Presence of a particular subpopulation of dopamine receptors within the septal nuclei: a behavioural study on cats.

The behavioural effects of intraseptal administration of dopaminergic drugs (apomorphine, haloperidol, (3,4-dihydroxy-phenylamino)-2-imidazoline (DPI), ergometrine and dopamine) and alpha-noradrenergic drugs (oxymetazoline, noradrenaline and phentolamine) were analysed in cats pretreated with morphine (5 mg/kg, i.p.). Changes in frequencies of stereotyped locomotor patterns were used for statistical evaluation of drug-induced effects. Taking advantage of the specificity of the drugs mentioned, a distinction could be made between effects mediated via excitation-mediating dopamine (DAe), inhibition-mediating dopamine (DAi) and alpha-noradrenaline (alpha-NA) receptors. Intraseptal injection of the DAi agonist DPI resulted in a decrease in the frequency of stereotyped locomotor patterns. This effect was dose-dependent and mimicked by that of intraseptally applied dopamine but not of any of the other drugs. Moreover, intraseptal injection of the DAi antagonist ergometrine inhibited the effect of DPI. The DAe agonist apomorphine as well as the DAe antagonist haloperidol remained ineffective when applied in low doses. The alpha-NA antagonist phentolamine and a rather high dose of haloperidol produced a slight but significant increase in the frequency of locomotor patterns; intraseptally applied oxymetazoline counteracted the phentolamine-induced effect. It is concluded that the septal nuclei of cats contain functionally active, alpha-NA receptors as well as functionally active, dopamine (DA) receptors having pharmacological properties identical to those of DA receptors present within the mesolimbic structures such as the nucleus accumbens: the so-called inhibition-mediating DAi receptors.