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PubMed2006

Organization of the coelomic lining and a juxtaposed nerve plexus in the suckered tube feet of Parastichopus californicus (Echinodermata: Holothuroida).

The coelomic lining of the water-vascular canal in a suckered tube foot from the sea cucumber, Parastichopus californicus, is a pseudostratified myoepithelium consisting of flagellated adluminal cells and myofilament-bearing retractor cells. The bodies of adluminal cells flank the water-vascular canal and send basal processes between the underlying retractor cells to confront the podial connective tissue. Retractor cells have a contractile apparatus of unregistered thick and thin myofilaments. The contractile apparatus is confined to the medullary sarcoplasm and oriented parallel to the primary axis of a tube foot. The bodies and processes of retractor cells intermingle with the basal processes of adluminal cells at the basal lamina of the coelomic lining. A ganglionated nerve plexus in the podial connective tissue approximates the basal lamina. Neuronal connectives link the ganglia to one another and to the nerve plexus in deep sectors of the podial epidermis. External laminae enveloping the ganglia and connectives in the podial connective tissue are continuous with the basal lamina of the epidermis. The adventitial nerve plexus, since it merges with the epidermal nerve plexus, is a component of the ectoneural division of the echinoderm nervous system.

Animals↗
PubMed1991

Interaction of myenteric neurons and extrinsic nerves in the intestinal inhibitory response induced by mesenteric nerve stimulation.

Effects of the mesenteric nerve stimulation (MNS) on the twitch contraction induced by field stimulation were investigated regarding the relationship between myenteric neurons and extrinsic cholinergic nerves in the guinea-pig mesenteric nerve-ileal preparation. The twitch contraction was inhibited after MNS. The inhibition of the twitch contraction after MNS was induced twice, just after MNS (1st inhibition) and 2-3 min later (2nd inhibition) (type I), or once, just after MNS (1st inhibition) (type II), in recovery course of twitch contraction for 6-8 min. The 1st inhibition was slightly decreased by guanethidine and hexamethonium. The inhibitory response (1st inhibition) in both types I and II was recovered to the control level by pretreatment with naloxone (recovered twitch contraction), but the late inhibitory response (2nd inhibition) was markedly observed after 2-3 min in types I and II. Either the 1st or the 2nd inhibition was not altered by capsaicin, desensitization to calcitonin gene-related polypeptide (CGRP), vasoactive intestinal polypeptide (VIP), somatostatin, or galanin. The recovered twitch contraction in types I and II was decreased by CGRP-desensitization, or capsaicin. These results suggest that the first inhibitory response was induced by enteric opioid neurons connected with extrinsic cholinergic nerves, but the 2nd inhibition was induced by unknown substances other than CGRP, VIP, somatostatin, and galanin. The twitch contraction may partly be induced by endogenous neurokinin-like substances. And, some CGRP containing neurons, which connect with extrinsic cholinergic nerves, probably activate the intrinsic excitatory neurons.

Animals↗
PubMed1996

Electron microscopic immunocytochemical evidence for the synaptic connections between tyrosine hydroxylase and substance P containing nerve elements in the coeliac ganglion of cat revealed by a double labelling technique.

In order to examine the morphological substrates for neuronal connections between neuronal elements of the coeliac-mesenteric ganglion containing immunoreactivity (IR) for tyrosine hydroxylase (TH) and substance P (SP), a double-immunostaining was performed. The first antigen to SP was labelled with gold-substituted silver-intensified peroxidase, which results in a granular gold deposit of high electron and light opacity. The second antigen was the TH labelled with peroxidase and a diaminobenzidine chromogen without silver-gold particles. About of 85% of the neurons contained TH immunoreactivity in the coeliac-mesenteric ganglia. The SP IR nerve fibres were mostly found around the principal ganglion cells throughout the ganglion. In most cases they made direct synaptic contact with TH positive nerve cells and dendrites. These SP-IR boutons were also found in synaptic contact with other non-labelled postsynaptic terminals and with the soma. SP-IR nerve terminals establish both symmetrical and asymmetrical synaptic contacts with TH-IR nerve elements. Some of the nerve cells which ware TH positive, were also labelled for SP. TH positive boutons were also observed in synaptic contact with other TH-IR perikarya and dendrites. Our results suggest that SP may play an important role for the integrative activities of the ganglion with regard to gastrointestinal functions.

Animals↗
PubMed1990

Relation Between Putative Transmitter Phenotypes and Connectivity of Subplate Neurons During Cerebral Cortical Development.

During development, the earliest generated neurons of the mammalian telencephalon reside in a region of the white matter, the subplate, just beneath the cortical plate. Neurons in the subplate are only transiently present in the telencephalon: shortly after birth in the cat the majority have disappeared. During their brief life, however, subplate neurons mature; they extend long-distance and local projections, and express immunoreactivity for GABA and several neuropeptides. In the present study we examined the relation between possible transmitter phenotypes of subplate neurons and their connectivity. To do so, we used a double-label technique in which immunohistochemistry for neuropeptide Y (NPY), somatostatin (SRIF) or calbindin (CaBP) was combined with retrograde tracing. Experiments were performed in neonatal cats and in ferret kits at equivalent postconceptional ages, times when subplate neurons are numerous. Subplate neurons immunoreactive for neuropeptides and CaBP could be double-labelled by an injection of retrograde tracer either into the cortical plate or the white matter, indicating that this particular subset of subplate neurons can make local circuit projections. In contrast, peptide or CaBP immunoreactive subplate neurons could never be retrogradely labelled from a tracer injection into the thalamus. Taken together, these observations indicate that subplate neurons immunoreactive for NPY, SRIF and CaBP are likely to be interneurons exclusively. On the other hand, subplate neurons with long-distance projections to the thalamus or the contralateral hemisphere could be labelled by the retrograde transport of d-[3H]aspartate, suggesting that at least some projection subplate neurons might use an excitatory amino acid as a neurotransmitter. These results indicate that there is a defined relationship between the putative transmitter phenotypes of subplate neurons and their patterns of projection. Interneurons of the subplate express peptidergic properties while projection neurons to the thalamus may use an excitatory amino acid. Thus, these basic organizational features of the transient subplate are reminiscent of those found in the adult cortical layers.

Journal Article↗
PubMedDate not supplied

Statistical analysis of the functional connections between the neurons of the visual and motor cortex in different forms of conditioned reflex behavior.

The organization of interneuronal cortical connections was studied in experiments on cats with the development of delayed alimentary instrumental reflexes in response to light. The dynamics of the intra- and interstructural neuronal network at the level of the cortical projection (visual and motor) zones of the cat brain in three forms of behavior was revealed through a cross correlation analysis: the realization of the CR, in the intersignal period with the presence and absence of instrumental movements. The predominance of "informational" or "motivational" neuronal connections was observed depending upon the forms of the behavior.

Animals↗
PubMed1994

Regulation of the POU domain gene SCIP during cerebral cortical development.

The mammalian cerebral cortex is patterned into layers of neurons that share characteristic morphologies, physiological properties, and axonal connections. Neurons in the various layers are thought to acquire their lamina-specific identities shortly before the time of their final mitosis in the cortical ventricular zone. In order to investigate the molecular basis of laminar patterning in the CNS, we have performed in situ hybridization studies of the POU homeodomain gene SCIP (also known as Tst-1 or Oct-6), which is expressed in proliferating Schwann cells in the PNS and O2A progenitor cells in the developing CNS. In the CNS of adult rats, SCIP is expressed at high levels in the cerebral cortex, specifically in layer 5 pyramidal neurons that form subcortical axonal connections. SCIP is both temporally and spatially regulated during cortical development. Its initial expression in the intermediate zone and cortical plate is correlated with the early migration and differentiation of layer 5 neurons. SCIP hybridization was not, however, observed within the ventricular zone during the period of neurogenesis. SCIP is also expressed at high levels in the neurons of cortical layer 2/3, during their migration and differentiation within the cortical plate. This expression in the upper layers is apparently downregulated during postnatal periods, with the adult pattern apparent by postnatal day 30 (P30). POU domain genes are thought to play a role in cell lineage and cell fate decisions in several systems; thus, SCIP may serve a function in generating discrete laminar phenotypes in the developing cerebral cortex. In addition, since SCIP is a putative repressor of myelin gene expression, our results suggest that SCIP plays a role in regulating transcription in differentiated CNS neurons as well as in proliferating glial precursors.

Aging↗
PubMed1997

Neurotrophic factors are required by mature sympathetic neurons for survival, transmission and connectivity.

1. Two neuronal growth factors, nerve growth factor (NGF) and neurotrophin 3 (NT3), have been studied for their action on the developing and mature sympathetic nervous system. 2. Antibodies to each factor have proved useful as reagents for the detection and quantification of NGF and NT3. They have also proved valuable in uncovering the functional roles of each factor by their ability to neutralize the endogenous molecules. 3. Nerve growth factor acts on postnatal neurons to control neurotransmission, connectivity and survival. Like NGF, NT3 is synthesized by effector tissues and is retrogradely transported by post-ganglionic neurons to prevent cell death. However, the two factors have been shown to have quite distinct functions in mature neurons, indicating the existence of different signalling pathways. This differential action extends to secondary influences on satellite glia. 4. Pathological consequences result from excessive growth factor synthesis leading, in the hypertensive rat, to hyperinnervation and elevated blood pressure. Satellite glial cell synthesis of the factors and their receptors following peripheral nerve damage appears to be responsible for the establishment of inappropriate neuronal connections between sympathetic nerve terminals and sensory somata. 5. It is concluded that these potent factors control, by both coincident and independent mechanisms, sympathetic neuronal function throughout the life of the animal.

Animals↗
PubMed1986

Cellular basis of neuronal synchrony in epilepsy.

Synchronized discharge of populations of cortical neurons are often observed to underly both the interictal spikes and tonic seizures generated in experimental epilepsy studies. Recently it has been shown that similar synchronized discharges occur in cortical brain slices treated with convulsants such as penicillin, picrotoxin, or bicuculline. The favorable experimental conditions offered by the in vitro preparation have facilitated a detailed examination on the cellular basis for the generation of the epileptic neuronal synchrony. In this chapter we shall review some experimental observations on the neuronal synchronization and describe a mechanism for its generation based on the computer simulation approach. Three factors are considered to be essential for epileptic synchronization observation in vitro. First, cortical neurons may intrinsically generate bursts of action potentials. Second, recurrent excitatory connections exist that are sufficiently powerful that bursting activity may spread between synaptically connected neurons. Third, inhibition within the local neuronal circuit must be adequately attenuated to allow excitation to spread through the recurrent excitatory connections. Computer simulation studies have been based on these assumptions, using neuronal networks where each cell is connected to more than one postsynaptic neuron. Bursting initiated in one cell excites all its follower cells, and the sequential recruitment of an increasing number of cells eventually leads to a simultaneous discharge of the population. A number of recent experimental observations lend credence to the proposed scheme for neuronal synchrony. Simultaneous paired intracellular recordings provided direct evidence that a burst of action potentials in a presynaptic cell can activate action potentials postsynaptically. Furthermore, it is shown that the rhythm of spontaneous discharge in a neuronal population can be influenced by the activity of one neuron within the population.

Animals↗
PubMed2002

Protein phosphorylation networks in motor neuron death.

The disorder amyotrophic lateral sclerosis (ALS) is characterized by the death of specific groups of neurons, especially motor neurons, which innervate skeletal muscle, and neurons connecting the cerebral cortex with motor neurons, such as corticospinal tract neurons. There have been numerous attempts to elucidate why there is selective involvement of motor neurons in ALS. Recent observations have demonstrated altered activities and protein levels of diverse kinases in the brain and spinal cord of transgenic mice that overexpress a mutant superoxide dismutase (mSOD) gene that is found in patients with the familial form of ALS, as well as in patients who have died with ALS. These results suggest that the alteration of protein phosphorylation may be involved in the pathogenesis of ALS. The changes in protein kinase and phosphatase expression and activity can affect the activation of important neuronal neurotransmitter receptors such as NMDA receptors or other signaling proteins and can trigger, or modify, the process producing neuronal loss in ALS. These various kinases, phosphatases and signaling proteins are involved in many signaling pathways; however, they have close interactions with each other. Therefore, an understanding of the role of protein kinases and protein phosphatases and the molecular organization of protein phosphorylation networks are useful to determine the mechanisms of selective motor neuron death.

Amyotrophic Lateral Sclerosis↗
PubMed2000

Prenatal alcohol exposure decreases the number of nitric oxide synthase positive neurons in rat superior colliculus and periaqueductal gray.

Because nitric oxide (NO) is involved in the development and refinement of axonal projections and synapses, it is of interest to know if developmental alcohol exposures affect NO producing neurons. Pregnant rats were fed artificial liquid diet throughout gestation as the only fluid or caloric source. The diet for experimental dams contained ethanol (6.7% v/v) while the pair-fed diet for control dams contained isocaloric maltose-dextrin instead of ethanol. This ethanol diet regime is known to produce peak blood alcohol concentrations of approximately 140 mg%. Cells stained histochemically for nitric oxide synthase (NOS) were counted at postnatal day 15 (P15) and 35 (P35) in cross-sections of the stratum griseum superficiale (SGS) of the superior colliculus (SC) and in the dorsolateral column of the periaqueductal gray (dlPAG). Compared to control tissues, alcohol caused the following effects: In the SC, the areal density of NOS+ neurons was decreased 24% at P15 but a similar decrease in means at P35 was not statistically significant (P=0.10); soma size was unaffected at either P15 or P35. In the dlPAG, both the areal density and the total number of NOS+ neurons per section were unaffected at P15 but were decreased at P35 (33% and 37% decreases); soma size was unaffected at either P15 or P35. The decrease in NOS+ neurons in the SC at P15 could be expected to have a negative impact on the refinement of neuronal connections while the decreases in NOS+ neurons in the dlPAG at P35 likely represent more permanent effects that could alter the function of that nucleus.

Aging↗
PubMed2003

From fragile X mental retardation protein to Rac1 GTPase: new insights from Fly CYFIP.

Mutations in either the Rho GTPase pathway or in the fragile X mental retardation (FMR1) gene produce neuronal connectivity defects. In this issue of Neuron, Schenck et al. use biochemical and genetic approaches in Drosophila to examine the interactions between dFMR1 and dRac1 and provide evidence that the cytoplasmic FMRP interacting protein (CYFIP) links Rac-dependent cytoskeleton remodeling and dFMR1-dependent control of translation in a unique pathway to modulate neuronal morphogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Odors regulate Arc expression in neuronal ensembles engaged in odor processing.

Synaptic activity is critical to developmental and plastic processes that produce long-term changes in neuronal connectivity and function. Genes expressed by neurons in an activity-dependent fashion are of particular interest since the proteins they encode may mediate neuronal plasticity. One such gene encodes the activity-regulated cytoskeleton-associated protein, Arc. The present study evaluated the effects of odor stimulation on Arc expression in rat olfactory bulb. Arc mRNA was rapidly increased in functionally linked cohorts of neurons topographically activated by odor stimuli. These included neurons surrounding individual glomeruli, mitral cells and transynaptically activated granule cells. Dendritic Arc immunoreactivity was also increased in odor-activated glomeruli. Our results suggest that odor regulation of Arc expression may contribute to activity-dependent structural changes associated with olfactory experience.

Animals↗
PubMed1999

Regulation of maternal behavior and offspring growth by paternally expressed Peg3.

Imprinted genes display parent-of-origin-dependent monoallelic expression that apparently regulates complex mammalian traits, including growth and behavior. The Peg3 gene is expressed in embryos and the adult brain from the paternal allele only. A mutation in the Peg3 gene resulted in growth retardation, as well as a striking impairment of maternal behavior that frequently resulted in death of the offspring. This result may be partly due to defective neuronal connectivity, as well as reduced oxytocin neurons in the hypothalamus, because mutant mothers were deficient in milk ejection. This study provides further insights on the evolution of epigenetic regulation of imprinted gene dosage in modulating mammalian growth and behavior.

Animals↗
PubMed1987

Target neurons of floccular caudal zone inhibition in Y-group nucleus of vestibular nuclear complex.

Extracellular unit spikes were recorded in and around the Y-group nucleus in the anesthetized cat. Target (T) neurons of floccular caudal zone inhibition were identified by observing cessation of their spontaneous discharges following stimulation of the floccular caudal zone. The axonal trajectories of the T neurons to the rostral brain stem were studied by observing the antidromic responses of single neurons during systematic tracking with a stimulating microelectrode in the brain stem. The axons of the T neurons pass through a region closely ventral to the lateral part of the brachium conjunctivum (BC), continue rostrally in a region between the BC and the lateral lemniscus, arch medially around the rostral part of the nucleus reticularis tegmenti pontis, cross the midline, continue to the contralateral side by about 1.5 mm lateral from the midline, arch rostrally, run in the central tegmental field on the contralateral side, arch dorsomedially around the caudal pole of the red nucleus, and enter the contralateral oculomotor nucleus (OMN) from the ventrolateral side. In the caudal half of the contralateral OMN, the axons of the T neurons branch out and terminate. The T neurons were exclusively located in the dorsal subdivision of the Y-group nucleus (DY), whereas some were in the medial part of the subnucleus lateralis parvocellularis (SLP, Ref. 12) of the lateral cerebellar nucleus. T neurons were not found in the ventral subdivision of the Y-group nucleus (VY). Differences in neuronal connections between the DY and VY neurons were investigated by observing responses of single neurons to stimulation of the contralateral OMN, the ipsilateral floccular caudal zone, the ipsilateral eighth nerve (i8N), and the contralateral eighth nerve (c8N). Most neurons in the DY and the adjacent medial part of the SLP, receiving inhibitory inputs from the ipsilateral flocculus (exclusively from the caudal zone), project to the contralateral OMN, and about one-half of these neurons receive polysynaptic inputs from the i8N and the c8N. On the other hand, most neurons in the VY receive monosynaptic inputs from the i8N, and some of these neurons project to the ipsilateral flocculus. The neuronal tract via the ventral part of the pontine tegmentum demonstrated in the present experiments is distinct from the classically established vestibulooculomotor tracts via the BC, the medial longitudinal fasciculus, or the ascending tract of Deiters. We call this tract the 'crossing ventral tegmental tract'. Previously, we reported that electrical stimulation of the caudal zone elicited conjugate downward eye movement.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

The anterior hypothalamus provides stimulatory input to tuberoinfundibular dopamine neurons which is not mediated by prolactin.

Complete or retrochiasmatic deafferentations of the mediobasal hypothalamus were made in female rats 7 days prior to experimentation in order to determine the role played by putative afferent neuronal connections (1) in maintaining the basal neuronal activity of tuberoinfundibular dopaminergic (TIDA) neurons, and (2) in the stimulatory actions of prolactin on these neurons. The neuronal activity of TIDA neurons was estimated by measuring the rates of synthesis, turnover or metabolism of dopamine (DA) in the terminals of these neurons in the median eminence. Complete deafferentation of the mediobasal hypothalamus reduced the basal rate of DA synthesis, and retrochiasmatic deafferentation decreased the rates of synthesis, turnover and metabolism of DA in the median eminence. A knife cut 1 mm rostral to the retrochiasmatic cut failed to alter basal TIDA neuronal activity. These results suggest that afferent neuronal inputs originating in or coursing through the caudal portion of the anterior hypothalamus mediate a tonic stimulatory influence on TIDA neurons in the female rat. Intracerebroventricular administration of rat prolactin or systemic administration of haloperidol (which increases circulating levels of prolactin) increased DA synthesis in the median eminence of both sham-operated rats and retrochiasmatic-deafferentated rats. Thus, the stimulatory action of prolactin was not blocked by retrochiasmatic deafferentation. In addition, elimination of the basal stimulatory action of endogenous prolactin by pretreating animals with bromocriptine reduced the rate of DA synthesis in the median eminence of both sham- and retrochiasmatic-deafferentated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Molecular mechanisms mediating axon pathway formation.

During nervous system formation nerve cells extend axons in order to form precise patterns of neuronal connectivity. These connections are often established after the neuronal growth cones have pioneered or navigated through complex pathways to their target area both within the CNS and to and from the periphery. Recent studies have provided evidence that the process of specific pathway formation may rely on a number of molecular guidance mechanisms and cues such as selective adhesion, growth cone avoidance, surface gradients, guidepost cells, and chemotropism. Analysis of the molecular basis for these guidance mechanisms show that the molecules involved often belong to distinct multigene families and that they can provide both short- and long-range attractive as well as repulsive cues. Many of these molecules have a modular structure that is made up of different tandemly arranged domains that allow for multiple functional interactions with a range of other molecules. This allows the same molecule to be multifunctional, for example, by attracting certain neurons while repelling others. This review is an overview of the molecular structure, as it relates to function and mechanisms of action of some of the major gene families thought to be mediating specific axonal guidance and pathway formation.

Animals↗
PubMed1986

[Mechanisms of development of long-periodicity oscillations in activity in nerve nets. Stochastically uniform nerve nets].

The possibility of generation of long-term activity in the stochastic uniform networks consisting of neuron-like threshold elements was analyzed by the mathematical simulation model. It was shown that the long-term (hundreds of milliseconds) self-stopping activity in the networks with a positive feed-back between units can be generated. Termination of the activity was based on the following factors: 1) stochastic properties of network processes which determine the fluctuations of the activity level; 2) neuronal interaction leading either to synchronization of neuronal discharges and respectively to postactivation inhibitory processes, or to reconstruction of the microstructure of the neuronal network activity when weak-connected neurons are predominantly excited. Basing on the data obtained possible participation of the mechanism involved in formation of the long-term self-stopping activity of interneuronal networks of the spinal cord realizing different types of programmed rhythmical activity (generators) is discussed.

Computers↗
PubMed1989

Neuronal assemblies.

This paper examines the concept of neuronal assembly as it has appeared in selected portions of the literature. The context is experimental access to real neuronal assemblies in working brains, as made possible by recent technological progress. One current measure of assembly organization is based on correlation of firing among neurons; recent observations show that such correlations can vary rapidly. In this paper, we demonstrate that dynamic firing correlation can be caused either by dynamic changes in neuronal connection strengths or, alternatively, by the effects of an unobserved (large) pool of other neurons. The static connectivity within the pool appears to be important in determining these effects.

Animals↗