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At least 505 records · Page 28Linked to original sources
PubMed2000

Infusion of 3alpha,5alpha-THP to the pontine reticular formation attenuates PTZ-induced seizures.

Whether progesterone (P(4)) and its metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) have anti-seizure effects through actions in the pontine reticular formation (PRF) was investigated. Concentrations of P(4) and 3alpha, 5alpha-THP in the PRF were greater in proestrous and hormone-primed rats, that are typically more resistant to seizure-induction, than diestrous and males rats. Ovx, Long-Evans rats with unilateral microinjections into the PRF of 3alpha,5alpha-THP (5 microg/0.2 microl), but not P(4) (11 microg/0.2 microl) or vehicle (beta-cyclodextrin), had a greater latency and lower incidence of tonic-clonic seizures induced by pentylenetetrazol (PTZ; 70 mg/kg, IP) administration. Infusions that missed the PRF were not effective. These data suggest 3alpha,5alpha-THP has anti-seizure effects in part through actions in the PRF.

Animals↗
PubMed2003

Spinal anaesthesia indirectly depresses cortical activity associated with electrical stimulation of the reticular formation.

BACKGROUND: Neuraxial blockade reduces the requirements for sedation and general anaesthesia. We investigated whether lidocaine spinal anaesthesia affected cortical activity as determined by EEG desynchronization that occurs following electrical stimulation of the midbrain reticular formation (MRF). METHODS: Six goats were anaesthetized with isoflurane, and cervical laminectomy performed to permit spinal application of lidocaine. The EEG was recorded before, during and after focal electrical stimulation (0.1, 0.2, 0.3 and 0.4 mA) in the MRF while keeping the isoflurane concentration constant. RESULTS: During lidocaine spinal anaesthesia, the spectral edge frequency (SEF) after MRF electrical stimulation (13.6 (SD 1.0) Hz, averaged across all stimulus currents) was less than the SEF during control and recovery periods (18.6 (3.6) Hz and 17.2 (2.2) Hz, respectively; P<0.05). Bispectral index values were similarly affected: 69 (10) at control compared with 55 (6) during the spinal block (P<0.05). CONCLUSIONS: These results suggest that lidocaine spinal anaesthesia blocks ascending somatosensory transmission to mildly depress the excitability of reticulo-thalamo-cortical arousal mechanisms.

Anesthesia, Spinal↗
PubMed1983

Enhancement of dorsal raphe discharge by medial pontine reticular formation stimulation depends on behavioral state.

Single cell activity was recorded with microwire electrodes from the dorsal raphe nucleus (DRN) of cats across multiple cycles of sleep and wakefulness. Electrical stimulation of the medial pontine reticular formation (mPRF) produced a 10-fold enhancement of DRN discharge during wakefulness and slow wave sleep but not during desynchronized sleep. The neuronal mechanisms likely to mediate the state-dependent effects of mPRF stimulation are discussed with regard to the hypothesis that DRN plays a major role in behavioral state control.

Animals↗
PubMedDate not supplied

[The phasic relations between the rhythmic activities of the rabbit cortical structures at different frequencies of stimulation of the midbrain reticular formation].

Phase shifts between the rhythmical activity of the hippocampus (CA1), somatosensory, motor and visual areas of the neocortex in the delta-, theta- and alpha-bands were studied during electrostimulation of the mesencephalic reticular formation with different frequencies. It was found that increasing stimulation frequency resulted in nonlinear decrease of the phase shifts in the theta-band between recordings which included the visual cortical area, and increase of the phase shifts between the theta-rhythm, recorded in the hippocampus, somatosensory and motor cortical areas. In the delta-band increase of the phase shifts was observed only in the pairs of recordings from the last-mentioned group of structures at stimulation frequencies more than 200 1/sec. Phase shifts in the alpha-rhythm between the cortical recordings varied at different stimulation frequencies. Reliable changes of the alpha-rhythm phase shifts were observed during stimulation with the frequency 60-200 1/sec between recordings from the hippocampus, motor and somatosensory areas, and at 500-700 1/sec--in the pairs of recordings which included the visual cortical area.

Animals↗
PubMed1991

[The neurochemical mechanisms of the inhibitory influences of stimulation of the central gray substance on the high-threshold reflex activity of the reticular formation].

Influences of bulbar microinjections of some neuromodulator antagonists (methysergide, haloperidol, naloxone) on depression dynamics of spino-bulbo-spinal (SBS) reflex from the periaqueductal grey (PAG) stimulation were studied in chloralose anesthetized rats. Microinjections were made into the reticular gigantocellular nucleus which is a main supraspinal centre of SBS reflexes. It is found that methysergide administration (10(-5) mol/l) causes a considerable (two to four times as less) decrease of SBS-reflex depression evoked by PAG stimulation by a short high-frequency series of stimuli. Long-lasting depression evoked usually by a long train of PAG stimuli is less reduced: from 6-10 to 2.5-4 min. A considerable (2 to 5 times) shortening of this depression is revealed after naloxone injections (10(-5)-10(-4) mol/l). The most expressed diminution of all types of inhibitions is shown to occur after haloperidol administration. Data obtained evidence that all the studied neuromodulatory systems (5-HT, catecholamine and opioidergic ones) are involved to inhibitory action of PAG on high-threshold reflex activity of the reticular formation. Some properties of neurochemical mechanisms of the studied PAG-evoked depression are discussed.

Animals↗
PubMed2001

Ocular flutter associated with a localized lesion in the paramedian pontine reticular formation.

Ocular flutter is a rare horizontal eye movement disorder characterized by rapid saccadic oscillations. It has been hypothesized that it is caused by loss of "pause" neuronal inhibition of "burst" neuron function in the paramedian pontine reticular formation (PPRF); however, there have been no imaging studies confirming such anatomical localization. We report the case of a woman with an acute attack of multiple sclerosis associated both with ocular flutter and a circumscribed pontine lesion, mainly involving the PPRF on magnetic resonance imaging. As she recovered from the attack, both the midline pontine lesion and the ocular flutter dramatically improved. This case is the first clear evidence that at least some cases of ocular flutter are due to lesions involving the PPRF.

Adult↗
PubMedDate not supplied

The determinant role of arterial hypertension in cardiac rhythm disturbances, both induced by electrical stimulation of the midbrain reticular formation in the cat.

The arrhythmogenic and hypertensive effect of electric stimulation of the midbrain reticular formation (MRF) is known. The aim of the present paper is to demonstrate that the hypertensive effect potentiates the arrhythmogenic effect. Ten semiacute experiments were carried out on curarized cats, stimulating the MRF by stereotoxically implanted electrodes. After stimulation complex cardiac rhythm disturbances developed (consisting in their order of appearance of tachycardia, bradycardia, ventricular extrasystoles and idioventricular paroxysmal tachycardia--IPT), as well as an increase in arterial pressure. IPT always appeared after the increase in arterial pressure reached almost maximum values and disappeared after pressure values fell below this threshold. During the transition period from sinusal rhythm to arrhythmia fusion contractions were observed and in the course of IPT frequent capture phenomena. In all the cases, the frequency of IPT was inferior to that of the control. The correlation coefficient between latency in the onset of IPT and latency in the peak rise in arterial pressure was = +0.840, and between the duration of arrhythmia and the duration of the rise in arterial pressure was = +0.768. In conclusion the increase in arterial pressure produced by stimulation of the MRF represents a definite correlation to the genesis of rhythm disturbances: produced by the same stimulation.

Animals↗
PubMed1981

[Activation response to photic stimulation in normal cats and after transection of the afferent pathways of the mesencephalic reticular formation].

In chronic experiments on waking unrestrained cats with implanted electrodes the reaction of EEG activation to light stimulation was recorded in two sets of experiments in normal cats and in animals with transsection of brachia colliculi superioris that separated mesencephalic reticular system. The intensity of the activating reaction in the intact cats increased ith a rise in the light stimulus intensity. In the cats with brachia-colliculi superioris transsected there was no definite dependence on the stimuli intensity and the intensity of the activating reaction changed randomly. It is suggested that this irregularity is accounted for by blocking of the excitating afferent flow usually coming to the mesencephalic reticular formation through brachia and colliculi both from the visual pathways (ascending flow) and from the cortex (descending activation regulating flow).

Animals↗
PubMed1993

Extracellular levels of serotonin in the medial pontine reticular formation in relation to sleep-wake cycle in cats: a microdialysis study.

Extracellular levels of endogenous serotonin (5-hydroxytryptamine; 5-HT) and its major metabolite, 5-hydroxyindoleacetic acid (5-HIAA) were measured in the medial pontine reticular formation (medial PRF) of intact cats. A microdialysis probe was inserted through a guide cannula into the medial PRF. At least 12 h after the probe insertion, in vivo brain microdialysis was initiated. The perfusion rate was 1 microliters/min, and perfusate fractions at regular intervals of 20 min were collected. Changes in extracellular 5-HT levels were compared across sleep-wake states of the animals, such as waking (W), slow wave sleep (SWS) and rapid eye movement (REM) sleep. To assess sleep-wake states, EEG, EMG, EOG and PGO waves were simultaneously recorded in parallel with microdialysis of the medial PRF. Extracellular 5-HT levels were highest (20-28 fmol/20 microliters) during W. As the animals entered SWS, 5-HT levels decreased to about 90% of those during W. The state of REM sleep usually interrupted SWS for 3-8 min. During the longer periods of REM sleep, during the 20 min periods in which the perfusates were collected, we observed the lowest 5-HT levels (60-50%).

Animals↗
PubMed1998

Caudal pontine reticular formation of C57BL/6J mice: responses to startle stimuli, inhibition by tones, and plasticity.

C57BL/6J (C57) mice were used to examine relationships between the behavioral acoustic startle response (ASR) and the responses of neurons in the caudal pontine reticular formation (PnC) in three contexts: 1) responses evoked by basic startle stimuli; 2) the prepulse inhibition (PPI) paradigm; and 3) the effects of high-frequency hearing loss and concomitant neural plasticity that occurs in middle-aged C57 mice. 1) Responses (evoked action potentials) of PnC neurons closely paralleled the ASR with respect to latency, threshold, and responses to rapidly presented stimuli. 2) "Neural PPI" (inhibition of responses evoked by a startle stimulus when preceded by a tone prepulse) was observed in all PnC neurons studied. 3) In PnC neurons of 6-mo-old mice with high-frequency (>20 kHz) hearing loss, neural PPI was enhanced with 12- and 4-kHz prepulses, as it is behaviorally. These are frequencies that have become "overrepresented" in the central auditory system of 6-mo-old C57 mice. Thus neural plasticity in the auditory system, induced by high-frequency hearing loss, is correlated with increased salience of the inhibiting tones in both behavioral and neural PPI paradigms.

Acoustic Stimulation↗
PubMed1991

Microinjections of muscimol and bicuculline into the pontine reticular formation modify the sleep-waking cycle in the rat.

The role of gamma-aminobutyric acid (GABA) in the sleep-waking cycle was evaluated by means of microinjections of muscimol and bicuculline into the rat pontine reticular formation (PRF). Muscimol (20 ng) produced a marked increase in wakefulness (70%), a decrease in slow-wave sleep (SWS) (35%) and a remarkable delay in the onset of both SWS and paradoxical sleep, without modifying the percentage of the latter. Bicuculline (4 ng) shortened SWS latency by about 70%. These results suggest that GABAergic transmission in the PRF is involved in the regulation of sleep-waking cycle in the rat.

Animals↗
PubMed1999

Muscimol in the deep layers of the superior colliculus/mesencephalic reticular formation blocks expression but not acquisition of fear-potentiated startle in rats.

Deposits of the retrograde tracer Fluoro-Gold into the ventrolateral nucleus reticularis pontis caudalis labeled neurons in the deep layers of the superior colliculus/mesencephalic reticular formation (deep SC/Me). To test the involvement of this area in the fear-potentiated startle effect, rats were implanted with cannulas into the deep SC/Me and trained for fear-potentiated startle after infusion of the GABA(A) agonist muscimol (0.1 microg/0.5 microl). Two days later, they were tested for fear-potentiated startle. Rats then received a 2nd training session without any infusions, and 2 days later they were reinfused with muscimol (0.1 microg/0.5 microl) and tested for fear-potentiated startle. Local infusion of muscimol into the deep SC/Me completely blocked the expression but not the acquisition of fear-potentiated startle. These results indicate that a synapse in the midbrain is critical for the expression of fear-potentiated startle.

Animals↗
PubMed1985

Gudden's tegmental nuclei and their connections to the hypothalamus and the reticular formation. I. An experimental study using retrograde labelling with HRP or iron-dextran in the rat.

31 rats were studied for the retrograde transport of HRP or dextran-fer from the corpus mamillare, anterior hypothalamus or reticular formation to the cells of the ventral (VG) and dorsal (DG) Gudden's tegmental nuclei. Judging by the position of the projection cells the VG was found divisible into the peripheral and central parts, a finding out of line with the conventional cytoarchitectonic division. The two parts differ in part of their projections. While both project jointly to the medial mamillary body, the peripheral part has a separate projection to the whole lateral hypothalamus whereas the central part projects also to the RF (ncl. pedunculopontinus and ncl. pontis oralis). The group of cells localized close to the cranial field of the VG, cytoarchitectonically referred to as the pars compacta ncl. centralis superioris, has the same projections as the external parts of the VG and can, therefore, be seen as a component of the VG peripheral part like the cells over the caudal field of the VG (pars intrafascucularis localized already among FLM fibres). The central part is made up of cells localized in the middle portions of the bulk of the VG cells. The dorsal Gudden's tegmental nucleus projects its ventral part to the lateral mamillary body, to the medial and lateral hypothalamus and to the RF (ncl. pontis oralis). The dorsal part of the DG projects solely to the RF (ncl. pontis oralis).

Animals↗
PubMed1994

Projections of vertical eye movement-related and head rotation-related neurons in the medial mesodiencephalic junction to pontine reticular formation in cat.

Spikes of single neurons related to vertical eye movements and vertical head rotation were recorded extracellularly in the medial mesodiencephalic junction (MDJ) of chronically prepared alert cats, and their antidromic responses to stimulation of the pontine reticular formation (PRF) were studied. Among the vertical eye movement-related-neurons, augmenting neurons (ANs) and tonic neurons (TNs) were activated antidromically from the lateral PRF. Stimulation of the midline PRF activated antidromically mainly ANs, long-lead burst neurons (LLBNs) and upward medium-lead burst neurons (MLBNs). The head rotation-related neurons were antidromically activated from the lateral PRF but not-from the midline PRF. These results suggest that some MDJ neurons related to vertical eye movements or head rotation directly project to the paramedian PRF.

Animals↗
PubMed1999

Progesterone microinjections into the pontine reticular formation modify sleep in male and female rats.

It has been reported that progesterone (P4) induces changes in sleep, but the brain regions involved in these actions are unknown. We studied the effects of P4 microinjections into the pontine reticular formation (PRF) upon rat sleep. Intact adult male and ovariectomized female rats were unilaterally injected with P4 into the PRF and the sleep-waking cycle was recorded for 6 h. P4 (1.0 and 5.0 microg/0.2 microl) did not modify sleep, but at a higher dose (7.5 microg/0.2 microl) it produced a marked decrease in rapid eye movement sleep (REM) latency in both male (55%) and female (63%) rats. A non-significant increase in the number of REM episodes was observed after P4 administration. These findings suggest that P4 should participate in the mechanisms related to REM initiation in the rat through its effects in the PRF.

Animals↗
PubMedDate not supplied

[The cross-correlation relations of the electrical activity of the cortical structures at different levels of the activation of the midbrain reticular formation in the rabbit].

Changes of correlation coefficients and coherence of the delta-, theta- and alpha-rhythms were studied between the somatosensory, motor and visual neocortex areas, dorsal hippocampus and dentate fascia at stimulation frequencies of the midbrain reticular formation from 60 to 1000 imp/s. It was shown that correlation coefficient between the structures studied increased at 60-200 imp/s and decreased at the further increase of stimulation frequency. In pairs with the visual area the correlation coefficient changed but little. The delta-rhythms coherence tended to decrease with the increase of stimulation frequency. Coherence of the theta-rhythms between the neocortical areas and the hippocampus increased with the increase of stimulation frequency up to 200 imp/s and decreased at higher frequency stimulation while in pairs of these areas with the dentate fascia it continued to rise with the increase of stimulation frequency up to 1000 imp/s. The coherence of the alpha-rhythms was almost unchanged at 60-200 imp/s and mostly had an increase at higher frequency stimulation.

Alpha Rhythm↗
PubMed1980

[Hypothalamic projections into the midbrain reticular formation and the parafascicular complex in the cat detected by means of retrograde horseradish peroxidase transport].

By the method of horseradish peroxidase (HP) retrograde transport (the injection was performed into the thalamic parafascicular complex in 7 cats) connections between the hypothalamus, the midbrain reticular formation and the parafascicular complex were followed. Other connections of the hypothalamus with some cerebral centers were also discussed.

Animals↗