GABA exerts opposite influence on warm and cold sensitive neurons in medial preoptic area in rats

Abstract

The preoptic area regulates body temperature. GABA-ergic terminals and receptors are present in this area. Local microinjection studies have shown that GABA, its agonist, and its antagonist in this area may modulate body temperature. However, there are warm and cold sensitive neurons, and they are known to be affected by local and peripheral temperatures. In order to understand the mechanism of action of GABA in temperature regulation at the cellular level it was necessary to study the effect of GABA on individual thermosensitive neurons in in vivo preparations. Hence, in this study the responses of preoptic area thermosensitive and insensitive neurons to microiontophoretic application of picrotoxin, a GABA-A antagonist, were studied in anaesthetized rats. It was observed that a majority of both the thermosensitive and insensitive neurons were affected by microiontophoretic application of picrotoxin. Although almost an equal number of cold and warm sensitive neurons were affected, a majority of the cold sensitive neurons were excited, while a majority of the warm sensitive neurons were inhibited by picrotoxin. The results suggested that in normal conditions GABA acts through GABA-A receptor in modulating the spontaneous activity of thermosensitive neurons in the preoptic area. Furthermore, the results of the present study taken together with other reports suggest that normally GABA exerts a direct inhibitory action on the cold sensitive neurons, while it acts on presynaptic heteroreceptors, possibly on norepinephrinergic afferent input terminals on the warm sensitive neurons, for mediating its action.

GABAergic/Glutamatergic–Glial/Neuronal Interaction Contributes to Rapid Adaptation in Pacinian Corpuscles

“…Concentrations of GABA and its antagonists were similar to those used in iontophoretic experiments (Caspary et al, 1994; Backoff et al, 1997, 1999; Jha, 2001; Gai and Carney, 2008). The neurite and the modified Schwann cells of the inner core are covered by at least 30 layers of outer lamellae that are joined by tight junctions, as well as an outer 5 layers of external capsule, making this preparation less readily accessible to drugs than cell-culture studies or other tactile receptor preparations, e.g., Panek et al (2002) or Fagan and Cahusac (2001).…”

Differential sensitivity to the motor and hypothermic effects of the GABAB receptor agonist baclofen in various mouse strains

“…Potential regional differences in GABA B receptor expression may also play a role in the altered hypothermic or ataxic responses to baclofen in the different mouse strains. Body temperature is coordinated primarily by the anterior hypothalamus and preoptic area (Boulant 2000;Frosini et al 2004), and is mediated at least partially through GABA B receptors in these regions (Yakimova et al 1996;Pierau et al 1997;Jha et al 2001). The posterior hypothalamus and brainstem nuclei are also implicated in body temperature regulation.…”

Distribution of vesicular glutamate transporter mRNA in rat hypothalamus

“…This region is known for its involvement in thermoregulation (Belugin et al, 1999;Ishiwata et al, 2001;Jha et al, 2001). The preoptic area contains thermosensitive neurons and is thought to influence body temperature via interconnections with related hypothalamic neuroendocrine systems and by descending projections to autonomic targets in the brainstem and spinal cord, which are then able to mobilize either metabolic thermogenesis or behavioral heat dissipation mechanisms (Belugin et al, 1999;Ishiwata et al, 2001;Jha et al, 2001).…”

“…This region is known for its involvement in thermoregulation (Belugin et al, 1999;Ishiwata et al, 2001;Jha et al, 2001). The preoptic area contains thermosensitive neurons and is thought to influence body temperature via interconnections with related hypothalamic neuroendocrine systems and by descending projections to autonomic targets in the brainstem and spinal cord, which are then able to mobilize either metabolic thermogenesis or behavioral heat dissipation mechanisms (Belugin et al, 1999;Ishiwata et al, 2001;Jha et al, 2001). In addition to its role in thermogenesis, the preoptic area is implicated in the regulation of male and female reproductive function and behavior (Coolen et al, 1998;Etgen et al, 1999) and in regulation of the hypothalamo-pituitary-adrenocortical axis (Viau and Meaney, 1996).…”