Role of Cerebellar Interpositus Nucleus in the Genesis and Control of Reflex and Conditioned Eyelid Responses

Abstract

The role of cerebellar circuits in the acquisition of new motor abilities is still a matter of intensive debate. To establish the contribution of posterior interpositus nucleus (PIN) to the performance and/or acquisition of reflex and classically conditioned responses (CRs) of the eyelid, the effects of microstimulation and/or pharmacological inhibition by muscimol of the nucleus were investigated in conscious cats. Microstimulation of the PIN in naive animals evoked ramp-like eyelid responses with a wavy appearance, without producing any noticeable plastic functional change in the cerebellar and brainstem circuits involved. Muscimol microinjections decreased the amplitude of reflex eyeblinks evoked by air puffs, both when presented alone or when paired with a tone as conditioned stimulus (CS). In half-conditioned animals, muscimol injections also decreased the amplitude and damped the typical wavy profile of CRs, whereas microstimulation of the same sites increased both parameters. However, neither muscimol injections nor microstimulation modified the expected percentage of CRs, suggesting a major role of the PIN in the performance of eyelid responses rather than in the learning process. Moreover, the simultaneous presentation of CS and microstimulation in well trained animals evoked CRs similar in amplitude to the added value of those evoked by the two stimuli presented separately. In contrast, muscimol-injected animals developed CRs to paired CS and microstimulation presentations, larger than those evoked by the two stimuli when presented alone. It is concluded that the PIN contributes to the enhancement of both reflex and conditioned eyelid responses and to the damping of resonant properties of neuromuscular elements controlling eyelid kinematics.

The Cerebellar Interpositus Nucleus and the Dynamic Control of Learned Motor Responses

“…It is possible that lesion studies performed in the anterior interpositus (Yeo et al, 1985;Krupa et al, 2003) did affect axons originated in the posterior part of the nucleus. Moreover, as reported in previous studies (Gruart et al, 1995(Gruart et al, , 2000Trigo et al, 1999;Jiménez-Díaz et al, 2004), there are important functional differences between rabbits and cats. The more important is that the retractor bulbi system seems not to be involved in the generation of CRs in cats (Trigo et al, 1999).…”

“…8). This phase-modulating device could play a damping role in eyelid performance, particularly during the process of acquiring new motor abilities (Jiménez-Díaz et al, 2004), a proposal already put forward by others (Thach et al, 1992). In this regard, it has been recently reported that disturbances in fast cerebellar oscillation in the cerebellar cortex could be related to cerebellar ataxia (Cheron et al, 2005).…”

“…Wires were soldered to a socket fixed to the holding system. A more detailed description of these chronic preparations have been published previously (Trigo et al, 1999;Gruart et al, 2000;Jiménez-Díaz et al, 2004).…”

“…The enigmatic role of cerebellar circuits in relation to the generation and control of spontaneous and acquired motor responses has been variously ascribed to a putative center for motor coordination and integration (Eccles et al, 1967;Thach et al, 1992), a neural center controlling motor timing of the different muscles involved in a given movement (Llinás and Welsh, 1993;Welsh and Llinás, 1997;Lang et al, 1999;Kitazawa and Wolpert, 2005), the place for motor learning and memory storage (Ito, 1984;Krupa et al, 1993;Mauk, 1997;Bracha et al, 2001;Christian and Thompson, 2003) and, in a more parsimonious way, that of a center designed for the reinforcement and/or proper performance of ongoing movements (Holmes, 1939;Welsh and Harvey, 1991;Llinás and Welsh, 1993;Gruart et al, 2000;DelgadoGarcía and Gruart, 2002;Seidler et al, 2002;Jiménez-Díaz et al, 2004). Nevertheless, for a proper understanding of cerebellar functioning, it will be necessary to approach the neural activity of cerebellar circuits during the actual performance of spontaneous, reflex, and learned movements.…”

Dynamic Associations in the Cerebellar–Motoneuron Network during Motor Learning

“…All the implanted electrodes were soldered to a socket fixed to the holding system. A detailed description of this chronic preparation can be found elsewhere (Trigo et al, 1999;Gruart et al, 2000;Jiménez-Díaz et al, 2004;Sánchez-Campusano et al, 2007).…”