Region specific changes in forebrain 5-hydroxytryptamine1A and 5-hydroxytryptamine2A receptors in isolation-reared rats: an in vitro autoradiography study.

The neurochemical correlates of the behavioural consequences of isolation rearing of rats are complex and involve many neurotransmitters, including the serotonergic system. Impaired functioning of the ascending serotonergic system has been implicated in many neuropsychiatric syndromes, including attention deficit hyperactivity disorder and schizophrenia. In the present investigation serotonergic function was assessed using in vitro receptor autoradiography. The 5-hydroxytryptamine(2A) (5-HT(2A)) receptor antagonist [(3)H]ketanserin and the 5-HT(1A) receptor antagonist, [(3)H]WAY100, 635 were used to compare 5-HT receptor subtype densities in the forebrains of socially and isolation-reared rats. Regions of highest receptor density were observed in the frontal cortex for 5-HT(2A) receptors and in the frontal cortex, dorsal hippocampus and lateral septum for 5-HT(1A) receptors. In isolation-reared rats, 5-HT(2A) receptor binding site densities were significantly increased by between 36 and 67% in the prelimbic, motor and cingulate cortices compared with socially reared controls. By contrast, 5-HT(1A) receptor binding site densities were significantly reduced by 22% in the prelimbic cortex, and significantly increased by between 10 and 50% in the motor cortex, somatosensory cortex, dentate gyrus and CA fields of the hippocampus. These data demonstrate that isolation-rearing produces significant effects on forebrain 5-HT(1A) and 5-HT(2A) receptor densities in the adult rat. It is hypothesised that altered serotonergic function, particularly in the hippocampus and prefrontal cortex, may underlie some of the behavioural abnormalities associated with isolation-rearing.