A stereological analysis of the neuronal and synaptic content of the frontal and cerebellar cortex of weanling rats undernourished from birth.

The frontal cortex and granular layer of the cerebellum have been examined in 30-day-old rats undernourished from birth. Quantitative stereological procedures at the light microscopical level have been used to estimate the volume proportion and numerical densities of neuronal nuclei. Similar methods at the electron microscopical level were employed to calculate the numerical densities of synapses. Hence, synapse-to-neuron ratios have been calculated in these brain regions. In the frontal cortex, the undernourished group of rats showed a 37% deficit (P less than 0.05) in the synapse-to-neuron ratio. This was due to a combination of an increase in the numberical density of neurons and a decrease in the numerical density of synapses, although, individually, neither of these reached statistical significance at the 5% level. In the granular layer of the cerebellum there was a 31% (P less than 0.01) deficit in the synapse-to-neuron ratio. This was a function of the reduced numerical density of synapses, with no difference in the numerical density of granule cells between groups. For the frontal cortex, the volume proportion of neuronal nuclei was significantly greater in the undernourished group of rats. There were no significant differences between control and undernourished rats in the volume of the 'forebrain' occupied by cortex. The mean diameters of neuronal nuclei and synaptic discs did not differ in any given region between treatment groups. These observations are discussed in context with the previously published results on synapses and neurons in undernourished animals.