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At least 433 records · Page 24Linked to original sources
PubMed1981

[Spike activity of neurons of the limbic cortex in response to stimulation of the mammillary bodies of the hypothalamus and midbrain reticular formation].

IN anesthetized cats, short-latency orthodromic and antidromic responses of the limbic cortex neurons to stimulation of the mamillary body and reticular formation (RF) suggest the existence of short direct and feedback connections among these three structures. Histogram analysis revealed the responses of maximal potential compactness to stimulation of the RF. High-frequency stimulation of the mamillary body and the RF exerted mainly an inhibitory effect upon the limbic cortex neurons.

Action Potentials↗
PubMed1981

[Functional state of the cerebral cortex and midbrain reticular formation during traumatic shock].

Acute experiments on cats were carried out during traumatic shock to study evoked potentials in the sensorimotor cortex and reticular formation (RF) of the midbrain in response to electrodermal irritation of the contralateral paw. The cortical function was judged by thresholds of convulsant reaction while function of RF by thresholds of activation reaction in the cortex of the course of high-frequency electrical stimulation of the structures under study. It was shown that in traumatic shock, initial and pronounced depression of the cortical function paralleled long enough stability of RF functional activity.

Animals↗
PubMed1983

Investigation of the connection between the substantia nigra and the medullary reticular formation in the rat.

Electrical stimulation of the rat substantia nigra (SN) has both excitatory and inhibitory effects on neurones in the medullary reticular formation (MRF). The SN does not appear to selectively influence neurones in either of the two MRF nuclei studied. Furthermore, SN stimulation does not preferentially influence nociceptive MRF neurones. Since only 1 of 75 neurons studied was antidromically activated by stimulation in the MRF, the present results do not support the suggestion that the nucleus reticularis gigantocellularis and SN are reciprocally linked in a monosynaptic fashion.

Animals↗
PubMed1981

Primary afferent depolarization of tooth pulp afferents by stimulation in nucleus raphe magnus and the adjacent reticular formation in the cat: effects of bicuculline.

In decerebrate cats electrical stimulation in nucleus raphe magnus (NRM) and the adjacent region of the reticular formation (NRGC) produced a decrease in the threshold of antidromic responses evoked in the tooth pulp following stimulation in the trigeminal nucleus oralis. This primary afferent depolarization (PAD) of Adelta afferents was unaffected by naloxone given intravenously. Bicuculline, given intravenously or applied directly to the terminal region by iontophoresis, selectively antagonised the PAD evoked by stimulating in NRM. The results suggest that GABA is involved in mediating presynaptic inhibition of Adelta tooth pulp input following stimulation in NRM.

Afferent Pathways↗
PubMedDate not supplied

[Effect of the midbrain reticular formation on the response of cortical neurons in the rabbit during learning].

The influence of low-frequency rhythmic stimulation of the midbrain reticular formation (RF) on neuronal activity in the visual cortex was studied in waking, non-immobilized rabbits during elaboration of defensive conditioned reflex to light flashes. In most neurones, the RF stimulation acted in the same direction as the painful reinforcement (electrocutaneous stimulation of the limb), potentiating the effect of the latter and contributing to changes of reactions to light flashes which became a signal of defensive response, with an increase of their similarity to reactions to paired stimuli. In some of the neurones RF stimulation produced changes in structure of phase reactions to light flashes, i.e. intensified the first phase of activation, reduced initial inhibitory pause, and augmented the number of periods of activation--inhibition alternation.

Animals↗
PubMed1984

Postnatal development of spontaneous neuronal discharges in the pontine reticular formation of free-moving rats during sleep and wakefulness.

A developmental study has been made of spontaneous neuronal activity within the pontine reticular formation (giant cell field: FTG) of the rat between one week and one month after birth. Through day 14, the recorded FTG neurons discharged more frequently during quite sleep (QS) than was generally true in older animals. In addition, they were active to the same extent during active-sleep (AS) as during waking-with-movements (AW). In contrast, most of the cells recorded from day 15 on were considerably more active during AS and AW, relative to the QS level, than had hitherto been the case. This new class of neurons, in turn, fell into two sub-groups, one of which was most active during AW while the other was more active during AS. Clomipramine selectively suppressed AS along with the neuronal activity patterns associated with it, and in many cases the QS firing level was even lower than it had been prior to the injection. It is concluded that FTG unit activity is an excellent monitor for controlling the effectiveness of experimental manipulations of AS but is probably not involved in its generation.

Aging↗
PubMed1999

Correlation of primate superior colliculus and reticular formation discharge with proximal limb muscle activity.

We studied the discharge of neurons from both the superior colliculus (SC) and the underlying mesencephalic reticular formation (MRF) and its relation to the simultaneously recorded activity of 11 arm muscles. The 242 neurons tested with a center-out reach task yielded 2,586 pairs of neuron/muscle cross-correlations (normalized, such that perfect correlations are +/-1.0). Of these, 43% had peaks with magnitude as large as 0.15, a value that corresponds to the 5% level of significance, and 16% were as large as 0.25. The great majority of peaks in this latter group was positive. The median lag time within this group was 52 ms, indicating that the neuronal discharge tended to precede the correlated muscle activity. We found a small but significantly higher proportion of cells with these relatively strong correlations in the MRF than in the SC. For both areas, these occurred most frequently with muscles of the shoulder girdle and became less frequent for axial as well as for increasingly distal arm musculature. The results support a role for the SC and MRF in guiding the arm during reach movements via the control of proximal limb musculature.

Action Potentials↗
PubMed1994

Increased responsiveness of pontine reticular formation neurons associated with audiogenic seizure susceptibility during ethanol withdrawal.

Susceptibility to audiogenic seizures (AGS) is observed during ethanol withdrawal (ETX). The pontine reticular formation (PRF) is implicated in the propagation pathway for AGS during ETX. The present study examined the changes in single PRF neuronal firing patterns produced by ethanol and during ETX following repeated intragastrically administered ethanol. Microwire electrode bundles were implanted into PRF and single neuronal responses in freely moving rats were examined. During initial ethanol administration the animals were stuporous, and spontaneous and acoustically-evoked PRF neuronal firing were reduced significantly. During ETX the animals were susceptible to AGS and displayed agitated and irritable behavior. At this time a significant increase in spontaneous and acoustically-evoked PRF neuronal firing was observed. Repetition-induced response attenuation (habituation) of PRF neuronal responses was significantly diminished during ETX, leading to an exaggerated acoustic startle response, which may be a physiological basis for AGS. Previous reports indicate that ethanol enhances the effects of GABA and decreases the effects of glutamate. The PRF neuronal firing increases during EXT in the present study may involve the down-regulation of GABAA receptors and supesensitivity of glutamate receptors reported to occur during ETX, which could contribute to AGS susceptibility. The PRF neuronal firing increases observed in the present study in concord with previous observation of AGS blockade by PRF microinjections during ETX further support an important role of this brain region in the propagation of AGS during ethanol withdrawal.

Acoustic Stimulation↗
PubMed1984

Electrical activity of the reticular formation during aversive and appetitive conditioning in rats.

Evoked potentials (EP) to a conditioned stimulus (CS) were recorded from several parts of the reticular formation (RF), the midbrain central gray (CG), the occipital cortex (OC), the basolateral amygdala and the ventrobasal thalamus during appetitive and aversive classical conditionings in rats. In addition, single unit activity to rewarding CS (+) and punishing CS (-) in a single discriminative classical conditioning was recorded from RF, OC, CG and the tectum. In the EP study, peak-to-peak (p-p) amplitudes, especially of the pontine RF, increased in the initial phase of pre-conditioning, in aversive conditioning and in appetitive conditioning but not in aversive pseudo-conditioning. The p-p amplitude in the pontine RF might reflect an amount of stimulus value the animal received. Slow negative potentials after CS presentation in RF was a reflection of body movements, indicating heavy involvement of RF in motor functions. In the single unit studies, cells which selectively responded to the CS (-) were more frequently found in the medial tegmental area close to the median raphe nucleus as compared to other areas. These results were considered to indicate high sensitivity of RF to the significance of the stimulus, and also the involvement of the medial tegmental area close to the median raphe nucleus in aversive emotional processes. Although many studies employing stimulation or lesion techniques have reported the steady relation between aversive emotional responses and CG, no supporting result was obtained in the present experiments.

Affect↗
PubMed1984

Projections from the superior colliculus to a region of the central mesencephalic reticular formation (cMRF) associated with horizontal saccadic eye movements.

Radioactive wheatgerm agglutinin (WGA) and horseradish peroxidase (HRP) were injected into portions of the mesencephalic reticular formation at sites where electrical stimulation induced either small or large contralateral horizontal saccadic eye movements. We have designated this region as the Central MRF (cMRF). It contains both cells and fiber tracts, including the efferent output of the superior colliculus (SC), destined for the dorsal tegmental decussation and the predorsal bundle. Cells labelled by WGA and HRP injections were found in the intermediate and deep layers of the superior colliculus and the adjacent central gray matter on the ipsilateral side. Injections into the dorsal cMRF, at sites where small saccades were induced, caused labelling of cells in the rostral intermediate layer of SC. Injections into the ventral cMRF, at points where large saccades were elicited, caused labelling of cells in the caudal intermediate layer of SC. The deepest layers of SC and the adjacent central gray were also labelled from the small eye movement region of dorsal cMRF. We interpret these findings to indicate that the intermediate layers of SC send axonal projections to the horizontal eye movement region of the MRF in a topographic fashion. The projection from the intermediate layer is organized so that regions in SC and cMRF related to small or to large eye movements are interconnected. The results support the hypothesis that cMRF is a topographically organized area, involved, like SC, in the control of eye movements. Since both cMRF and the superior colliculus project to areas of the pons and medulla where saccadic eye movements are produced, they could give rise to parallel pathways for the generation of contralateral saccades.

Animals↗
PubMed1997

Anatomical distribution of arm-movement-related neurons in the primate superior colliculus and underlying reticular formation in comparison with visual and saccadic cells.

We recorded from 389 "reach" neurons (two monkeys) in the superior colliculus (SC) and underlying reticular formation (RF) or adjacent periaqueductal grey, whose activity was related to visually guided arm movements. Reach neurons were present from approximately 0.7 mm down to a depth of 6 mm below the surface of the SC (mean 3.7+/-1.3, n=389). Although this mean distribution was different from that of cells with visual (mean depth 1.7+/-1.4 mm, n=283) or saccadic responses (mean depth 2.0+/-1.4 mm, n=232), there was a large amount of overlap. Fifty-five per cent of all reach cells (213/389) were assumed to be located inside the SC. The others were considered to be located in the underlying RF. The characteristics of visual responses and saccadic bursts (e.g. response latencies, discharge rates, burst durations) of arm-movement-related neurons were not different from those of typical visual or saccade cells in the SC. Although reach neurons could be recorded in a large area of the SC, they were found more often in the lateral than in the medial parts (chi-squared=19.3, P<0.001). Possible pathways by which arm-movement-related neuronal activity in and below the SC might gain access to spinal motor structures are discussed. The location of arm-movement-related neurons described in this study is in accordance with the known target areas of skeletomotor-related corticotectal projections and with the sites of origin of tectofugal pathways. It is concluded that this population of reach cells is in a position to relay and transmit limb movement information to the spinal motor system, where it may influence (or interact with) motor commands coming from other motor centres.

Animals↗
PubMed1995

Monosynaptic projections from the medullary gigantocellular reticular formation to sympathetic preganglionic neurons in the thoracic spinal cord.

Microinjection of L-glutamate into a restricted area of the medullary gigantocellular reticular formation, the gigantocellular depressor area (GiDA), lowers arterial pressure. Unlike the nuclei tractus solitarii and the caudal ventrolateral medulla, the two principle medullary vasodepressor areas, the GiDA projects directly to the spinal cord and not to the rostral ventrolateral medulla (Aicher et al. [1994] Neuroscience 60:761-779). We investigated whether neurons within GiDA directly innervate autonomic areas of the thoracic spinal cord. Fluoro-Gold injected into the thoracic spinal cord labeled neurons within functionally defined vasodepressor sites in the GiDA in the same animal. To examine the morphology of GiDA efferents to the spinal cord, the anterograde tracer Phaseolus vulgaris-leucoagglutinin was iontophoresed into the GiDA, and efferent processes in the intermediolateral cell column and nucleus intercalatus spinalis were examined by electron microscopy. Labeling was confined to axons and axon terminals (n = 144) that usually contained primarily small clear vesicles, contacted large and small dendrites, and formed symmetric (inhibitory) synapses. To determine whether some of the postsynaptic targets of GiDA efferent terminals in the thoracic spinal cord were sympathoadrenal preganglionic neurons, these neurons were retrogradely labeled from the adrenal gland with Fluoro-Gold in rats that had deposits of the anterograde tracer, biotinylated dextran amine (BDA), in the GiDA. Some BDA-containing terminals formed symmetric synapses with dendrites containing Fluoro-Gold. We conclude that a population of neurons in the GiDA monosynaptically innervates some sympathetic preganglionic neurons. The findings suggest the presence of a novel reticulospinal sympathoinhibitory projection originating in the GiDA.

Adrenergic Fibers↗
PubMed1990

Functional organization within the medullary reticular formation of intact unanesthetized cat. II. Electromyographic activity evoked by microstimulation.

1. The present study has examined the detailed organization of the medullary reticular formation (MRF) as revealed by microstimulation (33-ms trains of 0.2-ms duration pulses at 330 Hz and 35 microA or less) in the intact, chronically implanted, unanesthetized cat. Stimulus-locked electromyographic (EMG) responses were recorded from flexors and extensors of each of the four limbs, as well as bilaterally from muscles of the neck and back, during stimulation of the same 592 loci that formed the basis of the preceding article. 2. The thresholds of the responses were different for each group of muscles, with, on the average, the neck muscles being activated at the lowest range of currents, 13.8-16.5 microA; forelimb muscles at 16.9-17.9 microA; back muscles at 25.4-25.7 microA; and hindlimb muscles at 21.1-25.7 microA. 3. Whereas stimulation within the MRF evoked movement of the head only to the stimulated side (preceding article), analysis of the EMG responses showed there was frequently bilateral activation of the neck muscles. Similarly, even though stimulation produced predominantly ipsilateral elbow flexion and contralateral elbow extension, most loci caused cocontraction of antagonistic muscles at these joints. Cocontraction was also frequently observed for the hindlimbs. Reciprocal activation of antagonistic muscles was less frequent but was observed in the ipsilateral forelimb as well as in both hindlimbs; it was never observed in the contralateral forelimb. 4. Although excitatory responses were observed from widespread regions for all of the muscles under study, those regions of the MRF that evoked the strongest responses in each muscle showed a large degree of segregation. Muscles of the ipsilateral forelimb were most strongly activated from the rostrodorsal MRF, whereas muscles of the contralateral forelimb were most strongly effected by stimulation caudoventrally. Muscles of the hindlimbs were more strongly activated from the rostral brain stem, although with some exceptions. Responses in axial muscles were evoked from widespread regions of the brain stem but were concentrated further caudally than were the limb muscles. 5. Excitatory responses were much more prevalent than inhibitory responses and were evoked from all regions of the MRF, including the most caudal and ventral areas. The shortest latency responses in each track were, on the average, as follows: 6.6-8.8 ms for the neck; 11.2-13.4 ms for the forelimbs; 13.8-14.2 ms for the back; and 15.9-17.2 ms for the hindlimbs. Inhibitory responses were also evoked from widely distributed regions, which were intermingled with those loci evoking excitatory responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Organization of forebrain projections from the medullary reticular formation in the North American opossum. Evidence for connectional heterogeneity.

We have employed axonal transport techniques to study the organization of projections from the medullary reticular formation (RF) to the forebrain of the North American opossum. The results of retrograde transport studies using large injections of horseradish peroxidase (HRP), wheat germ agglutinin conjugated to HRP (WGA-HRP), and fluorescent markers suggest that all nuclei of the medullary RF project to the forebrain although the parvocellular reticular nucleus makes only a very small contribution. When injections of 3H-leucine or WGA-HRP are centered within areas shown by the retrograde transport studies to innervate the forebrain, characteristic patterns of orthograde labeling are produced. In most cases labeled axons form a major pathway which splits into dorsal and ventral divisions. The dorsal division innervates the parafascicular and central nuclei of the thalamus as well as the pretectum. In contrast, the ventral division projects to the lateral hypothalamus, the zona incerta, the ventral and dorsal lateral geniculate nuclei, the lateral part of the ventrobasal nucleus of the thalamus, the lateral preoptic area, the septal-diagonal band region, and the cerebral cortex. When injections are centered within specific ventrolateral areas of the medullary RF, ventral division labeling is also found within the dorsomedial, paraventricular and supraoptic nuclei of the hypothalamus. Relatively small injections of HRP or WGA-HRP into specific areas of the forebrain produce labeling which suggests that some areas receive projections from all nuclei of the medullary RF, whereas others do not. Our results suggest that forebrain projections of the medullary RF, like those to the spinal cord, are connectionally heterogeneous.

Amino Acids↗
PubMed1987

Influence of rostral and caudal brain stem reticular formation on thalamic neurons.

Single neuronal activity was recorded from the diffuse thalamic system. Influence of the rostral desynchronizing and caudal synchronizing structures of the brain stem reticular formation on these neurons was studied. Rostral stimulation produced an increase and caudal stimulation a decrease in the thalamic unit firing. A possible mechanism by which the brain stem reticular structures influence the cortical neurons is proposed on the basis of these findings.

Animals↗
PubMed1990

The rat parvocellular reticular formation: I. Afferents from the cerebellar nuclei.

The present report elucidates the location of the cells of origin of the cerebellar nuclear-parvocellular reticular projection in the rat. Injection of horseradish peroxidase (HRP) into the parvocellular reticular formation resulted in labeled neurons in the dorsolateral protuberance of the contralateral medial nucleus and bilaterally in the dorsolateral hump region and the large celled subgroup of the lateral nucleus. A small number of labelled cells were found in the middle part of the contralateral medial nucleus. The few HRP-positive cells in the interpositus nuclei were adjacent to the dorsolateral hump. No labeled neurons were observed in the caudomedial portion of the medial nucleus or the small-celled region of the lateral nucleus.

Animals↗
PubMed1986

Learning deficits in rats with early neurotoxic lesions to the globus pallidus, substantia nigra, median raphe or pontine reticular formation.

Previous studies have shown that weanling rats with electrolytic lesions of the globus pallidus (GP), substantia nigra (SN), median raphe (MR) or pontine reticular formation (PRF) are deficient in learning a wide variety of laboratory tasks. The current study was designed to investigate whether this nonspecific learning deficiency is due to destruction of cells intrinsic to these subcortical regions or to fibers passing through these regions. Accordingly, neurotoxic lesions of the GP, SN, MR or PRF were made in weanling rats using ibotenic acid. Rats were subsequently required to learn a visual discrimination, a 3-cul maze and a nonvisual (incline plane) discrimination. While those groups with GP, SN or MR lesions showed significant deficits on all three problems, only the animals with GP lesions exhibited deficits comparable in magnitude to those associated with corresponding electrolytic lesions. Animals with lesions to the PRF were impaired only on the nonvisual discrimination. These results suggest that while destruction of neurons alone within the GP, SN or MR can produce a nonspecific learning impairment, the combined destruction of neurons and fibers of passage within the SN, MR or PRF produces a more profound learning deficit.

Animals↗