Floccular Modulation of Vestibuloocular Pathways and Cerebellum-Related Plasticity: An In Vitro Whole Brain Study

• Published in: Journal of neurophysiology Vol. 84; no. 5; pp. 2514 - 2528
• Main Authors: Babalian, Alexander L, Vidal, Pierre-Paul
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01-11-2000
• Subjects: Abducens Nerve - cytology; Abducens Nerve - physiology; Animals; Cerebellum - cytology; Cerebellum - physiology; Electric Stimulation; Excitatory Postsynaptic Potentials - physiology; Female; flocculus; Guinea Pigs; In Vitro Techniques; Male; Neural Inhibition - physiology; Neuronal Plasticity - physiology; Neurons, Efferent - physiology; Oculomotor Nerve - cytology; Oculomotor Nerve - physiology; Purkinje Cells - physiology; Reflex, Vestibulo-Ocular - physiology; Vestibular Nerve - cytology; Vestibular Nerve - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.2000.84.5.2514

Laboratoire de la Neurobiologie des Réseaux Sensorimoteures,
Centre National de la Recherche Scientifique, 75270 Paris Cedex 06, France
Babalian, Alexander L. and
Pierre-Paul Vidal.
Floccular Modulation of Vestibuloocular Pathways and
Cerebellum-Related Plasticity: An In Vitro Whole Brain Study. J. Neurophysiol. 84: 2514-2528, 2000. The isolated whole brain (IWB) preparation of the guinea pig was used
to investigate the floccular modulation of vestibular-evoked responses
in abducens and oculomotor nerves and abducens nucleus; for
identification of flocculus target neurons (FTNs) in the vestibular nuclei and intracellular study of some of their physiological properties; to search for possible flocculus-dependent plasticity at
the FTN level by pairing of vestibular nerve and floccular stimulations; and to study the possibility of induction of long-term depression (LTD) in Purkinje cells by paired stimulation of the inferior olive and vestibular nerve. Stimulation of the flocculus had
only effects on responses evoked from the ipsilateral (with respect to
the stimulated flocculus) vestibular nerve. Floccular stimulation
significantly inhibited the vestibular-evoked discharges in oculomotor
nerves on both sides and the inhibitory field potential in the
ipsilateral abducens nucleus while the excitatory responses in the
contralateral abducens nerve and nucleus were free from such
inhibition. Eleven second-order vestibular neurons were found to
receive a short-latency monosynaptic inhibitory input from the
flocculus and were thus characterized as FTNs. Monosynaptic inhibitory
postsynaptic potentials from the flocculus were bicuculline sensitive,
suggesting a GABA A -ergic transmission from
Purkinje cells to FTNs. Two of recorded FTNs could be identified as
vestibulospinal neurons by their antidromic activation from the
cervical segments of the spinal cord. Several pairing paradigms were
investigated in which stimulation of the flocculus could precede,
coincide with, or follow the vestibular nerve stimulation. None of them led to long-term modification of responses in the abducens nucleus or
oculomotor nerve evoked by activation of vestibular afferents. On the
other hand, pairing of the inferior olive and vestibular nerve
stimulation resulted in approximately a 30% reduction of excitatory
postsynaptic potentials evoked in Purkinje cells by the vestibular
nerve stimulation. This reduction was pairing-specific and lasted
throughout the entire recording time of the neurons. Thus in the IWB
preparation, we were able to induce a LTD in Purkinje cells, but we
failed to detect traces of flocculus-dependent plasticity at the level
of FTNs in vestibular nuclei. Although these data cannot rule out the
possibility of synaptic modifications in FTNs and/or at other brain
stem sites under different experimental conditions, they are in favor
of the hypothesis that the LTD in the flocculus could be the essential
mechanism of cellular plasticity in the vestibuloocular pathways.