Rotational behaviour elicited by 5-HT in the rat: evidence for an inhibitory role of 5-HT in the substantia nigra and corpus striatum.

Unilateral intranigral microinjection of 5-HT or Wy 25093, a selective inhibitor of 5-HT uptake, elicited ipsiversive circling and a fall in striatal dopamine (DA) turnover. Conversely intranigral methysergide or unilateral lesions of the raphé-nigral 5-HT pathway produced contraversive turning and/or increased DA turnover. Both types of behaviour were accentuated by nialamide and attenuated by haloperidol. Caudate injections of 5-HT or Wy 25093 provoked contraversive turning which was increased by nialamide and hyoscine, partially diminished by haloperidol and antagonized by eserine. Ipsiversive circling was induced by intracaudate methysergide, which was potentiated by nialamide and eserine, unaffected by haloperidol and depressed by hyoscine. It is proposed that 5-HT normally subserves an inhibitory function both in the substantia nigra and corpus striatum.