Is there a primitive reflex residue underlying Marcus Gunn Syndrome? Rat electrophysiology

Marcus Gunn Syndrome in Primary Care: A Case Report

Marcus Gunn syndrome (MGS) is a rare craniofacial condition characterized by abnormal eyelid movements synchronized with jaw muscle activity. This case report describes a one-month-old girl with right eyelid ptosis and involuntary movements of the right eyelid during sucking. The diagnosis of MGS was made based on clinical observations. The etiology of MGS is not well-defined, and long-term follow-up is necessary to assess the progression of the condition. Early referral to ophthalmologists and neurologists/pediatricians is important to evaluate concomitant conditions and prevent secondary complications. Primary care physicians, who maintain continuous contact with patients, play a crucial role in detecting initial symptoms, initiating appropriate investigations, and coordinating multidisciplinary care. By raising awareness among primary care physicians about the signs, symptoms, and referral pathways for MGS, this case report aims to improve the recognition and management of this rare condition in primary care settings. Emphasizing the role of family doctors in the early identification and referral of MGS can lead to better outcomes for affected patients.

Convergent innervations of mesencephalic trigeminal and vestibular nuclei neurons onto oculomotor and pre-oculomotor neurons-Tract tracing and triple labeling in rats

In studies of vestibulo-ocular reflex (VOR), the horizontal VOR circuit is much clearer than vertical-torsional VOR. The circuit and mechanism of gravity-related vertical-torsional VOR is probably weak. "Somatosensory vestibular interaction" is a known extra source to facilitate VOR, and cervico-ocular reflex is a representative for torsional VOR compensation. Whereas, how the cervical afferents finally reach the oculomotor system is less documented. Actually, when the head tilts, which generates cervico-ocular reflex, not only the neck muscle is activated, but also the jaw muscle is stretched by gravity dragged mandible and/or tissue-muscle connection between the mandible and clavicle. We have previously identified a projection from the jaw muscle afferent mesencephalic trigeminal nucleus (Vme) neurons to oculomotor nuclei (III/IV) and their premotor neurons in interstitial nucleus of Cajal (INC)-a well-known pre-oculomotor center manipulating vertical-torsional eye movements. We hypothesized that these projections may interact with vestibulo-ocular signals during vertical-torsional VOR, because effects of gravity on jaw muscles and bones has been reported. Thus, we injected different anterograde tracers into the Vme and medial vestibular nucleus (MVN)-the subnuclear area particularly harboring excitatory vestibulo-ocular neurons, and immunostained III/IV motoneurons. Retrograde tracer was injected into the III in the same animals after dual anterograde tracers' injections. Under confocal microscope, we observed the Vme and MVN neuronal endings simultaneously terminated onto the same III/IV motoneurons and the same INC pre-oculomotor neurons. We consider that jaw muscle proprioceptive Vme neurons projecting to the III/IV and INC would sense spindle activity if the jaw muscle is stretched by gravity dragged mandible or connection between mandible and clavicle during head rolling. Therefore, the convergent innervation of the Vme and MVN neurons onto the oculomotor and pre-oculomotor nuclei would be a neuroanatomic substrate for interaction of masticatory proprioception with the vestibulo-ocular signals upon the oculomotor system during vertical-torsional VOR.