Response characteristics and vestibular receptor convergence of frog cerebellar purkinje cells. A natural stimulation study

A novel cerebellar commissure and other myelinated axons in the Purkinje cell layer of a pond turtle (Trachemys scripta elegans)

Parallel fibers in the molecular layer of the vertebrate cerebellum mediate slow spike conduction in the transverse plane. In contrast, electrophysiological recordings have indicated that rapid spike conduction exists between the lateral regions of the cerebellar cortex of the red-ear pond turtle (Trachemys scripta). The anatomical basis for this commissure is now examined in that species using neuronal tracing techniques. Fluorescently tagged dextrans and lipophilic carbocyanine dyes placed in one lateral edge of this nonfoliated cortex are transported across the midline of living brains in vitro and along the axonal membranes of fixed tissues, respectively. Surprisingly, the labeled commissural axons traversed the cortex within the Purkinje cell layer, and not in the white matter of the molecular layer or the white matter below the granule cell layer. Unlike thin parallel fibers that exhibit characteristic varicosities, this commissure is composed of smooth axons of large diameter that also extend beyond the cerebellar cortex via the cerebellar peduncles. Double labeling with myelin basic protein antibody demonstrated that these commissural axons are ensheathed with myelin. In contrast to this transverse pathway, an orthogonal myelinated tract was observed along the cerebellar midline. The connections of this transverse commissure with the lateral cerebellum, the vestibular nuclear complex, and the cochlear vestibular ganglia indicate that this commissure plays a role in bilateral vestibular connectivity.

Dynamic polarization vector of spatially tuned neurons

The study of the dynamic properties of otolith neurons has been difficult previously because of the differing response sensitivities of individual cells to specific stimulus directions and the lack of a general mathematical scheme that could explain and account for all their response features. The present paper describes a method for estimating both the spatial and temporal properties of neurons like the otolith neurons that are spatially tuned to different stimulus directions. At each stimulus frequency, a response elipse can be constructed from the neural responses elicited by stimulation along three linear independent axes. The semimajor axis of the ellipse will specify the neuron's direction of maximum sensitivity (polarization vector), whereas the semiminor axis will provide its sensitivity in the perpendicular direction. The predictions of the method for nonzero length of the semiminor axis are qualitatively the same as the experimentally observed dependance of response phase on stimulus orientation.

Temperature compensation in the vestibulo-ocular reflex: a novel hypothesis of cerebellar function

Some ectothermic animals are subject to changes of body temperature during routine activity. How are they able to maintain co-ordinated behaviour? Analysis of the available evidence on the effects of temperature on the vestibulo-ocular reflex suggests that there will be a degree of automatic temperature compensation. Temperature will increase the gain of some components of the reflex, and decrease the gain of others resulting in a reduced temperature sensitivity of the overall reflex. It is suggested that the cerebellum may provide the balance of temperature compensation required to maintain adequate reflex function. The hypothesis is that type III (bidirectionally sensitive) Purkinje cells receive temperature information as a common-mode signal from the opposing labyrinths, and use this information to regulate the gain of the vestibulo-ocular reflex pathway.

Response properties of cerebellar neurons to stimulation of the frog glossopharyngeal nerve and tongue

The cerebellum receives information from many kinds of sensory organs (muscle, somatosensory, auditory, vestibular, visual) as well as from the autonomic system. The cerebellum presumably has a role in the control of tongue movement and salivary secretion. However, the relationship between cerebellar neuron activity and tongue sensation has not been investigated previously. In the present study, negative cerebellar field potentials in the molecular layer and single unit responses of Purkinje cells induced by electrical stimulation of the bullfrog glossopharyngeal (IXth) nerve or tongue surface were investigated. The interaction between IXth nerve stimulation and natural (taste and touch) stimulation of the tongue in their effects on cerebellar neuron activity were investigated. The negative field potentials were potentiated by a brief train of electrical pulses to the tongue or IXth nerve. With electrical stimulation of the tongue surface, several fungiform papillae were needed to elicit cerebellar field potentials. The latency of Purkinje cells following IXth nerve stimulation was 44.4-53.6 msec for complex spikes, whereas for simple spikes two maxima were seen, with mean values at 33.9-36 msec and 96.8 msec. A preceding electrical stimulation of the IXth nerve depressed the negative field potentials or Purkinje cell complex spike responses induced by test stimulation of the IXth nerve. These depressive effects were also seen following a preceding natural stimulation of the tongue and were dependent upon the type of preceding stimulation. The depressive effects were produced by preceding stimulation with NaCl, CaCl2, water, and touch, but not with quinine and acetic acid stimulation. These results clearly demonstrate that gustatory and tactile signals from the tongue can influence cerebellar neuron activity.

Visual (optokinetic), somesthetic and vestibular inputs to the frog cerebellum

Unitary response to visual (optokinetic), somesthetic (neck and limb) and vestibular stimulation were recorded from the Purkinje cell layer throughout most of the dorsal surface of the frog cerebellum. Simple spike activity in Purkinje cells and activity from cells without complex spikes were considered. Optokinetic responses (types I-III) were restricted to the dorsal rim and auricular lobes. Units were sensitive to very small velocity of optokinetic cylinder rotation (0.02-0.03 degrees/s) with peak sensitivity at about 1 degree/s. On the average an approximately linear relation of response amplitude to stimulus velocity was observed from 0.02 to 1 degree/s. The response progressively diminished above 1 degree/s to become very small at 30 degrees/s. Asymmetric response and silencing of firing during part of the cycle were nonlinearities observed with sinusoidal optokinetic stimulation in the range of 0.02-1 Hz, +/- 5-10 degrees (peak velocities 0.8-30 degrees/s). Somesthetic responses were recorded throughout most of the corpus cerebelli proper but the strongest input was to rostral regions. No somatotopic arrangement was found. Rather, convergence from more than one limb and neck was relatively common. Adaptation to successive cycles of stimulation was characteristic of somesthetic responses. Vestibular responses (type I-IV) were recorded throughout most of the explored area but the strongest input was to the dorsal rim and auricular lobes. From the analysis of unitary activity, the dorsal rim and auricular lobes are shown to be functionally linked to the vestibular and optokinetic systems whereas the explored part of the corpus is linked to the somesthetic and vestibular systems.

Responses of units in the rat cerebellar flocculus during optokinetic and vestibular stimulation

The simple (SS) and complex spike (CS) responses of Purkinje (P-cells) and non-Purkinje (non P-cells) in the cerebellar flocculus were studied in alert pigmented rats (DA-HAN) during binocular and monocular optokinetic stimulation (OKS), vestibular stimulation and a combination of the two. Of a total of 98 P-cells whose SS discharges were activated by rotary stimulation of the horizontal canal in the dark (type I and type II P-cells), the vast majority (72%) responded to constant velocity binocular OKS that was produced by means of a horizontal shadow projector system. The remaining P-cells responded only to vestibular stimulation (19%), to OKS or to the presumed fast components of optokinetic and vestibular nystagmus (9%). The optokinetic responses of P-cells were generally bidirectional but asymmetrical, i.e., the increases in rate in one direction were larger in magnitude than decreases on opposite OKS and were synergistic with the semicircular canal input. During constant velocity OKS, the discharge of a few P-cells rose approximately exponentially, outlasted the stimulus by as much as 10-13.5s and, thus, resembled OKS responses of vestibular nucleus neurons. However, the majority exhibited a phasic-tonic response governed by a short "time constant" of from 0.5-3s. The velocity tuning curves of vestibular/OKS responding P-cells showed peak sensitivities with retinal slip velocities of 1.5-2 degrees/s. This is higher than the ca. 1 degree/s determined for other relay nuclei of the horizontal optokinetic pathway. The responses of non P-cells suggest that they originate from mossy fiber projections from vestibular, visual (optokinetic) and saccadic eye movement-related areas of the brainstem. Most of the units carried a combined vestibular and optokinetic signal. The majority showed a bidirection-selective response to OKS, and a small percentage showed unidirectional responses only. Monocular testing of P-cells revealed that most received a bidirection-selective, but asymmetrical, OKS input. Slightly more than half of these had a strongest OKS drive from the contralateral eye; the remaining units were driven most strongly by the ipsilateral eye. Unidirection-selective P-cells, driven by OKS to the ipsi- or contralateral eye, were uncommon; yet this class is common among other portions of the horizontal optokinetic system (e.g., vestibular nuclei, praepositus hypoglossi nucleus, nucleus reticularis tegmenti pontis).(ABSTRACT TRUNCATED AT 400 WORDS)

Input to the vestibulo cerebellum and triceps brachii motoneurons during natural vestibular stimulation in frog

The response of cerebellar Purkinje cells and nerve triceps brachii was recorded in paralyzed frogs during natural vestibular stimulation. The response from about 63% of the Purkinje cells (mossy fiber input) recorded in the vestibulo cerebellum and of the triceps nerve during triangular wave roll oscillation consisted of activity increase during the ipsilateral side-down half of the cycle and decrease during the contralateral side-down half. It was shown that this activity, which originates partially from ipsilateral vertical canals, can be added to, or suppressed by, otolithic activity, depending on head position and direction rotation. The fact that the response of Purkinje cells was similar to that of triceps nerve implies that the vestibulo-cerebellum receives information of vestibular signals passing to the motor system. The characteristics of otolithic-canal interaction recorded in triceps nerve may explain the motor disturbances that result from lesions of otolithic receptors.

A mechanism for type III vestibular responses of frog cerebellar Purkinje cells

Type III Purkinje cells (P-cells), which are excited with both directions of horizontal rotation, are found in high numbers in the frog auricular lobe and adjacent cerebellar areas. To examine the mechanisms underlying these responses, recordings were made from P-cells in curarized animals during rotational stimulation of the horizontal canals. The horizontal canal input to these cells was then modified unilaterally by VIIth nerve section, intraperilymphatic injection of local anesthetic, or by caloric stimulation. Control recordings were also obtained from peripheral canal neurons. Type III responses were abolished by unilateral lesions or reversible blockage of the VIIIth nerve with local anesthetic. The remaining responses were attributable only to the unaffected horizontal canal, ie. only type II or type I responses were observed upon interruption of the ipsi-or contralateral nerve, respectively. The level of spontaneous activity of cerebellar input fibers was low and during rotation produced 'cell silencing' response waveform asymmetries (facilitation greater than disfacilitation). When the level of peripheral resting activity was increased (warm water irrigation), thereby increasing horizontal canal response symmetry, type III responses were reduced in magnitude or abolished. Conversely, cold water irrigation, which decreases the resting rate and response symmetry of input fibers, enhanced type III response magnitudes. On the basis of these results, it is suggested that type III responses result from the fact that single P-cells receive a facilitatory input from both horizontal canals. Since these inputs are 180 degrees phase-reversed and their response waveforms asymmetrical, their resulting postsynaptic effect is a net excitation during both portions of the stimulus cycle.