PR29MASSETERIC‐FACIAL NERVE COAPTATION – AN ALTERNATIVE TECHNIQUE FOR FACIAL NERVE REINNERVATION

Introduction Facial nerve paralysis can be a disabling condition functionally, psychologically and aesthetically. When there has been an acquired proximal injury to the facial nerve in the presence of previously functional facial musculature, such as in acoustic neuroma surgery, neurotisation of the distal facial nerve is an appropriate choice of management. The hypoglossal nerve is most commonly used. However this is not without its limitations, notably subsequent hemilingual atrophy and facial synkinesis. We present an alternative technique of facial reinnervation utilising a motor branch of the trigeminal nerve, the nerve to masseter. We believe this technique has the potential to overcome problems encountered with use of other extra‐facial nerves. Methods Three patients with acquired facial nerve palsy following tumour resection underwent transfer of the ipsilateral masseteric nerve to facial nerve. In two patients the nerve was directly coapted to the trunk of the facial nerve while the third patient had transfer to the buccal branch. Results By twelve months postoperatively all three patients demonstrated significant improvement in facial muscle tone and symmetry at rest. All patients were able to produce a symmetrical smile with minimal synkinesis. Two of the three patients also had evidence of occasional spontaneous movements. Conclusion Use of the ipsilateral motor nerve to masseter offers an alternative technique for neurotisation of the facial nerve. The advantages of this technique include ease of dissection, constant and reliable anatomy, powerful innervation of the facial muscles, minimal donor site morbidity and the potential for return of spontaneous facial movements.     

Neural mechanisms underlying the clasp-knife reflex in the cat. II. Stretch-sensitive muscular-free nerve endings

1. The goal of this study was to determine the contribution of muscular free nerve endings to the clasp-knife reflex by comparing their response properties and reflex actions to the clasp-knife reflex. 2. The responses of single muscle afferents were examined in anesthetized cats using stretch and isometric contraction of ankle extensor muscles identical to those that evoked clasp-knife inhibition in decerebrated and dorsal spinal-hemisectioned cats. 3. Fifty-three stretch-sensitive mechanoreceptor afferents were identified as free nerve ending afferents based on their conduction velocities, location within the muscle, uniformity of response, and dissimilarity to other muscle proprioceptors. The afferent conduction velocities were in both the group III (56%) and group II (44%) range, including five fast-conducting group II afferents (greater than 55 m/s). 4. The stretch response of stretch-sensitive, free nerve endings (SSFNEs) showed several characteristic features: 1) afferents were excited only by large stretches that produced significant passive force; 2) afferent activity began after a brief delay and exhibited segmentation of discharge during ramp stretch, a maximum at the end of ramp stretch, and rapid and complete decay during static stretch, and 3) afferent response adapted to repeated stretches. These properties match those of clasp-knife inhibition described in the companion paper, except that the SSFNE segmentation and maximum were more pronounced and their decay during maintained stretch was more rapid. 5. Isometric contraction produced by electrical stimulation of the muscle nerve, which induced force-evoked inhibition in decerebrated and dorsal hemisectioned cats, also consistently excited SSFNEs. Stretch evoked greater excitation than contraction, indicating that both length and force contribute to SSFNE activity. 6. Stimulation of free nerve endings by squeezing the achilles tendon in cats exhibiting the clasp-knife reflex evoked powerful, homonymous inhibition and a flexion-withdrawal pattern of reflex action--that is, inhibition of extensor and excitation of flexor muscles throughout the hindlimb, which parallels the spatial divergence of the clasp-knife reflex. 7. Intrathecal application of capsaicin, which preferentially blocks the reflex actions of small afferent fibers, blocked clasp-knife inhibition in decerebrated, dorsal hemisectioned cats. 8. The similarities between the reflex actions and response properties of SSFNEs and the properties of the clasp-knife reflex suggest that SSFNEs mediate clasp-knife inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)     

The effect of methotrexate on lipoxygenase metabolism in neutrophils from rats:In vitro andex vivo studies

Studies were undertaken to examine the effect of methotrexate (MTX) administeredin vivo or addedin vitro upon the production of the 5-lipoxygenase (5-LO) metabolites of arachidonic acid (AA) by rat neutrophils. Peptone-induced peritoneal exudate cells were stimulated by A23187 and the cell suspensions assayed for leukotriene B₄ (LTB₄), the all-trans isomers of LTB₄ and 5-hydroxyeicosatetraenoic acid (5-HETE) using high-pressure liquid chromatography. MTX addedin vitro to rat cells was weakly inhibitory; however, no inhibition of LTB₄ production was seen followingin vivo administration of MTX by oral, subcutaneous or intraperitoneal routes. On the basis of these findings, inhibition of 5-LO metabolism does not appear to explain the anti-inflammatory effects of MTX.     

How synchronization properties among second-order sensory neurons can mediate stimulus salience

Spatial patterns of glomerular activity in the vertebrate olfactory bulb and arthropod antennal lobe reflect an important component of first-order olfactory representation and contribute to odorant identification. Higher concentration odor stimuli evoke broader glomerular activation patterns, resulting in greater spatial overlap among different odor representations. However, behavioral studies demonstrate results contrary to what these data might suggest: Honeybees are more, not less, able to discriminate among odorants applied at higher concentrations. Using a computational model of the honeybee antennal lobe, the authors show that changes in synchronization patterns among antennal lobe projection neurons, as observed electrophysiologically, could parsimoniously underlie these observations. The results suggest that stimulus salience, as defined behaviorally, is directly correlated with the degree of synchronization among second-order olfactory neurons.     

Opposing effects of D1 and D2 receptor activation on odor discrimination learning

Dopaminergic modulation of cortical activity has been implicated in the formation of reward associations. There is abundant evidence for dopaminergic effects on olfactory processing. Using an olfactory discrimination task, the authors show that D1 and D2 dopamine receptors can regulate rats' olfactory discrimination capacities and that the effects of receptor activation functionally oppose one another. Injection of either the D1 agonist SKF 38393 (10 mg/kg) or the D2 antagonist spiperone (0.62 mg/kg) facilitated the discrimination of similar odorants but had no effect on the discrimination of dissimilar odorants, whereas both the D, antagonist SCH 23390 (0.025 mg/kg) and the D2 agonist quinpirole (0.2 mg/kg) significantly impaired rats' ability to discriminate similar and dissimilar odorants.     

Primary sphincter repair in anorectal trauma

Two patients who sustained severe anorectal trauma from "fist fornication" were treated by irrigation, colostomy, drainage, antibiotics, and primary repair of the rectum and anal sphincters without complications. Both had complete return of continence. Primary sphincter repair is advocated for these and similar anorectal injuries.