Effects of precollicular decerebration on the vasomotor and sympathetic nerve responses to locus coeruleus stimulation.

In 25 cats under intraperitoneal alpha-chloralose (40 mg/kg) and urethane (400 mg/kg) anesthesia, cardiovascular reactive sites of locus coeruleus (L.C) were stimulated by rectangular pulses (0.5 ms, 80 Hz, 100 to 200 microA) and/or by microinjection of sodium glutamate (Glu, 0.25 M, 70-150 nl). Changes of systemic arterial blood pressure (SAP) and sympathetic vertebral (VNA) and renal (RNA) nerve activities following stimulations were analyzed and, furthermore, SAP responses were compared before and after precollicular decerebration (PD). Microinjection of Glu in this region often produced a moderate increase and less often decrease in SAP. Depressor points were located dorsal to the sites eliciting pressor responses. In the majority of LC stimulations (69%) VNA increased along with the increase of SAP, while the RNA decreased. In a few stimulations marked increase in VNA and decrease in RNA occurred with little change in SAP. PD itself produced various degrees of a temporary (lasted for 5 to 15 min) decrease in SAP from 40 to 100 mmHg. Following PD, three types of change in the LC induced SAP responses were observed in a decreasing order, i.e., the responses were slightly reduced or slightly augmented, or the LC induced depressor responses were converted to a pressor one. Findings of the present study showed that neural mechanism in LC responsible for the changes of SAP and sympathetic nerve activities may exist in a topographic organization. LC is different from the gigantocellular tegmental field (FTG) located in the same rostral pons. The marked pressor responses elicited by activation of the FTG depend entirely on the rostral brain structure, while LC is not. Some brain structures rostral to superior colliculi may exert both inhibitory and excitatory influences over LC in cardiovascular integration.