Cardiovascular and thermoregulatory responses to intrahypothalamically injected neurotransmitters in the pigeon

Abstract

1. 1.Cardiovascular and thermoregulatory responses to injections of neurotransmitters (1–10μ g of noradrenaline, NA; 10 μ g dopamine, DA; 10 μ g serotonin, 5-HT; 5 20 μ g acetylcholine, ACh) into the anterior hypothalamus were studied in the pigeon. 2. 2.All transmitters depressed mean arterial pressure (MAP). The order of potency was ACh, 5-HT, DA and NA. All monoamines (NA, DA, 5-HT) lowered also heart rate, while an intense tachycardia was seen during ACh-induced hypotension. The cardiovascular responses for NA, DA and ACh were similar at +25°C and +12°C, while 5-HT had a significantly smaller effect at +12°C. 3. 3.All transmitter reduced shivering intensity and body temperature ( T b ) at +12°C, but the degree of suppression did not correlate to changes in MAP. The order of potency for suppression of shivering was NA, DA, ACh and 5-HT. Foot temperature measurements showed that ACh induced a significant peripheral vasolidation, which enhanced the drop in T b . 4. 4.These results show that despite the strong neuronal interaction between cardivascular and thermoregulatory pathways in the avian hypothalamus, independent responses can also be elicited by exogenous transmitters. The previously described strong inhibition of shivering by intrahypothalamically injected NA is not caused by its effects on arterial pressure, but represents a more direct response of the thermoregulatory control system.