Enhancement of [m-methoxy H-3]MDL100907 binding to 5HT(2A) receptors in cerebral cortex and brain stem of streptozotocin induced diabetic rats

5-Hydroxytryptamine(2A) (5-HT2A) receptor kinetics was studied in cerebral cortex and brain stem of streptozotocin (STZ) induced diabetic rats. Scatch ard analysis with [H-3] (+/-) 2,3dimethoxyphenyl-1-[2-(4-piperidine)-methan ol] ([H-3]MDL100907) in cerebral cortex showed no significant change in max imal binding (B-max) in diabetic rats compared to controls. Dissociation co nstant (K-d) of diabetic rats showed a significant decrease (p < 0.05) in c erebral cortex, which was reversed to normal by insulin treatment. Competit ion studies of [H-3]MDL100907 binding in cerebral cortex with ketanserin sh owed the appearance of an additional low affinity site for 5-HT2A receptors in diabetic state, which was reversed to control pattern by insulin treatm ent. In brain stem, scatchard analysis showed a significant increase (p < 0 .05) in B-max accompanied by a significant increase (p < 0.05) in K-d. Comp etition analysis in brain stem also showed a shift in affinity towards a lo w affinity State for 5-HT2A receptors. All these parameters were reversed t o control level by insulin treatment. These results show that in cerebral c ortex there is an increase in affinity of 5-HT2A receptors without any chan ge in its number and in the case of brain stem there is an increase in numb er of 5HT(2A) receptors accompanied by a decrease in its affinity during di abetes. Thus, from the results we suggest that the increase in affinity of 5-HT2A receptors in cerebral cortex and upregulation of 5-HT2A receptors in brain stem may lead to altered neuronal function in diabetes.