title: Norepinephrine depletion impairs neuroendocrine responses to fear but not novel environmental stimuli in the rat.
abstract: Emotional stimuli suppress vasopressin secretion and potentiate oxytocin and prolactin secretion by the pituitary in the rat. We studied effects of central norepinephrine depletion on these hormonal responses to novel environmental or fear stimuli. Male Wistar rats were injected intracerebroventricularly with 5-amino-2,4-dihydroxy-alpha- methylphenylethylamine, a selective neurotoxin to noradrenergic fibers. The neurotoxin treatment reduced the hypothalamic content of norepinephrine by 71% but did not significantly affect the dopamine content. Novel environmental stimuli suppressed vasopressin secretion and augmented secretion of oxytocin and prolactin in the vehicle-injected rats. The neurotoxin did not block the neuroendocrine responses. Intermittently applied electric footshocks also induced the similar neuroendocrine responses in the vehicle-injected rats. The neurotoxin significantly reduced the neuroendocrine responses. The drug, however, did not significantly alter vasopressin release after continuously applied footshocks. Environmental stimuli previously paired with footshocks (conditioned fear stimuli) suppressed vasopressin secretion and augmented secretion of oxytocin and prolactin in the vehicle-injected animals. Motor activity was suppressed during the conditioned fear stimuli. The neurotoxin impaired the neuroendocrine and behavioral responses whether the drug was injected before or after the conditioning. These data demonstrate the distinction between the neural mechanisms underlying the neuroendocrine responses to fear and to novel stimuli, suggesting that noradrenergic neurons are selectively involved in the hypothalamo-hypophysial responses to fear stimuli.
authors.affiliation: Department of Physiology, Jichi Medical School, Tochigi-ker, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Onaka
authors.forename: J R
authors.initials: JR
authors.lastname: Palmer
authors.forename: K
authors.initials: K
authors.lastname: Yagi
mesh_terms: D000818:Animals; D003213:Conditioning, Psychological; D005239:Fear; D007031:Hypothalamus / Q000187:drug effects*; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D010121:Oxytocin / Q000097:blood; D010627:Phenethylamines / Q000494:pharmacology*; D011388:Prolactin / Q000097:blood; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D014667:Vasopressins / Q000097:blood
chemical_list: D010627:Phenethylamines; C072819:5-amino-2,4-dihydroxy-alpha-methylphenylethylamine; D014667:Vasopressins; D010121:Oxytocin; D011388:Prolactin; D009638:Norepinephrine