Single-cell responsiveness to sensory stimuli in the mediobasal hypothalamus of rats with partial hypothalamic deafferentations and medial forebrain bundle lesions

Neuroendocrine studies have demonstrated that photic, acoustic, and sciatic nerve stimulation produce adrenocortical discharges and these can be blocked by partial hypothalamic deafferentations and medial forebrain bundle (MFB) lesions. The effects of these sensory stimuli on single-cell activity of mediobasal hypothalamic (MBH) neurons were studied in intact male rats and in animals with anterior, anterolateral, and posterolateral hypothalamic deafferentations and bilateral MFB lesions. The data were analyzed as to changes in responsiveness, facilitation: inhibition ratio, patterns of firing, magnitude of response, frequency distribution, and sensory convergence. Photic projections enter the MBH both anteriorly and posteriorly and via the MFB, acoustic afferent fibers utilize the MFB, and the sciatic impulses arrive posteriorly. The MFB has also an inhibitory modulation on the photic, acoustic, and sciatic responses and AHD has the same effect on the latter. MFB lesions reduced most markedly the sensory convergence of the three modalities. The relation of these electrophysiologic findings to neuroendocrine studies on the neural pathways mediating adrenocortical responses are discussed.