The median preoptic nucleus is involved in the facilitation of heat-escape/cold-seeking behavior during systemic salt loading in rats.
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.
Konishi
Masahiro
M
Department of Physiology, Course of Health Science, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.
Kanosue
Kazuyuki
K
Kano
Masumi
M
Kobayashi
Akiko
A
Nagashima
Kei
K
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D001831:Body Temperature / Q000187:drug effects / Q000502:physiology; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology; D003080:Cold Temperature; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity; D006358:Hot Temperature; D007051:Ibotenic Acid / Q000633:toxicity; D008297:Male; D009994:Osmolar Concentration; D011301:Preoptic Area / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012201:Reward; D012462:Saline Solution, Hypertonic / Q000494:pharmacology
D018690:Excitatory Amino Acid Agonists; D012462:Saline Solution, Hypertonic; D007051:Ibotenic Acid