Anatomical and physiological relationships between the anterior cerebellar vermis and the pontine parabrachial nucleus in the rabbit.

The anatomical connections between the midline cerebellum and the pontine parabrachial nucleus (PBN) were investigated in the rabbit using anterograde and retrograde axonal transport techniques. Small injections (20-50 nl) of cholera toxin conjugated to horseradish peroxidase (CT-HRP) or wheat germ agglutinin conjugated HRP (WGA-HRP) into the cortex of the anterior cerebellar vermis resulted in retrograde and anterograde-like label in the PBN. Focal injections of tracer into the PBN resulted in anterogradely labeled processes in the ACV and retrogradely labeled a small, but distinct group of Purkinje cells within the anterior vermis. Focal injections into the rostral fastigial nuclei (FN) resulted in anterograde-like label in the PBN, and PBN injections labeled FN neurons. Furthermore, the projection from the PBN to ACV is effective in driving cerebellar neurons as electrical microstimulation of the PBN evoked short-latency, phasic responses in ACV Purkinje cells. These experiments generated anatomical and physiological evidence for the existence of a neuroanatomical circuit connecting the midline cerebellum (ACV, FN) with the PBN, that may serve as a functional interface between the midline cerebellum and other brain stem nuclei with cardiovascular function, particularly with respect to the midline cerebellar role in classically conditioned cardiovascular responses.