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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↗

PubMed1992

Afferent connections of the parvocellular reticular formation: a horseradish peroxidase study in the rat.

The afferent connections of the parvocellular reticular formation were systematically investigated in the rat with the aid of retrograde and anterograde horseradish peroxidase tracer techniques. The results indicate that the parvocellular reticular formation receives its main input from several territories of the cerebral cortex (namely the first motor, primary somatosensory and granular insular areas), districts of the reticular formation (including its contralateral counterpart, the intermediate reticular nucleus, the nucleus of Probst's bundle, the dorsal paragigantocellular nucleus, the alpha part of the gigantocellular reticular nucleus, the dorsal and ventral reticular nuclei of the medulla, and the mesencephalic reticular formation), the supratrigeminal nucleus and the deep cerebellar nuclei. Moderate to substantial input to the parvocellular reticular formation appears to come from the central amygdaloid nucleus, the parvocellular division of the red nucleus, and the orofacial and gustatory sensory cell groups (comprising the mesencephalic, principal and spinal trigeminal nuclei, and the rostral part of the nucleus of the solitary tract), whereas many other structures, including the substantia innominata, the field H2 of Forel, hypothalamic nuclei, the superior colliculus, the substantia nigra pars reticulata, the retrorubral field and the parabrachial complex, seem to represent relatively modest additional input sources. Some of these projections appear to be topographically distributed within the parvocellular reticular formation. From the present results it appears that the parvocellular reticular formation receives afferents from a restricted group of sensory structures. This finding calls into question the traditional characterization of the parvocellular reticular formation as an intermediate link between the sensory nuclei of the cranial nerves and the medial magnocellular reticular districts, identified as the effector components of the reticular apparatus. Some of the possible physiological correlates of the fiber connections of the parvocellular reticular formation in the context of oral motor behaviors, autonomic regulations, respiratory phenomena and sleep-waking mechanisms are briefly discussed.

Afferent Pathways↗

PubMed1994

Monosynaptic innervation of facial motoneurones by neurones of the parvicellular reticular formation.

In order to determine whether neurones in the parvicellular reticular formation are in direct synaptic contact with motoneurones innervating facial muscles, a combined retrograde and anterograde transport study was carried out in the rat. Animals received injections of the retrograde tracer cholera toxin B conjugated to horseradish peroxidase into facial muscles and of the anterograde tracer biocytin into the parvicellular reticular formation. The facial motor nucleus was then examined for anterograde and retrograde labelling in the light and electron microscopes. Retrogradely labelled neurones were found in the facial motor nucleus with a distribution that was dependent on the muscles injected. Terminals anterogradely labelled with biocytin from the parvicellular reticular formation was observed in the motor nucleus amongst the retrogradely labelled neurones. At the electron microscope, the retrogradely labelled cells were found to receive input from unlabelled terminals and from terminals that were anterogradely labelled from the injections of biocytin in the parvicellular reticular formation. The labelled terminals were 1-2 microns in diameter at the active zone and packed with spherical vesicles. They formed both symmetrical and asymmetrical synapses with their labelled or unlabelled targets. It is concluded that neurones in the parvicellular reticular formation form direct synaptic contact with motoneurones of facial muscles. This may represent a pathway by which the basal ganglia can directly influence orofacial movement, as the substantia nigra is known to project to that part of the reticular formation.

Animals↗

PubMed2004

Effects of chronic dorsal column lesions on pelvic viscerosomatic convergent medullary reticular formation neurons.

Single medullary reticular formation (MRF) neurons receive multiple somatovisceral convergent inputs originating from many different spinal and cranial nerves, including the pelvic nerve (PN), dorsal nerve of the penis (DNP), and the abdominal branches of the vagus. In a previous study, the input to MRF from the male genitalia was shown to be eliminated with chronic 30-day dorsal hemisection at the T8 spinal level. In this study, the effect of a smaller chronic lesion [dorsal column lesion (DCx)] on MRF neuronal responses was examined. Responses to bilateral electrical stimulation of the DNP remained. MRF neuronal responses to non-noxious (touch/stroke) levels of penile stimulation, however, were eliminated; only responses to noxious pinch remained. No differences were found for the number of neurons responding to noxious distention of the colon between the DCx and control groups. Although no differences were found across these groups for the percent MRF responses to vagal stimulation, the mean response latency for the DCx group was twice the sham-DCx/intact control group. Taken together, these results indicate that the MRF receives at least some of its input from the male genitalia via pathways located within the dorsal columns at the mid-thoracic spinal level.

Animals↗

PubMed1985

Horizontal saccades induced by stimulation of the central mesencephalic reticular formation.

The central mesencephalic reticular formation (cMRF) was electrically stimulated in the alert monkey. Saccadic eye movements were induced to the contralateral side in the horizontal plane at latencies of 18-35 ms. Smooth or slow eye deviations were not produced by cMRF stimulation. If the stimulus was given during slow phases of nystagmus, rapid eye movements were elicited, and the velocity of the slow phases was not affected. The function of cMRF neurons and/or of pathways that lie within it appear primarily related to generation of rapid eye movements in the horizontal plane. The amplitude of induced saccadic eye movements depended solely on the region of cMRF that was activated. When the stimulation frequency was lower, the latency was longer, but the size and characteristics of the induced movement were the same. The product of latency and stimulus frequency was approximately constant, suggesting that saccades had been triggered after a fixed number of pulses had been given. Stimulation of cMRF at frequencies that were too low to elicit rapid eye movements had a tonic effect on saccade generation. When the animal was having optokinetic nystagmus (OKN), stimulation modulated beat frequency according to the direction of the nystagmus: contralateral quick phases were facilitated and ipsilateral quick phases were suppressed. The frequencies of stimulation necessary to suppress ipsilateral quick phases increased as slow phase eye velocity increased. This demonstrates that both cMRF activity and slow phase velocity affect quick phase triggering. When the cMRF on both sides were simultaneously stimulated, the eyes were fixed in place, and no further rapid movements occurred until the stimulus had ended. Thus, activity in pathways and/or cells in cMRF is not only able to trigger saccades, but can also change the excitability of saccade generating mechanisms and promote fixation by suppressing eye movements. Two types of rapid eye movements were elicited from cMRF. From dorsal portions of cMRF saccades were induced whose size was relatively constant and not dependent on the initial position of the eyes in the orbit. The size of saccades increased from small to large as the stimulating electrode was advanced through cMRF from dorsal to ventral. This suggests that the tecto-bulbo-spinal efferents coursing through cMRF and/or cMRF neurons related to this input, are organized in a topographic fashion, with cells and fibers related to eye movements of increasing size being layered one beneath another.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMedDate not supplied

Involvement of the brain stem reticular formation in familial amyotrophic lateral sclerosis.

The reticular formation of the brain stem of three cases of familial amyotrophic lateral sclerosis (ALS) with posterior column and spinocerebellar tract involvement showed a paucity of large neurons, chromatolytic neurons and Lewy body-like intracytoplasmic inclusions. Some of the remaining neurons were stained focally by antibodies to phosphorylated neurofilaments and ubiquitin; the staining patterns were similar to those seen in anterior horn cells. Within the reticular formation, the medial part of the medulla oblongata was most pronouncedly affected. The reticular formation should be among the systems other than motor neurons that may be involved in this type of familial ALS.

Adult↗

PubMed1983

On the site of pentylenetetrazol-induced enhancement of auditory responses of the reticular formation: localized cooling and electrical stimulation studies.

Pentylenetetrazol (PTZ), administered systemically, enhanced the auditory responses of neurons of the mesencephalic reticular formation (MRF). Responses evoked in the mesencephalic reticular formation by electrical stimuli in several primary auditory nuclei (cochlear nucleus, superior olivary complex and lateral lemniscus, but not inferior colliculus) were also enhanced by pentylenetetrazol in the majority of cases. Bilateral cryoprobe cooling in the lateral lemniscal tract substantially reduced the auditory-evoked field potentials (EPs) in the mesencephalic reticular formation before and after administration of pentylenetetrazol. Cooling in the inferior colliculus (IC) produced a small reduction in auditory-evoked field potentials in the mesencephalic reticular formation before drug but a more substantial degree of reduction after administration of pentylenetetrazol. A relatively small degree of pentylenetetrazol-induced enhancement of the response was seen in neurons of the inferior colliculus (158% of control) as compared to that of neurons in the mesencephalic reticular formation (410%). These findings would be consistent with the reported ability of pentylenetetrazol to block presynaptic inhibition if the input from the inferior colliculus to the mesencephalic reticular formation has inhibitory as well as excitatory components. These data along with the present authors' recent finding of enhancement of response with microapplication of convulsants strongly suggest that enhancement of responses of neurons of the mesencephalic reticular formation, induced by systemically administered convulsants such as pentylenetetrazol is exerted, to a large extent, by direct actions on synaptic elements of the reticular formation.

Animals↗

PubMed1982

Olivary afferents from the brain stem reticular formation.

The projections from the brain stem reticular formation to the inferior olive have been studied in cats in which microinjections of horseradish peroxidase have been made into the inferior olive from a ventral approach. Retrogradely labelled cells were observed within the reticular formation proper of the medulla, pons and mesencephalon (within the nucleus reticularis parvicellularis, reticularis ventralis, reticularis gigantocellularis, reticularis lateralis, reticularis pontis caudalis, reticularis pontis oralis, cuneiformis and subcuneiformis). Labelled cells were also found within the lateral reticular nucleus (the nucleus of the lateral funiculus), the paramedian reticular and the perihypoglossal nuclei. The connections are bilateral (the projection from the lateral reticular nucleus is only contralateral). The observations demonstrate a more widespread origin for the reticulo-olivary fibres than has previously been shown and indicate that the medullary reticular formation is the area with the highest number of cells projecting to the olivary complex.

Afferent Pathways↗

PubMed1988

Autoradiographic analysis of ascending projections from the pontine and mesencephalic reticular formation and the median raphe nucleus in the rat.

Ascending projections from the medial pontine reticular formation, the mesencephalic reticular formation, and the median raphe nucleus were examined using the autoradiographic technique. The majority of the ascending fibers labeled after injections of [3H]-leucine into the nucleus pontis caudalis (RPC) course through the brainstem within the tracts of Forel (tractus fasciculorum tegmenti of Forel) and directly ventral to them. At the caudal diencephalon, Forel's bundle divides into dorsal and ventral components bound primarily for the dorsal thalamus and the subthalamus, respectively. RPC fibers project to several regions involved in oculomotor/visual functions. These include the abducens nucleus, the intermediate gray layer of the superior colliculus (SCi), the anterior pretectal nucleus (APN), the ventral lateral geniculate nucleus (LGNv), and regions of the central gray directly bordering the oculomotor nucleus, the interstitial nucleus of Cajal, and the nucleus of Darkschewitsch. Few, if any, fibers from RPC (or from nucleus pontis oralis-RPO) terminate within the oculomotor nucleus proper. Other sites receiving heavy projections from the RPC include adjacent regions of the pontomesencephalic reticular formation (RF), the parafascicular (PF) and central lateral (CL) nuclei of the thalamus and the fields of Forel/zona incerta (FF-ZI). RPO fibers also ascend predominantly in Forel's bundle. Other ascending tracts for these fibers are the medial longitudinal fasciculus and the central tegmental tract (CTT). RPO fibers distribute significantly to the same structures of the oculomotor/visual system receiving projections from RPC. The RPO projections to the SCi and the APN are particularly pronounced. RPO fibers terminate heavily in several nuclei located ventrally within the rostral midbrain/caudal diencephalon. These include major dopamine-containing cell groups (the retrorubral nucleus, the ventral tegmental area, and the substantia nigra-pars compacta) as well as the interpeduncular nucleus, the lateral mammillary nucleus, and the supramammillary nucleus. Other prominent targets for RPO fibers include the mesencephalic RF, specific regions of the central gray, the PF, the CL, the paracentral and central medial nuclei of the thalamus, and the FF/ZI. The major bundle of the ascending fibers labeled after injections of the mesencephalic reticular formation (MRF) travels within the CTT in a position just lateral to the central gray, but a significant number of labeled axons also course in Forel's bundle.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Descending Projections from the Substantia Nigra and Retrorubral Field to the Medullary and Pontomedullary Reticular Formation.

We have investigated the projection from the substantia nigra to the pontomedullary reticular formation in the rat using both retrograde and anterograde neuroanatomical tracers. Injections of a conjugate of wheatgerm agglutinin with horseradish peroxidase into the medullary or pontomedullary reticular formation resulted in the retrograde labelling of a continuous band of cells extending from the caudal half of the dorsolateral substantia nigra into the retrorubral field. Injections of the anterograde tracer Phaseolus vulgaris leukoagglutinin (PHA-L) into either the dorsolateral substantia nigra or the caudally adjacent retrorubral field revealed a descending projection to the lateral medullary and pontomedullary brainstem, which terminated mainly within the lateral (parvicellular) reticular formation. The anterograde PHA-L fibre labelling ran throughout the rostrocaudal extent of the parvicellular reticular formation and extended into the caudally continuous region, the medullary dorsal and medullary ventral reticular formation, where it tapered off. Also labelled, although more lightly, were the rostral and ventrolateral regions of the nucleus of the solitary tract and the magnocellular reticular formation. Electron microscopy established that the PHA-L-labelled fibres formed synaptic contacts with nerve cell bodies and dendrites in the parvicellular reticular formation. It is suggested that one role of this nigroreticular pathway might be to connect the basal ganglia with brainstem premotor neurons that influence orofacial musculature.

Journal Article↗

PubMed1990

Immunohistochemical study of choline acetyltransferase-immunoreactive processes and cells innervating the pontomedullary reticular formation in the rat.

The present study was undertaken to examine the cholinergic innervation of the brainstem reticular formation in an effort to understand the potential role of cholinergic neurons in processes of sensory-motor modulation and state control. The cholinergic cells and processes within the pontomedullary reticular formation were studied in the rat by application of peroxidase-antiperoxidase immunohistochemistry with silver intensification for choline-acetyltransferase (ChAT). ChAT-immunoreactive cells were located in the pontomesencephalic tegmentum within the laterodorsal and pedunculopontine tegmental (LDT and PPT) nuclei, where they numbered approximately 3,000 on each side and were scattered in the midline, medial, and lateral medullary reticular formation, where they numbered approximately 10,000 in total on each side. The cholinergic neurons within the reticular formation were commonly medium in size and gave rise to multiple dendrites that extended for considerable distances within the periventricular gray or the reticular formation, as is typical of other isodendritic reticular neurons. A prominent innervation of the entire pontomedullary reticular formation was evident by varicose ChAT-immunoreactive fibers that often surrounded large noncholinergic reticular neurons in a typical perisomatic pattern of termination, suggesting a potent influence of the cholinergic innervation on pontomedullary reticular neurons. The contribution of the pontomesencephalic cholinergic neurons to the innervation of the medial medullary and lateral pontine reticular formation was studied by retrograde transport of horseradish peroxidase conjugated wheat germ agglutinin (WGA-HRP) in combination with ChAT immunohistochemistry. A proportion of the cholinergic neurons within the laterodorsal tegmental nucleus (pars alpha) and the pedunculopontine tegmental nucleus were retrogradely labelled on the ipsilateral (10-15%) and contralateral (5-10%) sides from the medial medullary reticular formation, indicating a significant contribution to the cholinergic innervation of this region, which, however, also appeared to derive in part from intrinsic medullary cholinergic neurons. The major fiber system by which the medial medullary reticular formation was reached by the pontomesencephalic cholinergic neurons appeared to correspond to the lateral tegmentoreticular tract. Fibers passed from these cholinergic cells ventrally through the lateral pontine tegmentum, in the region of the subcoeruleus, where they also appeared to innervate by fibres en passage the noncholinergic neurons of the region. A significant proportion of the pontomesencephalic cholinergic neurons were retrogradely labelled from the lateral pontine tegmentum.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

Physiological studies of brainstem reticular connectivity. II. Responses of mPRF neurons to stimulation of mesencephalic and contralateral pontine reticular formation.

The connectivity between medial pontine reticular formation (mPRF) and the contralateral mPRF and between mPRF and the mesencephalic reticular formation (MRF) was studied by intracellular recordings of mPRF neuronal responses to microstimulation of the contralateral gigantocellular field (cFTG) portion of mPRF and ipsilateral MRF in unanesthetized, undrugged cats. There was a very high percentage (75-86%) of monosynaptic latency postsynaptic potentials (PSPs) in mPRF neurons in response to microstimulation of cFTG and MRF, and most PSPs (72-82%) were excitatory ones (EPSPs). The initial EPSPs from cFTG stimulation were characterized by a rapid rise time and a relatively constant latency, while those from MRF had a less rapid rise time and a longer plateau; EPSPs from both sites frequently led to spike potential generation. In contrast, the percentage of initial monosynaptic inhibitory PSPs (EPSPs) was less than 4% from each of these regions, statistically significantly less than that from bulbar FTM and bulbar FTG stimulation (about 12%) reported in the companion paper. Injection of depolarizing current in mPRF neurons unmasked hyperpolarizing PSP responses to stimulation that followed initial depolarizing PSPs. Intracellular HRP labeling indicated that these data were from recordings from neurons with 20-100 microns diameters, with 80% greater than 40 microns. Neurons with a different discharge pattern for this area of the pons, a stereotyped burst pattern, were recorded just ventral to mPRF; this discharge pattern resembled that found in inhibitory interneurons in other central nervous system regions. There were no differences in the density and pattern of orthodromic PSPs between those mPRF neurons that were antidromically activated from cFTG and the general population that was not antidromically activated from cFTG or other stimulated sites; this suggests, when combined with data of the companion paper, an identity of input and output elements in mPRF with respect to synaptic response properties. The high degree of connectivity between reticular regions may furnish a substrate for functional interaction.

Animals↗

PubMed2006

Nitric oxide in B6 mouse and nitric oxide-sensitive soluble guanylate cyclase in cat modulate acetylcholine release in pontine reticular formation.

ACh regulates arousal, and the present study was designed to provide insight into the neurochemical mechanisms modulating ACh release in the pontine reticular formation. Nitric oxide (NO)-releasing beads microinjected into the pontine reticular formation of C57BL/6J (B6) mice significantly (P < 0.0001) increased ACh release. Microdialysis delivery of the NO donor N-ethyl-2-(1-ethyl-2-hydroxy-2-nitrosohydrazino)-ethanamine (NOC-12) to the mouse pontine reticular formation also caused a concentration-dependent increase in ACh release (P < 0.001). These are the first neurochemical data showing that ACh release in the pontine reticular formation of the B6 mouse is modulated by NO. The signal transduction cascade through which NO modulates ACh release in the pontine reticular formation has not previously been characterized. Therefore, an additional series of studies quantified the effects of a soluble guanylate cyclase (sGC) inhibitor, 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), on ACh release in the cat medial pontine reticular formation. During naturally occurring states of sleep and wakefulness, but not anesthesia, ODQ caused a significant (P < 0.001) decrease in ACh release. These results show for the first time that NO modulates ACh in the medial pontine reticular formation of the cat via an NO-sensitive sGC signal transduction cascade. Isoflurane and halothane anesthesia have been shown to decrease ACh release in the medial pontine reticular formation. The finding that ODQ did not alter ACh release during isoflurane or halothane anesthesia demonstrates that these anesthetics disrupt the NO-sensitive sGC-cGMP pathway. Considered together, results from the mouse and cat indicate that NO modulates ACh release in arousal-promoting regions of the pontine reticular formation via an NO-sensitive sGC-cGMP pathway.

Acetylcholine↗

PubMed1986

Modification of paradoxical sleep following transections of the reticular formation at the pontomedullary junction.

A retractable wire knife was employed to transect the reticular formation at the pontomedullary junction in order to assess the respective importance of pontine and medullary reticular neurons and their pathways in paradoxical sleep. Thirteen cats were implanted with a standard array of electrodes for polygraphic recording of sleep-wakefulness states during 3 days in baseline condition and during 21 days after transections. Average electroencephalographic (EEG) amplitude, average electromyographic (EMG) amplitude, and ponto-geniculo-occipital (PGO) spike rate were measured per 1-min epoch for each day. A trivariate computer graphics display of 1 day's data revealed three major clusters of points that corresponded to wakefulness, slow wave sleep, and paradoxical sleep in baseline. (a) After transections through the entire reticular formation at the pontomedullary junction, paradoxical sleep was no longer evident in the trivariate computer graphics or polygraphic record, either by the presence of a high PGO spike rate or by that of muscle atonia in association with a low-amplitude EEG. These results indicated that the reticular fibers that pass through the pontomedullary junction and interconnect the pontine tegmentum and the medullary reticular formation are necessary for generating the cluster of electrographic variables that normally characterizes paradoxical sleep. (b) After transections through the dorsal half of the reticular formation, paradoxical sleep was still evident, though with a reduced PGO spike rate, and muscle atonia was normal. These results indicated that the descending noradrenaline locus coeruleus fibers and the "longitudinal catecholamine bundle," which course through the dorsal tegmentum, are not necessary for the generation of muscle atonia or the state of paradoxical sleep. (c) After transections through the ventral half of the reticular formation, paradoxical sleep was still apparent by the association of a moderate, though reduced, rate of PGO spiking in association with low-amplitude EEG activity and a high-amplitude EMG, indicating a loss of muscle atonia. The duration of the PS episodes, however, was greatly reduced. These results indicated that the descending "tegmentoreticular" and ascending reticulotegmental pathways, which course ventrally through the pontomedullary junction and interconnect the dorsolateral pontine tegmentum and the ventromedial medullary reticular formation, are essential for the muscle atonia of paradoxical sleep and important for the normal cyclic generation and maintenance of the state of paradoxical sleep.

Animals↗

PubMed2005

Eye movements evoked by electrical microstimulation of the mesencephalic reticular formation in goldfish.

Anatomical studies in goldfish show that the tectofugal axons provide a large number of boutons within the mesencephalic reticular formation. Electrical stimulation, reversible inactivation and cell recording in the primate central mesencephalic reticular formation have suggested that it participates in the control of rapid eye movements (saccades). Moreover, the role of this tecto-recipient area in the generation of saccadic eye movements in fish is unknown. In this study we show that the electrical microstimulation of the mesencephalic reticular formation of goldfish evoked short latency saccadic eye movements in any direction (contraversive or ipsiversive, upward or downward). Movements of the eyes were usually disjunctive. Based on the location of the sites from which eye movements were evoked and the preferred saccade direction, eye movements were divided into different groups: pure vertical saccades were mainly elicited from the rostral mesencephalic reticular formation, while oblique and pure horizontal were largely evoked from middle and caudal mesencephalic reticular formation zones. The direction and amplitude of pure vertical and horizontal saccades were unaffected by initial eye position. However the amplitude, but not the direction of most oblique saccades was systematically modified by initial eye position. At the same time, the amplitude of elicited saccades did not vary in any consistent manner along either the anteroposterior, dorsoventral or mediolateral axes (i.e. there was no topographic organization of the mesencephalic reticular formation with respect to amplitude). In addition to these groups of movements, we found convergent and goal-directed saccades evoked primarily from the anterior and posterior mesencephalic reticular formation, respectively. Finally, the metric and kinetic characteristics of saccades could be manipulated by changes in the stimulation parameters. We conclude that the mesencephalic reticular formation in goldfish shares physiological functions that correspond closely with those found in mammals.

Animals↗

PubMed2005

Neurones associated with saccade metrics in the monkey central mesencephalic reticular formation.

Neurones in the central mesencephalic reticular formation (cMRF) begin to discharge prior to saccades. These long lead burst neurones interact with major oculomotor centres including the superior colliculus (SC) and the paramedian pontine reticular formation (PPRF). Three different functions have been proposed for neurones in the cMRF: (1) to carry eye velocity signals that provide efference copy information to the SC (feedback), (2) to provide duration signals from the omnipause neurones to the SC (feedback), or (3) to participate in the transformation from the spatial encoding of a target selection signal in the SC into the temporal pattern of discharge used to drive the excitatory burst neurones in the pons (feed-forward). According to each respective proposal, specific predictions about cMRF neuronal discharge have been formulated. Individual neurones should: (1) encode instantaneous eye velocity, (2) burst specifically in relation to saccade duration but not to other saccade metrics, or (3) have a spectrum of weak to strong correlations to saccade dynamics. To determine if cMRF neurones could subserve these multiple oculomotor roles, we examined neuronal activity in relation to a variety of saccade metrics including amplitude, velocity and duration. We found separate groups of cMRF neurones that have the characteristics predicted by each of the proposed models. We also identified a number of subgroups for which no specific model prediction had previously been established. We found that we could accurately predict the neuronal firing pattern during one type of saccade behaviour (visually guided) using the activity during an alternative behaviour with different saccade metrics (memory guided saccades). We suggest that this evidence of a close relationship of cMRF neuronal discharge to individual saccade metrics supports the hypothesis that the cMRF participates in multiple saccade control pathways carrying saccade amplitude, velocity and duration information within the brainstem.

Action Potentials↗

PubMed2004

M2 muscarinic receptors in pontine reticular formation of C57BL/6J mouse contribute to rapid eye movement sleep generation.

Microinjecting the acetylcholinesterase inhibitor neostigmine into the pontine reticular formation of C57BL/6J (B6) mouse causes a rapid eye movement (REM) sleep-like state. This finding is consistent with similar studies in cat and both sets of data indicate that the REM sleep-like state is caused by increasing levels of endogenous acetylcholine (ACh). Muscarinic cholinergic receptors have been localized to the pontine reticular formation of B6 mouse but no previous studies have examined which of the five muscarinic receptor subtypes participate in cholinergic REM sleep enhancement. This study examined the hypothesis that M2 receptors in pontine reticular formation of B6 mouse contribute to the REM sleep-like state caused by pontine reticular formation administration of neostigmine. B6 mice (n=13) were implanted with electrodes for recording states of sleep and wakefulness and with microinjection cannulae aimed for the pontine reticular formation. States of sleep and wakefulness were recorded for 4 h following pontine reticular formation injection of saline (control) or neostigmine. Experiments designed to gain insight into the muscarinic receptor subtypes mediating REM sleep enhancement involved pontine reticular formation administration of neostigmine after pertussis toxin, neostigmine after methoctramine, and neostigmine after pirenzepine. Pertussis toxin was used to block effects mediated by M2 and M4 receptors. Methoctramine was used to block M2 and M4 receptors, and pirenzepine was used to block M1 and M4 receptors. Pertussis toxin and methoctramine significantly decreased the neostigmine-induced REM sleep-like state. In contrast, pretreatment with pirenzepine did not significantly decrease the REM sleep-like state caused by neostigmine. These results support the interpretation that M2 receptors in the pontine reticular formation of B6 mouse contribute to the generation of REM sleep.

Action Potentials↗

PubMed1990

Dopaminergic drugs influence the intensity of catalepsy induced by microinjections of carbachol into the reticular formation.

Carbachol microinjections into the mesencephalic and pontine reticular formation in rats induced intense and long-lasting catalepsy. Systemically administered haloperidol potentiated, while apomorphine and L-DOPA reduced the cataleptogenic effect of carbachol. These results indicate the existence of functional relations between the cholinergic cataleptogenic mechanism in the reticular formation and the dopaminergic system. They are interpreted in the light of known anatomical ascending and descending interconnections between the reticular formation and basal ganglia.

Animals↗