Carnosine has been characterized as a putative neurotransmitter and implicated as having a possible role in neuron-glia cell interactions. We previously confirmed that central administration of carnosine induced hyperactivity in chicks. In the present study, we investigated the effects of nitric oxide (NO) synthase (NOS) inhibitors on carnosine-induced hyperactivity in chicks. Carnosine-induced (3.2 μmol) hyperactivity was attenuated by intracerebroventricular (i.c.v.) co-administration with a non-selective NOS inhibitor NG-nitro-l-arginine methyl ester HCl (200 and 400 nmol) in a dose-dependent manner, while the hyperactivity was not attenuated by the inactive isomer of the NOS inhibitor NG-nitro-d-arginine methyl ester HCl (400 nmol). The i.c.v. injection of a selective inhibitor of inducible NOS (iNOS) l-N6-(1-iminoethyl) lysine HCl (400 nmol) did not affect carnosine-induced hyperactivity. These results suggest that carnosine-induced hyperactivity may be linked to the constitutive NOS (cNOS), rather than iNOS, in the brain. Central carnosine may regulate brain function and/or behaviors by NO generation via cNOS in chicks.
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