The brain of the horseshoe crab (Limulus polyphemus) II. Architecture of the corpora pendunculata

The corpora pedunculata, or mushroom bodies, of the horseshoe crab, Limulus polyphemus, form a bulbous ventral hemisphere composed of two internal lobes that are highly branched like a cauliflower. This organ is clothed with a deep layer of small association neurons called globuli or Kenyon cells. In an animal that is 50 mm in width, they number 3.7 × 10⁶, a value that rises to about 1 × 10⁸ in an adult (250 mm width). The neuropil of each corpus pedunculatum converges from its peripheral lobules toward several major peduncles, which are in communication with the protocerebral neuropil by a narrow stalk containing about 5000 fibers in a 50 mm animal. The numerical relations suggest that presumptive second-order chemosensory fibers enter the corpora pedunculata and synapse divergently onto Kenyon cells. The axons of Kenyon cells, in turn, converge onto efferent fibers that leave through the stalk.     

Synaptic morphology of the carotid body of the domestic fowl

Efferent and reciprocal synapses have been demonstrated in the carotid body of the domestic fowl (Gallus gallus domesticus). Synapses were also found with purely afferent morphology, but were probably components of reciprocal synapses. The general morphology of the endings suggested the presence of two types of axon, afferent axons making reciprocal and perhaps afferent synapses with Type I cells, and efferent axons making efferent synapses with Type I cells. A few axo-dendritic synapses were also found. The dense-cored vesicles associated with the afferent components of reciprocal synapses and with the possible true afferent synapses varied in diameter and core but could belong to one population of pre-synaptic vesicles. These observations are consistent wtih a new theory for the carotid body receptor mechanism. This proposes a spontaneously discharging afferent axon inhibited by an inhibitory transmitter substance released by the Type I cell via the "afferent" component of its reciprocal synapse, the "efferent" component inhibiting this release. Besides this chemoreceptor modulation of its afferent axon, the Type I cell may also have a general secretory function.     

A survey of the cytology and synaptic organization of the insular trigeminal-cuneatus lateralis nucleus in the rat, including an identification of spinal afferent inputs

The cytology and synaptic organization of the insular trigeminal-cuneatus lateralis (iV-Cul) nucleus was examined in the rat. In addition, the ultrastructural morphology and synaptic connectivity of anterogradely labeled spinal afferent axons terminating in iV-Cul were examined following injection of horseradish peroxidase (HRP) into the cervical spinal cord. The uniformity of the ultrastructural features of iV-Cul neurons supports the presence of a homogeneous neuronal population. The most prominent feature of the iV-Cul neuropil is the presence of numerous interdigitating astrocytic processes, which extensively isolate neuronal somata and processes. iV-Cul contains a heterogeneous population of axonal endings that can be separated into three categories, depending upon whether they contain predominantly spherical-shaped agranular synaptic vesicles (R endings), predominantly pleomorphic-shaped agranular synaptic vesicles (P endings), or a heterogeneous population of dense-core vesicles (DC endings). The R endings represent the majority of axonal endings in iV-Cul and establish asymmetrical axodendritic and axospinous synaptic contacts, primarily along the distal portions of the dendritic tree. P endings establish symmetrical axosomatic, axodendritic, and axospinous synaptic contacts and exhibit a more generalized distribution along the somadendritic tree. DC terminals establish asymmetrical axodendritic synaptic contacts with distal dendritic processes and are the least frequently observed endings in the iV-Cul neuropil. Numerous synaptic glomeruli, exhibiting a single large central R bouton that establishes multiple axodendritic or axospinous synapses, characterize the iV-Cul neuropil. Axoaxonic synapses are conspicuously absent from the iV-Cul neuropil and glomeruli. The anterograde HRP labeling of spinal afferent axons that terminate in iV-Cul indicates that the terminals along these fibers are of the R type and that they are engaged predominantly in synaptic glomeruli. The results of this study indicate that the synaptic organization of iV-Cul is distinctly different from that of neighboring somatosensory nuclei, and supports the recent suggestion that this nucleus should be considered a separate precerebellar spinal relay nucleus in the lateral medulla.     

Fine structural analysis of calcitonin gene-related peptide in the mouse inferior olivary complex

Climbing fiber afferents to the cerebellum, from the inferior olivary complex, have a powerful excitatory effect on Purkinje cells. Changes in the responsiveness of olivary neurons to their afferent inputs, leading to changes in the firing rate or pattern of activation in climbing fibers, have a significant effect on the activation of cerebellar neurons and ultimately on cerebellar function. Several neuropeptides have been localized in both varicosities and cell bodies of the mouse inferior olivary complex, one of which, calcitonin gene related peptide (CGRP), has been shown to modulate the activity of olivary neurons. The purpose of the present study was to investigate the synaptic relationships of CGRP-containing components of the caudal medial accessory olive and the principal olive of adult mice, using immunohistochemistry and electron microscopy. The vast majority of immunoreactive profiles were dendrites and dendritic spines within and outside the glial boundaries of synaptic glomeruli (clusters). Both received synaptic inputs from non-CGRP labeled axon terminals. CGRP was also present within the somata of olivary neurons as well as in profiles that had cytological characteristics of axons, some of which were filled with synaptic vesicles. These swellings infrequently formed synaptic contacts. At the LM level, few, if any, CGRP-immunoreactive climbing fibers, were seen, suggesting that CGRP is compartmentalized within the somata and dendrites of olivary neurons and is not transported to their axon terminals. Thus, in addition to previously identified extrinsic sources of CGRP, the widespread distribution of CGRP within olivary somata and dendrites identifies an intrinsic source of the peptide suggesting the possibility of dendritic release and a subsequent autocrine or paracrine function for this peptide within olivary circuits.     

Structure of anterior dorsal ventricular ridge in snakes.

Anterior dorsal ventricular ridge (ADVR) is a major subcortical, telencephalic nucleus in snakes. Its structure was studied in Nissl, Golgi, and electron microscopic preparations in several species of snakes. Neurons in ADVR form a homogeneous population. They have large nuclei, scattered cisternae of rough endoplasmic reticulum in their cytoplasm, and bear dendrites from all portions of their somata. The dendrites have a moderate covering of pedunculated spines. Clusters of two to five cells with touching somata can be seen in Nissl, Golgi, and electron microscopic preparations. The area of apposition may contain a series of specialized junctions which resemble gap junctions. Three populations of axons can be identified in rapid Golgi preparations of snake ADVR. Type 1 axons course from the lateral forebrain bundle and bear small varicosities about 1 mu long. Type 2 axons arise from ADVR neurons and bear large varicosities about 5 mu long. The origin of the very thin type 3 axons is not known; they bear small varicosities about 1 mu long. The majority of axon terminals in ADVR are small (1 mu to 2 mu long), contain round synaptic vesicles, and form asymmetric active zones. This type of axon terminates on dendritic spines and shafts and on somata. A small percentage of terminals are large, 5 mu in length, contain round synaptic vesicles, and form asymmetric active zones. This type of axon terminates only on dendritic spines. A small percentage of terminals are small, contain pleomorphic synaptic vesicles, and form symmetric active zones. This type of axon terminates on dendritic shafts and on somata.     

Immunofluorescent localization of dopamine-like and leucine-enkephalin-like neurons in the supraoesophageal ganglia of the American cockroach, Periplaneta americana

Leucine-enkephalin- and dopamine-like nerve cells and fibers were localized in the supraoesophageal ganglia (brain) of the American cockroach, Periplaneta americana, using immunofluorescence. The presence of leucine-enkephalin-like material was confirmed using immunoperoxidase staining. Several cells containing leucine-enkephalin-like material were found in the pars lateralis, and nerve fibers belonging to these cells were traced through the brain. Dopamine-like material was detected in deutocerebral neurons as well as the nerve processes arising from these cells which lead into the area of the deutocerebral glomeruli. Specific immunofluorescence was also obtained in the alpha and beta lobes of the corpora pedunculata with both the leucine-enkephalin and dopamine antibodies. However, the fluorescent banding pattern observed in both lobes was distinctly different with the two antibodies. No specific fluorescence was observed in the stalk or peduncle of the corpora pedunculata with either the leucine-enkephalin or the dopamine antibody. The findings suggest a possible interaction of leucine-enkephalinergic and dopaminergic nerve fibers in the alpha and beta lobes of the cockroach corpora pedunculata.     

Formation of new synaptic contacts by Purkinje axon collaterals in the granular layer of deafferented cerebellar cortex of adult rat

In addition to (i) mossy terminals, (ii) Golgi axons, (iii) granule cell dendrites and (iv), occasionally, Golgi cell dendrites, a third axonal profile identified by morphological criteria as the collateral of Purkinje axons, has been found in 2% of all cerebellar glomeruli. These infrequent components of a few glomeruli, however, were never seen in normal cerebellar cortex to establish specialized synaptic contact with glomerular dendrites. Two to four weeks after surgical isolation of the cerebellar cortex, i.e. following the destruction of both efferent and afferent fibres, the number of glomeruli containing (hypertrophic) axonal branches of Purkinje cells has increased to 13% of all surveyed glomeruli. In addition, the Purkinje axon terminals in the mossy fibre-deprived glomeruli were observed to establish numerous Gray II-type synaptic contacts with surrounding granule cell dendrites. It is suggested that the development of heterologous synapses between hypertrophic, or even intact, Purkinje axon collaterals on the one hand and the mossy fibre-vacated granule cell dendrites on the other, is a compensatory, reactive process to the synaptic "desaturation" of granule neurons, which demonstrate a dormant potential of Purkinje cells to form new synaptic contacts in the adult cerebellum.     

A Survey of the Cytology and Synaptic Organization of the Insular Trigeminal—Cuneatus Lateralis Nucleus in the Rat,Including an Identification of Spinal Afferent Inputs

The cytology and synaptic organization of the insular trigeminal—cuneatus lateralis (iV-Cul) nucleus was examined in the rat. In addition, the ultrastructural morphology and synaptic connectivity of anterogradely labeled spinal afferent axons terminating in iV-Cul were examined following injection of horseradish peroxidase (HRP) into the cervical spinal cord. The uniformity of the ultrastructural features of iV-Cul neurons supports the presence of a homogeneous neuronal population. The most prominent feature of the iV-Cul neuropil is the presence of numerous interdigitating astrocytic processes, which extensively isolate neuronal somata and processes. iV-Cul contains a heterogeneous population of axonal endings that can be separated into three categories, depending upon whether they contain predominantly spherical-shaped agranular synaptic vesicles (R endings), predominantly pleomorphic-shaped agranular synaptic vesicles (P endings), or a heterogeneous population of dense-core vesicles (DC endings). The R endings represent the majority of axonal endings in iV-Cul and establish asymmetrical axodendritic and axospinous synaptic contacts, primarily along the distal portions of the dendritic tree. P endings establish symmetrical axosomatic, axodendritic, and axospinous synaptic contacts and exhibit a more generalized distribution along the somadendritic tree. DC terminals establish asymmetrical axodendritic synaptic contacts with distal dendritic processes and are the least frequently observed endings in the iV-Cul neuropil. Numerous synaptic glomeruli, exhibiting a single large central R bouton that establishes multiple axodendritic or axospinous synapses, characterize the iV-Cul neuropil. Axoaxonic synapses are conspicuously absent from the iV-Cul neuropil and glomeruli. The anterograde HRP labeling of spinal afferent axons that terminate in iV-Cul indicates that the terminals along these fibers are of the R type and that they are engaged predominantly in synaptic glomeruli. The results of this study indicate that the synaptic organization of iV-Cul is distinctly different from that of neighboring somatosensory nuclei, and supports the recent suggestion that this nucleus should be considered a separate precerebellar spinal relay nucleus in the lateral medulla.     

Neurons with dopamine-like immunoreactivity target mushroom body Kenyon cell somata in the brain of some hymenopteran insects

The mushroom bodies of the insect brain are centers for olfactory and multimodal information processing and they are involved in associative olfactory learning. They are comprised of numerous (340,000 in the bee brain), small (3–8 μm soma diameter) local interneurons, the Kenyon cells. In the brain of honeybees (Apis mellifera) of all castes (worker bees, drones and queens), wasps (Vespula germanica) and hornets (Vespa crabro) immunostaining revealed fibers with dopamine-like immunoreactivity projecting from the pedunculus and the lip neuropil of the mushroom bodies into the Kenyon cell perikaryal layer. These fibers terminate with numerous varicosities, mainly around the border between medial and lateral Kenyon cell soma groups. Visualization of immunostained terminals in the transmission electron microscope showed that they directly contact the somata of the Kenyon cells and contain presynaptic elements. The somata of the Kenyon cells are clearly non-immunoreactive. Synaptic contacts at the somata are unusual for the central nervous systems of insects and other arthropods. This finding suggests that the somata of the Kenyon cells of Hymenoptera may serve an integrative role, and not merely a supportive function.     

Interactions between tectal radial cells in the red-eared turtle, Pseudemys scripta elegans: an analysis of tectal modules.

The optic tectum is a major subdivision of the visual system in reptiles. Previous studies have characterized the laminar pattern, the neuronal populations, and the afferent and efferent connections of the optic tectum in a variety of reptiles. However, little is known about the interactions that occur between neurons within the tectum. This study describes two kinds of interactions that occur between one major class of neurons, the radial cells, in the optic tectum of Pseudemys using Nissl, Golgi and electron microscopic preparations. Radial cells have somata which bear long, radially oriented apical dendrites from their upper poles and short, basal dendrites from their lower poles. They are divided into two populations on the basis of the distribution of their somata in the tectum. Deep radial cells have somata densely packed in the stratum griseum periventriculare. Their plasma membranes form casual appositions. Middle radial cells have somata scattered throughout the stratum griseum centrale and stratum fibrosum et griseum superficiale and do not contact each other. The apical dendrites of both populations of radial cells participate in vertically oriented, dendritic bundles. The plasma membranes of the dendrites in these bundles form casual appositions in the deeper tectal layers and chemical, dendrodenritic synapses within the stratum fibrosum et griseum superficiale. The synapses have clear, round synaptic vesicles and slightly asymmetric membrane densities. Thus, radial cells interact via both casual appositions and chemical synapses. These interactions suggest that radial cells may form a basic framework in the tectum. Because both populations of radial cells extend into the stratum fibrosum et griseum superficiale and stratum opticum, they may receive input from some of the same tectal afferent systems. Because the deep radial cells alone have somata and dendrites in the deep tectal layers, they may receive additional inputs that the middle radial cells do not. Neurons in the two populations interact via chemical dendrodentritic synapses, thereby forming vertically oriented modules in the tectum.     

An ultrastructural study of the development of afferent and efferent synapses on outer hair cells of the guinea pig organ of Corti

The guinea pig organ of Corti was studied using transmission electron microscopy, the second turn of the cochlea being examined at various ages between 20 days before birth and 30 days postnatal. Outer hair cells were examined at each of these ages. At all ages studied, the efferent (presynaptic) terminals are large and are packed with synaptic vesicles, whereas the afferent (postsynaptic) terminals are generally smaller, with a relatively small number of vesicles. During development, the subsynaptic cistern changes from a fragmented, diffuse profile extending over 50-70% of the length of the efferent contact zones, to a continuous, compact structure spanning neighbouring synapses. Synaptic vesicles in the efferent terminals are predominantly rounded in early development, flattened vesicles appearing postnatally. The synaptic bodies at afferent synapses do not change noticeably during development. Quantitative analysis revealed that the area of efferent terminals and the length of their active zone increase with increasing age, the same parameters decreasing in afferent terminals. Synaptic vesicles in the efferent terminals decrease in diameter, but remain constant in afferent terminals, with increasing age. The number of hair cell membrane invaginations decreases as development proceeds.     

Electron microscopic observations on the juxtamedullary efferent arterioles and Arteriolae rectae in kidneys of rats

Summary Efferent arterioles leaving juxtamedullary glomeruli in the kidneys of rats have a media comprized of a layer of closely packed smooth muscle cells. This muscle coat continues along the length of the efferent arterioles and arteriolae rectae to a level deep in the outer medullary zone, where smooth muscle cells are gradually replaced by pericytes characteristic of the non-muscular arterial vasa recta.Bundles of unmyelinated nerve fibers accompany the efferent arterioles and arteriolae rectae to the level where smooth muscle is no longer found in the media of the latter vessels. Close associations between smooth muscle cells and axons are marked by axonal dilatations which lie adjacent to muscle cells. There is no modification of either the axonal or the muscle cell membrane at these sites, nor do axons penetrate the basal lamina of muscle fibers. Large granular vesicles and small granular and agranular vesicles occur in most axons at the dilations, although the granular material in the small granular vesicles is usually sparse and in dispersed form.The nerves are considered to be primarily adrenergic because of strong catecholamine fluorescence demonstrated by other workers in association with the efferent arteries and arteriolae rectae. Poor definition of the small granular vesicles, which are commonly supposed to contain catecholamines, is ascribed to extraction of catecholamines during processing, discharge of granules prior to fixation, or inability of these axons to store catecholamines in quantity under physiological conditions.Financial assistance during the progress of this work was obtained from the Medical Research Council of Canada.     

Ultrastructure of the nerve cells and fibres in the urinary bladder wall of the cat.

The nerve elements in the urinary bladder of the cat were studied by electron microscopy. According to their ultrastructure, nerve cell somata can be classified into three types: the large cells with a cytoplasm rich in organelles, several processes and numerous synaptic contacts on their surface; the cytoplasm contained 80- 120-nm granulated vesicles. The second type is poor in cytoplasmic organelles and has very few processes and virtually no synaptic contacts on the soma. The third type contains numerous large 160- to 220-nm 'neurosecretory' vesicles in the cytoplasm. According to the morphology of the vesicle population, four types of nerve processes could be distinguished: Type a, with a dominant population of small (40-60 nm) agranular vesicles. These are thought to be sacral parasympathetic fibres. Type b, with small (40-60 nm) granular vesicles, which may be the noradrenergic sympathetic fibres. Type c, with 80- to 120-nm granulated vesicles, probably of local origin. Typed d, with large 160- to 220-nm 'neurosecretory' vesicles also of local origin. Different types of nerve fibres are converging on the local nerve cells. This suggests that the local circuits can play an important role in coordinating the function of the bladder. Therefore, ganglia may be considered as an elementary functional unit.     

Neuronal connections and the function of the corpora pedunculata in the brain of the American cockroach,Periplaneta americana (L.)

The fiber constituents and connections of the calyces — the input-receiving regions — of the corpora pedunculata (“mushroom bodies”) were studied in reduced silver preparations from the American cockroach, Periplaneta americana (L.). In the outer synaptic layer of the calyces five fiber classes were distinguished, the first three of which arise outside the mushroom body. (1) Four highly similar neurons with somata near the optic lobe branch into different parts of the ipsiateral protocerebrum, including both calyces. Their fibers are highly constant in arrangement and position and contain small nucleus-like bodies. (2) The tractus olfactorio-globularis (sensu lato) emits fiber groups which course along the calycal walls as “calycal tracts” before ultimately dissipating into the synaptic layer. Variability within these tracts is described. (3) Fibers of undertermined origin outside the mushroom body radiate from the calycal center outwards through the synaptic layer. (4) From the inner calycal layer of neurites belonging to intrinsic mushroom-body neurons, perpendicular collaterals enter the synaptic layer. (5) Intrinsic-neuron somata near the calycal rim emit fibers which course tangentially within the synaptic layer from calycal rim to center. These fibers form a special peripheral zone in the pedunculus. The predominant presumably afferent calycal fiber class is that derived from the tractus olfactorio-globularis. No evidence was found for tracts from optic lobe to calyces. On this basis, and in light of the experimental and comparative anatomical literature, it is suggested that the corpora pedunculata of P. americana and other pterygotes are fundamentally second-order antennal sensory processing centers. Conflicting observations in earlier reports are critically discussed.     

Inhibitory effects of beta-alanine on the vagal efferent and afferent excitatory responses of the stomach to stimulation of vagal trunk in cats.

The effects of beta-alanine on the electrically evoked vagal efferent (hexamethonium-sensitive initial excitatory response) and afferent (hexamethonium-resistant delayed excitatory response) responses of the cat stomach were studied. beta-alanine (30 to 300 micrograms/kg, i.v.) dose-dependently inhibited both the efferent and afferent response. The IC50 values of beta-alanine on the efferent and afferent response were 296 +/- 65 micrograms/kg and 128 +/- 35 microgram/kg, respectively. Maximal inhibitory effects of beta-alanine (300 micrograms/kg, i.v.) appeared about 1 hr after the injection. Glycine and taurine (100 to 10,000 micrograms/kg) did not affect these responses. Treatment with hexamethonium (10 mg/kg, i.v.) prevented the efferent response, but augmented the afferent response. The treatment with hexamethonium abolished the inhibitory effect of beta-alanine on the afferent response. Both picrotoxin (100 and 500 micrograms/kg, i.v.) and bicuculline (2000 micrograms/kg, i.v.) antagonized the inhibitory effects of beta-alanine on the vagal efferent and afferent responses of the stomach. The present experiments clearly demonstrated that beta-alanine inhibited both the vagal efferent and afferent excitatory responses of stomach to electrical stimulation of vagal trunk in cats.     

A major role for intracortical circuits in the strength and tuning of odor-evoked excitation in olfactory cortex

In primary sensory cortices, there are two main sources of excitation: afferent sensory input relayed from the periphery and recurrent intracortical input. Untangling the functional roles of these two excitatory pathways is fundamental for understanding how cortical neurons process sensory stimuli. Odor representations in the primary olfactory (piriform) cortex depend on excitatory sensory afferents from the olfactory bulb. However, piriform cortex pyramidal cells also receive dense intracortical excitatory connections, and the relative contribution of these two pathways to odor responses is unclear. Using a combination of in vivo whole-cell voltage-clamp recording and selective synaptic silencing, we show that the recruitment of intracortical input, rather than olfactory bulb input, largely determines the strength of odor-evoked excitatory synaptic transmission in rat piriform cortical neurons. Furthermore, we find that intracortical synapses dominate odor-evoked excitatory transmission in broadly tuned neurons, whereas bulbar synapses dominate excitatory synaptic responses in more narrowly tuned neurons.     

Morphology and physiology of multiglomerular olfactory projection neurons in the spiny lobster

Whole-cell patch-clamp recording was used to characterize olfactory projection neurons in an isolated brain preparation of the spiny lobster, Panulirus argus. Responses to electrical stimulation of the olfactory afferents were recorded from projection neuron somata using biocytin-filled electrodes. All projection neurons were multiglomerular, innervating up to 80% of all olfactory lobe glomeruli, but the innervation was heterogeneous. Most neurons densely innervated only 3–4 glomeruli; the remaining glomeruli in their dendritic arbor were sparsely innervated, thereby creating two distinct patterns of intraglomerular branching. Projection neurons responded to orthodromic stimulation with an initial depolarization and spiking followed by a 1–3 s hyperpolarization. The inhibitory phase of the response was lower in threshold and longer in latency than the excitatory phase, a response pattern also reported in olfactory projection neurons of insects and vertebrates. The somata of the projection neurons supported voltage-activated currents and TTX-sensitive action potentials, suggesting that the soma, although spatially separated from the axon and dendrites, may play a significant functional role in these cells. Dye coupling between some projection neurons correlated with the presence of multiple amplitude action potentials, suggesting that at least some projection neurons may be coupled via gap junctions.     

Localization of neurons innervating masticatory muscle spindle and periodontal receptors in the mesencephalic trigeminal nucleus and their reflex actions

The mesencephalic trigeminal nucleus was studied in anaesthetized and curarized rabbits by recording the unitary activity through extracellular microelectrodes and identifying the constituent cell types. Two types of units were found, namely primary afferents supplying jaw raising muscle spindles and periodontal or gingival mechanoreceptors. These two groups of neurons exhibited a rostrocaudal somatotopy: the former occupied the entire rostral portion of the nucleus (A7-P2.3; trochlear decussation being taken as an arbitrary 0 level), the latter was located caudally (P3-P4.5) while the somata of both types of afferent fibres were present between P2.2 and P3. No evidence was found for representation of both tendon organs of jaw muscles and joint receptors. Among the units innervating muscle spindles, secondary afferents were largely more numerous than the primary ones. Among periodontal and gingival mechanoreceptor afferents, incisors were the most widely represented, followed by interalveolar gingiva and molars; the axonal conduction velocity ranged between 9 and 40 m/sec and between 8 and 16 m/sec for ipsilaterally and contralaterally projecting neurons, respectively. The motor responses obtained by electrical stimulation of discrete areas of the MTN confirmed the presence of a high degree of segregation between the two different populations of neurons. In fact, jaw raising movements are obtained when stimulating the area within A7 and P2 containing the somata of spindle afferent neurons, while only jaw opening movements are elicited by stimulation of the caudal levels of the nucleus. These data also show that the periodontal neurons whose somata are located in the MTN participate in the jaw opening reflex, just as the more numerous periodontal mechanoreceptors whose somata are located in the Gasser ganglion. Soma-somatic and soma-axon hillock gap junctions were found among the neurons of the MTN, particularly in the caudal third of the nucleus.     

An electron microscopic study on the innervation of the gill filaments of a lamprey,Lampetra japonica

This paper reports observations on the innervation of gill filaments of the lamprey, Lampetra japonica. Nerve fibers run on each side of the afferent filament artery (AFA nerve) and in the connective tissue compartment along the efferent filament artery (EFA nerve). The AFA nerve supplies vasomotor fibers to the afferent filament artery and arteriovenous anastomoses and special visceral motor fibers to branchial muscle fibers (musculus compressor branchialis circularis). Nerve endings of the vasomotor fibers contain large, cored vesicles (60–180 nm in diameter) with a variable number of small, clear vesicles (30–70 μm in diameter), whereas those of the visceral motor fibers have many small, clear vesicles with few large, cored vesicles. The EFA nerve supplies vasomotor fibers to the efferent filament artery. Their endings, containing mixtures of predominantly large, cored vesicles and small, clear vesicles make close synaptic contacts with reticular cells. The latter in turn are connected with each other or with smooth muscle cells in the wall of the efferent filament artery by nexuses. No nerves are found in the axial plate between the afferent and efferent filament arteries nor in the secondary lamellae of individual gill filaments. No afferent nerve supply to the gill filament has been found.     

The projection of neuroendocrine fibers (NCC I and II) in the brains of three orthopteroid insects

Neuronal projections from neuroendocrine tracts (nervi corpori cordiaci I and II) in the brains of the locust (Schistocerca vaga), cricket (Acheta domesticus), and cockroach (Periplaneta americana) were studied using reconstructions of silver-intensified cobalt chloride preparations. Collaterals from the NCC I in these species branch extensively in the dorsal protocerebral neuropile, anterior to the stalk of the corpora pedunculata and ventral to its calyces. Other fibers project from the NCC I bilaterally into the medial protocerebral neuropile, anterior to the central body, and posterior to the beta lobes. NCC II collaterals arborize in the medial, dorsal, and lateral protocerebral neuropile, their region of projection partially overlapping with that of the NCC I. Several NCC II fibers terminate in the superior arch of the central body in Acheta but not in the other two species. Tritocerebral cells filled through the NCC I branch in the medial tritocerebral neuropile in all three species, but most extensively in Schistocerca. No NCC fibers were seen to penetrate any part of the corpora pedunculata, protocerebral bridge, olfactory glomeruli, ocellar tracts, or optic lobes. These neuronal projections from the NCC I and II lie anterior to regions of branching of second-order ocellar fibers and thus provide no anatomical basis for direct ocellar input to neurosecretory cells, contrary to previous reports for orthopteroid species (Brousse-Gaury, '71a, b). However, interneurons filled from the optic lobes were found to terminate in the same region of dorsal protocerebral neuropile as NCC I and II fibers in Acheta, thus providing a possible pathway for optic input to the cerebral neuroendocrine system.