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PubMed1990

Excitatory amino acid projections to the periaqueductal gray in the rat: a retrograde transport study utilizing D[3H]aspartate and [3H]GABA.

The afferents to the periaqueductal gray utilizing excitatory amino acid transmitters have been described in rat brain by autoradiography following microinfusion and retrograde transport of D[3H]aspartate. Parallel experiments employing injections of [3H]GABA established that the retrograde labelling found with D[3H]aspartate was transmitter-selective. Following infusion of D[3H]aspartate, perikaryal labelling was found in nine subcortical areas, particularly infralimbic and cingulate cortices, with a predominance of ipsilateral labelled perikarya. Heaviest cortical labelling was localized in perirhinal cortex, in an extensive band of cells adjoining the rhinal sulcus. The hypothalamus contained the heaviest perikaryal labelling within brain: D[3H]aspartate labelled cells in 11 hypothalamic and mammillary nuclei. Intense bilateral labelling was obtained in ventromedial hypothalamus, although the number of perikarya was lower contralaterally. D[3H]Aspartate also produced heavy ipsilateral labelling of perikarya in posterior hypothalamus. Labelling patterns in cortex and hypothalamus were precise and topographic, and [3H]GABA never labelled cells in these regions. Other telencephalic and diencephalic areas containing prominent, retrogradely labelled cells were the lateral septum, amygdala, zona incerta and lateral habenula. The relative density of labelled cells in mesencephalic areas was much lower than that found in cortex and hypothalamus, although D[3H]aspartate labelled a moderate number of perikarya in the inferior colliculus and cuneiform nucleus. A smaller number of heavily labelled cells was found in the parabrachial nuclei, Kolliker-Fuse nucleus and laterodorsal tegmental nucleus. Only occasional labelled perikarya were observed in the myencephalon. Low densities of labelled cells were found after the injection of [3H]GABA into the periaqueductal gray, and the only regions in which a small number of perikarya were labelled by both [3H]GABA and D[3H]aspartate were the dorsal raphe and parabrachial nuclei. Overall, the retrograde transport of D[3H]aspartate revealed a complex topographic and convergent network of afferent pathways to the periaqueductal gray likely to utilize an excitatory amino acid transmitter. Our findings confirm the selectivity of this neurochemical mapping technique and provide evidence that hypothalamic, habenular, subthalamic and cuneiform afferents to the periaqueductal gray utilize an acidic amino acid as their transmitter. They also confirm that corticofugal afferents to periaqueductal gray utilize an excitatory amino acid.

Afferent Pathways↗
PubMed1987

Time course of the reaction of glial fibers in the somatosensory thalamus after lesions in the dorsal column nuclei.

These experiments were designed to examine the relationship of glial hypertrophy to the time course of reactive synaptogenesis in the ventral posterolateral nucleus of the rat thalamus after lesions in the dorsal column nuclei. Because synaptogenesis is delayed for 30 days following lesions of the dorsal column nuclei, the initial hypertrophy of the glial processes in response to degeneration can be separated temporally from synaptogenesis. Glial hypertrophy was determined by measuring the relative area of neuropil occupied by profiles of glial processes on electron micrographs. The initial glial hypertrophy reached its peak 2 days after the lesion. However, at the time when synaptogenesis began, the area of neuropil occupied by glial processes was less than normal. When synaptogenesis was complete, the area of glial profiles also returned to normal. The role of glia in synaptogenesis was clearly different from its role in response to degeneration. In those systems such as the hippocampus, in which reactive synaptogenesis starts early in the recovery sequence, the relationship of glia to synaptogenesis may be masked by the glial response to degeneration. Hypertrophy of glial processes after lesions of other afferent pathways to the ventral posterolateral nucleus was compared to the hypertrophy following lesions of the dorsal column nuclei in order to see if there was a special relationship between glia and the lemniscal afferents to the ventral posterolateral nucleus. Lesions were placed in the medial lemniscus, somatosensory cortex, and the mesencephalon in addition to the dorsal column nuclei. The area of neuropil occupied by the glial processes expanded markedly after each of the lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1997

Study of human forearm posture maintenance with a physiologically based robotic arm and spinal level neural controller.

The goals of this research are: (1) to apply knowledge of human neuro-musculo-skeletal motion control to a biomechanically designed, neural controlled, 'anthroform' robotic arm system, (2) to demonstrate that such a system is capable of responses that match those of the human arm reasonably well in comparable experiments, and (3) to utilize the anthroform arm system to study some controversial issues and to predict new phenomena of the human motion control system. A physiologically analogous artificial neural network controller and an anatomically accurate robotic testing elbow are applied in this study. In order to build the physical elbow system to have mechanical properties as close as possible to the human arm, McKibben pneumatic artificial muscles, force sensors, and mechanical muscle spindles are integrated in the system with anatomically accurate muscle attachment points. A physiologically analogous, artificial neural network controller is used to emulate the behavior of spinal segmental reflex circuitry including Ia and Ib afferent feedbacks. Systematic experiments of elbow posture maintenance are performed and compared with physiological experimental data. New experiments are performed in which responses to torque perturbation are measured when selected afferent pathways are blocked. A 'covariance diagram' is introduced. And a linear model is used to help to analyze the roles of system components. The results show that muscle co-contraction and Ia afference with gamma dynamic motoneuron excitation are two efficient ways to increase joint stiffness and damping, which in turn reduces the mechanical sensitivity of the joint to external perturbation and shortens the settling time of the system.

Afferent Pathways↗
PubMed2001

Development of the evoked potentials in the thalamus and cerebral cortex after stimulation of the stellate ganglion afferents in kittens.

The primary evoked potentials (EP) were studied in newborn, 10-, 20-day-old, 1-month-old kittens in the thalamus and cerebral cortex after stimulation of the stellate ganglion (SG) afferents. The nerves were irritated with single square-wave pulses with an amplitude of 1.2-1.3 threshold for EP appearance. In all kittens, EP were registered in the same zones as in adult animals. In the thalamus, this zone was represented by the centromedial part of the ventralis posterior lateralis (n. VPL), contralaterally to the stimulation place. In the cerebral cortex, the EP were observed in the cerebral cortex, specifically in the somatosensory zones S1 and S2 also contralaterally to the stimulation place. In postnatal ontogenesis, the latency of evoked potentials decreases, amplitude increases and the form of these potentials transforms from negative in newborn kittens to positive-negative wave in 1-month-old animals. Maturation of the SG afferent pathways exists in parallel with the somatosensory ones and does not finish at 1 month of life.

Afferent Pathways↗
PubMed2005

The role of the vagal nerve in peripheral PYY3-36-induced feeding reduction in rats.

Peptide YY (PYY), an anorectic peptide, is secreted postprandially from the distal gastrointestinal tract. PYY(3-36), the major form of circulating PYY, binds to the hypothalamic neuropeptide Y Y2 receptor (Y2-R) with a high-affinity, reducing food intake in rodents and humans. Additional gastrointestinal hormones involved in feeding, including cholecystokinin, glucagon-like peptide 1, and ghrelin, transmit satiety or hunger signals to the brain via the vagal afferent nerve and/or the blood stream. Here we determined the role of the afferent vagus nerve in PYY function. Abdominal vagotomy abolished the anorectic effect of PYY(3-36) in rats. Peripheral administration of PYY(3-36) induced Fos expression in the arcuate nucleus of sham-operated rats but not vagotomized rats. We showed that Y2-R is synthesized in the rat nodose ganglion and transported to the vagal afferent terminals. PYY(3-36) stimulated firing of the gastric vagal afferent nerve when administered iv. Considering that Y2-R is present in the vagal afferent fibers, PYY(3-36) could directly alter the firing rate of the vagal afferent nerve via Y2-R. We also investigated the effect of ascending fibers from the nucleus of the solitary tract on the transmission of PYY(3-36)-mediated satiety signals. In rats, bilateral midbrain transections rostral to the nucleus of the solitary tract also abolished PYY(3-36)-induced reductions in feeding. This study indicates that peripheral PYY(3-36) may transmit satiety signals to the brain in part via the vagal afferent pathway.

Afferent Pathways↗
PubMed2004

Purinergic and vanilloid receptor activation releases glutamate from separate cranial afferent terminals in nucleus tractus solitarius.

Vanilloid (VR1) and purinergic (P2X) receptors are found in cranial afferent neurons in nodose ganglia and their central terminations within the solitary tract nucleus (NTS), but little is known about their function. We mechanically dissociated dorsomedial NTS neurons to preserve attached native synapses and tested for VR1 and P2X function primarily in spindle-shaped neurons resembling intact second-order neurons. All neurons (n = 95) exhibited spontaneous glutamate (EPSCs) and GABA (IPSCs)-mediated synaptic currents. VR1 agonist capsaicin (CAP; 100 nm) reversibly increased EPSC frequency, effects blocked by capsazepine. ATP (100 microm) increased EPSC frequency, actions blocked by P2X antagonist pyridoxalphosphate-6-azophenyl-2', 4'-disulfonic acid (PPADS; 20 microm). In all CAP-resistant neurons, P2X agonist alphabeta-methylene-ATP (alphabeta-m-ATP) increased EPSC frequency. Neither CAP nor alphabeta-m-ATP altered EPSC amplitudes, kinetics, or holding currents. Thus, activation of VR1 and P2X receptors selectively facilitated presynaptic glutamate release on different NTS neurons. PPADS and 2',3'-O-(2,4,6-trinitrophenyl)-ATP blocked alphabeta-m-ATP responses, but P2X1-selective antagonist NF023 (8,8'-[carbonylbis (imino-3,1-phenylene carbonylimino)]bis-1,3,5-naphthalenetrisulfonic acid) did not. The pharmacological profile and transient kinetics of ATP responses are consistent with P2X3 homomeric receptors. TTX and Cd(2+) did not eliminate agonist-evoked EPSC frequency increases, suggesting that voltage-gated sodium and calcium channels are not required. In nodose ganglia, CAP but not alphabeta-m-ATP evoked inward currents in slow conducting neurons and the converse pattern in myelinated, rapidly conducting neurons (n = 14). Together, results are consistent with segregation of glutamatergic terminals into either P2X sensitive or VR1 sensitive that correspondingly identify myelinated and unmyelinated afferent pathways at the NTS.

Adenosine Triphosphate↗
PubMed1984

Central representation and functional connections of afferent and efferent pathways of Helix pomatia L. lip nerves.

Localization and distribution of cerebral neurones sending axons into the three pairs of Helix pomatia lip nerves were investigated by the method of retrograde axonal NiCl2 transport. Using electrophysiological technics (extracellular recordings) the dependence of lip nerve's activity on inputs of other lip nerves was studied after application of various types of stimuli to the lip of semi-intact preparations. All lip nerves have neuronal representation in each lobe of the cerebral ganglia but in different proportions. Labelled neurones were located mainly on the ventral surface of the cerebral ganglia, most of them projecting to the medial, the least to the inner lip nerve. Lip nerves differ from each other according to the proportions of neurones of various size. They share in the axons of large (55-70 microns) and medium sized (30-40 microns) neurones in the order inner greater than outer greater than medial and medial greater than outer greater than inner lip nerve, respectively. Most neurones projecting to different nerves are located in discrete groups. According to the electrophysiological results the medial lip nerve has the most prominent afferent, while the inner one has the strongest efferent activity. Both the afferent and efferent activities of the outer lip nerve proved to be the least significant compared to the other lip nerves. Contralateral cerebral connections play an important role in the sensory information processing. The sensory input of a given nerve usually activates the contralateral member of another pair of lip nerves. Mechano- and chemo-afferent pathways have almost the same properties but there are some differences in latencies and other parameters.

Afferent Pathways↗
PubMed1982

[Organization of the afferent subcortical inputs of the visual area of the cat cerebral cortex].

By means of the horseradish peroxidase retrograde transport method some complexes of the thalamic subcortical structures (external geniculate body, associative nucleus and non-specific nuclei). giving origin to the afferent pathways towards the sensory cortical area (visual area, field 17) have been described in the cat. It has been demonstrated that the external geniculate body, a part of the posterolateral thalamic nucleus, paracentral and centro-lateral nuclei make the complex of the visual cortical area. The investigation performed supports the fundamental principle that for each projection zone of the cerebral cortex afferentation from several thalamic nuclear groups is a specific feature.

Afferent Pathways↗
PubMed1981

Primary afferent axons in the tract of Lissauer in the monkey.

The main thrust of the present study was to determine the numbers of primary afferent fibers in the tract of Lissauer in the monkey. The findings are that approximately 40% of the axons in the tract of Lissauer are primary afferent axons from a single segment, and approximately another 40% are primary afferents from segments cranial and caudal to the segment under consideration. Presumably, the remaining 20% are propriospinal axons. There is relatively little difference in the proportions of primary afferents in medial as opposed to lateral parts of the tract, and in this respect the monkey differs somewhat from the rat and cat. Thus in the monkey the tract of Lissauer should probably be regarded as a primary afferent pathway with the propriospinal forming a distinct but relatively minor component of the tract.

Afferent Pathways↗
PubMed1993

[Major anatomico-functional relations in the cerebellum].

In this paper the main anatomico-functional data concerning the cerebellum are presented. The numerous hypotheses put forward on the functions of the cerebellum, such as they are listed in introduction, illustrate both the advances achieved and the problems awaiting to be solved. Following a general view of phylogenesis, the peculiar characteristics of the cerebellar cortex structure are emphasized; they include, notably, the properties of the olivo-cerebellar system, which is a source of climbing fibres and the organization into microzones, which constitutes the basic elements of the cerebellum. Finally, two aspects of functional organization are treated: the definition of three types of cerebellum (vestibular, somaesthetic and visual) based on the sensorial afferent pathways and the definition of efferent functional subsets based on sagittal bands identified in the vermis, the intermediate area and the hemispheric portion.

Afferent Pathways↗
PubMed1986

Sensory projections to the nucleus basalis prosencephali of the pigeon.

The afferent pathways to the nucleus basalis prosencephali of the pigeon were studied by use of the horseradish peroxidase (HRP) technique. It was confirmed that this nucleus receives a direct pathway from the nucleus sensorius principalis nervi trigemini and that, as in the starling, it receives a direct input from the nucleus lemnisci lateralis, pars ventralis, an auditory relay. Totally novel is the finding that the nucleus basalis prosencephali is the target of a direct pathway originating in the medullary nucleus vestibularis superior. All three pathways bypass the thalamus. From within the telencephalon the nucleus basalis prosencephali also receives fibres from the tuberculum olfactorium and the peri-ectostriatal belt, suggestive of olfactory and visual input. Marked cell bodies were also found in the neostriatum frontolaterale. It is assumed that these arose from HRP uptake by axons of the tractus fronto-archistriatalis that course through the nucleus basalis prosencephali to the anterodorsal archistriatum. Marked fibres and bouton-like formations were observed in the latter structure. The afferents to the nucleus basalis prosencephali are discussed in conjunction with the probable role of the nucleus as a sensorimotor coordinator of the pecking/feeding behaviour of the pigeon.

Afferent Pathways↗
PubMed1982

Neural control of intraocular pressure.

Efferent and afferent pathways by which the central nervous system (CNS) may control intraocular pressure (IOP) are considered. As experience with pharmaceutical agents has suggested, the targets for autonomic influence on ocular tension are both aqueous formation and resistance to outflow. The afferent input to the brain must be served by sensory fibers which are sensitive to intraocular pressure levels or which respond to changes in intraocular pressure. The location and physiology of such receptors is discussed.

Afferent Pathways↗
PubMed1997

Reflex vascular responses to alterations in abdominal arterial pressure and flow in anaesthetized dogs.

The existence of abdominal arterial baroreceptors has long been controversial. Previously difficulties have been encountered in localizing a stimulus to abdominal arteries without affecting reflexogenic areas elsewhere. In these experiments, using anaesthetized dogs, the abdomen was vascularly isolated at the level of the diaphragm, perfused through the aorta, and drained from the inferior vena cava to a reservoir. Changes in abdominal arterial pressure were effected by changing the perfusion pump speed. During this procedure the flow back to the animal from the venous outflow reservoir was held constant. Increases and decreases in abdominal arterial pressure resulted, respectively, in decreases and increases in perfusion pressure to a vascularly isolated hind-limb and in some dogs also a forelimb. Responses were significantly larger when carotid sinus pressure was high (120-180 mmHg) than when it was low (60 mmHg). Responses were still obtained after cutting vagus, phrenic and splanchnic nerves, but were abolished by spinal cord lesion at T12. These experiments provide evidence for the existence of abdominal arterial baroreceptors. The afferent pathway for the reflex vasodilatation appears to run in the spinal cord.

Abdomen↗
PubMed1997

Cortical somatosensory and trigeminal inputs to the cat superior colliculus: light and electron microscopic analyses.

Two different axonal transport tracers were used in single animals to test the hypothesis that the expansive intermediate gray layer of the cat superior colliculus (stratum griseum intermediale, SGI) is composed of sensorimotor domains. The results show that two sensory pathways, the trigeminotectal and the corticotectal arising from the fourth somatosensory area, commingle in patches across the middle tier of the SGI. Furthermore, the data reveal that tectospinal cells are distributed within these patches. Taken together, these results show a commingling of functionally related afferents and a consistent spatial relationship between these afferents and tectospinal neurons. These relationships indicate that the SGI consists of domains that can be distinguished by their unique combinations of afferent and efferent connections. The ultrastructural characteristics and synaptic relationships of these somatosensory afferent pathways suggest that they have distinct roles within the sensorimotor domain of the SGI. The trigeminotectal terminals are relatively small, contain round vesicles and make asymmetrical synapses on small, presumably distal, dendrites. We submit that these trigeminal terminals bestow the basic receptive field properties upon SGI neurons. In contrast, the somatosensory corticotectal terminals are relatively large, contain round vesicles, make asymmetrical synapses, participate in triads, and are presynaptic to proximal dendrites. We suggest that these cortical terminals bestow integrative abilities on SGI neurons.

Afferent Pathways↗
PubMed1996

Influence of gravity on cardiovascular reflexes from skeletal muscle receptors.

Skeletal muscles are important reflexogenic areas of the cardiovascular system. The afferent pathways of the reflex loops involve slow-conducting group III and group IV fibers that are excited by mechanical and chemical events in the muscle. The present paper reviews a series of experiments dealing with the question of whether those afferents are also influenced by gravitational forces. The results of these studies suggest the following answers: 1) gravitational forces can modulate cardiovascular reflexes from exercising skeletal muscles. 2) This effect is primarily due to changes in the interstitial fluid volume rather than to a direct mechanical influence, venous pressure, or venous volume. 3) The amplitudes of heart rate and blood pressure responses during exercise are inversely related to the local interstitial volume. Measurements during post-exercise circulatory arrest indicate that this sensitivity is mainly mediated by muscle chemoreceptors. These receptors, which also contribute to the spinal control of movement, generally appear to be sensitized by regional fluid losses and desensitized by overhydration of their environment.

Afferent Pathways↗
PubMed1997

Changes in specific binding sites of girisopam after chemical and surgical lesions in the striato-nigral system.

Neurotoxin (AMPA)-induced lesions in the caudate nucleus as well as unilateral surgical transection of the striato-nigral pathway strongly depleted the binding of a homophthalazine (formerly called 2,3-benzodiazepines) girisopam (GYKI-51189, EGIS 5810) selectively in the substantia nigra of the rat, ipsilateral to the lesions. In contrast to this, AMPA injections into the substantia nigra failed to effect on girisopam binding to either components of the nigro-striatal system. Data indicate that this homophthalazine may bind to a descending component of the striatum (striato-nigral projecting neurons), or its binding capacity to substantia nigra neurons depends on the integrity of striatal afferent pathways to the substantia nigra.

Afferent Pathways↗
PubMed2004

Task dependent gain regulation of spinal circuits projecting to the human flexor carpi radialis.

In humans, the flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles act as antagonists during wrist flexion-extension and as functional synergists during radial deviation. In contrast to the situation in most antagonist muscle pairs, Renshaw cells innervated by the motor neurons of each muscle inhibit the motoneurons, but not Ia inhibitory interneurons, of the opposite motor pool. Here we compared gain regulation of spinal circuits projecting to FCR motoneurons during two tasks: flexion and radial deviation of the wrist. We also investigated the functional consequences of this organisation for maximal voluntary contractions (MVCs). Electromyographic (EMG) recordings were taken from FCR, ECR longus and ECR brevis using fine-wire electrodes and electrical stimulation was delivered to the median and radial nerves. Ten volunteers participated in three experiments. 1. To study the regulation of the Renshaw cell-mediated, inhibitory pathway from ECR to FCR motoneurons, forty stimuli were delivered to the radial nerve at 50% of the maximal M-wave amplitude for ECR brevis. Stimuli were delivered during both isometric wrist flexions and radial deviation actions with an equivalent EMG amplitude in FCR (approximately 5% wrist flexion MVC). 2. To explore the homonymous Ia afferent pathway to FCR motoneurons, 50 stimuli were delivered to the median nerve at intensities ranging from below motor threshold to at least two times that which evoked a maximal M-wave during wrist flexion and radial deviation (matched FCR EMG at approximately 5% wrist flexion MVC). 3. EMG amplitude was measured during MVCs in wrist flexion, extension and radial deviation. There was no significant difference in the inhibition of FCR EMG induced via ECR-coupled Renshaw cells between radial deviation and wrist flexion. However, the mean FCR H-reflex amplitude was significantly (P<0.05) greater during wrist flexion than radial deviation. Furthermore, EMG amplitude in FCR and ECR brevis was significantly (P<0.05) greater during MVCs in wrist flexion and extension (respectively) than radial deviation. ECR longus EMG was significantly greater during MVCs in radial deviation than extension. These results indicate that the gain of the Renshaw-mediated inhibitory pathway between ECR and FCR motoneurons is similar for weak flexion and radial deviation actions. However, the gain of the H-reflex pathway to FCR is greater during wrist flexion than radial deviation. Transmission through both of these pathways probably contributes to the inability of individuals to maximally activate FCR during radial deviation MVCs.

Adult↗
PubMed2002

Reflex control of human jaw muscles.

The aim of this review is to discuss what is known about the reflex control of the human masticatory system and to propose a method for standardized investigation. Literature regarding the current knowledge of activation of jaw muscles, receptors involved in the feedback control, and reflex pathways is discussed. The reflexes are discussed under the headings of the stimulation conditions. This was deliberately done to remind the reader that under each stimulation condition, several receptor systems are activated, and that it is not yet possible to stimulate only one afferent system in isolation in human mastication experiments. To achieve a method for uniform investigation, we need to set a method for stimulation of the afferent pathway under study with minimal simultaneous activation of other receptor systems. This stimulation should also be done in an efficient and reproducible way. To substantiate our conviction to standardize the stimulus type and parameters, we discuss the advantages and disadvantages of mechanical and electrical stimuli. For mechanical stimulus to be delivered in a reproducible way, the following precautions are suggested: The stimulus delivery system (often a probe attached to a vibrator) should be brought into secure contact with the area of stimulation. To minimize the slack between the probe, the area to be stimulated should be taken up by the application of pre-load, and the delivered force should be recorded in series. Electrical stimulus has advantages in that it can be delivered in a reproducible way, though its physiological relevance can be questioned. It is also necessary to standardize the method for recording and analyzing the responses of the motoneurons to the stimulation. For that, a new technique is introduced, and its advantages over the currently used methods are discussed. The new method can illustrate the synaptic potential that is induced in the motoneurons without the errors that are unavoidable in the current techniques. We believe that once stimulation, recording, and analysis methods are standardized, it will be possible to bring out the real "wiring diagram" that operates in conscious human subjects.

Afferent Pathways↗