This paper describes the fine structure of granule cells and granule-associated interneurons (termed Golgi cells) in the cochlear nuclei of cat, rat and mouse. Granule cells and Golgi cells are present in defined regions of ventral and dorsal cochlear nuclei collectively termed "cochlear granule cell domain'. The granule cells are small neurons with two or three short dendrites that give rise to a few branches with terminal expansions. These participate in glomerular synaptic arrays similar to those of the cerebellar cortex. In the glomeruli the dendrites form short type 1 synapses with a large, centrally-located mossy bouton containing round synaptic vesicles and type 2 synapses with peripherally located, smaller boutons containing pleomorphic vesicles. The granule cell axons is thin and beaded and, on its way to the molecular layer of the DCN, takes a straight course, which in ventral nucleus is parallel to the pial surface. Neurons of the second category resemble cerebellar Golgi cells and occur everywhere interspersed among the granule cells. They are usually larger than the granule cells and give rise to dendrites which may branch close to and curve around the cell body. The dendrites contain numerous mitochondria and are laden with thin appendages, giving them a hairy appearance. Both the cell body and the stem dendrites participate in glomerular synaptic arrays. Golgi cell glomeruli are distinguishable from the granule cell glomeruli by unique features of the dendritic profiles and by longer, type 1 synaptic junctions with the central mossy bouton. The Golgi cell axon forms a beaded plexus close to the parent cell body. The synaptic vesicle population of the mossy boutons suggests that they are a heterogeneous group and may have multiple origins. Apparently, each of the various classes participates in both granule and Golgi cell glomeruli. The smaller peripheral boutons with pleomorphic vesicles in the two types of glomeruli may represent Golgi cell axons which make synaptic contacts with both granule and Golgi cells. The Golgi cell axons which make synaptic contacts with both granule and Golgi cells. The Golgi cell dendrites, on the other hand, are also contacted by small boutons en passant with round synaptic vesicles, which may represent granule cell axons. A tentative scheme of the circuitry in the cochlear granule cell domain is presented. The similarity with the cerebellar granule cell layer is striking.

The projection of the vestibular nerve to the cerebellum of the cat was examined with silver degeneration methods after complete lesions of the vestibular ganglion. The majority of the primary vestibular afferents were traced to the cortex of the ipsilateral nodulus and uvula, relatively fewer entering the ipsilateral flocculus. Fibers were not traced to the paraflocculus, lingula or lateral cerebellar nucleus. A sparse projection to the ipsilateral fastigial nucleus may exist, but it remains equivocal until confirmed with additional methods. Light microscopic examination of plastic sections confirmed these observations and showed further details of the organization of the primary vestibular projection to the nodulus and uvula. These results show that the region of the cerebellum densely innervated by primary vestibular afferents is smaller than previously believed.

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The projection of the vestibular nerve to the brainstem of the cat was re-examined with silver degeneration methods after complete lesions of the vestibular ganglion. Whereas previous investigations emphasize that only parts of the major vestibular nuclei are innervated by the vestibular nerve, the present investigation shows that only the dorsal division of the lateral vestibular nucleus is uninnervated. Thus, the terminal field of the vestibular nerve extends to the cytoarchitectonic boundaries of the superior, medial, descending, and the ventral division of the lateral vestibular nuclei. Vestibular nerve fibers were also traced to discrete terminal fields in the reticular formation lateral to the abducens nucleus and in the rostral, lateral parts of the accessory cuneate nucleus. These observations indicate a more widespread distribution of vestibular nerve fibers in the brainstem of the cat than previously believed.

Rats that receive intravenous injections of sodium iodate develop a retinopathy characterized by the partial loss of the retinal pigment epithelium (RPE). In thin sections examined by transmission electron microscopy the choriocapillaris atrophied adjacent to areas of RPE destruction. The endothelial cells thickened and lost their fenestrae and the lumen of the capillary was reduced. At sites where the RPE remained normal in appearance the choriocapillaris did not atrophy. Scanning electron microscopy of vascular casts of the choriocapillaris showed the coexistence of atrophic and normal choriocapillaris throughout the retina, presumably adjacent to sites where the RPE was destroyed or spared, respectively. Our observations support the concept that the RPE exerts some control over the structure and function of the choriocapillaris.