Physiological Studies on Facial Reflexes in the Rat

Abstract

Experiments were performed on 36 male albino rats anaesthetized with pentobarbitone sodium and paralyzed with gallamine triethiodide. Recordings were made with single and multibarrel glass microelectrodes in the facial nucleus and monopolar silver wire electrodes on the lingual, facial, glossopharyngeal and hypoglossal nerves. The absolute refractory period for facial motoneurones is 2-3 ms, the relative refractory period has a duration of 26-34 ms and the range in axonal conduction velocities is from 15 to 45 m.sec-1. No evidence for afferent fibres in the muscle branches of the facial and hypoglossal nerves could be found. The lingual and glossopharyngeal nerves show reflex connexions with both the facial and hypoglossal nerves. The time courses of the potentiations and depressions of test facial antidromic field potentials following lingual and glossopharyngeal conditioning stimuli are given. Evoked synaptic activity and the distribution of field potentials in the facial nucleus following lingual and glossopharyngeal nerve stimulation are also described. The observed lingual and glossopharyngeal-facial reflexes are discussed with respect to blink reflexes.It is held that the facial nucleus receives efferent fibres from the reticular formation, red nucleus, spinal trigeminal nucleus, spinal cord and the trapezoid and superior olivary complex [Ramon y Cajal, 1952;Courville, 1966a;Martin and Dom, 1970;Mizuno and Nakamura, 1971]. Facial motoneurones do not receive direct afferent inputs from any of the cranial nerves and there is no anatomical evidence for a monosynaptic reflex arc [Szentagothai, 1948].

Nociceptive Afferents to the Premotor Neurons That Send Axons Simultaneously to the Facial and Hypoglossal Motoneurons by Means of Axon Collaterals

“…The doubly labeled premotor neurons were mainly distributed in the brainstem, especially in the RF and probably subserved the coordination of orofacial movements required for the complex oral motor behaviors. Furthermore, physiological studies showed that stimulating various trigeminal nerve branches could elicit reflex responsiveness of different groups of brainstem motoneurons [38] , [39] . Based on these experiments, we hypothesized that shared brainstem circuits could transmit trigeminal afferent information (such as nociceptive information) to more than one motor nuclei, influence the responses of different motoneurons and play a role in orofacial coordinated muscle movements.…”

Hypoglossal and reticular interneurons involved in oro‐facial coordination in the rat

“…Physiologic experiments using stimulation of various trigeminal nerve branches have characterized the reflex responsiveness of different groups of brainstem motoneurons (Martin and Biscoe, 1977). Based mainly on such experiments, it has been postulated that shared brainstem circuits could influence more than one motor nucleus (Stennert and Limberg, 1982; Willer et al, 1984; McFarland and Lund, 1993) and play a role in coordinated muscle activities.…”

“…Electrical stimulation of the lingual nerve, which conducts mechanoreceptive information from the anterior two‐thirds of the tongue (Porter, 1966; Yamamoto, 1975), elicits excitatory postsynaptic potentials in the hypoglossal retractor motoneurons, whereas pronounced inhibitory effects were noted in both protruder and retractor motoneurons (Morimoto et al, 1968; Lowe, 1984). Likewise, after stimulation of the same sensory branch, a polysynaptic positive‐going field potential was recorded from inferior buccolabial facial motoneurons, a negative‐going field potential from orbito‐fronto‐preauricular facial motoneurons, and no response from the medial facial subnucleus (Martin and Biscoe, 1977). Despite the bulk of physiologic studies supporting the notion of common brainstem circuits, suggesting that more than one synapse is involved, the available morphologic reports still cannot provide unequivocal direct evidence (but see Travers and Norgren, 1983; Li et al, 1993a,b; Fay and Norgren, 1997a,b,c).…”

Blink Restoration in Adult Facial Paralysis

“…Lindquist and Mårtensson 21 in 1970 described the blink reflex mechanism in a cat model, whereas Black-Cleworth et al 22 in 1975 demonstrated a conditioned blink obtained by using electrical stimulation of the facial nerve in a similar cat model. Martin and Biscoe in 1977 23 presented their extended physiologic studies in rat models. Otto et al in 1986 24 described a method of electrical restoration of the blink reflex in the rodent model.…”