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At least 19 recordsLinked to original sources
PubMed1994

Descending projections from the superior colliculus to the reticular formation around the motor trigeminal nucleus and the parvicellular reticular formation of the medulla oblongata in the rat.

We observed by the anterograde and retrograde tracing techniques in the rat that the lateral part of the superior colliculus (SC), where the nigrotectal fibers from the dorsolateral part of the substantia nigra pars reticulata (SNr) terminated, sent projection fibers to the reticular region around the motor trigeminal nucleus (RFmt) and parvicellular reticular formation (RFp) of the medulla oblongata, where many premotor neurons for the orofacial motor nuclei were known to be distributed. The SC neurons sending their axons to the RFmt and RFp were mainly located in the stratum griseum intermedium, and additionally in the stratum griseum profundum. Our results suggest that neuronal signals conveyed through the nigro-tecto-bulbar pathway to the RFmt and RFp may exert control influences upon oral behavior.

Animals↗
PubMed1988

Evolution of the reticular formation.

The reticular formation of mammals contains numerous nuclei which can be recognized by their projection patterns, cytoarchitectonics, and neuropeptide/neurotransmitter content. We have identified reticular nuclei in representatives from numerous reptilian groups and ascertained presence or absence of these reticular nuclei in an attempt to use neuronal occurrence as a tool to determine phylogenetic relationships. Recently these studies have been extended to two elasmobranchs, a galeomorph shark and a ray. In this report, we concentrate on three medullary spinal projecting reticular nuclei, reticularis gigantocellularis, reticularis magnocellularis, and reticularis paragigantocellularis. We found that all three nuclei were present in rats, lizards, and elasmobranchs, but one nucleus was absent in crocodilians, and two nuclei were absent in turtles. Thus brain organization may give us clues to phylogenetic relationships. Moreover, these three reticular nuclei exhibited remarkably similar cellular morphology in mammals, reptiles, and elasmobranchs.

Animals↗
PubMed1985

Noxious cardiac input onto neurons in medullary reticular formation.

Responses of reticular formation neurons to electrical stimulation of cardiopulmonary afferents as well as cardiac application of bradykinin were determined. Experiments were performed in chloralose anesthetized, vagotomized and sino-aortic denervated cats paralyzed with pancuronium. The medial reticular formation in the medulla was explored with microelectrodes until single neurons responding to electrical stimulation of the cardiac nerve were isolated. Electrical stimulation evoked an early (latency less than 40 ms) burst only (most common), both an early burst and a late burst, or a late (latency greater than 90 ms) burst only (least common) from medullary neurons. Cells were subsequently tested for responses to epicardial or intracardiac administration of bradykinin. Of the 62 neurons tested, one-third responded to bradykinin. Cells typically exhibited a bursting pattern of spontaneous activity; bradykinin enhanced the duration and intensity of the bursts. Neurons were also tested for somatic, visual and auditory input. Most cells were excited by somatic as well as auditory stimuli, while a fewer number also received visual input. Furthermore, most cells responsive to epicardial bradykinin also received these other inputs. The neurons recorded in this study may mediate cardiac pain, cardiovascular reflexes, alerting responses, and/or arousal responses.

Animals↗
PubMed1985

[Relay levels of acoustic and tactile startle reflexes in the reticular formation of the cat].

Reticular mechanisms of startle reflexes evoked by acoustic and tactile stimulation were studied in cat anesthetized with chloralose. Marked similarity in changes of both reflexes following surgical lesions and reversible hydrocompression blockade of the medial brain stem reticular formation structures were found. The data obtained evidenced for similarity of reticular substrates of these nonnociceptive reflexes (the pontine reticular formation, especially nucleus reticularis, pontis caudalis) in contrast to nociceptive spino-bulbo-spinal startle reflexes relayed mainly over the bulbar reticular formation.

Animals↗
PubMed1983

[Comparative analysis of the role of the secondary and primary somatosensory areas of the cortex in the formation of the somatic responses of the reticular formation of the medulla oblongata in the rat].

Evoked potentials and unit activity of the medullar reticular formation were investigated in unanesthetized, immobilized albino rats either under cooling or lesion of the cortical representation of one of stimulated forepaws. The local cooling (lesion) of the cortex area C2 changed the amplitude and time parameters of the reticular evoked potentials to electrically stimulated contralateral forepaw whose representation was affected. As compared with the effect of C1 inhibition, changes in the amplitude and time parameters were insignificant and were not more then 30% and 10 ms, respectively. There were more corticofugal influences from C1 than from C2, both in experiments with evoked potentials and in analysis of somatic responses of reticular neurons. Thus corticofugal control of the medullar reticular formation in albino rats implemented by neuronic mechanisms of somatosensory areas C2 and C1 is qualitatively and quantitatively different.

Animals↗
PubMed2000

The feedback circuit connecting the superior colliculus and central mesencephalic reticular formation: a direct morphological demonstration.

The central mesencephalic reticular formation (cMRF) has been distinguished from the surrounding reticular formation due to its involvement in the control of saccades. A role in saccade function has been proposed for this region based on electrical-stimulation experiments, its neuronal activity, and its pattern of connections. The present study was undertaken in an attempt to further characterize the location of the central mesencephalic reticular formation by anatomical methods and to examine its connections with the superior colliculus at the neuronal level. Biotinylated dextran amine (BDA) was injected into the superior colliculus of two cynomolgus monkeys (Macaca fascicularis). This resulted in the retrograde labeling of a large number of neurons in a restricted area of the mesencephalic reticular formation. They were distributed bilaterally, with an ipsilateral predominance, forming a cellular band in the ventral half of the midbrain reticular formation that was 2.7 mm in its rostrocaudal extent. Its rostral pole lay dorsolateral to the red nucleus and ventrolateral to, but not immediately adjacent to, the interstitial nucleus of Cajal. The cell band was widest caudally, where it occupied an area of approximately 2.7 mm wide and 2 mm in depth. Labeled neurons displayed a wide variety of multipolar somatic shapes and sizes, with long, slightly tapering, sparsely branched dendrites. Tectal terminal arbors were also labeled within the mesencephalic reticular formation. They were concentrated bilaterally, with an ipsilateral predominance, in the same areas that contained retrogradely labeled neurons. Numerous, primarily en passant labeled boutons of various sizes and shapes were seen in close association with both labeled and unlabeled neurons. They formed axosomatic and, more commonly, axodendritic relationships with labeled neurons. The extensive relationship of labeled terminals and labeled cells suggests the existence of a strong interconnection between the deeper layers of the colliculus and the central mesencephalic reticular formation neurons projecting back to the tectum. The bidirectional neural circuit directly demonstrated in this study presumably provides an anatomical substrate for feedback modification of gaze signals generated in the colliculus. However, the presence of tectal terminals around unlabeled reticular neurons suggests that the collicular signal may also be fed forward to the downstream targets of the central mesencephalic reticular formation.

Animals↗
PubMed1996

Processing of vestibular and other inputs by the caudal ventrolateral medullary reticular formation.

Lesions of the lateral medullary reticular formation caudal to the obex abolish vestibulosympathetic and somatosympathetic responses; this area also contains neurons that mediate baroreceptor reflexes. Recordings were made from neurons in the caudal medullary reticular formation of cats that were decerebrate or anesthetized using alpha-chloralose-urethan to determine whether common neurons responded to electrical stimulation of vestibular and hindlimb afferents and had cardiac-related (i.e., baroreceptor) inputs. Many neurons in the ventrolateral portion of the caudal reticular formation received labyrinthine inputs, and they were interspersed with neurons that received baroreceptor signals. However, virtually none of the units received convergent baroreceptor and vestibular inputs, suggesting that separate pathways from the caudal ventrolateral medulla mediate baroreceptor and vestibulosympathetic reflexes. Furthermore, the neurons that received labyrinthine signals could not be antidromically activated from electrodes inserted into the rostral ventrolateral medulla, which is known to mediate vestibulosympathetic responses; thus an indirect pathway must convey vestibular inputs from the caudal to rostral medullary reticular formation. Over 75% of both neurons with baroreceptor inputs and cells with vestibular signals responded to sciatic nerve stimulation, suggesting that more than one pathway from the caudal medulla may mediate somatosympathetic responses.

Afferent Pathways↗
PubMed1988

Neuroanatomy of the oculomotor system. The reticular formation.

The afferent and efferent connections of specific subdivisions of the reticular formation involved in the control of gaze are reviewed. Three regions of the medial brainstem reticular formation: the paramedian pontine reticular formation (PPRF), the dorsomedial rostral medullary reticular formation and the rostral interstitial nucleus of the MLF (riMLF) have direct projections to the extraocular motor nuclei, and play a well-defined role in the generation of saccadic eye movements only. The interstitial nucleus of Cajal (iC) also has direct premotor control of vertical extraocular motoneurons and is probably involved in the maintenance of vertical eye position. Reticulospinal neurons, which modulate the activity of neck and postural musculature, originate from all these regions. The neuroanatomy of other cell groups associated with the reticular formation are also described: the central mesencephalic reticular formation (cMRF), the posterior commissure nuclear complex (nPC), nucleus reticularis tegmenti pontis (nrtp), nucleus intercalatus (nic), nucleus of Roller (Ro) and nucleus interfascicularis hypoglossi (ifh), nucleus supragenualis (sg) and finally the cell groups lying within the paramedian tracts (pmt) of the pons and medulla. These have diverse and generally less well understood roles in the control of gaze.

Afferent Pathways↗
PubMed1985

Comparative effects of convulsant drugs on the sensory responses of neurons in the amygdala and brainstem reticular formation.

The sensory responses of neurons in the amygdala and mesencephalic reticular formation in the cat were enhanced following the intravenous administration of subconvulsant doses of bicuculline, strychnine, bemegride, pentylenetetrazol and physostigmine. The degree and intensity of the enhancement of the response was considerably greater in the reticular formation than in the amygdala. The latency of the response in simultaneously-recorded pairs of neurons in the amygdala and reticular formation was significantly shorter in the mesencephalic reticular formation. The enhancement induced by convulsants does not appear to be transmitter-specific, since enhancement was produced with sequential administration of convulsant drugs which affect gamma-aminobutyric acid (GABA), glycine or acetylcholine. These findings suggest that the reticular formation is involved, to a larger degree than the amygdala, in the ability of sensory stimuli to initiate generalized convulsive seizures in animals treated with these convulsant drugs. The enhancement of the response in the hippocampus and cortex, which has previously been shown to exhibit a longer latency and a lower degree of enhancement than the reticular formation, coupled with the findings in the amygdala, suggest that the reticular formation may mediate the enhancement of the response of these other regions of the brain. The spread of the enhancement of the response to other structures in the brain via the widely distributed output pathways from the reticular formation may lead to initiation of generalized seizures by a recruitment-like process, which may involve enlargement of the sensory hyperresponsive neural network of the brain until a critical neural mass is reached and initiation of seizures results.

Amygdala↗
PubMed1983

Projections from the reticular formation of the medulla, the spinal trigeminal and lateral reticular nuclei to the inferior olive.

Injections of tritiated L-leucine were placed in the reticular formation of the medulla, the spinal trigeminal and lateral reticular nuclei of cats and silver grain accumulations in the inferior olivary nucleus were demonstrated by autoradiography. Cells of the reticular formation located at the junction of nuclei reticularis magnocellularis and reticularis parvocellularis in the rostral medulla and within nucleus reticularis ventralis in the caudal medulla contribute four distinct projections to the olive. Three projections are distributed ipsilaterally in the caudal part of the medial accessory olive, at mid-level of the dorsal accessory olive and in the ventrolateral bend of the principal olive, at rostral levels. There is also a small controlateral projection to the caudal part of the medial accessory olive. the spinal trigeminal nucleus sends crossed projections to the rostral part of the dorsal accessory olive and adjacent ventral lamella as well as to the caudal part of the medial accessory olive. The lateral reticular nucleus sends an extensive ipsilateral projection to the caudal part of the medial accessory olive and provides a small contribution to the same subdivision, contralaterally. All these projections converge with other known afferents to the olive.

Afferent Pathways↗
PubMed1987

Physiological studies of brainstem reticular connectivity. I. Responses of mPRF neurons to stimulation of bulbar reticular formation.

The connectivity between medial pontine reticular formation (mPRF) and bulbar reticular formation (BRF) was studied by intracellular recordings of mPRF neuronal responses to microstimulation of BRF in unanesthetized, undrugged cats. There was a very high percentage (75-90%) of monosynaptic latency postsynaptic potentials (PSPs) in mPRF neurons in response to microstimulation of 3 BRF areas: the magnocellular tegmental field (FTM), the bulbar gigantocellular tegmental field (BFTG), and bulbar lateral tegmental field (BFTL). The type of initial orthodromic response produced in mPRF neurons by BRF stimulation was predominantly (75-95%) a monosynaptic excitatory PSP (EPSP) which was characterized by a rapid rise time, a nearly constant latency, and often led to spike potential generation. In contrast, the percentage of initial monosynaptic inhibitory PSPs (IPSPs) was much lower for FTM (12.3%), for BFTG (12.5%) and was zero for BFTL. While microstimulation techniques alone cannot differentiate between excitation of fibers of passage and neuronal somata, the very high percentage of initial EPSPs in our data and the anatomical evidence for dense BRF to mPRF neuronal projections as compared with less dense projections from fibers passing through BRF to mPRF suggest that excitatory BRF-mPRF connections are predominant. The high degree of connectivity between BRF and mPRF may furnish an important substrate for functional interaction. Comparison of the mPRF neuronal population that was not antidromically activated by FTM microstimulation vs the mPRF neuronal population that was antidromically activated from FTM and also studied for orthodromic responsiveness showed no statistically significant differences between these populations on the parameters of percentage of monosynaptic input, monosynaptic initial EPSPs, monosynaptic initial IPSPs and presence of a PSP with a latency of less than 5 ms. For BRF connectivity this suggests an identity of mPRF input and output neurons with respect to synaptic response properties.

Animals↗
PubMed1993

Monosynaptic innervation of trigeminal motor neurones involved in mastication by neurones of the parvicellular reticular formation.

In order to determine whether neurones in the parvicellular reticular formation are in direct synaptic contact with motor neurones innervating masticatory muscles, a combined retrograde and anterograde transport study was carried out in the rat at both light and electron microscopic levels. The animals received injections of the retrograde tracers wheat germ agglutinin conjugated to horseradish peroxidase or cholera toxin B conjugated to horseradish peroxidase into the masticatory muscles and of the anterograde tracer biocytin into the ipsilateral parvicellular reticular formation. The trigeminal motor nucleus was then examined for both anterograde and retrograde labelling in the light and electron microscopes. Retrogradely labelled motor neurones were identified in the trigeminal motor nucleus. They were large and their locations within the nucleus depended on the muscle injected. In addition, terminals anterogradely labelled with the biocytin that was injected in the parvicellular reticular formation were identified throughout the motor nucleus. At the electron microscopic level, the retrogradely labelled cells were found to receive input both from distinct types of unlabelled terminals and from terminals that were anterogradely labelled from the parvicellular reticular formation. The labelled terminals comprised one of the four classes of afferent terminals, being 1-2 microns in diameter and densely packed with spherical vesicles. They formed mostly asymmetrical but also symmetrical synapses with the labelled perikarya and dendrites. Anterogradely labelled terminals were also observed to form both symmetrical and asymmetrical synaptic contacts with unlabelled structures in the motor nucleus. It is concluded that neurones in the parvicellular reticular formation form direct synaptic contact with motor neurones of masticatory muscles. This pathway may represent the anatomical substrate by which the reticular formation exerts at least part of its influence on mastication. Since the parvicellular reticular formation receives input from the substantia nigra pars reticulata, it is possible that this pathway represents a system whereby the basal ganglia directly influence orofacial movement.

Animals↗