Frontolateral hypothalamic knife cuts: interruption of paraventricular efferents to the thoracolumbar cord

Bilateral thoracolumbar cord injections of the fluorescent tracer bisbenzimide produced extensive retrograde labelling of cell bodies in the paraventricular nucleus of the hypothalamus. Unilateral retrochiasmatic knife cuts (1.5 mm radius) located anterolateral to the paraventricular nucleus dramatically reduced or eliminated the labelling of paraventricular neurons on the ipsilateral side following bilateral bisbenzimide injections into the thoracolumbar cord. Thus paraventricular efferents to the thoracolumbar cord must project in a lateral direction at the level of the nucleus prior to descending toward the spinal cord. Changes in endocrine function, reproductive and feeding behavior reported following similar hypothalamic knife cuts may be related to this efferent system.