Single-unit activity of dorsomedial arcuate neurons and diurnal changes of tuberoinfundibular dopaminergic neuron activity in female rats with neonatal monosodium glutamate treatment.
Neonatal monosodium glutamate (MSG)-treated rats were used in this study to answer two questions: (1) whether or not the dopamine-responsive dorsomedial arcuate (dm-ARN) neurons are tuberoinfundibular dopaminergic (TIDA) neurons, and (2) whether or not the remaining TIDA neurons in MSG-treated rats are functioning normally. MSG (4 mg/g b. wt., subcutaneously [s.c.]) or saline was given to neonatal Sprague-Dawley rats on days 1, 3, 5, 7, and 9 after birth. The female rats were ovariectomized at 50 days of age and treated with estrogen for 1 week before they were used between 65-90 days of age. The tyrosine hydroxylase-immunoreactive (TH-ir) neurons located in the dm and ventrolateral (vl) parts of the ARN were significantly reduced in MSG-treated rats, as determined by immunohistochemical method. Some TH-ir cells, however, were visible along the border of the third ventricle. Using single-unit recording in brain slices, we found that dopamine inhibited significantly fewer percentage of dm-ARN neurons in MSG-treated (28.2%, n = 39) than in saline-treated rats (73.3%, n = 15). In contrast, bombesin exhibited similar effects (over 70% excitation) in both groups. Using neurochemical means, neonatal MSG treatment produced significant decreases of both 3,4-dihydroxyphenylacetic acid and dopamine levels, but not their ratios, in the median eminence. Moreover, the diurnal change of TIDA neuronal activity persisted in the MSG-treated rats; so did the estrogen-induced afternoon prolactin surge. All these results indicate that neonatal MSG-treatment reduced the number and altered the location of TIDA and dopamine-responsive dm-ARN neurons. The remaining TIDA neurons seemed to be able to maintain their basal activities and diurnal rhythm.
Lin
J Y
JY
Department of Medical Technology, Chung-Tai Institute of Medical Science and Technology, Taichung, Taiwan.
Pan
J T
JT
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001111:Arcuate Nucleus of Hypothalamus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D004298:Dopamine / Q000378:metabolism / Q000502:physiology*; D005260:Female; D008473:Median Eminence / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012970:Sodium Glutamate / Q000494:pharmacology*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D015102:3,4-Dihydroxyphenylacetic Acid; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine; D012970:Sodium Glutamate