Thermoregulatory Changes After Neurochemical Lesions of Catecholaminergic and Serotonergic Neurons in the Lower Brain Stem of the Guinea Pig

Abstract

Much experimental evidence indicating an antagonistic modulatory action of the monoamines 5-hydroxytryptamine (5-HT) and noradrenaline (NA) on hypothalamic thermosensitive and ther-mointegrative neurons, as well as their roles in thermoregulation and thermal adaptation has been reviewed previously (1). Although our knowledge concerning the participating neurochemical transmitter systems has significantly increased, our understanding of their functional role in different species is yet very limited. In different species the thermoregulatory and adaptive strategies may be different and seem to depend on animals’ individual or the inherited experience (2). In the guinea pig, we described the changes in regulatory characteristics, defined as deviations in threshold and gain of thermoregulatory responses to thermal changes during the ontogenic development and adaptation to warm and cold climates (3). In previous experiments we tried to influence these responses by monoamines microinjected or microinfused into the thermointegrative hypothalamic area (cf. refs. 1 and 2 for reviews). Opposite changes could be evoked by microinjections of substances blocking the aminergic receptors in this area or by neurotoxins specifically destroying the synaptic structures (4, 5). From these experiments it was concluded that in the guinea pig the hypothalamic release of NA due to activation of brain stem afferents may increase body temperature, whereas the blockade of hypothalamic adrenergic receptors or a neurochemical lesion induced by microinjected 6-hydroxydopamine (6-OHDA) reduced body temperature.