alpha2-Adrenoceptor activation with
moxonidine (alpha2-
adrenergic/
imidazoline receptor agonist) into the lateral parabrachial nucleus (
LPBN) enhances
angiotensin II/hypovolaemia-induced
sodium intake and drives cell dehydrated rats to ingest hypertonic
sodium solution besides water.
Angiotensin II and osmotic signals are suggested to stimulate meal-induced water intake. Therefore, in the present study we investigated the effects of bilateral
injections of
moxonidine into the
LPBN on food deprivation-induced food intake and on meal-associated water and 0.3M NaCl intake. Male Holtzman rats with cannulas implanted bilaterally into the
LPBN were submitted to 14 or 24h of food deprivation with water and 0.3M NaCl available (n=6-14). Bilateral
injections of
moxonidine (0.5nmol/0.2microl) into the
LPBN increased meal-associated 0.3M NaCl intake (11.4+/-3.0ml/120min versus vehicle: 2.2+/-0.9ml/120min), without changing food intake (11.1+/-1.2g/120min versus vehicle: 11.2+/-0.9g/120min) or water intake (10.2+/-1.5ml/120min versus vehicle: 10.4+/-1.2ml/120min) by 24h food deprived rats. When no food was available during the test,
moxonidine (0.5nmol) into the
LPBN of 24h food-deprived rats produced no change in 0.3M NaCl intake (1.0+/-0.6ml/120min versus vehicle: 1.8+/-1.1ml/120min), nor in water intake (0.2+/-0.1ml/120min versus vehicle: 0.6+/-0.3ml/120min). The results suggest that signals generated during a meal, like
dehydration, for example, not hunger, induce hypertonic NaCl intake when
moxonidine is acting in the
LPBN. Thus, activation of
LPBN inhibitory mechanisms seems necessary to restrain
sodium intake during a meal.