Involvement of the septum in central dopamine-acetylcholine interactions in morphine-treated cats

The involvement of the septum in central dopamine-acetylcholine (DA-ACh) interactions was investigated by analysis of the behavioural effects of intracerebrally injected drugs in cats pretreated with morphine (5 mg/kg, IP). The intracerebrally evoked effects on the morphine-induced behaviour were analyzed both quantitatively (changes in the incidence of locomotor patterns) and qualitatively (changes in the stereotyped nature of the behaviour patterns). Activation of a particular subclass of dopamine receptors (DAi receptors) within the septum by means of the DAi agonist (3,4-dihydroxyphenylamino)-2-imidazoline (DPI) suppressed the effect of intraseptal injections of the cholinergic agonist carbachol. Simultaneous activation of the DAi receptors within the septum and those within the caudate nucleus produced an effect characteristics of activation of septal DAi receptors; the effect characteristic of activation of caudate DAi receptors was suppressed. Analogous results were obtained when the DAi receptors within the septum and those within the caudate nucleus were simultaneously inhibited by the DAI antagonist ergometrine. Finally, it was found that the effect of intraseptal injections of the cholinergic agonist carbachol was suppressed by inhibition of the DAi receptors within the caudate nucleus. In the latter case, the effect characteristic of inhibition of caudate DAi receptors was also suppressed. The present results indicate the existence of interactions between (1) septal ACh activity and septal DAi activity, (2) septal DAi activity and caudate DAi activity, and (3) septal ACh activity . A mechanism of action for the observed interactions is discussed.