In vivo microdialysis was used to measure extracellular concentrations
of norepinephrine in the diagonal band of Broca (DBB) during changes
in blood pressure in conscious rats. Dialysate norepinephrine concentr
ation was significantly increased during acute hypertension (280 +/- 4
0% of control), but was not changed by hypotensive hemorrhage. These r
esults are consistent with the proposal that noradrenergic innervation
of the DBB is selectively activated by increased blood pressure.