The nucleus magnocellularis in the red-eared turtle, Chrysemys scripta elegans: eighth nerve endings and neuronal types.

Eighth nerve endings and neuronal types in the nucleus magnocellularis were analyzed in the red-eared turtle (Chrysemys scripta elegans). One group of turtles had horseradish peroxidase (HRP) injected into the surgically exposed inner ear. Following injection the animals survived for 3-5 days and then their 8th nerve fibers and endings were analyzed. A second group of turtles were impregnated by the Golgi-Kopsch technique. This also demonstrated 8th nerve endings and neurons in the nucleus magnocellularis. A third group had brains stained with cresyl violet to demonstrate normal morphology. Two types of neurons were present in the nucleus magnocellularis; bushy and stellate. Bushy neurons had a single primary dendrite with little branching and spines. Stellate neurons had 3-5 primary dendrites with secondary order branching and dendritic spines. Thick 8th nerve axons gave rise to endbulbs of Held and their axons formed bouton-type ending. Endbulbs of Held were presently only on bushy neurons while bouton-type terminals were only on stellate neurons. Endbulbs of Held had two patterns; one group was cup-shaped and surrounded approximately 1/2 of the soma without appendages. A second type had a smaller cup with 3-5 extensions to other parts of the cell. Stellate neurons had terminal boutons adjacent to the cell membrane. They appeared in some situations as a necklace surrounding the neuron.

Ultrastructural features of the ventromedial region of the laminar nucleus in the red-eared turtle (Chrysemys scripta elegans).

The nuclei of the torus semicircularis, in particular the laminar nucleus, have been functionally implicated in sound localization, vocalization, and mating behavior. In the red-eared turtle the ventromedial region of the laminar nucleus (containing two discrete dense cellular areas and the surrounding neuropil) was examined electron microscopically in the present study. Neuronal cell bodies in the two cellular areas were different in size, shape, cytoplasmic constituents, and their relationship to each other. Cell bodies in the layer beneath the ependymal surface were almost always surrounded by lamellae while cell bodies in the layer above the central nucleus were in close apposition. We are speculating that cell bodies in the superficial layer may be neuroendocrine in nature. This speculation is based on the presence of lipidlike droplets within cell bodies, and previous findings indicating steroid binding and synthesis in this region in reptilian brains. Cell bodies located above the central nucleus were characteristic in that they contained lamellar bodies and extensive well-developed Golgi regions. Closely apposed groups of these cell bodies were frequently surrounded by or in close apposition to large axonal profiles. These profiles were filled with clear core vesicles, numerous mitochondria, and clusters of small dense core particles. Synaptic contacts between large axonal profiles and cell bodies were not observed. The neuropil surrounding cell bodies of the inner layer of this region of the laminar nucleus contained glomeruli composed of a central axon surrounded, and in synaptic contact, with dendrites. Throughout the area of the laminar nucleus studied, synapses appeared to be primarily of the asymmetrical type.

The reconnection of auditory posterior root fibers in the red-eared turtle, Chrysemys scripta elegans.

The auditory portion of the eighth nerve, the posterior root, was transected in Chrysemys scripta elegans. Two groups of animals were allowed to survive; one for 22 days and the second for 64 days. Each group was then reoperated to inject HRP into the cochlear duct and allowed to survive for an additional three days - for a total survival time of 25 days and 67 days. The 67 day survivors had HRP reaction product in the eighth nerve and the primary auditory nuclei, while the 25-day survivors did not. Degeneration byproduct was present in the same structures in the 25-day survivors while little was in the 67-day survivors. These results indicate as reconnection of the eighth nerve fibers to the acoustic tubercle.

The ascending connections of the torus semicircularis central nucleus in Chrysemys scripta elegans.

Horseradish peroxidase was injected into the torus semicircularis central nucleus of the red-eared turtle Chrysemys scripta elegans. The following observations were made. Axons originating in the central nucleus project ipsilaterally through the tectoreuniens tract to the ipsilateral nucleus reunions. A second tract leaves the central nucleus medioventrally, courses under the floor of the cerebral aqueduct and terminates as an axonal field in the contralateral central nucleus. Finally, there was a small pathway to the deep layers of the ipsilateral optic tectum.

The cytoarchitecture of the dorsal cochlear nucleus in the 3-month- and 26-month-old C57BL/6 mouse: a Golgi impregnation study.

The cytoarchitecture of the dorsal cochlear nucleus (DCN) was compared in 3- and 26-month-old C57BL/6 mice. The effects of genetically controlled progressive hearing loss present in the CNS in this mouse strain were analyzed with Nissl-stained and Golgi-impregnated material. The DCN was divided into the superficial molecular, an intermediate fusiform-granule, and the deep polymorphic layers. The molecular layer (ML) consisted of many fibers and a few small ovoid to spherical, fusiform, and granule cells. The fusiform-granule layer (FL) contained large fusiform and many granule cells. Most FL fusiform cells were oriented with their long axes perpendicular to the DCN surface and were present as small aggregations or individually. Cartwheel cells were adjacent to the FL fusiform cells. The deep polymorphic layer (PL) contained spherical, fusiform, granule, and multipolar neurons. The granule cells formed a dorsal cap of the DCN. From this cap, sheets of granule cells separated the DCN from the posterior ventral cochlear nucleus (PVCN) and from the brainsteM. The internal organization, neuronal location, orientation, and morphology were similar in both age groups. The granule cells had four to five primary dendrites, varicosities, and few to no dendritic appendages. The FL fusiform cells displayed different dendritic morphology in the two ages. One or two elaborate primary ML apical dendrites in the 3-month-old mice were covered with spikelike dendritic spines. The basal one or two PL dendrites were less elaborate and had few dendrite spines. In contrast, FL fusiform neurons in 26-month-old mice had regular dendritic varicosities and fewer spines which were short and stumpy. Basal dendrites had varicosities and interruptions. Cartwheel neurons in 3-month-old mice had elaborate ML dendritic trees covered with dendritic spines. In 26-month-old mice the dendrites had many varicosities and fewer short blunted dendritic spines. Large multipolar neurons in older mice had thinner dendrites with more varicosities than were in the 3-month group. In both age groups multipolar cells had few dendritic spines limited distally. Small and large spherical cells had two to five primary dendrites with varicosities, little higher-order branching, and spines. Fusiform cells had one or two primary dendrites, little secondary branching, and few to no spines. Minor degenerative changes were noted in spherical and fusiform cells in the two age groups. These included dendritic varicosities, interruptions, and some irregularities of somata surface. Degenerative changes present in the cochlea had significant effects on a limited population of DCN neurons. Finally, the neuronal morphology and architecture of the DCN in C57BL/6 mouse is similar to other mammalian species.

The cytoarchitecture of the torus semicircularis in the Tegu lizard, Tupinambis nigropunctatus.

The torus semicircularis (TS) of the Tegu lizard extends from the superficial caudal mesencephalon, dorsal to the exiting trochlear nerve, to a position ventral to the middle part of the optic tectum and its ventricle. It has an oblique orientation with the caudal pole abutting the midline while the rostal end is lateral and slightly ventral. The TS consists of a central nucleus and several adjacent cell groups. The central nucleus and the laminar nucleus, situated medially, extend the entire length of the TS while the cortical nucleus, situated dorsally and laterally, is present only in the caudal superficial portion. The central nucleus is composed of ovoid neurons with branched, radiating dendrites. The dendrites are directed medially and laterally with spines on the distal portion of the dendritic tree. The laminar nucleus consists of three to five neuronal layers. It is mainly composed of fusiform neurons with one dendritic trunk from each extremity of the soma. There is little branching and few dendritic spines. The cortical nucleus is a laminated region consisting of alternating layers of neurons and lateral lemniscal fibers. The neurons of the superficial layers are fusiform with their long axis perpendicular to the long axis of the brainstem. They possess two main dendritic trunks which parallel the laminae and are covered with dendritic spines. The deeper layers consist of pyramidal neurons with three dendritic trunks, secondary branches, and few spines. The long axis of these neurons extends from the center of the TS to the periphery. Two dendritic trunks extend dorsally or laterally towards the surface, while the third extends towards the central nucleus. The dendrites, thus, extend across the laminae. In addition, a cell-free lateral zone is described.

Projections of the trapezoid body and the superior olivary complex of the Kangaroo rat (Dipodomys merriami).

Glass micropipettes filled with 2 M sodium cyanide were used to physiologically locate and iontophoretically damage the nucleus of the trapezoid body (NTB), the medial superior olive (MSO), and the lateral superior olive (LSO). Mechanical lesions were made in the trapezoid body as it leaves the cochlear nuclei. After a 3- to 10-day survival time the projections and terminal degeneration were traced with the Fink-Heimer and Nauta-Gygax stains. The ventral cochlear nucleus (VCN) projects via the trapezoid body to ipsilateral LSO, ipsilateral preolivary nuclei, ipsilateral lateral and a contralateral medial dendritic fields of MSO, and contralateral NTB; there is also a small ipsilateral projection to the ventral nucleus of the lateral lemniscus (VNLL) and the central nucleus of the inferior colliculus (CNIC). Some trapezoid body fibers ascend via the contralateral lateral lemniscus to VNLL, DNLL (dorsal nucleus of the lateral lemniscus), and CNIC. There is no projection from the ventral cochlear nucleus to the ipsilateral NTB and contralateral preolivary nuclei. All portions of NTB project ipsilaterally to LSO (ventral NTB to dorsomedial LSO, dorsal NTB to ventral LSO) and to the retro-olivary nucleus. In two animals with NTB lesions there is also degeneration in the ventromedial portion of the ipsilateral facial nucleus. NTB projects contralaterally by way of the stria of Monakow to the pyramidal and molecular cell layers of the dorsal cochlear nucleus (DCN). The NTB does not project ipsilaterally to MSO, preolivary nuclei, VNLL, DNLL and CNIC. Contralaterally there are no projections to any of the nuclei of the auditory pathway except the DCN. Most MSO projections are ipsilateral. The densest goes by way of the lateral lemniscus to the lateral aspect of the ipsilateral CNIC, terminating throughout its dorsoventral axis. MSO also projects bilaterally to the pyramidal and molecular cell layers of dorsal cochlear nucleus (DCN), and ipsilaterally to the ventral portion of the motor nucleus of V and to the facial nucleus. MSO does not project ipsilaterally to the LSO, NTB, preolivary, VCN and retro-olivary nuclei. On the contralateral side, all structures except the DCN are free of projection patterns from axons originating in the MSO. LSO projects bilaterally to the central and ventral portions of CNIC and to the nuclei of the lateral lemnisci, and ipsilaterally to the large and small spherical cell areas of anterior ventral cochlear nucleus (AVCN) and to all portions of DCN. The LSO does not project ipsilaterally to the NTB, MSO, preolivary and retro-olivary nuclei. On the side opposite, this nucleus does not project to NTB, MSO, retro-olive, VCN, preolivary and LSO. For all lesions regardless of the site, there is no degeneration found rostral to the CNIC. The medial geniculate body or other structures in the diencephalon or cortex are free of any fields of terminal degeneration.