Ipsilateral hypothalamic deafferentation blocks the increase in serum FSH following hemi-castration

In two experiments hypothalamic hemi-islands or sham surgeries were produced on the right side of prepubertal male rats with an extrudable Halàsz-type knife (1.5 mm radius). Animals were then sham castrated or else hemi-castrated on the contralateral or ipsilateral side with respect to brain surgery. Eight or 21 days later, hemi-castrated rats given sham knife cuts showed a significant increase in serum FSH, relative to sham animals with intact testes. Also, animals given hypothalamic hemi-islands and hemi-castrated on the contralateral side showed a significant increase in serum FSH comparable to that seen in hemi-castrated rats with sham brain surgeries. However, hypothalamic hemi-island rats which were hemi-castrated on the ipsilateral side failed to show an increase in serum FSH and were similar to sham operated controls with both gonads. Serum LH levels were comparable among all groups, verifying a clear dissociation between LH and FSH secretion associated with hemi-castration in prepubertal males. In addition, the differences between contralateral and ipsilateral hemi-castrated animals with identical unilateral brain surgeries strongly suggest that FSH release is, in part, under direct neural control. However, in a third experiment, differences in FSH release between ipsi- and contralateral hemi-castrated rats were not found in animals with hypothalamic hemi-islands on the left side of the brain. Thus the hypothalamus may be asymmetrically involved in various components of neuroendocrine control.