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At least 1,243 records · Page 69Linked to original sources
PubMed1986

Excitatory synaptic drive for swimming mediated by amino acid receptors in the lamprey.

In order to investigate the properties and pharmacology of the excitatory synaptic drive received by motoneurons during swimming in the lamprey, propriospinal excitatory interneurons were activated as a population by the regional application of N-methyl-D,L-aspartate (NMA) to either the 6-8 rostral-most or the 6-8 caudal-most segments of lengths of isolated spinal cord. This caused a rhythmic motor output to be generated in these regions. Synaptic potentials that were phase-locked to, and dependent on, the rhythmic motor activity of the segments exposed to the agonist could be recorded in motoneurons lying outside the activated regions. The synaptic drive to motoneurons located rostral or caudal to the activated regions was studied. Motoneurons received both descending and ascending synaptic input, which consisted of alternating excitatory and inhibitory phases. The inhibition could be reversed by chloride injection and blocked by strychnine, leaving an oscillating excitatory phase. The descending excitatory drive could extend 1-9 segments from the active region, while the ascending excitatory drive was recorded only in motoneurons that were 1-3 segments rostral to the active region. Both types of drive occurred in phase with the ipsilateral ventral root discharge: The peak depolarization of the descending drive occurred at the same point in the swimming cycle as that of the depolarizing phase seen during fictive swimming, while that of the ascending drive occurred significantly later. Both ascending and descending drives were partially reduced in amplitude by 2-amino-5-phosphonovaleric acid or Mg2+. The blocking action of Mg2+ was, in both cases, voltage dependent. Cis-2,3-piperidine dicarboxylic acid or kynurenic acid caused a much greater reduction in the amplitude of the oscillations. These results suggest that a major part of the excitatory drive for swimming in lamprey motoneurons is generated by populations of propriospinal interneurons with relatively long descending and/or short ascending axons, which fire rhythmically during swimming and release an amino acid transmitter that excites motoneurons through N-methyl-D-aspartate (NMDA) and non-NMDA receptors. This information will allow these important neurons to be identified in future experiments.

Afferent Pathways↗
PubMed1986

Connectional basis for frequency representation in the nuclei of the lateral lemniscus of the bat Eptesicus fuscus.

To study the role of the lateral lemniscus as a link in the ascending auditory pathway, injections of neuronal tracers were placed in the anteroventral cochlear nucleus (AVCN) and in the inferior colliculus of the bat Eptesicus fuscus. To correlate the anatomical results with tonotopic organization, the characteristic frequency of cells at each injection site was determined electrophysiologically. Pathways from AVCN diverge to 3 major targets in the lateral lemniscus, the intermediate nucleus and 2 divisions of the ventral nucleus (VNLL). Projections from these 3 nuclei then converge at the inferior colliculus. One cell group is particularly notable for its cytoarchitectural appearance. It is referred to here as the columnar area of VNLL because its cells are organized as a tightly packed matrix of columns and rows. The connections of the columnar area are organized in sheets that are precisely related to the tonotopic organization of both AVCN and the inferior colliculus. Sheets of cells in the dorsal part of the columnar area receive projections from low-frequency parts of AVCN and project to low-frequency parts of the inferior colliculus. These sheets of connections occupy successively more ventral locations as the tonotopic focus of the injection site increases in frequency. The entire range of frequencies audible to the bat is systematically represented along the dorsal-ventral dimension of the columnar area. Because each column is only 20-30 cells in height, frequency representation must be compressed in this dimension. Within the columnar area there is an overrepresentation of frequencies between 25 and 50 kHz, which corresponds roughly to the range of the FM echo-location call in Eptesicus. The connections of the other nuclei of the lateral lemniscus are not as precisely related to the tonotopic organization of the system as are those of the columnar area.

Afferent Pathways↗
PubMed1981

The laminar origin and distribution of the crossed tectoreticular pathways.

The superior colliculus is the source of a prominent descending pathway which crosses the midline in the mesencephalon and projects to the paramedian pontine reticular formation. The primary goal of the present study was to identify the cells in the superior colliculus of the grey squirrel which give rise to this pathway by using a combination of anterograde and retrograde tracing techniques. Results from the anterograde studies demonstrated the course and terminal distribution of this pathway and suggested that its laminar origin is the intermediate grey layer, stratum griseum intermediale. The retrograde studies were used to confirm the results of the anterograde experiments and to provide a more quantitative estimate of the laminar distribution of the cells which give rise to this pathway. In most cases, over 90% of the cells retrogradely labeled following injections of horseradish peroxidase along the course of this pathway were located in the intermediate grey lamina. This origin is in contrast to that of the ipsilateral tectoreticular pathway which originates primarily in stratum griseum profundum (Holcombe, V., and W. C. Hall (1981) Neuroscience 6: 255-260) and suggests that these two grey layers of the deep tectum are functionally distinct.

Afferent Pathways↗
PubMed1983

The laminar organization of the lateral geniculate body and the striate cortex in the squirrel monkey (Saimiri sciureus).

The organization of the projection from the lateral geniculate body to the striate cortex in the squirrel monkey has been re-examined using the anterograde and retrograde transport of horseradish peroxidase (HRP) and wheat germ agglutinin conjugated to HRP. The results confirm earlier findings that the projections of the magnocellular and parvocellular layers of the lateral geniculate body terminate in separate sublaminae of layer IV of striate cortex; a more superficial projection of the parvocellular layers to a narrow strip at the base of layer III (IVA in Brodmann's terminology) has also been confirmed. In addition to these well characterized pathways, our results show that the projections of the lateral geniculate body terminate in more superficial levels of layer III and sparsely in layer I of striate cortex. The projections to the upper portion of layer III terminate in distinct patches which coincide precisely with patches of cytochrome oxidase activity previously identified in this zone. The projections to the patches originate primarily from small, pale-staining cells of the "intercalated layers" which surround the magnocellular layers of the lateral geniculate body. A comparison of the organization of the geniculo-cortical projections in the squirrel monkey with that of the cat, Galago, and Tupaia suggests that, despite marked species differences in the laminar organization of the lateral geniculate body and striate cortex, there are striking similarities in the pathway which terminates in the most superficial layers of striate cortex.

Afferent Pathways↗
PubMedDate not supplied

Projections from and to the superior colliculus in the nucleus of the optic tract combined with postembedding GABA immunocytochemistry in the rabbit.

The reciprocal connection between the nucleus of the optic tract and the superior colliculus has been described for several species. In both nuclei GABA is an important transmitter and recently it has been shown that GABA plays a significant role in this connection. To investigate this reciprocal connection at the ultrastructural level in the rabbit, anterograde and retrograde tracers were injected in the superior colliculus. Ultrathin sections were incubated with anti-GABA to elucidate the presence of GABA in retrogradely labeled neurons or anterogradely labeled terminals in the nucleus of the optic tract. The present results show that GABA is present in several neurons projecting from the nucleus of the optic tract to the superior colliculus and that all neurons involved in this projections are contacted by GABA immunopositive terminals. In the projection from the superior colliculus to the nucleus of the optic tract GABA play a less significant role.

Afferent Pathways↗
PubMed1996

Response of the neuromuscular unit to spaceflight: what has been learned from the rat model.

Despite the inherent limitations placed on spaceflight investigations, much has been learned about the adaptations of the neuromuscular system to weightlessness from studies of rats flown for relatively short periods (approximately 4-22 days). Below is a summary of the major effects of spaceflight observed in muscles of rats that are not in their rapid growth stage: 1. Skeletal muscles atrophy rapidly during spaceflight; significant atrophy is observed as early as after 4 days of flight. 2. The atrophic response appears to be related to the primary function of the muscle. In the hindlimb, the relative amount of atrophy can be characterized as slow extensors > fast extensors > fast flexors. This pattern of relative atrophy does not appear to be occurring in the forelimb; however, not enough data are available to draw any definitive conclusions at this time. 3. Both slow and fast fibers atrophy during spaceflight, with the largest fibers within an individual muscle generally showing the greatest atrophic response. Interestingly, the amount of fiber atrophy appears to reach a plateau after about 14 days of flight. 4. Adaptations have been observed in the concentration and content of all muscle proteins pools, with the protein pools in slow muscles the most affected. 5. Some slow and fast fibers in predominantly slow and fast muscles show shifts in their histochemical and biochemical properties, toward those observed in a "faster" phenotype. 6. Some fibers, presumably expressing slow MHC isoforms before flight, begin to express fast MHC isoforms during flight. 7. The oxidative capacity of the muscles or fibers is relatively unaffected by spaceflight, particularly in the slow muscles. Any change in whole-body fatigability associated with spaceflight most likely reflects the loss in muscle and fiber mass. 8. The glycolytic capacity of the muscles and muscle fibers is enhanced after spaceflight. This metabolic adaptation seems to be related to the shift in the contractile proteins towards "faster" isoforms. 9. The vascularity of muscles appears to be maintained after flight, based, at least, on histological observations of capillarity. 10. The force capabilities of the muscles and fibers appear to decrease in parallel with the decreases in size, i.e., the specific tension is not significantly affected after flight. 11. Changes in the speed-related properties of the slow muscles are consistent with the adaptations in the myosin molecule, i.e., the slow muscles and some fibers in the slow muscles become "faster." 12. Some muscle fiber and neuromuscular junction damage has been observed after flight, particularly in the slow muscles. The extent of damage may be related to the amount of time that the muscles are allowed to reload before removal, i.e., in general, shorter intervals result in less fiber damage. 13. Adaptations in the motor (ventral horn) and sensory (spinal ganglia) neurons have been quite variable, but this may be related to the amount of time that the muscles are allowed to reload before removal. Morphological adaptations after relatively short periods of reloading may reflect a decrease in the activation of the neural elements during flight.

Adaptation, Physiological↗
PubMed1996

Evidence for differential control of posterior hypothalamic, supramammillary, and medial mammillary theta-related cellular discharge by ascending and descending pathways.

Single-unit discharge was recorded from cells in the posterior hypothalamic nucleus (PH), supramammillary nucleus (SuM), and medial mammillary nucleus (MM) during hippocampal theta (theta) elicited by stimulation of the reticular nucleus pontis oralis (RPO). In agreement with previously published work, theta-related cells in the PH (12 cells) were all classified as tonic theta-ON (increased tonic discharge rate during hippocampal theta), whereas those in the SuM (9 cells) and MM (15 cells) were all classified as phasic theta-ON (rhythmic discharge, in phase with ongoing theta). The effect of RPO stimulation on cell discharge was tested after hippocampal theta was abolished by infusion of procaine into the medial septum/vertical limb of the diagonal band. The RPO-elicited discharge patterns of all PH tonic theta-ON cells and all SuM phasic theta-ON cells survived septal procaine infusion. Further, the discharge rate of PH cells and the frequency of burst discharge of SuM cells during RPO stimulation both increased after the infusion. In contrast, septal procaine infusion abolished the RPO-elicited rhythmic discharge pattern in MM phasic theta-ON cells and attenuated their discharge rates. These results indicate that the PH and SuM form parts of an ascending system mediating hippocampal theta, whereas the MM receives (and perhaps relays to other parts of the limbic system) rhythmic input descending from the septo-hippocampal system. In addition, PH and SuM receive descending inputs that limit the discharge rates of their theta-related cells during hippocampal theta.

Afferent Pathways↗
PubMed1997

[The dorsal motor nucleus of the vagus nerve and its role in innervating the digestive tract].

Findings on topography of dorsal motor vagal nucleus neurons from which axons towards functionally different regions of digestive tract extend were analysed. Based on that and on the data available in literature main peculiarities of these cells topical organization were formulated. It is noted that "gastrointestinal" neurons are localised in dorsal motor nucleus as narrow stripes oriented caudo-rostrad. Stripes (or columns) of neurons from axons towards the digestive trace different parts arise do not cross. Digestive tract oral parts receive parasympathetic efferent inputs from neurons of medial and dorsomedial parts of the nucleus and caudal--from ventromedial cells of dorsal motor nucleus. Sites of maximal accumulation of initial "gastrointestinal" neurons that occupy an area within +0.5-(+)2.0 mm of functionally different regions of stomach and gut were demonstrated in cat and rat.

Animals↗