Aa. Dunnmeynell et Be. Levin, ALPHA-1-ADRENOCEPTORS IN THE ADULT-RAT BARREL FIELD - EFFECTS OF DEAFFERENTATION AND NOREPINEPHRINE REMOVAL, Brain research, 623(1), 1993, pp. 25-32
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.