The median preoptic nucleus is involved in the facilitation of heat-escape/cold-seeking behavior during systemic salt loading in rats

Abstract

Systemic salt loading has been reported to facilitate operant heat-escape/cold-seeking behavior. In the present study, we hypothesized that the median preoptic nucleus (MnPO) would be involved in this mechanism. Rats were divided into two groups (n = 6 each): one group had the MnPO lesion with ibotenic acid (4.0 mug) and the other was the vehicle control. After subcutaneous injection (10 ml/kg) of either isotonic- (154 mM) or hypertonic-saline (2,500 mM), each rat was placed in a behavior box, where the ambient temperature was changed to 26 degrees C, 35 degrees C, and 40 degrees C every 1 h. The position of a rat in the box and the body core temperature (T(core)) were monitored. A rat could trigger 0 degrees C air for 45 s in the 35 degrees C and 40 degrees C heat when moved in a specific area in the box (operant behavior). In the control group, counts of the operant behavior were greater (P < 0.05) in the hypertonic- than in the isotonic-saline injection (17 +/- 2 and 10 +/- 2 at 35 degrees C, 24 +/- 2 and 18 +/- 1 at 40 degrees C). T(core) remained unchanged throughout the exposure, although the level was lower (P < 0.05) in the hypertonic- than in the isotonic-saline trial (36.6 +/- 0.2 degrees C and 37.4 +/- 0.1 degrees C at 26 degrees C and 36.9 +/- 0.2 degrees C and 37.4 +/- 0.1 degrees C at 40 degrees C, respectively). However, in the MnPO-lesion group, counts of the behavior were similar between the hypertonic- and isotonic-saline injection trials (10 +/- 2 and 8 +/- 1 at 35 degrees C, and 17 +/- 1 and 16 +/- 1 at 40 degrees C, respectively). T(core) increased (P < 0.05) in the heat in both trials (36.8 +/- 0.1 degrees C and 37.4 +/- 0.1 degrees C at 26 degrees C and 37.4 +/- 0.2 degrees C and 37.8 +/- 0.2 degrees C at 40 degrees C in the hypertonic- and isotonic-saline injection trials, respectively). These results may suggest that, at least in part, the MnPO is involved in the facilitation of heat-escape/cold-seeking behavior during osmotic stimulation.

Modulation of body temperature and LH secretion by hypothalamic KNDy (kisspeptin, neurokinin B and dynorphin) neurons: A novel hypothesis on the mechanism of hot flushes

“…For example, lesion studies suggest that neurons in the dorsomedial hypothalamus and neural fibers traveling though the paraventricular hypothalamic nucleus may play a role in cold-seeking behavior during endotoxin shock (Almeida et al, 2006b). In addition, the MnPO may be involved in operant cold-seeking behavior following systemic salt loading (Konishi et al, 2007). …”

The Transient Receptor Potential Vanilloid-1 Channel in Thermoregulation: A Thermosensor It Is Not

“…In our study (Almeida et al, 2006b), large bilateral preoptic lesions (including the entire MPO) did not change cold-and warmth-seeking responses of rats to thermal (cold and heat exposure), chemical (TRPV1 and TRPM8 agonists), or inflammatory [low and high doses of bacterial lipopolysaccharide (LPS)] stimuli. Although MPO neurons are unlikely to be involved in most thermoregulatory behaviors, MnPO neurons may be involved in at least some [e.g., in the intensification of an operant thermoregulatory behavior (moving to a reward zone during heat exposure to receive a breeze of cold air) caused by hypertonic saline (Konishi et al, 2007)]. Overall, not much is known about the neural pathways underlying thermoregulatory behaviors (Nagashima et al, 2000;Romanovsky, 2007b).…”

“…Because TRPV1-mediated signals from the abdominal viscera affect autonomic thermoregulatory responses but do not affect the selection of preferred T a , these signals are likely to impinge on the neural pathways for autonomic thermoregulation downstream from the point of separation from the pathways for thermoregulatory behaviors. This may happen in the MPO, because even large POA lesions (that destroy the MPO completely or nearly completely) do not affect thermoregulatory locomotion in a thermogradient apparatus (Almeida et al, 2006b), whereas a more upstream (closer to the afferent input) structure, the MnPO, seems to be involved in at least some behavioral thermoregulatory responses (Konishi et al, 2007). This hypothesis is schematically represented in Fig.…”

Functional architecture of behavioural thermoregulation

“…Data from thermal stimulation experiments in rats suggested that diVerent thermoregulatory behaviours such as thermoregulatory grooming (i.e., spreading saliva on the skin to increase evaporative heat loss), relaxed postural extension, and locomotion use distinct neural circuitries (Roberts 1988), while neurons in the median preoptic nucleus are implicated in moving to a reward zone during heat exposure to trigger a breeze of cold air, at least during osmotic stimuli (Konishi et al 2007). …”