Resumo em Inglês:

The discovery of non-adrenergic, non-cholinergic neurotransmission in the gut and bladder in the early 1960's is described as well as the identification of adenosine 5'-triphosphate (ATP) as a transmitter in these nerves in the early 1970's. The concept of purinergic cotransmission was formulated in 1976 and it is now recognized that ATP is a cotransmitter in all nerves in the peripheral and central nervous systems. Two families of receptors to purines were recognized in 1978, P1 (adenosine) receptors and P2 receptors sensitive to ATP and adenosine diphosphate (ADP). Cloning of these receptors in the early 1990's was a turning point in the acceptance of the purinergic signalling hypothesis and there are currently 4 subtypes of P1 receptors, 7 subtypes of P2X ion channel receptors and 8 subtypes of G protein-coupled receptors. Both short-term purinergic signalling in neurotransmission, neuromodulation and neurosecretion and long-term (trophic) purinergic signalling of cell proliferation, differentiation, motility, death in development and regeneration are recognized. There is now much known about the mechanisms underlying ATP release and extracellular breakdown by ecto-nucleotidases. The recent emphasis on purinergic neuropathology is discussed, including changes in purinergic cotransmission in development and ageing and in bladder diseases and hypertension. The involvement of neuron-glial cell interactions in various diseases of the central nervous system, including neuropathic pain, trauma and ischemia, neurodegenerative diseases, neuropsychiatric disorders and epilepsy are also considered.

Resumo em Inglês:

The pancreatic acinar cell is a classical model for studies of secretion and signal transduction mechanisms. Because of the extensive endoplasmic reticulum and the large granular compartment, it has been possible - by direct measurements - to obtain considerable insights into intracellular Ca2+ handling under both normal and pathological conditions. Recent studies have also revealed important characteristics of stimulus-secretion coupling mechanisms in isolated human pancreatic acinar cells. The acinar cells are potentially dangerous because of the high intra-granular concentration of proteases, which become inappropriately activated in the human disease acute pancreatitis. This disease is due to toxic Ca2+ signals generated by excessive liberation of Ca2+ from both the endoplasmic reticulum and the secretory granules.

Resumo em Inglês:

Calcium (Ca2+) is a versatile second messenger that regulates a wide range of cellular functions. Although it is not established how a single second messenger coordinates diverse effects within a cell, there is increasing evidence that the spatial patterns of Ca2+ signals may determine their specificity. Ca2+ signaling patterns can vary in different regions of the cell and Ca2+ signals in nuclear and cytoplasmic compartments have been reported to occur independently. No general paradigm has been established yet to explain whether, how, or when Ca2+ signals are initiated within the nucleus or their function. Here we highlight that receptor tyrosine kinases rapidly translocate to the nucleus. Ca2+ signals that are induced by growth factors result from phosphatidylinositol 4,5-bisphosphate hydrolysis and inositol 1,4,5-trisphosphate formation within the nucleus rather than within the cytoplasm. This novel signaling mechanism may be responsible for growth factor effects on cell proliferation.

Resumo em Inglês:

Mammalian cells contain several proteolytic systems to carry out the degradative processes and complex regulatory mechanisms to prevent excessive protein breakdown. Among these systems, the Ca2+-activated proteolytic system involves the cysteine proteases denoted calpains, and their inhibitor, calpastatin. Despite the rapid progress in molecular research on calpains and calpastatin, the physiological role and regulatory mechanisms of these proteins remain obscure. Interest in the adrenergic effect on Ca2+-dependent proteolysis has been stimulated by the finding that the administration of β2-agonists induces muscle hypertrophy and prevents the loss of muscle mass in a variety of pathologic conditions in which calpains are activated. This review summarizes evidence indicating that the sympathetic nervous system produces anabolic, protein-sparing effects on skeletal muscle protein metabolism. Studies are reviewed, which indicate that epinephrine secreted by the adrenal medulla and norepinephrine released from adrenergic terminals have inhibitory effects on Ca2+-dependent protein degradation, mainly in oxidative muscles, by increasing calpastatin levels. Evidence is also presented that this antiproteolytic effect, which occurs under both basal conditions and in stress situations, seems to be mediated by β2- and β3-adrenoceptors and cAMP-dependent pathways. The understanding of the precise mechanisms by which catecholamines promote muscle anabolic effects may have therapeutic value for the treatment of muscle-wasting conditions and may enhance muscle growth in farm species for economic and nutritional purposes.

Resumo em Inglês:

Two major stress-activated protein kinases are the p38 mitogen-activated protein kinase (MAPK) and the c-Jun amino terminal kinase (JNK). p38 and JNK are widely expressed in different cell types in various tissues and can be activated by a diverse range of stimuli. Signaling through p38 and JNK is critical for embryonic development. In adult kidney, p38 and JNK signaling is evident in a restricted pattern suggesting a normal physiological role. Marked activation of both p38 and JNK pathways occurs in human renal disease, including glomerulonephritis, diabetic nephropathy and acute renal failure. Administration of small molecule inhibitors of p38 and JNK has been shown to provide protection from renal injury in different types of experimental kidney disease through inhibition of renal inflammation, fibrosis, and apoptosis. In particular, a role for JNK signaling has been identified in macrophage activation resulting in up-regulation of pro-inflammatory mediators and the induction of renal injury. The ability to provide renal protection by blocking either p38 or JNK indicates a lack of redundancy for these two signaling pathways despite their activation by common stimuli. Therefore, the stress-activated protein kinases, p38 and JNK, are promising candidates for therapeutic intervention in human renal diseases.

Resumo em Inglês:

Experimental and clinical evidence suggests that angiotensin II (AII) participates in renal development. Renal AII content is several-fold higher in newborn rats and mice than in adult animals. AII receptors are also expressed in higher amounts in the kidneys of newborn rats. The kidneys of fetuses whose mother received a type 1 AII receptor (AT1) antagonist during gestation present several morphological alterations. Mutations in genes that encode components of the renin-angiotensin system are associated with autosomal recessive renal tubular dysgenesis. Morphological changes were detected in the kidneys of 3-week-old angiotensin-deficient mice. Mitogen-activated protein kinases (MAPKs) are important mediators that transduce extracellular stimuli to intracellular responses. The MAPK family comprises three major subgroups, namely extracellular signal-regulated protein kinase (ERK), c-jun N-terminal kinases (JNK), and p38 MAPK (p38). Important events in renal growth during nephrogenesis such as cellular proliferation and differentiation accompanied by apoptosis on a large scale can be mediated by MAPK pathways. A decrease in glomerulus number was observed in embryos cultured for 48 and 120 h with ERK or p38 inhibitors. Many effects of AII are mediated by MAPK pathways. Treatment with losartan during lactation provoked changes in renal function and structure associated with alterations in AT1 and type 2 AII (AT2) receptors and p-JNK and p-p38 expression in the kidney. Several studies have shown that AII and MAPKs play an important role in renal development. However, the relationship between the effects of AII and MAPK activation on renal development is still unclear.

Resumo em Inglês:

Focal adhesion kinase (FAK) is a broadly expressed tyrosine kinase implicated in cellular functions such as migration, growth and survival. Emerging data support a role for FAK in cardiac development, reactive hypertrophy and failure. Data reviewed here indicate that FAK plays a critical role at the cellular level in the responses of cardiomyocytes and cardiac fibroblasts to biomechanical stress and to hypertrophic agonists such as angiotensin II and endothelin. The signaling mechanisms regulated by FAK are discussed to provide insight into its role in the pathophysiology of cardiac hypertrophy and failure.

Resumo em Inglês:

Electrical stimulation of baroreceptor afferents was used in the 1960's in several species, including human beings, for the treatment of refractory hypertension. This approach bypasses the site of baroreceptor mechanosensory transduction. Chronic electrical stimulation of arterial baroreceptors, particularly of the carotid sinus nerve (Hering's nerve), was proposed as an ultimate effort to treat refractory hypertension and angina pectoris due to the limited nature of pharmacological therapy available at that time. Nevertheless, this approach was abandoned in the early 1970's due to technical limitations of implantable devices and to the development of better-tolerated antihypertensive medications. More recently, our laboratory developed the technique of electrical stimulation of the aortic depressor nerve in conscious rats, enabling access to hemodynamic responses without the undesirable effect of anesthesia. In addition, electrical stimulation of the aortic depressor nerve allows assessment of the hemodynamic responses and the sympathovagal balance of the heart in hypertensive rats, which exhibit a well-known decrease in baroreflex sensitivity, usually attributed to baroreceptor ending dysfunction. Recently, there has been renewed interest in using electrical stimulation of the carotid sinus, but not the carotid sinus nerve, to lower blood pressure in conscious hypertensive dogs as well as in hypertensive patients. Notably, previous undesirable technical outcomes associated with electrical stimulation of the carotid sinus nerve observed in the 1960's and 1970's have been overcome. Furthermore, promising data have been recently reported from clinical trials that evaluated the efficacy of carotid sinus stimulation in hypertensive patients with drug resistant hypertension.

Resumo em Inglês:

The involvement of the hypothalamic-pituitary-adrenal axis in the control of body fluid homeostasis has been extensively investigated in the past few years. In the present study, we reviewed the recent results obtained using different approaches to investigate the effects of glucocorticoids on the mechanisms of oxytocin and vasopressin synthesis and secretion in response to acute and chronic plasma volume and osmolality changes. The data presented here suggest that glucocorticoids are not only involved in the mechanisms underlying the fast release but also in the transcriptional events that lead to decreased synthesis and secretion of these neuropeptides, particularly oxytocin, under diverse experimental conditions of altered fluid volume and tonicity. The endocannabinoid system, through its effects on glutamatergic neurotransmission within the hypothalamus and the nuclear factor κB-mediated transcriptional activity, seems to be also involved in the specific mechanisms by which glucocorticoids exert their central effects on neurohypophyseal hormone synthesis and secretion.

Resumo em Inglês:

Neurotransmitters are also involved in functions other than conventional signal transfer between nerve cells, such as development, plasticity, neurodegeneration, and neuroprotection. For example, there is a considerable amount of data indicating developmental roles for the glutamatergic, cholinergic, dopaminergic, GABA-ergic, and ATP/adenosine systems. In this review, we discuss the existing literature on these "new" functions of neurotransmitters in relation to some unconventional neurotransmitters, such as the endocannabinoids and nitric oxide. Data indicating both transcriptional and post-transcriptional modulation of endocannabinoid and nitrinergic systems after neural lesions are discussed in relation to the non-conventional roles of these neurotransmitters. Knowledge of the roles of neurotransmitters in brain functions other than information transfer is critical for a more complete understanding of the functional organization of the brain and to provide more opportunities for the development of therapeutical tools aimed at minimizing neuronal death.

Resumo em Inglês:

The brain is a complex system, which produces emergent properties such as those associated with activity-dependent plasticity in processes of learning and memory. Therefore, understanding the integrated structures and functions of the brain is well beyond the scope of either superficial or extremely reductionistic approaches. Although a combination of zoom-in and zoom-out strategies is desirable when the brain is studied, constructing the appropriate interfaces to connect all levels of analysis is one of the most difficult challenges of contemporary neuroscience. Is it possible to build appropriate models of brain function and dysfunctions with computational tools? Among the best-known brain dysfunctions, epilepsies are neurological syndromes that reach a variety of networks, from widespread anatomical brain circuits to local molecular environments. One logical question would be: are those complex brain networks always producing maladaptive emergent properties compatible with epileptogenic substrates? The present review will deal with this question and will try to answer it by illustrating several points from the literature and from our laboratory data, with examples at the behavioral, electrophysiological, cellular and molecular levels. We conclude that, because the brain is a complex system compatible with the production of emergent properties, including plasticity, its functions should be approached using an integrated view. Concepts such as brain networks, graphics theory, neuroinformatics, and e-neuroscience are discussed as new transdisciplinary approaches dealing with the continuous growth of information about brain physiology and its dysfunctions. The epilepsies are discussed as neurobiological models of complex systems displaying maladaptive plasticity.

Resumo em Inglês:

Nitric oxide (NO) donors produce NO-related activity when applied to biological systems. Among its diverse functions, NO has been implicated in vascular smooth muscle relaxation. Despite the great importance of NO in biological systems, its pharmacological and physiological studies have been limited due to its high reactivity and short half-life. In this review we will focus on our recent investigations of nitrosyl ruthenium complexes as NO-delivery agents and their effects on vascular smooth muscle cell relaxation. The high affinity of ruthenium for NO is a marked feature of its chemistry. The main signaling pathway responsible for the vascular relaxation induced by NO involves the activation of soluble guanylyl-cyclase, with subsequent accumulation of cGMP and activation of cGMP-dependent protein kinase. This in turn can activate several proteins such as K+ channels as well as induce vasodilatation by a decrease in cytosolic Ca2+. Oxidative stress and associated oxidative damage are mediators of vascular damage in several cardiovascular diseases, including hypertension. The increased production of the superoxide anion (O2-) by the vascular wall has been observed in different animal models of hypertension. Vascular relaxation to the endogenous NO-related response or to NO released from NO deliverers is impaired in vessels from renal hypertensive (2K-1C) rats. A growing amount of evidence supports the possibility that increased NO inactivation by excess O2- may account for the decreased NO bioavailability and vascular dysfunction in hypertension.

Resumo em Inglês:

The calyx of Held, a specialized synaptic terminal in the medial nucleus of the trapezoid body, undergoes a series of changes during postnatal development that prepares this synapse for reliable high frequency firing. These changes reduce short-term synaptic depression during tetanic stimulation and thereby prevent action potential failures during a stimulus train. We measured presynaptic membrane capacitance changes in calyces from young postnatal day 5-7 (p5-7) or older (p10-12) rat pups to examine the effect of calcium buffer capacity on vesicle pool size and the efficiency of exocytosis. Vesicle pool size was sensitive to the choice and concentration of exogenous Ca2+ buffer, and this sensitivity was much stronger in younger animals. Pool size and exocytosis efficiency in p5-7 calyces were depressed by 0.2 mM EGTA to a greater extent than with 0.05 mM BAPTA, even though BAPTA is a 100-fold faster Ca2+ buffer. However, this was not the case for p10-12 calyces. With 5 mM EGTA, exocytosis efficiency was reduced to a much larger extent in young calyces compared to older calyces. Depression of exocytosis using pairs of 10-ms depolarizations was reduced by 0.2 mM EGTA compared to 0.05 mM BAPTA to a similar extent in both age groups. These results indicate a developmentally regulated heterogeneity in the sensitivity of different vesicle pools to Ca2+ buffer capacity. We propose that, during development, a population of vesicles that are tightly coupled to Ca2+ channels expands at the expense of vesicles more distant from Ca2+ channels.

Resumo em Inglês:

Besides other physiological functions, adenosine-5'-triphosphate (ATP) is also a neurotransmitter that acts on purinergic receptors. In spite of the presence of purinergic receptors in forebrain areas involved with fluid-electrolyte balance, the effect of ATP on water intake has not been investigated. Therefore, we studied the effects of intracerebroventricular (icv) injections of ATP (100, 200 and 300 nmol/µL) alone or combined with DPCPX or PPADS (P1 and P2 purinergic antagonists, respectively, 25 nmol/µL) on water intake induced by water deprivation. In addition, the effect of icv ATP was also tested on water intake induced by intragastric load of 12% NaCl (2 mL/rat), acute treatment with the diuretic/natriuretic furosemide (20 mg/kg), icv angiotensin II (50 ng/µL) or icv carbachol (a cholinergic agonist, 4 nmol/µL), on sodium depletion-induced 1.8% NaCl intake, and on food intake induced by food deprivation. Male Holtzman rats (280-320 g, N = 7-11) had cannulas implanted into the lateral ventricle. Icv ATP (300 nmol/µL) reduced water intake induced by water deprivation (13.1 ± 1.9 vs saline: 19.0 ± 1.4 mL/2 h; P < 0.05), an effect blocked by pre-treatment with PPADS, but not DPCPX. Icv ATP also reduced water intake induced by NaCl intragastric load (5.6 ± 0.9 vs saline: 10.3 ± 1.4 mL/2 h; P < 0.05), acute furosemide treatment (0.5 ± 0.2 vs saline: 2.3 ± 0.6 mL/15 min; P < 0.05), and icv angiotensin II (2.2 ± 0.8 vs saline: 10.4 ± 2.0 mL/2 h; P < 0.05), without changing icv carbachol-induced water intake, sodium depletion-induced 1.8% NaCl intake and food deprivation-induced food intake. These data suggest that central ATP, acting on purinergic P2 receptors, reduces water intake induced by intracellular and extracellular dehydration.

Resumo em Inglês:

We investigated the involvement of GABAergic mechanisms of the central amygdaloid nucleus (CeA) in unanesthetized rats subjected to acute isotonic or hypertonic blood volume expansion (BVE). Male Wistar rats bearing cannulas unilaterally implanted in the CeA were treated with vehicle, muscimol (0.2 nmol/0.2 µL) or bicuculline (1.6 nmol/0.2 µL) in the CeA, followed by isotonic or hypertonic BVE (0.15 or 0.3 M NaCl, 2 mL/100 g body weight over 1 min). The vehicle-treated group showed an increase in sodium excretion, urinary volume, plasma oxytocin (OT), and atrial natriuretic peptide (ANP) levels compared to control rats. Muscimol reduced the effects of BVE on sodium excretion (isotonic: 2.4 ± 0.3 vs vehicle: 4.8 ± 0.2 and hypertonic: 4.0 ± 0.7 vs vehicle: 8.7 ± 0.6 µEq·100 g-1·40 min-1); urinary volume after hypertonic BVE (83.8 ± 10 vs vehicle: 255.6 ± 16.5 µL·100 g-1·40 min-1); plasma OT levels (isotonic: 15.3 ± 0.6 vs vehicle: 19.3 ± 1 and hypertonic: 26.5 ± 2.6 vs vehicle: 48 ± 3 pg/mL), and ANP levels (isotonic: 97 ± 12.8 vs vehicle: 258.3 ± 28.1 and hypertonic: 160 ± 14.6 vs vehicle: 318 ± 16.3 pg/mL). Bicuculline reduced the effects of isotonic or hypertonic BVE on urinary volume and ANP levels compared to vehicle-treated rats. However, bicuculline enhanced the effects of hypertonic BVE on plasma OT levels. These data suggest that CeA GABAergic mechanisms are involved in the control of ANP and OT secretion, as well as in sodium and water excretion in response to isotonic or hypertonic blood volume expansion.

Resumo em Inglês:

Circadian timing is structured in such a way as to receive information from the external and internal environments, and its function is the timing organization of the physiological and behavioral processes in a circadian pattern. In mammals, the circadian timing system consists of a group of structures, which includes the suprachiasmatic nucleus (SCN), the intergeniculate leaflet and the pineal gland. Neuron groups working as a biological pacemaker are found in the SCN, forming a biological master clock. We present here a simple model for the circadian timing system of mammals, which is able to reproduce two fundamental characteristics of biological rhythms: the endogenous generation of pulses and synchronization with the light-dark cycle. In this model, the biological pacemaker of the SCN was modeled as a set of 1000 homogeneously distributed coupled oscillators with long-range coupling forming a spherical lattice. The characteristics of the oscillator set were defined taking into account the Kuramoto's oscillator dynamics, but we used a new method for estimating the equilibrium order parameter. Simultaneous activities of the excitatory and inhibitory synapses on the elements of the circadian timing circuit at each instant were modeled by specific equations for synaptic events. All simulation programs were written in Fortran 77, compiled and run on PC DOS computers. Our model exhibited responses in agreement with physiological patterns. The values of output frequency of the oscillator system (maximal value of 3.9 Hz) were of the order of magnitude of the firing frequencies recorded in suprachiasmatic neurons of rodents in vivo and in vitro (from 1.8 to 5.4 Hz).

Resumo em Inglês:

The aim of the present study was to determine the effect of the histaminergic precursor L-histidine and the H3 receptor antagonist thioperamide on the learning process of zebrafish submitted or not to confinement stress. On each of the 5 consecutive days of experiment (D1, D2, D3, D4, D5), animals had to associate an interruption of the aquarium air supply with food offering. Non-stressed zebrafish received an intraperitoneal injection of 100 mg/kg L-histidine, 10 mg/kg thioperamide or saline after training. Stressed animals received drug treatment and then were submitted to confinement stress for 1 h before the learning procedure. Time to approach the feeder was measured (in seconds) and was considered to be indicative of learning. A decrease in time to approach the feeder was observed in the saline-treated group (D1 = 141.92 ± 13.57; D3 = 55 ± 13.54), indicating learning. A delay in learning of stressed animals treated with saline was observed (D1 = 217.5 ± 25.66). L-histidine facilitated learning in stressed (D1 = 118.68 ± 13.9; D2 = 45.88 ± 8.2) and non-stressed (D1 = 151.11 ± 19.20; D5 = 62 ± 14.68) animals. Thioperamide inhibited learning in non-stressed (D1 = 110.38 ± 9.49; D4 = 58.79 ± 16.83) and stressed animals (D1 = 167.3 ± 26.39; D5 = 172.15 ± 27.35). L-histidine prevented the increase in blood glucose after one session of confinement (L-histidine = 65.88 ± 4.50; control = 53 ± 3.50 mg/dL). These results suggest that the histaminergic system enhances learning and modulates stress responses in zebrafish.

Resumo em Inglês:

The effect of post-training treatment with L-histidine (LH) on the memory consolidation of inhibitory avoidance was investigated in Carassius auratus submitted to cerebellar ablation. The inhibitory avoidance procedure included 3 days: one habituation day, one training day (5 trials, T1-T5) and one test day. On the training day, each fish was placed individually in a white compartment separated from a black compartment by a sliding door. When the fish crossed into the black compartment, a weight was dropped in front of it (aversive stimulus) and the time to cross was recorded. Saline or LH (100 mg/kg) was injected intraperitoneally 10 min after the trials. Data were log10 transformed and analyzed by ANOVA and the Student-Newman-Keuls test (P < 0.05). In T5, all groups [ablation/LH (N = 15; 189.60 ± 32.52), ablation/saline (N = 14; 204.29 ± 28.95), sham/LH (N = 14; 232.36 ± 28.15), and sham/saline (N = 15; 249.07 ± 25.82)] had similar latencies that were significantly higher than T1 latencies [ablation/LH (89.33 ± 20.41), ablation/saline (97.00 ± 25.16), sham/LH (73.86 ± 18.42), and sham/saline (56.71 ± 17.59)], suggesting acquisition of inhibitory avoidance. For the test, there was a significant reduction in latencies of ablation/LH (61.53 ± 17.70) and sham/saline (52.79 ± 25.37) groups compared to the ablation/saline (213.64 ± 29.57) and sham/LH (199.43 ± 24.48) groups, showing that cerebellum ablation facilitated retention of inhibitory avoidance and LH reversed the effect of ablation. The results support other evidence that LH impairs memory consolidation and/or reduces the interpretation of aversion value.

Resumo em Inglês:

We have shown that the peripheral and spinal cord heme oxygenase (HO)-carbon monoxide (CO)-soluble guanylate cyclase-cGMP pathways play an important role in antinociception in the rat experimental formalin model. Our objective was to determine if there is synergism between peripheral (paw) and spinal HO-CO pathways in nociception. Rats were handled and adapted to the experimental environment for a few days before the formalin test, in which 50 µL of a 1% formalin was injected subcutaneously into the dorsal surface of the right hind paw. The animals were then observed for 1 h and the frequency of flinching behavior was taken to represent the nociceptive response. Thirty minutes before the test, rats were pretreated with intrathecal injections of the HO inhibitor, zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) or heme-lysinate, which is a substrate of the HO pathway. The paw treatments took place 20 min before the test. Low doses of ZnDPBG did not increase nociception, while a low heme-lysinate dose did not change flinching behavior after paw or spinal injections. Combined subactive spinal (50 nmol) and peripheral (40 nmol) low doses of ZnDPBG induced hypernociception (increase of 80% in the first and 25% in the second phase flinching), whereas combined spinal-peripheral heme-lysinate (50 and 30 nmol) led to second phase antinociception (40% reduction in flinching). These findings suggest a synergy between the peripheral and spinal HO-CO pathways. Local activation of the HO system probably regulates the nociception initiation in peripheral tissue and participates in buffering the emerging nociceptive signals at the peripheral and spinal sites of action. In short, an antinociceptive synergy exists between peripheral and spinal HO pathways, which may reduce the doses required and side effects.