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At least 19 recordsLinked to original sources

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↗

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↗

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↗

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↗

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↗

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↗

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↗

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↗

PubMed1992

Excitatory amino acid-mediated responses and synaptic potentials in medial pontine reticular formation neurons of the rat in vitro.

Neurons of the medial pontine reticular formation (mPRF) are involved in the execution of numerous behaviors including initiation of locomotion, eye movements, startle responses, and rapid eye movement sleep phenomena. Approximately half of the afferent projections to mPRF neurons come from within the reticular formation (Shammah-Lagnado et al., 1987). In spite of the importance of reticulo-reticular connections, virtually nothing is known about transmitters mediating these synapses. In order to identify a candidate excitatory neurotransmitter, the actions of excitatory amino acids (EAAs) on the membrane properties of mPRF neurons recorded in rat brainstem slices in vitro were studied. Standard intracellular recording methods, including single-electrode voltage clamp, were used to examine the postsynaptic actions of EAAs. We also tested whether EAA antagonists block EPSPs evoked by stimulation of the contralateral reticular formation in the slices. mPRF neurons responded to both non-NMDA and NMDA agonists. NMDA-induced conductances were voltage dependent and depressed by physiological concentrations of magnesium. Stimulation of the contralateral reticular formation elicited EPSPs that were depressed by the general EAA antagonist kynurenate. Evoked EPSPs were partially depressed by 6,7-dinitroquinoxaline-2,3-dione. The evoked EPSP was further reduced by the NMDA antagonist (+/-)-2-amino-5-phosphonopentanoic acid in some cases. These results suggest that excitatory reticulo-reticular neurotransmission is mediated by an EAA. Both non-NMDA and NMDA receptors contribute to EAA neurotransmission in the mPRF formation and play an integral role in reticular formation function.

Amino Acids↗

PubMed1979

Behavioral functions of the reticular formation.

Studies of the behavioral correlates of activity in reticular formation cells, usually performed in restrained animals, have found units whose discharge relates to sensory stimuli, pain and escape behavior, conditioning and habituation, arousal, complex motivational states, REM sleep, eye movements, respiration and locomotion. Units with these different behavioral correlates were found in the same anatomical areas. Most studies report that a large proportion of encountered cells related to the behavior being studied. If one adds up the reported percentages, the total far exceeds 100%. Therefore it appears that many investigators are looking at the same cells and reaching very different conclusions about their behavioral roles. On the basis of observations in unrestrained cats, it is hypothesized that discharge in most RF cells is primarily related to the excitation of small groups of muscles. This hypothesis can parsimoniously explain many previous observations on the behavioral correlates of these cells, and is consistent with anatomical, physiological and phylogenetic studies of the reticular formation. The hypothesized simplicity of reticular formation unit function is contrasted with the complexity of the behavioral functions mediated by the RF, and the implications of this contrast discussed.

Animals↗

PubMed1988

Changes in intracranial pressure elicited by electrical stimulation of the brainstem reticular formation in spinal cats with vagotomy.

The momentary changes in intracranial pressure (ICP) were explored using electrical stimulation of the brainstem reticular formation and the nucleus fastigii of the cerebellum in cats under artificial ventilation after spinalization (C2) and vagotomy. Regions that yielded an increase in ICP in the arterial pressor area were: the central part of the pontine recticular formation, the dorsal medullary reticular formation, the central part of the medullary reticular formation, and the nucleus fastigii of the cerebellum; and one region in the arterial depressor area was the paramedial and ventral medial region of the medullary reticular formation. Since the arterial blood pressure and respiration was maintained constant during electrical stimulation by spinalization and vagotomy, the increase in ICP in the cranium, a semi-closed box, momentarily reflected an increase in cerebral blood volume due to cerebral vasodilatation. It is suggested that excitation of cell bodies or fibres within these regions may produce cerebral vasodilatation.

Animals↗

PubMedDate not supplied

[Sensory organization of the reticular formation: Specific integrative activity].

On the basis of personal investigations including 1) electrophysiological methods (EEG, averaged evoked potentials), 2) behavior methods, 3) destruction of various parts of the brain (mesencephalic reticular formation, auditory pathways) and 4) pharmacological methods, conducted in the years 1953-1974 the author put forward a concept of sensory organization of reticular formation postulating existence of special systems in the reticular formation differing in their relative physiological and chemical specificity. This relative specificity is, in this concept, the ability of the so-called non-specific neurons in the reticular formation to be included under certain experimental conditions into specific functional systems. The author suggests the term "paraspecific systems" for designating these relatively specific systems. It seems that these systems determine the integrative role of reticular formation in the process of learning. In contrast to this important role the reticular formation is without any greater importance for the process of memory storage. The dynamic and relatively specific functional organization of reticular formation provides potential possibilities of its utilization in the processes of reeducation or rehabilitation in central nervous system damage and in pharmacological treatment of psychic disturbances.

Acoustic Stimulation↗

PubMed1990

Single cholinergic mesopontine tegmental neurons project to both the pontine reticular formation and the thalamus in the rat.

Microinjections of the cholinergic agonist carbachol into a caudal part of the pontine reticular formation of the rat induce a rapid eye movement sleep-like state. This carbachol-sensitive region of the pontine reticular formation is innervated by cholinergic neurons in the pedunculopontine and laterodorsol tegmental nuclei. The same population of cholinergic neurons also project heavily to the thalamus, where there is good evidence that acetylcholine facilitates sensory transmission and blocks rhythmic thalamocortical activity. The present study was undertaken to examine the degree to which single cholinergic neurons in the mesopontine tegmentum project to both the carbachol-sensitive region of the pontine reticular formation and the thalamus, by combining double fluorescent retrograde tracing and immunofluorescence with a monoclonal antibody to choline acetyltransferase in the rat. The results indicated that a subpopulation (5-21% ipsilaterally) of cholinergic neurons in the mesopontine tegmentum projects to both the thalamus and the carbachol-sensitive site of the pontine reticular formation, and these neurons represented the majority (45-88%) of cholinergic neurons projecting to the pontine reticular formation site. The percentage of cholinergic neurons with dual projections was higher in the pedunculopontine tegmental nucleus (6-27%) than in the laterodorsal tegmental nucleus (4-11%). In addition, mixed with cholinergic neurons in the mesopontine tegmentum, there was a small population of dually projecting neurons that did not appear to be cholinergic. Mesopontine cholinergic neurons with dual projections may simultaneously modulate neuronal activity in the pontine reticular formation and the thalamus, and thereby have the potential of concurrently regulating different aspects of rapid eye movement sleep.

Animals↗

PubMedDate not supplied

[Responses of sensomotor cortex neurons of rats to stimulation of the midbrain reticular formation].

High frequency stimulation of the mesencephalic reticular formation produces significant inhibition of neuronal activity in the sensorimotor cortex, the effect being equally observed in both hemispheres. In case of low frequency stimulation, marked difference was observed between the reaction of ipsi- and contralateral neurons. Under these conditions, contralateral neurons produce mainly facilitation responses. In both hemispheres evident predominance of tonic effects was observed which revealed itself in the continuation of the reaction in the poststimulation period. Single shocks applied to the midbrain reticular formation elicited in the cortex the evoked potentials of two types: one with a constant and the other with varying latent periods. The former exhibited a latency of 4-18 msec. Responses with varying latencies were predominant. In general, latent periods were longer in contralateral hemisphere.

Animals↗

PubMed1992

Loss of the acoustic startle response following neurotoxic lesions of the caudal pontine reticular formation: possible role of giant neurons.

The effect of the excitotoxic N-methyl-D-aspartate agonist quinolinic acid in the caudal pontine reticular formation on the acoustic startle response was investigated in rats. Bilateral injections of 90 nmol of quinolinic acid led to large lesions in the reticular formation characterized by the loss of all neurons and a marked reduction or even abolition of the acoustic startle response; 18 nmol of quinolinic acid led to smaller lesions characterized by a selective loss of giant neurons within the caudal pontine reticular formation and a reduction of the startle amplitude. The partial correlation analysis revealed that the reduction of the amplitude of the acoustic startle response can be correlated with the loss of the giant neurons (r = 0.575; d.f. = 29; P less than 0.001) but not with the reduction of the number of all neurons (r = 0.207; d.f. = 29; P greater than 0.2) in the caudal pontine reticular formation. These findings were reconciled with electrophysiological and anatomical data indicating that the giant neurons in the caudal pontine reticular formation receive acoustic input and project to motoneurons of the spinal cord. It is concluded that the caudal pontine reticular formation is an important element of the startle pathway and that the giant reticulospinal neurons constitute an important part of the sensorimotor interface mediating this response.

Acoustic Stimulation↗

PubMed1978

[Ultrastructure of the dendrites of neurons of the brain stem reticular formation in acute hypoxic hypoxia].

In 45 adult rats (Wistar strain) neuronal dendrites of the reticular formation were studied electron microscopically at an acute hypoxic hypoxia. Structural changes in neurons of the reticular formation, were demonstrated to begin, as a rule, in the terminal portions of the dendrites. Dystrophic and destructive changes in dendrites are always more pronounced than in the pericaryon and are not infrequently they terminate in destruction of cytoplasmic islets. Submicroscopic changes in the dendrites are classified according to the dynamics of their development. Taking into consideration a specific role of the neuronal dendrites of the reticular formation under certain physiological conditions, it is possible to conclude that dendritic damage is of major importance in functional disturbance of the reticular formation at hypoxic hypoxia.

Acute Disease↗

PubMed1991

Projections from the rostral parvocellular reticular formation to pontine and medullary nuclei in the rat: involvement in autonomic regulation and orofacial motor control.

The efferent connections of the rostral parvocellular reticular formation to pontine and medullary nuclei in the rat were studied with anterogradely transported Phaseolus vulgaris leucoagglutinin. Dense innervations from the rostral parvocellular reticular formation were found in the mesencephalic trigeminal nucleus, the supratrigeminal area, the motor trigeminal nucleus, the motor trigeminal nucleus, the facial, hypoglossal and parabrachial nuclei and specific parts of the caudal parvocellular reticular formation, including nucleus linearis and the dorsal reticular nucleus of the medulla. The raphe nuclei, nucleus of the solitary tract, inferior olive, dorsal principal sensory, spinal trigeminal nuclei and gigantocellular reticular nucleus and the ventral reticular nucleus of the medulla received moderate projections. In general, the projections from the rostral parvocellular reticular formation were bilateral with an ipsilateral dominance. The dorsal motor vagus and the ambiguus nuclei were not labeled. It is concluded that the rostral parvocellular reticular formation participates in regulation of orofacial motor control and in neural networks for limbic control of metabolic homeostasis.

Animals↗