W. C. Wong

Ultrastructural changes in the dorsal motor nucleus of monkey following bilateral cervical vagotomy.

SummaryThe neurons of the dorsal motor nucleas (DMN) of the monkey (Macaca fascicularis) were of two main types: small (13 × 8 μm) and medium-sized (20 × 13 μm). The latter, which were the predominant form, contained a pale oval nucleus surrounded by organelle-rich cytoplasm. Between one and three long principal dendrites per section profile arose from eac1 of the somata. Both axosomatic and axodendritic synapses were seen on these cells although the latter were more common.No structural changes were noted in the DMN 1–3 days after bilateral cervical vagotomy. Some of the dendrites of the medium-sized axotomized vagal neurons appeared darkened 5–10 days after the operation. With longer surviving intervals, i.e. 21 and 28 days after operation, darkened dendrites were more commonly seen and the cytoplasmic density of these dendrites was dramatically enhanced. Their mitochondria were pale and some of them also showed vesiculation. Both normal and degenerating axon terminals were seen to form synaptic contacts with the darkened dendrites. The degenerating axon terminals were characterized by the clumping of their round agranular vesicles. Both darkened dendrites and degenerating axon terminals were phagocytosed by hypertrophied astrocytes and activated microglial cells. Blood elements infiltrating into the DMN were a possible source for some of the neural macrophages.It was concluded from the present study that the dendrites of the vagal neurons were the first structures to degenerate in axotomy and these were subsequently removed by glial elements. Degenerating axon terminals on the darkened dendrites could represent endings of the central processes of peripheral vagal ganglion cells that had undergonetransganglionic degeneration after damage to their peripheral processes.

An electron microscopic study of the nodose (inferior vagal) ganglion cells in the monkey

SummaryThe present study described the normal ultrastructure of the monkey nodose ganglion cells. Furthermore, experimental monkeys were subjected to supranodose vagotomy in order to ascertain if the parent cell bodies would undergo degeneration following severance of their central processes. In the normal materials, most of the ganglion cells possessed a single neurite. However, occasional cells bearing more than one process in a sectioned profile were observed. The neurites, ranging between 2–4 μm in diameter, displayed a relatively regular contour. Their cytoplasm contained parallel arrays of microtubules, ribosomes, endoplasmic reticulum and slender mitochondria. The electron density of some of these neurites was abnormally high. Embedded in these darkened neurites were a variable number of swollen mitochondria characterized by disrupted cristae. Axon terminals containing round agranular and a few large dense cored vesicles formed synaptic contacts primarily with the neurites of some of the ganglion cells. Three days after supranodose vagotomy, darkened neurites were more commonly observed but their incidence was comparable to that of the normal ganglion in longer survival animals. Another reactive change was the appearance of axon terminals undergoing various degrees of degeneration. There was no evidence of cell death in the duration studied.It was concluded from this study that the occasional darkened neurites from the normal ganglion cells was probably undergoing ‘spontaneous degeneration’ which appeared to be accentuated when their central process was severed by supranodose vagotomy. The degeneration of axon terminals associated with some of the ganglion cells following the vagotomy suggested that they were derived from vagal descending fibres which were undergoing anterograde degeneration. The presence of synapses on some of the ganglion cells was also discussed and the possibility considered that the latter may represent ‘aberrant’ or displaced autonomic neurons.

Ultrastructure of the pineal gland of the monkey, Macaca fascicularis, with special reference to the presence of synaptic junctions on pinealocytes

SummaryThe present study described the normal ultrastructure of the monkey pineal gland. The gland was composed of the principal pinealocytes, intramural neurons and glial cells. The nucleus of the pinealocytes was deeply infolded with evenly distributed chromatin materials. The abundant cytoplasm was rich in organelles including the well-developed Golgi apparatuses, multivesicular bodies, dense-cored vesicles and widely scattered free and polyribosomes. A variety of axon terminals was observed and the majority of them contained pleomorphic agranular vesicles with a few large dense-cored vesicles. A few terminals showed flattened vesicles or small dense cored vesicles. Some of the axon terminals formed synaptic contacts with the cell bodies of pinealocytes. These synapses were mainly concentrated in the posterior third of the gland. The occasional intramural neurons observed were postsynaptic to axon terminals containing round agranular vesicles. The sources of the nerve fibres and terminals forming synaptic junctions with pinealocytes and intramural neurons were discussed.

Gracile nucleus of streptozotocin-induced diabetic rats

SummaryThis study reports ultrastructural changes in the gracile nucleus of male Wistar rats after streptozotocin-induced diabetes. During the acute phase (3–7 days) degenerating electron-dense dendrites and axon terminals were dispersed in the neuropil. Degenerating dendrites were characterized by an electron-dense cytoplasm, swollen mitochondria, dilated endoplasmic reticulum and scattered ribosomes. Degenerating axon terminals were characterized by an electron-dense cytoplasm and clustering of small spherical agranular vesicles. Degenerating axon terminals may form part of a synaptic glomerulus with a central electron-dense dendrite, or they may form the central element of a synaptic glomerulus. These degenerating profiles were absent in the gracile nucleus of the 3 and 7 days insulin-treated post-streptozotocin rats. Macrophages were present in the neuropil and were in the process of engulfing neuronal elements. During the medium phase (1–6 months), most of the degenerating dendrites and axon terminals had been engulfed or removed by macrophages. During the late phase (9–12 months) a second wave of degeneration occurred in the gracile nucleus, similar to the acute phase. During the medium and late phases, dystrophic axonal profiles were also significantly increased in the rats after streptozotocin treatment.It is concluded that the ultrastructural changes observed in the gracile nucleus in the present study were the result of streptozotocin-induced diabetes rather than a toxic effect of streptozotocin, even in the acute phase.

Degenerative changes of neurons in the superior cervical ganglion following an injection of ricinus communis agglutinin-60 into the vagus nerve in hamsters

SummaryThe present study describes neuronal changes in the superior cervical ganglion of hamsters following injection of Ricinus communis agglutinin-60 (RCA-60) into the ipsilateral vagus nerve in the cervical region. There were no noticeable structural changes in the ganglion 1 day after injection. Between 3 and 15 days after injection, a small number of neurons located in the caudal part of the ganglion underwent degenerative changes including disappearance of rough endoplasmic reticulum and cytoplasmic vacuolation. The structural alterations were most acute 7 days after the injection when some neurons showed signs of total vacuolation and lysis. A second phase of neuronal change occurred after longer survival periods extending from 60 to 120 days after injection. The most striking feature of such neurons was darkening of their dendrites associated with abnormally high density cytoplasm that contained mitochondria with disrupted cristae. As distinct from the early phase in which cell necrosis was observed, there was no evidence of cell death of neurons bearing darkened dendrites. Since examples of exfoliation of the affected dendrites and their phagocytosis by satellite cells were extremely rare, it is postulated that these structural alterations are probably reversible but over an extended period. The significance of the two phases of degenerative change is discussed in connection with the acute and possible chronic effects of the toxic lectin. The present study also confirms the presence of postganglionic sympathetic axons in the cervical vagus nerve.

Synaptic junctions between sympathetic axon terminals and pinealocytes in the monkey Macaca fascicularis

SummaryThe distribution of axon terminals in the pineal gland of monkeys was studied by electron microscopy. Numerous terminals bearing small pleomorphic agranular and dense-cored vesicles were localized in the perivascular space and among the pinealocytes in the parenchyma in normal monkeys. Following bilateral superior cervical ganglionectomy, they underwent degenerative changes, including the accumulation of glycogen masses, appearance of dense residual bodies and the displacement of synaptic vesicles. Some of these degenerating terminals showed synaptic contacts with the cell bodies of pinealocytes. At the synaptic junction the postsynaptic membrane was thickened asymmetrically. Examples of synaptic contacts were most frequently observed in 5 and 7 days postoperative animals. In the longer surviving (30 days) monkey, most of the axon terminals showed round agranular vesicles, and they were mainly presynaptic to the intrapineal ganglion cells with some of the pinealocytes. They remained structurally unchanged following the resection of both the superior cervical ganglia. A few axon terminals containing small dense-cored vesicles appeared to have survived the initial insult, but some of their vesicles appeared swollen 30 days after the operation. It is concluded from this study that some of the pinealocytes are under the influence by the postganglionic neurons in the superior cervical ganglia through direct synaptic contacts. The intrapineal ganglion cells are postsynaptic to fibres originating exclusively from the central nervous system. Some of these fibres, however, may be presynaptic directly to pinealocytes.

A qualitative and quantitative study of substance P immuno-cytochemistry of the trigeminal ganglion in the monkey.

The immunoreactivity of substance P(SP) in the monkey trigeminal ganglion was examined and the distribution of immunoreactive cells determined. The monkey trigeminal ganglion is composed of clusters of sensory cells arranged in cords parallel to the long axis of the nerve fibres. The cells have prominent nuclei and are surrounded by satellite cells. Abundant organelles are randomly distributed throughout the cytoplasm. A striking feature of the ganglion was the presence of some axon-like prolifes containing mainly dense-cored vesicles and some agranular vesicles. Between 16 and 32% of the ganglion cells displayed SP-immunoreactivity. Most of the SP-IR cells were unipolar, small to medium-sized ganglion cells and they had no specific pattern of distribution. The staining of the SP-IR cells varied considerably, ranging from weak or moderate to heavy staining, although the majority of them were moderately stained. Immuno-electron microscopy showed that the SP-IR products were distributed throughout the soma of ganglion cells and not associated with any particular organelles or inclusions. The reaction products were also found in both myelinated and unmyelinated fibres between the ganglion cells. Another remarkable feature of the trigeminal ganglion was the occurrence of some SP-IR nerve fibres forming a rich “glomerular” network of pericellular arborizations around some of the SP-negative cells. Ultrastructural study showed the presence of some SP-IR nerve terminals in close approximation to some SP-negative cells, but there were no synaptic contacts. The relative frequency of the SP-IR pericellular arborizations paralleled the frequency of all the SP-IR cells. The results may imply that the pericellular arborizations function as a medium of communication between SP-positive and SP-negative sensory cells within the ganglion. It was suggested that the fibres forming the pericellular arborizations may originate from the intrinsic ganglion cells that are SP-positive.

Effects of vagotomy on the ultrastructure of the atrial myocardium in the monkey (Macaca fascicularis)

SummaryThe ultrastructure of the atrial myocardium in the monkey (Macaca fascicularis) was studied after bilateral cervical vagotomy and survival times of 1, 3, 5, 7, 10, 21 and 28 days. During the first week after vagotomy, a few atrial cells showed a reduction in the sarcoplasm, crowding of the myofibrils, peripheral dispersion and reduced intercristal density of the mitochondria and increased sarcoplasmic reticulum and glycogen particles. In some profiles, there was increased electron density and granularity at the I bands and the intercalated discs. The number of such affected cells increased in the subsequent days such that by 21 to 28 days about 50% of the cells were estimated to be affected. During the latter stages further changes included, the degradation of the myofilaments and increased electron density, disorganisation and disintegration of the digital extensions at the intercalated discs. Throughout the experiments there was a leucocytic infiltration, more evident in the longer survival times.