Changes in the activity of the limbic-hypothalamic neural pathways under the repeated immobilization stress

Electrical activity of hypothalamus during activation of pituitary-adrenocortical system

Multiunit activity in anterior (AHA), medial (MHA) and lateral (LHA) areas of hypothalamus during activation of the pituitary-adrenocortical system was measured in chronic experiments on rabbits. Immobilization causing blood-corticosteroid levels to rise was followed by the excitation of most pools of neurons in MHA, and by inhibition in AHA and LHA. When immobilization failed to induce stimulation of MHA (as a result of pretreatment with large doses of cortisol), it did not cause blood-corticosteroid levels to rise, either. The switching off activity in AHA and MHA is considered to be a manifestation of functional changes which are responsible for stress-induced activation of the adrenocortical system.

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.