Tubero-infun-dibular dopamine neurons
Springer Online Journal Archives 1860-2000
Summary The response of central dopamine (DA) systems to physical stress (10 s footshock, 0.5 mA, to naive rats) or psychological stress (10 s stay in experimental chamber 1 day after footshock) was studied in male rats in view of possible interactions between these neuron groups and endogenous α-MSH. Three hours before stress, part of the animals were injected i.v. or intraventricularly with antiserum against α-MSH or with inactivated normal rabbit serum (NRS). Characteristic response patterns were observed in different DA neuron groups by histochemical microfluorimetry: In substantia nigra, increased fluorescence intensity of DA neurons indicating increased neuronal activity, was seen on the first day (1) 5 min after physical stress or (2) 30 min after a first transfer to the experimental chamber without footshock, and on the second day (3) immediately after the psychological stress in rats given a footshock on the previous day, or (4) 5 min after the second stay in the experimental chamber in animals previously exposed to the chamber without shock. Hence, the reaction appears to occur faster the second day. No significant intensity changes were detected in the ventromedial tegmental DA neurons (A10). The arcuate DA neurons which i.a. control α-MSH secretion, responded to physical stress or control manipulations in a complex way, while no significant reaction was seen after psychological stress. Differences between physical and psychological stress were also seen in serum levels of α-MSH (determined by RIA). Intravenous antiserum against α-MSH enhanced the response of nigral DA neurons to physical stress and led to elevated intensity levels 5 min after psychological stress when values were again decreasing in uninjected rats. Moreover, a marked rise in intensity was elicited after psychological stress in the A10 DA neurons where no change was detected in the absence of antiserum. Anti-α-MSH also affected the arcuate DA neurons in psychological stress. Intraventricular antiserum did not display any specific effects. These data point to a modulatory influence of circulating α-MSH on the functional state of central DA systems. They further reveal different temporal response patterns of nigral and also arcuate DA neurons in relation to the two stress situations and to other types of manipulations considered to be less stressful.
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