Stellate neurons in rat dorsal cochlear nucleus studied with combined Golgi impregnation and electron microscopy: synaptic connections and mutual coupling by gap junctions

Abstract

Stellate neurons in the outer two layers of the rat dorsal cochlear nucleus (DCN) were studied by the Golgi-EM method. Stellate cell bodies are usually spherical or ovoidal and range from 9 microns to 14 microns in mean diameter. The smallest cells are situated underneath the ependymal layer and the largest cells in layer 2. Primary dendrites are short, thin and smooth and arise abruptly from the perikaryon, without a tapering main stem. Meandering secondary and tertiary dendrites extend in all directions, carry few pleomorphic spines lacking a spine apparatus and often show artifactual beading. The axons are impregnated only for a short distance (10-45 microns). The nucleus is indented, the nucleolus varies in position, and the chromatin, evenly dispersed in the centre, forms small clumps along the nuclear envelope. The cytoplasm is rich in free polyribosomes and contains scattered cisterns of granular endoplasmic reticulum. Varicosities of thin fibres, containing round synaptic vesicles, form asymmetric synapses on perikarya, dendritic shafts and spines of stellate cells. Such fibres run parallel to the long axis of the DCN or are oriented radially and are interpreted as axons of cochlear granule cells. Two kinds of bouton containing pleomorphic vesicles, one kind electron lucent and the other electron dense, form symmetric synapses on perikarya and dendritic shafts of stellate cells. The lucent boutons occur more frequently than the dense boutons, especially on the distal dendritic branches. The boutons with pleomorphic vesicles presumably represent terminals of local circuit neurons, probably the stellate and cartwheel cells. In addition, stellate cells show numerous dendro-somatic and dendro-dendritic appositions characterized by gap junctions and puncta adhaerentia. Most of the dendrites involved in these appositions resemble stellate cell dendrites and it is concluded that DCN stellate cells are coupled electrotonically with one another. The axons of stellate cells acquire a thin myelin sheath. Since the Golgi impregnation did not stain axons of stellate cells past this point, we were unable to demonstrate the synaptic targets of stellate cells.

γ‐aminobutyric acid and glycine in the baboon cochlear nuclei: An immunocytochemical colocalization study with reference to interspecies differences in inhibitory systems

“…, 1987Osen et al, 1990;Kolston et al, 1992;Ottersen et al, 1995). They receive input from parallel fibers, and their short axoris contact the dendrites of pyramidal and cartwheel cells in the molecular layer (Wouterlood et al, 1984). Their terminals may account for the higher density of GABA puncta in the outer DCN than in the rest of the CNC.…”

The neuropeptide cerebellin is a marker for two similar neuronal circuits in rat brain.

“…Axons of the cochlear granule cells make up a system of parallel fibers in layer 1 (molecular layer) of the DCoN that synapse with neurons arborizing in this region (8), including the spiny cartwheel cells (9), the nearly aspiny stellate cells (10), and the apical spiny arbor of pyramidal cells (11). Whereas analogy of pyramidal neurons to mammalian cerebellar neurons, if any, remains to be ascertained, cartwheel and stellate neurons bear several distinctive cellular and synaptological similarities to cerebellar Purkinje cells and stellate cells, respectively (9,10). This analogy even goes beyond the wiring strategy in that some of the neuronal cell types show biochemical similarities, perhaps emphasizing common functions.…”

Synaptic connections in the dorsal cochlear nucleus of mice, in vitro.

“…The neuronal composition of each lamina is different. The two classes of neurones which project from the DCN are called fusiform and giant cells, and the main classes of interneurones are cartwheel, stellate and granule cells (Lorente de No, 1933Osen, 1969;Brawer et al 1974;Kane, 1974;Mugnaini, Osen, Dahl, Freidrich & Korte, 1980a;Mugnaini, Warr & Osen, 1980b;Webster & Trune, 1982;Blackstad, Osen & Mugnaini, 1984; Wouterlood, Mugnaini, Osen & Dahl, 1984; Smith & Rhode, 1985).…”