Male Sprague-Dawley rats were injected with either ibotenic acid or vehicle in the region of the median preoptic nucleus (MnPO) during methoxyflurane anesthesia. Later, the rats were tested for drinking responses elicited by angiotensin II (1 and 2 mg/kg s.c.) and hypertonic saline (3 and 6% w/v s.c.). Tests were conducted at 3 different phases of a 12:12 light-dark (LD) cycle (in the middle of the light phase and in the early and midportion of the dark phase). The rats with ibotenate lesions of the MnPO drank significantly less than vehivle-injected and lesion control groups regardless of when the tests were conducted. Subsequent monitoring of the diurnal rhythm of drinking, employing electrical lickometers, detected no difference between the rhythms of 4 rats with ibotenate lesions of the MnPO who failed to drink to homeostatic challenges and 4 vehicle-injected control rats. The results indicate that ibotenic acid lesions of the MnPO block drinking behavior stimulated by angiotensin II and hypertonic saline without disrupting the entrainment or pattern of ad libitum drinking.
- Angiotensin II
- Anteroventral region of the third ventricle
- Cellular dehydration
- Circadian rhythm