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Results for “Reticular Formation”

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PubMed1983

Direct projections to the pretectum and the midbrain reticular formation from auditory relay nuclei in the lower brainstem of the cat.

Direct projections to the pretectum and the midbrain reticular formation from auditory relay nuclei in the lower brainstem were examined by the retrograde and anterograde tracer methods in the cat. After horseradish peroxidase (HRP) injection into the pretectomesencephalic reticular region (Pt-MRF), which includes caudoventral regions of the pretectum and rostrodorsal regions of the midbrain reticular formation, labeled neurons were seen in the dorsal nucleus of the lateral lemniscus (DLL), the pericentral (PC) and external (EN) nuclei of the inferior colliculus (IC), the rostral process of IC (RP) and the nucleus of the brachium of IC (NB); no labeled neurons were found in the main laminated portion of the central nucleus of IC. Subsequently, tritiated leucine was injected into DLL, EN, RP or NB for autoradiographic fiber tracing. After injection into DLL or EN, terminal labeling was confined to the ventral portions of the anterior pretectal nucleus. After injection into RP or NB, heavy terminal labeling was observed in the midbrain reticular formation, extending dorsally into the anterior pretectal nucleus. Thus, 3 sectors are distinguishable in Pt-MRF in terms of termination of fibers from the midbrain auditory relay nuclei; the dorsomedial, intermediate or ventrolateral Pt-MRF sector receives fibers arising from DLL, RP or NB, respectively. Fibers from EN terminate only in the dorsal portion (pretectal regions) of the intermediate sector.

Afferent Pathways↗

PubMedDate not supplied

[Effect of a dominant focus in the midbrain reticular formation on the functional state of the motor analyzer].

In chronic experiments on rabbits it was shown that after two-three stimulations of the midbrain reticular formation (stimulation frequency 200 cps, pulse duration 0.1-0.5 ms, voltage 1-3 V, stimulation duration 5 s) a dominant focus was formed in it, which led simultaneously to a statistically significant increase in the amplitude of evoked potential in the sensorimotor cerebral cortex and in motor reactions to afferent stimuli (light, sound). The state of increased excitability persisted for a long time (10-30 days depending on the number of stimulations of the reticular formation). Multiple stimulation of the reticular formation (5-12 times) led to creation of a pathological defensive dominant, manifested in a unitype series of legs movements in response to light and sound stimuli.

Animals↗

PubMed2005

Serotonergic reticular formation cells in Rana pipiens: categorization, development, and tectal projections.

The reticular formation contributes serotonin to many brain regions, including the optic tectum. We examined the organization and development of its serotonergic neurons in the leopard frog. Serotonin-immunoreactive (5-HT-ir) cells in adult frogs were organized into 10 distinct populations that were identified on the basis of their location and cellular morphology. Populations ranged in size from 16 to 2,066 cells and sometimes spanned more than one previously identified nuclear region. Four of the ten populations were absent in tadpoles. The remaining populations, though present, had two contrasting patterns of development. Half of the populations were established early and showed little change in numbers during tadpole stages but increased in size in juvenile and adult frogs. The other half increased dramatically during tadpole stages but failed to add many more cells in juveniles and adults. Three populations provided 90% of the serotonergic projections from the reticular region to the adult optic tectum. These projections were established early in development and likely originated from the dorsal raphe, median raphe, raphe pontis, raphe magnus, and reticularis pontis oralis. Termination sites were located in midtectal layers and were not topographically organized. We conclude that serotonergic cells within the reticular formation of the leopard frog have an organization similar to that found in mammals, that the overall increase in numbers of these cells is attributable to growth in different cell populations at different stages, and that input from this region changes activity levels in the optic tectum in a global rather than a site-specific manner.

Animals↗

PubMed1981

[Primary trigeminal projection to the brain stem-reticular formation. Experimental study in the rat].

By means of a transauricular approach, the trigeminal ganglion of the rat was lesioned in order to study the presence and distribution of the primary trigeminal afferents to the brain stem reticular formation. We could observe such projections to the reticular formation close to the trigeminal nuclei (lateral part of the n. reticularis ventralis and dorsalis, n. reticularis parvocellularis, reticular zone between the trigeminal n. principalis and the n. motorius trigemini) and also to the reticular formation more medially situated (medial part of the n. reticularis dorsalis and ventralis, n. reticularis gigantocellularis and n. reticularis pontis caudalis). Topographically, those projections correlated fair well with the extent of the trigeminal nuclei more related with sensorial transmission (n. principalis and subnuclei oralis and caudalis), specially the most medial of them. Moreover, although in a very much lesser intensity, we could see projections on the nuclei pallidus and magnus of the raphe system, and on the caudodorsal part of the central grey matter. The possible modulatory actions on the sensorial transmission and motor coordination of those projections are discussed.

Afferent Pathways↗

PubMed1981

[Reactions of reticular formation neurons in the rat during functional suppression of the cortical representation of the extremity stimulated].

Responses of single neurons of the reticular formation were studied in the unanaesthetized immobilized rats. Local cooling of the cortical sensory representation of the stimulated forepaw evoked reversible changes in the responses of most studied units (60 of 86) in different nuclei of the reticular formation. The responses of 25 cells changed only during stimulation of the paw the sensory cortex of which was cooled. The changes of the other unit responses to the same stimulus were more strong (in 13 neurons) or almost equal (in 22 neurons) to the changes in responses to the stimulation of the another paw the sensory projection of which was not cooled. The data suggest that local alteration of the signal transfer in the cortex changes the conditions for the transfer of the same signal in the reticular formation.

Animals↗

PubMedDate not supplied

Chronic pain as a reticular formation syndrome.

Evidence was previously presented to support the thesis that chronic pain is activated by neuronal elements that make up the multisynaptic short axon core of the reticular system (Andy and Peeler 1985). The present thesis, that chronic pain is a reticular formation syndrome, is based on a retrospective analysis of four patients with chronic pain who were successfully treated with a lesion in the anterior thalamus and stimulation electrode implants in the posterior thalamus and pontomesencephalic brain stem. The reticular formation was the common underlying anatomic substrate at those three sites. In addition to chronic pain, all the patients had other symptoms attributable to other body organs and systems. The number and type of symptoms that made up the syndrome differed between patients. Symptoms making up the core of the syndrome were pain, anxiety, nervousness, insomnia, and depression. Experimental and clinical findings are briefly presented to demonstrate the various reticular formation sites, pragmatically considered "reticular functional systems," from which symptoms may arise. It is hypothesized that the symptoms are recruited by a low threshold "pain oscillator" that is generated at one reticular site and subsequently permeates the rest of the reticular system. Therapeutic stimulation inactivates the low threshold system by "jamming" it.

Adult↗

PubMed1990

Disruptive effect of the mesencephalic reticular formation on tonic immobility in guinea pigs.

Cholinergic stimulation of the mesencephalic reticular formation with carbachol impairs the induction of tonic immobility (TI) by restraining maneuvers and reduces the duration of immobility episodes in guinea pigs. This finding apparently disagrees with the hypothesis that environmental monitoring occurs during TI which permits the animal to evaluate the best time for escape. It is possible that this monitoring involves circuits and neurotransmitters other than the ascending cholinergic system originating in the mesencephalic reticular formation.

Animals↗

PubMed1995

Activity of neurons in the medial pontomedullary reticular formation during orienting movements in alert head-free cats.

1. Single unit activities of 236 neurons were recorded in the medial pontomedullary reticular formation during visually triggered orienting gaze shifts in 10 alert cats under head-free conditions using movable tungsten-needle electrodes attached to the skull. The activities were analyzed mainly in relation to the head movement that was triggered by presentation of a light-emitting diode (LED) in one of eight directions separated radially by 45 deg after fixation of the center LED. Of these, 120 neurons were recorded in the pontine reticular formation, chiefly in the nucleus reticularis pontis caudalis, and the remaining 116 were in the medullary reticular formation, chiefly in the nucleus reticularis gigantocellularis. Activities of 65 pontine and 65 medullary neurons were modulated in relation to the dynamic phase of orienting movements ("orienting-related neurons"). Activities of the remaining neurons were modulated either irregularly or not at all during orienting movement ("irregular or no-response neurons"). Input from the contralateral superior colliculus and cerebral cortex and projections to the spinal cord were also investigated. 2. Among the orienting-related neurons, 62 pontine and 55 medullary neurons showed increases in activity preceding the onset of eye and head movement by 0-155 ms ("pretype"). Three pontine and 10 medullary neurons showed increases in activity only after the onset of movement ("posttype"). Of the pretype neurons, 61 pontine and 51 medullary neurons showed directional preference of activity ("directional" neurons). One pontine and four medullary neurons were classified as "omnidirectional" because these neurons increased activity preceding movements in all directions tested, and no directional preference was apparent. 3. In the pretype-directional cells, the average firing frequency during bursts was correlated with amplitude and angular velocity of head movements. Activities of the directional neurons during movements in the eight different directions could be well fitted with cosine functions in the majority of cases. The preferred directions of most pontine neurons and of about half the medullary neurons, as determined by first-degree sinusoidal regression analysis, were distributed around the ipsiversive horizontal axis. However, there were also a considerable number of neurons whose preferred directions were upward, downward, contraversive, or oblique in the medulla. 4. Among the directional cells preferring ipsiversive horizontal movements, 11 pontine neurons showed activity, the onset of which was locked to visual stimuli with latencies of 40-70 ms, in addition to phasic discharges locked to the onset of movement. This "stimulus-locked activity" was sometimes modulated depending on the attentional state of the animal.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1975

[Modulation of the photically evoked potentials in the motor cortex of cats by influences of the somatosensory system and the reticular formation].

The influence of somatosensor stimulation and electric stimulation in the mesencephalic reticular formation upon evoked potentials (EP) of the motor cortex (MC) produced by electric stimulation of the Chiasma opticum and the Corpus geniculatum laterale, respectively, was investigated in unnarcotized, immobilized cats. By preliminary electrical stimulation of the contralateral front limb, intensity-dependent changes of the early positive component of the EP in the MC could be produced. Similar changes were found after passive movement of the limb and following electrical stimulation in the reticular formation of the mesencephalon. The EP in the MC completely disappeared after i.v. administration of 15 mg/kg Nembutal. It is concluded that the impulses reaching the MC after stimulation in the visual system can be modulated in various ways, and thus exhibit a relatively high information content. Possible mechanisms of the modulating influences and their significance are discussed.

Animals↗

PubMed1994

Seizures during ethanol withdrawal are blocked by focal microinjection of excitant amino acid antagonists into the inferior colliculus and pontine reticular formation.

Physical dependence on ethanol can result in seizure susceptibility during ethanol withdrawal. In rats, generalized tonic-clonic seizures are precipitated by auditory stimulation during the ethanol withdrawal syndrome. Excitant amino acids (EAAs) are implicated as neurotransmitters in the inferior colliculus and the brain stem reticular formation, which play important roles in the neuronal network for genetic models of audiogenic seizures (AGSs). Ethanol blocks the actions of EAAs in various brain regions, including the inferior colliculus. In this study, dependence was produced by intragastric administration of ethanol for 4 days. During ethanol withdrawal, AGSs were blocked by systemic administration of competitive or noncompetitive NMDA antagonists 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) or dizocilpine (MK-801). Focal microinjections of NMDA or non-NMDA antagonists into the inferior colliculus or the pontine reticular formation also inhibited AGSs. MK-801 was the most potent anticonvulsant systemically. When injected into the inferior colliculus, CPP had a more potent anticonvulsant effect than either MK-801 or the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. The inferior colliculus was more sensitive than the pontine reticular formation to the anticonvulsant effects of both competitive NMDA and non-NMDA antagonists. The results of the present support the idea that continued ethanol administration may lead to development of supersensitivity to the action of EAAs in inferior colliculus and pontine reticular formation neurons. This may be a critical mechanism subserving AGS susceptibility during ethanol withdrawal.

Acoustic Stimulation↗

PubMed1986

[Participation of neurons of the midbrain reticular formation of the cat in conditioned reflex activity].

Spike discharges of mesencephalic reticular formation neurons were investigated during classical and instrumental conditional reflexes in chronic experiments on cats. Neurons were divided into several functional groups according to patterns of their responses. Two groups of neurons produced continuous tonic spike discharges. One of them was activated by positive conditional stimuli and did not respond to the same stimulus after extinction. Another group was involved in reaction only after extinction. Thus the neurons of these two groups developed additional tonic ascending action not only during fulfillment of conditional reflex but under its internal inhibition too. Neurons of the third group revealed double phasic responses: the first--to sound and the second--in connection with initiation of the conditioned movement. They decreased the level of the background and evoked activity during differentiation and extinction. Initial changes of reticular neuron responses were similar under conditioning and under pseudoconditioning. It is concluded that mesencephalic reticular formation takes an active and differential participation in elaboration, fulfillment and internal inhibition of classical and instrumental conditional reflexes.

Animals↗

PubMed1976

[Development of the brain stem reticular formation during ontogenesis of lower simians as compared with man].

The work has shown a number of common features in the structural organization of the brain stem reticular formation in the adult rhesus monkey and man. According to the peculiar features and developmental features the reticular nuclei may be divided into 3 sections (median, medial and lateral) having different genesis. In ontogenesis all the nuclei of the reticular formation undergo differentiation and specialization due to the complication of the brain as a whole. This process, however, goes differently in ontogenesis of the macaque and man which can be seen in the heterochronous rate of their development, namely, in the macaque the terms of maturation of the reticular nuclei are somewhat more accelerated. The work shows changes in the density of cells, the volume of neurones and all the reticular formation in relation to the volume of the brain stem as a whole. However, the differences found in ontogenesis of the macaque and man are mainly of quantitative and idioadaptive character.

Animals↗

PubMed1985

[Ascending and descending efferent pathways of the midbrain reticular formation of the cat (radioautographic study)].

By means of the anterograde axoplasmic transport technique for a mixture of labelled aminoacids (3H-leucine and 3H-proline), ascending and descending systems of the reticular formation fibers in the cat mesencephalon have been studied. Projections from the mesencephalon reticular formation (MRF) ascend to the subthalamus, lateral, dorsal and periventricular hypothalamus, to the periventricular nuclei of the midline and to the intralaminar nuclei of the thalamus. The descending pathways project to the grey substance surrounding the aqueduct of cerebrum, locus coeruleus, parabrachial region and reticular formation of the pons and medulla oblongata. The projections to the reticular nucleus of the thalamus, ventral nucleus of the external geniculate body and superior colliculi arise from the dorsal half of the MRF, and projections to the striatum, lateral reticular nucleus of the medulla oblongata--from its ventral half. Most of the structures are reciprocally connected with the MRF.

Animals↗

PubMed1993

Crossed reticular formation connections that mediate the startle reflex in rats.

The startle response is a bilateral response even when elicited by unilateral acoustic or tactile stimuli. Similarly, unilateral electrical stimulation of the reticular formation also elicits a bilateral startle-like response. To examine whether crossed reticular formation connections can distribute the effects of unilateral stimulation across the midline, we delivered one pulse to the caudal pontine (RPC) or medullary reticular formation (MRF) and a second pulse to the opposite side of the brain, at various interpulse intervals. The symmetric collision effects suggest that axons which produce at least 37% (range 23-53%) of the startle response efficacy cross from RPC to RPC with a mean conduction velocity of 13 m/s. Similar collision effects were observed between RPC and MRF sites but at shorter conduction times. To examine which axons might cause these collision effect, the axonally transported label DiI was injected post mortem into 37 RPC sites. Many coarse axons were observed to cross in fascicles between bilateral RPC sites and then separate in the contralateral RPC. The fiber diameters and trajectories of these DiI-labelled axons are consistent with the conduction velocities and trajectories of the substrates mediating the startle-like response determined in collision tests.

Animals↗

PubMed1984

A generalized learning deficit in albino rats with early median raphe or pontine reticular formation lesions.

Recent studies suggest that lesions of the median raphe or pontine reticular formation in adult rats are associated with a nonspecific (generalized) learning impairment. The present study showed that lesions in the region of the median raphe or pontine reticular formation in 21 day old rats likewise produced a nonspecific learning impairment, as evidence by significant deficits on a visual discrimination, nonvisual incline plane discrimination, 3-cul maze, and three simple spatial problems. The finding that relatively large lateral pontomesencephalic lesions did not lead to deficient learning of any of these tasks indicates that lesion locus rather than lesion size is responsible for the production of the learning deficits observed in this study.

Animals↗

PubMed1985

Phrenic afferent input to the lateral medullary reticular formation of the cat.

The afferent inputs from phrenic nerve stimulation to the lateral reticular formation of the lower brain stem were studied in anesthetized spontaneously breathing cats. The activity of reticular neurons was recorded by means of extracellular tungsten microelectrodes. Electrical stimulation of the central end of the right phrenic nerve evoked excitatory or inhibitory responses in the lateral reticular nucleus (LRN), in the nucleus ambiguus (AMB) and in a region dorsal to the AMB of ipsi- and contralateral sides. Phrenic afferents belonging to the flexor reflex afferent group were involved in these responses. The discharge pattern of the respiratory related units (RRU) of the AMB were exceptionally affected by phrenic nerve stimulations. It is concluded that high threshold phrenic afferents relay in the LRN before projecting to the cerebellar cortex. The overlapping of respiratory and non-respiratory afferents in the reticular formation may participate to the adaptations of respiratory and somatomotor functions during specific behaviors.

Afferent Pathways↗

PubMed1978

A cell group associated with vertical eye movements in the rostral mesencephalic reticular formation of the monkey.

A cytologically distinct group of cells in the rostral mesencephalic reticular formation was strongly labelled by injections of anterograde tracer substances into the caudal paramedian pontine reticular formation (PPRF) of the monkey. The cell group lies ventral to nucleus of Darkschewitsch (nD), rostral to the interstitial nucleus of Cajal (iC) and the tractus retroflexus (TR). It receives inputs from areas which control eye movements, PPRF and the vestibular nuclei, and sends efferents to the oculomotor nucleus. Physiological, anatomical and clinical evidence support the conclusion that this cell group is involved in the generation of vertical eye movements. In an attempt to be anatomically specific the name rostral interstitial nucleus of the medial longitudinal fasciculus (rostral iMLF) has been used.

Animals↗

PubMed1981

Evoked potentials in the reticular formation during auditory conditioning of the corneal reflex in the chronic decerebrate rat.

The chronic decerebrate rat preparation was used to study electrical activity in the reticular formation during development of the classically conditioned eyeblink reflex to a tone. With persistent training a conditioned blink reflex was established in 8 out of 11 rats. A control group of four rats received unpaired presentations of the conditioned and unconditioned stimuli and served as a control. Evoked potentials in response to the auditory conditioned stimulus were recorded in medullary and pontine reticular nuclei during conditioning. The amplitude of the main negative wave of the response showed a significant increase during the establishment of a conditioned response but the amplitude of potentials recorded from the medullary reticular formation showed no significant change. There was no change in the amplitude of potentials recorded in either the pontine or medullary reticular nuclei in the control "pseudoconditioning" group or in the three rats which underwent training but did not develop a conditioned response. It is concluded that structures within the pontine reticular formation play an active part in the acquisition phase of the conditioned blink reflex in the chronic decerebrate rat.

Acoustic Stimulation↗