Functional antagonism between dopamine and noradrenaline within the caudate nucleus of cats: A phenomenon of rhythmically changing susceptibility

Two aspects of the functional interaction between the neurotransmitters dopamine (DA) and noradrenaline (NE) were studied: the role of NE within brain structures marked by DA terminals and the occurrence of annual changes in their functional interaction. The behavioral changes produced by single or combined administration of DA, (3,4-dihydroxyphenylamino)-2-imidazoline (DPI), ergometrine, ET-495, NE, oxymetazoline, and phentolamine into the caudate nucleus of freely moving cats were analyzed. NE and oxymetazoline produced effects that differed from those elicited by DA or DPI. NE-dependent effects were antagonized by phentolamine, and DA- or DPI-induced effects were antagonized by ergometrine. Ergometrine, NE, and oxymetazoline were effective in November, December, and January, lost their effectiveness in March, April, and May, regained it in July, and lost it again in August, September, and October. The annual pattern of DA, DPI, and phentolamine on the other hand, was just the opposite. DA agonists suppressed NE- or oxymetazoline-induced effects, while the DA antagonist suppressed phentolamine-induced effects. Noradrenergic agents were unable to modulate the DA-dependent effects under certain circumstances. It is concluded that (1) NE-dependent processes within the feline caudate nucleus inhibit DA-dependent processes within this structure, and (2) there exists a reciprocal relationship between the annual changes in the feline's susceptibility to DA, DPI, and phentolamine, on the one hand, and to ergometrine, NE, and oxymetazoline, on the other hand.