Cell Axons Research Articles

The histological organization of the pacemaker for the hippocampal theta rhythm in the rabbit

The neurons of the upper part of the rabbit's septum discharge in bursts synchronous with the hippocampal theta rhythms, acting as its pacemaker. A detailed Golgi study of neurons and their connections was under taken with the obejct of understanding the possible neuronal mechanisms by which the septal neurons might transform the variations in degree of reticular excitation into rhythmic bursts of carying (theta) frequencies. Two fundatmentally different types of cell can be distinguished in the dorsal nucleus of the diagonal band (BD): (1) large and medium sized cells the axons of which leave the nucleus in the doral direction, and (2) small cells somewhat resembling Golgi type II neurons. Initial axon collaterals of the type (1) cells can regularly be seen and their termination on the type (2) cells is assumed. The profuse arborizations of the short type (2) cell axons can be traced easily to both cell bodies and proximal dendrites of the type (1). Various kinds of afferent axons and their terminal arborizations have been identified in the (BD) nucleus. In spite of differences in detailed arborization patterns most of these axons have the common feature of establishing contracts with various kinds of cell in relatively widespread regions of the nucleus. A considerable degree of divergence and of convergence appears to be secured by their connections with the neurons of the nucleus. On the analogy with the neuron linkage in many other regions of the CNS the small cells resembling Golgi type II neurons might be interpreted as an inhbitory feedback circuit established within the nucleus. Such feedback loops are generally assumed to produce rhythmic bursts on continuous input both in physiological observations and in model experiments.

The Larval and Pupal Neurosecretory System of Calliphora Erythrocephala Meigen

Neurosecretory cells are present in the pars intercerebralis and the sub-oesophageal ganglion of the larvae and pupae of Calliphora erythrocephala Meigen. On account of their topography these cells are subdivided into 6 groups in the brain and into 2 groups in the sub-oesophageal ganglion; the time of appearance and disappearance is discribed. A modification of the paraldehyd-fuchsine method was used to demonstrate neurosecretory cells. During larval and pupal development there are marked differences amongst the neurosecretory cell types concerning their staining-intensity and changes in this intensity throughout larval and pupal life. The average total number of neurosecretory cells in the hemispheres increases in the first instar from 2 to 8, in the second from 8 to 16, in the feeding period of the third instar from 16 to 20, in the resting period of that instar from 20 to 30 and at the beginning of pupation it decreases to 16 to 20. In the pupae the number of neurosecretory cells is constantly 18. The staining-intensity varies also and shows distinct maxima: in the first two instars 3 to 5 hours before moulting and in the resting period 15 to 20 hours before pupation is started. The axons of the neurosecretory cells transport the neurosecretory material via the nervi corporis cardiaci I and II to the corpus cardiacum. The amount of neurosecretory material in these axons and the corpus cardiacum fluctuates. They possess maxima in stainability at the same time as the cells. It is difficult to correlate these fluctuations with the activity of the neurosecretory system, but there are indications for the function of some cell types. There are indications for a higher activity of two types of neurosecretory cells at the moment the ecdyson production has been started, about 15 to 20 hours before the beginning of pupation. This observation is also made some hours before or at the time of the first and second moult. There are some indications that the neurosecretory cells of the sub-oesophageal ganglion are concerned with locomotor activity. After a strong desiccation it is obvious that the neurosecretory activity of the neurosecretory cells in the brain and sub-oesophageal ganglion has decreased considerably, except for one cell type. Distinct differences in acid phosphatase activity have been found between the neurosecretory cells of the brain.

Efferent association fibers from the anterior limbic cortex of cats and dogs

1. Anterior limbic association fibers pass into the cortex of the sigmoid and orbital gyri and also into the visual cortex. 2. Association connections of the anterior limbic cortex are bilateral. 3. Axons of anterior limbic cortical cells in dogs and cats do not pass directly into the hippocampal formation. 4. The anterior limbic areas have no commissural connections. 5. Passage of anterior limbic association fibers into the cortical apices of the gyri and not into the sulci indicates that within a single cortical area portions exist which differ sharply in the number of impulses received. In this respect the most active areas lie on the apices of gyri, and the least active in the walls and floor of the sulci.

Retrograde degeneration study of somatic sensory thalamocortical connections in brain of Virginia opossum

The method of retrograde degeneration was used to study thalamocortical relationship in the somatic sensory system of the forebrain of the Virginia opossum. Lesions were placed by aspiration in the primary somatic sensory cortex or subdivisions of it in 16 hemispheres and resultant retrograde degeneration in the ventrobasal complex and other thalamic nuclei was examined microscopically. Lesions placed in an electrophysiologically defined cortical region of representation of a given body part resulted in retrograde degenerative changes in the functionally corresponding part of the thalamic ventrobasal complex. Results are interpreted as supporting the hypothesis that axons of cells in the ventrobasal complex project upon the primary neocortical somatic sensory area in a topographic fashion, and thus the organization of somatic sensory thalamocortical projections in the opossum does not appear to be fundamentally different from that of eutherian mammals.

RNA of nerve cell bodies and axons after beta,beta-iminodipropionitrile.

The RNA content of single nerve cell bodies from the anterior horn of rat spinal cord shows no increase during the 12 weeks of feeding of IDPN (β,β-iminodipropionitrile), but a slight decrease is noted during the last four weeks. The RNA concentration in the axonal balloons is only 0.23% as compared to 5.3% in the nerve cell body. The A/U ratio of RNA in the axonal balloons is 0.61 as compared to 0.90 in cell bodies of normal nerve cells. The A/U ratio of RNA in cell bodies of rats fed IDPN is also reduced to 0.68 (6–8 weeks) while the A/U for rats fed IDPN for 1–12 weeks is 0.77.

The fine structure of the statocyst of Octopus vulgaris

The macula and crista in the statocyst of Octopus vulgaris are composed of hair cells and supporting cells. Below these cells is a nerve plexus, which contains a third type of cell, the “dark” cell. Each hair cell bears kinocilia and microvilli at its distal end. The kinocilia have the typical 9 + 2 arrangement of filaments and in each cell the cilia are arranged in an elongated group of up to 200. Roots of the kinocilia are present in the hair cells and they have banding periodicity of 700 A. The supporting cells bear microvilli at their distal ends and are attached to the hair cells by desmosomes. The plexus contains the “dark” cells, which appear to send processes throughout the plexus. Synapses have not been found upon their perikaryon or processes and it is suggested that the “dark” cells may be a sort of glial cell. Apart from containing the axons of the hair cells, and the processes and cell bodies of the “dark” cells, the plexus contains synapses. These synapses are of several different sorts. There are synapses at the bases of the hair cells or with their processes. There are spines projecting into the hair cells, the spines being post-synaptic, and there are also other synapses involving processes or axons of cells whose identity is uncertain. The synapses are provisionally grouped as collateral or centrifugal.

Orientation and directed growth of Mauthner's cell axons from duplicated vestibular nerve roots

The axons of duplicated Mauthner's cells, associated with extra auditory and vestibular nerve roots grafted into the medulla in amphibians, show consistent growth tendencies apparently related to axial gradients within the surrounding tissues. In cases in which the grafted segment is correctly oriented with reference to the long axis of the host, the Mauthner's-cell axons decussate immediately and grow directly back into the spinal cord like normal Mauthner's-cell axons. If the grafted segment is in reversed anteroposterior orientation, however, the axons first grow forward, then recurve and grow caudally into the cord. The level at which the axons recurve corresponds approximately to the anterior junction of graft with host tissues. These results indicate that the axons not only have a very strong affinity for their normal terminations in the spinal cord, but also that their orientation may be influenced by localized cytochemical interactions with other cell types.

THE ORIGIN OF THE ALDEHYDE-FUCHSIN-NEGATIVE NERVE FIBRES OF THE MEDIAN EMINENCE OF THE HYPOPHYSIS: A GONADOTROPIC CENTRE.

In a large number of adult female and male specimens of Rana temporaria, the pars ventralis of the tuber cinereum of the hypothalamus was completely isolated from the brain. The pars ventralis retained its normal connections with the hypophysis. The vascular supply of the whole isolated region was left intact. Two and a half months after operation, in some animals, the interruption of the nervous pathways was still complete. In these animals it could be shown that all or nearly all A. F.-negative nerve fibres of the median eminence are axons of nerve cells localized in the area periventricularis of the pars ventralis tuberis. According to our results in Rana, the same A. F.-negative nerve fibres of the higher vertebrates are probably also axons of homologous nuclei of the tuber cinereum.

CHOLINESTERASES IN THE HYPOTHALAMO-HYPOPHYSIAL NEUROSECRETORY SYSTEM OF THE WHITE-CROWNED SPARROW, ZONOTRICHIA LEUCOPHRYS GAMBELII.

The distribution of cholinesterases in hypothalamo-hypophysial neurosecretory system of the White-crowned Sparrow has been examined histochemically. The perikarya of the neurosecretory cells of the paraventricular and supraoptic nuclei have a high acetylcholinesterase activity. Acetylcholinesterase activity also occurs in the cells of the infundibular nucleus. The proximal parts of the axons of the cells of the neurosecretory and infundibular nuclei have strong acetylcholinesterase activity and weak non-specific cholinesterase activity. In the median eminence, the activity of acetylcholinesterase is strongest in the palisade layer. In the pars nervosa, there is definite, although weak, acetylcholinesterase activity.

Two inhibitory mechanisms in the Mauthner neurons of goldfish.

Two inhibitory mechanisms in the Mauthner neurons of goldfish.

The retina of cephalopods and its degeneration after optic nerve section

Each retinal cell ofOctopuscarries a rhabdomere on two opposite faces. Rhabdomeres from four cells combine to make a square rhabdome. The cells are mainly arranged with their axes in approximately either the vertical or horizontal plane as the eye is usually held in the head. Counts show that there are about twice as many retinal cell nuclei as there are rhabdomes. There are altogether about 2 x 107retinal cells in each eye, with a density of about 50 000/mm2. The retinal cells at the centre of the retina are longer and thinner than those at the periphery. There is a strip of longer, thinner cells running horizontally along the equator. These often have less pigment in their distal ends than do the cells dorsally and ventrally, but other distributions of the pigment are seen, depending on the previous illumination. There are several types and sizes of retinal cell and not all are associated in fours to make rhabdomes. The proximal segments carry fine collateral twigs, these interdigitate and may allow mutual interaction between neighbours. The main meshes of the retinal plexus are not formed by fibres of the retinal cells but by the axons of cells in the optic lobes, presumably efferents. After severing the optic nerves to any region of the retina all the retinal cells undergo retrograde degeneration, leaving only the supporting cells intact. The retinal nerve plexus disappears almost completely, but a few fibres remain. At the boundary between a region with severed and intact nerves the plexus continues for some distance into the denervated region. After removal of all the optic lobe except a portion of its outermost (plexiform) zone the retinal receptors do not degenerate completely but are reduced in length. Their axons have not been interrupted by the operation and this is therefore a partial transneuronal retrograde degeneration.

Some aspects of the structure and function of the nervous system ofArchachatina (Calachatina) marginata(Swainson)

This account is restricted to the ganglia of the central nervous system and the pallial, visceral and cervical nerves. The histology of the ganglia, nerves and their sheaths is described, attention being drawn to the vascular sheaths which enclose the system. Cell sizes within the ganglia are indicated and the giant cells and their axons are described. The possibility that a synaptic connexion exists between medium sized (40 to 60μ) nerve cells and the giant axons is discussed. The active and contractile nature of the peripheral nerves is described and some measurements of nerve lengths and diameters under extended and contracted conditions are given. Maximum extended lengths are approximately double the contracted lengths and under extended conditions, their mean diameters are reduced by a factor of 0⋅75. More than 60 nerve fibres are estimated to be present in the middle fine right pallial nerve and more than 1000 in the right pallial nerve. The innervation of the collar and the lateral body wall receives brief mention. Observations and measurements of active snails and of dead, expanded animals, have lead to the development of a technique for the estimation of maximum functional lengths of the nerves in terms of the shell dimensions. The method is discussed with reference to the danger of multiple pick-up of single-action potentials during investigations into the electrical activity in the nerves. A factor based upon the breadth of the shell gives reliable estimates of maximum nerve lengths. Attention is directed to the following activities. Protraction and retraction of the head and cervical region; pedal locomotory waves and the dorsal body waves, their relative velocities and wavelengths; the opening and closure of the pneumostome. Activity in the collar and the cervical region is important in relation to electro-physiological investigations reported elsewhere. The nerves concerned are the pallial and cervical nerves. It is possible that an integration centre for the pallial system is situated in the abdominal ganglion. The enclosure of the nervous system within a special part of the vascular system is discussed with reference to conditions in the primitive gastropod. The visceral nerve ofArchachatinais compared with the nervus intestinalis ofHelix pomatiaas described by Schlote (1955) and attention is drawn to the relative advantages to be gained from the use of the pallial nerves, in which cell somata are few in number. Conditions within the ganglia are discussed. Little is known of cell relationships but it is suggested that (i) the large fibres in the pallial nerves are the axons of the giant cells, (ii) the form of their collaterals in the ganglia furnishes a possible explanation for observed changes in the action potentials of the peripheral nerves, (iii) the regular patterns of nervous activity may be due to group control of discharge rates through the mediation of the giant cells.

The effect of photoperiodic stimulation on phosphatase activity in the hypothalamo-hypophysial system of the white-crowned sparrow, Zonotrichia leucophrys gambelii.

1. The metabolic activity of the hypothalamo-hypophysial neurosecretory system of the White-crowned Sparrow, Zonotrichia leucophrys gambelii, has been investigated by means of quantitative estimates of acid- and alkaline-phosphatase activity. The activities of samples from the median eminence, samples from the supraoptic region, the adenohypophyses, and the neurohypophyses of photosensitive and refractory birds, both subjected to short and long daily photoperiods, have been compared. Histochemical demonstrations of the distribution of acid- and alkaline-phosphatase activity have been effected to provide a better basis for interpretation of the quantitative data. 2. The photosensitive birds which were subjected to 20-hour daily photoperiods showed the typical photoperiodically induced testicular growth and fat deposition. There was an increase in acid-phosphatase activity in the supraoptic region. This increase in acid-phosphatase activity may be correlated with increased activity of the neurosecretory cells as indicated by cytologic criteria, including an increased rate of formation of aldehyde-fuchsin stainable material. No such increase in acid phosphatase occurred in refractory birds on 20-hour photoperiods. In photosensitive birds, there was also an increase in acid-phosphatase activity in the median eminence, an increase which appears to be attributable primarily to changes in activity of the axons in the glandular layer although a contribution by the nucleus tuberis cannot be excluded. The change in acid-phosphatase activity in the median eminence coincides well with the observed increase in rate of disappearance of aldehyde-fuchsin-positive granules from the axons. Neither an increase in acid phosphatase nor a decrease in granules occurred in the median eminences of refractory birds subjected to 20-hour daily photoperiods. The acid-phosphatase activity of the adenohypophyses of photosensitive birds was greater than in refractory birds although neither was affected by long daily photoperiods. These results are consistent with the hypothesis that the photoperiodic response in Zonotrichia leucophrys gambelii involves, in the supraoptic region, an increase in acid-phosphatase activity associated with increased synthesis of aldehyde-fuchsin-positive material in the neurosecretory cells, and, in the axons of the glandular layer of the median eminence, an essentially simultaneous increase in acid-phosphatase activity associated with a humoral transfer to the capillaries of the hypophysial portal system. Our data suggest that the higher rate of production of gonadotropins in the adenohypophysis by photosensitive birds involves a higher acid-phosphatase activity but that the photoperiodically induced increase in release of these gonadotropins, mediated by a humoral agent in the hypophysial blood, does not involve a detectable further increase in acid-phosphatase activity. 3. The data on alkaline phosphatase in supraoptic-region, median-eminence region, and adenohypophysis give no indication that this enzyme is involved in the photoperiodically induced activity of the hypothalamo-hypophysial system. 4. In agreement with previous investigations in this laboratory (Okscheet al., 1959), the data obtained in this investigation on phosphatase activity indicate no participation by the neurohypophysis in the photoperiodic response. 5. The histochemical observations indicate that the neurosecretory cells of the paraventricular and supraoptic nuclei have acid- and alkaline-phosphatase activities similar to those of ordinary neurones. The axons of neurosecretory cells, except in the median eminence, are not identifiable by histochemical demonstration of phosphatase activity. In the fibers of the glandular layer of the median eminence there is a pronounced acid-phosphatase, but no alkaline-phosphatase reaction, in these fibers. Also the nuclei and nucleoli of cells of the mammillary and tuberal nuclei have a fairly strong acid-phosphatase activity. In the adenohypophysis there is a conspicuous acid-phosphatase and a strong alkalinephosphatase reaction in the nuclei and nucleoli, but only slight activities in the cytoplasm.

Organization of cerebral cortex. IV. Posttetanic potentiation of hippocampal pyramids.

The response of hippocampal pyramidal cells following single and repetitive stimulation of ascending fornical and commissural afferents has been studied in anesthetized rabbits and cats. Low intensity single pulse stimulation evokes a response of 10–15 msec. duration. The region of the apical dendrites is positive and the region of the cell body, basal dendrites and axon negative with respect to a distant electrode. Single stimuli did not produce a detectable efferent discharge in the alveus or fimbria. Following repetitive stimulation at 5–20/sec., a 3–5-mv potential with a duration of 3 msec. is superimposed upon the response seen following a single stimulus. This large spike shows both a tetanic and posttetanic potentiation characterized by an increased amplitude and a decreased latency. Minimal latency occurs 1–2 seconds following the termination of repetitive stimulation while maximum amplitude is attained during the repetitive stimulation. During potentiation the spike may decrease its latency up to 8 msec. When the high amplitude spike is present an efferent volley may be recorded from the alveus and fimbria. Isopotential contour mapping of these responses indicates that the spike which displays potentiation is a reflection of depolarization of the cell body and stem of the apical dendrites of hippocampal pyramidal cells.

Further Studies of the Positive Visual After-image

The binocular matching technique, in which the sensation of brightness of an after-image formed in one eye only is balanced by a comparison light stimulus in the other eye, has been used for further studies of the positive after-image. By dark-adapting each eye in turn, it is shown that the cone receptors in the retina are mainly responsible for the after-image, whereas the matching stimulus acts mainly on the rods. The decay curves of the after-image in white light for two observers are given, with a discussion of the region in which after-image effects follow a reciprocity law. The after-images formed by monochromatic stimuli give exponential decay curves, compared with power-law decay curves for white light stimuli. It is suggested that the origin of positive after-images may be the electrotonic polarisation of the axons of the ganglion cells. La technique de fusionnement binoculaire dans laquelle la sensation de brillance d'une « image consecutive » formee dans un œil est compensee par un stimulus lum...

The hypothalamo-hypophyseal neurosecretory system of Gegenophis carnosus beddome.

1. The brain of Gegenophis carnosus Beddome resembles that of Ichthyophis glutinosus in general organisation. In size, shape and structure the hypophysis of Gegenophis differs from that of other groups of Amphibians. The pars nervosa is at the posterior tip of the hypophysis and is connected to the brain by a nervous tract. 2. The preoptic nucleus is situated on either side of the third ventricle. The neurons of this nucleus produce two types of neurosecretory matter. The first type, stainable blue by Gomori's chrome alum-haematoxyline-phloxine get transported through the axons of the neurosecretory cells to the pars nervosa. The second type of larger colloids are extruded into extracellular spaces and are later released into the third ventricle.

The neurosecretory system of the fruit flyChjætodacus Cucurbitæ coq.

1. The neurosecretory system of the adult Chaetodacus Cucurbitae (Trypetidae: Diptera) consists of the cerebral, thoracic and abdominal centres of secretory neurons. 2. The cerebral neurosecretory centres consist of the median and lateral neurosecretory cells of the pars intercerebralis. The cells show characteristic tintorial properties when stained in chrome-haematoxylinphloxin and in Azan, recalling the nature of similar cells in other insects. 3. The axons of the median cerebral neurosecretory cells are fairly long, and the nervi corporis cardiaci and corpus cardiacum show granules similar to those observed in the cytoplasm and axons of the cells. 4. The thoracic ganglion shows a more conspicuous set of neuro-secretory cells. They consist of an anterior, lateral anterior, lateral posterior and posterior cell clusters, which in the first three are paired. 5. The single abdominal ganglion contains a few neurosecretory cells also showing characteristic tintorial properties. 6. The nerve emerging from the abdominal ganglion and going to the gut shows blue granules traceable from the neurosecretory cells at the posterior end of the ganglion. 7. Phase contrast observations of the cells show that the neurosecretory cells of the fly have a general structure with prominent cytoplasmic products in the form of dark granules and large and small spheroids and globules. 8. Measurements of the thoracic neurosecretory cells, which forms the larger cells of the system, have been given.

EFFECTS EVOKED IN AN AXON BY THE ACTIVITY OF A CONTIGUOUS ONE

EFFECTS EVOKED IN AN AXON BY THE ACTIVITY OF A CONTIGUOUS ONE