WARM AND COLD SIGNALS FROM THE PREOPTIC AREA - WHICH CONTRIBUTE MORE TO THE CONTROL OF SHIVERING IN RATS

1. To find out whether the thermosensitive neurones in the preoptic ar ea that control shivering are predominantly warm or cold sensitive, we tested the effects of injecting the excitatory amino acid L-glutamate at various sites in and adjacent to the preoptic area of anaesthetize d rats shivering at ambient temperatures of 15-21 degrees C. 2. L-Glut amate injections (0.2 mM in 0.5-1.0 mu l), as well as preoptic warming and electrical stimulation, suppressed shivering, whereas central sal ine injections had no effect. Effective sites were restricted to the a nterior part of the preoptic area, and a tenfold lower concentration o f L-glutamate did not influence shivering. 3. Injections of procaine ( 0.2 M) into the sites where L-glutamate suppressed shivering did not a ffect strong shivering activity, but facilitated shivering in three ou t of seven cases when shivering was weak or absent at higher ambient t emperatures (25-30 degrees C). 4. L-Glutamate injections, as well as p reoptic warming and electrical stimulation, also elicited vasodilatati on of the paw skin and the tail. Procaine elicited vasoconstriction wh en it was applied during vasodilatation induced by local preoptic warm ing. 5. These results indicate that the contribution of the preoptic a rea to the control of shivering and vasomotion is influenced more by s ignals from warm-sensitive neurones than by signals from cold-sensitiv e neurones.