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PubMed1988

Preganglionic vagus nerve fibers also enter the greater curvature of the stomach in rats and ferrets.

The efferent gastric vagus nerve fibers appear to enter the stomach by several routes. For example, the rate of gastric acid secretion is directly affected by the nerves of the greater curvature of the stomach. Specifically, acid secretion decreases abruptly after division of the gastroepiploic nerve(s). To determine whether efferent vagus nerve fibers are contained in the gastroepiploic nerve(s), horseradish peroxidase, a protein that undergoes retrograde axonal transport, was applied to these nerves; the brainstem locus of the nuclei of the vagus nerves was examined 2 days later. Typical peroxidase labeling was observed in the dorsal motor nucleus of the vagus nerve in 5 of 6 rats and 3 of 3 ferrets; the hypothesis that efferent vagus nerves enter the greater curvature of the stomach was thus supported in two vertebrate species. These previously unrecognized nerves should be considered in the interpretation of experimental and clinical phenomena.

Animals↗
PubMed1987

Non-invasive evaluation of input-output characteristics of sensorimotor cerebral areas in healthy humans.

The topography of scalp SEPs to mixed and sensory median nerve (MN) and to musculocutaneous nerve stimulation was examined in 20 healthy subjects through multichannel (12-36) recording in a 50 msec post-stimulus epoch. MN-SEPs in both frontal leads were characterized by an N18, P20, N24, P28 complex showing maximal amplitude at contralateral parasagittal sites. This was sometimes partly obscured by a wide wave N30 having a fixed latency, but a steep amplitude gradient moving toward the scalp vertex. A P40 component followed, having longer peak latencies, moving the recording sites from contralateral medial parietal toward the vertex and frontal ipsilateral positions. MN-SEPs in contralateral parietal leads contained a widespread N20 with a maximum source posterior to the Cz-ear line. The following P25 enveloped two subcomponents - early and late P25 - having different distributions. The late P25 showed a maximum - coincident with that of wave N20 - which was localized more posteriorly than that of the early P25. An inconstant wave N33 with progressively longer peak latencies from sagittal toward lateral positions was then recorded. MN-SEPs in contralateral central positions showed a well-localized P22 wave in which both the parietal early P25 and the frontal P20 were vanishing. Common or separate generators for frontal, central and parietal SEPs were discriminated by evaluating the influence of stimulus rate and intensity, as well as of general anesthesia and transient CBF deficits, investigated in 7 patients undergoing carotid endarterectomy. Unifocal anodal threshold shocks were separately delivered to each of the scalp electrodes and motor action potentials were recorded from the target muscle in order to delineate the scalp representation of the motor strip for the upper limb and, consequently, to monitor, through SEP tracings, the short-latency sensory input to the motor cortex for hand and shoulder muscles. This was characterized by a boundary zone separating the parietal N20-early P25 complex, from the fronto-central N18-P22 one. This zone had an oblique direction strongly resembling that of the central sulcus.

Adult↗
PubMed1986

Supratrigeminal neurons mediate the shortest, disynaptic pathway from the central amygdaloid nucleus to the contralateral trigeminal motoneurons in the rat.

Stimulation of the supratrigeminal area (STA) of the rat induced a monosynaptic EPSP in most mylohyoid-digastric motoneurons and a monosynaptic IPSP or EPSP in the majority of masseteric ones, contralaterally. Stimulation of the central amygdaloid nucleus induced the ipsilateral STA activity immediately followed by the contralateral mylohyoid nerve activities. The same amygdaloid stimulated excited 19 of 46 STA neurons, which were antidromically identified to project to the contralateral trigeminal motor nucleus. Nine of these were monosynaptically excited. The mean of the antidromic and monosynaptic latencies of these neurons explains the mean onset latencies of the amygdaloid influences on the contralateral trigeminal motoneurons. Therefore, the shortest crossing amygdalo-motoneuronal pathway is probably disynaptic and mediated by commissural STA neurons.

Action Potentials↗
PubMed1987

Integration of cortical and peripheral information in the lateral vestibular nucleus in the cat.

Neuronal discharges in the lateral vestibular nucleus (LVN) of the cat were studied during stimulation of a forelimb muscle and of a site in the contralateral motor cortex (area 4) capable of activating the same muscle. About one third of the LVN units were reactive to both stimulations or at least responded to one (cortex or muscle) but modified the response pattern when the other was stimulated also. The patterns evoked by a muscle were mostly enhanced on simultaneous stimulation of the cortical zone controlling the same muscle and vice versa. Only in the dorsal division the excitatory responses to muscle stimulation were depressed by simultaneous cortical stimulation. Some functional implications are proposed.

Afferent Pathways↗
PubMed1987

Descending and segmental spinal pathways differently regulate contractions of antagonistic muscles of frogs in vitro.

A comparison of fibres descending through the ventral column and segmental afferent fibres was carried out using an isolated frog spinal cord-nerve-muscle preparation with a pair of antagonistic muscles. The m. tibialis anterior (TIB) was contracted with stimulation of the ventral column much stronger than with that of the dorsal root (DR). Contraction of the m. gastrocnemius (GAS) was selectively induced with DR stimulation. These results suggest that the descending fibres and segmental afferent fibres preferentially regulate contractions of the flexor (the TIB) and the extensor (the GAS), respectively. Effects of alpha-aminoadipate, methysergide and LSD were also examined.

2-Aminoadipic Acid↗
PubMed2006

Neurogastroenterology: imaging of the sensory and motor control of the GI tract.

The central nervous system plays a major role in the receipt and processing of gastrointestinal signals both at a conscious and subconscious level. It also provides major input into the motor control of the gut, most particularly with regard to swallowing and defecation. This review indicates how this control operates and provides recent experimental evidence of mechanisms underlying it both in health and disease.

Afferent Pathways↗
PubMed2005

Navigating a sensorimotor loop.

Touch is an active process, but how do the body's somatic sensors influence its movement? In this issue of Neuron, Nguyen and Kleinfeld show that afferent activity from the whiskers on a rat's face trigger rapid and prolonged excitation of the motor neurons that drive movements of the same whiskers. Positive feedback through this sensorimotor loop may serve to optimize the interaction between sensors and stimuli.

Afferent Pathways↗
PubMed2006

Mechanisms underlying the recovery of lower urinary tract function following spinal cord injury.

The lower urinary tract has two main functions, the storage and periodic expulsion of urine, which are regulated by a complex neural control system in the brain and lumbosacral spinal cord. This neural system coordinates the activity of two functional units in the lower urinary tract: (1) a reservoir (the urinary bladder) and (2) an outlet (consisting of bladder neck, urethra and striated muscles of the pelvic floor). During urine storage the outlet is closed and the bladder is quiescent, thereby maintaining a low intravesical pressure over a wide range of bladder volumes. During micturition the outlet relaxes and the bladder contracts to promote the release of urine. This reciprocal relationship between bladder and outlet is generated by visceral reflex circuits, some of which are under voluntary control. Experimental studies in animals indicate that the micturition reflex is mediated by a spinobulbospinal pathway passing through a coordination center (the pontine micturition center) located in the rostral brainstem. This reflex pathway is in turn modulated by higher centers in the cerebral cortex that are presumably involved in the voluntary control of micturition. Spinal cord injury at cervical or thoracic levels disrupts voluntary control of voiding as well as the normal reflex pathways that coordinate bladder and sphincter functions. Following spinal cord injury, the bladder is initially areflexic but then becomes hyperreflexic due to the emergence of a spinal micturition reflex pathway. Studies in animals indicate that the recovery of bladder function after spinal cord injury is dependent in part on plasticity of bladder afferent pathways and the unmasking of reflexes triggered by capsaicin-sensitive C-fiber bladder afferent neurons. The plasticity is associated with changes in the properties of ion channels and electrical excitability of afferent neurons, and appears to be mediated in part by neurotrophic factors released in the spinal cord and the peripheral target organs.

Adrenergic Fibers↗
PubMed1997

Primary motor cortex influences on the descending and ascending systems.

The motor cortex plays a crucial role in the co-ordination of movement and posture. This is possible because the pyramidal tract fibres have access both directly and through collateral branches to structures governing eye, head, neck trunk and limb musculature. Pyramidal tract axons also directly reach the dorsal laminae of the spinal cord and the dorsal column nuclei, thus aiding in the selection of the sensory ascendant transmission. No other neurones in the brain besides pyramidal tract cells have such a wide access to different structures within the central nervous system. The majority of the pyramidal tract fibres that originate in the motor cortex and that send collateral branches to multiple supraspinal structures do not reach the spinal cord. Also, the great majority of the corticospinal neurones that emit multiple intracraneal collateral branches terminate at the cervical spinal cord level. The pyramidal tract fibres directed to the dorsal column nuclei that send collateral branches to supraspinal structures also show a clear tendency to terminate at supraspinal and cervical cord levels. These facts suggest that a substantial co-ordination between descending and ascending pathways might be produced by the same motor cortex axons at both supraspinal and cervical spinal cord sites. This may imply that the motor cortex co-ordination will be mostly directed to motor responses involving eye-neck-forelimb muscle synergies. The review makes special emphasis in the available evidence pointing to the role of the motor cortex in co-ordinating the activities of both descending and ascending pathways related to somatomotor integration and control. The motor cortex may function to co-operatively select a unique motor command by selectively filter sensory information and by co-ordinating the activities of the descending systems related to the control of distal and proximal muscles.

Afferent Pathways↗
PubMed1997

Magnetic stimulation of the descending and ascending tracts at the foramen magnum level.

To test the possibility that stimulation over the foramen magnum activates ascending tracts as well as descending tracts, we studied 4 patients with myoclonic epilepsy all of whom had enhanced cortical long loop reflexes (LLRs) and 10 normal subjects, using our previously reported method (Ugawa et al., Ann. Neurol., 1994, 36: 618-624). For latency comparisons, peripheral nerve stimulation at the elbow and spinal motor root were also performed. In all patients, magnetic stimulation at the foramen magnum consistently elicited long loop reflexes as well as direct responses caused by stimulation of the descending tracts. In contrast, no LLRs were ever seen in any normal subjects. The latencies of both types of response were the same whether stimulation used upward or downward current in the brain, although the former was always more effective. This indicates that stimulation at the level of the foramen magnum activates ascending tracts as well as descending tracts at a fixed position. The threshold for LLRs was lower than that for activation of the descending tracts. This threshold difference is compatible with the hypothesis that large diameter fibers from muscle afferent conduct the central afferent volley for LLRs (Marsden et al., Brain, 1977, 100: 185-200).

Afferent Pathways↗
PubMed1998

Corticofugal modulation of the midbrain frequency map in the bat auditory system.

The auditory system, like the visual and somatosensory systems, contains topographic maps in its central neural pathways. These maps can be modified by sensory deprivation, injury and experience in both young and adult animals. Such plasticity has been explained by changes in the divergent and convergent projections of the ascending sensory system. Another possibility, however, is that plasticity may be mediated by descending corticofugal connections. We have investigated the role of descending connections from the cortex to the inferior colliculus of the big brown bat. Electrical stimulation of the auditory cortex causes a downward shift in the preferred frequencies of collicular neurons toward that of the stimulated cortical neurons. This results in a change in the frequency map within the colliculus. Moreover, similar changes can be induced by repeated bursts of sound at moderate intensities. Thus, one role of the mammalian corticofugal system may be to modify subcortical sensory maps in response to sensory experience.

Animals↗