Influence of rearing condition on 5-HT1A receptor responsiveness

Noppamars Wongwitdecha, Nattaporn Yoopan, Paungpayom Panya
1Centre of Neuro-Psychopharmacology, School of Medicine, Walailak University, Nakhon Si Thammarat, Thailand, 2Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand, 3Department of Medical Nursing, Faculty of Nursing, Chiang Mai University, Chiang Mai, Thailand

Rearing conditions in the early stages of life have been reported to alter the behavioral and neurochemical effects in the later life and modify the responsitivity to many drugs. The aims of these experiments were to investigate the effects of difference rearing conditions on anxiety and depression and to compare the effects of the selective 5-HT1A receptor agonist, 8-OH-DPAT in isolation and socially reared rats. Male Wistar rats were obtained weaning, and reared either alone (isolation rearing) or in groups of six rats/cage (social rearing). After four weeks, these rats were tested for their sensitivity to 8-OH-DPAT using the elevated plus-maze and the forced swimming tests. The results from the plus-maze test showed that the plus-maze behaviors of drug free isolation reared rats were not significantly difference from socially reared rats. Pre-treatment of 8-OH-DPAT (0.05, 0.1 and 0.5 mg/kg s.c.) dose-dependently produced an anxiogenic profile, indicated by a decrease in the percentage of open arm entries and the percentage of time spent on the open arms. These effects of 8-0H-DPAT were more pronounced in isolation than socially reared rats (P<0.05). The results from the forced swimming test demonstrated that drug free isolation reared rats showed significantly less immobility time and more struggling than the socially reared rats. Pretreatment of 8-OH-DPAT (0.1, 0.25, 0.5 and 1 mg/kg s.c., 24, 5 and 1 h before a 5 min test) in both isolation and socially reared rats produced a dose-dependent reduction of immobility and elevation in struggling compared to the saline treated group. These effects were greater in the isolation reared rats than the socially reared rats. The results suggest that rearing in isolation may produce some of its behavioural effects through central serotonergic mechanisms.