Rationale: Histaminergic neurotransmission has been implicated in the pathophysiology of stress-related psychiatric diseases. Although several atypical antipsychotics are potent H1 antagonists, the clinical significance of interaction between atypical antipsychotics and H1 receptors is still unknown.
Objective: In this study, we investigated the effects of H1 receptors blockage on social isolation-induced behavioral changes in H1 receptor gene knockout (H1KO) mice and their wild-type (WT) mice.
Methods: Both H1KO and their WT mice were subjected to 4-week social isolation rearing after weaning (21 postnatal days). After the 4-week isolation period, mice behavioral changes were evaluated using behavioral tests.
Results: Locomotor activity in home cages was significantly lower in isolation-reared WT mice than in socially reared WT mice. However, no change in locomotor activity was observed between socially and isolation-reared H1KO mice. Social isolation significantly impaired prepulse inhibition (PPI) of startle response in WT mice but not in H1KO mice. In addition, social isolation significantly impaired spatial learning and memory in WT mice but not in H1KO mice. Furthermore, H1KO mice treated with methamphetamine (METH) showed no enhancement in isolation-induced disruption of PPI. A neurochemical study revealed that isolation-reared WT mice had significantly lower dopamine (DA) levels and slightly increased DA turnover in the cortex than socially reared WT mice. Conversely, isolation-reared H1KO mice showed significantly higher DA contents as compared with socially reared H1KO mice.
Conclusion: The results of our study indicate that blockage of H1 receptor-mediated neurotransmission attenuates social isolation-induced behavioral changes and that the therapeutic effects of atypical antipsychotics are mediated, at least in part, by interaction with H1 receptors in the brain.