Maternal separation and early social deprivation in Octodon degus: Quantitative changes of nicotinamide adenine dinucleotide phosphate-diaphorase-reactive neurons in the prefrontal cortex and nucleus accumbens

The influence of postnatal socio-emotional deprivation on the development o f nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase-reactive n eurons in prefrontal cortical areas and in subdivisions of the nucleus accu mbens was quantitatively investigated in the precocious rodent Octodon degu s. Forty-five-days-old O. degus from two animal groups were compared: (i) d egus which were repeatedly separated from their mothers during the first th ree postnatal weeks and after weaning oared in complete isolation; and (ii) degus which were reared under normal undisturbed social conditions. Social ly-deprived animals displayed a significant decrease of NADPH-diaphorase-co ntaining neurons in anterior cingulate cortex (85.5%), the same tendency wa s observed in the infralimbic, precentral medial and prelimbic prefrontal a reas. Similarly, the core region of nucleus accumbens expressed reduced NAD PH-diaphorase-reactive neuron numbers in deprived animals (70%), whereas th e shell region remained unchanged. Since during normal postnatal developmen t the number of NADPH-diaphorase-reactive neurons gradually decreases in al l prefrontal cortical and accumbal regions, the observed deprivation induce d changes may reflect either an excessive reduction of NADPH-diaphorase-pos itive neurons or a down-regulation of the enzyme in neurons that normally e xpress it. Since some NADPH-diaphorase-containing neurons in the prefrontal cortex have been shown to be GABAergic, it is tempting to speculate that a reduction of these inhibitory neurons in the anterior cingulate cortex may result in an enhanced excitatory output activity of disinhibited projectio n neurons in this cortical region, including those that project to the core region of the nucleus accumbens. Our results indicate a link between early adverse socio-emotional experienc e and the maturation of NADPH-reactive neurons and further studies are requ ired to analyse the functional implication for this experience-induced brai n pathology. (C) 1999 IBRO. Published by Elsevier Science Ltd.