FIGURE 3. C-Fos activation in LHRH neurons during the rising phase of 
an LH surge. A plot from an animal whose plasma LH had 
only begun to rise within the hour prior to sacrifice (A) is 
compared with a plot from a rat whose plasma LH had nearly 
reached peak values (B). LHRH neurons expressing c-Fos are 
depicted as closed squares (it). LHRH neurons devoid of c-Fos 
immunoreactivity are shown as open squares (n)- Note that the 
higher degree of c-Fos activation in LHRH is associated with a 
greater elevation of plasma LH. 
SOURCE: Lee et al., in press, copyright 1992, by permission of Oxford 
University Press (Oxford, England). 
activity, did not allow the authors to analyze changes in baseline activity. 
Screening antisera that might allow a broader picture of IEG expression and 
examining other neuroendocrine systems provided some insight into this 
problem. Recently, Dragunow and Faull (1990) as well as Jacobsen and 
colleagues (1990) observed that staining with antisera generated against the 
M-peptide region of c-Fos revealed many nuclei in the cerebral cortex of control 
animals, whereas staining with an N-terminally directed c-Fos antiserum (or in 
situ hybridization of c-Fos mRNA) showed little or no baseline c-Fos expression. 
Since Western blots of the M-peptide antiserum indicated recognition of multiple 
proteins, it was reasoned that, in baseline conditions, some FRAs, but not 
c-Fos, are expressed. Consequently, the authors sought to determine if the 
basal FRA expression could be manipulated in a fashion to allow the 
examination of decreases in activity following stimulus delivery. 
The test system was the tuberoinfundibular dopamine system. This 
neuroendocrine system, located within the arcuate nucleus of the 
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