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Results for “Neuronal Connectivity”

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PubMed1984

The intercollicular region in the cat: a possible relay in the parallel somatosensory pathways from the dorsal column nuclei to the posterior complex of the thalamus.

Neuronal connections of the intercollicular region were studied in the cat by the anterograde and retrograde WGA-HRP and HRP methods. The results indicate that some neurons in the intercollicular region, which comprises the intercollicular nucleus, external and pericentral nuclei of the inferior colliculus, and nucleus of the brachium of the inferior colliculus, receive afferent fibers from the dorsal column nuclei, bilaterally with a contralateral dominance, and send their axons to the lateral division of the posterior complex of the thalamus, bilaterally with an ipsilateral predominance.

Afferent Pathways↗
PubMed1987

The neuronal growth-associated protein GAP-43 (B-50, F1): neuronal specificity, developmental regulation and regional distribution of the human and rat mRNAs.

The protein that has been designated as GAP-43, B-50, F1 or pp46 is associated with the growth and modulation of neuronal connections. cDNA clones for the rat and human genes were isolated and used to demonstrate that the messenger RNA for the protein is expressed only in neurons, that its overall level is highest in the developing brain, and that in the adult human brain levels of the mRNA are highest in the associative neocortex.

Animals↗
PubMed2005

Ral GTPases regulate neurite branching through GAP-43 and the exocyst complex.

Neurite branching is essential for the establishment of appropriate neuronal connections during development and regeneration. We identify the small GTPase Ral as a mediator of neurite branching. Active Ral promotes neurite branching in cortical and sympathetic neurons, whereas Ral inhibition decreases laminin-induced branching. In addition, depletion of endogenous Ral by RNA interference decreases branching in cortical neurons. The two Ral isoforms, RalA and -B, promote branching through distinct pathways, involving the exocyst complex and phospholipase D, respectively. Finally, Ral-dependent branching is mediated by protein kinase C-dependent phosphorylation of 43-kD growth-associated protein, a crucial molecule involved in pathfinding, plasticity, and regeneration. These findings highlight an important role for Ral in the regulation of neuronal morphology.

Actins↗
PubMed2000

[Application of electrophysiological methods in vivo to study circadian clock mechanisms in mammals].

The suprachiasmatic nuclei (SCN) of the hypothalamus and the intergeniculate leaflet (IGL) of the thalamic lateral geniculate complex are two main oscillators for circadian timing system. A lot of anatomical evidences indicated a strong neuronal connections between SCN and IGL. Relatively less, however, is know about the electrophysiology and functional interactions between SCN and IGL. The spontaneous firing rate of SCN neurons exhibits a remarkable circadian rhythm with a higher activity in the day and a lower at the night both in vivo and in vitro preparations. However, these rhythms my represent only clock output rather then the intrinsic clock mechanism. Last data described for the first time ultradian rhythmic neuronal oscillation recorded in vivo in the rat SCN and IGL. These isoperiodic phasic discharge probably constitute a basis necessary to generate circadian rhythms in mammals.

Animals↗
PubMed1998

Localized sources of neurotrophins initiate axon collateral sprouting.

The sprouting of axon collateral branches is important in the establishment and refinement of neuronal connections during both development and regeneration. Collateral branches are initiated by the appearance of localized filopodial activity along quiescent axonal shafts. We report here that sensory neuron axonal shafts rapidly sprout filopodia at sites of contact with nerve growth factor-coated polystyrene beads. Some sprouts can extend up to at least 60 micro(m) through multiple bead contacts. Axonal filopodial sprouts often contained microtubules and exhibited a debundling of axonal microtubules at the site of bead-axon contact. Cytochalasin treatment abolished the filopodial sprouting, but not the accumulation of actin filaments at sites of bead-axon contact. The axonal sprouting response is mediated by the trkA receptor and likely acts through a phosphoinositide-3 kinase-dependent pathway, in a manner independent of intracellular Ca2+ fluctuations. These findings implicate neurotrophins as local cues that directly stimulate the formation of collateral axon branches.

Actins↗
PubMed1996

Long-term potentiation and long-term depression of horizontal connections in rat motor cortex.

This paper reviews studies that investigate conditions resulting in long-lasting modifications of synaptic efficacy in horizontal connections within layers II/III of adult rat motor cortex using the in vitro slice preparation. Long-term potentiation (LTP) was induced by high frequency theta burst stimulation (TBS) when local synaptic inhibition was transiently suppressed by bicuculline methiodide application at the recording site immediately prior to TBS of the horizontal pathway. Without bicuculline, TBS failed to produce LTP. LTP could also be induced without Bic application by conjoint TBS of horizontal and vertical (ascending) inputs. By contrast, long-term depression (LTD) of horizontal transmission was induced by 10 min of 2 Hz stimulation. Depressed horizontal connections nevertheless retained the capability for synaptic strength increases. These studies indicate that synaptic modification across horizontally connected neurones is regulated both by the arrangement of their intrinsic circuits and by the availability of mechanisms for modification at individual synapses. Activity dependent forms of synaptic plasticity operating within horizontal connections may form a spatial substrate and mechanism for experience-dependent regulation of cortical representations.

Animals↗
PubMed1991

Efferent projections from the lateral geniculate nucleus to the pineal complex of the Mongolian gerbil (Meriones unguiculatus).

The intergeniculate leaflet of the lateral geniculate nucleus is considered to modulate circadian activity rhythms probably mediated by a direct neuronal connection to the suprachiasmatic nucleus. The present study in the gerbil demonstrates, by anterograde tracing with Phaseolus vulgaris-leucoaglutinin (PHA-L), the existence of an additional neuronal projection from a subportion of the lateral geniculate nucleus, involving the intergeniculate leaflet, directly to the pineal gland. PHA-L-immunoreactive nerve fibers originating from perikarya at the injection site were located under the optic tract projecting towards the midsagittal plane. Delicate PHA-L-immunoreactive nerve fibers were observed in the posterior paraventricular thalamic nucleus, precommissural nucleus, olivary pretectal nucleus, anterior and posterior pretectal nuclei, and posterior commissure. Single fibers could be followed from the caudal part of the medial habenular nucleus and the pretectal area into the rostral part of the deep pineal gland. Other fibers continued through the posterior commissure into the contralateral hemisphere to terminate in the same structures as on the ipsilateral side. From the posterior commissure, small bundles of thick fibers entered the deep pineal gland where they arborized among the endocrine cells. A few nerve fibers were observed in the habenular commissure and the pineal stalk, but no fibers were identified in the superficial pineal. This direct geniculo-pineal connection suggests that the pineal gland is directly influenced by the optic system.

Animals↗
PubMed1997

Reestablishment of the olivocerebellar projection map by compensatory transcommissural reinnervation following unilateral transection of the inferior cerebellar peduncle in the newborn rat.

It is unclear whether reparative processes in the injured mammalian brain are able to restore the topographic organisation of neuronal connections. To address this question, we have investigated the plasticity of the olivocerebellar system. This pathway has a precise topographic arrangement, in which subsets of inferior olivary neurons project to parasagittally oriented Purkinje cell compartments. Following unilateral transection of the inferior cerebellar peduncle in newborn rats, axons from the contralateral projection cross the cerebellar midline and reinnervate the deafferented hemicerebellum. By this experimental approach, we first analysed the behaviour of calcitonin gene-related peptide (CGRP)-immunoreactive climbing fibres. This marker is transiently expressed by a subset of developing inferior olivary axons, which terminate in the cerebellar cortex into several parasagittal strips. We show that transcommissural axons reestablish the original pattern of climbing fibre bands within a few days after lesion. Then, in adult animals injured at birth, we assessed whether the newly formed climbing fibre bands align with zebrin II+/- Purkinje cell compartments, as in normal conditions. The newly formed projection is organised in parasagittally oriented strips which mirror the distribution of their counterparts on the intact side and are precisely aligned to the heterogeneous Purkinje cell compartments. In addition, the patchy distribution of olivo-nuclear fibres suggests that specific reinnervation is also achieved in the deep nuclei. Thus, transcommissural olivocerebellar reinnervation is not random, but it is regulated by selective interactions between distinct subsets of olivocerebellar axons and target neurons aimed at reestablishing the correct projection map.

Animals↗
PubMed1980

The laminar organization of dorsal horn cells responding to peripheral C fibre stimulation.

Cat dorsal horn was searched for all detectable units that responded to peripheral C fibre input. Fifty-seven such units were examined in detail. They were located in two main areas. One group was in the superficial laminae 1, 2, and possibly dorsal 3 (n = 29), and the other group was much deeper in laminae 5 and 6 (n = 24). Only four units were situated in the region of lamina 4. Differences were found in the responses to C fibre stimulation of these two groups, both in the optimum stimulus and in the timing of responses to repeated stimulation. Superficial units often did not respond to C fibre stimulation unless a train of two or more stimuli (10 ms apart) were applied, but when responses did occur they were usually very even and regular, with precise onset latencies on repeated stimulation. Deep units tended to need only one peripheral C fibre stimulus for excitation, but the responses were irregular with latencies fluctuating with each stimulus. Some superficial and deep units showed a steady increase in latency of the late C response on repeated stimulation. Increases of up to 80 ms after 30 s of stimulation at 1 Hz were observed. The results are discussed in terms of the neuronal connections in the dorsal horn.

Animals↗
PubMed2005

Thinking about visual behavior; learning about photoreceptor function.

Visual behavioral assays in Drosophila melanogaster were initially developed to explore the genetic control of behavior, but have a rich history of providing conceptual openings into diverse questions in cell and developmental biology. Here, we briefly summarize the early efforts to employ three of these behaviors: phototaxis, the UV-visible light choice, and the optomotor response. We then discuss how each of these assays has expanded our understanding of neuronal connection specificity and synaptic function. All of these studies have contributed to the development of sophisticated tools for manipulating gene expression, assessing cell fate specification, and visualizing neuronal development. With these tools in hand, the field is now poised to return to the original goal of understanding visual behavior using genetic approaches.

Animals↗
PubMed2000

Combining loose cell-attached stimulation and recording.

Many synaptic-physiology experiments require selective stimulation of presynaptic neurones. No single method for achieving this is entirely satisfactory. Presynaptic whole-cell or microelectrode recordings offer outstanding control, but establishing such recordings of synaptically-connected neurones can be very time consuming. Minimal stimulation provides too little information regarding the condition and excitation of the presynaptic neurone(s). In the loose cell-attached configuration, it is possible both to stimulate individual cells and to record their action potentials, but most commercially-available equipment will not enable combining stimulation and recording. We demonstrate simultaneous loose cell-attached stimulation and recording of action potentials using a specially-designed patch-clamp amplifier. Since no tight seal is required, the method permits electrode re-use, thus enabling rapid screening of presynaptic cells while stimulating them selectively.

Action Potentials↗
PubMed2005

Neuronal activity regulates viral replication of herpes simplex virus type 1 in the nervous system.

Herpes simplex virus types 1 and 2 (HSV-1, -2) infect and also establish latency in neurons. In the present study, the authors investigated the influence of neuronal activity on the replication of HSV-1. The results showed that the sodium channel blocker tetrodotoxin (TTX) and the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) could significantly increase viral replication in primary neuronal cultures, by two- to fourfold. In contrast, KCl reduced viral production by at least 80% in the same cultures. Inhibitors of GABA(A) receptors completely abolished the effects of GABA. Intravitreously injected TTX in a mouse corneal scarification model enhanced the viral titers > 10-fold in both the trigeminal ganglia and the brain. At 2 h post infection, both TTX and GABA significantly up-regulated the levels of transcription for the viral immediate early (IE) genes ICP0, ICP4, and ICP27, as revealed by real time PCR. These results indicate that the neuronal excitation status may dictate the efficiency of HSV-1 viral replication, probably by regulating the levels of viral IE gene expression. These are the first findings connecting neuronal activity to the molecular mechanisms of HSV replication in the nervous system, which may significantly influence our view of herpesvirus infection and latency.

Animals↗
PubMed2003

Risk of detrusor denervation in antireflux surgery demonstrated in a neurophysiological animal model.

PURPOSE: Earlier anatomical studies have shown a close connection between the ureterovesical junction and detrusor innervation. It prompted us to develop an animal model to demonstrate the risk of partial or complete impairment of this neuronal connection during antireflux surgery. MATERIALS AND METHODS: Six female Göttinger minipigs were anesthetized and laminectomized. After placement of the S3 sacral nerves into separate electrode compartments of a modified Brindley electrode the lower urinary tract was exposed by an abdominal midline incision. After bladder instillation with 150 ml NaCl 1 bilateral and 2 unilateral stimulations (left and right sides) were performed and intravesical pressure was recorded urodynamically. The left ureter was then prepared circularly in 3 steps 10, 5 and 1 cm, respectively, proximal to the ureterovesical junction. After each preparation step bilateral and unilateral stimulation was repeated. Results were recorded urodynamically and video documented. RESULTS: Bilateral stimulation before preparation of the left ureter led to a concentric detrusor contraction with an average maximum detrusor pressure of 51 cm H(2)O. Unilateral stimulation resulted in ipsilateralbound bladder tilting with an intravesical pressure of 18 and 19 cm H(2)O on the right and left sides, respectively. After preparation of the left ureter 10, 5 and 1 cm from the ureterovesical junction a maximum detrusor pressure of 17, 10 and 1 cm H(2)O was documented, respectively. While there was almost no stimulation response of the bladder after the last preparation step at 1 cm on the left ureter, the initial bladder pressure of 18 cm H(2)O could be reproduced under stimulation on the right side. CONCLUSIONS: Analogous to human cadaver studies, we were able to prove neurophysiologically strictly unilateral detrusor innervation, drawing from the pelvic plexus dorsomedial to the ureterovesical junction into the bladder. Preparation of this ureterovesical junction during antireflex surgery, coagulating measures in this area or the affixation of anchor sutures after a Vest suture involves the risk of unilateral or bilateral detrusor decentralization.

Animals↗
PubMed1998

Corelease of two fast neurotransmitters at a central synapse.

It is widely accepted that individual neurons in the central nervous system release only a single fast transmitter. The possibility of corelease of fast neurotransmitters was examined by making paired recordings from synaptically connected neurons in spinal cord slices. Unitary inhibitory postsynaptic currents generated at interneuron-motoneuron synapses consisted of a strychnine-sensitive, glycine receptor-mediated component and a bicuculline-sensitive, gamma-aminobutyric acid (GABA)A receptor-mediated component. These results indicate that spinal interneurons release both glycine and GABA to activate functionally distinct receptors in their postsynaptic target cells. A subset of miniature synaptic currents also showed both components, consistent with corelease from individual synaptic vesicles.

Animals↗
PubMed1990

Neural mechanisms of emesis.

Emesis is a reflex, developed to different degrees in different species, that allows an animal to rid itself of ingested toxins or poisons. The reflex can be elicited either by direct neuronal connections from visceral afferent fibers, especially those from the gastrointestinal tract, or from humoral factors. Emesis from humoral factors depends on the integrity of the area postrema; neurons in the area postrema have excitatory receptors for emetic agents. Emesis from gastrointestinal afferents does not depend on the area postrema, but probably the reflex is triggered by projections to some part of the nucleus tractus solitarius. As with a variety of other complex motor functions regulated by the brain stem, it is likely that the sequence of muscle excitation and inhibition is controlled by a central pattern generator located in the nucleus tractus solitarius, and that information from humoral factors via the area postrema and visceral afferents via the vagus nerve converge at this point. This central pattern generator, like those for motor functions such as swallowing, presumably projects to the various motor nuclei, perhaps through interneuronal pathways, to elicit the sequential excitation and inhibition that controls the reflex.

Animals↗
PubMed1998

[Effects of arginine-vasopressin on neuronal interaction from the area postrema to the nucleus tractus solitarii in rat brain slices].

The effects of vasopressin (AVP) on area postrema (AP) neurons and the neuronal connection between the AP and nucleus tractus solitarii (NTS) were investigated electrophysiologically in slices preparation of the medulla oblongata of rats. In the AP, 27.9% of 129 neurons were excited by AVP and 20.5% were inhibited. The excitation was blocked by a V1 receptor antagonist. Synaptic transmission of the AP to the NTS was mainly mediated by non-NMDA receptors. Local application of AVP to the AP activated the NTS neurons. This activation was blocked by an NMDA antagonist. These results suggest that the excitation originating in the AP is conveyed to the NTS via non-NMDA receptors and modified by NMDA receptor activation secondly. These processes may be important in regulation of the arterial baroreceptor reflex.

Animals↗
PubMed1997

Nerve growth factor modulates synaptic transmission between sympathetic neurons and cardiac myocytes.

Regulation of heart rate by the sympathetic nervous system involves the release of norepinephrine (NE) from nerve terminals onto heart tissue, resulting in an elevation in beat rate. Nerve growth factor (NGF) is a neurotrophin produced by the heart that supports the survival and differentiation of sympathetic neurons. Here we report that NGF also functions as a modulator of sympathetic synaptic transmission. We determined the effect of NGF on the strength of synaptic transmission in co-cultures of neonatal rat cardiac myocytes and sympathetic neurons from the superior cervical ganglion (SCG). Synaptic transmission was assayed functionally, as an increase in the beat rate of a cardiac myocyte during stimulation of a connected neuron. Application of NGF produced a pronounced, reversible enhancement of synaptic strength. We found that TrkA, the receptor tyrosine kinase that mediates many NGF responses, is expressed primarily by neurons in these cultures, suggesting a presynaptic mechanism for the effects of NGF. A presynaptic model is further supported by the finding that NGF did not alter the response of myocytes to application of NE. In addition to the acute modulatory effects of NGF, we found that the concentration of NGF in the growth medium affects the level of synaptic transmission in cultures of sympathetic neurons and cardiac myocytes. These results indicate that in addition to its role as a survival factor, NGF plays both acute and long-term roles in the regulation of developing sympathetic synapses in the cardiac system.

Animals↗
PubMed2005

Functions and mechanisms of retrograde neurotrophin signalling.

Neuronal connections are established and refined through a series of developmental programs that involve axon and dendrite specification, process growth, target innervation, cell death and synaptogenesis. Many of these developmental events are regulated by target-derived neurotrophins and their receptors, which signal retrogradely over long distances from distal-most axons to neuronal cell bodies. Recent work has established many of the cellular and molecular events that underlie retrograde signalling and the importance of these events for both development and maintenance of proper neural connectivity.

Animals↗