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Results for “Neuronal Connectivity”

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At least 163 records · Page 9Linked to original sources
PubMed1980

Peptide-containing neurones connect the two ganglionated plexuses of the enteric nervous system.

The enteric nervous system (ENS) of the mammalian gut consists principally of two ganglionated plexuses, the myenteric and submucous, which are embedded in the gut wall. Little is known about the anatomical and functional connections between the two plexuses and further clarification of their relationship is of central importance for the understanding of the ENS. In the present study we have approached this problem in a new way, using methods we have previously developed for maintaining the myenteric and submucous plexuses separately in vitro for several weeks. In an immunohistochemical study of these preparations and also of sections from normal and extrinsically denervated gut wall, we have found evidence for reciprocal projections between the myenteric and submucous plexuses, by nerve fibres containing two putative neurotransmitters, vasoactive intestinal polypeptide (VIP) and substance P (ref. 5) (see Fig. 1). Our observations were supported by radioimmunoassay of tissue extracts. These results suggest that one of the roles of these peptides in the gut is to coordinate the function of the two enteric plexuses.

Animals↗
PubMed1973

Structure and development of neuronal connections in isogenic organisms: cellular interactions in the development of the optic lamina of Daphnia.

Some details of the growth and initial cellular interactions of optic nerve axons were examined in a parthenogenetic clone of Daphnia magna. Results are summarized as follows: (i) the final structure of the optic lamina is dependent upon interactions between growing optic nerve fibers and optic lamina neuroblasts closest to the midplane of the animal, which trigger the morphological differentiation of the neuroblasts; the specificity of connections is achieved by well-defined sequences of cell migration in the ganglion; (ii) only one of the eight optic nerve axons growing back from each ommatidium in the eye possesses a structure similar to the growth cones seen on termini of nerve fibers growing in vitro; and (iii) undifferentiated neuroblasts in the ganglion react to surface contact by this "lead axon" by enveloping the axon in a glial-like relationship.

Axons↗
PubMed1989

Reorganization of neuronal connections following CNS trauma: principles and experimental paradigms.

The present review summarizes how the nervous system responds to trauma. The goal is to provide an introduction to the problems, techniques, experimental paradigms, current issues, and future promise. The review is especially designed for basic scientists and clinicians who are not currently involved in research on CNS reorganization, and for students just entering the field. The review characterizes the secondary degenerative events that occur after trauma, and the types of growth that commonly occur. A standard terminology is set forth with criteria for differentiating between related phenomena. Experimental methods are described that can be used documenting reorganization of circuitry. The principles that determine whether a given process will or will not occur are summarized, and some of the factors that may regulate the nature and extent of growth are considered. Research strategies are outlined that have been used to evaluate whether reorganization of circuitry is functionally significant. Finally, future directions in research and clinical application are discussed, focusing especially on the efforts to facilitate regeneration, and the work on transplants of CNS tissue to facilitate growth of surviving connections, and to replace tissue destroyed by trauma.

Animals↗
PubMed1990

Tracing of Neuronal Connections in the Human Brain by Magnetic Resonance Imaging in vivo.

Axon degeneration after disruption of fibre tracts in the mammalian nervous system is accompanied by myelin breakdown which leads to changes in its magnetic resonance properties. In two patients with pure motor strokes due to small ischaemic lesions restricted to the internal capsule, magnetic resonance imaging disclosed a narrow band of pathological signal increase descending band-like into the brain stem and ascending to the precentral gyrus, which corresponded to the well-known path of the pyramidal tract. The findings suggest that in man anterograde and possibly retrograde fibre degeneration can be traced in vivo by conventional magnetic resonance imaging techniques. Critical conditions are the presence of small, strategically located lesions, appropriate choice of imaging plane, and the interval between time of lesion and of imaging. This demonstration may open a new era for functional neuroanatomy of man.

Journal Article↗
PubMed2001

Susceptibility to kindling and neuronal connections of the anterior claustrum.

The claustrum has been implicated in the kindling of generalized seizures from limbic sites. We examined the susceptibility of the anterior claustrum itself to kindling and correlated this with an anatomical investigation of its afferent and efferent connections. Electrical stimulation of the anterior claustrum resulted in a pattern of rapid kindling with two distinct phases. Early kindling involved extremely rapid progression to bilaterally generalized seizures of short duration. With repeated daily kindling stimulations, early-phase generalized seizures abruptly became more elaborate and prolonged, resembling limbic-type seizures as triggered from the amygdala. We suggest that the rapid rate of kindling from the anterior claustrum is an indication that the claustrum is functionally close to the mechanisms of seizure generalization. In support of our hypothesis, we found significant afferent, efferent, and often reciprocal connections between the anterior claustrum and areas that have been implicated in the generation of generalized seizures, including frontal and motor cortex, limbic cortex, amygdala, and endopiriform nucleus. Additional connections were found with various other structures, including olfactory areas, nucleus accumbens, midline thalamus, and brainstem nuclei including the substantia nigra and the dorsal raphe nucleus. The anatomical connections of the anterior claustrum are consistent with its very high susceptibility to kindling and support the view that the claustrum is part of a forebrain network of structures participating in the generalization of seizures.

Afferent Pathways↗
PubMed1986

A role for action-potential activity in the development of neuronal connections in the kitten retinogeniculate pathway.

The role of action potentials in the development of proper synaptic connections in the mammalian CNS was studied in the kitten retinogeniculate pathway. Our basic finding is that there is improper segregation of retinal inputs onto LGN cells after prolonged retinal action-potential blockade. Retinal ganglion cell firing was silenced from birth by repeated monocular injections of TTX. The resulting ganglion cell connections in the LGN were studied electrophysiologically after the action-potential blockade was ended. Most cells in the deprived LGN layers received excitatory input from both ON-center and OFF-center type ganglion cells, whereas LGN cells normally receive inputs only from ON-center or OFF-center ganglion cells, but not from both types. Improper segregation of ON and OFF inputs has never been reported after other types of visual deprivation that do not block ganglion cell activity. Control experiments showed that receptive fields in the nondeprived LGN layers were normal, that ganglion cell responses remained normal, and that there was no obvious ganglion cell loss. We also showed that individual LGN cells with ON and OFF excitatory inputs were not present in normal neonatal kittens. Two other types of improper input segregation in response to action-potential blockade were also found in the deprived LGN layers. (1) A greater than normal number of LGN cells received both X- and Y-type ganglion cell input. (2) Almost half of the cells at LGN layer borders were excited binocularly. Recovery of LGN normality was rapid and complete after blockade that lasted for only 3 weeks from birth, but little recovery was seen after about 11 weeks of blockade. The susceptibility to action-potential blockade decreased during the first 3 postnatal weeks. These findings may result from axon-terminal sprouting or from the failure of axon terminals to retract. The results are consistent with the idea that normally synchronous activity of neighboring ganglion cells of like center-type may be used in the refinement of retinogeniculate synaptic connections.

Action Potentials↗
PubMed1998

Development of walking, swimming and neuronal connections after complete spinal cord transection in the neonatal opossum, Monodelphis domestica.

Development of coordinated movements was quantitatively assessed in adult opossums (Monodelphis domestica) with thoracic spinal cords transected by (1) crushing 7-8 d after birth [postnatal days 7-8 (P7-P8)]; at 2-3 years of age, systematic behavioral tests (e.g., climbing, footprint analysis, and swimming) showed only minor differences between control (n = 5) and operated (n = 10) animals; and (2) cutting on P4-P6; at 1 month these opossums exhibited coordinated walking movements but were unable to right themselves from a supine position, unlike controls (n = 6). When tested at 2 or 6 months, they could right themselves and showed remarkable coordination, albeit with more differences from controls than after a crush. No animals with spinal cords that were crushed at P14-18 survived because of cannibalism by the mother. Morphological studies (n = 10) 3 months-3 years after crush at 1 week showed restoration of structural continuity and normal appearance at the lesion site. Animals with cut rather than crushed cords showed continuity but greater morphological deficits. That lesions were complete was demonstrated by examining morphology and nerve impulse conduction immediately after crushing or cutting the spinal cord in controls. After lumbar spinal cord injection of 10 kDa dextran amine, retrogradely labeled cells were found rostral to the lesion in hindbrain and midbrain nuclei. Conduction was restored across the site of the lesion. Thus complete spinal cord transection in neonatal Monodelphis was followed by development of coordinated movements and repair of the spinal cord, a process that included development of functional connections by axons that crossed the lesion.

Animals↗