Involvement of β3-adrenergic receptors in the control of food intake in rats

This study examined the food intake changes evoked by intracerebroventricular (icv) injection of a selective agonist (BRL37344, 2 and 20 nmol) or antagonist (SR59230A, 10 and 50 nmol) of β3-adrenergic receptors in 24-h fasted rats (adult male Wistar rats, 200-350 g, N = 6/treatment). The animals were also pretreated with saline icv (SAL) or SR59230A (50 nmol) followed by BRL37344 (20 nmol) or SAL in order to determine the selectivity of the effects evoked by BRL37344 on food intake or the selectivity of the effects evoked by SR59230A on risk assessment (RA) behavior. The highest dose of BRL37344 (N = 7) decreased food intake 1 h after the treatment (6.4 ± 0.5 g in SAL-treated vs 4.2 ± 0.8 g in drug-treated rats). While both doses of SR59230A failed to affect food intake (5.1 ± 1.1 g for 10 nmol and 6.0 ± 1.8 g for 50 nmol), this treatment reduced the RA frequency (number/30 min) (4 ± 2 for SAL-treated vs 1 ± 1 for 10 nmol and 0.5 ± 1 for 50 nmol SR59230A-treated rats), an ethological parameter related to anxiety. While pretreatment with SR59230A (7.0 ± 0.5 g) abolished the hypophagia induced by BRL37344 (3.6 ± 0.9 g), BRL37344 suppressed the reduction in RA frequency caused by SR59230A. These results show that the hypophagia caused by BRL37344 is selectively mediated by β3-adrenergic receptors within the central nervous system. Moreover, they suggest the involvement of these receptors in the control of anxiety.

Modulation of food and water intake by catecholamines injected into the lateral ventricle of the pigeon brain

The effects of noradrenaline, adrenaline and dopamine on food and water intake were investigated in satiated (food ad libitum) adult pigeons weighing 320-360 g (N+10 per group). Catecholamines (80 nmol in 1 ul of saline) were injected into the right lateral ventricle. A significant increase in food consumption during the first hour was induced only by noradrenaline (8.1 ñ 1.8 g) and adrenaline (8.0 ñ 2.7 g) vs 1.9 ñ 0.6 g for the saline control. Noradrenaline also caused a significant drop during the secondar hour (1.7 ñ 0.6 g for the saline control). Dopamine decreased food intake at 2 h (1.4 ñ 0.3 g vs 3.5 ñ 0.7 g for the saline control) and 3 h (1.4 ñ 0.4 g vs 3.2 ñ 0.7 g for the saline control) post-injection, with a subsequent elevation in the feeding response during the 4th h (4.9 ñ 0.9 g vs 2.6 ñ 0.7 gf for the saline control). The total food ingestion for the 6-h period was similar for the control and experimental groups. Water consumption was not significantly affected by any catecholamine during any specific period but total ingestion was increased by noradrenaline (44.7 ñ 3.0 ml vs 29.6 ñ 5.1 ml for the saline control). These results suggest that catecholamines are involved in the neural control of food, but not water, intake in pigeons

Participation de alpha receptors in the neural control of food intake in pegeons

The effects of noradrenaline (NA) on food intake were investigated in 69 satiated (food ad libitum) adult pigeons (320-360 g). NA (30 nmol, N = 10, and 80 nmol, N = 12, in 1 µl NaCl) was injected into the right lateral ventricle. Both doses caused a significant increase in food consumption; the higher dose caused a more prolonged effect. The 30-nmol NA injection induced significant increases in the 1st (from 1.6 to 4.5 g) and 6th (19.4 to 25.9g) hours. The 80-nmol dose caused significant increases from the 1st to the 5th hour (1.6 to 6.8,4.4 to 8.7,7.1 to 10.8,10.1 to 14.1 and 14.9 to 21.0g). Previous intracerebroventricular administration of phentolamine (50 nmol, N = 12), but not of propranolol (100 nmol, N= 13) suppressed food ingestion increased by NA administration, with identical results to those of the control group (N = 22). These results indicate that central adrenergic synapses are likely to be involved in the mediation of food intake regulation

Central glucoregulation in the pigeon columba livia. Effects of intraventricular injections of carbachol and catecholamines on blood glucose concentration

The effect of chemical stimulation of the central nervous system on glucoregulation was studied in pigeons (Columba livia). Adrenaline (30 nmol), noradrenaline (30 or 80 nmol) and carbachol (27 nmol) were injected in 1 micron1 NaCl directly into the lateral ventricle and changes in blood glucose concentration were measured. The intraventricular injection of adrenaline resulted in rapid hyperglycemia, whrereas the injection of either carbachol or noradrenaline into the lateral ventricle did not cause any significant changes in blood concentration. These results suggest that adrenaline-containing neurons may be involved in central mechanisms controlling blood glucose concentration in the pigeon