Location of CNS neurons mediating the blood pressure fall after shock-induced fighting in the rat.

Previous research has demonstrated a fall in systolic blood pressure in the rat measured 2--5 min following shock-induced fighting. This blood pressure fall appears to depend on intact CNS catecholamine neurons. The locus coeruleus is known to supply noradrenergic neuron terminals to much of the brain. In this study, we attempted to identify the location of the CNS catecholamine neurons mediating the blood pressure response to fighting by studying the blood pressure response to shock-induced fighting in locus coeruleus-lesioned and shamlesioned rats. The locus coeruleus-lesioned animals showed a blood pressure increase after fighting on the average across 2 days of testing, while sham-lesioned animals showed a blood pressure decrease after fighting. The difference between the blood pressure responses of the two groups was highly reliable. Since both histofluorescence and biochemical studies indicated that CNS norepinephrine levels were decreased in lesioned as compared to control animals, the findings are interpreted as showing that noradrenergic neurons originating in the locus coeruleus play an important role in mediating aspects of the relationship between fighting behavior and blood pressure response.