Axonal connections of thalamic posterior paralaminar nuclei with amygdaloid projection neurons to the cholinergic basal forebrain in the rat.

Stimulation of the amygdala elicits cortical activation mediated by the corticopetal basal forebrain. An unresolved question is whether the involved amygdala neurons that project to the basal forebrain receive direct thalamic input. Using combined retrograde and anterograde tracing techniques, we demonstrate a monosynaptic contact between thalamic posterior paralaminar nuclei axons and neurons in the central amygdala that project to corticopetal cholinergic basal forebrain regions. These contacts may constitute the morphological substrate for the induction of fast cortical arousal and attention triggered by emotional events.