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PubMed1991

Extrapyramidal disturbances after cyanide poisoning (first MRT-investigation of the brain).

A 29 year old student of chemistry took 50 ml of a 1% potassium cyanide solution (500 mg) in attempted suicide. He became comatose, mydriatic and was admitted to hospital in an apneic state. He woke up after seven hours and developed Parkinsonism in the following weeks. This regressed slowly in the second month after the poisoning apart from dysarthria, bradykinesia of the upper limbs and very brisk monosynaptic reflexes. Three weeks after the intoxication, CCT was largely normal, and there was CSF-dense hypodensity in both putamina after five months. Sharply delimited signal elevation in T2 corresponding to the two putamina was detected in the MRI eight weeks and five months after ingestion of the poison.

Adult↗
PubMed1991

Influence of different properties of a reaction time task on the pre-movement gating of input from Ia afferents to motoneurons.

The monosynaptic reflex (H reflex) is facilitated before movement onset in human subjects who are performing a conditioned plantar flexion of the ankle in a reaction time task. The aim of this study was to investigate how tightly this gating of Ia spindle input is coupled with the conditioned muscle contraction. Test H reflexes were elicited at various times during the reaction time (RT) in order to test the efficacy of Ia volleys on the soleus motoneurons. Tactile, auditory and visual go stimuli were used. The RT to a tactile stimulus was about the same as the RT to an auditory stimulus although distance and therefore conduction time from the site of stimulation to the cerebral cortex was much larger for the tactile than for the auditory modality. The RT to visual stimulation was about 20 ms longer than to the other two modalities. Although central latencies depended clearly on the stimulus modality the duration of the H reflex facilitation, i.e. the interval between the onset of the facilitation and the onset of the voluntary muscle contraction, was always the same. Similarly, the reflex facilitation was insensitive to the succeeding contrast of a visual go stimulus. The subjects were also examined in visual RT tasks in which different advance information about the laterality and the execution of the contraction was given. By combination the following four RT situations were realized: (1) simple, go, (2) choice, go, (3) simple, go-no go and (4) choice, go-no go.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1980

Localization and neurophysiological properties of motoneurones of the M. triceps surae of the rat after retrograde labelling with Evans blue.

Evans blue was injected into either the medial and lateral gastrocnemius or the soleus muscle of adult albino rats to mark retrogradely the corresponding motoneurones in the spinal cord. The labelled motoneurones were identified by the red fluorescence of their perikarya in the ventral horn of segments L4--L6. In addition, a monosynaptic reflex action potential was recorded only in the ventral roots L4--L6 after stimulation of the nerves to the medial and lateral gastrocnemius and the soleus muscle. Excitability and reflex latencies of labelled and unlabelled motoneurones of segment L4--L6 as well as the conduction velocities of their axons were measured. Apart from a small but statistically nonsignificant increase in excitability, no functional differences were found between labelled and control neurones. Thus, retrograde labelling of motoneurones with Evans blue prior to performing electrophysiological experiments has the advantage that the marked motoneurones can be identified under the fluorescence microscope without the need of additional staining or fixation.

Action Potentials↗
PubMed1986

Habituation and conditioning of the human long latency stretch reflex.

The effects of stretch repetition rate, prior warning stimuli and self administered stretch were examined on the size of the short and long latency components of the stretch reflex electromyographic EMG response in flexor pollicis longus and the flexor muscles of the wrist and fingers. Stretches of constant velocity and extent were given every 10 s, 5 s, 2 s, or 1 s to either the wrist or thumb during a small background contraction of the flexor muscles. The size of the long latency component of the stretch reflex (measured as the area under the averaged rectified EMG responses) declined dramatically at faster repetition rates, especially in the wrist and finger flexors. The size of the short latency component was relatively unaffected. The size of the electrically elicited H-reflex in forearm muscles also failed to habituate under the same conditions. If each individual trial of a series was examined, the long latency component of the stretch reflex EMG could be seen to decrease in size over the first three to six stretches if stretches were given every 1 s, but not if stretches were given every 10 s. When stretches were given every 5 s to either wrist or thumb, an electrical stimulus applied to the digital nerves of the opposite hand 1 s before stretch reduced the size of the long latency component of the reflex EMG response. The short latency component was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1975

The vestibulospinal tract: crossed and uncrossed effects on hindlimb motoneurones in the cat.

Effects produced by stimulation of Deiters' nucleus on contralateral hindlimb motoneurones were investigated in the cat with intracellular and monosynaptic reflex recording. Polysynaptic PSPs were evoked in all species of motoneurone examined. The minimal synaptic linkage was found to be disynaptic in the excitatory path and prisynaptic in the inhibitory path. Experiments with various lesions to the spinal funiculus and those with mapping of the stimulated sites in the brain stem showed that the effects were evoked almost exclusively via the lateral vestibulospinal tract of the stimulated side. The crossed effects were excitatory in extensor motoneurones of all species studied except for hip extensors (ABSm) in which EPSPs and/or IPSPs were evoked. The effects on flexors, by contrast, were not simple and consisted of EPSPs, IPSPs or a mixture of both. The difference in effects depended, though not entirely, on the species of motor nucleus. Between the excitatory and inhibitory effects on knee flexor (PBSt) motoneurones the former predominated under chloralose and the latter under pentobarbital anaesthesia. By recording PSPs evoked from the two vestibulospinal tracts in the same motoneurone, the convergence pattern and the magnitude of effects from the two tracts were studied. The interneuronal organization of the crossed vestibulo-motoneuronel pathway and its functional significance are discussed.

Animals↗
PubMed1975

Recurrent inhibition of individual Ia inhibitory interneurones and disinhibition of their target alpha-motoneurones during muscle stretches.

The effects of ramp stretches applied to triceps surae muscle on the discharge patterns of single Ia inhibitory interneurones, monosynaptically invaded from various nerves, were studied in either decerebrate or anesthetized cats. Interneurones which received direct excitatory Ia input from the stretched muscle exhibited augmented activity both during the dynamic and static phase of stretch, which was, however, interrupted by a transient inhibitory influence during the dynamic phase of stretch. The influences on Ia inhibitory interneurones, monosynaptically invaded from hamstring or tibial nerve, were exclusively inhibitory. These stretch-induced inhibitions were better demonstrable in decerebrate than in anesthetized preparations. The timing of the discharge patterns of additionally recorded Renshaw cells during stretch, and the disappearance or reduction of the above described inhibitory effects after administration of DHE, strongly support the idea that these inhibitory actions are caused by Renshaw inhibition. In Ia inhibitory interneurones, monosynaptically activated from the antagonistic peroneal nerve, stretch induced also pronounced inhibitory effects, which were most probably caused by mutual inhibition between Ia inhibitory interneurones. The suppression of agonistic Ia inhibitory interneurone activity below the tonic resting activity corresponded to an enhancement of the monosynaptic reflex amplitude of the antagonistic motoneurone pool. The findings suggest that normal orthodromic activation of Renshaw cells, and consequently the recurrent inhibition of the Ia inhibitory interneurones, is predominantly linked with rapid phasic, rather than slow tonic, motoneuronal firing. The functional role of this mechanism for the performance of rapidly alternating movements and the damping of ballistic agonist contractions is discussed.

Animals↗
PubMed1991

CSF baclofen levels after intrathecal administration in severe spasticity.

The pharmacokinetic parameters in the CSF of baclofen given to 4 patients as an intrathecal bolus are reported. Considerable inter-individual variability in the parameters was observed. The elimination half-life ranged from 0.9 to 5 h and the clearance from 0.013 to 0.08 l.h-1. In order to optimize treatment, it is suggested that CSF baclofen levels be matched to changes in Hoffman's monosynaptic reflex (H reflex).

Adult↗
PubMed1986

Effects of "partial axotomy" upon synaptic function.

A lesion limited to the dorsal columns, at the level of L3-L4, was carried out in chronic cats. This operation produced a "partial axotomy" type of lesion on the ascending branches of Ia hind limb afferents. Two to six months after this operation, intracellular studies on L7-S1 motoneurons were carried out. Similar studies were done in normal animals. The peak amplitude and the rate of rise (dV/dt) of heteronymous EPSP's were studied during control conditions (sampling at 1 Hz) and during the post-tetanic potentiation produced by a 500 Hz tetanus (for 3 s). The analysis of these synaptic potentials makes us conclude that: The amplitude of the enlarged EPSP's, observed during PTP, seems to be linearly dependent on their amplitude during control (i.e., pre-tetanus) conditions. Judging by their amplitude, there is no difference between potentiated EPSP's of operated and normal animals. There is also a linear relationship between the rate of rise of EPSP's and their peak amplitude. The slope of this relationship becomes steeper after "partial axotomy", i.e., for a given EPSP amplitude, the dV/dt of its rising part is steeper in operated cats. This steeper slope is also present in EPSP's studied during PTP. The sharper rate of rise of EPSP's, induced by the "partial axotomy" of Ia fibers, would be the mechanism behind the larger monosynaptic reflex previously observed in these operated cats.

Afferent Pathways↗
PubMed1988

Computer tomography and magnetic resonance imaging in cyanide poisoning.

A 29-year-old chemistry student took 50 ml of a 1% potassium cyanide solution (500 mg) in an attempted suicide. He became comatose, mydriatic, and was admitted to hospital in an apneic state. He woke up after 7 h and developed Parkinsonism in the following weeks. This regressed slowly during the 2 months after the poisoning apart from dysarthria, bradykinesia of the upper limbs, and very brisk monosynaptic reflexes. At 3 weeks after the intoxication, computerized tomography was largely normal, and there was CSF-dense hypodensity in both putamina after 5 months. Sharply delimited signal elevation in T2 corresponding to the two putamina was detected by magnetic resonance imaging 8 weeks and 5 months after ingestion of the poison.

Adult↗
PubMed1988

Coerulospinal influence on recurrent inhibition of spinal motonuclei innervating antagonistic hindleg muscles of the cat.

The locus coeruleus's (LC's) effect on recurrent inhibition of gastrocnemius-soleus (GS) and common peroneal (CP) monosynaptic reflexes (MSRs) was demonstrated to exceed the concomitant facilitation, indicating the independency of LC's disinhibition and facilitation measures in this study. In contrast, the disinhibition effect correlated closely with the recurrently inhibited MSRs. The disinhibition phenomenon was also accompanied by progressive delay and diminution in the Renshaw cell field potential. Hence, the recovery of recurrently inhibited MSRs was probably due, in part at least, to the LC's inhibition of the related Renshaw cell activity. Furthermore, the site-specific, discordant changes in the disinhibition of GS, compared with CP MSRs, as revealed by tracking studies imply that representations of these antagonistic motonuclei may occupy different LC loci. Accordingly, the nonuniform disinhibition may be due to the activation of discrete aggregates of LC neurons which are responsible predominantly in controlling the recurrent inhibitory pathway belonging to one or the other of the antagonistic motonuclei. These findings support a differential LC inhibitory control of Renshaw cell activity, releasing the related motoneurones for the Ia synaptic transmission - a disinhibitory process that is crucial for the LC's independent control of the recurrent circuit of antagonistics extensor and flexor motoneurons.

Animals↗
PubMed1990

Spatial properties of second-order vestibulo-ocular relay neurons in the alert cat.

Second-order vestibular nucleus neurons which were antidromically activated from the region of the oculomotor nucleus (second-order vestibuloocular relay neurons) were studied in alert cats during whole-body rotations in many horizontal and vertical planes. Sinusoidal rotation elicited sinusoidal modulation of firing rates except during rotation in a clearly defined null plane. Response gain (spike/s/deg/s) varied as a cosine function of the orientation of the cat with respect to a horizontal rotation axis, and phases were near that of head velocity, suggesting linear summation of canal inputs. A maximum activation direction (MAD) was calculated for each cell to represent the axis of rotation in three-dimensional space for which the cell responded maximally. Second-order vestibuloocular neurons divided into 3 non-overlapping populations of MADs, indicating primary canal input from either anterior, posterior or horizontal semicircular canal (AC, PC, HC cells). 80/84 neurons received primary canal input from ipsilateral vertical canals. Of these, at least 6 received input from more than one vertical canal, suggested by MAD azimuths which were sufficiently misaligned with their primary canal. In addition, 21/80 received convergent input from a horizontal canal, with about equal number of type I and type II yaw responses. 4/84 neurons were HC cells; all of them received convergent input from at least one vertical canal. Activity of many vertical second-order vestibuloocular neurons was also related to vertical and/or horizontal eye position. All AC and PC cells that had vertical eye position sensitivity had upward and downward on-directions, respectively. A number of PC cells had MADs centered around the MAD of the superior oblique muscle, and 2/3 AC cells recorded in the superior vestibular nucleus had MADs near that of the inferior oblique. Thus, signals with spatial properties appropriate to activate oblique eye muscles are present at the second-order vestibular neuron level. In contrast, none of the second-order vestibuloocular neurons had MADs near those of the superior or inferior rectus muscles. Signals appropriate to activate these eye muscles might be produced by combining signals from ipsilateral and contralateral AC neurons (for superior rectus) or PC neurons (for inferior rectus). Alternatively, less direct pathways such as those involving third or higher order vestibular or interstitial nucleus of Cajal neurons might play a crucial role in the spatial transformations between semicircular canals and vertical rectus eye muscles.

Animals↗
PubMed1997

Development in neonatal rats of the sensory resetting of the locomotor rhythm induced by NMDA and 5-HT.

Developmental changes in the effects of quadriceps (Q) nerve stimulation on the locomotor rhythm induced by a mixture of N-methyl-D-aspartic acid and 5-hydroxytryptamine were examined using in vitro preparations from neonatal rats at postnatal days (P) 1-6. The effects of such stimulation on the rhythm were dependent both on stimulus strength and on the age of the animal. Low-intensity stimulation (< or =3.0 x T, where T=threshold for the monosynaptic reflex) during the flexor phase reset the rhythm via a prolongation of the flexor burst in most rats at P1-3, but via flexor burst truncation at P4-6. At any age, low-intensity stimulation during the extensor phase had no consistent effect on the ongoing rhythm. Activation of muscle afferents evoked via isometric contraction of the Q muscle caused effects similar to those obtained on low-intensity electrical stimulation in all age groups. In all age groups, high-intensity stimulation (> or =5.0 x T) caused resetting when delivered during the flexor phase via a prolongation of the flexor burst and during the extensor phase via a truncation of the extensor burst. These results suggest that the type of resetting evoked from low-threshold muscle afferents changes drastically during postnatal weekl, while effects evoked from high-threshold afferents remain unchanged.

Aging↗
PubMed1985

Influences of periodontal and mandibular-joint receptors on reflex sensitivity of human jaw-closing muscles.

Reflex sensitivity from stimulating the chin or the dental arch of the mandible and the influences of periodontal and mandibular joint receptors on jaw muscles were investigated by experiments with and without anaesthesia. The findings showed that periodontal receptors exert an inhibitory influence on motoneural excitability of jaw-closing muscles and facilitate alpha-motoneurones of the digastric muscle and that the silent period following a jaw jerk is partly caused by inhibition of alpha-motoneurones of jaw-closing muscles due to activity of periodontal receptors. The ratio of reflex activity in temporal and masseter muscles appeared to depend on the position of the applied stimulus. The mandibular joint receptors appear to play a major part in distributing active muscle-force over these muscles.

Adult↗