ISSN:
1432-1106
Keywords:
Cerebellar flocculus
;
Rat
;
Vestibular and optokinetic stimulation
;
Purkinje cell responses
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary 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 10–13.5 s 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 0.5–3 s. The velocity tuning curves of vestibular/OKS responding P-cells showed peak sensitivities with retinal slip velocities of 1.5–2°/s. This is higher than the ca. 1°/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 ipsior 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). These data suggest that there is a strong bilateral convergence of OKS input on P-cells for which there is supportive anatomical and electrophysiological evidence. Our results show that most floccular P-cells receive a strong head velocity signal and a synergistic optokinetic input which, as judged from the response time course, appear to be mediated by vestibular neurons as well as by other precerebellar neurons. In addition, P-cell discharge is presumably modulated by vestibular and optokinetic quick phases. The results are compared to those obtained in other species.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00239393
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