The afferent input and functional organization of the hypothalamus in reactions regulating pituitary-adreno-cortical activity.

In chronic experiments on rabbits, stimulation of the dorsal tegmentum of the midbrain caused an increase in serum corticosteroid level. In acute experiments, stimulation of the same region resulted in changes in the activity of hypothalamic neurons. Neurons in the anterior (AHA), medial (MHA), including the medial dorsal (MHAd) and medial ventral (MHAv) areas, and lateral (LHA) areas of the hypothalamus were studied. When the midbrain was stimulated, more neurons in LHA, MHAd and MHAv were excited than inhibited; in AHA, more neurons were inhibited. These changes suggest that the activation of the pituitary-adrenocortical system caused by stimulation of the dorsal tegmentum is associated with changes in the influx of afferent impulses to the hypothalamus, which are responsible for AHA inhibition and MHA and LHA excitation.