FIGURE 9. Baseline FRA expression in the somatomotor cortex. (A) In the 
diestrus rat many neurons thoughout all cell layers express FRAs. 
(B) In the lactating rat the baseline FRA expression in the cerebral 
cortex is markedly reduced. 
the neocortex of a diestrus rat and a lactating rat is shown in figure 9. These 
changes are consistent with the attenuation of many responses to stress 
observed in lactating rats and offer another example of the use of FRA staining 
as a means of identifying neuronal populations whose activity diminishes in 
response to neuronal stimuli and/or hormonal changes. 
REPRODUCTIVE STATE AS A VARIABLE IN STUDYING BRAIN 
ACTIVATION: LACTATION AND STIMULATION BY NMA 
Lactating rats, in addition to showing blunted behavioral changes to stress, fail 
to possess spontaneous pulses of LH release. In investigating the possible 
mechanisms of this reproductive quiescence, the authors treated lactating 
animals with the excitatory amino acid N-methyl-aspartate (NMA) at doses that 
stimulate LH secretion in cycling rats (Smith and Lee 1990). Attention in these 
studies was returned to c-Fos as a marker for stimulated activity. Lactating rats 
and a group of diestrus female rats were fitted with jugular cannulae, and four 
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