Biomedical subjects

G Hesslow

Publications and source records attributed to G Hesslow.

26 records · Page 2Linked to original sources

PubMed1986

Inhibition of inferior olivary transmission by mesencephalic stimulation in the cat.

Cerebellar climbing fiber responses (CFRs) evoked in anesthetized cats by stimulation of peripheral nerves, contralateral inferior olive and cerebellar white matter were investigated by recording unit activity and surface field responses in anterior lobe of cerebellar cortex. When nerve and olive stimulation was preceded at long intervals (greater than 35 ms) by weak electrical stimulation of an ipsilateral mesencephalic area close to the locus coeruleus and brachium conjunctivum, CFRs could be virtually abolished in the pars intermedia but not in the vermis. White-matter evoked CFRs were not affected; thus the site of the inhibition was the inferior olive.

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PubMed1986

The secondary spikes of climbing fibre responses recorded from Purkinje cell somata in cat cerebellum.

Extracellularly recorded climbing fibre responses in Purkinje cell somata in the cerebellar cortex were investigated in cats deeply anaesthetized with barbiturate. The effects on the amplitude of initial and secondary spikes of preceding climbing fibre activation, on-beam parallel fibre activation and off-beam parallel fibre activation were studied. When a climbing fibre response was preceded by climbing fibre activation there was a decrease in the amplitude of the initial spike of the second response at intervals up to 25 ms and little effect at longer intervals. Secondary spike amplitude was greatly increased at intervals up to 100 ms. When a complex spike was preceded by on-beam parallel fibre activation there was a decrease in the initial spike amplitude at short intervals and an increase in the amplitude at long intervals. Secondary spike amplitude was increased up to 150 ms after an on-beam parallel fibre volley. When a complex spike was preceded by off-beam parallel fibre stimulation there was an increase in initial spike amplitude at intervals up to about 200 ms and a decrease in secondary spike amplitude at intervals up to about 150 ms. The results show that the amplitude of the secondary spikes can be modified by a preceding input to the Purkinje cell. The results also suggest that the secondary spikes are generated in the Purkinje cell dendrites and the initial spike in the soma.

Action Potentials↗

PubMed1986

The secondary spikes of climbing fibre responses recorded from Purkinje cell axons in cat cerebellum.

Responses evoked in Purkinje cells by climbing fibre activity were investigated by recording from Purkinje cell axons in the cerebellum of anaesthetized cats. Purkinje cell axons were identified by firing pattern and by latency of responses to stimulation of peripheral nerve and of the inferior olive. Axonal climbing fibre responses usually consisted of one to two spikes, suggesting that normally only the initial spike or, at most, this and one of the secondary spikes are propagated down the Purkinje cell axon. When two successive climbing fibre responses were evoked, the number of spikes in the second response was increased, usually up to three to five. This effect could be obtained at stimulation intervals of up to 100 ms. In a few cases it was possible for a climbing fibre response to be preceded by a parallel fibre volley evoked by stimulation of the cerebellar surface. This increased the number of spikes in the axonal climbing fibre response. The results suggest that the number of propagated spikes in the climbing fibre response can be modified by a preceding input to the Purkinje cell.

Action Potentials↗

PubMed1984

Plateau potentials evoked by climbing-fibre stimulation are restricted to the Purkinje cell dendrites of the cat.

The present study investigated the duration of afterdepolarizations in Purkinje cell somata following climbing-fibre activation. Intracellular recordings revealed that, in cells with membrane potentials more negative than -50 mV and with normal spike-generating capabilities, climbing-fibre activation resulted in somatic responses with short afterdepolarizations. As the cell deteriorated and the resting membrane potential became more positive, the duration and form of the climbing-fibre response resembled the plateau potentials recorded from proximal dendrites. The absence of plateau potentials in undamaged Purkinje cell somata was confirmed by extracellular recording of test spike amplitudes following evoked climbing-fibre responses.

Animals↗

PubMed1983

Dendritic plateau potentials evoked in Purkinje cells by parallel fibre volleys in the cat.

Responses evoked in Purkinje cell dendrites by parallel fibre volleys and climbing fibre impulses were investigated by intra- and extracellular recording from cat cerebellar cortex. The depth distribution of recording sites suggested that the intracellular recordings were predominantly from proximal dendrites whereas the extracellular recordings were predominantly from distal dendrites. Parallel fibre stimulation evoked monosynaptic excitation and disynaptic inhibition in the dendrites and, at higher strength, prolonged plateau-like responses in distal dendrites but only rarely in proximal dendrites. However, when the inhibitory synapses were blocked with topically applied picrotoxin, parallel fibre volleys evoked plateau potentials also in proximal dendrites. The duration of the parallel-fibre-evoked plateau potentials in distal dendrites was prolonged by increasing the intensity of the eliciting stimulus or by increasing the number of stimuli. A similar prolongation in the duration of climbing-fibre-evoked plateau potentials was observed when brief repetitive stimulation was applied to the inferior olive. The investigation provided evidence that under physiological conditions plateau potentials in Purkinje cell dendrites are exclusively evoked by climbing fibre impulses.

Action Potentials↗

PubMed1983

Interaction between responses in Purkinje cells evoked by climbing fibre impulses and parallel fibre volleys in the cat.

The plateau-like depolarizing potentials evoked in Purkinje cell dendrites by impulses in climbing fibres (Ekerot & Oscarsson, 1981) were conditioned by single parallel fibre volleys and investigated by intra- and extracellular recording from cat cerebellar cortex. The conditioning parallel fibre volleys evoked predominantly inhibitory potentials of long duration in the Purkinje cell dendrites. Massive parallel fibre volleys, which may evoke plateau-like depolarizing potentials (Campbell, Ekerot, Hesslow & Oscarsson, 1983) were avoided. In proximal dendrites parallel fibre volleys preceding climbing fibre responses reduced or abolished the plateau potential, whereas the initial spike-like component of the climbing fibre responses was largely unaffected. Parallel fibre stimulation during already established plateau potentials immediately terminated the plateaus. In distal dendrites parallel fibre stimulation preceding climbing fibre responses reduced or abolished both the plateau potential and the initial component of the climbing fibre responses. Parallel fibre stimulation during established plateau potentials did not immediately terminate the plateau potentials but reduced their duration. The results of the present investigation suggest that single dendritic branches of Purkinje cells serve as independent integrators of mossy fibre and climbing fibre inputs.

Action Potentials↗

PubMed1983

Interaction between mossy fibre and climbing fibre responses in Purkinje cells.

A major problem in cerebellar physiology relates to the manner in which information from mossy fibres and climbing fibres is integrated in the efferent neurones of the cerebellar cortex, the Purkinje cells. Recent findings by Ekerot and Oscarsson [8] and by Ito, Sakurai and Tongroach [13] indicate that the important interaction between mossy fibres and climbing fibres takes place in the dendrites rather than in the Purkinje cell somata. It has been demonstrated that impulses in climbing fibres evoke not only the so-called "complex spikes" in the somata but also plateau-like depolarizations in the distal dendrites which may have durations of hundreds of ms. The plateau potentials are presumably produced by a voltage dependent calcium conductance increase which, under physiological conditions, is triggered off exclusively by the large synaptic potentials generated by climbing fibre impulses. The spread of the plateau potentials to the distal dendrites and their long duration would facilitate spatial and temporal interaction between the mossy fibre and climbing fibre inputs. The findings suggest two kinds of interaction. (1) The duration of the plateau potentials in individual dendritic branches is modulated by the local mossy fibre/parallel fibre input. Thus, it might be postulated that dendritic branches act as independent integrators of mossy fibre and climbing fibre inputs. (2) It has been suggested that interaction between mossy fibres and climbing fibres forms the basis of learning processes in the cerebellum mediated through plastic changes in the synapses between parallel fibres and Purkinje cell dendrites. The plateau potentials would influence parallel fibre synapses by increasing the intradendritic calcium which, in turn, would lastingly depress the sensitivity of the postsynaptic receptors of the parallel fibre synapses that are activated in conjunction with the climbing fibres.

Animals↗

PubMedDate not supplied

Effect of varying the intensity and train frequency of forelimb and cerebellar mossy fiber conditioned stimuli on the latency of conditioned eye-blink responses in decerebrate ferrets.

To study the role of the mossy fiber afferents to the cerebellum in classical eye-blink conditioning, in particular the timing of the conditioned responses, we compared the effects of varying a peripheral conditioned stimulus with the effects of corresponding variations of direct stimulation of the mossy fibers. In one set of experiments, decerebrate ferrets were trained in a Pavlovian eye-blink conditioning paradigm with electrical forelimb train stimulation as conditioned stimulus and electrical periorbital stimulation as the unconditioned stimulus. When stable conditioning had been achieved, the effect of increasing the intensity or frequency of the forelimb stimulation was tested. By increasing the intensity from 1 to 2 mA, or the train frequency from 50 to 100 Hz, an immediate decrease was induced in both the onset latency and the latency to peak of the conditioned response. If the conditioned stimulus intensity/frequency was maintained at the higher level, the response latencies gradually returned to preshift values. In a second set of experiments, the forelimb stimulation was replaced by direct train stimulation of the middle cerebellar peduncle as conditioned stimulus. Varying the frequency of the stimulus train between 50 and 100 Hz had effects that were almost identical to those obtained when using a forelimb conditioned stimulus. The functional meaning of the latency effect is discussed. It is also suggested that the results support the view that the conditioned stimulus is transmitted through the mossy fibers and that the mechanism for timing the conditioned response is situated in the cerebellum.

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