect (p = 0.448). There was also no interaction between the experimental groups and training days in relation to the latency period to find the hidden platform (p = 0.827, Figure 2). The same result was observed for young animals (p = 0.301, p = 0.053, and p = 0.941, respectively; Figure 3). Regarding young adult animals, there was an experimental group effect (p = 0.027); however there was neither a training day effect (p = 0.846) nor an interaction between the experimental group and training days in relation to the latency period to find the hidden platform (p = 1.000, Figure 4). Regarding the group effect of young adult animals, the latency period of CE animals was significantly lower than that measured in the EE group animals on general training days (Tukey’s post-hoc, p < 0.05). The latencies to find the hidden platform on each training day are presented in Table 2.
Latency period to find the hidden platform for the weanling control and enriched groups according to the training days. The symbols and bars represent the means and standard errors of means.
Latency period to find the hidden platform for the young control and enriched groups according to the training days. The symbols and bars represent the means and standard errors of means.
Latency period to find the hidden platform for the young adult control and enriched groups according to the training days. The symbols and bars represent the means and standard errors of means.
DISCUSSION
EE has been widely studied to evaluate whether it can stave off memory declines related to age. Here, we investigated the influence of EE on spatial memory in weanling, young, and young adult female Swiss mice. We did not observe statistically significant alterations of spatial memory in the EE groups relative to the controls or among the age groups in the final spatial memory test. Regarding MWM training trials before spatial memory testing, although there was an experimental group effect for young adult mice (lower latency period of the control group to find the hidden platform), there was no statistical significance for this interaction in the final spatial memory test.
Studies evaluating the ability of EE to prevent age-related memory decline in mice
have reported contradictory results. While some found significant positive effects
on spatial memory only in aged mice77 .Harburger LL, Lambert TJ, Frick KM. Age-dependent effects of
environmental enrichment on spatial reference memory in male mice. Behav Brain
Res. 2007;185(1):43-8.
http://dx.doi.org/10.1016/j.bbr.2007.07.009
https://doi.org/10.1016/j.bbr.2007.07.00...
, other studies also demonstrated such effects in
middle-aged mice66 .Frick KM, Stearns NA, Pan JY, Berger-Sweeney J. Effects of
environmental enrichment on spatial memory and neurochemistry in middle-aged
mice. Learn Mem. 2003;10(3):187-98.
http://dx.doi.org/10.1101/lm.50703
https://doi.org/10.1101/lm.50703...
. Still, some
studies have reported improvement on spatial task execution by both young and young
adult mice groups88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
,99 .Gresack JE, Kerr KM, Frick KM. Life-long environmental enrichment
differentially affects the mnemonic response to estrogen in young, middle-aged,
and aged female mice. Neurobiol Learn Mem. 2007;88(4):393-408.
http://dx.doi.org/10.1016/j.nlm.2007.07.015
https://doi.org/10.1016/j.nlm.2007.07.01...
,1010 .Diniz DG, Foro CA, Rego CMD, Gloria DA, Oliveira FR, Paes JM et al.
Environmental impoverishment and aging alter object recognition, spatial
learning, and dentate gyrus astrocytes. Eur J Neurosci. 2010;32(3):509-19.
http://dx.doi.org/10.1111/j.1460-9568.2010.07296.x
https://doi.org/10.1111/j.1460-9568.2010...
,1212 .Kulesskaya N, Rauvala H, Voikar V. Evaluation of social and
physical enrichment in modulation of behavioural phenotype in C57BL/6J female
mice. PLoS ONE. 2011;6(9):e24755.
http://dx.doi.org/10.1371/journal.pone.0024755
https://doi.org/10.1371/journal.pone.002...
. However, studies conducted with mice in age groups
similar to those used here did not find significant results for spatial memory
tasks77 .Harburger LL, Lambert TJ, Frick KM. Age-dependent effects of
environmental enrichment on spatial reference memory in male mice. Behav Brain
Res. 2007;185(1):43-8.
http://dx.doi.org/10.1016/j.bbr.2007.07.009
https://doi.org/10.1016/j.bbr.2007.07.00...
,88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
,1515 .Prusky GT, Reidel C, Douglas RM. Environmental enrichment from
birth enhances visual acuity but not place learning in mice. Behav Brain Res.
2000;114(1-2):11-5.
http://dx.doi.org/10.1016/S0166-4328(00)00186-8
https://doi.org/10.1016/S0166-4328(00)00...
.
EE duration seems to influence the magnitude of behavior effects in mice, as do the
age when they are housed1616 .Amaral OB, Vargas RS, Hansel G, Izquierdo I, Souza DO. Duration of
environmental enrichment influences the magnitude and persistence of its
behavioral effects on mice. Physiol Behav. 2008;93(1-2):388-94.
http://dx.doi.org/10.1016/j.physbeh.2007.09.009
https://doi.org/10.1016/j.physbeh.2007.0...
and the
EE protocols used1717 .Simpson J, Kelly JP. The impact of environmental enrichment in
laboratory rats: behavioural and neurochemical aspects. Behav Brain Res.
2011;222(1):246-64. http://dx.doi.org/10.1016/j.bbr.2011.04.002
https://doi.org/10.1016/j.bbr.2011.04.00...
. A long
duration EE is associated with higher habituation to novelty and hippocampal
neurogenesis in mice1818 .Kempermann G, Gage FH. Experience-dependent regulation of adult
hippocampal neurogenesis: effects of long-term stimulation and stimulus
withdrawal. Hippocampus. 1999;9(3):321-32.
http://dx.doi.org/10.1002/(SICI)1098-1063(1999)9:3<321::AID-HIPO11>3.0.CO;2-C
https://doi.org/10.1002/(SICI)1098-1063(...
. Despite
this fact, there is considerable variation among studies in relation to housing
periods in different studies. We hypothesized that a 7-week housing period would be
sufficient to improve spatial memory in weanling, young, and young adult mice.
Nevertheless, we did not obtain significant results, which is in accordance with
studies that used similar housing periods (from six to eight weeks) and complex EE
protocols (cognitive and physical stimulation and social interaction)77 .Harburger LL, Lambert TJ, Frick KM. Age-dependent effects of
environmental enrichment on spatial reference memory in male mice. Behav Brain
Res. 2007;185(1):43-8.
http://dx.doi.org/10.1016/j.bbr.2007.07.009
https://doi.org/10.1016/j.bbr.2007.07.00...
,88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
,1515 .Prusky GT, Reidel C, Douglas RM. Environmental enrichment from
birth enhances visual acuity but not place learning in mice. Behav Brain Res.
2000;114(1-2):11-5.
http://dx.doi.org/10.1016/S0166-4328(00)00186-8
https://doi.org/10.1016/S0166-4328(00)00...
. On the other hand, those studies with significant
results in relation to spatial memory, despite using similar enrichment protocols,
maintained the EE for longer periods, from 2 to 21 months99 .Gresack JE, Kerr KM, Frick KM. Life-long environmental enrichment
differentially affects the mnemonic response to estrogen in young, middle-aged,
and aged female mice. Neurobiol Learn Mem. 2007;88(4):393-408.
http://dx.doi.org/10.1016/j.nlm.2007.07.015
https://doi.org/10.1016/j.nlm.2007.07.01...
,1010 .Diniz DG, Foro CA, Rego CMD, Gloria DA, Oliveira FR, Paes JM et al.
Environmental impoverishment and aging alter object recognition, spatial
learning, and dentate gyrus astrocytes. Eur J Neurosci. 2010;32(3):509-19.
http://dx.doi.org/10.1111/j.1460-9568.2010.07296.x
https://doi.org/10.1111/j.1460-9568.2010...
,1212 .Kulesskaya N, Rauvala H, Voikar V. Evaluation of social and
physical enrichment in modulation of behavioural phenotype in C57BL/6J female
mice. PLoS ONE. 2011;6(9):e24755.
http://dx.doi.org/10.1371/journal.pone.0024755
https://doi.org/10.1371/journal.pone.002...
. Some of the groups that reported significant results
with an EE period and enrichment protocol similar to this study66 .Frick KM, Stearns NA, Pan JY, Berger-Sweeney J. Effects of
environmental enrichment on spatial memory and neurochemistry in middle-aged
mice. Learn Mem. 2003;10(3):187-98.
http://dx.doi.org/10.1101/lm.50703
https://doi.org/10.1101/lm.50703...
,77 .Harburger LL, Lambert TJ, Frick KM. Age-dependent effects of
environmental enrichment on spatial reference memory in male mice. Behav Brain
Res. 2007;185(1):43-8.
http://dx.doi.org/10.1016/j.bbr.2007.07.009
https://doi.org/10.1016/j.bbr.2007.07.00...
,88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
evaluated middle-aged and aged mice. This might explain the
discrepant result; effects might not be seen until memory decline begins around
middle age1919 .Frick KM, Burlingame LA, Arters JA, Berger-Sweeney J. Reference
memory, anxiety and estrous cyclicity in C57BL/6NIA mice are affected by age and
sex. Neuroscience. 2000;95(1):293-307.
http://dx.doi.org/10.1016/S0306-4522(99)00418-2
https://doi.org/10.1016/S0306-4522(99)00...
.
In addition to EE protocols, considering each species or strains’ behavior is
necessary when designing studies. Due to their natural tendency to dig and build
nests2020 .Hutchinson EK, Avery AC, Vandewoude S. Environmental enrichment for
laboratory rodents. ILAR J. 2005;46(2):148-61.
http://dx.doi.org/10.1093/ilar.46.2.148
https://doi.org/10.1093/ilar.46.2.148...
, mice prefer nesting
materials over any others2121 .Olsson IA, Dahlborn K. Improving housing conditions for laboratory
mice: a rewiew of “environmental enrichment”. Lab Anim. 2002;36(3):243-70.
http://dx.doi.org/10.1258/002367702320162379
https://doi.org/10.1258/0023677023201623...
. This
explains the different results between our study and that of Kulesskaya et al.1212 .Kulesskaya N, Rauvala H, Voikar V. Evaluation of social and
physical enrichment in modulation of behavioural phenotype in C57BL/6J female
mice. PLoS ONE. 2011;6(9):e24755.
http://dx.doi.org/10.1371/journal.pone.0024755
https://doi.org/10.1371/journal.pone.002...
, who found better MWM performance
for enriched weanling mice using only nesting material as an enrichment strategy.
However, complex enrichment applied over brief periods seems to benefit mice
starting only at middle age88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
when
memory decline begins. Nevertheless, physical stimulation seems to benefit spatial
memory at ages when there is still no memory impairment2222 .Mello PB, Benetti F, Cammarota M, Izquierdo I. Effects of acute and
chronic exercise and stress on different types of memory in rats. An Acad Bras
Cienc. 2008;80(2):301-9., likely by promoting changes in glial cells
involved in synaptic remodeling and affecting brain plasticity2323 .Bernardi C, Tramontina AC, Nardin P, et al. Treadmill exercise
induces hippocampal astroglial alterations in rats. Neural Plast.
2013(2013):id709732. http://dx.doi.org/10.1155/2013/709732
https://doi.org/10.1155/2013/709732...
. Studies that used more than one running wheel in
their EE protocol reported positive results88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
,99 .Gresack JE, Kerr KM, Frick KM. Life-long environmental enrichment
differentially affects the mnemonic response to estrogen in young, middle-aged,
and aged female mice. Neurobiol Learn Mem. 2007;88(4):393-408.
http://dx.doi.org/10.1016/j.nlm.2007.07.015
https://doi.org/10.1016/j.nlm.2007.07.01...
,1010 .Diniz DG, Foro CA, Rego CMD, Gloria DA, Oliveira FR, Paes JM et al.
Environmental impoverishment and aging alter object recognition, spatial
learning, and dentate gyrus astrocytes. Eur J Neurosci. 2010;32(3):509-19.
http://dx.doi.org/10.1111/j.1460-9568.2010.07296.x
https://doi.org/10.1111/j.1460-9568.2010...
. This could be explained by enhanced overall effects due
to greater access to physical stimulation, which is associated with higher exposure
time to the stimulus. The one running wheel available might have been insufficient
for the number of mice housed.
Stressful situations such as novelty exposure in EE and aversion to water on MWM2424 .Hölscher C. Stress impairs performance in spatial water maze
learning tasks. Behav Brain Res. 1999;100(1-2):225-35.
http://dx.doi.org/10.1016/S0166-4328(98)00134-X
https://doi.org/10.1016/S0166-4328(98)00...
, as well as hormonal alterations
related to aging2525 .Sadeghian R, Fereidoni M, Soukhtanloo M, Azizi-Malekabadi H,
Hosseini M. Decreased nitric oxide levels in the hippocampus may play a role in
learning and memory deficits in ovariectomized rats treated by a high dose of
estradiol. Arq Neuropsiquiatr. 2012;70(11):874-9.
http://dx.doi.org/10.1590/S0004-282X2012001100010
https://doi.org/10.1590/S0004-282X201200...
, inhibit the
process of long-term potentiation, which harms learning and spatial memory2424 .Hölscher C. Stress impairs performance in spatial water maze
learning tasks. Behav Brain Res. 1999;100(1-2):225-35.
http://dx.doi.org/10.1016/S0166-4328(98)00134-X
https://doi.org/10.1016/S0166-4328(98)00...
,2525 .Sadeghian R, Fereidoni M, Soukhtanloo M, Azizi-Malekabadi H,
Hosseini M. Decreased nitric oxide levels in the hippocampus may play a role in
learning and memory deficits in ovariectomized rats treated by a high dose of
estradiol. Arq Neuropsiquiatr. 2012;70(11):874-9.
http://dx.doi.org/10.1590/S0004-282X2012001100010
https://doi.org/10.1590/S0004-282X201200...
. Super-enrichment, achieved by introducing new
objects, might increase stress and aggressiveness among mice, and static and
repetitive objects might attenuate behavioral responses to novelty2020 .Hutchinson EK, Avery AC, Vandewoude S. Environmental enrichment for
laboratory rodents. ILAR J. 2005;46(2):148-61.
http://dx.doi.org/10.1093/ilar.46.2.148
https://doi.org/10.1093/ilar.46.2.148...
. Pre-training in different
spatial memory tasks might improve MWM task performance2424 .Hölscher C. Stress impairs performance in spatial water maze
learning tasks. Behav Brain Res. 1999;100(1-2):225-35.
http://dx.doi.org/10.1016/S0166-4328(98)00134-X
https://doi.org/10.1016/S0166-4328(98)00...
, mitigating those negative effects (impaired
performance due to water aversion may be mistakenly interpreted as deficient spatial
learning).
Female mice seem to be more negatively susceptible to stress-causing factors2626 .Adamec R, Head D, Blundell J, Burton P, Berton O. Lasting
anxiogenic effects of feline predator stress in mice: sex differences in
vulnerability to stress and predicting severity of anxiogenic response from the
stress experience. Physiol Behav. 2006;88(1-2):12-29.
http://dx.doi.org/10.1016/j.physbeh.2006.03.005
https://doi.org/10.1016/j.physbeh.2006.0...
. Lin et al.2727 .Lin EJD, Choi E, Liu X,; Martin A, During MJ. Environmental
enrichment exerts sex-specific effects on emotionality in C57BL/6J mice. Behav
Brain Res. 2011;216(1):349-57.
http://dx.doi.org/10.1016/j.bbr.2010.08.019
https://doi.org/10.1016/j.bbr.2010.08.01...
verified an anxiety effect in female mice
submitted to EE and depressive behavior due to longer immobility time on the forced
swim test. Although we did not evaluate emotional behavior, we observed an increase
in immobility and floating time during the MWM among EE animals. This might explain
the higher latency period to find the hidden platform for young adult EE mice
relative to the control group during training trials. Furthermore, chronic stress
caused by EE (exposure to many objects) and aversion to water during MWM) and
absence of pre-training tasks previously to MWM tasks might explain this unexpected
result. Gresack et al.99 .Gresack JE, Kerr KM, Frick KM. Life-long environmental enrichment
differentially affects the mnemonic response to estrogen in young, middle-aged,
and aged female mice. Neurobiol Learn Mem. 2007;88(4):393-408.
http://dx.doi.org/10.1016/j.nlm.2007.07.015
https://doi.org/10.1016/j.nlm.2007.07.01...
and
Harburger et al.88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
observed longer
swim speeds and shorter swim times, respectively, in one of their control groups
relative to their enriched ones. The outcome was better MWM performance by the
control groups. However, the enriched group described by Harburger et al.88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
overcame its control group during
training trials. In both studies, the authors performed more training trials per
day, which might explain why the enriched young adult mice in our study did not
overcome their controls over training days.
Moreover, the EE housing period could have been insufficient for the super-enrichment
habituation of female mice in the age groups studied. This would be in accordance
with other studies that used female mice, age groups, and EE durations similar to
ours88 .Harburger LL, Nzerem CK, Frick KM. Single enrichment variables
differentially reduce age-related memory decline in female mice. Behav Neurosci.
2007;121(4):679-88.
http://dx.doi.org/10.1037/0735-7044.121.4.679
https://doi.org/10.1037/0735-7044.121.4....
,1515 .Prusky GT, Reidel C, Douglas RM. Environmental enrichment from
birth enhances visual acuity but not place learning in mice. Behav Brain Res.
2000;114(1-2):11-5.
http://dx.doi.org/10.1016/S0166-4328(00)00186-8
https://doi.org/10.1016/S0166-4328(00)00...
.
Exposure to novelty and non-familiar situations can induce anxiety, and mice
responses vary by strain2828 .Ennaceur A, Michalikova S, van Rensburg R, Chazot PL. Models of
anxiety: responses of mice to novelty and open spaces in a 3D maze. Behav Brain
Res. 2006;174(1):9-38.
http://dx.doi.org/10.1016/j.bbr.2006.07.001
https://doi.org/10.1016/j.bbr.2006.07.00...
. Swiss
mice seem to be resistant to environment variations relative to other strains2929 .Silva CF, Duarte FS, Lima TCM, Oliveira CL. Effects of social
isolation and enriched environment on behavior of adult Swiss mice do not
require hippocampal neurogenesis. Behav Brain Res. 2011;22(1)5:85-90.
http://dx.doi.org/10.1016/j.bbr.2011.07.007
https://doi.org/10.1016/j.bbr.2011.07.00...
, showing an inferior performance
in MWM tasks in comparison to other strains1111 .Santos AF. Influência do enriquecimento ambiental na aquisição,
retenção e evocação da memória espacial em duas linhagens de camundongos
[dissertação]. Campo Grande: Universidade Católica Dom Bosco;
2009.,3030 .Van Dam D, Lenders G, De Deyn PP. Effect of Morris water maze
diameter on visual-spatial learning in different mouse strains. Neurobiol Learn
Mem. 2006;85(2):164-72.
http://dx.doi.org/10.1016/j.nlm.2005.09.006
https://doi.org/10.1016/j.nlm.2005.09.00...
, and requiring a longer enrichment period to achieve
significant results1010 .Diniz DG, Foro CA, Rego CMD, Gloria DA, Oliveira FR, Paes JM et al.
Environmental impoverishment and aging alter object recognition, spatial
learning, and dentate gyrus astrocytes. Eur J Neurosci. 2010;32(3):509-19.
http://dx.doi.org/10.1111/j.1460-9568.2010.07296.x
https://doi.org/10.1111/j.1460-9568.2010...
.
In summary, EE did not improve spatial memory acquisition in female Swiss mice in the analyzed age groups. It is likely that the lack of significant results was related to the insufficient EE period. Moreover, the analyzed age groups could have had significant spatial memory results if there had been more running wheels to promote physical activity.
ACKNOWLEDGMENTS
Our sincere thanks to the staff of the Biomorphophysiology Laboratory and the Central Vivarium of the Universidade Federal de Mato Grosso do Sul; this research would not have been possible without their help.
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» https://doi.org/10.1258/002367702320162379 -
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» https://doi.org/10.1155/2013/709732 -
24Hölscher C. Stress impairs performance in spatial water maze learning tasks. Behav Brain Res. 1999;100(1-2):225-35. http://dx.doi.org/10.1016/S0166-4328(98)00134-X
» https://doi.org/10.1016/S0166-4328(98)00134-X -
25Sadeghian R, Fereidoni M, Soukhtanloo M, Azizi-Malekabadi H, Hosseini M. Decreased nitric oxide levels in the hippocampus may play a role in learning and memory deficits in ovariectomized rats treated by a high dose of estradiol. Arq Neuropsiquiatr. 2012;70(11):874-9. http://dx.doi.org/10.1590/S0004-282X2012001100010
» https://doi.org/10.1590/S0004-282X2012001100010 -
26Adamec R, Head D, Blundell J, Burton P, Berton O. Lasting anxiogenic effects of feline predator stress in mice: sex differences in vulnerability to stress and predicting severity of anxiogenic response from the stress experience. Physiol Behav. 2006;88(1-2):12-29. http://dx.doi.org/10.1016/j.physbeh.2006.03.005
» https://doi.org/10.1016/j.physbeh.2006.03.005 -
27Lin EJD, Choi E, Liu X,; Martin A, During MJ. Environmental enrichment exerts sex-specific effects on emotionality in C57BL/6J mice. Behav Brain Res. 2011;216(1):349-57. http://dx.doi.org/10.1016/j.bbr.2010.08.019
» https://doi.org/10.1016/j.bbr.2010.08.019 -
28Ennaceur A, Michalikova S, van Rensburg R, Chazot PL. Models of anxiety: responses of mice to novelty and open spaces in a 3D maze. Behav Brain Res. 2006;174(1):9-38. http://dx.doi.org/10.1016/j.bbr.2006.07.001
» https://doi.org/10.1016/j.bbr.2006.07.001 -
29Silva CF, Duarte FS, Lima TCM, Oliveira CL. Effects of social isolation and enriched environment on behavior of adult Swiss mice do not require hippocampal neurogenesis. Behav Brain Res. 2011;22(1)5:85-90. http://dx.doi.org/10.1016/j.bbr.2011.07.007
» https://doi.org/10.1016/j.bbr.2011.07.007 -
30Van Dam D, Lenders G, De Deyn PP. Effect of Morris water maze diameter on visual-spatial learning in different mouse strains. Neurobiol Learn Mem. 2006;85(2):164-72. http://dx.doi.org/10.1016/j.nlm.2005.09.006
» https://doi.org/10.1016/j.nlm.2005.09.006
Publication Dates
-
Publication in this collection
Aug 2015
History
-
Received
21 July 2014 -
Reviewed
04 Mar 2015 -
Accepted
24 Mar 2015