Contralateral Reticular Formation Research Articles

システムニューロサイエンス講座 １１． 上丘による眼球運動制御

The appearance of a novel or attractive stimulus induces saccadic eye movements and head movements towards the stimulus (orienting response). The mammalian superior colliculus (SC) has been shown to be an important structure for generation of the orienting response. This paper reviews the function of the SC in relation to saccade in the monkey and the cat. Functionally, the SC can be divided into dorsal (superficial) and ventral (intermediate and deep) layers. The former serves primarily as a visual structure receiving input directly from the retina and the striate cortex. Neurons in this layer respond to visual stimuli in the contralateral visual field. These visually responsive neurons are arranged topographically forming a retinotopic map over the SC's surface. The latter receives convergent inputs of multi-sensory modalities (auditory, somatosensory and visual). The auditory, somatosensory and visual receptive fields are arranged in a topographic fasion within the intermediate and deep layers corresponding well to the retinotopic map of the superficial layer. It also receives inputs from the motor-relating areas such as frontal and parietal association cortices and basal ganglia. Electrical stimulation in a given point of the intermediate layer evokes a saccade with a given direction and amplitude. A map of the direction and amplitude can be developed. This motor map is aligned with the retinotopic map. Neurons discharge in relation to the saccade directed to the motor field. It has been suggested that these neurons send descending axons to the contralateral reticular formation including the saccade-generation center. Recent studies reveal that another class of neurons, fixation neurons, are located in the intermediate layer of the rostral SC. These show sustained activities during active fixation and pause during saccade. It is suggested that saccade-related and the fixation neurons have connected mutually inhibitory roles : when the former fires the latter pauses and vice versa. Thus, both the visual and motor maps for the saccade are represented within the SC, suggesting that the SC serves as an important center for sensorimotor transformation for the saccade.

PS-37-2 Optimal joint angles to elicit triceps and quadriceps reflexes

Extra- and intracellular recording was made from neurones in laminae VII and VIII of the C6-Th1 segments, which were disynaptically excited from the contralateral pyramid, nucleus ruber and monosynaptically from the ipsilateral lateral reticular nucleus. The results suggest collateral excitation from the C3–C4 propriospinal neurones which are excited monosynaptically from the former two inputs and antidromically from the latter nucleus. The cells were antidromically activated from the ipsilateral nucleus fastigius, and from the ipsilateral or contralateral reticular formation. Some of the spinocerebellar and spinoreticular neurones were also antidromically activated from Th13. It is suggested that spinocerebellar, spinoreticular and bifurcating spinocerebellar and spinoreticular neurones receive collateral input from the same excitatory C3–C4 propriospinal neurones which project to motoneurones and/or Ia inhibitory interneurones.

Excitatory amino acid-mediated responses and synaptic potentials in medial pontine reticular formation neurons of the rat in vitro

Neurons of the medial pontine reticular formation (mPRF) are involved in the execution of numerous behaviors including initiation of locomotion, eye movements, startle responses, and rapid eye movement sleep phenomena. Approximately half of the afferent projections to mPRF neurons come from within the reticular formation (Shammah-Lagnado et al., 1987). In spite of the importance of reticulo-reticular connections, virtually nothing is known about transmitters mediating these synapses. In order to identify a candidate excitatory neurotransmitter, the actions of excitatory amino acids (EAAs) on the membrane properties of mPRF neurons recorded in rat brainstem slices in vitro were studied. Standard intracellular recording methods, including single-electrode voltage clamp, were used to examine the postsynaptic actions of EAAs. We also tested whether EAA antagonists block EPSPs evoked by stimulation of the contralateral reticular formation in the slices. mPRF neurons responded to both non-NMDA and NMDA agonists. NMDA-induced conductances were voltage dependent and depressed by physiological concentrations of magnesium. Stimulation of the contralateral reticular formation elicited EPSPs that were depressed by the general EAA antagonist kynurenate. Evoked EPSPs were partially depressed by 6,7-dinitroquinoxaline-2,3-dione. The evoked EPSP was further reduced by the NMDA antagonist (+/-)-2-amino-5-phosphonopentanoic acid in some cases. These results suggest that excitatory reticulo-reticular neurotransmission is mediated by an EAA. Both non-NMDA and NMDA receptors contribute to EAA neurotransmission in the mPRF formation and play an integral role in reticular formation function.

Projection from excitatory C3–C4 propriospinal neurones to spinocerebellar and spinoreticular neurones in the C6-Th1 segments of the cat

Extra- and intracellular recording was made from neurones in laminae VII and VIII of the C6-Th1 segments, which were disynaptically excited from the contralateral pyramid, nucleus ruber and monosynaptically from the ipsilateral lateral reticular nucleus. The results suggest collateral excitation from the C3–C4 propriospinal neurones which are excited monosynaptically from the former two inputs and antidromically from the latter nucleus. The cells were antidromically activated from the ipsilateral nucleus fastigius, and from the ipsilateral or contralateral reticular formation. Some of the spinocerebellar and spinoreticular neurones were also antidromically activated from Th13. It is suggested that spinocerebellar, spinoreticular and bifurcating spinocerebellar and spinoreticular neurones receive collateral input from the same excitatory C3–C4 propriospinal neurones which project to motoneurones and/or Ia inhibitory interneurones.

Characteristics and functional identification of saccadic inhibitory burst neurons in the alert monkey.

1. With the use of single-unit recording, the reticular formation immediately caudal to the abducens nucleus was searched for saccadic burst neurons in alert, trained rhesus monkeys. We recorded 80 short- and long-lead burst neurons, investigated their connections, and quantitatively analyzed their discharge characteristics. 2. Like excitatory burst neurons located rostral to the abducens, these caudal burst neurons fire optimally for ipsilaterally directed saccades, fire less for vertical saccades, and fire minimally, if at all, for contralateral saccades. The direction associated with the maximum number of spikes was approximately along the horizontal axis (1 +/- 12 degrees (SD); n = 33). 3. The first spike of the burst led the saccade by 2-120 ms, depending on the unit. Neurons were divided into short lead (45%) and long lead (55%) using a burst-lead criterion of 15 ms. In the on-direction, the discharges of both types exhibited strong correlations between number of spikes in the burst and size of the horizontal saccade component; duration of the burst and duration of the saccade; and peak frequency of the burst and peak velocity of the saccade. These relations were looser for long-lead neurons than for short-lead neurons. 4. Horseradish peroxidase injected into the abducens nucleus retrogradely labeled cells in the contralateral reticular formation where burst neurons were recorded, showing that cells in this region make crossed monosynaptic connections. There was good agreement between the limits of this region, as determined physiologically and anatomically. 5. Microstimulation at the locus of recorded burst neurons elicited EMG potentials in the contralateral lateral rectus muscle of the appropriate sign and latency for a monosynaptic inhibitory projection to abducens motoneurons. Stimulation also elicited eye movements consistent with inhibition of the contralateral lateral rectus. 6. It is argued that these characteristics make it likely that the short-lead neurons are the source of the afference which generate the pause in contralateral abducens motoneuron firing during adducting saccades. These neurons are therefore analogous to the inhibitory burst neurons (IBNs) found in the cat. The characteristics of long-lead burst neurons, particularly their lead, make them less likely to subserve this function. These cells might be better suited to providing input to omnipause neurons or to the short-lead IBNs.

Nervous Control of Occlusion

Receptors that convey sensory information about occlusal relationships to the CNS are found in the teeth, periodontal ligaments, muscles of mastication, and the temporomandibular joints. This sensory information enters the CNS largely through the maxillary and mandibular divisions of the trigeminal nerve. Cell bodies of these afferent neurons are found in the trigeminal ganglion (exteroceptive) and mesencephalic nucleus (proprioceptive). Axons of exteroceptive neurons are segregated into those conveying general sensory modalities such as touch, which enter the main sensory nucleus, and those conveying pain and temperature, which descend in the spinal tract of V and enter the spinal nucleus of V. Axons of proprioceptive neurons terminate in the motor nucleus of the trigeminal nerve. Second order neurons of the main sensory and spinal nuclei of the trigeminal nerve project to the thalamus. Third order neurons from the thalamus project bilaterally to the frontal and parietal cortex. The muscles of mastication, responsible for mandibular movement, are innervated by alpha motor neurons from the motor nucleus of V. When these neurons are stimulated, the masticatory muscles contract. The motor nucleus receives fibers from the frontoparietal motor cortex, trigeminal sensory nuclei, cerebellum, contralateral reticular formation, hypothalamus, amygdaloid nucleus, caudate nucleus, tectum of the midbrain, and cranial nerve nuclei (especially VII, which controls the muscles of the mouth and cheek and XII, which controls the musculature of the tongue). Input from all of these areas controls the muscles of mastication through the alpha and gamma motor neurons. Occlusal forces are produced during mastication, swallowing, and other activities. Tooth contacts stimulate sensory neurons. This information is conveyed to the CNS and integrated, and the appropriate adjustment of the mandible is made. Many questions concerning how the nervous system controls occlusion remain unanswered. How do the nervous pathways for the control of occlusal forces differ for individuals with normal occlusion or malocclusion, or for edentulous individuals or those with dentures? If the receptors of the teeth or periodontal ligaments provide the primary sensory input for the muscles of mastication, then clearly the individual with dentures or the edentulous individual must utilize alternative pathways to provide the appropriate control. Why do some people with obvious malocclusion not experience pain and others with minor occlusal problems experience great discomfort in the temporomandibular joint? Perhaps it is genetic, or the pathways used by each of these individuals may differ. What is the effect of repositioning the teeth or the entire jaw on established neuronal pathways? Perhaps the pathways are modified, or they degenerate and other pathways are established.

Inhibition from nucleus raphe magnus of tooth pulp responses in medial reticular neurones of the cat can be antagonized by bicuculline

In decerebrate cats stimulation in nucleus raphe magnus (NRM) inhibited the response of neurones in the medial brain stem reticular formation to electrical stimulation of the tooth pulp. These evoked responses were also reduced by iontophoretically applied GABA. The inhibition from NRM was blocked by bicuculline applied by iontophoresis in 10 out of 16 neurones and the actions of GABA were also antagonized. Inhibition following stimulation in the contralateral reticular formation was not blocked by bicuculline. The results suggest that GABA is involved as a neurotransmitter in mediating the effects of NRM stimulation on reticular neurones.

Projections of the optic tectum in the longnose gar, lepisosteus osseus

Efferent projections of the optic tectum were studied with the anterograde degeneration method in the longnose gar. Ascending projections were found bilaterally to 3 pretectal nuclei — the superficial pretectal nucleus, nucleus pretectalis centralis and nucleus pretectalis profundus — and to a number of targets which lie further rostrally — the central posterior nucleus, dorsal posterior nucleus, accessory optic nucleus, nucleus ventralis lateralis, nucleus of the ventral optic tract, rostral part of the preglomerular complex, suprachiasmatic nucleus, anterior thalamic nucleus, nucleus ventralis medialis, nucleus intermedius, nucleus prethalamicus and rostral entopeduncular nucleus. Projections of the tectum reach the contralateral side via the supraoptic decussation and are less dense contralaterally than ipsilaterally. Descending projections resulting from tectal lesions include: (1) a tectal commissural pathway to the core of the torus longitudinalis bilaterally and the contralateral tectum and torus semicircularis; and (2) a pathway leaving the tectum laterally from which fibers terminate in the ipsilateral torus semicircularis, an area lateral to the nucleus of the medial longitudinal fasciculus, lateral tegmental nucleus, nucleus lateralis valvulae, nucleus isthmi and the reticular formation. A component of this bundle decussates at the level of the lateral tegmental nucleus to project to the contralateral reticular formation. On the basis of comparisons of these findings with the pattern of retinal projections in gars and other data, it is argued that the nuclei previously called the lateral geniculate and rotundus in fish are not the homologues of the nuclei of those names in land vertebrates but are rather pretectal cell groups. The overall organization of both retinal and tectal projections in gars is strikingly similar to that in land vertebrates; at present, the best candidate for a rotundal homologue is the dorsal posterior nucleus.

Sources of direct excitatory and inhibitory inputs from the medial rhombencephalic tegmentum to lateral and medial rectus motoneurons in the cat.

The paramedian pontine and bulbar tegmentum was explored by microstimulation to outline the sites of origin of direct excitatory and inhibitory inputs to lateral rectus (LR) and medial rectus (MR) motoneurons (MNs). In order to avoid activation of fibers of passage and axon reflexes originating outside the stimulation sites, experiments were carried out 4--22 days after brain stem transections causing degeneration of vestibulo-ocular pathways. Additionally, in some experiments the paramedian tegmentum was isolated from the contralateral side by midline transections. Mapping of stimulus sites from which monosynaptic EPSPs and IPSPs were elicited brought out the following preoculomotor reticular regions: 1. LR-MNs received monosynaptic IPSPs from the contralateral reticular formation corresponding to Nucl. reticularis points caudalis (R.p.c.) and the rostral part of Nucl. reticularis gigantocellularis (R.gc.). 2. Monosynaptic inhibitory input to MR-MNs could only be demonstrated after degeneration of excitatory pathways ascending from the internuclear neurons of the VIth nucleus and from the ipsilateral vestibular nuclei. Monosynaptic IPSPs originated in the ipsilateral dorso-medial tegmentum through the entire extent of the Nucl. reticularis pontis oralis and rostral R.p.c. including the region of the ipsilateral VIth nucleus. 3. Monosynaptic excitation of LR-MNs was induced by stimulation of the ipsilateral R.p.c. and the rostral half of the paramedian bulbar tegmentum (R.gc.). 4. The sites from which monosynaptic EPSPs were evoked in MR-MNs were confined to the contralateral VIth nucleus and its immediate vicinity. No evidence could be obtained for direct excitatory inputs to MR-MNs from the ipsilateral paramedian tegmentum. It is concluded that the paramedian rhombencephalic reticular formation contains four pools of premotor neurons related to coordination of conjugate horizontal eye movements. Two of them are excitatory for LR- and MR-MNs with ipsilateral ON-directions, the other two mediate reciprocal inhibition of the antagonistic motor nuclei.

Location of abducens afferent neurons in the cat

The sites of afferent neurons to the abducens nucleus were determined by the use of horseradish peroxidase hydraulically placed into the VIth nucleus in nine cats. Labeled neurons were found bilaterally in the medial vestibular nuclei, the prepositus nucleus of the hypoglossus, the contralateral dorsomedial gigantocellular tegmental field, the contralateral reticular formation, and the ipsilateral vestibular nerve ganglion.

Reticulospinal excitation and inhibition of neck motoneurons.

Responses of neck motoneurons to electrical stimulation of the pontomedullary reticular formation were recorded intracellularly in cerebellectomized cats anesthetized with chloralose. Stimulation of nucleus reticularis (n.r.) ventralis and the dorsal part of n.r. gigantocellularis evoked short latency, monosynaptic inhibitory postsynaptic potentials (IPSPs) in the majority of motoneurons supplying the ipsilateral splenius, biventer cervicis and complexus muscles and in 25% of motoneurons projecting in the ipsilateral spinal accessory nerve. Monosynaptic IPSPs were also evoked by stimulating the medial longitudinal fasciculus (MLF) but lesion and collision experiments indicated that these IPSPs were independent of those evoked by reticular stimulation. Monosynaptic IPSPs were also occasionally observed following stimulation of the contralateral reticular formation, especially of the dorsal part of n.r. gigantocellularis. Monosynaptic excitatory postsynaptic potentials (EPSPs) were evoked in all classes of neck motoneurons studied by stimulation of n.r. pontis caudalis, gigantocellularis and ventralis. Each reticular nucleus appeared to contribute to this excitation. The excitation was bilateral but large monosynaptic EPSPs were most often seen in motoneurons ipsilateral to the stimulus site. Data indicated that pontine EPSPs were mediated by ventromedial reticulospinal fibers while medullary EPSPs were mediated by ventrolateral reticulospinal fibers. Neck motoneurons thus receive at least three distinct direct reticulospinal inputs, two excitatory and one inhibitory.

Cat spinoreticular neurons: Locations, responses and changes in responses during repetitive stimulation

Neurons in the lumbosacral spinal cord which project to the medial pontomedullary reticular formation were studied in the chloralose-anesthetized cat. Such neurons, identified by antidromic activation, were found predominantly in lamina VIII and medial lamina VII, and most were found to project to the contralateral reticular formation. Receptive fields for natural stimuli were generally complex, having various combinations of excitatory and inhibitory areas ipsi- and/or contralaterally. Adequate stimuli ranged from innocuous to noxious, with the stimuli required for decreasing a neuron's activity usually more intense than the stimulus required for increasing it. Electrical stimulation of hindlimb nerves indicated the presence of extensive convergence. Responses of spinoreticular neurons were found to decline during periods of repetitive stimulation. The response decrements were found to have many of the parametric features of behavioral habituation and were similar to response decrements previously observed in the medial pontomedullary reticular formation.

Pontomedullary reticular projections into the region of the ascending medial longitudinal fasciculus in cat.

The medial longitudinal fasciculus (MLF) and immediately adjacent reticular formation were stimulated electrically just caudal to the trochlear nucleus in the cat. In the pontomedullary reticular formation within 1.5 mm of the midline, antidromically excited neurons were detected in (1) the contralateral abducens nucleus, (2) the contralateral reticular formation just caudal and caudoventral to the abducens nucleus, and (3) the ipsilateral nucleus reticularis pontis caudalis beneath and rostral to the abducens nucleus. The possible involvement of these neurons in eye or body movements is discussed.

Inhibitory effects of reticulospinal fibers of the lateral funiculus on neurons of thoracic spinal reflex pathways

Experiments on anesthetized cats with partial transection of the spinal cord showed that reticulo-spinal fibers in the ventral part of the lateral funiculus participate in the inhibition of polysynaptic reflexes evoked by stimulation of the ipsi- and contralateral reticular formation. The reticulo-fugal wave in the ventrolateral funiculus evoked comparatively short (up to 70 msec) IPSPs in some motoneurons of the internal intercostal nerve investigated and at the same time evoked prolonged (up to 500 msec) inhibition of IPSPs caused by activation of high-threshold segmental afferents. This wave also led to the appearance of IPSPs in 14 of 91 (15.5 %) thoracic spinal interneurons studied. The duration of these IPSPs did not exceed 100 msec; meanwhile, segment excitatory responses of 21 of 43 interneurons remained partly suppressed for 120–500 msec. It is concluded that the inhibitory action of the lateral reticulo-spinal system on segmental reflexes is due to several synaptic mechanisms, some of them unconnected with hyperpolarization of spinal neurons. The possible types of mechanisms of this inhibition are discussed.

Properties of projections from vestibular nuclei to medial reticular formation in the cat.

In one series of experiments, vestibular neurons that could be activated antidromically by stimulation of the contralateral medial reticular formation were studied with extracellular recording in cats under pentobarbital anesthesia. These neurons were found in all of the four main vestibular nuclei, but were less prevalent in dorsal Deiters' nucleus and in the central region of the superior vestibular nucleus than elsewhere. Regions of the pontine and medullary reticular formation from which neurons in different vestibular nuclei were activated corresponded to the pattern of vestibuloreticular projections described by neuroanatomists. 2. Latencies of antidromic responses to stimulation of the contralateral reticular formation ranged from 0.6 to over 3 ms, indicating a relatively slow transfer of activity from vestibular nuclei to reticular formation.

Reticular influences on lateral geniculate neuron activity

1. 1. Post-stimulus histograms were obtained from single neurons in the cat lateral geniculate nucleus (LGN) following stimulation of the midbrain reticular formation (RF). 2. 2. Stimulating in the same place in the RF gave a variety of responses in LGN neurons, including excitation, depression, and combinations of these. 3. 3. Ipsilateral and contralateral RF stimulations had similar effects on the same unit in the LGN. 4. 4. Removal of the eyes or visual cortices did not change the nature of the RF effect. Therefore, the pathway from RF to LGN seems to be confined to the brain-stem and diencephalon. 5. 5. In some neurons, oscillations in firing rate followed RF stimulation; these were very similar to the oscillations reported by others following optic nerve and visual cortex stimulation. Removal of the eyes and visual cortices did not prevent the oscillations. It is suggested that they may be due to reverberating circuits within the LGN.

Contralateral and ipsilateral projections of cerebral somatic areas to the medulla oblongata of cat.

Summary Single electrical shock stimuli delivered alternatively to various somatic areas of paralyzed cats evoked electrical activities, contralaterally and ipsilaterally, in the territories of: the spinal trigeminal nucleus (V), the posterior funicular nuclei (PF), the reticular formation (RF), ventral region of the lateral funiculus, the anterior funiculus, and the lateral pyramidal tract. In the territories of V and PF at the inferior olivary level the initial latencies of the contralateral responses were mostly less than 2 or 4 msec, while those of the ipsilateral responses ranged widely from 2 msec or less to over 10 msec. In the territories of V at the pyramidal decussation level the initial latencies of the contralateral responses were mostly 2 msec or less, while those of the ipsilateral responses were almost 4–10 msec. On the contrary, in the territories of PF at this level, no latency difference was seen between the contralateral and the ipsilateral responses. The initial latencies were 2 msec or less at both sides. At the inferior olivary level, the latencies of the responses in the contralateral RF and in the interior part of the ipsilateral RF were mostly 4 msec or less, while those in the lateral part of the ipsilateral RF were mostly 2–10 msec. It is confirmed that somatic areas send many fibers directly though the contralateral RF to the contralateral territories of V and PF. It also seems possible that somatic areas appear to send many fibers ipsilaterally to the interior part of RF from which fibers terminate transsynapti-cally to the territories of V and PF, although the possibility that direct ipsilateral fibers of very small diameter might exist is not excluded.