Yoshimitsu Shiraishi

Direct inhibitory projection of pontine omnipause neurons to burst neurons in the Forel's field H controlling vertical eye movement-related motoneurons in the cat

SummaryThis study examines the nature of the efferent projection of omnipause neurons (OPNs) in the midline pontine tegmentum to medium-lead burst neurons (BNs) in the Forels field H (FFH), both of which exhibit activities related to vertical eye movements, using chronically prepared alert cats. Antidromic spikes of the BNs evoked by oculomotor nucleus stimulation were suppressed by shortly preceding (less than 5 ms) microstimulation within the OPN area including actual recording sites of OPNs. Many OPNs were antidromically activated by microstimulation at recording sites of the BNs. Furthermore, systematic tracking in and around the FFH with the stimulating microelectrode substantiated that the OPNs issued axonal branches within the BN area. These results suggest direct inhibitory projection of OPNs to the BNs.

Direct excitatory and inhibitory synaptic inputs from the medial mesodiencephalic junction to motoneurons innervating extraocular oblique muscles in the cat

SummaryThis study investigated the nature of synaptic inputs from the Forels field H (FFH) in the medial mesodiencephalic junction to inferior oblique (IO) motoneurons in the oculomotor nucleus and superior oblique (SO) motoneurons in the trochlear nucleus in anesthetized cats, using intracellular recording techniques. Stimulation of the FFH induced monosynaptic EPSPs in IO motoneurons on both sides. Paired stimulation of the ipsilateral FFH and contralateral vestibular nerve substantiated that the FFH-induced EPSPs were caused mainly by direct excitatory fibers from the FFH to IO motoneurons and partly by axon collaterals of excitatory neurons in the vestibular nuclei. Among parts of the FFH, the medial part was most effective for producing the EPSPs. Systematic tracking with the stimulating electrode in and around the FFH revealed that effective sites of stimulation inducing negative field potentials in the IO subdivision of the oculomotor nucleus, identified as extracellular counterparts of the EPSPs in IO motoneurons, were also located in the interstitial nucleus of Cajal, nearby reticular formation and posterior commissure, besides within and near the medial part of the FFH. Areas far rostral, dorsal and ventral to the FFH were ineffective. EPSP-IPSPs or EPSPs were mainly induced in SO motoneurons on both sides by FFH stimulation. Latencies of these EPSPs and IPSPs were close to those of the EPSPs in IO motoneurons, indicating their monosynaptic nature. Effective stimulation sites for inducing these synaptic potentials overlapped those for the EPSPs in IO motoneurons. Based on these results, it was suggested that excitatory and inhibitory premotor neurons directly controlling IO and SO motoneurons were located within and near the medial part of the FFH.

Mono- and disynaptic excitatory inputs from the superior colliculus to vertical saccade-related neurons in the cat Forel's field H.

SummaryExcitatory inputs to neurons in the Forels field H (FFH) related to visually induced vertical saccades from the ipsilateral superior colliculus (SC) were investigated in chronically prepared alert cats. By stimulation of the deep or intermediate layer of the SC, upward augmenting neurons (ANs) and one long-lead downward burst neuron (BN) were found to be activated monosynaptically, while medium-lead BNs were activated disynaptically. The monosynaptically activated neurons were not antidromically activated from the oculomotor nucleus, whereas disynaptically activated neurons were also activated antidromically from the inferior rectus subdivision of the nucleus. These results suggest that an excitatory input to the FFH from the SC for inducing vertical saccades of visual origin first reaches upward ANs and/or long-lead downward BNs in the FFH, which in turn drive medium-lead BNs in the same area synapsing with motoneurons related to vertical eye movements.

Excitatory and inhibitory synaptic inputs from the medial mesodiencephalic junction to vertical eye movement-related motoneurons in the cat oculomotor nucleus

The nature of synaptic inputs from the medial mesodiencephalic junction to motoneurons in the oculomotor nucleus innervating the superior and inferior rectus muscles was investigated in anesthetized cats, using intracellular recording techniques. Stimulation of the region produced mono- or disynaptic EPSPs and IPSPs in inferior and superior rectus motoneurons, respectively, on both sides. In a number of superior rectus motoneurons, EPSP-IPSPs or EPSPs were also induced in a similar latency range. The effective sites for inducing the monosynaptic PSPs were found within and near the dorsomedial part of the campus prerubralis.

Direct projection of cat mesodiencephalic neurons to the inferior rectus subdivision of the oculomotor nucleus

This study examines electrophysiologically the projection of neurons in the mesodiencephalic junction to the inferior rectus subdivision of the oculomotor nucleus, using cats anesthetized with pentobarbital sodium. Many of these neurons projected directly to the ipsilateral inferior rectus subdivision and some to both sides. The neurons appeared to distribute axon branches probably terminating within and near the subdivision. They were located in the medial region of the mesodiencephalic junction between A 6.5 and 8.0 histologically corresponding to the campus prerubralis.

An electrophysiologically defined trigemino-reticulo-facial pathway related to the blink reflex in the cat

This study examines the direct projection of neurons in the pontomedullary reticular formation (RF) to the dorsal division of the facial nucleus (FN), where the orbicularis oculi motoneuron pool is located, and the nature of synaptic inputs to the RF neurons from the supraorbital branch of the trigeminal nerve (SON), using electrophysiological techniques in anesthetized cats. A large number of the RF neurons directly projected to the ipsilateral FN dorsal division, and some of these neurons issued axon branches probably terminating on motoneurons in the division. Many of the RF neurons projecting to the dorsal division were synaptically activated by ipsilateral SON stimulation. Most latencies of their activation were between the latencies of the early and late blink reflex responses, and the remaining latencies were shorter than those of the early response. These results suggest that the RF neurons mediate both the early and the late blink reflex responses, but mainly the late response, as premotor relay neurons.

Effects of head-down tilt on the intracranial pressure in conscious rabbits.

Head-down tilt (HDT) causes a fluid shift towards the upper body, which increases intracranial pressure (ICP). In the present study, the time course of ICP changes during prolonged exposure to HDT was investigated in conscious rabbits through a catheter chronically implanted into the subarachnoid space. The production of cerebrospinal fluid (CSF) after exposure to 7-days HDT was also examined by a ventriculo-cisternal perfusion method. The ICP increased from 4.3+/-0.4 (mean+/-S.E.M.) mmHg to 8.0+/-0.8 mmHg immediately after the onset of 45 degrees HDT, reached a peak value of 15.8+/-1.9 mmHg at 11 h, and then decreased to 10.4+/-1.1 mmHg at 24 h. During 7-days HDT, it also increased from 4.8+/-0.9 mmHg to 9.2+/-1.6 mmHg immediately after the onset of 45 degrees HDT, reached a peak value of 12.8+/-2.5 mmHg at 12 h of HDT, and then decreased gradually towards the pre-HDT baseline value for 7 days. The rate of CSF production was 10.1+/-0.6 microl/min in rabbits exposed to 7-days HDT, and 9.7+/-0.5 microl/min in control rabbits. These results suggest that the rabbits begin to adapt to HDT within a few days and that the production of CSF is preserved after exposure to 7-days HDT. The time course of ICP changes during HDT in conscious rabbits seems to be considerably different from that in anesthetized rabbits.

P300-like potential disappears in rabbits with lesions in the nucleus basalis of Meynert

Abstract The nucleus basalis of Meynert (nbM, substantia innominata) in the basal forebrain provides a single major source of cholinergic innervation for the entire cerebral cortex. We tested the effects of nbM lesions on rabbit P300-like potentials. The P300-like event-related potential (ERP) was recorded in 14 female adult white rabbits using a conventional auditory oddball paradigm. The probability of occurrence for the 2-kHz and 1-kHz stimulus tones was 90% (frequent) and 10% (rare), respectively. The nbM was destroyed bilaterally in seven rabbits referred to as the nbM (+) group. In the other seven rabbits [nbM (–) group], putamen nuclei (n=6) or amygdaloid nuclei (n=1) were destroyed bilaterally. The evoked responses were recorded before and 1 week after the destruction. In the nbM (+) group, P300 amplitude to rare stimuli significantly decreased after the lesion. In the nbM (–) group, no component of ERPs showed changes after the lesions. These results indicate that the nbM might be involved in the generation of the rabbit P300.

Direct projection of cat midbrain tegmentum neurons to the medial rectus subdivision of the oculomotor complex

This study explores neurons in the medial midbrain tegmentum of cats projecting directly to the medial rectus subdivision of the oculomotor complex, using antidromic microstimulation techniques. Many of these neurons were located in areas just lateral and dorsal to the oculomotor complex, e.g. in the medial part of the midbrain reticular formation and ventralmost part of the periaqueductal gray. These results suggest that at least some neurons in the midbrain tegmentum presumed to be the site of origin of vergence eye movements directly project to the medial rectus subdivision to control medial rectus motoneurons.

Topographical organization of cat mesodiencephalic areas for monosynaptic activation of vertical oculomotoneurons.

This study investigated the topographical organization of mesodiencephalic areas for monosynaptic activation of vertical eye movement-related oculomotoneurons (OMNs) in anaesthetised cats. Systematic mapping of effective sites for inducing monosynaptic, excitatory field potentials in vertical OMN pools was performed bilaterally using one concentric bipolar stimulating electrode. These OMN pools included superior rectus, inferior oblique, inferior rectus and superior oblique pools of the oculomotor and trochlear nuclei. All the field potentials induced in each OMN pool were negative and had a latency of 0.8–1.2 ms, indicating monosynaptic activation of the OMNs. Effective stimulating sites for inducing the field potentials were distributed at a rostrocaudal level of A 7.0–9.0 and 1.0–4.0 mm lateral from the midline, but especially at A 7.0–8.0 and 2.0–3.0 mm lateral from the midline. Histologically, they were located within and near the medial part of the Forels field H. Stimulation at a more caudal level of A 5.0–6.0 and 1.0–2.0 mm from the midline was also particularly effective. This area correspond to the interstitial nucleus of Cajal and the nearby reticular formation. For each OMN pool, the above field potentials were induced bilaterally, but predominantly ipsilaterally. These results suggest the existence of a bilateral, but ipsilaterally predominant, monosynaptic excitatory pathway from Forels field H to each vertical OMN pool.