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Results for “Reticular Formation”

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At least 199 records · Page 11Linked to original sources

PubMed2000

Nocturnal enuresis and the pontine reticular formation.

OBJECTIVES: To assess the previously proposed hypothesis that enuretic patients have a dysfunction in the pontine reticular formation. METHODS: In 18 patients with intractable nocturnal enuresis, rapid eye movement (REM)-related phasic chin muscle activity loss in REM sleep was examined by means of a single-night polysomnography. RESULTS: In 5 of 18 patients, this physiologically seen phenomenon was found to be disturbed. CONCLUSIONS: Since REM-related phasic chin muscle activity loss is disturbed by the functional impairment in the pontine reticular formation, some enuretic patients could be considered as presenting a dysfunction in this structure.

Adolescent↗

PubMed1998

A neural model of the saccade generator in the reticular formation.

A neural model is developed of the neural circuitry in the reticular formation that is used to generate saccadic eye movements. The model simulates the behavior of identified cell types-such as long-lead burst neurons, short-lead excitatory and inhibitory burst neurons, omnipause neurons, and tonic neurons-under many experimental conditions. Simulated phenomena include: saccade staircases, duration and amplitude of cell discharges for saccades of variable amplitude, component stretching to achieve straight oblique saccades, saturation of saccade velocity after saturation of saccade amplitude in response to high stimulation frequencies, trade-offs between saccade velocity and duration to generate constant saccade amplitude, conservation of saccade amplitude in response to sufficiently brief stimulation of omnipause neurons, and high velocity smooth eye movements evoked by high levels of electrical stimulation of the superior colliculus. Previous saccade generator models have not explained this range of data. These models have also invoked mechanisms for which no neurophysiological evidence has been forthcoming, such as resetable integrators, perfect integrators, or target position movement commands. The present model utilizes only known reticular formation neurons. It suggests that a key part of the feedback loop within the saccade generator is realized by inhibitory feedback from short-lead to long-lead burst neurons, in response to excitatory feedforward signals from long-lead to short-lead burst neurons. When this property is combined with opponent interactions between agonist and antagonist muscle-controlling neurons, and motor error, or vector, inputs from the superior colliculus and other saccade-controlling brain regions, all of the above data can be explained. Taken together, these components generate a saccade reset cycle whereby activation of long-lead burst neurons inhibits omnipause neurons and thereby disinhibits short-lead excitatory burst neurons. The excitatory short-lead burst neurons can then respond to excitatory inputs from the long-lead burst neurons. Outputs from the excitatory short-lead burst neurons are integrated by the tonic cells while they also inhibit the long-lead burst neurons via inhibitory burst interneurons. When this inhibition is complete, the omnipause neurons are disinhibited. The omnipause neurons can then, once again, inhibit the short-lead burst neurons, whose inhibition of the long-lead burst neurons is thereby removed. The saccadic cycle can then begin again. In response to sustained electrical input, this cycle generates a staircase of identical saccades whose properties match the data much better than the staircases proposed by alternative models. A comparative analysis of the hypotheses and predictive capabilities of other saccade generator models is provided.

Journal Article↗

PubMed1976

Activation of neurons in the cerebellar nuclei and ascending reticular formation by stimulation of the cerebellar surface.

Electrical stimulation of the cerebellar surface has been used therapeutically for the control of certain epileptic seizure and motor disorders. Recent hypotheses suggest that the therapeutic results in the treatment of epilepsy might be a consequence of the activation of Purkinje cells which subsequently inhibit the epileptic activity in the cerebrocellular loop. These experiments establish that an anatomical substrate exists whereby the effects of stimulating the cerebellar surface might be mediated by the ascending reticular formation and the non-specific thalamic nuclei. Specifically, the stimulation of the cerebellar surface activates not only Purkinje cells but also cerebellar afferent systems, climbing fibers and mossy fibers, and neurons in the cerebellar nuclei and reticular formation. In addition, recordings from neurons in the ascending reticular formation suggest that stimulation of the cerebellar surface can affect processing of ascending sensory information, thus influencing neural integration of non-specific sensory system.

Afferent Pathways↗

PubMed1984

Effects of iontophoretic application of convulsants on the sensory responses of neurons in the brain-stem reticular formation.

Iontophoretic or pneumatic application of convulsants produced enhancement of the sensory responses of brain-stem reticular formation (RF) neurons in cat and rat. Enhanced sensory responsiveness is observed with visual, auditory, somatosensory and vibrissa manipulation following application of strychnine, bicuculline or pentylenetetrazol. The effect was not transmitter-specific, since it could be produced by sequential application of bicuculline and strychnine which are thought to affect different neurotransmitters. Intravenous administration of convulsant also enhanced the responsiveness of RF neurons which had previously been affected by application of a different convulsant. Both systemic and iontophoretic effects could be antagonized by application of GABA and glycine. These data, coupled with previous findings in primary sensory pathways, indicate that sensory response enhancement in the RF induced by intravenous administration of these convulsants is in large part due to actions on synaptic elements of reticular formation neurons.

Animals↗

PubMed1981

Brain stem afferents to the periabducens reticular formations (PARF) in the cat. An HRP study.

Six injections of HRP were placed in the periabducens reticular formation (PARF). Two were placed ventromedial to the caudal half of the abducens nucleus (VIn), two were placed further laterally and ventral to the rostral half of the nucleus, and two were placed rostral to the nucleus. Most injections in PARF produced cell labeling in the vestibular and perihypoglossal nuclei bilaterally and labeled cells in the reticularis gigantocellularis (Rgc) and reticularis pontis caudalis (Rpc) nuclei contralateral to the injection site. Few labeled neurons were found in the caudal part of the paramedian pontine reticular formation (PPRF). In the mesencephalon, bilateral but more numerous ipsilateral labeled cells were found in the medial mesodiencephalic region including the nuclei of Cajal, Darkschewitsch and the posterior commissure. Injections placed caudomedial to VIn resulted in a characteristic concentration of labeled cells in the ipsilateral nucleus cuneiformis and rostral half of the contralateral superior colliculus (SC). Injections placed rostral to VIn in PARF produced cell labeling in the nucleus campi Foreli. The results are related to physiological evidence which suggests that PARF is an important premotor center for coordination of oculomotor, head and body movements.

Abducens Nerve↗

PubMed1989

[The autonomic nervous system and reticular formation in normal and pathologic states].

Patients with autonomic disorders that are located in the brain and spinal cord also have abnormalities in the corresponding reticular formation, especially in the brain stem. Treatment should be adequate and combined because the same adreno- and cholinoreceptor structures are damaged as those in autonomic innervation. This also refers to the limbic formations which are intimately connected with autonomic structures and the reticular formation.

Autonomic Nervous System↗

PubMed1987

Stimulation of the pontomedullary reticular formation initiates locomotion in decerebrate birds.

The initiation and control of spinal locomotor mechanisms by supraspinal brainstem centers has been studied in many vertebrate species. However there is very little information regarding brainstem-spinal pathways involved in avian locomotion. To undertake these studies, birds (geese or ducks) were placed in a stereotaxic frame and decerebrated under halothane anesthesia. After anesthesia was discontinued, discrete brainstem regions were electrically stimulated. Locomotion could be evoked from several areas within the pontomedullary reticular formation. The stimulus threshold for evoking walking ranged from 25-50 microA at 30-80 Hz (pulse duration 0.5 ms). At slightly higher current strengths (50-100 microA) wing flapping ('flying') was initiated. Histological examination of the stimulation sites indicated that the predominant locomotor areas were restricted to the ventromedial gigantocellular reticular formation and a more dorsolateral location within the parvocellular reticular formation. To ascertain whether neurons in these regions of the avian brainstem project directly to the spinal cord, a retrograde fluorescent tracer dye, True blue, was injected into either the cervical or low thoracic spinal cord. Comparing the positions of the retrogradely labeled neurons and the effective locomotor stimulation sites indicated a high degree of overlap. The present results, when compared with previous studies, suggest strong similarities in descending brainstem control of locomotion for all vertebrates.

Animals↗

PubMed1989

[Immobilization stress-induced lesions of structures of the midbrain reticular formation].

Emotional stress in rats resulted in blood-brain barrier increased permeability and brain parenchymal vessel disruptions. Stress induced microvascular damages were mainly observed in midbrain reticular formation. In this article the components of midbrain reticular formation were studied 1, 2, 4 and 6 weeks after immobilization stress. The destructive changes in some neurons, glia cells and myelin fibers were shown up to 6 weeks after immobilization. The signs of the recovery were also observed. It was supposed that the brain parenchymal vessel damages under emotional stress were due to the stress induced locus coeruleus dysfunctions.

Animals↗

PubMed1977

[Changes in the hypothalamus, reticular formation and pituitary of rats during development of subcutaneous tumors].

Dynamics of structural changes was studied in the hypothalamus, reticular formation and the hypophysis of rats, depending on the phases of development in them of 9m10-dimethyl-1,2-benzanthracene-induced tumours. The phase of subcutaneous tumours appearance proved to be accompanied by structural and functional changes in the hypothalamus, reticular formation and the hypophysis.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1996

Activation by attention of the human reticular formation and thalamic intralaminar nuclei.

It has been known for over 45 years that electrical stimulation of the midbrain reticular formation and of the thalamic intralaminar nuclei of the brain alerts animals. However, lesions of these sectors fail to impair arousal and vigilance in some cases, making the role of the ascending activating reticular system controversial. Here, a positron emission tomographic study showed activation of the midbrain reticular formation and of thalamic intralaminar nuclei when human participants went from a relaxed awake state to an attention-demanding reaction-time task. These results confirm the role of these areas of the brain and brainstem in arousal and vigilance.

Adult↗

PubMed1985

Neuronal development in the medullary reticular formation in sudden infant death syndrome and premature infants.

Morphological and morphometrical development of the neurons in the medullary reticular formation was observed in control, sudden infant death syndrome (SIDS) and prematurely born infants, using Golgi stains. With increasing gestational age, in controls dendrites became long, spines increased and the distribution of spines assumed a mature pattern. The number of spines reached a peak at 34 to 36 weeks gestation and after birth it decreased rapidly. Term and prematurely born SIDS infants showed a persistence of reticular dendritic spines. On the other hand, ventilator-dependent prematurely born infants had decreased numbers of dendritic spines with thin dendrites and long, thin spines. Persistence of reticular dendritic spines in SIDS infants may suggest incomplete development to the mature, higher level of respiratory control. Spine abnormalities in the ventilator-dependent prematurely born infants may indicate secondary neuronal changes in the reticular formation.

Dendrites↗

PubMed1980

Brain stem activation of the hippocampus: a role for the magnocellular reticular formation and the MLF.

In previous reports (Vertes 1977, 1979) we have shown that cells of the medial magnocellular reticular formation (MMRF) discharge at high rates of activity during both waking-movement and REM sleep and at low rates during quiet waking and slow wave sleep. We suggest that some of these reticular cells may be involved in the generation of the hippocampal theta rhythm since they fire maximally during the identical states (general movement and REM sleep) in which theta is present in the hippocampus of the rat. In the present study the influence of the brain stem on the hippocampus was analyzed by systematically mapping the entire brain stem with stimulation to determine its effect on hippocampal slow wave activity. The results showed that the most effective stimulation sites for eliciting hippocampal synchronization were those within the medial magnocellular reticular formation and in or near the medial longitudinal fasciculus (MLF) at the level of the pons. These results suggest that cells of the MMRF are critically involved in hippocampal theta generation and that the fibers of these theta-eliciting cells primarily ascend in the MLF in their route rostrally from the brain stem.

Animals↗

PubMed1990

Convergence of cardiovascular and vestibular inputs on neurons in the medullary paramedian reticular formation.

Extracellular recordings were made from 47 neurons in the caudal medullary paramedian reticular formation of chloralose-urethan anesthetized cats. The firing rate of all of these neurons was affected by stimulation of the contralateral vestibular nerve. The onset latency of the response to vestibular nerve stimulation was accurately determined for 43 of these neurons. The large majority (36 of 43) received short-latency (onset latency less than 5 ms) inputs; 7 were driven within 2 ms and were classified as receiving disynaptic inputs. Twenty of the 47 neurons also received inputs from the ipsilateral carotid sinus nerve. The paramedian reticular formation thus appears to be an important site for the integration of cardiovascular afferent and vestibular signals. However, only a small fraction of the neurons (2 of 13 tested) which received such convergent inputs could be antidromically driven from the upper thoracic spinal cord.

Action Potentials↗

PubMed1991

Progressive supranuclear palsy: loss of choline-acetyltransferase-like immunoreactive neurons in the pontine reticular formation.

We performed a quantitative immunocytochemical study using a polyclonal antibody directed against choline acetyltransferase (ChAT) in the lower pontine reticular formation in four control subjects and three patients with progressive supranuclear palsy (PSP). In the normal brains, there was detectable ChAT-like immunoreactivity in the nucleus papillioformis, a precerebellar reticular nucleus, and in the nucleus pontis centralis caudalis. In PSP patients, the mean estimated total number of ChAT-like immunoreactive cells was 54% of controls in nucleus papillioformis and 40% of controls in nucleus pontis centralis caudalis. The demonstration of ChAT-like immunoreactivity in nucleus papillioformis is consistent with studies suggesting an extrinsic cholinergic innervation of the cerebellar cortex. Loss of cholinergic cells in nucleus pontis centralis caudalis that corresponds largely to the paramedian pontine reticular formation may be related to disturbances of horizontal saccades in PSP patients.

Aged↗

PubMed1976

[Mechanism of the effect of the midbrain reticular formation on the hypothalamus-hypophysis-thyroid gland system].

The role of the posterior hypothalamic nuclei in the transmission of the influences of the mesencephalic reticular formation upon the thyroid hormone secretion was studied. Stimulation of the mesencephalic reticular formation in anesthetized cats was followed by the excitation of the thyroid hormoone secretion: the content of the blood protein-bound iodine was increased. This effect was eliminated after the bilateral coagulation of the posterior hypothalamic nuclei. These findings confirmed the hypothesis on the leading role of the posterior hypothalamic nuclpeus in the stimulation of the hormone secretion.

Animals↗

PubMed2000

Effects of reversible inactivation of the primate mesencephalic reticular formation. I. Hypermetric goal-directed saccades.

Single-neuron recording and electrical microstimulation suggest three roles for the mesencephalic reticular formation (MRF) in oculomotor control: 1) saccade triggering, 2) computation of the horizontal component of saccade amplitude (a feed-forward function), and 3) feedback of an eye velocity signal from the paramedian zone of the pontine reticular formation (PPRF) to higher structures. These ideas were tested using reversible inactivation of the MRF with pressure microinjection of muscimol, a GABA(A) agonist, in four rhesus monkeys prepared for chronic single-neuron and eye movement recording. Reversible inactivation revealed two subregions of the MRF: ventral-caudal and rostral. The ventral-caudal region, which corresponds to the central MRF, the cMRF, or nucleus subcuneiformis, is the focus of this paper and is located lateral to the oculomotor nucleus and caudal to the posterior commissure (PC). Inactivation of the cMRF produced contraversive, upward saccade hypermetria. In three of eight injections, the velocity of hypermetric saccades was too fast for a given saccade amplitude, and saccade duration was shorter. The latency for initiation of most contraversive saccades was markedly reduced. Fixation was also destabilized with the development of macrosaccadic square-wave jerks that were directed toward a contraversive goal in the hypermetric direction. Spontaneous saccades collected in total darkness were also directed toward the same orbital goal, up and to the contraversive side. Three of eight muscimol injections were associated with a shift in the initial position of the eyes. A contralateral head tilt was also observed in 5 out of 8 caudal injections. All ventral-caudal injections with head tilt showed no evidence of vertical postsaccadic drift. This suggested that the observed changes in head movement and posture resulted from inactivation of the caudal MRF and not spread of the muscimol to the interstitial nucleus of Cajal (INC). Evidence of hypermetria strongly supports the idea that the ventral-caudal MRF participates in the feedback control of saccade accuracy. However, development of goal-directed eye movements, as well as a shift in the initial position following some of the cMRF injections, suggest that this region also contributes to the generation of an estimate of target or eye position coded in craniotopic coordinates. Last, the observed reduction in contraversive saccade latency and development of macrosaccadic square-wave jerks supports a role of the MRF in saccade triggering.

Animals↗

PubMed1985

Reticular formation of the lower brainstem. A common system for cardio-respiratory and somatomotor functions. Considerations aided by computer simulations.

Parallel investigations were done using the reticular formation of the lower brainstem of dogs and computer simulated neuronal networks with properties of reticular neurones. By the aid of the simulations, understanding of the functional organisation of the common brainstem system, reticular formation and the experiments performed were optimized. The fact that discharge sequences of model neurones are very similar to those of reticular neurones was proved by interval histograms and covariance histograms. Discharges of neighbouring reticular neurones tend to be strongly coupled. In the model the discharges of the neurones could be coupled by common afferent inflows. Physiologically, neighbouring reticular neurones receive common afferents from peripheral somato-sensory systems. Neighbouring neurones with strongly coupled discharging are organized in subpopulations. The configurations of the subpopulations are determined by number and type of afferents actively influencing neurones and by the level of intrinsic activity of the network. Signal processing and transfer by neuronal subpopulations depend on the level of activity and on the degree of coupled discharging, i.e. the local organisation of the neurones.

Afferent Pathways↗

PubMed1984

Primary afferent projections of the octavus nerve to the inferior reticular formation and adjacent nuclei in the elasmobranch, Rhinobatos sp.

Projections of primary afferent fibers from the octavus nerve to the inferior reticular formation were determined by nerve degeneration and HRP labeling. Descending afferents from the horizontal ampullary nerve exit the ventral border of the nucleus octavus descendens via arcuate fiber tracts, and project to a group of neurons adjacent to the spinal lemniscus; to the inferior reticular formation; and to the nucleus funiculi lateralis. The possible influence of these afferent projections on directed swimming motion is discussed.

Animals↗