Carlo Desole

Eye muscle proprioception and the semilunar ganglion

Abstract A cellular pool was found in the medial dorsolateral part of the semilunar ganglion of lambs which contains the soma of afferent proprioceptive fibers from extraocular muscles. The unitary discharge of these cells was recorded by means of tungsten microelectrodes. The responses of the units to stretching the extraocular muscles were characterized by a sustained increase in the discharge rate which ceased as soon as the stretch was released. The latencies were very short: 1–3 msec. The firing of the units during stretching was inhibited by electrical stimulation of the extraocular muscles. The units could thus be identified as muscle spindle afferents. The units responsive to stretching the extraocular muscles were unaffected by stimulation of other trigeminal fields or by jaw movements. Nembutal anesthesia did not eliminate the responses. The responses were abolished completely by severing the ipsilateral ophthalmic branch of the trigeminal nerve. The conclusion was reached that the semilunar ganglion contains the cells bodies of afferent fibers from the extraocular muscles coursing through the ophthalmic branch of the trigeminal nerve.

Peripheral pathway of eye muscle proprioception

Abstract A cellular pool containing the soma of the afferent fibers from the spindles of the extraocular muscles has been found in the medial dorsolateral part of the semilunar ganglion of pig. In this regard there is no differences between pigs and sheep. But no responses to stretching extraocular muscles of the cat were found in the semilunar ganglion. In another group of animals, experiments were carried out in order to trace the course of the afferents from the eye muscle spindles to enter the brainstem. Responses to the stretch of the extraocular muscles were recorded from the trigeminal root in both sheep and pigs, but this was not the case for the root of the oculomotor nerve. Section of an ophthalmic branch of the trigeminal nerve immediately distal to the semilunar ganglion abolished such responses and was followed by degeneration of the spindles of the extraocular muscles in pigs and sheep. The ganglionic responses persisted after sectioning the connections between the oculomotor nerve and the ophthalmic branch at the level of the cavernous sinus. Intracranial section of the oculomotor nerve did not provoke degeneration of the eye muscle spindles. The conclusion was reached that the proprioceptive cells contained in the semilunar ganglion of pig and sheep have a central process which enters the brain stem through the trigeminal root, while the peripheral one courses through the ophthalmic branch and reaches the extraocular muscles.

Cerebellar projections of the masticatory and extraocular muscle proprioception

Abstract The purpose of our investigation was to look for the cerebellar projections of the masticatory and extraocular muscle proprioception in both the lamb and duck. Units responding to the lowering of the jaw or the stretching of single masticatory or extraocular muscles were recorded from some different areas of the cerebellar cortex by means of tungsten microelectrodes. As far as masticatory proprioception is concerned, cerebellar responses in birds were led from the ipsilateral part of the declive, folium, and tuber vermis (lobules VI, VII), while in lambs, the masticatory proprioception projected on the ipsilateral paravermian region of the simplex and ansiformis lobules (HVI, HVIIa). Units influenced by extraocular muscles were found on the lateral part of the ipsilateral simplex lobule of the lamb.

On whether eye muscle spindles are innervated by ganglion cells located along the oculomotor nerves

Abstract This research attempted to verify the hypothesis that the ganglion cells along the eye-muscle nerves innervate eye-muscle spindles. Our investigations were performed on calves. The intracranial portion of the oculomotor nerve sometimes contains a rather large number of ganglion cells in comparison with the peripheral part. Therefore, intracranial and peripheral parts of the left oculomotor nerve in 9 calves were chronically separated at the base of the skull before the nerve entered the orbit. Responses to stretching individual eye muscles either of the left or of the right side were recorded from the ipsilateral trigeminal ganglion. They were of the type induced by muscle-spindle excitation elsewhere. However, no responses were obtained from the intracranial course of the right oculomotor nerve. The spindles innervated by the left oculomotor nerve were normal in seven calves whose central oculomotor stump contained few ganglion cells. However, very few degenerated spindles were found in the extraocular muscles of two calves in which the intracranial stump of the nerve exhibited more than 100 ganglion cells. Thus, we conclude that the trigeminal ganglion of the calf contains the soma of the afferents from the eye-muscle spindles, as is the case for the lamb and pig. The ganglion cells in the oculomotor nerve can play only an accessory and negligible role in innervating the eye-muscle spindles.

Responses of vestibular units to stimulation of individual semicircular canals

Abstract The convergence of influences elicited by circumscribed warming of individual semicircular canals of curarized guinea pigs was analyzed for single units in the lateral vestibular nucleus. The units responded to the labyrinthine stimulations with either activation or inhibition of the discharge rate. Of 72 units, 60 (84%) were influenced by separate stimulation of single semicircular canals of either labyrinth. The highest number (23) of units responded to all six semicircular canals, while the response of only 12 units was limited to stimulation of the canals of a single labyrinth. Facilitation of unitary discharge was the most frequent response regardless of which canal was stimulated. Thus, for the first time, single vestibular units have been demonstrated to receive converging influences from each of the six semicircular canals, stimulation of which produces nystagmus in different planes.

Responses of oculomotor units to stimulation of single semicircular canals

Abstract Extracellular recording of the electrical activity of the oculomotor nuclei was carried out in paralyzed guinea pigs by means of tungsten microelectrodes. The influence of each one of the three semicircular canals of one side on such unitary discharge was studied. Labyrinthine stimulation was carried out by short-lasting (1–2 sec) localized warming or cooling of each single semicircular osseous canal. All the recorded oculomotor units underwent modifications. These consisted either of rhythmical (slow or quick) responses or of a long-lasting increase in the discharge rate of the units with recruitment of new units without clear signs of rhythm (continuous activation). In about 40% of the experiments the recorded units responded differently to the warm stimulation of each semicircular canal, while in the remaining 60% of the case two out of three canals elicited the same type of response. In the great majority of the experiments the warm stimulation of the lateral ampulla induced a type of response different from that provoked by stimulating the superior one.

A trigeminal monosynaptic reflex in reptilia

Abstract The masseterine reflex has been investigated in Caiman sclerops . Electrical stimulation of the trigeminal mesencephalic nucleus induced in the ipsilateral mandibular branch of the nerve a response which consisted of two waves. The first one, s, with a short latency, represented the spread of the stimulus along the afferent proprioceptive fibers, while the latter one, m, was the motor reflex response. The motor reflex response was depressed by fatigue and anoxia, whereas it was enhanced by high-frequency stimulation (post-tetanic potentiation). The masseterine reflex was monosynaptic as is the case for mammals and birds; in fact, if we deduct from the total reflex time (1.7 ± 0.2 msec) that spent by the nervous impulse in travelling through the fibers at a conduction velocity of 38 ± 4 m/sec (0.3 ± 0.05 msec), we have a synaptic delay of 1.3 ± 0.19 msec. This figure is in good agreement with those reported by other researchers in cold-blood animals.

Influence of hypothermia on eye nystagmus

Abstract The effect of progressive cooling and rewarming on the labyrinthine, central, optokinetic nystagmi of awake, uncurarized guinea pigs was investigated. During hypothermia the three eye nystagmi decreased progressively in amplitude and in frequency. At a diencephalic temperature of 28-21 C the quick phase of the eye nystagmus faded away and was replaced by a tonic conjugate ocular deviation. In most cases, the quick component of the optokinetic nystagmus disappeared and reappeared at a higher temperature than that at which the quick jerk of the other two nystagmi was abolished. Usually the quick phase of cerebral and vestibular nystagmi faded away and reappeared at the same diencephalic temperature. We concluded that hypothermia acts particularly on visual pathways as far as the optokinetic nystagmus is concerned, and on brain stem structures in the case of the central and vestibular nystagmi.