Effects of immobilization stress on tuberoinfundibular dopaminergic (TIDA) neuronal activity and prolactin levels in lactating and non-lactating female rats

Abstract

The effects of immobilization stress on the prolactin secretory response and on the activity of the tuberoinfundibular dopaminergic (TIDA) neurons were determined in intact, virgin female rats on the morning of diestrus or proestrus and in post-partum, lactating female rats. The virgin females exhibited a significant increase in circulating levels of prolactin which was evident by 1 minute and persisted during the immobilization (5 minutes). In contrast, the prolactin secretory response in lactating females was significantly attenuated compared to non-lactating animals. The activity of the TIDA neurons was not altered by the 5 minutes of stress. Even after 30 minutes of immobilization, TIDA neuronal activity was not affected in either the lactating or cycling females. These data suggest that the cycling female rat is capable of a prolactin secretory response to the stressor without inhibition of TIDA neuronal activity. It seems likely that prolactin releasing factors mediate this response. In contrast, stress did not produce a similar prolactin increase during lactation. It seems likely that, during lactation, the pituitary is not sensitive to releasing factors unless the TIDA neurons are inhibited. There appear to be differences in the sensitivity of the pituitary depending on the physiological state of the model employed.