Michael F Nolan

Ultrastructure and quantitative synaptology of the sacral parasympathetic nucleus

SummaryThis study examines the anatomical substrate for the spinal micturition reflex. Light microscopy of pyridine silver-stained sections revealed that the sacral parasympathetic nucleus (SPN) exists as a broken column or chain of cell clusters located along the intermediolateral portion of the dorsal horn in sacral segments S2–S4. Quantitative analysis of neuropil components in electron micrographs provides data for each type of bouton identified in this nucleus. On the somata of these neurons, boutons containing clear spherical vesicles (S type) comprise 70% of the bouton population. Terminals containing three or more dense core vesicles (GS boutons) account for 26% and boutons containing flattened vesicles (F boutons) comprise 4% of the population. F boutons are more common on large dendrites where they comprise 10% of the total bouton population.The actual population density of each bouton type is most evident when the number of boutons is expressed as boutons per 100 μm of membrane length (btn/100 μm). S type boutons are the most frequently encountered type. The population density of S boutons is the same on soma and dendrites at 6.66 btn/100 μm. F boutons are more numerous on large (> 2 μm) dendrites (1.28 btn/100 μm) than on small dendrites (0.63 btn/100 μm) or on somata (0.36 btn/ 100 μm). GS boutons occur more frequently on small dendrites (3.66 btn/100 μm) than on somata (2.29 btn/100 μm), large dendrites (2.88 btn/100 μm) or medium dendrites (2.27 btn/ 100 μm). These data suggest that the dense core vesicle-containing boutons are applied primarily to small (<1 μm) dendrites and that F boutons are associated mostly with large or proximal dendrites.These results provide a quantitative profile of the synaptic input to the sacral autonomic (parasympathetic) neurons which innervate the urinary bladder and demonstrate specific population differences on various postsynaptic structures in this nucleus.This study examines the anatomical substrate for the spinal micturition reflex. Light microscopy of pyridine silver-stained sections revealed that the sacral parasympathetic nucleus (SPN) exists as a broken column or chain of cell clusters located along the intermediolateral portion of the dorsal horn in sacral segments S2–S4. Quantitative analysis of neuropil components in electron micrographs provides data for each type of bouton identified in this nucleus. On the somata of these neurons, boutons containing clear spherical vesicles (S type) comprise 70% of the bouton population. Terminals containing three or more dense core vesicles (GS boutons) account for 26% and boutons containing flattened vesicles (F boutons) comprise 4% of the population. F boutons are more common on large dendrites where they comprise 10% of the total bouton population.

An ultrastructural examination of dorsal root input to the sacral secondary visceral gray.

Dorsal root input to the sacral secondary visceral gray was examined in the adult cat using an orthograde degeneration technique. Five days after unilateral, intradural section of sacral dorsal roots electron-microscopic evidence of synaptic degeneration was seen throughout the nucleus ipsilateral to the side of the lesion. Degenerating sacral primary afferents in this nuclear region were associated mainly with S and GS type boutons. S type synapses showed two distinct degenerative responses. Some of the degenerating boutons were swollen with synaptic vesicles clustered tightly near the presynaptic membrane. Others appear shrunken with consequent packing of vesicles and mitochondria within the presynaptic terminal. Degenerating S terminals were found mainly on dendrites. S type synapses on nerve cell bodies appeared to be unaffected by dorsal root section. The degenerative response of sacral primary afferents associated with GS boutons was characterized by marked swelling of the presynaptic terminal and the presence of significant amounts of glycogen. Degenerating GS boutons were observed on both cell bodies and dendrites. These observations provide morphologic evidence of a direct synaptic link between dorsal root afferents and nerve cells in the sacral secondary visceral gray.

A quantitative ultrastructural analysis of the synaptic population in the sacral visceral gray

Abstract The synaptic distribution in the sacral visceral gray of the cat was examined. Synaptic complexes exhibiting a distinct membrane specialization were identified and classified according to vesicle type and number. Boutons containing clear spherical vesicles (S type) account for more than 63% of the synaptic contacts on both cell bodies and dendrites. Terminals containing three or more granular vesicles (GS type) comprise between 23 and 31% of the synapses in the nucleus. F boutons are less frequently seen (3–6%) as are T type boutons (1–2%). Presynaptic terminals containing a predominance of dense core vesicles (GG type) constitute less than 1% of the total synapses in this neuropil and are found only on dendrites. Nerve cell bodies receive approximately five synaptic contacts per 100 μm of postsynaptic membrane. Large and medium size dendrites are contacted by an average of seven boutons per 100 μm of postsynaptic membrane and small dendrites have the highest distribution (approximately 12 per 100 μm). Comparison of the percentage distribution of various types of synapses in this nucleus reveals little variation between cell bodies and dendrites. However, expression of the synaptic population as boutons per 100 μm of available postsynaptic membrane clearly illustrates intranuclear differences in synaptic distribution not seen in percentage type comparisons.

Primary afferent projections to the sacral secondary visceral gray: A quantitative electron microscopic examination in the cat

Afferent input to the sacral secondary visceral gray matter was studied by quantitatively assessing synaptic degeneration that follows ipsilateral sacral dorsal rhizotomy. Five days after the lesions, slightly more than 25% of the synaptic contacts showed degenerative changes. The majority of the reactive synapses contained clear spherical vesicles (S type). Boutons containing dense core vesicles (GS type) also showed degenerative changes, and together with S boutons constituted more than 96% of the reactive terminals. Degenerating S type synapses were found only on dendrites whereas GS boutons were observed on both cell bodies and dendrites. Further examination revealed that although there were more S than GS synapses in the nucleus, the percentage of GS terminals affected was greater than that for S type boutons. These results demonstrate a direct primary afferent input to the sacral secondary visceral gray matter utilizing chiefly two different synaptic types.

Sandblasting injury of the hand.

Sandblasting equipment may produce serious hand injuries even though emission pressures are relatively low in comparison to forces generated by airless sprayers. This report describes a permanent injury caused by the injection of sandblast dust into the hand. Diagnosis of the injury was aided by electrodiagnostic investigation of the first lumbrical muscle.

Laminar location of cervical spinal neurons contributing to the crossed ascending pathways in the kitten

Abstract Cervical neurons in the newborn kitten contributing to the crossed ascending spinal pathways have been identified by retrograde changes following unilateral interruption of the fibers of the spinal lemniscus at the level of the midbrain. Responses to axotomy in neonatal animals include both cellular loss and chromatolysis. The laminar and intralaminar location of reacting cells was determined from serial, parasagittal sections of the C5 spinal segment. Significant numbers of neurons responding to axonal injury were observed in all laminae with the exception of II and III, contralateral to the side of the midbrain lesion. Both large and small nerve cells were affected by the unilateral division of axons in the mesencephalon. These results confirm the widespread but nonrandom distribution of cervical level source cells of the contralateral spinal lemniscus for this species reported by other investigators utilizing alternative methods.

A Plea about PhC

To the Editor: Because of its various responsibilities assigned by the Board of Directors, the Associations Committee on Research has occasion to take note of the credentials of members, especially of those members who have been, or are, engaged in research. A number of months ago, under our previous chairman, we had occasion to note the use of the initials “PhC” after a members name. We were at first a bit nonplussed by what “PhC” meant but an informal inquiry, and other information available to us, revealed that the initials are used in at least one academic setting to indicate “candidate for the PhD.” Quite naturally, we were disturbed by the apparent public use of initials, after a name, that ordinarily (in the United States) indicate academic degree, professional degree, or official registration, licensure, or certification, but that, in this instance, represented none of these things.…