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At least 1,207 records · Page 67Linked to original sources
PubMed2002

Intrinsic GABA neurons inhibit proenkephalin gene expression in slice cultures of rat neostriatum.

In the neostriatum, the proenkephalin gene is expressed in medium spiny GABA neurons, which project to the globus pallidus. The expression is activated by glutamatergic projections from the neocortex via NMDA receptors. In these experiments we have used slice cultures of rat neostriatum to study the role of GABA in proenkephalin gene expression. Our results show that GABA is released from neostriatal neurons and negatively regulates the proenkephalin gene expression induced by NMDA receptor stimulation. The GABAA receptors involved seem to be colocalized with NMDA receptors on the projection neurons, which express the proenkephalin gene. In further experiments, we have found that the proenkephalin gene expression is not only activated by neocortical projection neurons but also by intrinsic striatal neurons as well as by projections from the thalamus. All these glutamatergic afferents enhance the proenkephalin gene expression via NMDA receptors. Their efficacy is regulated by endogenous GABA.

Afferent Pathways↗
PubMed1999

The neuronal control of the lower urinary tract: A model of architecture and control mechanisms.

The human micturition cycle is controlled by central and peripheral nervous structures and connections. In literature, no complete or generally accepted model describes the principles of micturition control. In this paper, the integration of (neuro-)anatomy, (neuro-)physiology and control theory is used to describe and model the neuronal control of the lower urinary tract. Neuroanatomy supplies the most basic information necessary for the modellation of the peripheral pathways and central connections involved in the control of the uropoetic system. It is found that not all the nervous structures and connections have been identified as such yet. The linking up between several nervous structures (e.g., the presence of central and peripheral relay stations) is not completely clear. A s a consequence, each model to describe the micturition cycle from the perspective of control theory is yet of limited physiological value as it cannot exceed a rather general level of modellation. Adding functional considerations (neurophysiology and control theory) to the neuroanatomical skeleton completes the model. Some control mechanisms active during the micturition cycle can still not be revealed in detail. Crucial questions on the neuronal innervation of the human uropoetic system and the control mechanisms active during the micturition cycle remain, like how the supraspinal trigger mechanisms for micturition are organised, or how the voluntary cessation of voiding is realised. A simplified version of the model discussed in this paper can already be used for mathematical modelling, e.g., neural network simulations.

Afferent Pathways↗
PubMed2002

The pontine micturition centres.

OBJECTIVE: To review recent literature on the function of the two postulated pontine regions (the M- and L-regions) concerned with lower urinary tract control. MATERIAL AND METHODS: The work reviewed is based on stimulation and lesion experiments and post-operative follow-up in the cat, supported by acute chemical stimulation and blocking experiments in the rat and PET functional brain scanning in humans. RESULTS AND CONCLUSIONS: The M-region in the cat, homologous to Barrington's micturition centre and to a similar area in humans, is a small region both specific and necessary to voiding, the origin of the final common pathway to bladder and urethra, and the locus of co-ordination of the bladder and the striated sphincter. The L-region in the cat is part of a larger, less specific area that probably serves sphincter control in various circumstances, not exclusively micturition. The homolog of this region in the human or in the rat has not been adequately established.

Afferent Pathways↗
PubMed2003

Closed-loop neuronal computations: focus on vibrissa somatosensation in rat.

Two classes of neuronal architectures dominate in the ongoing debate on the nature of computing by nervous systems. The first is a predominantly feedforward architecture, in which local interactions among neurons within each processing stage play a less influential role compared with the drive of the input to that stage. The second class is a recurrent network architecture, in which the local interactions among neighboring neurons dominate the dynamics of neuronal activity so that the input acts only to bias or seed the state of the network. The study of sensorimotor networks, however, serves to highlight a third class of architectures, which is neither feedforward nor locally recurrent and where computations depend on large-scale feedback loops. Findings that have emerged from our laboratories and those of our colleagues suggest that the vibrissa sensorimotor system is involved in such closed-loop computations. In particular, single unit responses from vibrissa sensory and motor areas show generic signatures of phase-sensitive detection and control at the level of thalamocortical and corticocortical loops. These loops are likely to be components within a greater closed-loop vibrissa sensorimotor system, which optimizes sensory processing.

Afferent Pathways↗
PubMedDate not supplied

Feeding genes.

Explore the source record for details and available documents.

Afferent Pathways↗
PubMed1996

Evidence for an anuran homologue of the mammalian spinocervicothalamic system: an in vitro tract-tracing study in Xenopus laevis.

Evidence is presented for an anuran homologue of the mammalian spinocervicothalamic system. In vitro tract-tracing experiments with biotinylated dextran amine Xenopus laevis show that ascending spinal fibres from all levels of the spinal cord, passing via the dorsolateral funiculus, terminate in a cell area ventrolateral to the dorsal column nucleus. This cell area can be considered a possible homologue of the mammalian lateral cervical nucleus. After tracer applications to the ventral thalamus or to the torus semicircularis (both targets for somatosensory projections), the anuran lateral cervical nucleus was retrogradely labelled contralateral to the application sites. Tracer applications to the dorsolateral funiculus at the obex level and rostral spinal cord resulted in labelling of the cells of origin of the spinocervical tract. These were found, mainly ipsilaterally, in the ventral part of the dorsal horn, and were rather evenly distributed throughout the spinal cord. These data suggest the presence of an anuran homologue of the mammalian spinocervicothalamic system. A brief survey of the literature shows that such a system is much more common in vertebrates than previously thought.

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↗
PubMed2003

Age and sex differences in human motor cortex input-output characteristics.

Stimulus-response curves for motor evoked potentials (MEPs) induced in a hand muscle by transcranial magnetic stimulation (TMS) were constructed for 42 subjects with the aim of identifying differences related to age and sex. There was no effect of age on the resting threshold to TMS, the maximal amplitude of the MEP that could be evoked (MEP(max)) or the maximal slope of the stimulus-response curve. However, higher stimulus intensities were required to achieve both MEP(max) and the maximal slope in the older subjects. The trial-to-trial variability of MEPs was greater in the older subjects, particularly at intensities near threshold. There was a significant interaction between age, threshold and trial-to-trial variability of MEP amplitude. Overall, MEP variability fell markedly as stimulus intensity increased above threshold but less rapidly in older than in younger subjects. Females tended to have larger MEP variability than males, but age and threshold were much stronger modulators than sex. These differences in input-output characteristics are likely to be due either to a decreased number of spinal motoneurones being activated synchronously in older subjects, or to the activation of the same number of motoneurones in a less synchronous manner, leading to phase cancellation in the surface electromyogram.

Adult↗
PubMed2005

Navigation in space--the role of the macaque ventral intraparietal area.

Goal-directed self-motion through space is anything but a trivial task. What we take for granted in everyday life requires the complex interplay of different sensory and motor systems. On the sensory side most importantly a target of interest has to be localized relative to one's own position in space. On the motor side the most critical step in neural processing is to define and perform a movement towards the target as well as the avoidance of obstacles. Furthermore, the multisensory (visual, tactile and auditory) motion signals as induced by one's own movement have to be identified and differentiated from the real motion of visual, tactile or auditory objects in the outside world. In a number of experimental studies performed in recent years we and others have functionally characterized a subregion within monkey posterior parietal cortex (PPC) that appears to be well suited to contribute to such multisensory encoding of spatial and motion information. In this review I will summarize the most important experimental findings on the functional properties of this very region in monkey PPC, i.e. the ventral intraparietal area.

Afferent Pathways↗
PubMed1981

Abdominal vagotomy blocks the satiety effect of cholecystokinin in the rat.

The site where peripherally administered cholecystokinin-8 elicits satiety was investigated by injecting rats with cholecystokinin-8 (1 to 8 micrograms per kilogram of body weight, intraperitoneally) after they had received bilateral lesions of the ventromedial hypothalamus or after they had undergone bilateral abdominal vagotomy or selective vagotomies. Abdominal vagotomy or gastric vagotomy abolished or reduced the satiety effect of cholecystokinin, but lesions of the ventromedial hypothalamus did not. These results demonstrate that peripherally administered cholecystokinin acts in the abdomen through gastric vagal fibers and not directly on the brain to produce satiety in the rat.

Afferent Pathways↗
PubMed2004

Synaptic transmission in simple motility reflex pathways excited by distension in guinea pig distal colon.

We examined specific receptor/transmitter combinations used at functionally identified synapses in ascending and descending reflex pathways of guinea pig distal colon. Excitatory (EJPs) or inhibitory junction potentials (IJPs) were recorded intracellularly from nicardipine-paralyzed circular smooth muscle in either the oral or anal recording chamber of a three-chambered organ bath, respectively. Blockade of synaptic transmission in the central chamber with a 0.25 mM Ca2+/12 mM Mg2+ solution abolished EJPs evoked by distension applied either in the central or the far (anal) chamber. IJPs evoked by distension in the central or the far (oral) chamber were depressed to approximately 50% of control. Hexamethonium (nicotinic receptor antagonist, 200 microM) in the central chamber reduced IJPs evoked by far or central distension to 50%, whereas EJPs evoked by far distension were abolished and EJPs evoked by central distension were reduced to 70% of control. Hexamethonium in the recording chambers reduced both IJPs and EJPs evoked by central distension to approximately 50%. EJPs in the ascending pathway were unaffected by blockade of muscarinic receptors in the central chamber or blockade of neurokinin 3 tachykinin receptors in this or the recording chamber. In the descending pathway, blockade of P2 receptors in the same chambers had only a minor effect on distension-evoked IJPs. Thus some intrinsic sensory neurons of guinea pig colon have long descending projections (>30 mm), but ascending projections of <15 mm. In contrast to the ileum, transmission between ascending or descending interneurons and from sensory neurons to descending interneurons is predominantly via nicotinic receptors; but transmission to inhibitory or excitatory motoneurons and from sensory neurons to ascending interneurons involves nicotinic and other unidentified receptors.

Afferent Pathways↗