Neurons Of Rat Cerebral Cortex Research Articles

Electrophysiological effects of enkephalin analogs in rat cortex

The microiontophoretic potencies of methionine-enkephalin (ME) analogs with similar charges but different potencies in the in vitro assays were studied with respect to spontaneous and evoked activity of rat cerebral cortex neurons (CX). ME slowed discharge in 65% of the 62 CX tested; activity evoked by acetylcholine (ACh) or glutamate, as well as spontaneous discharge, was affected. The vast majority of responsive cells were deeper than 500 μ and excited by ACh. Antidromic spikes were elicited in many of these neurons by pyramidal tract stimulation. The electrophysiological effects of D-Ala 2 ME amide, a more potent analog in vitro , was similar to ME when tested on the same parietal CX, however, D-Ala 2 ME amide was much more potent than ME on frontal CX. On the other hand N-acetyl D-Ala 2-Lys 3 ME amide, which has low potency in vitro , had little effect on CX which were readily depressed by equivalent doses of ME or the D-Ala 2 analog. The depressions induced by ME or the D-Ala 2 derivative were readily and reversibly antagonized by prior iontophoretic administration of naloxone. It is concluded that opiate receptor interactions may play an important role in electrophysiological responses to iontophoretically administered ME and that the deeper cholineceptive cortical cells, possibly pyramidal neurons, may be preferentially affected.

Electron microscopical studies on rat brain neurons. Localization of acid phosphatase and mode of formation of lipofuscin bodies

Neurons in rat cerebral cortex and pontine ganglia contain increasing numbers of lipofuscin bodies with age. At all ages studied, i.e. from 3 to 25 months, these bodies contain acid phosphatase, as demonstrated by the Gomori technique in dimethyl sulfoxide-treated frozen sections of glutaraldehyde-perfused brains. Endogenous osmiophilic granular and dense material in the lipofuscin may simulate reaction product in “postosmicated” tissues. Autophagic vacuoles were observed in neurons of all ages. Apparent transitional forms between autophagic vacuoles and lipofuscin-like bodies were noted. The findings indicated that the lipofuscin bodies represented the residual body type of lysosomes resulting mainly from cellular autophagy. Accumulation of these bodies appears to be due to inability of the cells for exocytosis of residues accumulating in lysosomes. Acid phosphatase activity was demonstrated in Golgi cisternae, “fenestrated Golgi lamellae,” Golgi-associated coated vesicles, conventional lysosomes, and lipofuscin bodies in neurons of all ages. The evidence suggested that acid phosphatase was continuously transported to the lipofuscin bodies throughout the life-span of the cells.

An electron microscopic study of neurons during postnatal development of the rat cerebral cortex.

AbstractThe differentiation and maturation of the neurons of rat cerebral cortex during the first three weeks of postnatal life has been studied with the light and electron microscopes. At birth, the supeficial cortex is largely made up of undifferentiated cells, tightly packed together in vertical columns between which the developing process and blood vessels, and relatively extensive extracellular spaces are found. During the first two weeks, these cells diferentiate into either neuroblasts and neurons, or into spongioblasts and neuroglia. In the case of neurons but not neuroglia, this maturation occurs in a gradient from the depths toward the surface. The round undifferendtiated cells are characterized by an absence of processes, a thin rim of perinuclear cytoplasm containing few organelles, and a peripheral clumping of condensed nuclear chromatin. The differentiating neuroblasts display increasing numbers of cytoplasmic organelles, especially endoplasmic reticulum, evenly dispersed nuclear chromatin, and presumptive apical dendrites. The rough endoplasmic reticulum of neuroblasts become swollen during the transition into neurons during the second week. The endoplasmic reticulum forms subsurface cisterns that transiently evaginate the cell membrane, forming conspicuous diverticuli in the neuropil at the same time that the cells display an increase of cytoplasmic matrix density and increasing numbers of ribosomes. During the three weeks following birth, organelles increase in number and complexity, synapses develop, the extracellular spaces disappear, and the maturing neurons become separated from one another by the growth of neuropil and nonnervous elements. At the end of this three week period the cortical tissue and its neurons are apparently mature and the adult pattern of cortical fine structure is established.