Investigation of influence of diazepam, valproate, cyproheptadine and cortisol on the rewarding ventral tegmental self-stimulation behaviour.

Experiments were carried on in the Wistar rats having self-stimulation (SS) electrodes implanted chronically in substantia nigra-ventral tegmental area (SN-VTA) to examine whether modulations of GABAergic, serotonergic, histaminergic, dopaminergic, and glucocorticoid neuronal receptor functions will affect or not the brain reward system and the SS behaviour. The modulators are the wellknown drugs: diazepam which is a facilitator of some of the GABA receptors, and used clinically for its tranquilizing, anxiolytic, sedative-hypnotic and anti-convulsant properties; sodium valproate which is known to enhance the GABA synapse function, and used clinically for its anti-convulsant property; haloperidol which is a dopaminergic receptor (D2) blocker, and clinically used for its anti-psychotic property; cyproheptadine which is both anti-histaminic and anti-serotonergic (blocks 5-HT2 receptor), used clinically for its antihistaminic and other beneficial properties; and hydrocortisone which is the stress-resisting glucocorticoid having direct effects on both brain and body cells, used clinically for the wide-ranging glucocorticoid therapeutic effects. The results revealed that systemic administration of these drugs, except haloperidol, caused no significant influence on the SS behaviour, thereby indicating that these nondopaminergic drugs have no effect on brain-reward system and also these categories of synaptic actions are not likely to be involved in the primary organization of the mechanisms of the brain-reward system.