title: Immunoelectron microscopic study of glutamate inputs from the retrosplenial granular cortex to identified thalamocortical projection neurons in the anterior thalamus of the rat.
abstract: We have carried out an ultrastructural study to determine the characteristics and distribution of glutamate-containing constituents of the anterodorsal (AD) and anteroventral (AV) thalamic nuclei in adult rats. We used a polyclonal antibody to glutamate and a postembedding immunogold detection method in animals in which the neurons of AD/AV projecting to the cortex had been retrogradely labelled and the terminals of corticothalamic afferents anterogradely labelled by injection of cholera toxin-horseradish peroxidase (HRP) into the retrosplenial granular cortex. The heaviest immunogold labelling was over axon terminals 0.42 to 2.2 microm in diameter containing round synaptic vesicles and establishing Gray type 1 (asymmetric) synaptic contact (type 1 terminals) on HRP-labelled or non-labelled dendrites. Mean gold particle densities over such terminals were 3-4 times higher than the densities over the dendrites to which they were presynaptic and 5-6 times higher than over terminals establishing Gray type 2 (symmetric) synaptic contacts (type 2 terminals). Gold particle densities over neuronal cell bodies and dendrites and over a subpopulation of myelinated axons were intermediate between the densities over type 1 and type 2 terminals. In adjacent serial sections immunoreacted for gamma aminobutyric acid, type 2 terminals were heavily immunolabelled whereas type 1 terminals and other profiles with moderate gold particle densities after glutamate immunoreaction displayed very low labelling. A subpopulation of small type 1 axon terminals (up to 1 microm diameter) contained HRP reaction product identifying them as cortical in origin; they contacted small dendritic profiles (most <1 microm diameter) many of which also contained HRP reaction product. We conclude that terminals of the corticothalamic projection from retrosplenial granular cortex to AD/AV are glutamatergic and innervate predominantly distal dendrites of thalamocortical projection neurons.
authors.affiliation: Department of Anatomy and Developmental Biology, University College London, UK.
authors.forename: B
authors.initials: B
authors.lastname: Wang
authors.forename: A
authors.initials: A
authors.lastname: Gonzalo-Ruiz
authors.forename: L
authors.initials: L
authors.lastname: Morte
authors.forename: G
authors.initials: G
authors.lastname: Campbell
authors.forename: A R
authors.initials: AR
authors.lastname: Lieberman
mesh_terms: D000818:Animals; D020643:Anterior Thalamic Nuclei / Q000166:cytology*; D002540:Cerebral Cortex / Q000166:cytology*; D002772:Cholera Toxin; D018698:Glutamic Acid / Q000502:physiology*; D006735:Horseradish Peroxidase; D016253:Microscopy, Immunoelectron; D009434:Neural Pathways; D009474:Neurons / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D016610:Tissue Embedding
chemical_list: C052635:cholera toxin, B subunit-horseradish peroxidase; D018698:Glutamic Acid; D002772:Cholera Toxin; D006735:Horseradish Peroxidase