Effects of isolation-rearing on serotonin-1A and M1-muscarinic receptor messenger RNA expression in the hipocampal formation of rats

The aim of the present work was to investigate if isolation rearing could change 5-HT1A or M1 muscarinic receptors messenger RNA (mRNA) expression in the hippocampal formation. Male Wistar rats were isolated either in single cages or in groups of six per cage soon after wearing during 30 days. After this period they were sacrificed and their brains removed for 'in situ' hybridization study using P-32-labeled oligonucleotide probes complementary to 5-HT1A or M1 muscarinic receptor mRNA. The results were analyzed by computerized densitometry. They showed a significant (P < 0.05, Mann-Whitney test) serotonin 1A (5-HT1A) mRNA expression increase in the dentate gyrus and CA3 areas of isolated animals. The signal also tended to be higher (P < 0.10) in CA1 and CA4 regions. No significant change on M1 mRNA expression was found. These results may reflect up-regulation of 5-HT1A gene transcription in response to deficits in hippocampal serotonin neurotransmission induced by social isolation. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.