ALPHA-1-ADRENOCEPTORS IN THE ADULT-RAT BARREL FIELD - EFFECTS OF DEAFFERENTATION AND NOREPINEPHRINE REMOVAL

Norepinephrine (NE), acting on brain adrenoceptors, plays an important role in barrel field neuronal activity and plasticity. For this reaso n, the distribution of alpha1- and alpha2-adrenoceptors in the somatos ensory cortex barrel field was studied by autoradiographic techniques in rats undergoing plastic change or NE depletion. In layers IV and V of the cortex, the pattern of alpha1-adrenoceptors (assessed by [H-3]p razosin binding) varied across the barrel field. There was relatively low binding within the barrels themselves, with 21% higher binding in the surrounding septa. alpha2-Adrenoceptor binding (assessed with [H-3 ]paraminoclonidine) was almost homogeneous across the entire barrel fi eld. Two weeks after noradrenergic deafferentation by unilateral lesio ning of the locus coeruleus, there was a 16% upregulation of [H-3]praz osin binding. This then returned to control levels by 8 weeks. Periphe ral deafferentation of sensory input to the barrel field produced the opposite effect on alpha1-adrenoceptors. Unilateral removal of all but the central (C3) vibrissa (which induces plastic changes in the corti cal representation of the spared vibrissa) caused a 12% decrease in [H -3]prazosin binding in the whole barrel field at 2 weeks after surgery which returned to normal by 8 weeks. Therefore, alpha1-adrenoceptors in the barrel field of the rat are affected in opposite ways by change s in NE content and afferent sensory input. We hypothesize that alpha1 -adrenoceptor levels are modulated after vibrissectomy through either an indirect reaction to reduced cortical gamma-aminobutyric acid level s, or by a reordering of metabolic priorities during plastic change of the cortical neuronal network.