Morphology of neurons and axon terminals associated with descending and ascending pathways of the lateral forebrain bundle in Rana esculenta

Summary The cells of origin of afferent and efferent pathways of the lateral forebrain bundle were studied with the aid of the cobalt-filling technique. Ascending afferents originated from the lateral thalamic nucleus, central thalamic nucleus, posterior tuberculum and the cerebellar nucleus. They terminated in the anterior entopeduncular nucleus, amygdala and the striatum. Telencephalic projection neurons, which are related to the lateral forebrain bundle, were located mainly in the ventral striatum and the anterior entopeduncular nucleus, but were not so numerous in the dorsal striatum. Irrespective of their location, most of the neurons projecting axons into the lateral forebrain bundle had piriform or pyramidal perikarya. Long apical dendrites usually arborized in a narrow space, whereas widely arborizing secondary dendrites originated from short dendritic trunks. The other neurons that contributed to the lateral forebrain bundle were fusiform or multipolar cells. Striatal efferents terminated in the pretectal area and in the anterodorsal, anteroventral and posteroventral tegmental nuclei.     

大白鼠脚内核的传入性联系

众所周知,肉食动物和大白鼠的脚内核,相当于灵长类的内侧苍白球(Nagy et al.1978;Fox and Schmitz 1944);它们的细胞形态、传入及传出均相同。早期以及近年来的一些研究工作者,虽然在研究其他核团的投射时,联系到一些本核团的传入,但是尚缺乏对本核团传人的系统研究。本实验即是应用辣根过氧化物酶的逆行传递法来研究大白鼠脚内核的传入性联系。     

Projections of the optic tectum and the mesencephalic nucleus of the trigeminal nerve in the tegu lizard (Tupinambis nigropunctatus)

Summary Fibers undergoing Wallerian degeneration following tectal lesions were demonstrated with the Nauta and Fink-Heimer methods and traced to their termination. Four of the five distinct fiber paths originating in the optic tectum appear related to vision, while one is related to the mesencephalic nucleus of the trigeminus. The latter component of the tectal efferents distributes fibers to 1) the main sensory nucleus of the trigeminus, 2) the motor nucleus of the trigeminus, 3) the nucleus of tractus solitarius, and 4) the intermediate gray of the cervical spinal cord.The principal ascending bundle projects to the nucleus rotundus, three components of the ventral geniculate nucleus and the nucleus ventromedialis anterior ipsilaterally, before it crosses in the supraoptic commissure and terminates in the contralateral nucleus rotundus, ventral geniculate nucleus and a hitherto unnamed region dorsal to the nucleus of the posterior accessory optic tract.Fibers leaving the tectum dorso-medially terminate in the posterodorsal nucleus ipsilaterally and the stratum griseum periventriculare of the contralateral tectum. The descending fiber paths terminate in medial reticular cell groups and the rostral spinal cord contralaterally and in the torus and the lateral reticular regions ipsilaterally. The ipsilateral fascicle also issues fibers to the magnocellular nucleus isthmi.     

Stress-related serotonergic systems: implications for symptomatology of anxiety and affective disorders

Previous studies have suggested that serotonergic neurons in the midbrain raphe complex have a functional topographic organization. Recent studies suggest that stimulation of a bed nucleus of the stria terminalis-dorsal raphe nucleus pathway by stress- and anxiety-related stimuli modulates a subpopulation of serotonergic neurons in the dorsal part of the dorsal raphe nucleus (DRD) and caudal part of the dorsal raphe nucleus (DRC) that participates in facilitation of anxiety-like responses. In contrast, recent studies suggest that activation of a spinoparabrachial pathway by peripheral thermal or immune stimuli excites subpopulations of serotonergic neurons in the ventrolateral part of the dorsal raphe nucleus/ventrolateral periaqueducal gray (DRVL/VLPAG) region and interfascicular part of the dorsal raphe nucleus (DRI). Studies support a role for serotonergic neurons in the DRVL/VLPAG in inhibition of panic-like responses, and serotonergic neurons in the DRI in antidepressant-like effects. Thus, data suggest that while some subpopulations of serotonergic neurons in the dorsal raphe nucleus play a role in facilitation of anxiety-like responses, others play a role in inhibition of anxiety- or panic-like responses, while others play a role in antidepressant-like effects. Understanding the anatomical and functional properties of these distinct serotonergic systems may lead to novel therapeutic strategies for the prevention and/or treatment of affective and anxiety disorders. In this review, we describe the anatomical and functional properties of subpopulations of serotonergic neurons in the dorsal raphe nucleus, with a focus on those implicated in symptoms of anxiety and affective disorders, the DRD/DRC, DRVL/VLPAG, and DRI.     

The motor nuclei of the glossopharyngeal-vagal and the accessorius nerves in the rat

Retrograde cobalt labeling was performed by incubating the rootlets of cranial nerves IX, X and XI, or the central stumps of the same nerves, in a cobaltic lysine complex solution, and the distribution of efferent neurons sending their axons into these nerves was investigated in serial sections of the medulla and the cervical spinal cord in young rats. The following neuron groups were identified. The inferior salivatory nucleus lies in the dorsal part of the tegmentum at the rostral part of facial nucleus. It consists of a group of medium-sized and a group of small neurons. Their axons make a hair-pin loop at the midline and join the glossopharyngeal nerve. The dorsal motor nucleus of the vagus situates in the dorsomedial part of the tegmentum. Its rostral tip coincides with the first appearance of sensory fibres of the glossopharyngeal nerve, the caudal end extends into the pyramidal decussation. The constituting cells have globular or fusiform perikarya and they are the smallest known efferent neurons. The ambiguous nucleus is in the ventrolateral part of the tegmentum. The rostral tip lies dorsal to the facial nucleus, and the caudal tip extends to the level of the pyramidal decussation. The rostral one third of the ambiguous nucleus is composed of tightly-packed medium sized neurons, while larger neurons are arranged more diffusely in the caudal two thirds. The long dendrites are predominantly oriented in the dorsoventral direction. The dorsally-oriented axons take a ventral bend anywhere between the ambiguous nucleus and dorsal motor nucleus of the vagus. The motoneurons of the accessorius nerve are arranged in a medial, a lateral and a weak ventral cell column. The medial column begins at the caudal aspect of the pyramidal decussation and terminates in C2 spinal cord segment. The lateral and ventral columns begin in C2 segment and extend into C6 segment. The neurons have large polygonal perikarya and characteristic cross-shaped dendritic arborizations. The axons follow a dorsally-arched pathway between the ventral and dorsal horns. The accessorius motoneurons have no positional relation to any of the vagal efferent neurons. It is concluded that the topography and neuronal morphology of accessorius motoneurons do not warrant the designation of a bulbar accessorius nucleus and a bulbar accessorius nerve.     

The classification of neurons in the corpus geniculatum laterale pars ventralis of the albino rat: a Golgi-Kopsch study

Neurons in the ventral lateral geniculate nucleus of 120 rats of a wistar strain were investigated with the Golgi Kopsch technique. Various features, such as size of neurons, their dendritic fine structure and their localization inside the nucleus were used to find new aspects for the classification of vLGN neurons except geniculo tectal relay neurons (GTR neurons). The results of our detailed investigation are in accordance with the classification given by Brauer et al. (1984). The dendrites show different morphological surface specializations, as there are smooth and varicose dendrites besides the spiny ones. Medium-sized neurons are most variable in their dendritic structure. It can be assumed that they represent a heterogenous group. The density of spines in the neurons investigated is much lower than in GTR neurons.     

NADPH-Diaphorase-containing neurons in the medullary structures involved in generation of the respiratory activity in neonatal rats

Using a histochemical technique, we examined distribution of the neurons containing a marker of nitric oxide synthase (NOS), NADPH-diaphorase (NADPH-d), on frontal slices of the medulla and upper cervical spinal segments of 4-day-old rats. It was demonstrated that NADPH-d-positive cells are present within the dorsal and ventral medullary respiratory groups. The highest density of the labeled middle-size multipolar neurons (27.9±2.6 cells per 0.1 mm² of the slice) was observed in the rostral part of the ventral respiratory group, within the reticular lateral paragigantocellular nucleus. Similar NADPH-d-positive neurons were also observed in other reticular formation structures: rostroventrolateral reticular, gigantocellular, and ventral medullary nuclei, and in the ventral part of the paramedial nucleus. There were no labeled neurons in the lateral reticular nucleus. Single small and medium-size labeled neurons were found at all rostro-caudal levels of thenucl. ambiguous (nuclei retrofacialis, ambiguous, andretroam-biguous). Groups of NADPH-d-positive neurons were also revealed within the dorsal respiratory group, along the whole length of thenucl. tractus solitarii (mostly in its ventrolateral parts). Single labeled neurons were also observed in thenucl. n. hypoglossi, and their groups were observed in the dorsal motor part of thenucl. n. vagus. Involvement of the structures containing NADPH-d-positive neurons in the processes related to generation of the respiratory activity is discussed. Our neuroanatomical experiments prove that in early postnatal mammals NO is actively involved in generation and regulation of the medullary respiratory rhythm. Neirofiziologiya/Neurophysiology, Vol. 32, No. 2, pp. 128–136, March–April, 2000.     

Differential responsiveness to the chemorepellent Semaphorin 3A distinguishes Ipsi- and contralaterally projecting axons in the chick midbrain.

In the chick dorsal mesencephalon, the optic tectum, the developing axons must choose between remaining on the same side of the midline or growing across it. The ipsilaterally projecting axons, forming the tectobulbar tract, course circumferentially toward the ventrally situated floor plate but before reaching the basal mesencephalon, the tegmentum, gradually turn caudally. Here, they follow the course of the medial longitudinal fasciculus (MLF), located parallel to the floor plate. By in vivo labeling of tectal axons, we could demonstrate that these axons arise primarily in the dorsal tectum. To test the idea that chemorepellent molecules are involved in guidance of the nondecussating axons, we performed coculture experiments employing tectal explants from various positions along the dorso-ventral axis. Axons emanating from dorsal tectal explants were strongly repelled by diencephalic tissue containing the neurons that give rise to the MLF whereas ventral tectal axons showed only a moderate response. This inhibitory effect was substantially neutralized by the addition of anti-neuropilin-1 antibodies. A similar differential response of axons was observed when tectal explants were cocultured with cell aggregates secreting the chemorepellent Semaphorin 3A (Sema3A). Sema3B and Sema3C, respectively, did not inhibit growth of tectal axons. In addition, neither the floor plate nor Slit2-secreting cell aggregates influenced outgrowth of dorsal fibers. In Sema3A-deficient mice, DiI-labeling revealed that dorsal mesencephalic axons cross the MLF instead of turning posteriorly upon reaching the fiber tract, thus behaving like the ventrally originating contralaterally projecting axons. A differential responsiveness of tectal axons to Sema3A most likely released by the MLF thus contributes to pathfinding in the ventral mesencephalon.     

Convergence of multisensory inputs in Xenopus tadpole tectum

The integration of multisensory information takes place in the optic tectum where visual and auditory/mechanosensory inputs converge and regulate motor outputs. The circuits that integrate multisensory information are poorly understood. In an effort to identify the basic components of a multisensory integrative circuit, we determined the projections of the mechanosensory input from the periphery to the optic tectum and compared their distribution to the retinotectal inputs in Xenopus laevis tadpoles using dye‐labeling methods. The peripheral ganglia of the lateral line system project to the ipsilateral hindbrain and the axons representing mechanosensory inputs along the anterior/posterior body axis are mapped along the ventrodorsal axis in the axon tract in the dorsal column of the hindbrain. Hindbrain neurons project axons to the contralateral optic tectum. The neurons from anterior and posterior hindbrain regions project axons to the dorsal and ventral tectum, respectively. While the retinotectal axons project to a superficial lamina in the tectal neuropil, the hindbrain axons project to a deep neuropil layer. Calcium imaging showed that multimodal inputs converge on tectal neurons. The layer‐specific projections of the hindbrain and retinal axons suggest a functional segregation of sensory inputs to proximal and distal tectal cell dendrites, respectively. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2009     

Neuropeptide Y innervation of amygdaloid and hypothalamic neurons that project to the dorsal vagal complex in rat

The anatomic relationship between neuropeptide Y (NPY)-immunoreactive terminals and forebrain areas in the rat that contain neurons that project to the dorsal vagal complex (DVC) was examined. To accomplish this, the combined retrograde fluorescent tracer and immunofluorescent technique was used. Neurons projecting to the DVC within the parvocellular divisions of the paraventricular nucleus of the hypothalamus were the most heavily innervated of the regions studied. A relatively high density of NPY-immunoreactive terminals innervated regions of the arcuate, dorsomedial and lateral hypothalamic areas that contained DVC efferent cells. Neurons that projected to the DVC within the medial division of the central nucleus of the amygdala and the lateral part of the bed nucleus of the stria terminalis were also innervated by NPY immunoreactive terminals. The results suggest an important role for NPY terminals in the modulation of neurons within the amygdala and hypothalamus that directly influence visceral-autonomic functions of the dorsal vagal complex. The source and possible function of NPY within these regions is discussed.     

Changes in electric activity of neurons of dorsal raphe nuclei in the development of generator of pathologically enhanced excitation in the nociceptive system

In the experiments on rats it was proved by the method of extracellular registration of impulse neuron activity of dorsal raphe nucleus, that the formation of generator of pathologically enhanced excitation (GPEE) in nociceptive structures of spinal brain underlying the pain syndrome of spinal origin, results in a change of electric neuron activity of dorsal raphe nucleus. These changes are manifested by growing number of background nucleus neurons, the increase of middle frequency of discharges, and assuming pack character of impulse activity. These changes are greater marked in a ventral nucleus part, than in a dorsal one, which is evident of the activation of this antinociceptive system structure. The changes of electric activity of dorsal raphe neurons are stable for a long time after GPEE is formed in nociceptive system, and participate in suppression of GPEE and corresponding pain syndrome.     

Demonstration of a different localization of perikarya immunoreactive to oxytocin and vasopressin in the cat hypothalamus

Using immunohistochemical techniques, we demonstrated oxytocin (OT) and vasopressin (AVP) neurons in the cat hypothalamus. The OT immunoreactive neurons were found mainly in the paraventricular nucleus, supraoptic nucleus and dorsal accessory group located lateral to the fornix. In addition to these hypothalamic structures, the AVP immunoreactive neurons were observed in the suprachiasmatic nucleus, ventral accessory group located in the retrochiasmatic area and lateral accessory group, dorsal to the supraoptic nucleus caudally, and ventral to the medial part of the internal capsule rostrally. We further demonstrated a different localization of the OT and AVP immunoreactive neurons in the paraventricular and supraoptic nuclei.     

Anatomy,neurophysiology and functional aspects of the nucleus isthmi in salamanders of the family Plethodontidae

Summary Tongue-projecting plethodontid salamanders have massive direct ipsilateral retinal afferents to the tectum opticum as well as a large and well developed nucleus isthmi. Retrograde staining revealed two subnuclei: A ventral one projecting to the contralateral tectal hemisphere and a dorsal one projecting back to the ipsilateral side. The isthmic nuclei show a retinotopic organization, which is in register with that of the tectum. Electrophysiological recordings from nucleus-isthmi neurons revealed response properties that are very similar to those found in tectal neurons. Thus, there is no substantial processing of tectal neural activity in the nucleus isthmi. Measurements of peak latencies after electrical and light stimulation suggest the continuous coexistence of 4 representations of the visual field in the tectum mediated by (1) the contralateral and (2) the ipsilateral direct retinal afferents, (3) the uncrossed and (4) the crossed isthmo-tectal projection. (1) and (2) originate at the same moment in the retina and arrive simultaneously in the tectum. It is assumed that in plethodontid salamanders with massive ipsilateral retino-tectal projections depth perception based on disparity cues is achieved by comparison of these images.Representations mediated by (3) and (4) arriving in the tectum at the same time as (1) and (2) originate 10–30 ms earlier in the retina. It is hypothesized that these time differences between (1)/(2) and (3)/(4) are used to calculate three-dimensional trajectories of fast-moving prey objects.Abbreviations EL edge length - FDA fluoresceine dextranamine - RDA tetramethylrhodamine dextranamine - RF receptive field     

The relation between soma position and fibre trajectory of neurons in the mesencephalic trigeminal nucleus of Xenopus laevis

In adult Xenopus laevis the mandibular and ophthalmic branches of the trigeminal nerve were backfilled with CoCl2 or cobaltous lysine and whole brains silver intensified to reveal neurons of the mesencephalic Vth nucleus (mes. V). The nucleus contains about 100 cells arranged in a band extending arch-like from the ventrolateral margin of the optic tectum to the midline. Many cells possess a small number of short dendritic processes that arborize in the tectal neuropil; in some cells one dendrite terminates within the ependyma or ventricle. A single axon arises from each cell and courses in layer 7 to the margin of the tectum. Axon collaterals arise close to the cell body to terminate principally within layer 6, but occasionally also in layers 8 and 9. Collaterals occurring more caudally terminate in layer 6. These findings suggest that mes. V cells acts as tectal interneurons as well as conveying somatosensory information to the tectum from the mouth region. In the dorsal roof of the tectum the trajectory of a fibre is related to the distance of the soma from the midline. Mes. V cells located at the lateral end of the nucleus possess axons that course initially in a mediolateral direction before turning along the ventrolateral margin of the tectum. Cells positioned close to the midline have axons that project rostrocaudally the entire length of the tectum. The axons of cells located at intermediate positions within the nucleus course at correspondingly oblique angles through the dorsal roof of the tectum. Thus in this area there is a more or less 90 degrees rang in the orientation of mes. V fibres to the longitudinal axis. It is proposed that this topographical relationship between soma position and axon trajectory arises through a developmental mechanism, in which mes. V fibres grow during larval life sequentially into the medial zone of tectal growth and become subsequently displaced rostrolaterally, owing to the further addition of tectal tissue medially, through an angle dependent upon the parent cell's date of birth.     

Neural mechanisms of sound localization in owls

Barn owls localize sound by using the interaural time difference of the horizontal plane and the interaural intensity difference for the vertical plane. The owl's auditory system possesses the two binaural cues in separate pathways in the brainstem. Owls use a process similar to cross-correlation to derive interaural time differences. Convergence of different frequency bands in the inferior colliculus solves the problems of phase-ambiguity which is inherent in cross-correlating periodic signals. The two pathways converge in the external nucleus of the inferior colliculus to give rise to neurons that are selective for combinations of the two cues. These neurons form a map of auditory space. The map projects to the optic tectum to form a bimodal map which, in turn, projects to a motor map for head turning. The visual system calibrates the auditory space map during ontogeny in which acoustic variables change. In addition to this tectal pathway, the forebrain can also control the sound-localizing behaviour.     

Localization of GRF-like immunoreactive neurons in the rat brain

The localization of human GRF1-44-immunoreactive neurons was studied in the rat brain. A dense accumulation of GRF-containing fibers was noted in the external layer of the median eminence. Cell bodies were observed in colchicine-treated rats. The most intensely fluorescent cluster of cells was contained in the arcuate nucleus. Other cells were seen on the base of the hypothalamus, within the median forebrain bundle, dorsal and ventral aspects of the ventromedial nucleus, zona incerta and dorsal part of the dorsomedial nucleus. These cells may influence the pulsatile release of pituitary growth hormone.     

Chemically defined collateral projections from the pons to the central nucleus of the amygdala and hypothalamic paraventricular nucleus in the rat

Triple fluorescence labelling was employed to reveal the distribution of chemically identified neurons within the pontine laterodorsal tegmental nucleus and dorsal raphe nucleus which supply branching collateral input to the central nucleus of the amygdala and hypothalamic paraventricular nucleus. The chemical identity of neurons in the laterodorsal tegmental nucleus was revealed by immunocytochemical detection of choline-acetyltransferase or substance P; in the dorsal raphe nucleus, the chemical content of the neurons was revealed with antibody recognizing serotonin. The projections were defined by injections of two retrograde tracers, rhodamine-and fluorescein-labelled latex microspheres, in the central nucleus of the amygdala and paraventricular nucleus, respectively. Neurons projecting to both the central nucleus of the amygdala and the paraventricular nucleus were distributed primarily within the caudal extensions of the laterodorsal tegmental nucleus and dorsal raphe nucleus. Approximately 11% and 7% of the labelled cells in the laterodorsal tegmental nucleus and dorsal raphe nucleus projected via branching collaterals to the paraventricular nucleus and central nucleus of the amygdala. About half of these neurons in the laterodorsal tegmental nucleus were cholinergic, and one-third were substance-P-ergic; in the dorsal raphe nucleus, approximately half of the neurons containing both retrograde tracers were serotonergic. These results indicate that pontine neurons may simultaneously transmit signals to the central nucleus of the amygdala and paraventricular nucleus and that several different neuroactive substances are found in the neurons participating in these pathways. This coordinated signalling may lead to synchronized responses of the central nucleus of the amygdala and paraventricular nucleus for the maintenance of homeostasis. Interactions between different neuroactive substances at the target site may serve to modulate the responses of individual neurons.     

Immunohistochemical absence of adrenergic neurons in the dorsal part of the solitary tract nucleus in sudden infant death

The immunohistochemical distribution of TH and PNMT containing neuronal elements was investigated utilizing peroxidase anti-peroxidase methods in newborn control and sudden infant death syndrome (SIDS) brainstems. The TH immunoreactive neurons, within the medulla oblongata, displayed a similar distribution in both control and SIDS tissue. However, PNMT immunoreactive neurons seen in the dorsal part of the nucleus of tractus solitarius in control tissue were not observed in SIDS tissue. This alteration of adrenergic neurons in the dorsal part of NTS (region reported to be implicated in the control of blood pressure and respiration) could explain the cardiorespiratory disorders in SIDS.     

Effect of electric stimulation of the somatosensory cortex and caudate nucleus on extinctive inhibition of a conditioned alimentary reflex to sound]

In experiments performed on 9 dogs with alimentary method, extinctive inhibition was deepened and its elaboration was aceelerated by electrical stimulation of somatosensory and motor cortical areas and ventral segment of the caudate nucleus head. The extinction of the conditioned reflex was slowed down by stimulation of the anterolateral gyrus and the central segment of the caudate nucleus head. General motor excitation of animals during stimulation of the dorsal zone of caudate nucleus head impaired the elaboration of extinctive inhibition.     

The interstitial system of the spinal trigeminal tract in the rat: anatomical evidence for morphological and functional heterogeneity

Utilizing cyto-, myelo-, and chemoarchitecture as well as connectional criteria, the present study reveals the interstitial system of the spinal trigeminal tract (InSy-SVT) in the rat to be composed of five morphologically and functionally distinct components that are distributed within spatially restricted regions of the lateral medulla. The first component is represented by scattered interstitial cells and neuropil, which extend laterally into SVT from the superficial laminae of the medullary dorsal horn (MDH). The second component, the dorsal paramarginal nucleus (PaMd), consists of a small group of marginal (lamina I)-like neurons and neuropil situated within the dorsolateral part of SVT at the rostral pole of MDH. The third component represents a trigeminal extension of the parvocellular reticular formation (V-Rpc) into the ventromedial aspect of SVT at levels extending from rostral MDH to the caudal part of trigeminal nucleus interpolaris (Vi). The fourth component, the paratrigeminal nucleus (PaV), consists of a large accumulation of neurons and neuropil situated within the dorsal part of SVT throughout the caudal half of Vi. The fifth component is the insular trigeminal-cuneatus lateralis nucleus (iV-Cul), which is a discontinuous collection of neurons and neuropil interspersed among fibers of SVT as well as wedged between it and the spinocerebellar tract. Thalamic projection neurons are located in PaMd and V-Rpc, whereas cerebellar projecting neurons are confined to iV-Cul.