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C F Ekerot

Publications and source records attributed to C F Ekerot.

36 records · Page 2Linked to original sources
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↗
PubMed1982

Branching of olivary axons to innervate pairs of sagittal zones in the cerebellar anterior lobe of the cat.

Four of the eight sagittal zones in the cortex of the cerebellar anterior lobe, the x, c1, c3 and d2 zones, receive similar climbing fibre input from the ipsilateral forelimb through pathways ascending in the dorsal funiculus (DF-SOCPs) and have disynaptic relays in the main cuneate nucleus (Ekerot and Larson 1979a). The present investigation demonstrates that the forelimb areas of these four zones are innervated by climbing fibres from three groups of olivary neurones with branching axons (Fig. 6). The termination sites of climbing fibre branches were determined by identifying the low-threshold spots on the cerebellar surface from which short-latency (3.1-7.5 ms), "direct" climbing fibre responses could be evoked in Purkinje cells. In some Purkinje cells these responses were followed by late (8.2-13.5 ms) climbing fibre responses ("olivary reflex" responses). Each group projects to a pair of these zones which is separated by an intervening zone innervated from a private group of olivary neurones. The three groups of olivary neurones have been denoted the x-c1 group, the c1-c3 group, and the c3-d2 group in accordance with the zones they innervate. They project to the following areas: (a) The x-c1 group to the x zone in the vermal cortex and the lateral part of the c1 zone in the intermediate cortex; (b) the c1-c3 group to the medial parts of the c1 and c3 zones in the intermediate cortex; and (c) the c3-d2 group to the lateral part of the c3 zone in the intermediate cortex and the d2 zone in the extreme lateral part of the anterior lobe. Olivary axons belonging to the x-c1 and c1-c3 groups often send several climbing fibres to each projection area, whereas only single termination sites were found in the c3 zone for olivary axons belonging to the c3-d2 group. The two projection areas of each group of olivary neurons have a similar topographical organization: the areas innervated by the x-c1 group lack distinct somatotopical organization, whereas the areas innervated by the c1-c3 and c3-d2 groups have a detailed somatotopical representation of the ipsilateral forelimb. The low threshold spots for the late climbing fibre responses ("olivary reflex" responses) were restricted to the same sagittal strips as the low-threshold spots for the "direct" responses.

Afferent Pathways↗
PubMed1981

Prolonged depolarization elicited in Purkinje cell dendrites by climbing fibre impulses in the cat.

1. Responses evoked in Purkinje cell dendrites by impulses in climbing fibres were studied by recording from the cat cerebellar cortex. Intra- and extracellular responses from dendrites of single Purkinje cells were recorded, as well as field responses from the intact cerebellar surface. The intracellular responses were presumably recorded from relatively proximal dendrites. The resting potential usually was 20-40 mV. The responses consisted of an initial spike-like component (amplitude 10-30 mV) followed by a plateau-like component (amplitude 2-12 mV) with a duration of about 100 ms. The duration of consecutive responses varied little. 3. The extracellular unitary responses were recorded from more distal dendrites. These responses were negative deflexions consisting of an initial component followed by a plateau-like component (amplitude 5-15 mV). The duration of consecutive responses varied widely from about 25 ms to more than 1 s. The negative deflexions are assumed to correspond to dendritic depolarizations. 4. The field responses recorded from the cerebellar surface consisted of a positivity followed by a negativity lasting several hundred milliseconds. The positivity signals the e.p.s.p.s generated by the climbing fibre synapses which do not extend to the most distal dendrites. The negativity presumably signals the plateau-like dendritic depolarizations which would involve also the most distal dendrites. 5. The nature and significance of the plateau-like depolarizations evoked by climbing fibre impulses in the purkinje cell dendrites are discussed.

Animals↗
PubMed1980

Termination in overlapping sagittal zones in cerebellar anterior lobe of mossy and climbing fiber paths activated from dorsal funiculus.

The termination patterns in the cerebellar anterior lobe of one mossy fiber path, the exteroceptive component of the cuneocerebellar tract (E-CCT), and one climbing fiber system, the dorsal spino-olivocerebellar paths (DF-SOCPs), which both relay in the main cuneate nucleus, were compared in the cat. The E-CCT terminates in the ipsilateral half of the anterior lobe in five sagittal zones which overlap five of the eight zones activated from the DF-SOCPs. In at least one zone the E-CCT projection has a somatotopical organization which is similar to and overlaps that of the DF-SOCP.

Afferent Pathways↗
PubMed1979

The dorsal spino-olivocerebellar system in the cat. II. Somatotopical organization.

The somatotopical organization of the projection through the dorsal spino-olivocerebellar path (DF-SOCP) to the c3 zone in the cerebellar anterior lobe was studied by recording climbing fiber field potentials in the cerebellar cortex evoked on stimulation of peripheral nerves. The c3 zone was shown to contain a detailed and systematic representation of the ipsilateral body half with the follwing characteristics: 1. Single nerves project to one or two sagittal strips of cortex which extend across several folia. The width of the strips varies between 0.2 and 1 mm and the length may be as long as 15-20 mm along the unfolded cortex. 2. The strips activated from different nerves occur in an order which usually follows the segmental innervation, the hindlimb being represented rostrally and the forelimb caudally in the zone. 3. The double representation of some nerves makes it possible to distinguish one medial and one lateral part of the c3 zone with the projection areas organized approximately as mirror images. Additional observations on other zones activated by the DF-SOCP system (Ekerot and Larson, 1979a) indicate that the c1 zone, has a somatotopical organization which is reminiscent of that of the c3 zone, whereas the x and d1 zones have different topographical organizations.

Animals↗
PubMed1975

The lateral reticular nucleus in the cat. IV. Activation from dorsal funiculus and trigeminal afferents.

1. The activation of neurones in the mLRN (major portion of lateral reticular nucleus comprising its parvi- and magnocellular parts) be a spinal path ascending in the dorsal funiculus (DF) and by trigeminal afferents has been studied. 2. Stimulation of the DF at C3 activated about one half of the mLRN neurones. The latencies were 2-28 ms. In experiments with the spinal cord interrupted at C3 except for the DF it was shown that cutaneous and high threshold muscle afferents in mainly forelimb nerves were effective. The latencies of the responses to nerve stimulation were 8-27 ms. 3. Stimulation of trigeminal afferents evoked a response in about one third of the mLRN neurones. The latencies were 2-27 ms. 4. Activation from the DF- and trigeminal paths occurred often in the same mLRN neurones and the neurones activated from the two paths had a similar location in the nucleus and a similar termination in the cerebellar cortex. 5. The DF- and trigeminal paths had similar properties. Activation was evoked from both ipsilateral and contralateral nerves. Fast adapting hair receptors were commonly effective. 6. Evidence is presented indicating that the DF- and trigeminal paths share a common final path to the mLRN neurones which is formed by brain stem interneurones intercalated between the DF- and trigeminal nuclei and the mLRN. It is suggested that these interneurones represent a supraspinal motor centre. 7. Activation from the DF- and trigeminal paths occurred with unequal frequency among groups of mLRN neurones activated from different spinal paths ascending in the ipsilateral lateral funiculus (cf. Clendenin et al., 1974a).

Afferent Pathways↗