The enhanced availability of tryptophan in the brain, as a consequence of exogenous tryptophan administration, can increase neuronal serotonin synthesis and this can interfere with brain function. REM sleep deprivation (D) constitutes another external factor that can change brain excitability, facilitating, in some cases, the manifestation of neurological diseases like epilepsy. Here we used cortical spreading depression (CSD) as a neurophysiological parameter to investigate the effects of a single L-tryptophan intraperitoneal injection combined or not with 72h D-condition (water-tank technique) in rats. A 1h baseline CSD-recording was performed under urethane+chloralose (1g/kg + 40mg/kg) anesthesia and revealed increased CSD propagation velocities in D rats, as compared with non-deprived (ND), or pseudo-deprived (Pseudo) controls. After the baseline CSD recording, L-tryptophan was immediately injected (125 mg/kg ip, dissolved in water at pH about 3) and this was followed by a significant decrease of CSD propagation velocities, as compared to the baseline values in the same animals of the Pseudo, ND and D condition. In an additional control group (ND rats injected with the vehicle), no CSD propagation change was seen. Our findings indicate an important acute antagonistic influence of tryptophan on CSD propagation, which is not affected by REM sleep deprivation. We suggest that this tryptophan effect may be due to a serotonin-mediated action, probably caused by increased serotonin synthesis as a consequence of enhanced tryptophan availability in the brain.

RESUMO: É feita uma revisão sobre as estratégias e efeitos da estimulação sensorial e ambiental de indivíduos desnutridos. Reportam os autores evidências provenientes de experimentos com modelos animais e de estudos em seres humanos, mostrando os benefícios da administração da estimulação sensorial ou psicossocial programadas sobre as funções neuro-comportamentais. Mostram ainda a importante participação que a plasticidade cerebral pode ter neste processo. Finalmente enfatizam que as evidências eletrofisiológicas - obtidas pela técnica da depressão alastrante cortial em animais - e as observações em seres humanos indicam que as regiões cerebrais comportam-se diferencialmente nesta recuperação. Daí, sugerem uma abordagem nos cuidados médicos em indivíduos desnutridos levando em conta estas peculiaridades regionais do cérebro.

Evidences from studies in animal models and human beings are reviewed, showing the benefits produced by programed sensorial and psychosocial stimulation on neuro-behavioral functions of early malnourished individuals. It is emphasized that brain plasticity might play a fundamental role in this process. It is showed also that recent electrophysiological experiments - by using the cortical spreading depression technique - as well as observational studies in children indicate that brain regions may have a differential participation in the recovering of the brain and behavioral functions damaged by malnutrition. A new health care approach, taking into account that regional differences for treatment of children suffering early malnutrition, is suggested.