Distribution of alpha2-adrenergic binding sites in the parabrachial complex of the rat

Abstract

The present study describes the distribution of alpha 2-adrenoceptors in the parabrachial and Kölliker-Fuse nucleus of the rat by employing the tritium-labeled alpha 2-receptor antagonist rauwolscine ([3H]-RAUW) as a ligand. The [3H]-RAUW binding was densitometrically quantified in five nuclei of the parabrachial (PB) complex in serial coronal sections. We found that cytoarchitectonically and anatomically distinct nuclei of the PB complex exhibit different numbers of [3H]-RAUW-binding sites. The largest number of binding sites was observed over the external lateral PB and caudally over the waist area of the PB. Lower numbers of binding sites were found in the remaining lateral PB nuclei, followed by the medial PB and the Kölliker-Fuse nucleus. In addition we disclosed that the internal lateral PB contains a very low number of binding sites while the external medial PB is marked by dense [3H]-RAUW binding. Also, the affinities of the binding sites differed between the PB areas. High affinities were observed in the external lateral PB, the remaining lateral PB nuclei and in the waist area of the PB, while the medial PB and the Kölliker-Fuse nucleus exhibited only low affinities for the ligand. Furthermore, saturation curves demonstrated non-linear profiles, indicating the presence of more than one population of binding sites in the PB nuclei for the radioligand. Our data demonstrate that the PB exhibits a distinct distribution of alpha 2-adrenergic binding sites. These correlate well with the cytoarchitectonically defined nuclei of the PB complex and with the pattern of ascending axons from the medial nucleus of the solitary tract and the area postrema terminating in the PB. Since a large number of these projection neurons utilize adrenaline or noradrenaline as their transmitters, we conclude that solitary-parabrachial neurotransmission to the forebrain is, at least in part, mediated via alpha 2-adrenoceptors.

Expression of N-methyl-D-aspartate receptor subunits in the rat parabrachial and K�lliker-Fuse nuclei and in selected pontomedullary brainstem nuclei

“…Other neurotransmitter receptors in the PB/KF, or their subunits, are expressed in a more differential pattern. These include ␣-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA)-type (Chamberlin and Saper, 1995;Guthmann and Herbert, 1999b) and metabotropic glutamate receptors (Guthmann and Herbert, 1999a), ␥-aminobutyric acid (GABA) A receptors , glycine receptors , ␣ 2 -adrenoceptors (Herbert and Flü gge, 1995), and also various neuropeptide receptors (Delfs et al, 1994;Nakaya et al, 1994;Ding et al, 1996;Moriwaki et al, 1996). It is interesting to note that the external and internal lateral PB, which express NR2B and NR2A, respectively, in addition to NR1/NR2D subunits, are an exception also with respect to the presence and distribution of several other neurotransmitter receptors or receptor subunits (for discussion see Guthmann et al, 1998).…”

GABA, GABA transporters, GABAAreceptor subunits, and GAD mRNAs in the rat parabrachial and K�lliker-Fuse nuclei

“…Since the PB nuclei and the KF are anatomically and functionally quite distinct, it would be interesting to know in more detail whether or not they are subject to GABAergic inhibition and whether they might express specific types of receptors. That this is in fact the case, has already been shown for ␣ 2 -adrenergic receptors (Herbert and Flü gge, 1995), for subunits of the ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor (Chamberlin and Saper, 1995), and for the glycine receptor .…”

“…This finding is in line with previous studies demonstrating that the PBel and the PBw are an exception also with respect to the presence and distribution of several other neurotransmitter receptors or receptor subunits. For example, the PBel and the PBw exhibit the largest number of ␣2-adrenergic high-affinity binding sites (Herbert and Flü gge, 1995), but lack immunoreactivity for the ␣1-subunit of the strychnine-sensitive inhibitory glycine receptor . Furthermore, the PBel is strongly immunoreactive for µ-opioid receptors (Ding et al, 1996) and also for the GluR2/3-subunit of the AMPA-type glutamate receptor (Chamberlin and Saper, 1995).…”

Role of the lateral parabrachial nucleus in the control of sodium appetite

“…Serotonergic, adrenergic, and noradrenergic neurons are present in projections from the AP/NTS to the LPBN, and binding and immunohistochemical studies indicate the presence of ␣ 2 -adrenergic sites in the LPBN (70,83,98). There is evidence from both receptor binding and in situ hybridization studies indicating that there are GABA receptors in the PBN (7,16).…”