Sexual dimorphism in the organization of the rat hypothalamic infundibular area.
The hypothalamic infundibular area is located outside the blood-brain barrier and includes, the ventromedial arcuate nucleus (vmARC) sensing circulating substances, and the median eminence (ME) where neurohormones are released into the hypothalamo-hypophysial vasculature. This integrated functional unit, pivotal in endocrine control, adjusts neuroendocrine output to feedback information. Despite a differing physiology in males and females, this functional unit has not appeared differently organized between sexes. Using immunocytochemistry, we describe here for the first time in adult rats, a conspicuous sex-difference in its axonal wiring by intrinsic glutamatergic neurons containing the neuropeptides neurokinin B (NKB) and dynorphin. In the male, NKB neurons send axons to capillary vessels of the vmARC and of the ME (only where gonadotropin-releasing hormone (GnRH) axons terminate). Electron microscopy revealed that NKB axons target the barrier of tanycytes around fenestrated capillary vessels (in addition to GnRH axons), suggesting a control of regional bidirectional permeability. In the female, NKB neurons send axons to the neuropile of the vmARC, suggesting a direct control of its sensor neurons. The other projections of NKB neurons, studied by surgical isolation of the ARC-ME complex and confocal microscopy, are not sexually dimorphic and target both integrative and neuroendocrine centers controlling reproduction and metabolism, suggesting a broad influence over endocrine function. These observations demonstrate that the mechanisms subserving hypothalamic permeability and sensitivity to feedback information are sexually dimorphic, making the infundibular area a privileged site of generation of the male-to-female differences in the adult pattern of pulsatile hormonal secretions.
Ciofi
P
P
INSERM U378, Institut François Magendie, 146 rue Léo Saignat, F-33077 Bordeaux, France. philippe.ciofi@bordeaux.inserm.fr
Leroy
D
D
Tramu
G
G
D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000033:anatomy & histology* / Q000502:physiology; D005260:Female; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D008473:Median Eminence / Q000033:anatomy & histology* / Q000502:physiology; D016253:Microscopy, Immunoelectron / Q000379:methods; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010907:Pituitary Hormones / Q000378:metabolism; D051381:Rats; D012727:Sex Characteristics; D012737:Sex Factors
D009419:Nerve Tissue Proteins; D010907:Pituitary Hormones