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R Rokyta

Publications and source records attributed to R Rokyta.

At least 55 records · Page 3Linked to original sources
PubMed1998

Reciprocal connections between the red nucleus and the trigeminal nuclei: a retrograde and anterograde tracing study.

An anterograde biocytin and a retrograde WGA-colloidal gold study in the rat can provide information about reciprocal communication pathways between the red nucleus and the trigeminal sensory complex. No terminals were found within the trigeminal motor nucleus, in contrast with the facial motor nucleus. A dense terminal field was observed in the parvicellular reticular formation ventrally to the trigeminal motor nucleus. The parvicellular area may be important for the control of jaw movements by rubrotrigeminal inputs. On the other hand, the contralateral rostral parvicellular part of the red nucleus receives terminals from the same zone in the rostral part of the trigeminal sensory complex, where retrogradely labelled neurones were found after tracer injections into the red nucleus. Such relationships could be part of a control loop for somatosensory information from the orofacial area.

Animals↗
PubMed1997

Potentiation of fentanyl suppression of the jaw-opening reflex by transcranial electrical stimulation.

Stinus et al. [L. Stinus, M. Auriacombe, J. Tignol, A. Limoge, M. Le Moal, Transcranial electrical stimulation with high frequency intermittent current (Limoge's) potentiates opiate-induced analgesia: blind studies, Pain, 42 (1990) 351-363.] observed that transcranial electrical stimulation (TCES) with high-frequency intermittent current potentiated opiate-induced analgesia using the tail-flick test. In unanesthetized, chronic preparations, electrical stimulation (0.5 Hz) of the lower incisor pulp of rats elicits a short-(6 ms) and a long-latency (12-18 ms) jaw-opening reflex (JOR) without any evidence of aversive behavior [J. Azerad, F. Fuentes, I. Lendais, A. Limoge, B. Pollin, Methods for selective tooth pulp stimulation in acute and chronic preparations in rats, J. Physiol., 406 (1988) 3P.]. Fentanyl increases thresholds of both reflexes and transiently suppresses the long-latency JOR. We then decided to look at the influence of TCES on both drug-induced mean of maximal threshold variation (MMTV) and duration of JOR suppression period. These parameters have been investigated in 43 Wistar rats with or without TCES administered for 3 h before the drug injection and throughout the testing period. TCES alone has no effect. In contrast, it significantly increases the duration of the reflex suppression period (149 +/- 5% vs. control, P < 0.001) while fentanyl-increased reflex thresholds remain unchanged. The fentanyl-induced JOR suppression period returns to the control values 2 days later. When a second 3-h TCES session is delivered 2 or 4 days after the first TCES session, a similar increase of this suppression period is observed. Moreover, 2 days after a second TCES session, an increase of the duration of the fentanyl-induced JOR suppression period is systematically observed. In contrast, a 6-h TCES session never induces such effects. These results confirm a potentiating effect of TCES on opioid action and demonstrate the value of repeated TCES sessions.

Analgesics, Opioid↗
PubMed1997

Comparison of microsurgical suture with fibrin glue connection of the sciatic nerve in rabbits.

The regeneration of the sciatic nerve after microsuture was compared with the connection of transected nerve with a coagulum of autologous blood plasma in 20 rabbits. The epineuroperineural suture was performed in 10 rabbits (group A). The severed nerve was approximated with fibrin glue of autologous blood plasma in 10 rabbits (group B). Their skin sensation margin during a 3-month-period of regeneration was examined, 90 days after surgery the connection was inspected and the nerve conduction velocity was measured across the site of the anastomosis. The microsuture was found to be firm in all 10 animals of group A. On the other hand, in 2 animals of group B, the glue failed to keep the nerve stumps approximated (dehiscence occurred in 20% of the animals). There were no significant differences found on clinical and electrophysiological testing of regenerated nerves of both groups. The method of autologous fibrin glue in the repair of peripheral nerve transection does not provide a sufficiently firm connection. This procedure with the preparation of the centrifuged plasma is a more time-consuming method in comparison with the microsuture. Epineuroperineural microsuture with maximal effort to adapt the corresponding nerve fibres remains the method of choice for peripheral nerve reconstruction.

Animals↗
PubMed1997

Effect of glycosylated and non-glycosylated prolactin on the proliferation of normal human lymphocytes.

We evaluated the effects of 2.5x10(-10) M or 5x10(-10) M concentrations of human pituitary prolactin (pPRL), human recombinant non-glycosylated (NG-PRL) and glycosylated (GL-PRL) prolactin on the proliferation of normal human lymphocytes with or without coactivation by interleukin-2 (IL-2). None of the PRL forms alone affected the lymphocyte proliferation in a serum-free medium, however, the stimulatory activity of IL-2 was significantly potentiated with all 3 PRL variants. Since the 5x10(-10) M concentrations of individual PRLs exerted the same effects, this result suggests that GL-PRL in primary lymphocyte culture is not a less mitogenic form, if sufficient amounts of IL-2 are available.

Cell Division↗
PubMed1997

Reciprocal interactions between intralaminar and lateral thalamic nuclei in rats.

Reciprocal interactions between intralaminar thalamic nuclei (ncl. centralis lateralis, CL, and ncl. parafascicularis, Pf), the pretectal area (Pt) and lateral thalamic nuclei (ventrobasal complex, VB, ncl. anterior ventralis, AV, and ncl. ventralis anterior, VA) have been observed in ketamine-anaesthetized rats. Extracellular single unit activity has been recorded after single electrical stimuli. Electrical stimulation of the VB evoked a short latency orthodromic response followed by a pause in spontaneous activity in neurones of medial thalamic nuclei. Lateral thalamic neurones responded to electrical stimulation of the intralaminar nuclei or the pretectal area with the same pattern of response. Striatal, sensorimotor cortical or peripheral electrical stimulation also evoked similar responses. The pauses in spontaneous activity were shown to be the result of inhibition since the responsiveness of the intralaminar nuclei or the lateral thalamic neurones to all inputs was abolished or reduced after a conditioning electrical single-shock stimulation in the VB or in the intralaminar nuclei, respectively. The two components of the response were of a different origin, since most of the short latency responses disappeared after medullary, upper cervical sections or large decortications, while the inhibitions persisted. These inhibitions were shown to be of thalamic origin since their duration was decreased after extensive decortications increased after medullary section. It is concluded that the neuroneal properties studied in this report are probably broadly represented throughout the thalamus and that thalamic neurones are under inhibitory control elicited by afferent volleys. This inhibitory control includes a relay in the nucleus reticularis thalami (nRT). The mechanisms of sensory interaction can be purely thalamic, but they can be modulated by suprathalamic and/or mesencephalic loops.

Animals↗
PubMed1997

Abnormal neuroneal activities in intralaminar thalamic nuclei following chronic lesions of nucleus reticularis thalami in rats.

Extracellular single unit activity in the intralaminar thalamic nuclei (ncl. centralis lateralis, CL, n = 77 and ncl. parafascicularis, Pf, n = 163) and in the pretectal area (Pt, n = 75) was examined following chronic electrolytic lesions of the nucleus reticularis thalami (nRT) in ketamine-anaesthetized rats after single electrical stimuli to the ventrobasal complex (VB). Extensive alterations of either the ongoing ("spontaneous") activity or the pattern of VB evoked responses were observed. Four major changes were observed in the activity of these intralaminar or pretectal neurones: 1) many neurones were silent, two times more frequently than in a parallel study with control intact rats; 2) the firing pattern of all the other neurones was in the form of tonic (stationary-like) discharge, without burst discharges as previously described in intact animals. They were ranked into classes according to their spontaneous discharge: class I, silent (no resting discharge) 12%, class II (1-15 Hz), 54 % and class III (> 16 Hz), 34%. Class III neurones were never found in intact rats; 3) electrical stimulation of the VB evoked a short latency orthodromic excitatory response in these neurones but this response was not followed by any slowing or depression of the spontaneous activity in more than 40% of recorded cells. When it occurred, this pause was shorter than that always observed in intact rats by more than 35% and longer in 7% of the responsive cells. All these changes were correlated with the extent of damage to the ipsilateral nRT; 4) VB stimulation evoked prolonged excitatory responses lasting more than 150 ms in 13% of the responsive cells, and nRT stimulation led to a short latency response followed by a pause of activity. These findings suggest that the nRT is involved in sensory integration and modulation.

Animals↗
PubMed1996

[Free radicals in the central nervous system].

Central nervous system has a low antioxidative capacity, which is formed mainly by ascorbic acid. Therefore the cerebral tissue is threatened by the increased formation of free radicals and their metabolites (ROS--reactive oxygen species). ROS are formed such as in reperfusion phase after ischemia and in catecholamine metabolism, in oxidative stress due to hyperglycaemia. Polyunsaturated fatty acids (PUFA) are peroxidased by ROS; proteins and DNK are damaged as well. Free radicals are involved in etiology and pathogenesis of many CNS diseases, such as neuritis, Alzheimer disease, Parkinson disease, Huntington disease, aging and atherosclerosis of the brain, epilepsy, etc. During the antioxidant therapy it is necessary to consider the types of ROS, their origin and their mode of action, whether to administer hydrophilic or lipophilic antioxidants, eventually chelate agents, etc. Hydrophylic antioxidants are acting very soon after the administration, whereas the lipophilic ones reach their target tissues with a great delay. Therefore it is better to apply them preferentially like a prevention, if possible. Enzymatic antioxidants (SOD, GSPHx and catalase and others) are usually acting only for a short time. The methods of estimation of free radicals attacks are discussed as well their possible pathophysiological effects.

Animals↗
PubMed1995

Meso-tetra-(4-sulfonatophenyl)-porphine of low neurotoxicity.

The acute toxicity of specially purified meso-tetra-(4-sulfonatophenyl)-porphine (TPPS4) was measured in mice DBA/2 and Wistar rats after i.v. administration of the dye dissolved in saline solution. LD50 of our preparation was 352.5 mg/kg for mice and 574.9 mg/kg for rats. Motor nerve conduction velocity was measured in rats and rabbits in ether anesthesia N. ischiadicus and n. tibialis were stimulated by surface electrodes and M response was registered. No signs of neurotoxicity were found, even after application of 150 mg/kg b.w. of our TPPS4. Histologic evaluation was performed by routine method and standard electron microscopic procedure. Only minimal and sporadic axonal changes were found. The clinical application of low toxic TPPS4 was reconsidered.

Animals↗
PubMed1993

Ethosuximide suppresses seizures and lethality induced by picrotoxin in developing rats.

The action of ethosuximide (125 or 250 mg/kg, IP) against picrotoxin-induced seizures (3-6 mg/kg, IP) was assessed in rats 12, 18, 25, and 90 days old. In 18-day-old and older controls, picrotoxin regularly elicited clonic seizures; tonic-clonic seizures were induced in all age categories with high consequent mortality. Only the higher dose of ethosuximide (250 mg/kg) increased the latency of clonic seizures in 18- and 25-day-old pups. Tonic-clonic seizures were delayed by ethosuximide in 12-, 18-, and 90-day-old rats. Picrotoxin-induced lethality was suppressed only in 18- and 90-day-old rats by the 250-mg/kg dose of ethosuximide. In contrast, ethosuximide pretreatment increased the incidence of clonic seizures in 12-day-old rats. The results suggest that only high doses of ethosuximide can suppress clonic seizures, and this action is not consistent. Tonic-clonic seizures probably have model-specific sensitivity to ethosuximide because in previous studies ethosuximide completely suppressed pentylenetetrazol-induced tonic-clonic seizures but had no effect on kainic acid-induced tonic-clonic seizures. The suppression of mortality rates is probably due to nonspecific effects of high doses of ethosuximide.

Animals↗
PubMed1991

Bicuculline-induced neocortical epileptiform foci and the effects of 6-hydroxydopamine in developing rats.

Catecholamines (dopamine and norepinephrine) are considered to be predominantly inhibitory neurotransmitters in the brain and their depletion produced by 6-hydroxydopamine may result in proconvulsant effects. In our experiments on rats aged 5, 7, 9, 12, 15, 18, 25 and 90 days under urethane anesthesia we demonstrated the development of neocortical epileptic focus evoked by topical application of bicuculline methiodide. In experimental groups aged 7, 12, 18, 25 and 90 days a chronic depletion of catecholamines was induced using pretreatment with 6-hydroxydopamine early postnatally. An epileptogenic focus was induced in all age groups; duration of a single discharge decreased with age in both control and experimental animals. The spread of activity from the primary focus to contralateral frontal cortex via callosal connections was as rapid as in controls. However, the transfer of discharge to occipital regions was delayed and the number of discharges decreased in experimental rats. Our study demonstrated a substantial role of catecholamines for synchronization of focal discharges in neocortex and a promoting role of catecholamines in association pathways within neocortex.

Animals↗
PubMed1991

Thalamocaudate projections in the macaque monkey (a horseradish peroxidase study).

The distribution of thalamocaudate neurons was studied in four macaque monkeys (Macaca mulatta) using the method of retrograde horseradish peroxidase (HRP Sigma VI) transport following previous aspiration of part of the frontal cortex and subcortical white matter covering the head of the caudate nucleus. After HRP injections into the head of the caudate nucleus we found retrogradely labelled neurons mainly in the intralaminar nuclei (nc. paracentralis, nc. centralis lateralis, nc. parafascicularis) and in the midline nuclei (nc. parataenialis, nc. centralis pars densocellularis, nc. centralis superior, nc. centralis intermedialis, nc. centralis inferior, nc. reuniens). Some labelled neurons were seen in the anterior thalamic nuclei (nc. anterodorsalis, nc. anteromedialis, nc. anteroventralis). In the ventral thalamus labelled neurons were seen in the nc. ventralis anterior (pars magnocellularis) and in the nc. ventralis lateralis (pars medialis). Some labelled neurons were distributed in the marginal parts of the nc. mediodorsalis. As for the caudal portion of the thalamus, labelled neurons were found in the nc. pulvinaris medialis and nc. limitans. The thalamocaudate projection is an exclusively ipsilateral projection system. The position of the thalamocaudate neurons coincides, to a certain degree, with the termination intrathalamic area of the nigrothalamic and tectothalamic projections arising from the deep layers of the superior colliculus.

Animals↗
PubMed1990

Ketamine suppresses both bicuculline- and picrotoxin-induced generalized tonic-clonic seizures during ontogenesis.

An anticonvulsant action of ketamine, a noncompetitive N-methyl-D-aspartate (NMDA) antagonist (5-40 mg/kg IP), on the bicuculline-induced (3-8 mg/kg IP) or picrotoxin-induced seizures (3-6 mg/kg IP) was assessed in male Wistar rats aged 7, 12, 18, 25 and 90 days. Ketamine alone caused moderate ataxia which was more pronounced in younger animals. In combination with both aforementioned convulsants, ketamine exerted anticonvulsant effects against generalized tonic-clonic seizures in all developmental stages studied. This effect was more pronounced in bicuculline-treated animals. Moreover, ketamine also suppressed the lethality induced by both drugs during all the development. On the contrary, the action of ketamine on minimal (clonic) seizures was moderate or absent. Our results suggest an important role of ketamine-affected transmission in the generation of the generalized tonic-clonic seizure pattern; moreover, an action of high doses of ketamine on GABA-A receptors might be present.

Aging↗
PubMed1990

Claustro-neocortical projections in the rhesus monkey (projections to area 6).

The distribution of claustral neurons projecting to area 6 on the convexity and medial wall of the hemisphere was studied in four macaque monkeys. In all cases, HRP-positive neurons were found almost throughout the antero-posterior extent of the claustrum in its dorsal half. Following HRP injections in area 6 on the medial wall of the hemisphere most of the labelled neurons were found in the dorsal and dorsolateral portions of the claustrum. After injections in area 6 on the hemispheral convexity, labelled neurons predominated in about the middle third of the vertical extent of the claustrum. Perikaryal polymorphism and considerable differences in perikaryal size are features characteristic of claustral neurons projecting to area 6. There is a preponderance of labelled neurons whose perikarya are noted for their multipolar or pyramidal (triangular) shape. Oval and spindle-shaped neurons were found less frequently. The size of the perikarya ranged from 11 to 26 microns while most of the labelled neurons had perikarya ranging form 14 to 18 microns in size.

Animals↗