Synaptic mechanisms of central control of motoneuronal activity in the facial nerve nucleus

The responses of motoneurons of the facial nerve nucleus (FNN), evoked by stimulations of the oculomotor nerve nucleus, Edinger-Westphal's nucleus,substantia nigra, and entopeduncular nucleus, were studied in acute experiments on anesthetized and immobilized cats. The FNN motoneurons were identified by their antidromic activation after stimulation of various branches of the facial nerve. Stimulation of the oculomotor nerve nucleus, Edinger-Westphal's nucleus, and ipsi- or contralateral parts of thesubstantia nigra evoked mono- and polysynaptic EPSP in the FNN motoneurons, while stimulation of the entopeduncular nucleus elicited only polysynaptic EPSP. The influences from the above structures were shown to converge on the same FNN motoneurons. The findings are discussed considering morphological peculiarities of the afferent inputs to the FNN.Neirofiziologiya/Neurophysiology, Vol. 27, No. 2, pp. 116–125, March–April, 1995.     

Physiological studies on facial reflexes in the rat.

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 hypoglassal nerves could be found. The lingual and glossopharyngeal nerves show reflex connexions with both the facial and hypoglassal 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 mucleus following lingual and glossopharyngeal nerve stimulation are also described. The observed lingual and glossopharyngeal-facial reflexes are discussed with respect to blink reflexes.     

Neuronal analysis of projections from trigeminal nucleus caudalis to the facial nucleus in cats

Properties of neurons of the trigeminal nucleus caudalis, with projections into the facial nucleus, were investigated in cats by a microelectrode technique. These neurons were found to be located mainly in the ventral parts of the trigeminal nucleus caudalis and in the adjacent lateral reticular formation. Monosynaptic and polysynaptic activation of efferent neurons of the trigeminal nucleus caudalis was found in response to pyramidal impulsation. Repeated discharges were recorded in the test neurons in response to stimulation of their axons, to direct stimulation of the trigeminal nucleus caudalis, and also to stimulation of the pyramidal tract and facial nerve. The synaptic mechanisms of regulation of motoneuron activity in the facial nerve nucleus are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 264–269, May–June, 1981.     

Electrosensory systems in the mormyrid fish, Gnathonemus petersii : special emphasis on the fast conducting pathway

1. Rhombencephalic and mesencephalic structures involved in electroreception were investigated by electrophysiological methods in the weakly electric fish Gnathonemus petersii. 2. The existence of a synchronous response to electric field stimulation of the fish in the mesencephalic exterolateral nucleus (n.ext.-lat.mes) with 2.5-3 ms latency was confirmed. The lateral line lobe nucleus (nLLL) is identified as the rhombencephalic relay for the mesencephalic responses because of the short latency synchronous response in the nLLL obtained by threshold stimulation of the posterior lateral line nerve. Responses in both the nLLL and the n.ext.-lat.mes. appear and their amplitudes increase simultaneously with increasing stimulus intensity. 3. Comparison of latencies supports a three-neuron pathway hypothesis which also agrees well with the various functional properties described. 4. The nLLL-n.ext.-lat.mes. pathway is blocked sharply for a period of 1 ms occurring 3 ms after the electric organ discharge (EOD). This inhibitory period is phase-related to the Mesencephalic Command Associated Signal (MCAS) of Aljure (1946) ; The phase relation is such that no response is observed to the fish's own EOD. 5. Long-lasting responses of 10-12 ms duration to higher stimulation intensities were obtained in the ganglionic layer of the lateral line lobe (LLL). Intensities evoking maximal responses in the nLLL and n.ext.lat.mes. are still threshold stimulation for lateral line lobe responses. 6. Long-lasting responses (of the same order as in the LLL) to the fish' own EOD were observed in the mesencephalic lateral nucleus. Responses to artificial electric pulses were obtained only if delivered in a certain phase realtion to the MCAS. The MCAS displays a facilitating effect on the slow conducting electrosensory system. 7. Results indicate the existence in mormyrids of a double, fast and slow conducting, electrosensory system similar to that of gymnotid fish. The mormyrids can control both of these electrosensory systems by means of the MCAS, the effect of which is opposite for the same time period on the two systems.     

Facial motor responses to microstimulation of the superior colliculi in the white mouse

Facial motor responses to microstimulation of different zones of the superior colliculi have been investigated in the albino mice craniotomized under thiopental anaesthesia. Local responses of the mystacial vibrissae, upper lip and eyelids were initiated by microstimulation of the rostral parts of the inner layers of the colliculus superior (high-frequency volleys of 5-7 pulses with a current limit of 35 microA). Sequential changes in the pattern of facial responses were observed within microelectrode traces indicating vertical orientation of facial motor representations in the superior colliculus. Some differences in the localization and pattern of facial responses in the right and left superior colliculi were revealed: 1) vibrissae and lip representations in the right superior colliculus occupy more extensive zone (vertical distribution from 300 to 2,300 microns) as compared to those in the left one (700-2,000 microns); 2) microstimulations of the right superior colliculus produce both uni- and bilateral vibrissal motor responses, whereas stimulation of the left superior colliculus evokes only unilateral responses. The duration of the latent period of the vibrissal and lip motor responses to stimulation of the right superior colliculus varied from 10 to 26 ms (16.1 +/- 2.4 ms; n = 199), to stimulation of the left one-from 10 to 18 ms (mean 14.9 +/- 1.8 ms; n = 55). It is suggested that polysynaptic motor responses to microstimulation of the superior colliculi are realized via the reticular and other premotor nuclei of the brain stem which have direct inputs from the superior colliculus and direct projections to the facial motor nucleus.     

Synaptic mechanisms of the action of subcortical formations on motoneurons in cat facial nerve

Characteristics of the synaptic processes produced by stimulating the head of the caudate nucleus, theglocus pallidus, and the central amygaloid nucleus were investigated in motoneurons of the facial nerve during acute experiments on cats using intracellular recording techniques. It was found that stimulating the first two of these structures causes polysynaptic activation, while both mono- and polysynaptic excitation of facial nerve motoneurons are produced by stimulation of the central amygdaloid nucleus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 800–809, November–December, 1985.     

Anatomy of the frontal branch of the facial nerve: the significance of the temporal fat pad

The anatomy of the temporal region, with reference to the frontal branch of the facial nerve, was examined in 12 fresh cadaver dissections. In all dissections, the frontal branch traveled in a constant plane along the undersurface of the temporoparietal fascia and was quite superficial as it crossed the zygomatic arch. The deep temporal fascia and superficial temporal fat pad are anatomically important structures which adjoin the periosteum of the zygomatic arch and lie deep to the frontal nerve. Based on these relationships, a safe method of dissection within the temporal region is formulated.     

Factors responsible for multiple discharge of motoneurons in the facial nucleus in cats

The multiple discharge evoked by stimulation of the caudal trigeminal nucleus in motoneurons of the cat facial nucleus was investigated by an intracellular recording method in acute experiments on cats. The multiple discharge was shown to arise on the basis of gradual depolarization of the motoneuron membranes produced as a result of effective summation of high-frequency excitatory influences arriving from the caudal trigeminal nucleus. Factors facilitating the development of this process are the dendritic localization of synaptic endings of projection neurons of the caudal trigeminal nucleus, the dendritic origin of delayed depolarization processes, and the high input resistance of the motoneuron membrane in the facial nerve nucleus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 520–530, September–October, 1981.     

Preganglionic neurons of the sphenopalatine ganglia reside in the dorsal facial area of the medulla in cats

Stimulation of the sphenopalatine ganglion (SPG), a parasympathetic ganglion of the facial nerve, or the dorsal facial area (DFA), an area in the lateral tegmental field just dorsal to the facial nucleus, induces an increase in blood flow of the common carotid artery (CCA). This study attempted to clarify the anatomical and functional relationships between the SPG and the DFA, and to demonstrate putative serotonergic (5-HT) and substance P (SP) innervations to the neurons of the DFA in regulation of the CCA blood flow in cats. Horseradish peroxidase (HRP), a retrograde tracer, was injected in the SPG. All HRP-labeled neurons were distributed in the reticular areas dorsal and lateral to the superior olivary nucleus and the facial nucleus, extending from the caudal half of the superior olivary nucleus to the rostral 3/4 of the facial nucleus on the HRP-injected side. They were grouped into five clusters, namely lateral circumference of the superior olivary nucleus, dorsal circumference of the superior olivary nucleus, lateral circumference of the facial nucleus, dorsal circumference of the facial nucleus, and the DFA. The percentage of HRP-neurons in each cluster was 0.5 +/- 0.1% (mean +/- S.E., n=6), 15.2 +/- 1.9%, 23.7 +/- 0.9%, 52.5 +/- 1.7%, and 8.3 +/- 0.7%, respectively. Glutamate stimulation of the DFA (at 5.0 to 7.0 mm rostral to the obex, 2.8 to 4.0 mm lateral to the midline, and 2.5 to 3.5 mm ventral to the dorsal surface of the medulla), but not other areas, resulted in the increased CCA blood flow. The 5HT- and SP-immunoreactive nerve terminals abutted on the ChAT-immunoreactive cell body (preganglionic neurons) in the DFA. In conclusion, parasympathetic preganglionic neurons in the DFA project fibers to the SPG, are innervated by 5HT- and SP-like nerve terminals, and are responsible for regulation of the CCA blood flow. They may be also important in regulation of the cerebral blood flow.     

Postsynaptic potentials of facial motoneurons evoked by afferent and corticofugal impulses

Postsynaptic potentials of motoneurons in the facial nerve nucleus, evoked by stimulation of the cranial nerves (trigeminal, hypoglossal, facial) and of the sensomotor cortex were investigated in cats anesthetized with chloralose and pentobarbital. Two functionally opposite groups of motoneurons were found to exist in the facial nucleus. Stimulation of the afferent nerves and cortex evoked the appearance of EPSPs in the first of these groups and IPSPs in the second. The latency and duration of the PSPs indicate that afferent and corticofugal impulses reach the facial motoneurons along polysynaptic pathways. Interneurons on which wide convergence of influences travelling along afferent fibers and of the cortex, were found in the region of the facial nucleus. The possible neuronal pathways concerned with the transmission of afferent and corticofugal impulses to the facial motoneurons are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.4, No.4, pp. 391–400, July–August, 1972.     

Response of the spinal trigeminal nucleus neurons to electric stimulation of the rat dura mater

Aseptic inflammation of tissues surrounding large meningeal blood vessels, e.g. the superior sagittal sinus, underlies pathogenesis of migraine. This inflammation develops due to antidromic activation of sensory trigeminal nerve endings and is followed by changes in responses of the spinal nucleus of the trigeminal nerve neurons to electrical stimulation of the superior sagittal sinus. However, characteristics of these reactions are still unclear. In experiments ou urethane-anesthetized rats, responses of 387 neurons of the spinal nucleus of the trigeminal nerve to electrical stimulation of the superior sagittal sinus, were recorded. It was tial discharge with the latency 7 to 19 ms (11.4 +/- 0.17 ms) and a subsequent long-lasting discharge with the latency 20 to 50 ms (34.2 +/- 0.8 ms). It is presumed that the first phase reflects orthodromic activation of prevascular A delta and C-fibers of the trigeminal nerve while the second phase is connected with activation of meningeal C-fibers which have low conduction velocity, and/or with a secondary activation of perivascular sensory endings of trigeminal nerve by releasing algogenic and vasoactive substances. These changes could be used as an indicator of efficacy of some antimigraine substances in animal experiments.     

Botulinum toxin: a treatment for facial asymmetry caused by facial nerve paralysis

Injury to the frontal or other facial nerve branches can result in an asymmetry that can be very distressful to both patient and surgeon. This is especially true following cosmetic procedures such as rhytidectomy. We propose a means to create temporary symmetry while awaiting the possible return of nerve function. Botulinum neurotoxin causes a muscle paralysis lasting for approximately 3 months, and it is well established as the preferred treatment for blepharospasm. A case is presented in which botulinum toxin type A was injected into the opposite functioning frontalis muscle of a patient with unilateral frontal nerve paralysis. The patient experienced satisfactory relief of the asymmetry caused by onesided forehead wrinkling and brow elevation. Botulinum toxin therapy should be considered for both temporary and permanent facial asymmetries due to facial nerve paralysis as well as spasm.     

Electrophysiological analysis of facial reflex in monkeys: trigemino-naso-labial reflex]

Electrical stimulation of the awake monkey's supra orbital nerve, elicits two successive reflex discharge in both naso-labialis muscles (NL). The responses have a similar high threshold. Similar responses are also elicited on electrical stimulation of the facial skin, whereas flash, click or tapping on the muscle belly are ineffective. These responses bear some resemblances to those obtained in orbicularis oculi muscles ; but the higher threshold and the different organization of the NL responses would suggest that such reflexes may serve a different function from that of the blink reflex.     

Vestibular responses of neurons in the anterior suprasylvian gyrus in cats and their interaction with responses to acoustic and facial stimulation

Unit responses in the anterior sigmoid gyrus of cats anesthetized with chloralose (70 mg/kg) to vestibular nerve stimulation and their interaction with responses to acoustic and facial nerve stimulation were investigated. The focus of maximal activity of the vestibular projection was shown to lie a little rostrally to the anterior suprasylvian sulcus. The modality specificity of this part of the cortex to vestibular impulses is reflected in the shortest values of latent periods and the distinct phasic character of the responses, and also in the numerical preponderance of neurons with short-latency responses. Although considerable topographic overlapping of the vestibular projection by acoustic and somatosensory (facial zone) projections is found, the vestibular afferent input predominates over the other afferent inputs.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 353–358, July–August, 1981.     

Synaptic processes in facial motoneurons evoked by stimulation of the caudal trigeminal nucleus

Field potentials and postsynaptic potentials of facial motoneurons evoked by stimulation of the caudal trigeminal nucleus were investigated in acute experiments on cats by extra- and intra-cellular recording. Pre- and postsynaptic components of field potentials were found. Four types of motoneuron response were distinguished: EPSP with generation of single action potentials; a gradual shift of depolarization inducing grouped action potentials; a rhythmic discharge of action potentials arising at a low level of depolarization; and EPSPs or EPSP-IPSP sequences. The monosynaptic and (chiefly) polysynaptic nature of these responses was demonstrated. The possible mechanism of afferent control over facial motoneurons are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 272–282, May–June, 1980.     

Electrophysiological features of facial motoneurons in cats

Antidromic activation of facial motoneurons in cats during stimulation of different branches of the facial nerve was studied by intracellular recording. Time and amplitude characteristics of individual components of the antidromic action potentials were analyzed and fast and slow after-potentials distinguished. Correlation was found between the duration of the descending phase of the SD spike, duration of its after-hyperpolarization, and the spike conduction time along the axon. Data were obtained to show absence of a recurrent collateral pathway in motoneurons of the facial nucleus. The functional significance of the after-potentials is discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 261–270, May–June, 1978.     

Effects of abdominal or cardiopulmonary sympathetic afferents on upper cervical inspiratory neurons

Responses of upper cervical inspiratory neurons (UCINs) to abdominal visceral or cardiopulmonary sympathetic stimulation were studied using extracellular recordings from 213 UCINs in 54 pentobarbital sodium-anesthetized and paralyzed rats. Phrenic nerve activity was used to assess inspiration. The UCINs discharging during inspiration only were mainly in the C(1) segment, whereas phase-spanning UCINs were mostly in the C(2) segment. Phase-spanning activity was typically retained after overventilation or vagotomy. When greater splanchnic nerve (GSN) or cardiopulmonary sympathetic afferent (CPSA) fibers were electrically stimulated, augmented UCIN activity was observed in 65% of cells responding to CPSA stimulation but in only 17% of cells responding to GSN. Response latencies were 10.7 +/- 0.5 and 20.6 +/- 1.5 (SE) ms, respectively. Many augmented responses to CPSA stimulation (64%) and all augmented responses to GSN stimulation were followed by suppression of UCIN discharge (biphasic response). Phrenic nerve activity was suppressed by both GSN and CPSA stimulation, but with shorter latency for the latter (29 +/- 0.7 vs. 14.0 +/- 0.7 ms). Excitation of UCINs using CPSA stimulation occurs more often and by a more direct pathway than for GSN input.     

Amygdaloid or cortical facilitation of antidromic activity of trigeminal motoneurons in the rat

1. Electrical stimulation of the rat's contralateral central amygdaloid (CAm) nucleus or the contralateral frontal cortex markedly augmented the antidromic field potential evoked by stimulation of mylohyoid (Myl) nerve. 2. This facilitation was shown to be due to EPSPs of the mylohyoid-anterior digastric (Myl-Dig) motoneurons. 3. In a few motoneurons, cortical EPSPs had fixed short latencies following high-frequency double stimuli and this is believed to be due to a monosynaptic pathway. 4. The amygdaloid or cortically evoked EPSPs relieved IS-SD blockade in a few motoneurons and also facilitated antidromic discharge in others which did not show any IS or M spike response to the same subthreshold antidromic stimulation. The underlying mechanisms are discussed.     

Afferent and efferent components of the facial nerve in the bullfrog (Rana catesbeiana).

The afferent and efferent components of the facial nerve were traced within the brain stem of Rana catesbeiana, using three different neuroanatomical techniques. Primary afferent fibers could be traced to the spinal tract of trigeminal nerve and to fasciculus solitarius as far caudally as the first or second spinal segment, using silver degeneration methods. Cobalt filling of of the entire nerve showed the same distribution of afferent fibers, as well as the filling of the cells within the mesencephalic nucleus of trigeminal, indicating the origin of a proprioceptive component of the facial nerve. Cobalt iontophoresis and horseradish perioxidase experiments showed that the motor nucleus of the facial nerve was located just ventral to the fourth ventricle, and caudal to the motor nucleus of trigeminal. The distribution of afferent fibers to fasciculus solitarius and the spinal tract of trigeminal is similar in some respects to the distribution of afferent fibers from the trigeminal and vagal nerves in the bullfrog. The afferent fibers from the three cranial nerves are found as far caudally in the brain stem as the second spinal segment.     

Cells of origin of the branches of the facial nerve: a retrograde HRP study in the rabbit

The origin of different branches of the facial nerve in the rabbit was determined by using retrograde transport of HRP. Either the proximal stump of specific nerves was exposed to HRP after transection, or an injection of the tracer was made into particular muscles innervated by a branch of the facial nerve. A clear somatotopic pattern was observed. Those branches which innervate the rostral facial musculature arise from cells located in the lateral and intermediate portions of the nuclear complex. Orbital musculature is supplied by neurons in the dorsal portion of the complex, with the more rostral orbital muscles receiving input from more laterally located cells while the caudal orbital region receives innervation from more medial regions of the dorsal facial nucleus. The rostral portion of the ear also receives innervation from cells located in the dorsomedial part of the nucleus, but the caudal aspect of the ear is supplied exclusively by cells located in medial regions. The cervical platysma, the platysma of the lower jaw, and the deep muscles (i.e., digastric and stylohyoid) receive input from cells topographically arranged in the middle and ventral portions of the nuclear complex. It is proposed that the topographic relationship between the facial nucleus and branches of the facial nerve reflects the embryological derivation of the facial muscles. Those muscles that develop from the embryonic sphincter colli profundus layer are innervated by lateral and dorsomedial portions of the nuclear complex. The muscles derived from the embryonic platysma layer, including the deep musculature, receive their input from mid to ventral regions of the nuclear complex.