USE OF FOS-RELATED ANTIGENS (FRAS) AS MARKERS OF NEURONAL-ACTIVITY - FRA CHANGES IN DOPAMINE NEURONS DURING PROESTRUS, PREGNANCY AND LACTATION

This manuscript describes the use of staining of Fos-related antigens (FRAs) as markers for changes in neuronal activity. The model system c onsisted of the tuberoinfundibular dopamine (TIDA) neurons located in the arcuate nucleus of the hypothalamus. Under normal conditions, thes e neurons are devoid of c-Fos staining even though the neurons are ton ically active and can express FRAs. During specific neuroendocrine sta tes the neurons undergo changes in activity, as described by other stu dies. At times when the activity is relatively high as in pregnancy an d during proestrus, approximately 50%-60% of the TIDA neurons expresse d FRA immunoreactivity. Moreover changes over the course of proestrus paralleled known shifts in TIDA activity (declining as the day progres sed). At times when TIDA activity is suppressed, such as during lactat ion, FRA staining in TIDA neurons was markedly reduced or absent. Upon removal of the suckling stimulus, FRA staining rose to reach peak exp ression 12-24 h after pup removal (without coordinate induction of c-F os). These data suggest that FRA staining can serve as a useful marker of activity in the TIDA neurons which permits not only assessment of stimulated activity but also suppressed function in the neurons. A cau tionary note in using this approach along with acquisition of serial b lood samples for hormone measurement is that surgical procedures for m onitoring plasma hormone levels are associated with strong long-lived induction of FRAs (and c-Fos) in many neurons (including the TIDA neur ons) that can confound interpretation of FRA staining.