Possible neuronal mechanisms involved in neurotensin-induced catalepsy in mice

The neuronal mechanisms of neurotensin (NT)-induced catalepsy were investigated in mice. NT administered intracerebroventricularly (ICV 0.5, 1.0 and 2.0 g) produced catalepsy in a dose-dependent fashion. A significant effect was observed at 2.0 g and a maximal effect 2–3 h after injection. The NT-induced catalepsy was inhibited by pretreatment with atropine, trihexyphenidyl or biperiden (each drug, 0.8–5.0 mg/kg, IP), anticholinergic drugs, and L-DOPA (100, 200 mg/kg, IP). However, the catalepsy was not significantly antagonized by p-chlorphenylalanine (300 mg/kg×3 days, IP) or methysergide (5, 10 mg/kg, IP), antiserotonergic drugs, and was not potentiated by the GABAergic drugs, aminooxyacetic acid (25 mg/kg, IP) or muscimol (1 mg/kg, IP). In addition, the NT-induced catalepsy was dose-dependently reduced by antihistamines, such as diphenhydramine (0.8–10 mg/kg, IP) and tripelennamine (0.4–5.0 mg/kg, IP) and was potentiated after treatment with histidine (250, 500 mg/kg, IP), a precursor of brain histamine. NT-induced catalepsy was also reduced by ICV pretreatment with diphenhydramine (1–5 g/rat), a H₁ antagonist, but not by cimetidine (5, 20 g/rat), a H₂ antagonist. These findings suggest that the catalepsy induced by NT may involve not only central cholinergic and dopaminergic mechanisms but also a histaminergic mechanism mediated via H₁-histamine receptors, and seems to differ from the catalepsy induced by neuroleptics.