The Journal of comparative neurology
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Comparative Study
Synaptic localization of NMDA receptor subunits in the rat retina.
The distribution and synaptic clustering of N-methyl-D-aspartate (NMDA) receptors were studied in the rat retina by using subunit specific antisera. A punctate immunofluorescence was observed in the inner plexiform layer (IPL) for all subunits tested, and electron microscopy confirmed that the immunoreactive puncta represent labeling of receptors clustered at postsynaptic sites. Double labeling of sections revealed that NMDA receptor clusters within the IPL are composed of different subunit combinations: NR1/NR2A, NR1/NR2B, and in a small number of synapses NR1/NR2A/NR2B. ⋯ The postsynaptic neurons are a subset of amacrine cells and most ganglion cells. Usually only one of the two postsynaptic processes at the bipolar cell ribbon synapses expressed NMDA receptors. In the outer plexiform layer (OPL), punctate immunofluoresence was observed for the NR1C2; subunit, which was shown by electron microscopy to be localized presynaptically within both rod and cone photoreceptor terminals.
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Except during blinks, movements of the upper eyelid are tightly coupled to vertical eye movements. The premotor source for the coordination of lid and eye movements is unknown. The present paper provides the anatomical identification of a new premotor cell group in the rostral mesencephalon of the monkey and human, which lies in close proximity to the premotor center for vertical saccades and is thought to participate in lid-eye coordination. ⋯ This projection pattern of the M-group suggests a role in the coordination of the upper eyelid and eyes during upgaze. Double-labeling experiments in macaque monkeys revealed that the M-group is strongly parvalbumin immunoreactive and contains high levels of cytochrome oxidase activity. With these two histochemical markers, the homologue of the M-group was identified in the human brain as well.
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Sodium channel 6 (NaCh6) is the alpha-subunit of a voltage-gated sodium channel expressed in the rat nervous system. The mRNA for this isoform has been shown to be expressed in both neuronal and glial cells by in situ hybridization. To examine localization of NaCh6 protein, polyclonal antibodies specific for NaCh6 were generated against peptides from two cytoplasmic domains and a fusion protein from an extracellular domain. ⋯ Dendrites of pyramidal cells in the cortex, hippocampus, and cerebellum were labeled. NaCh6 is the first NaCh subtype to be localized either at the node of Ranvier or to a dendrite. We conclude that NaCh6 is widely distributed in the central and peripheral nervous systems and is likely to be important for the electrical properties of the axon and dendrite.