RESUMO Neste trabalho, implementamos um modelo matemático de transmissão sináptica conectando neurônios em um circuito de descargas reverberantes, a fim de investigar seu comportamento diante de variações paramétricas. Usando um programa desenvolvido em linguagem C, verificamos se o modelo se comportaria como um circuito de memória de curto prazo. Na simulação, usamos valores paramétricos de medidas experimentais realizadas em animal. Nosso modelo foi capaz de reproduzir a atividade polissináptica de um grupo neuronal de cérebro de rato (tempo de loop de cerca de 102 ms). Por outro lado, verificamos que as sinapses de feedback inibitório no circuito, com pesos variando com o tempo e a frequência dos disparos pré-sinápticos, são capazes de alterar as características do circuito para reproduzir o comportamento típico de circuitos neurais. Os resultados sugerem que, diferentemente de algumas considerações recentes, o modelo de circuito reverberante tem grande potencial para reproduzir o comportamento típico dos circuitos neurais e pode ser visto como um modelo possível para memória imediata.

ABSTRACT In this work we implement a mathematical model of synaptic transmission connecting neurons in a circuit of reverberating discharges in order to investigate its behavior in front of parametric variations. Using a program developed in C language, we verified if this model would behave as short-term memory circuit. In the simulation, we used neural parametric values from experimental measures in animal. Our model was able to reproduce polysynaptic activity of a neuronal group of rat brain (looping time of about 102 ms). On the other hand, we verified that the inhibitory feedback synapses in circuit with weight varying with presynaptic firing time and frequency are capable to change the circuit characteristic to reproduce the typical behavior of neural circuits. The results suggest that, differently from some recent considerations, the reverberating circuit model has great potential to reproduce the typical behavior of neural circuits and could be seen as a possible model for immediate memory.

The present work investigates the corticoid action on the growth of the superior cervical ganglion of the rat and describes the cortisol effect during early stages of development. The study was based on morphometric and stereological analysis of the perikarya. Eight rats were treated intraperitoneally with cortisol (1mg/Kg/day) during 36 days. Treatment was initiated in the 8th day after birth and was withdrawn one day before the sacrifice. There was a significant difference (<=P0,05) for the neural mean diameter between the control group (16.78 ± 1.11mm) and treated animals (15.84 ±0.99mm). The decrease of perikarya neuronal diameter was also demonstrated by stereological methods. Morphometrical findings may suggest alterations in superior cervical ganglion neuronal activity in rats treated for long term with cortisol

Se investigó la acción de corticoides en el crecimiento del ganglio cervical superior de rata y se describieron los efectos del cortisol durante las fases tempranas de desarrollo. El estudio se basó en los análisis morfométrico y estereológico del pericario. Fueron inyectadas intraperitonealmente 8 ratas con cortisol (1mg/Kg/día) durante 36 días. El tratamiento se comenzó en el día 8 después del nacimiento, finalizándose un día antes del sacrificio. Hubo una diferencia significativa (<=P0,05) en el promedio del diámetro neuronal entre el grupo control (16.78 ± 1.11 mm) y los animales tratados (15.84 ± 0.99 mm). La disminución del diámetro neuronal del pericario también fue demostrada a través de la estereología. Los hallazgos morfométricos pueden hacer pensar en alteraciones de la actividad neuronal del ganglio cervical superior, en ratas tratadas por un largo periodo con cortisol