Muscimol inactivation caudal to the interstitial nucleus of Cajal induces hemi-seesaw nystagmus

Abstract

Hemi-seesaw nystagmus (hemi-SSN) is a jerk-waveform nystagmus with conjugate torsional and disjunctive vertical components. Halmagyi et al. in Brain 117(Pt 4):789-803 (1994), reported hemi-SSN in patients with unilateral lesions in the vicinity of the Interstitial Nucleus of Cajal (INC) and suggested that an imbalance in projections from the vestibular nuclei to the INC was the source of the nystagmus. However, this hypothesis was called into question by Helmchen et al. in Exp Brain Res 119(4):436-452 (1998), who inactivated INC in monkeys with muscimol (a GABA A agonist) and induced failure of vertical gaze-holding (neural integrator) function but not hemi-SSN. We injected 0.1-0.2 μl of 2% muscimol into the supraoculomotor area, 1-2 mm dorso-lateral to the right oculomotor nucleus and caudal to the right INC. A total of seven injections in two juvenile rhesus monkeys were performed. Hemi-SSN was noted within 5-10 min after injection for six of the injections. Around the time the hemi-SSN began, a small skew deviation also developed. However, there was no limitation of horizontal or vertical eye movements, suggesting that the nearby oculomotor nucleus was not initially compromised. Limitations in eye movement range developed about ½-1 h following the injections. Clinical signs that were observed after the animal was released to his cage included a moderate to marked head tilt toward the left (contralesional) side, consistent with an ocular tilt reaction. We conclude that hemi-SSN can be caused by lesions just caudal to the INC, whereas lesions of the INC itself cause down-beat nystagmus and vertical gaze-holding failure, as demonstrated by Helmchen et al. Combined deficits may be encountered with lesions that involve several midbrain structures.

Patterns of dissociate torsional–vertical nystagmus in internuclear ophthalmoplegia

“…In two patients (patients 2 and 12) with INO, the initial MRIs including diffusionweighted images were normal, but follow-up MRIs revealed a focal lesion in the pontine tegmentum where MLF locates. In three patients (patients [26][27][28], no responsible lesion was detected on MRI.…”

“…Previously, jerky seesaw nystagmus was also reported in mesodiencephalic lesions and has been ascribed to unilateral inactivation of the torsional eyevelocity integrator, the interstitial nucleus of Cajal (INC), or the torsional fast-phase generator, the rostral interstitial nucleus of MLF (riMLF). 4 Muscimol inactivation caudal to the INC-induced hemiseesaw nystagmus 28 while injection of muscimol into or rostral to the INC failed to evoke hemiseesaw nystagmus. 18 In some of our patients, the jerky seesaw nystagmus changed into mainly upbeating nystagmus during upward gaze, which also suggests dysfunction of the vertical neural integrator.…”

Role of neural integrators in oculomotor systems: a systematic narrative literature review

“…Conversely, previous studies of the INC did not elicit this nystagmic condition (Crawford et al 1991;Rambold et al 2000;B€ uttner et al 2002). Moreover, Das et al (2010) were able to identify the aetiology of this nystagmus using primates. Muscimol was injected to an area 2 mm beneath the INC which produced HSSN.…”

“…Moreover, Das et al. () were able to identify the aetiology of this nystagmus using primates. Muscimol was injected to an area 2 mm beneath the INC which produced HSSN.…”

Static ocular counterroll reflex in skew deviation

“…Conversely, muscimol inactivation of undetermined fibers in the supraoculomotor area caudal to the interstitial nucleus of Cajal in monkeys causes the ipsilesional eye to elevate and the contralesional eye to depress, with head tilt toward the contralesional side. 23 Relatively few studies have documented abnormal utricular function quantitatively in patients with skew deviation. 5,24 -26 The otolith receptors act as gravito-inertial force sensors and contribute to 3 major functions: 1) perception of spatial orientation (earth verticality); 2) generation of the translational VOR during lateral (heave), vertical (bob), and foreaft (surge) motion of the head; and 3) generation of OCR during static head roll.…”