Phenylephrine into the median raphe nucleus evokes an anxiolytic-like effect in free-feeding rats but does not alter food intake in free feeding rats

This study investigated the role of MnR alpha(1)-adrenergic receptors in the control of anxiety-like and feeding behaviors and attempted to reveal a possible functional association between both behaviors. The alpha(1)-adrenergic agonist phenylephrine (PHE) (at doses of 0.2, 2, 6, 20 nmol) or saline was injected into the MnR or into the pontine nucleus (Pn) of free-feeding rats. The animals were exposed to the elevated plus maze to analyse spatial-temporal and ethological variables. Subsequently, the ingestive and non-ingestive behaviors were recorded during 30 min and feeding and drinking behaviors were measured. Both in the elevated plus-maze and in the feeding chamber, all PHE doses injected into the MnR decreased the risk assessment frequency, an ethological parameter of anxiolytic-like effect. The spatial-temporal variables remained unchanged after PHE treatment. Feeding behavior was not affected by PHE into the MnR. The anxiety-like or ingestive behaviors were not affected by PHE treatment in the Pn, an area adjacent to the MnR. These data indicate that alpha(1)-adrenergic receptors within MnR participate in the control of anxiety-like behaviors. The absence of effects on feeding behavior after MnR alpha(1)-adrenergic activation could be due to an elevated alpha(1)-adrenergic tonus and its possible strong facilitatory influence on 5-HT neurons within MnR. Furthermore, the present results suggest that anxiety-like and feeding behaviors controled by MnR adrenergic circuits operate by independent neural pathways. (C) 2010 Elsevier B.V. All rights reserved.