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PubMed1987

Influences of the basal ganglia on the medullary reticular formation.

Units were recorded extracellularly in the medullary reticular formation of chloralose-anesthetized cats during electrical stimulation of the basal ganglia (BG). Stimulating portions of the BG (caudate nucleus, entopeduncular nucleus, substantia nigra) evoked unit responses in a considerable proportion of these neurons. The majority of reticular cells that were affected by the BG were also receptive to somatic sensory inputs from the face. These units' sensory properties were influenced by BG stimulation. Cells exclusively responsive to either BG or facial inputs were uncommon. The areas of the reticular formation affected by the BG give rise to portions of the reticulospinal tracts and thereby afford the BG access to the final common path.

Animals↗

PubMed1990

Connections between hypothalamus and medullary reticular formation mediate coronary vasoconstriction.

We have recently identified discrete sites within the lateral hypothalamus and medullary reticular formation that, when stimulated electrically, produce neurally mediated coronary vasoconstriction. This study examined whether these sites are part of the same coronary vasomotor pathway. The neuronal tracing dye fast blue was injected in cats into the coronary vasoconstrictor site within medullary reticular formation. Fluorescence microscopy revealed major afferent projections originating from within the same region of midbrain ventrolateral periaqueductal gray that receives projections from lateral hypothalamus. To determine the functional importance of the proposed connections between the hypothalamic and medullary sites, anesthetized cats were prepared for continuous hemodynamic measurements. Constant current electrical stimulation within lateral hypothalamus produced significant increases in heart rate (21 +/- 6%), arterial pressure (11 +/- 3%), and femoral (36 +/- 18%) and coronary resistances (14 +/- 9%) with no change in coronary flow velocity (-1.1 +/- 2.5%). After beta-adrenoreceptor blockade, significantly greater increases in arterial pressure (35 +/- 8%) and coronary resistance (39 +/- 5%) with transient decreases in coronary flow velocity (21 +/- 6%) were seen. Microinjections of lidocaine into the medullary site blocked coronary constriction produced by lateral hypothalamic stimulation (39 +/- 5% increase in coronary resistance to electrical stimulation before and 2.4 +/- 2% increase after lidocaine in medullary reticular formation). These data provide evidence that specific regions of lateral hypothalamus and medullary reticular formation are part of a common central vasomotor projection that mediates coronary vasoconstriction in addition to other hemodynamic effects.

Amidines↗

PubMed2003

Connectivity of the goldfish optic tectum with the mesencephalic and rhombencephalic reticular formation.

The optic tectum of goldfish, as in other vertebrates, plays a major role in the generation of orienting movements, including eye saccades. To perform these movements, the optic tectum sends a motor command through the mesencephalic and rhombencephalic reticular formation, to the extraocular motoneurons. Furthermore, the tectal command is adjusted by a feedback signal arising from the reticular targets. Since the features of the motor command change with respect to the tectal site, the present work was devoted to determining, quantitatively, the particular reciprocal connectivity between the reticular regions and tectal sites having different motor properties. With this aim, the bidirectional tracer, biotin dextran amine, was injected into anteromedial tectal sites, where eye movements with small horizontal and large vertical components were evoked, or into posteromedial tectal sites, where eye movements with large horizontal and small vertical components were evoked. Labeled boutons and somas were then located and counted in the reticular formation. Both were more numerous in the mesencephalon than in the rhombencephalon, and ipsilaterally than contralaterally, with respect to the injection site. Furthermore, the somas showed a tendency to be located in the area containing the most dense labeling of synaptic endings. In addition, labeled boutons were often observed in close association with retrogradely stained neurons, suggesting the presence of a tectoreticular feedback circuit. Following the injection in the anteromedial tectum, most of the boutons and labeled neurons were found in the reticular formation rostral to the oculomotor nucleus. Conversely, following the injection in the posteromedial tectum, most of the boutons and neurons were also located in the caudal mesencephalic reticular formation. Finally, boutons and neurons were found in the rhombencephalic reticular formation surrounding the abducens nucleus. They were more numerous following the injection in the posteromedial tectum. These results demonstrate characteristic patterns of reciprocal connectivity between physiologically different tectal sites and the mesencephalic and rhombencephalic reticular formation. These patterns are discussed in the framework of the neural substratum that underlies the codification of orienting movements in goldfish.

Animals↗

PubMed1990

Connections of the parabrachial nucleus with the nucleus of the solitary tract and the medullary reticular formation in the rat.

We examined the subnuclear organization of projections to the parabrachial nucleus (PB) from the nucleus of the solitary tract (NTS), area postrema, and medullary reticular formation in the rat by using the anterograde and retrograde transport of wheat germ agglutinin-horseradish peroxidase conjugate and anterograde tracing with Phaseolus vulgaris-leucoagglutinin. Different functional regions of the NTS/area postrema complex and medullary reticular formation were found to innervate largely nonoverlapping zones in the PB. The general visceral part of the NTS, including the medial, parvicellular, intermediate, and commissural NTS subnuclei and the core of the area postrema, projects to restricted terminal zones in the inner portion of the external lateral PB, the central and dorsal lateral PB subnuclei, and the "waist" area. The dorsomedial NTS subnucleus and the rim of the area postrema specifically innervate the outer portion of the external lateral PB subnucleus. In addition, the medial NTS innervates the caudal lateral part of the external medial PB subnucleus. The respiratory part of the NTS, comprising the ventrolateral, intermediate, and caudal commissural subnuclei, is reciprocally connected with the Kölliker-Fuse nucleus, and with the far lateral parts of the dorsal and central lateral PB subnuclei. There is also a patchy projection to the caudal lateral part of the external medial PB subnucleus from the ventrolateral NTS. The rostral, gustatory part of the NTS projects mainly to the caudal medial parts of the PB complex, including the "waist" area, as well as more rostrally to parts of the medial, external medial, ventral, and central lateral PB subnuclei. The connections of different portions of the medullary reticular formation with the PB complex reflect the same patterns of organization, but are reciprocal. The periambiguus region is reciprocally connected with the same PB subnuclei as the ventrolateral NTS; the rostral ventrolateral reticular nucleus with the same PB subnuclei as both the ventrolateral (respiratory) and medial (general visceral) NTS; and the parvicellular reticular area, adjacent to the rostral NTS, with parts of the central and ventral lateral and the medial PB subnuclei that also receive rostral (gustatory) NTS input. In addition, the rostral ventrolateral reticular nucleus and the parvicellular reticular formation have more extensive connections with parts of the rostral PB and the subjacent reticular formation that receive little if any NTS input. The PB contains a series of topographically complex terminal domains reflecting the functional organization of its afferent sources in the NTS and medullary reticular formation.

Animals↗

PubMed1975

Differential effects of the optical isomers of amphetamine on neuronal activity in the reticular formation and caudate nucleus of the rat.

The activity of neurons in the caudate nucleus and reticular formation was recorded following intraperitoneal injection of the optical isomers of amphetamine. In general, D-amphetamine sulfate (2.0 mg/kg) produced an initial increase in firing rate of neurons in the caudate nucleus approximately 8-10 min following intraperitoneal injection, and a subsequent depression of firing rat which lasted for a period of time of from 70 to 120 min. Similar injections of L-amphetamine sulfate produced only a depression of activity in the caudate nucleus which was less marked and of lesser duration. Mephentermine sulfate (6.0 mg/kg), a peripheral sympathomimetic, did not produce these effects. Both D-amphetamine and L-amphetamine sulfate at the same dose produced an increase in firing rate of neurons in the reticular formation, although that produced by the L-isomer was less marked and of lesser duration. Mephentermine sulfate also produced an increase in reticular formation neuronal activity comparable to that produced by L-amphetamine sulfate. In some cases, neuronal activity was held for prolonged periods of time following injection. In the caudate nucleus, a rebound increase in firing rate was observed following the marked depression produced by both isomers of amphetamine. A rebound depression of activity was observed in the reticular formation following the initial increase in neuronal activity produced by these drugs. The results are discussed in terms of the known biochemical and behavioral effects of the stereoisomers of amphetamine.

Amphetamine↗

PubMed1984

Prefrontal cortex and bulbar reticular formation and behavioral inhibition in the rat.

Electrical stimulation in the bulbar reticular formation will produce response suppression that is observably the same as that produced by stimulation in the prefrontal cortex. This includes suppression of bar-pressing for food and running in an activity wheel, but no suppression of approach and eating of food or general activity. These results, together with previous research, support the hypothesis that this inhibitory influence of the prefrontal cortex is mediated through the bulbar reticular formation. This hypothesis is not incompatible with the concept that the prefrontal cortex serves to suppress the activating influence of the rostral reticular formation.

Animals↗

PubMed1988

Double-labelled nigral compacta and reticulata cells from injections in the reticular formation and in the striatum. An experimental study using retrograde double labelling with HRP and iron-dextran in the rat.

14 rats were studied for the nigro-reticular projection. All animals had a relatively large quantity of dextran-fer injected in the middle of the striatum (to label the nigro-striatic cells and to facilitate distinction between the compacta and reticulata zones). 5 days later, HRP was injected in the reticular formation of the ponto-mesencephalic junction (in the ncl. pedunculo-pontinus, pontis oralis et caudalis, and in the caudal parts of the ncl. cuneiformis). Retrogradely labelled nigro-striatic, nigro-reticular and double-labelled nigrostriato-reticular cells were found. In the zona compacta substantiae nigrae, about 1/3 of the total number of labelled cells were identified as nigro-striatic, 1/3 as nigro-reticular, and 1/3 as collateralizing to the striatum and the reticular formation. In the zona reticulata substantiae nigrae, 2/3 of the total number of labelled cells constituted the nigro-reticular and 1/6 the nigro-striatic projections, while 1/6 collateralized to the striatum and the reticular formation. Retrograde HRP transport in the non-collateralized nigro-reticular and in the collateralized nigrostriato-reticular projections originated mainly from the ncl. pedunculo-pontinus and ncl. pontis oralis. Retrograde transport from the ncl. pontis caudalis was much less prominent. The numerous connections projecting from the zona compacta to the reticular formation point to the essentially dopaminergic nature of this projection. Collaterals of the nigro-striatic projection directed towards the reticular formation have not yet been described in the literature available to the author.

Animals↗

PubMed1984

[Role of the reticular formation in regulating movement. Several intrareticular mechanisms and functional properties of the reticulospinal system].

The aim of this work was to obtain further information about some mechanisms of participation of the reticular formation and its descending reticulo-spinal systems in the regulation of the motor functions of the spinal cord. Following questions were studied: membrane characteristics of the reticulospinal neurons with slow and rapid axonal conduction and peculiarities of monosynaptic control influences on these groups of reticulospinal neurons from the motor cortex; characteristics of population responses of the reticular formation with respect to its ability to discriminative sensory and motor functions; reactions of the reticular formation neurons correlated with learned movements. Data obtained evidence that the reticular formation can be involved in control of specialized motor actions. Functional significance of the specific properties of the reticular formation as well as further prospects of exploration of its functional organization are discussed.

Animals↗

PubMed1997

Connections of the caudal ventrolateral medullary reticular formation in the cat brainstem.

A region of the caudal ventrolateral medullary reticular formation (CVLM) participates in baroreceptor, vestibulosympathetic, and somatosympathetic reflexes; the adjacent retroambigual area is involved in generating respiratory-related activity and is essential for control of the upper airway during vocalization. However, little is known about the connections of the CVLM in the cat. In order to determine the locations of terminations of CVLM neurons, the anterograde tracers Phaseolus vulgaris leucoagglutinin and tetramethylrhodamine dextran amine were injected into this region. These injections produced a dense concentration of labeled axons throughout the lateral medullary reticular formation (lateral tegmental field), including the retrofacial nucleus and nucleus ambiguus, regions of the rostral ventrolateral medulla, the lateral and ventrolateral aspects of the hypoglossal nucleus, nucleus intercalatus, and the facial nucleus. A smaller number of labeled axons were located in the medial, lateral, and commissural subnuclei of nucleus tractus solitarius, the A5 region of the pontine reticular formation, the ventral and medial portions of the spinal and motor trigeminal nuclei, locus coeruleus, and the parabrachial nucleus. We confirmed the projection from the CVLM to both the rostral ventrolateral medulla and lateral tegmental field using retrograde tracing. Injections of biotinylated dextran amine or Fluorogold into these regions resulted in retrogradely labeled cell bodies in the CVLM. However, the neurons projecting to the lateral tegmental field were located mainly dorsal to those projecting to the rostral ventrolateral medulla, suggesting that these neurons form two groups, possibly with different inputs. Injections of retrograde tracers into the lateral tegmental field and rostral ventrolateral medulla also produced labeled cell bodies in other regions, including the medial and inferior vestibular nuclei and nucleus solitarius. These data are consistent with the view that the CVLM of the cat is a multifunctional area that regulates blood pressure, produces vocalization, affects the shape of the oral cavity, and elicits contraction of particular facial muscles.

Animals↗

PubMed1989

Effects of basal forebrain stimulation on the waking discharge of neurons in the midbrain reticular formation of cats.

Neurons in the lateral basal forebrain which discharge selectively during slow-wave sleep have been identified as projecting to the midbrain reticular formation. Such cells have been hypothesized to participate in sleep-related changes in reticular formation excitability. The effects of stimulation at these sites on reticular formation single unit discharge in behaving cats was quantified in the present study. Effects were compared to those evoked from medial basal forebrain sites, including the preoptic area/anterior hypothalamus. Stimulation at all of these basal forebrain sites typically produced biphasic responses, consisting of a brief, short-latency excitation, followed by discharge suppression. Stimulation at lateral sites resulted in significantly longer periods of discharge suppression compared to stimulation at medial sites. These results support the hypothesis that laterally situated basal forebrain neurons participate in the regulation of behavioral state, in part, via descending modulation of midbrain reticular formation arousal mechanisms.

Animals↗

PubMed1977

Effects of benzodiazepines on PGO firings and multiple unit activity in the midbrain reticular formation in cats.

Effects of benzodiapines administered by the intraperitoneal route on PGO firings and multiple unit activity in the midbrain reticular formation in chronic cat preparations were investigated at various levels of consciousness. Changes in the sleep-wakefulness cycle induced by direct injection of benzodiazepines into the reticular formation were also investigated. Benzodiazepines markedly decreased multiple unit activity in the midbrain reticular formation during each stage of sleep, but had little effect during behavioral and EEG arousal. Benzodiazepines did not affect PGO firing rate, but attenuated all increase of multiple unit activity following PGO firings. The bilateral injection of benzodiazepines into the midbrain reticular formation induced an increase of arousal and a decrease of slow wave sleep, but did not change the amount of paradoxical sleep. It is concluded that benzodiazepines show a mixture of depressant and facilitatory effects, which seem to vary with the state of consciousness of the animal.

Animals↗

PubMed1998

A crossed projection from the optic tectum to craniocervical premotor areas in the brainstem reticular formation. An anterograde and retrograde tracing study in the mallard (Anas platyrhynchos L.).

The optic tectum in birds receives visual information from the contralateral retina. This information is passed through to other brain areas via the deep layers of the optic tectum. In the present study the crossed tectobulbar pathway is described in detail. This pathway forms the connection between the optic tectum and the premotor area of craniocervical muscles in the contralateral paramedian reticular formation. It originates predominantly from neurons in the ventromedial part of stratum griseum centrale and to a lesser extent from stratum album centrale. The fibers leave the tectum as a horizontal fiber bundle, and cross the midline through the caudal radix oculomotorius and rostral nucleus oculomotorius. On the contralateral side fibers turn to ventral and descend caudally in the contralateral paramedian reticular formation to the level of the obex. Labeled terminals are found in the ipsilateral medial mesencephalic reticular formation lateral to the radix and motor nucleus of the oculomotor nerve, and in the contralateral paramedian reticular formation, along the descending tract. Neurons in the medial mesencephalic reticular formation in turn project to the paramedian reticular formation. Through the crossed tectobulbar pathway visual information can influence the activity of craniocervical muscles via reticular premotor neurons.

Animals↗

PubMed1994

Cholinergic mechanisms in canine narcolepsy--II. Acetylcholine release in the pontine reticular formation is enhanced during cataplexy.

Cataplexy in the narcoleptic canine has been shown to increase after local administration of carbachol into the pontine reticular formation. Rapid eye movement sleep has also been shown to increase after local administration of carbachol in the pontine reticular formation, and furthermore, acetylcholine release in the pontine tegmentum was found to increase during rapid eye movement sleep in rats. Therefore, in the present study we have investigated acetylcholine release in the pontine reticular formation during cataplexy in narcoleptic canines. Extracellular acetylcholine levels were measured in the pontine reticular formation of freely moving narcoleptic and control Doberman pinschers using in vivo microdialysis probes. Cataplexy was induced by the Food-Elicited Cataplexy Test and monitored using recordings of electroencephalogram, electrooculogram and electromyogram. Basal levels of acetylcholine in the microdialysis perfusates were approximately 0.5 pmol/10 min in both control and narcoleptic canines. Local perfusion with tetrodotoxin (10(-5) M) or artificial cerebrospinal fluid without Ca2+ produced a decrease, while intravenous injections of physostigmine (0.05 mg/kg) produced an increase in acetylcholine levels, indicating that the levels of acetylcholine levels measured are derived from neuronal release. During cataplexy induced by the Food-Elicited Cataplexy Test, acetylcholine levels increased by approximately 50% after four consecutive tests in narcoleptic canines, but did not change after four consecutive tests in control canines. Motor activity and feeding behavior, similar to that occurring during a Food-Elicited Cataplexy Test, had no effect on acetylcholine levels in the narcoleptic canines.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed2002

Medullary reticulospinal tract mediating the generalized motor inhibition in cats: II. Functional organization within the medullary reticular formation with respect to postsynaptic inhibition of forelimb and hindlimb motoneurons.

We compared postsynaptic inhibitory effects on forelimb motoneurons and those on hindlimb motoneurons during generalized motor inhibition evoked by stimulating the medullary reticular formation in decerebrate cats. Here, we address two questions. First, whether the medullary inhibitory effects upon forelimb motoneurons are equivalent to those upon hindlimb motoneurons. Second, whether there is a somatotopographical organization within the medullary reticular formation in terms of inhibitory connections with motoneurons. Repetitive stimulation (20-50 microA, 50-100 Hz) delivered to the dorsomedial medullary reticular formation bilaterally suppressed muscle tone of both the forelimbs and hindlimbs. The medullary stimulation hyperpolarized the membrane potentials of the forelimb (5.4+/-1.8 mV, n=46) and hindlimb (5.4+/-2.0 mV, n=59) motoneurons together with a decrease in input resistance. The degree of membrane hyperpolarization and input resistance was not different in the forelimb and hindlimb motoneurons. The medullary stimulation also depressed the capability of generating antidromic and orthodromic spikes in the motoneurons. Stimuli with pulse trains (one to three pulses, 5-10-ms intervals, 20-50 microA) applied to the medullary inhibitory region induced a mixture of excitatory and inhibitory postsynaptic potentials in the motoneurons. The most noteworthy potentials were the inhibitory postsynaptic potentials with a late latency. They were observed in most forelimb (n=57/58, 98.3%) and hindlimb (n=63/64, 98.4%) motoneurons. The inhibitory potentials in forelimb motoneurons had a latency of 25-30 ms and a peak latency of 35-40 ms, and those in hindlimb motoneurons had a latency of 30-35 ms and a peak latency of 50-60 ms. A difference was not observed in the location of the effective sites for evoking the inhibitory effects in the forelimb and hindlimb motoneurons. These sites were homogeneously distributed in the dorsomedial part of the medullary reticular formation corresponding to the location of the nucleus reticularis gigantocellularis. From these findings we suggest that there is an equivalent amount of the postsynaptic inhibitory effects exerted on forelimb and hindlimb motoneurons during medullary-induced generalized motor inhibition. In addition, the medullary reticular formation may be functionally organized as a homogeneous or non-specific region in terms of the medullary reticulospinal inhibitory connections with forelimb and hindlimb motoneurons.

Animals↗

PubMed1996

Convergence of visceral and somatic afferents on single neurones in the reticular formation of the lower brain stem in dogs.

The reticular formation of the lower brain stem contains neuronal circuits for the generation of sympathetic tone, respiratory rhythm, muscle tone and the control of vigilance. In anesthetized dogs single neurone activities were recorded in the medial two-thirds of the reticular formation to investigate the organizing principles of this multifunctional system. The results from 110 recordings demonstrate that single neurones receive information from somatosensory afferents of skin, joints and muscles together with afferents from baro-, chemo- and lung inflation and deflation receptors. Whereas the composition of afferent spectra from somatosensory sources was different from neurone to neurone, baroreceptors had a more generalized activity-decreasing effect and chemoreceptors had a generalized activity-increasing influence, the former directing physiological systems to a trophotropic and the latter towards an ergotropic state. The functional significance of the results for the co-ordination of different physiological systems is discussed.

Afferent Pathways↗

PubMed1975

Properties of projections from vestibular nuclei to medial reticular formation in the cat.

In one series of experiments, vestibular neurons that could be activated antidromically by stimulation of the contralateral medial reticular formation were studied with extracellular recording in cats under pentobarbital anesthesia. These neurons were found in all of the four main vestibular nuclei, but were less prevalent in dorsal Deiters' nucleus and in the central region of the superior vestibular nucleus than elsewhere. Regions of the pontine and medullary reticular formation from which neurons in different vestibular nuclei were activated corresponded to the pattern of vestibuloreticular projections described by neuroanatomists. 2. Latencies of antidromic responses to stimulation of the contralateral reticular formation ranged from 0.6 to over 3 ms, indicating a relatively slow transfer of activity from vestibular nuclei to reticular formation.

Animals↗

PubMed1991

Strychnine blockade of the non-reciprocal inhibition of trigeminal motoneurons induced by stimulation of the parvocellular reticular formation.

Stimulation of a region within the parvocellular medullary reticular formation (PcRF) that contains somas of premotor interneurons produces short latency inhibitory synaptic potentials (IPSPs) in cat trigeminal motoneurons. The present study was undertaken to determine whether glycinergic synapses are responsible for these IPSPs. The intravenous administration of strychnine, an established glycine antagonist, abolished these PcRF-IPSPs. This effect appears to be specific for glycinergic inhibitory synapses because the short lasting component of the IPSP produced by inferior alveolar nerve (IAN) stimulation was also abolished, whereas, in contrast, the long lasting non-glycinergic component of this IPSP was not suppressed. These results indicate that a glycinergic system in the reticular formation is responsible for the non-reciprocal postsynaptic inhibition of trigeminal motoneurons.

Animals↗

PubMed1986

Alumina cream-induced focal motor seizures in cats: bilateral lesions of the mesencephalic reticular formation.

The effect of bilateral lesions of the mesencephalic reticular formation on the EEG-EMG patterns of types B and C alumina cream-induced focal motor seizures was studied in cats with chronically implanted electrode and cannula lesion systems. EEG patterns included number, amplitude, and contralateral propagation of type B spikes and occurrence and duration of type C tonic-clonic discharges. EMG patterns included changes in muscular multiple-unit activity time locked to the onset of type B spikes and to the onset and end of type C tonic-clonic EEG paroxysmal discharges. The lesions persistently blocked the orienting response to visual, auditory, and tactile stimuli to both sides in all cats and produced other neurologic symptoms partially or totally recovered in some cats. The lesions significantly increased the number, amplitude, and contralateral propagation of type B EEG spikes and the occurrence, but not the duration, of type C EEG tonic-clonic discharges. Ipsi- and contralateral adversion of the tonic phase were completely blocked and the muscular contractions of the clonic phase were reduced and delayed. These facts suggest that in intact epileptic cats, the mesencephalic reticular formation has an ascending suppressive influence on the mechanism related to EEG spike generation and precipitation of seizures but also a descending facilitatory control on the corticospinal epileptic impulses mediated through pyramidal and extrapyramidal pathways.

Aluminum Oxide↗