INPUT FROM THE AMYGDALA TO THE RAT NUCLEUS-ACCUMBENS - ITS RELATIONSHIP WITH TYROSINE-HYDROXYLASE IMMUNOREACTIVITY AND IDENTIFIED NEURONS

Both tyrosine hydroxylase-positive fibres from the mesolimbic dopamine system and amygdala projection fibres from the basolateral nucleus ar e known to terminate heavily in the nucleus accumbens. Caudal amygdala fibres travelling dorsally via the stria terminalis project densely t o the nucleus accumbens shell, especially in the dopamine rich septal hook. The amygdala has been associated with the recognition of emotion ally relevant stimuli while the mesolimbic dopamine system is implicat ed with reward mechanisms. There is behavioural and electrophysiologic al evidence that the amygdala input to the nucleus accumbens is modula ted by the mesolimbic dopamine input, but it is not known how these pa thways interact anatomically within the nucleus accumbens. Using a Var iety of neuroanatomical techniques including anterograde and retrograd e tracing, immunocytochemistry and intracellular filling, we have demo nstrated convergence of these inputs on to medium-sized spiny neurons. The terminals of the basolateral amygdala projection make asymmetrica l synapses predominantly on the heads of spines which also receive on their necks or adjacent dendrites, symmetrical synaptic input from the mesolimbic dopamine system. Some of these neurons have also been iden tified as projection neurons, possibly to the ventral pallidum. We hav e shown a synaptic level how dopamine is positioned to modulate excita tory limbic input in the nucleus accumbens.