The ultrastructure of the spinal tract of the trigeminal nerve and the substantia gelatinosa

Ultrastructure and synaptology of the paratrigeminal nucleus in the rat: primary pharyngeal and laryngeal afferent projections

The paratrigeminal nucleus (PTN) receives primary afferent projections from the aerodigestive tract and orofacial regions and plays a role in the integration of visceral and somatic information. This study describes the fine structure of the rat PTN and the synaptology of primary afferent projections from the pharynx and larynx. Injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or cholera toxin-HRP (CT-HRP) were made into the wall of the pharynx or larynx to label primary afferent axon terminals. Light microscopic observations demonstrated that afferent axons terminated bilaterally in overlapping fields in the PTN. Electron microscopic observations of the PTN revealed that there were three distinct classes of neurons, based on morphology and axosomatic contacts. The most abundant neurons, Type 1, were fusiform in shape and received very few or no axosomatic contacts. Type 2 neurons contained prominent Nissl substance (rough endoplasmic reticulum) and few axosomatic contacts, while Type 3 neurons had many axosomatic synapses. Terminals containing round, clear vesicles and forming asymmetric contacts (round asymmetric, RA) with dendrites were the predominant synaptic type in the PTN. Primary afferent terminals from the pharynx and larynx were of the RA type and formed synaptic contacts with small-diameter (<1 microm) dendrites. Visceral primary afferent inputs from the pharynx and larynx overlap with trigeminal somatic afferents in the PTN and have similar synaptic morphology. The results support the concept that the PTN provides an anatomical substrate for mediating viscerovisceral and somatovisceral reflexes via efferent connections with autonomic centers in the brainstem.

The synaptic microcircuitry associated with primary afferent terminals in the interpolaris and caudalis of trigeminal sensory nuclear complex

Previous ultrastructural studies indicating a higher number of axoaxonic contacts on individual low-threshold mechanoreceptive afferents in the principalis (Vp) than in the oralis (Vo) of cat trigeminal sensory nuclear complex (TSNC) suggest that the synaptic microcircuitry associated with primary afferents manifests unique differences across the sensory nuclei of TSNC. To address this issue, we analyzed synaptic microcircuits associated with fast adapting vibrissa afferent terminals in the interpolaris (Vi) and caudalis (Vc, laminae III/IV) by using intraaxonal injections of horseradish peroxidase (HRP) in cats. Forty-two and 65 HRP-labeled boutons were analyzed in the Vi and Vc, respectively. The labeled boutons contained clear, spherical vesicles. They most frequently formed asymmetric axodendritic synapses and were commonly postsynaptic to unlabeled axon terminals containing pleomorphic vesicles (p-endings) with symmetric junctions. The examination of synaptic contacts over the entire surface of individual boutons indicated that the afferent boutons made contacts with an average of two postsynaptic targets in the Vi and Vc. In contrast, axoaxonic contacts, and labeled boutons participating in synaptic triads, where p-endings contacted both the boutons and their postsynaptic targets, were, on average, higher in the Vi than in the Vc. These results suggest that the output of sensory information conveyed through low-threshold mechanoreceptive afferents is more strongly controlled at the level of the first synapse by presynaptic and postsynaptic mechanisms in the Vi responsible for sensory discriminative functions than in the Vc for sensorimotor reflexive functions.

Quantitative ultrastructure of slowly adapting lingual afferent terminals in the principal and oral nuclei in the cat

Previous studies provide evidence that a structure/function correlation exists in the cytoarchitectonically different zones of the trigeminal sensory nuclei. To extend this relationship, we examined the ultrastructural features of trigeminal primary afferent neurons in the cat dorsal principal nucleus (Vpd) and the rostrodorsomedial oral nucleus (Vo.r) using intra-axonal labeling with horseradish peroxidase and morphometric analyses. All labeled boutons contained round synaptic vesicles. Eighty-two percent of the boutons in the Vo.r and 99% of the boutons in the Vpd were presynaptic to nonprimary dendrites. The remaining boutons in the Vo.r were presynaptic to somata (8%) or primary dendrites (10%). The average number of postsynaptic profiles per labeled bouton did not differ in the Vpd and Vo.r. Most labeled boutons in the two nuclei were postsynaptic to unlabeled axon terminals with pleomorphic vesicles (p-ending). The number of p-endings per labeled bouton was higher in the Vpd than Vo.r A morphometric analysis indicated that labeled bouton volume and apposed surface area were larger in the Vpd than Vo.r while active zone area and vesicle number did not differ. All these parameters were larger than those of p-endings in each nucleus. In both labeled boutons and p-endings, the parameters were positively correlated with bouton size. These results suggest that sensory information conveyed through trigeminal afferents is more strongly controlled at the level of the first synapse by presynaptic mechanisms in the Vpd than in the Vo.r, while the efficacy of transmission at primary afferent synapses does not differ.

Ultrastructural observations of synaptic connections of vibrissa afferent terminals in cat principal sensory nucleus and morphometry of related synaptic elements

Previous work suggests that slowly adapting (SA) periodontal afferents have different synaptic arrangements in the principal (Vp) and oral trigeminal nuclei and that the synaptic structure associated with transmitter release may be related directly to bouton size. The present study examined the ultrastructures of SA and fast adapting (FA) vibrissa afferents and their associated unlabeled axonal endings in the cat Vp by using intra-axonal labeling with horseradish peroxidase and a morphometric analysis. All SA and FA afferent boutons contained clear, round, synaptic vesicles. All the FA and most SA boutons were presynaptic to dendrites, but a few SA boutons were axosomatic. Both types of bouton were frequently postsynaptic to unlabeled axonal ending(s) containing pleomorphic, synaptic vesicles (P-ending). The size of labeled boutons was larger in FA than SA afferents, but the size of dendrites postsynaptic to labeled boutons was larger for SA than FA afferents. Large-sized FA and SA boutons made synaptic contacts with small-diameter dendrites. The size of FA and SA boutons was larger than that of their associated P-endings. A morphometric analysis made on the pooled data of SA and FA boutons indicated that apposed surface area, active zone number, total active zone area, vesicle number, and mitochondrial volume were highly correlated in a positive linear manner with labeled bouton volume. These relationships were also applicable to unlabeled P-endings, but the range of each parameter was smaller than that of the labeled boutons. These observations provide evidence that the two functionally distinct types of vibrissa afferent manifest unique differences but share certain structural features in the synaptic organization and that the ultrastructural "size principle" proposed by Pierce and Mendell ([1993] J. Neurosci. 13:4748-4763) for Ia-motoneuron synapses is applicable to the somatosensory system.

Ultrastructural study of NADPH-d positive neurons in laminae I and II of the rat caudal spinal trigeminal nucleus

The present study investigated the ultrastructure of neurons in the caudal spinal trigeminal nucleus. These neurons which are believed to function as interneurons in the transmission of orofacial nonreflexive nociceptive information, measured 20 microns x 11 microns, and were nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) positive. The reaction product, formazan, was localized in the nuclear envelope, mitochondria, rough endoplasmic reticulum, and multivesicular bodies of these neurons. It was also localized in the membrane of the smooth endoplasmic reticulum at the axon terminal. The neurons were contacted by both axosomatic and axodendritic synapses formed by both NADPH-d positive and NADPH-d negative axon terminals. Two types of NADPH-d positive axon terminals could be recognized. The first was a large terminal containing many stained mitochondria and unstained small round agranular vesicles mixed with some slightly flattened ones. It formed asymmetrical axodendritic synapse. The second type of axon terminals contained pleomorphic synaptic vesicles and formed asymmetrical synapses upon both dendrites and soma. The sources of NADPH-d positive axon terminals were discussed. Most of the unstained axon terminals forming axosomatic and axodendritic synapses with stained cell bodies and dendrites contained flattened vesicles. In addition to the above, complicated synaptic configurations showing NADPH-d positive axoaxonic synapses in relation to NADPH-d negative dendritic spines were also seen in which a NADPH-d negative dendritic spine was completely contacted by a NADPH-d positive bouton which was in turn contacted by another NADPH-d positive bouton.

Cluster-like signs and symptoms respond to myofascial/craniomandibular treatment: a report of two cases

Two cases with pain profiles characteristic of cluster-like headache, both within and outside the trigeminal system, are reported. One male patient would typically awaken from sleep with severe unilateral temporal head pain and autonomic signs of ipsilateral lacrimation and nasal congestion. A female patient exhibited severe unilateral boring temporal and suboccipital head pain with associated ipsilateral lacrimation and rhinorrhea. In addition, both patients presented with signs and symptoms of masticatory and/or cervical disorders. These two cases illustrate possible treatment alternatives, as well as possible influences from cervical and masticatory structures in the development of cluster or cluster-like headache.

Morphology and synaptic connections of slowly adapting periodontal afferent terminals in the trigeminal subnuclei principalis and oralis of the cat

Previous studies suggest that sensory information from primary afferent fibers is processed in a distinct manner in the individual subnuclei of trigeminal sensory nuclear complex. The present study has addressed this issue by using intra-axonal labeling with horseradish peroxidase to examine the ultrastructure and synaptic organization of axon terminals from slowly adapting (SA) periodontal afferents in the ventral subdivision (Vpv) of principalis and the rostro-dorsomedial part (Vo.r) of oralis. Our observations are based on complete or near-complete reconstructions of 139 synaptic boutons in Vpv and 105 in Vo.r. All the labeled boutons contained clear, spherical, synaptic vesicles and were presynaptic to unlabeled dendrites, and they were frequently postsynaptic to unlabeled axon terminals containing pleomorphic synaptic vesicles (P-endings). The P-endings frequently formed axodendritic synapses on dendrites which received axodendritic synapses from labeled boutons (synaptic triads). On the basis of the number of contacts, synaptic arrangements associated with the labeled boutons could be subgrouped into simple (one or two contacts), intermediate (three or four contacts), and complex (five or more contacts) types. The labeled boutons varied from round to elongated forms with smooth to more irregular or scalloped contours. The boutons with scalloped contour were much more frequent in the complex type. The boutons of the intermediate type were significantly smaller than the complex type and larger than the simple type. The SA periodontal afferent terminals participated in each type of synaptic arrangements in Vpv, but were mostly of the simple type in Vo.r. The size of labeled boutons was significantly larger in Vpv than in Vo.r. The total number of axodendritic and axoaxonic contacts per labeled bouton was significantly higher in Vpv than in Vo.r. Another difference was the more frequent occurrence of synaptic triads in Vpv than in Vo.r. These observations provide evidence that sensory information from primary afferent fibers is processed in a different manner in the two subnuclei.

Surgical management of refractory craniomandibular pain using radiofrequency thermolysis: a report of thirty patients

Radiofrequency thermolysis has traditionally been used to treat pain disorders of differing etiologies primarily in the low back and cervical areas. This paper describes the use and results of a different and simplified approach to surgical management of extracapsular disorders, namely, temporal tendinitis, Ernest Syndrome, and occipital myalgia-neuralgia where conservative attempts have failed. A brief discussion of the pain disorders are addressed along with the methods of differential diagnosis, conservative therapy, and traditional surgical treatment. Finally, surgical management using radiofrequency thermolysis is described with results of treatment in 30 patients showing a 96% success rate.

Afferent C fibre innervation of cat tooth pulp: confirmation by electrophysiological methods

1. The presence of afferent C fibres innervating the lower canine tooth was investigated in Nembutal-anaesthetized cats. 2. Twenty-five single fibres with conduction velocities (CVp) of less than 2.5 m/s, as calculated from the shortest response latency using monopolar electrical stimulation of the tooth, were recorded from the inferior alveolar nerve. In addition, the extradental conduction velocity (CVn) of the fibres was determined by using bipolar electrical stimulation of the trunk of the inferior alveolar nerve. 3. The mean CVp was 1.4 +/- 0.4 m/s (n = 25; range, 0.6-2.4 m/s); the mean CVn was higher, 1.7 +/- 0.9 m/s (n = 25; range, 0.6-4.0 m/s). For 20% of the fibres CVn exceeded 2.5 m/s; these were slowly conducting A delta fibres. For 80% of the fibres, however, the extradental conduction velocity was in the C fibre range. 4. The relationship between CVp (y) and CVn (x) was y = 0.66 + 0.40x, the correlation coefficient being r = 0.85. According to the present results this implies that for a reliable classification of pulpal C fibres (CVn less than or equal to 2.5 m/s) by monopolar tooth stimulation alone, CVp should be less than 1.7 m/s. 5. For twenty-three of the twenty-five fibres, one to three discrete shortenings of the response latency occurred when the intensity of the tooth stimulation was increased. When the nerve trunk itself was stimulated, a constant response latency was measured at all stimulus intensities applied. 6. For twelve fibres tested, the mean rate of electrical stimulation of the tooth, which the response followed with a constant latency, was 4.1 +/- 2.3 Hz (range, 1.5-10.0 Hz). With higher rates of stimulation the response latency increased until the fibres failed to follow each stimulus pulse. 7. Fifteen of the nineteen fibres tested responded to radiant heat stimulation of the tooth they were innervating. The mean temperature threshold was 41.4 +/- 2.7 degrees C (n = 11; range, 37.4 +/- 46.4 degrees C). 8. For eight heat-sensitive pulpal C fibres the receptive field was determined by mechanical stimulation of the exposed pulp tissue. Four C fibres developed a long-lasting on-going discharge after intense mechanical stimulation of the receptive field. 9. The discharge evoked by heat and mechanical stimulation of the tooth occluded the response evoked by simultaneously applied electrical current pulses to the nerve trunk, indicating that the same fibres were activated by both tooth and nerve stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Fine structure of synapses associated with characterized postsynaptic dorsal column neurons in the cat

Fourteen dorsal horn neurons with axons projecting through the dorsal columns were identified either by electrophysiological methods (and subsequently injected with horseradish peroxidase) or by retrograde labelling with horseradish peroxidase in cats. All neurons were contacted by small (less than 2 micron) boutons containing spherical or elongated agranular vesicles. One neuron with its soma located in lamina III received additional contacts from central elements of glomerular complexes. Neurons with somata located more ventrally (deep lamina IV and V) were also postsynaptic to large (greater than 2 microns) electron lucent profiles which formed multiple synapses with the labelled cells. Some boutons presynaptic to postsynaptic dorsal column neurons were themselves postsynaptic to profiles containing pleiomorphic agranular vesicles at axoaxonic synapses. They also occasionally participated in triadic complexes. It is concluded that the synaptic arrangements formed by boutons in association with postsynaptic dorsal column neurons differ significantly from those associated with spinocervical neurons. Such differences might provide the anatomical substrate for the observed receptive field characteristics of these neurons.

Mapping of the normal distribution of substance P-like immunoreactivity in the spinal trigeminal nucleus of the cat

Although a recent preliminary report indicated a pattern of substance P-like immunoreactivity within the spinal trigeminal nucleus that is similar to the projection sites for dental afferent fibers, details of this substance P distribution are lacking. Our purpose was to describe in cats the complete normal pattern of this immunoreactivity within each of the spinal trigeminal subnuclei. Special emphasis was given to the distribution of substance P-like immunoreactive axons and terminals located in the rostral subnucleus caudalis and the periobex region of subnucleus interpolaris, as these are regions shown to receive dental afferent fibers. Careful mapping in normal cats showed, within the resolution of the light microscope, a consistent pattern of distribution that included only a portion of the previously identified dental relay sites, but was somewhat broader in certain levels and more restricted in others. The results are compared with those provided by others from regions such as the dorsal horn and subnucleus caudalis of the spinal trigeminal nucleus. The findings also provide an anatomical basis for a recent physiologic report on specific cell types associated with dental nociceptive afferent fibers. This study also provides a baseline control for future investigations of possible changes in substance P-like immunoreactivity that follows various peripheral, including dental and central, lesions.

Fine structure of normal and degenerating primary afferent boutons associated with characterized spinocervical tract neurons in the cat

Spinocervical tract neurons in the dorsal horn of the cat spinal cord were intracellularly stained with horseradish peroxidase. The neurons came from one intact animal and from animals with dorsal rhizotomies (L3-S2) 3, 5, 10, 28 and 42 days previously. The morphology of terminals associated with spinocervical tract neurons was examined in a combined light and electron microscopical study. Some terminals containing agranular, circular vesicles degenerated as a result of deafferentation; these are therefore the terminals forming monosynaptic inputs to the neurons from primary afferent fibres. Other terminals containing agranular circular vesicles and terminals containing ovoid agranular vesicles survived deafferentation; these boutons therefore do not originate from primary afferent fibres.

Soma size comparison of the trigeminal ganglion cells giving rise to the ascending and descending tracts: a horseradish peroxidase study in the cat

Soma size was compared between the trigeminal ganglion cells projecting to the main sensory trigeminal nucleus (Vs) and those projecting to the nucleus caudalis (Vc) of the spinal trigeminal nucleus in the cat after injection of horseradish peroxidase (HRP) into each nucleus. The results showed that the cells projecting to the Vc (Vc cells) contained by far a greater percentage of small cells than do those projecting to the Vs (Vs cells). In the Vc case, about one-half the total number of measured labeled cells were the smallest with a diameter less than 36 microns, whereas in the Vs cases, only a small proportion of the total number of measured labeled cells were that small. In addition, the results also made it clear that the Vs cells in the ophthalmic and maxillary divisions contained a higher percentage of larger cells than those in the mandibular division.

Dental sensory receptors

Teeth are innervated by unmyelinated sympathetic axons, and by unmyelinated and small myelinated sensory axons. Some sensory axons in teeth are terminal branches of larger parent axons, so that conduction from teeth to CNS in trigeminal nerves includes C-fiber, A-delta, and A-beta velocities. Sensory dental axons contain acetylcholine or substance P-like immunoreactivity. The sympathetic axons contain noradrenalin. Other neuropeptides may also be present, such as vasoactive intestinal peptide and serotonin. Dental axons of mature teeth of many species (man, monkey, cat, rodents, fish) are essentially the same, but continuously erupting teeth have smaller and fewer axons. Free sensory nerve endings in mature teeth are found in the peripheral plexus of Raschkow, the odontoblastic layer, the predentin, and the dentin. Free nerve endings are most numerous in those regions near the tip of the pulp horn, where more than 40% of the dentinal tubules can be innervated. Many dentinal tubules contain more than one free nerve ending. Intradentinal axons can extend as far as 0.2 mm into dentin but usually end less than 0.1 mm from the pulp. Some sensory endings also occur along pulpal blood vessels. In continuously erupting teeth nerve endings do not enter the dentin but remain within the pulp. Nerve endings in dentin are labeled by axonal transport. They are therefore as viable and active as the nerve endings in pulp. The axoplasm of the free nerve endings contains organelles typical of other somatosensory receptors. These organelles are most common in the successive beaded regions along the free nerve endings and include mitochondria, clear and dense-core vesicles, multivesicular bodies, profiles of smooth endoplasmic reticulum, and relatively few microtubules and neurofilaments. The beads can vary in size from about 0.2 to 2.0 microns and can have varying amounts of receptor organelles. The interbead axonal regions are thin and contain mainly microtubules and neurofilaments. Nerve endings are associated with companion cells after they leave the coronal nerve bundles; these companion cells include Schwann cells, fibroblasts, and odontoblasts. There is no good evidence of gap junctions or synapses between nerve endings and odontoblasts. Instead, the two cell types form appositions that have a 20-40 nm extracellular cleft and parallel apposed plasmalemmas but no unusual membrane-associated material. No special organelles occur in the odontoblastic cytoplasm at these sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphological properties of physiologically characterized lamina III neurones in the cat spinal cord

Six lamina III interneurones of the cat spinal cord were impaled and stained with intracellular injections of horseradish peroxidase. The responses of these neurones varied considerably: 1 neurone responded to light brushing of its receptive field, whilst 4 cells were excited by strong pressure. Morphologically, they were also a heterogeneous population. Two neurones had rostro-caudally orientated dendritic arbors that were confined to the lamina, while four of the cells were vertically orientated and possessed dendrites that crossed lamina boundaries. There was no correlation between the physiological characteristics of a neurone and its morphology. Three of the vertically orientated neurones were examined ultrastructurally. The first of these cells received several types of synaptic terminal which were distributed in an organised pattern over the entire dendritic tree. This neurone possessed recurrent dendrites which participated in a variety of complex synaptic arrangements. The second neurone also participated in a variety of synaptic arrangements, including glomeruli in lamina II, and received contacts from vesicle-containing dendrites. It gave rise to collateral axons which arborized in lamina II and formed boutons which formed synapses with dendrites. The third cell possessed varicose dendrites which were probably artifactual. It is concluded that lamina III interneurones are a heterogeneous population by electrophysiological, morphological and ultrastructural criteria. They differ in many respects from lamina II neurones and from the cells of origin of ascending systems. The diversity of their inputs and their variation in morphology suggests that they receive input from a variety of primary afferent fibres and dorsal horn neurones and hence may integrate information from these sources.

Mechanisms regulating the activity of facial nucleus motoneurones--2. Synaptic activation from the caudal trigeminal nucleus

Field and postsynaptic potentials of facial motoneurones evoked by stimulation of the caudal trigeminal nucleus were studied in cats by means of extra- and intracellular recording. Mono- and polysynaptic input onto facial motoneurones from the caudal trigeminal nucleus were shown. Four types of responses were distinguished: excitatory postsynaptic potentials generating a single action potential; a gradual shift of depolarization inducing multiple discharges; a rhythmic discharge of action potentials appearing at a low level of depolarization; excitatory postsynaptic potentials or a sequence of excitatory and inhibitory postsynaptic potentials. Multiple discharge was shown to appear as a result of effective summation of high frequency excitatory influences from efferent neurones of the caudal trigeminal nucleus projecting into the facial nucleus. Factors facilitating the development of gradual depolarization are: dendritic localization of synaptic terminals, dendritic origin of after-depolarizing processes and the high input resistance of the facial motoneurone membrane. It is thought that specific features of facial motoneurones and properties of afferent inputs are supposed to provide high sensitivity of neuronal organization of the facial nucleus to afferent signals as well as wide diversity in controlling its activity.

Ultrastructure of hair follicle afferent fibre terminations in the spinal cord of the cat

In acute electrophysiological experiments on anaesthetized cats, single identified hair follicle afferent fibres were injected with horseradish peroxidase (HRP). The HRP was injected from an intra-axonal microelectrode in the lumbosacral spinal cord. One to six hours after injection the animals were perfused and the tissue prepared for light and electron microscopy (EM). Axon collateral arborizations containing HRP reaction product were identified in thick sections under the light microscope and the same tissue then cut on the ultramicrotome for EM study. The terminal branches of the collaterals kept their myelin sheaths until they were 0.45-1.0 micron in diameter, just before they formed synaptic boutons. Synaptic boutons (1.0-4.0 microns in diameter) were usually of the en passant variety and made contact with dendrites. The contacts were asymmetrical (Type I) and contained round, clear synaptic vesicles of 35-60 nm diameter. Both the non-myelinated portion of the terminal axon and the synaptic boutons received axo-axonic contacts. These axo-axonic boutons contained clear (agranular) vesicles irregular in profile.

Synaptic complexes formed by functionally defined primary afferent units with fine myelinated fibers

The individual fine myelinated fibers of cutaneous mechanical nociceptors and "D-hair" receptors were identified by electrophysiological recording with micropipette electrodes in cats and monkeys. Their intraspinal terminations were labeled by iontophoresing horseradish peroxidase intracellularly and subsequent diaminobenzidine histochemistry. These terminations were examined with light and electron microscopy to determine the nature and organization of their synaptic contacts. Myelinated fibers of the mechanical nociceptors became unmyelinated before exhibiting many enlargements that made multiple synaptic contacts in the marginal zone (lamina I) and lamina V. Pre- or postsynaptic contacts were found only on enlargements. In the marginal zone of the cat, enlargements made simple axodendritic contacts or were scalloped, central terminals in glomeruli. In glomeruli, myelinated mechanical nociceptor enlargements were presynaptic to several dendritic appendages and postsynaptic to two different types of profiles. One type was interpreted as a presynaptic axon terminal, the other as a presynaptic, vesicle-containing, dendritic appendage. In lamina V of the cat the nociceptor synaptic complexes were similar, but simpler, and only axonal profiles were found to be presynaptic to them. In the monkey marginal zone and deep nucleus proprius, myelinated nociceptor terminations formed the central element of glomeruli, which consisted of postsynaptic dendritic appendages and presynaptic axon terminals. D-hair axons terminated in large numbers of enlargements in the nucleus proprius (laminae III and IV) and inner substantia gelatinosa (lamina IIi). Their large rounded enlargements formed the central terminals in glomeruli and were presynaptic to both ordinary and vesicle-containing dendritic appendages; the presynaptic dendritic profiles also often contacted each other. Profiles interpreted as axonal in origin were the only terminals presynaptic to the primary ending within the D-hair glomeruli. The results suggest that transfer of primary afferent information occurs only at enlargements of the primary fiber and that each primary fiber enters into more than one kind of synaptic arrangement. They also point out that synaptic glomeruli are common to functionally different types of primary afferent fibers and that the internal organization of glomeruli varies with the kind of primary fiber and the locus of the complex.

Morphological identification of axo-axonic and dendro-dendritic synapses in the rat substantia gelatinosa

Axo-axonic and dendro-dendritic synapses of the rat substantia gelatinosa Rolandi (SGR) have been studied in 14 adult rats by means of thin section and freeze-etch electron microscopy. Out of 6045 synaptic contacts we identified 54 between axon terminals, 10 between dendritic processes. Aside from vesicle shape the following parameters were used in a morphometric study; width of synaptic clefts, depth and length of postsynaptic densities. There are two main types of axo-axonic synapses, those with agranular vesicles (AA-type) and those with an increased population of large granular vesicles (AAgr-type). The former is prevailing and can be subdivided into two subgroups: AA1 and AA2. The pre- and postsynaptic terminals of AA1 contain spherical vesicles, the depth and length of postsynaptic densities as well as the width of the junctional clefts being significantly larger than that of AA2. Presynaptic terminals of AA2 synapses contain predominantly flattened vesicles, while spherical vesicles were found exclusively in the postsynaptic boutons. AAgr-type is rarely encountered; it is characterized by large granular vesicles (65-110 nm) which accumulate postsynaptically and occasionally in both pre- and postsynaptic boutons. Two types of dendro-dendritic synapses (DD1 and DD2) constitute another SGR feature. The difference between DD1 and DD2 is analogous to that between AA1 and AA2 except that pleomorphic synaptic vesicles appear in both groups. The width of subsynaptic membrane appositions turned out to be the most consistent criterion by which the two groups could be differentiated.

[Neuroanatomy of the optic, trigeminal, facial, glossopharyngeal, vagus, accessory and hypoglossal nerves (author's transl)]

1. The intracranial and intraorbital course of the optic nerve is described concisely, the intracanicular one in full details. Apart from the wide and small sections of the optic canal, its axis opposite to the cranial planes, the coating of the canal and the adjacency to the paranasal sinuses and arteries are exactly described. 2. At the trigeminal nerve the trigeminal ganglion, its roots and also the mandibular nerve have great importance in the practical medicine considering thermo-coagulation or surgery of the trigeminal nerve. This segments and also the adjacency of the fifth nerve to the internal carotid artery and subarachinoid brain vessels are exactly, the nuclei areas and central tracts are briefly explained. 3. The nuclei of the facial nerve the intracerebral and intracisternal course and its development, the facial canal and its narrow passes are described. Also the position of the internal acoustic pore in the skull, the dimensions of the internal acoustic meatus and the relations between nerves and vessels are explained. In addition to the geniculate ganglion and the chorda tympani the communications of the facial nerve inside the temporal bone, the tympanic intumescentia (ganglion) and the nervus intermedius, also the petrosal nerves are included in the description. The sheaths of the segments of the seventh cranial nerve and also the fasciculation are exactly, the somatotopic organization is briefly described. 4. The extracranial course of the glossopharyngeal nerve is briefly, its intracranial sections are included exactly in the investigation. 5. The nuclei of the vagus nerve and the intra- und extracranial course are described. 6. The accessory nerve, its nucleus and the intra- and extracranial course are concisely explained. 7. The hypoglossal nerve, its nucleus, the emergence of the fibres and also the relations of nerves and vessels in the posterior cranial fossa are described. The hypoglossal canal and also the extracranial course are explained as briefly as possible.

Fine structure and organization of the infrared receptor relay, the lateral descending nucleus of the trigeminal nerve in pit vipers

The morphology of the nucleus of the lateral descending tract of V has been studied in species of two genera of pit vipers, cottonmouth moccasin (Agkistrodon piscivorus piscivorus), and rattlesnake (Crotalus ruber and Crotalus horridus horridus). The nucleus is the site of termination of primary afferent neurons forming the infrared receptors in the facial pits. It is located on the external surface of the common descending tract of V and contains somata that range in size from 7 to 22 micrometer in A. p. piscivorus and 7 to 27 micrometer in C. ruber. Electron microscopy reveals that the lateral descending tract contains both A delta and C fibers. Degeneration experiments indicate that the A delta fibers are primary afferents. The source of the C fibers is unknown. The lateral descending nucleus in both the cottonmouth and rattlesnake is fundamentally similar in organization. Afferent terminals containing clear spherical vesicles make synaptic contact with dendritis processes within the main neuropil. These axon terminals are also postsynaptic to boutons containing pleomorphic vesicles and some large dense-core vesicles. The C fibers terminate in a neuropil at the margin of the lateral descending tract on small dendritic processes that appear to come from neurons within the nucleus. This neuropil is found external to the tract in the cottonmouth and internal to the tract in the rattlesnake. The terminals contain clear spherical vesicles and large dense-core vesicles. The singularity of input to this nucleus is apparently reflected in the morphology. This is discussed in relation to the subnucleus caudalis of the mammalian brainstem.

Unmyelinated axons in the trigeminal motor root of human and cat

The fiber composition of the human and cat trigeminal "motor roots" were studied utilizing the electron microscope. Twelve to twenty percent of fibers in the human trigeminal motor root are unmyelinated whereas 9-15% are unmyelinated in the cat. The only previous examination of the fiber composition of the peripheral trigeminal motor nerve utilized the light microscope and indicated that less than 5% of fibers were unmyelinated in cat. No study of the fiber composition of the motor nerve root is available. The present results are similar to those recently obtained by others for spinal ventral roots. The function of unmyelinated fibers in the trigeminal "motor root" is unknown, however indirect evidence, both laboratory and clinical, suggests a potential sensory function for them. The findings question seriously the concept that the functional separation of the nervous system into motor and sensory systems has anatomical correlates in the spinal and cranial nerve roots. The results relate directly to our conceptualization of the nervous system and also to the design of methods for the treatment of intractable pain.

Relative numbers of several types of synaptic connections in the substantia gelatinosa of the cat spinal cord

The relative numbers of axo-dendritic, axo-axonic, dendro-axonic and dendro-dendritic synapses were determined by classifying and recording all such specialized contacts in sample areas of the substantia gelatinosa. The samples were taken from segments L1-L5 of the cat spinal cord. In the glomerular complexes 97% of all synapses were recorded as axo-dentritic. In substantia gelatinosa deprived of glomerular complexes by dorsal root section, 96.5% were axo-dendritic. The remainders were about equally divided between axo-axonic, dendro-dendritic and dendro-axonic synapses.

Preterminal and terminal axon arborizations in the substantia gelatinosa of cat's spinal cord

Extensive terminal branchings of fine fibers in the substantia gelatinosa of Golgi-Kopsch preparations of the adult cat spinal cord were subjected to a semi-quantitative analysis. transverse sections suggest that these fibers are probably unmyelinated primary afferent elements of dorsal root origin. In transverse sections these elements pass medially and ventrally and shortly disappear due to a change in orientation. Similar thin fibers in sagittal sections can be followed for several hundred microns as they give rise to side branches that also run mainly in a longitudinal direction. The side branches divide in turn to produce preterminal axon arborizations. The arborizations were distributed in 150 mum wide zones in the dorsal horn region corresponding to Rexed's lamina II. The end terminals are large bulbs, usually preceded by two to three equally large en passant enlargements. Seven to eight terminals stem from each side branch. The terminals and enlargements are arranged in narrow (16-26 mum thick) sagittal sheets. The terminals of several side branches often converge upon a common region so that clusters of terminals occur within the sagittal sheet. It is proposed that these observations are consistent with the substantia gelatinosa (lamina II) as the termination of unmyelinated (C) primary afferent fibers and that the latter are the only type of primary fibers ending in this portion of the spinal cord.

Myelin formation in cultures of previously dissociated mouse spinal cord

Myelin formation in cultures of previously dissociated spinal cord from foetal mice is described. In addition to the expected pattern of myelination, in which axons are closely wrapped by myelin lamellae, redundant folds of myelin have been found, as have double sheaths surrounding a single axon. Hypotheses concerning the generation of these appearances are discussed. It is suggested that certain intracytoplasmic laminar bodies found in oligodendrocytes in vitro may be of mitochondrial origin.

Fiber spectrum of the trigeminal sensory root of the baboon determined by electron microscopy

✓ Using random sampling methods and the electron microscope we have verified the impression gained from light microscopy that unmyelinated fibers compose only about 40% of the total fiber count of the trigeminal root. By contrast, recent electron microscopic studies of segmental dorsal roots indicate that, at least in lower vertebrates, unmyelinated fibers compose up to 80% or more of the total. This observation is considered to be of descriptive rather than physiological or pathological significance. The morphological alterations that occur in the spinal trigeminal tract appear to restore the balance in favor of unmyelinated fibers at the functional termination of the trigeminal sensory root.