Neuronal activity of identified posterior hypothalamic neurons projecting to the brainstem peribrachial area of the cat.

Following horseradish peroxidase injections in the brainstem peribrachial (PB) area, massive retrograde labeling was found in the posterior hypothalamic region. Single-unit recordings posterior hypothalamic neurons with antidromically identified projections to the PB area revealed that these neurons have higher firing rates in waking than in slow-wave sleep and dissimilar discharge patterns as compared with intralaminar thalamic neurons. The results are discussed in the context of reciprocal hypothalamo-brainstem circuits.