Synapse-to-neuron ratios of the frontal and cerebellar cortex of 30-day-old and adult rats undernourished during early postnatal life.

Male rats undernourished from birth to 30 days were nutritionally rehabilitated till 160 days of age. Quantitative stereological procedures at the light and electron microscopical levels were employed to estimate, among other things, the synapse-to-neuron ratios in the frontal cortex and granular layer of the cerebellum. In the frontal cortex, the 30-day-old undernourished rat had a mean +/- SE of about 14,020 +/- 1,540 synapses-per-neuron compared with 22,270 +/- 3,250 for the controls. This was a deficit of 37% (p < 0.05). By 160 days of age the previously undernourished rats showed no statistically significant deficit in this ratio compared with controls (11,800 +/- 690 and 13,360 +/- 1,110 respectively, p > 0.1). This was due mainly to a fall in the synapse-to-neuron ratio with age. A much larger fall in the ratio occurred in the control than in the previously undernourished group. In the granular layer of the cerebellum the 30-day-old undernourished rats had 341 +/- 17 synapses-per-neuron compared with 495 +/- 25 for the controls. This was a deficit of 31% (p < 0.01). By 160 days of age the previously undernourished rats again showed no statistically significant deficit in this ratio compared with controls (627 +/- 56 and 688 +/- 38, respectively (p > 0.1). These results show that the previously undernourished rats are capable of at least some (if not complete) "catch-up" with regard to the synapse-to-neuron ratio.