Distributions of GABA_A, GABA_B, and benzodiazepine receptors in the forebrain and midbrain of pigeons

Abstract

Autoradiographic and immunohistochemical methods were used to study the distributions of GABAA, GABAB and benzodiazepine (BDZ) receptors in the pigeon fore- and midbrain. GABAA, GABAB and BDZ binding sites were found to be abundant although heterogeneously distributed in the telencephalon. The primary sensory areas of the pallium of the avian telencephalon (Wulst and dorsal ventricular ridge) tended to be low in all three binding sites, while the surrounding second order belt regions of the pallium were typically high in all three. Finally, the outermost rind of the pallium (termed the pallium externum by us), which surrounds the belt regions and projects to the striatum of the basal ganglia, was intermediate in all three GABAergic receptors types. Although both GABAA and benzodiazepine receptors were abundant within the basal ganglia, GABAA binding sites were densest in the striatum and BDZ binding sites were densest in the pallidum. Among the brainstem regions receiving GABAergic basal ganglia input, the anterior and posterior nuclei of the ansa lenticularis showed very low levels of all three receptors, while the lateral spiriform nucleus and the ventral tegmental area/substantia nigra complex contained moderate abundance of the three binding sites. The dorsalmost part of the dorsal thalamus (containing nonspecific nuclei) was rich in all three binding sites, while the more ventral part of the dorsal thalamus (containing specific sensory nuclei), the ventral thalamus and the hypothalamus were poor in all three binding sites. The pretectum was also generally poor in all three, although some nuclei displayed higher levels of one or more binding sites. The optic tectum, inferior colliculus, and central gray were rich in all three sites, while among the isthmic nuclei, the parvicellular isthmic nucleus was conspicuously rich in BDZ sites. The results show a strong correlation of the regional abundance of GABA binding sites with previously described distributions of GABAergic fibers and terminals in the avian forebrain and midbrain. The regional distribution of these binding sites is also remarkably similar to that in mammals, indicating a conservative evolution of forebrain and midbrain GABA systems among amniotes.

Organization of the avian “corticostriatal” projection system: A retrograde and anterograde pathway tracing study in pigeons

“…The Ac, BNST, and TO constitute ventral striatal regions (horizontal shading). The P P forms the dorsal pallidum, and Wild et al, 1990;Veenman and Reiner, 1994;Veenman et al, 1994a). In the present paper, however, we refer to them simply as ventral striatum (Ac, BNST, and TO) or ventral pallidum (VP; ventral paleostriatum).…”

Oscillatory Bursts in the Optic Tectum of Birds Represent Re-Entrant Signals from the Nucleus Isthmi Pars Parvocellularis

“…Ipc neurons have paintbrush endings that make dense, presumably cholinergic (Sorenson et al, 1989;Bagnoli et al, 1992;Medina and Reiner, 1994;Hellmann et al, 2001;Wang et al, 2004), axonal connections across many tectal layers in the same location of the tectum from which their visual inputs come (Wang et al, 2004). In contrast, Imc neurons make presumably GABAergic (Veenman and Reiner, 1994;Tömböl and Németh, 1998;Hellmann et al, 2001;Wang et al, 2004), inhibitory (Tömböl and Németh, 1998) connections over most of the Ipc as well as most of the tectum (Fig. 7).…”

GABAB and group I metabotropic glutamate receptors in the striatopallidal complex in primates

“…Furthermore, the interpretation of many of these functional studies is hampered by the lack of information on the synaptic localisation of these receptors in basal ganglia neurons. Indeed, most data on the distribution of the different mGluR subtypes and GABA B receptors were obtained by autoradiographic ligand binding studies (Wilkin et al 1981 ;Bowery et al 1984Bowery et al , 1987Gehlert et al 1985 ;Chu et al 1990 ;Albin et al 1992 ;Veenman et al 1994), in situ hybridisation methods and light or confocal microscope immunocytochemical techniques (Martin et al 1992 ;Testa et al 1994Testa et al , 1998Kaupmann et al 1997Kaupmann et al , 1998Kerner et al 1997 ;Petralia et al 1997 ;Berthele et al 1998 ;Kinoshita et al 1998 ;Kosinki et al 1998 ;Mun4 oz et al 1998 ;Shigemoto et al 1998 ;Bradley et al 1999 ;Castelli et al 1999 ;Fritschy et al 1999 ;Lu et al 1999 ;Margeta-Mitrovic et al 1999).…”