Right-left asymmetry of tyrosine hydroxylase in rat median eminence: influence of arterial baroreflex nerves.
Arterial baroreceptor nerves consist of 2 pairs of nerves, carotid sinus and aortic. The latter nerves differ bilaterally as to size and origin suggesting that central baroreceptor activity could be asymmetrical. This was tested by studying activity of tyrosine hydroxylase (TH), the rate limiting enzyme for catecholamine synthesis, on right and left sides of the brain in median eminence (ME), arcuate nucleus (ARCN), paraventricular nucleus (PVN) and supraoptic nucleus (SON). Seven days after right or left sinoaortic denervation (SAD), bilateral SAD or sham-operation (SO), in situ TH activity was determined by the rate of dihydroxyphenylalanine (DOPA) accumulation following administration of a dopa decarboxylase inhibitor. Unexpectedly, the intact, SO rats had significantly lower DOPA concentrations on the left than right sides of ME in two separate studies; right-left differences averaged 24% and 38%. Evidence supporting asymmetry of TH activity was the lower concentrations of catecholamines on left than right sides of the brain in intact SO rats, namely, dopamine in ME and ARCN and norepinephrine and epinephrine in ARCN. Unilateral and bilateral SAD further suppressed TH activity on the left side of the ME; the maximum right-left difference was 58% in rats with right SAD. Their ARCN also showed asymmetry of TH activity. Asymmetry of TH activity was attributable to asymmetry of TH protein which was significantly lower on the left sides of ME and ARCN. This is the first demonstration of bilateral asymmetry of TH in mediobasal hypothalamus and its enhancement by interruption of left or right afferents from the arterial vascular system.
Alexander
N
N
Department of Medicine, University of Southern California School of Medicine, Los Angeles 90033.
Kaneda
N
N
Ishii
A
A
Mogi
M
M
Harada
M
M
Nagatsu
T
T
D000818:Animals; D001011:Aorta / Q000294:innervation*; D001921:Brain / Q000201:enzymology*; D002346:Carotid Sinus / Q000294:innervation*; D003714:Denervation; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D007839:Functional Laterality; D008297:Male; D008473:Median Eminence / Q000201:enzymology*; D009131:Muscle, Smooth, Vascular / Q000294:innervation; D011311:Pressoreceptors / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
D004295:Dihydroxyphenylalanine; D014446:Tyrosine 3-Monooxygenase