Evidence for two different afferent pathways carrying stress-related information (noxious and amygdala stimulation) to the bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BNST) is an important nucleus involved in mediating amygdala-regulated endocrine effects. Since the amygdala is important in mediating the endocrine response to noxious somatosensory stimuli and olfactory stimulation, this experiment studies whether noxious input (tail pinch, TP) and stress-related input (amygdala stimulation, AmygS) will modulate BNST neuronal activity. One hundred and fifty-eight BNST neurons were studied following AmygS, TP and cutaneous stroke. AmygS was effective in 66% of BNST neurons and produced one of the following five responses: oligosynaptic excitation (43%), polysynaptic excitation (5%), time-locked inhibition (4%), generalized increase in firing rate (8%), or generalized decrease in firing rate (6%). TP produced an increase in firing rate in 27% of BNST neurons tested. Analysis of a contingency table constructed to determine the degree of correspondence between neurons responsive to AmygS and neurons responsive to TP showed that the distributions of reactivity to these stimuli in BNST neurons are independent of each other. This suggests that although AmygS and TP are both capable of altering the firing rate of BNST neurons, the pathways by which they reach BNST differ.