THE INVOLVEMENT OF DOPAMINE IN THE STRIATUM IN PASSIVE-AVOIDANCE TRAINING IN THE CHICK

Quantitative receptor autoradiography was used to investigate the dist ribution of binding of [H-3]SCH 23390 to dopamine (D-1) and [H-3]spiro perone to D-2 receptors in regions of the forebrain of the one-day-old domestic chick (Gallus domesticus). High levels of specific binding o f the D-1 and D-2 ligands were found in the striatal regions (paleostr iatum augmentatum and lobus parolfactorius) of the one-day-old chick, as reported previously in the pigeon, turtle and rat, whilst binding l evels were considerably lower in the pallidum (paleostriatum primitivu m), hippocampus and hyperstriatum ventrale. The proportions of D-1 and D-2 receptor binding in the chick were relatively similar in the stri atum and pallidum, apart from the paleostriatum augmentatum, where D-2 receptors outnumber those of D-1 by a factor of two. Binding of the D -1 and D-2 ligands to forebrain regions was also investigated 30 min a fter one-trial passive avoidance training of one-day-old chicks in whi ch the aversive stimulus was a bead coated with a bitter tasting subst ance, methyl anthranilate. These experiments demonstrated a large and highly significant bilateral increase (compared to control birds) in b inding to D-1 (but not D-2) receptors in the lobus parolfactorius. In this striatal region, equivalent to the caudate-putamen of mammals, pr evious studies have shown that synaptic and dendritic alterations occu r following avoidance training. It is concluded that alterations in do pamine binding may be involved in processes that result in modificatio n of the pecking response in chicks after avoidance training.