title: Preferential innervation of immunoreactive choline acetyltransferase synapses on relay cells of the cat's lateral geniculate nucleus: a double-labelling study.
abstract: Relationships between cholinergic axons and GABA cells in the lateral geniculate and the perigeniculate nuclei were quantitatively assessed by combining pre-embedding immunocytochemical visualization of choline acetyltransferase with post-embedding immunogold labelling of GABA at the electron microscopic level. In the lateral geniculate nucleus, vesicle-containing profiles immunoreactive for choline acetyltransferase made synapses exclusively with dendritic profiles both within and outside synaptic glomeruli. Only 7.0% (seven of 100 dendrites) of the target dendrites tested were positive for GABA. Of these, the majority (85.7%; 6/7) were dendritic profiles containing synaptic vesicles. This is in contrast with the overall population of geniculate synapses where 21.3% of the targets were GABA-immunopositive, a three-fold significant difference. In the perigeniculate nucleus, immunoreactive choline acetyltransferase synapses targeted mainly dendritic profiles (93.9%; 31/33) and to a lesser extent somata (6.1%). In this nucleus, all unequivocally defined targets were GABA-immunopositive. Cholinergic inputs thus show a preference to target geniculate relay neurons without a strong innervation of GABA-immunoreactive interneurons. In the perigeniculate, however, cholinergic synapses provide a powerful input to GABAergic cells. This suggests that the facilitatory effects of acetylcholine on the excitability of relay cells would be mediated through (i) a direct innervation of the geniculate relay cells, and (ii) a cholinergic inhibitory innervation of the recurrent inhibition to the lateral geniculate nucleus via the perigeniculate nucleus.
authors.affiliation: University of British Columbia, Department of Ophthalmology, Vancouver, Canada.
authors.forename: C
authors.initials: C
authors.lastname: Beaulieu
authors.forename: M
authors.initials: M
authors.lastname: Cynader
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism; D002415:Cats; D002795:Choline O-Acetyltransferase / Q000276:immunology / Q000378:metabolism*; D005829:Geniculate Bodies / Q000201:enzymology* / Q000502:physiology; D007124:Immunoenzyme Techniques; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D009411:Nerve Endings / Q000201:enzymology; D009474:Neurons / Q000201:enzymology / Q000502:physiology; D013569:Synapses / Q000201:enzymology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology
chemical_list: D005680:gamma-Aminobutyric Acid; D002795:Choline O-Acetyltransferase