GABAergic projection from the basal forebrain to the visual sector of the thalamic reticular nucleus in the cat

Abstract

We examined the projection from the basal forebrain to thalamic and cortical regions of the visual system in cats, with particular reference to the visual sector of the thalamic reticular nucleus, the lateral geniculate nucleus, and the striate cortex. First, we made injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the visual sector of the thalamic reticular nucleus and found cells labeled by retrograde transport in the lateral nucleus basalis magnocellularis. Injection of biocytin into the basal forebrain resulted in the anterograde labeling of a dense band of fibers and terminals within the entire thalamic reticular nucleus; this labeling extended through the visual sector including the perigeniculate nucleus. No orthograde labeling was found in the lateral geniculate nucleus. Next, we addressed the issue of putative neurotransmitters used by this pathway using a variety of immunocytochemical and histochemical markers. In this fashion, we identified two populations of cells in the nucleus basalis magnocellularis of the cat; large cholinergic cells that contain choline acetyltransferase, NADPH-diaphorase, and calbindin and that project to striate cortex and smaller cells that contain gamma-aminobutyric acid (GABA), glutamic acid decarboxylase, and parvalbumin and that project to the visual sector of the thalamic reticular nucleus. We also examined at the electron microscopic level terminals in the visual sector of the thalamic reticular nucleus that were labeled from a biocytin injection in the basal forebrain. Most of these terminals form symmetric contacts onto dendrites and were revealed by postembedding immunocytochemical staining to be positive for GABA.

Synaptic organization of thalamocortical axon collaterals in the perigeniculate nucleus and dorsal lateral geniculate nucleus

“…The ChAT antibody specifically binds a protein with a molecular weight of 68 kDa that forms 153 mol acetylcholine/minute/mg (Eckenstein and Thoenen, 1982). In cat tissue, this antibody stains the same pattern of thalamic terminals, and basal forebrain and mesopontine tegmentum cells, as has been demonstrated with other cholinergic markers in a variety of species Bickford et al, 1993Bickford et al, , 1994.…”

“…Thus, it can be concluded that all corticogeniculate terminals are smaller than RLD profiles. Furthermore, all other inputs to the dLGN and PGN either are smaller than RLD profiles or contain distinct neurotransmitters (Fitzpatrick et al, 1984Montero, 1986;Raczkowski and Fitzpatrick, 1989;Bickford et al, 1993Bickford et al, , 1994Erisir et al, 1997;Wang et al, 2001Wang et al, , 2002a. Therefore, all available evidence indicates that RLD profiles originate from the collaterals of geniculocortical axons.…”

Predominance of corticothalamic synaptic inputs to thalamic reticular nucleus neurons in the rat

“…GABAergic inputs to RTN cells derive from at least two sources. GABAergic projection cells located in the basal forebrain and the pars reticulata of the substantia nigra (Jourdain et al, 1989;Asanuma and Porter, 1990;Paré et al, 1990;Bickford et al, 1993Bickford et al, , 1994 send axons to end on proximal dendrites of RTN cells (Asanuma, 1994). Another source of GABAergic inputs is from neighboring RTN cells via axon collaterals and in some species from dendritic processes (Deschênes et al, 1985; Yen et al, 1985).…”

Distribution of synapses in the lateral geniculate nucleus of the cat: Differences between laminae A and A1 and between relay cells and interneurons

“…For this, we followed our previously described protocol (Bickford et al, 1994;Erişir et al, 1997a), modified from Phend et al (1992). Briefly, all solutions except the primary and secondary antibodies were filtered through a 0.22-µm Millipore filter.…”

“…Finally, the sections were rinsed in TBST at pH 7.6 and deionized water, placed in 2% glutaraldehyde (EM grade) for 10 minutes, rinsed again in deionized water, and counterstained with uranyl acetate and lead citrate to increase contrast. We used our previously described method (Bickford et al, 1994;Erişir et al, 1997a) for distinguishing significant postembedding levels from background labeling. The control for GABA labeling background were excitatory terminals of extraretinal origin, known as ''RD'' terminals.…”