ULTRASTRUCTURAL FEATURES OF THE LATERAL GENICULATE NUCLEUS OF THE CAT

Immunocytochemical and ultrastructural organization of the taste thalamus of the tree shrew (Tupaia belangeri)

Ventroposterior medialis parvocellularis (VPMP) nucleus of the primate thalamus receives direct input from the nucleus of the solitary tract, whereas the homologous thalamic structure in the rodent does not. To reveal whether the synaptic circuitries in these nuclei lend evidence for conservation of design principles in the taste thalamus across species or across sensory thalamus in general, we characterized the ultrastructural and molecular properties of the VPMP in a close relative of primates, the tree shrew (Tupaia belangeri), and compared these to known properties of the taste thalamus in rodent, and the visual thalamus in mammals. Electron microscopy analysis to categorize the synaptic inputs in the VPMP revealed that the largest-size terminals contained many vesicles and formed large synaptic zones with thick postsynaptic density on multiple, medium-caliber dendrite segments. Some formed triads within glomerular arrangements. Smaller-sized terminals contained dark mitochondria; most formed a single asymmetric or symmetric synapse on small-diameter dendrites. Immuno-EM experiments revealed that the large-size terminals contained VGLUT2, whereas the small-size terminal populations contained VGLUT1 or ChAT. These findings provide evidence that the morphological and molecular characteristics of synaptic circuitry in the tree shrew VPMP are similar to that in nonchemical sensory thalamic nuclei. Furthermore, the results indicate that all primary sensory nuclei of the thalamus in higher mammals share a structural template for processing thalamocortical sensory information. In contrast, substantial morphological and molecular differences in rodent versus tree shrew taste nuclei suggest a fundamental divergence in cellular processing mechanisms of taste input in these two species.

Electron-lucent degenerating geniculate terminals in cat striate cortex

Degenerating geniculate axon terminals in cat striate cortex have been previously described as electron-dense. After electrolytic lesion of the lateral geniculate nucleus, we observed degenerating terminals in layer 4 of striate cortex which were electron-lucent. The lucent terminals --which co-exist with the dense terminals--are characterized by a pale matrix, large size, distorted mitochondria, and a paucity of synaptic vesicles. They preferentially (82.5%) contact dendritic spines. Lucent terminals were common in layer 4, rare in layer 6, and absent from layers 1 through 3 and layer 5. This distribution is consistent with the projection of the lateral geniculate nucleus to the striate cortex. Thus, geniculate terminals undergo both the electron-lucent and electron-dense degeneration reactions in cat striate cortex, and the lucent terminals make a significant contribution to the amount of degeneration present. The relationship of lucent degeneration to other forms of degeneration is discussed.

Complex convolutions in neurons of the dorsal lateral geniculate nucleus of the normal albino rat

The postnatal development of complex convolutions (CCs) of the dorsal lateral geniculate nucleus (LGNd) in normal rats has been studied quantitatively with light microscopy. We report that immature neurons do not contain these scarcely understood organelles, since they can be seen for the first time in very few, mature neurons of the 30 day rat; their number constantly increases during the following 4 months. These cytoplasmic inclusions can be equally seen in the aged rat. CCs are present in neurons of all sizes, except the smallest, which correspond to the interneuron population. Although, morphologically, CCs of the LGNd of the rat are similar, but not identical, to the cytoplasmic multilaminated bodies of the cat, intermediate forms are described.

A quantitative study of the complex laminated body in the lateral geniculate nucleus of the cat

A quantitative study has been made of the proportions and distribution of cells with complex laminated bodies (CLBs) in the lateral geniculate nucleus of the cat. They develop between 55 and about 70 days postnatal and are distributed irregularly across the medio-lateral extent of lamina A. There was no indication that the proportion of cells with CLBs is higher in the region of lamina A where the area centralis is represented, but the proportion in the binocular segment as a whole was higher than for the monocular segment. In kittens reared with unilateral or bilateral eyelid suture the proportions of cells with CLBs was above normal in the deprived laminae and below normal in the undeprived laminae.

A quantitative study of the occurrence and distribution of cytoplasmic laminated bodies in the lateral geniculate nucleus of the normal adult cat

The proportion of neurons containing cytoplasmic laminated bodies (CLB) in the dorsal lateral geniculate nucleus (dLGN) of normal cats was determined by using a new method which permitted examination of large areas of this nucleus. Near the medial border of the dLGN (projection of the area centralis) in the A-laminae 30--60% of the neurons contain CLBs. Within the same region in lamina B only 10--30% of the nerve cells contain CLBs. In the monocular segment (MS) of lamina A 27--48% of the nerve cells contain CLBs. In the medial interlaminar nucleus (MIN) 25% of the neurons contain CLBs; these cells were distributed throughout the medio-lateral extent of the MIN. CLBs were also observed in neurons of the perigeniculate nucleus (PN) and in nerve cells embedded in the fiber sheet separating the dLGN from the pulvinar complex. The distribution of cells containing CLBs is extremely variable in all portions of the dLGN studied. The data presented in this paper indicate that CLB-containing cells in the dLGN may not be X-cells, as has been suggested by LeVay and Ferster ('77) because: (1) the distribution of neurons containing CLBs in lamina A does not match the distribution of X-cells recorded in this lamina; (2) some nerve cells in the MIN contain CLBs but very few X-cells have been found in this region.

Electron microscopic observations of nodes of Ranvier in the external cuneate nucleus

During the course of an investigation of the synaptic organization of the external cuneate nucleus (ECN) in the Sprague-Dawley albino rat, the ultrastructural morphology of nodes of Ranvier in the neuropil has been studied. The majority of nodes observed have the basic morphological features of conventional central nodes but there is individual variation with regard to length, surface area and cytoplasmic organelles. In addition, nodes with multiple myelinated branches are observed. Some nodes of Ranvier were observed to form specialized synaptic boutons. Two types of nodal synaptic boutons were present; a simple type and a complex type. Simple nodal boutons were observed more frequently. These nodes usually synapse upon a single dendritic element; the portion of the node opposite the presynaptic area has a morphology similar to conventional nodes. Complex nodal boutons are of greater dimension than simple nodal boutons and are usually in contact with several neuronal elements. They may be presynaptic to dendritic shafts or spines and are occasionally observed to be postsynaptic to small axonic profiles, a synaptic relationship which, until this report, has not been demonstrated in the central nervous system (CNS). The possible functional significance of these observations is discussed.

An unusual modification of endoplasmic reticulum in epithelial cells of the mouse ascending colon

A rarely occurring structure that is apparently a modification of endoplasmic reticulum was observed in the epithelial cells of the ascending colon of the mouse. The structure consists of a stack of 3 to 15 parallel cisterna-like elements separated by about 67 nm. The stacked cisternae usually are located adjacent to the basal end of the nucleus or in the region between nucleus and basal cell membrane. Top and bottom cisternae of many of the stacks have patent lumens and their outer membranes are lined by ribosomes. Most frequently, middle cisternae have attenuated lumens in their central regions. In some instances the width of the cisternal lumens is similar throughout. Closely apposed pairs of cisternae also occur. Some stacks have a concentric configuration. The intercisternal space contains tightly packed vesicles (38 nm) arranged in a hexagonal array. Many of the vesicles are connected to the membranes of the cisternae by stalk-like projections. The vesicles also occur between the nuclear envelope and the adjacent parallel cisternae. Mitochondria are situated close to each stack.

An electron microscopic study of the otolithic maculae of the lamprey (Entosphenus japonicus)

The sensory epithelium of the otolithic maculae from the inner ear of the lamprey (Entosphenus japonicus) was studied under the scanning and transmission electron microscope. Two different types of sensory hair cells were discerned and each had a patterned distribution over the various maculae. One type of hair cell had 20-30 short stereocilia and one long kinocilium on its surface. The other type exhibited much longer stereocilia which were arranged in graded heights (organ-pipe configuration) from one side of the cell to the other. So-called striated organelles were found in the cytoplasm of both types of sensory cells. These striated organelles exhibited periodic electron-dense and less dense striations of 170 mum extending from the cuticular plate down to the basal portion of the cell. Generally, this organelle was found in profusion in the sensory cells with long hair bundles but rarely found in the other type of cells.

Electron microscopic and electrophysiological studies on the carotid body following intracranial section of the glossopharyngeal nerve

1. The innervation of carotid body Type I cells has been investigated in seventeen cats. At a sterile operation the glossopharyngeal and vagus nerve roots were cut intracranially on one side.2. From 1(1/2) to 378 days after the operation the carotid bodies were fixed in situ and prepared for electron microscopy. Nerve endings on Type I cells were found to degenerate with a prolonged time course. In each cat there was a decrease in the number of nerve endings on the operated side as compared with the non-operated side.3. Before the carotid bodies were fixed, recordings were made from chemoreceptor, and baroreceptor, afferent fibres in the sinus nerve on the operated side. The chemoreceptors responded in the usual way to changes in arterial O(2), CO(2) and pH; the injection of cyanide evoked a brisk response.4. It is concluded that the nerve endings on Type I cells are efferent rather than afferent and the cell bodies of their axons are probably in the brain stem.

Cytoplasmic inclusions resembling nucleoli in sympathetic neurons of adult rats

A distinctive cytoplasmic inclusion consisting of a convoluted network of electron-opaque strands embedded in a less dense matrix was identified in the neurons, but not in the supporting cells, of rat sympathetic ganglia. This ball-like structure, designated "nematosome," measures approximately 0.9 micro and lacks a limiting membrane. Its strands (diameter = 400-600 A) appear to be made of an entanglement of tightly packed filaments and particles approximately 25-50 A thick. Cytochemical studies carried out with the light microscope suggest the presence of nonhistone proteins and some RNA. Usually only one such structure is present in a cell, and it appears to occur in most ganglion cells. Although they can be seen anywhere in the cell body, nematosomes are typically located in the perinuclear cytoplasm, where they are often associated with smooth-surfaced and coated vesicles. In fine structure and stainability, they bear a resemblance to the fibrous component of the nucleolus. Subsynaptic formations, which are a special feature of some of the synapses in sympathetic ganglia, appear similar to the threadlike elements in the nematosomes. The possibility that these three structures-nucleolus, nematosome, and subsynaptic formation-may be interrelated in origin and function is discussed.

Recovery of responsiveness of cells of lateral geniculate nucleus of rat

1. Recovery of responsiveness of single cells in lateral geniculate nucleus of rat has been determined in both P and I cells. There are three types of recovery curve among P cells; (a) early recovery, (b) early partial recovery followed by depression and then complete recovery, (c) prolonged depression followed by cyclic recovery. Type (c) is by far the commonest recovery curve. In contrast to the spike in a P cell, the synaptic potential recovers to its full amplitude in about 20 msec. All I cells exhibit similar rapid recovery curves after a prolonged depression.2. Conditioning stimuli applied to visual cortex also produce a prolonged depression in most P cells but I cells can be re-excited at short intervals from cortex. Decortication does not prevent the prolonged depression of the multineuronal response produced by optic nerve stimulation.3. A neuronal model is proposed to explain these observations. It is supposed that I cells (interneurones) are innervated by axon collaterals of the P cells (principal cells, projecting to visual cortex) and that the I cells exert an inhibitory influence on the P cells.

The effect of deprivation of glucose on the ultrastructure and function of the superior cervical ganglion of the rat in vitro

The superior cervical sympathetic ganglion of the rat kept in vitro in a bicarbonate-buffered Krebs' solution retains its capacity for synaptic transmission and axonal conduction during more than 36 hr. After glucose withdrawal, synaptic transmission is lost in 2(1/2) hr and this loss is irreversible; on the other hand, axonal conduction can still be measured on the postganglionic nerve for more than 24 hr after glucose deprivation. Electrophysiological measurements as well as electron microscope studies revealed specific changes at the level of the presynaptic terminal processes, while the ganglion cells and the satellite cells remained relatively unaltered. The presynaptic lesion due to lack of glucose can be prevented by keeping the preparation in vitro at 6 degrees C. This strongly suggests that this lesion results from a major disturbance of the metabolism of the presynaptic fibers.