Kiyoji Matsuyama

Site-specific postural and locomotor changes evoked in awake, freely moving intact cats by stimulating the brainstem

Locomotor behaviors evoked by stimulating the hypothalamus and the brainstem were studied in freely moving, awake cats. To do this, stimulating microelectrodes were chronically implanted into the subthalamic locomotor region (SLR) in the lateral hypothalamic area (LHA), the mesencephalic locomotor region (MLR) corresponding to the nucleus cuneiformis, the dorsal tegmental field (DTF) and the ventral tegmental field (VTF) of caudal pons along its midline. After recovery from surgery (2-3 days), open field tests were performed to study stimulus effects upon posture and locomotor movements. The stimuli consisted of pulses of 0.2 ms duration of less than 80 microA delivered at 50 pulses/s for 5-20 s. DTF stimulation resulted in suppression of postural support by the hindlimbs. When the cat was in a standing posture, DTF stimulation simply resulted in a sequential alteration of posture to a squatting and then to a final lying posture. In contrast, VTF stimulation evoked an almost opposite series of postural changes to those induced by DTF stimulation. With VTF stimulation, the cat changed from a lying or a squatting position, and then started to walk during continuation of the stimulation. With MLR stimulation, the cat invariably exhibited fast walking and then running movements. It ran straight forward, avoiding collision with walls or other obstacles, and even tried to jump over a fence placed in front of it. With LHA stimulation, the cat started to walk slowly extending its head forward and looking around repeatedly. It tended to walk with a stoop and stealthy steps along the corners of the room. Induced postural and locomotor changes were always accompanied by behavioral arousal reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical and chemical stimulations of the pontine micturition center

In an acute decerebrate cat, electrical stimulation of the pontine micturition center (PMC) resulted in micturition. Carbachol injection into the PMC also resulted in micturition. The pattern of changes in bladder pressure and the sphincter activity observed during carbachol-induced micturition was almost identical to that observed during reflex micturition. The injection site corresponded to the nucleus locus coeruleus alpha (LC alpha). These results suggest that activation of cholinoceptive neurons in the LC alpha presumably becomes a trigger to recruit any one of a number of neuronal circuits involved in micturition.

Discharge properties of medullary reticulospinal neurons during postural changes induced by intrapontine injections of carbachol, atropine and serotonin, and their functional linkages to hindlimb motoneurons in cats

The present study was aimed at elucidating the pontomedullary and spinal cord mechanisms of postural atonia induced by microinjection of carbachol and restored by microinjections of serotonin or atropine sulfate into the nucleus reticularis pontis oralis (NRPo). Medullary reticulospinal neurons (n=132) antidromically activated by stimulating the L1 spinal cord segment were recorded extracellularly. Seventy-eight of them were orthodromically activated with mono- or disynaptic latencies by stimulating the NRPo area at the site where carbachol injections effectively induced postural atonia. Most of these reticulospinal neurons (71 of 78) were located in the nucleus reticularis gigantocellularis (NRGc). Following carbachol injection into the NRPo, discharge rates of the NRGc reticulospinal neurons (29 of 34) increased, while the activity of soleus muscles decreased bilaterally. Serotonin or atropine injections into the same NRPo area resulted in a decrease in the discharge rates of the reticulospinal neurons with a concomitant increase in the levels of hindlimb muscle tone. Membrane potentials of hindlimb extensor and flexor alpha motoneurons (MNs) were hyperpolarized and depolarized by carbachol and serotonin or atropine injections, respectively. In all pairs of reticulospinal neurons and MNs (n=11), there was a high correlation between the increase in the discharge rates and the degree of membrane hyperpolarization of the MNs. Spike-triggered averaging during carbachol-induced atonia revealed that inhibitory postsynaptic potentials (IPSPs) were evoked in 15 MNs by the discharges of nine reticulospinal neurons. Four of them evoked IPSPs in more than one MN. The mean segmental delay and the mean time to the peak of IPSPs were 1.6 ms and 2.0 ms, respectively. Axonal trajectories of reticulospinal neurons (n=6), which evoked IPSPs in MNs, were investigated in the lumbosacral segments (L1-S1) by antidromic threshold mapping. The stem axons descended through the ventral (n=2) and ventrolateral (n=4) funiculi in the lumbar segments. All axons projected their collaterals to the intermediate region (laminae V, VI) and ventromedial part (laminae VII, VIII) of the gray matter. All these results suggest that the reticulospinal pathway originating from the NRGc is involved in postural atonia induced by pontine microinjection of carbachol, and that the pathway is inactivated during the postural restoration induced by subsequent injections of serotonin or atropine. It is further suggested that the pontine inhibitory effect is mediated via segmental inhibitory interneurons projecting to MNs.

Ascending and descending projections of the nucleus reticularis gigantocellularis in the cat demonstrated by the anterograde neural tracer, Phaseolus Vulgaris Leucoagglutinin(PHA-L)

Ascending and descending projections of the nucleus reticularis gigantocellularis (NRGc) were studied in the cat by the anterograde tracer, Phaseolus vulgaris leucoagglutinin. Ascending fibers from the left or the right NRGc coursed through the bilateral medial reticular formation and some of them reached the diencephalon. In the brainstem, PHA-L-labeled fibers and their terminals were observed in the medial reticular formation, the cranial motor nuclei (III, IV, V, VI, VII, XII), the vestibular complex, the LC complex, the raphe nuclei, the periaqueductal gray, the red nucleus, the Edinger-Westphal nucleus and the interstitial nucleus of Cajal. In the diencephalon, they were observed in the dorsal thalamus and the hypothalamic regions. In the caudal medulla, labeled fibers and their terminals were observed in the nucleus prepositus hypoglossi, the nucleus intercalatus and the inferior olive. Descending axons from the NRGc coursed bilaterally through the ventral and ventrolateral funiculi as far caudal as the upper thoracic cord. Single axon collaterals arising from the descending axons gave off terminal fibers to the left or the right gray matter. Their terminals were located in laminae V-X, mainly in laminae VII and VIII. In lamina IX, they were distributed mainly in the medial portion. A few fibers originating from the descending axons ipsilateral to the PHA-L injection side coursed through the anterior or posterior commissure, and ended in laminae VI, VII and VIII. The functional implications of these findings are discussed in relation to the behavioral state control and the generalized motor inhibition.

Extracellular levels of serotonin in the medial pontine reticular formation in relation to sleep-wake cycle in cats: a microdialysis study.

Extracellular levels of endogenous serotonin (5-hydroxytryptamine; 5-HT) and its major metabolite, 5-hydroxyindoleacetic acid (5-HIAA) were measured in the medial pontine reticular formation (medial PRF) of intact cats. A microdialysis probe was inserted through a guide cannula into the medial PRF. At least 12 h after the probe insertion, in vivo brain microdialysis was initiated. The perfusion rate was 1 microliters/min, and perfusate fractions at regular intervals of 20 min were collected. Changes in extracellular 5-HT levels were compared across sleep-wake states of the animals, such as waking (W), slow wave sleep (SWS) and rapid eye movement (REM) sleep. To assess sleep-wake states, EEG, EMG, EOG and PGO waves were simultaneously recorded in parallel with microdialysis of the medial PRF. Extracellular 5-HT levels were highest (20-28 fmol/20 microliters) during W. As the animals entered SWS, 5-HT levels decreased to about 90% of those during W. The state of REM sleep usually interrupted SWS for 3-8 min. During the longer periods of REM sleep, during the 20 min periods in which the perfusates were collected, we observed the lowest 5-HT levels (60-50%).

Termination mode and branching patterns of reticuloreticular and reticulospinal fibers of the nucleus reticularis pontis oralis in the cat: an anterograde PHA-L tracing study

By utilizing an anterograde neural tracer, Phaseolus vulgaris leucoagglutinin (PHA-L), pontomedullary reticuloreticular connections and reticulospinal connections were studied, including their fiber trajectories and distribution of PHA-L labeled terminals in close apposition to target reticular and spinal neurons, and branching patterns of axon collaterals at the levels of the cervical and upper thoracic cord. PHA-L was focally microinjected into the medial pontine reticular formation corresponding to the nucleus reticularis pontis oralis. A great number of PHA-L labeled thin fibers descended bilaterally coursing through the medial part of the pontine and medullary reticular formation with an ipsilateral predominance. Labeled terminal boutons were closely apposed to somata of various sized pontomedullary reticular neurons. Labeled thick fibers descended ipsilaterally coursing through the ventral half of the medial longitudinal fasciculus, and further descended through the ventral funiculus of the spinal cord. At the levels of the cervical and upper thoracic cord, these reticulospinal fibers gave off axon collaterals sending terminal fibers to small- to large-sized neurons in Rexeds laminae VII and VIII. Some of the axon collaterals innervated not only ipsilateral but also contralateral gray matter. By reconstructing branching patterns of axon collaterals, each axon collateral was found to innervate spinal neurons located in a disk-like spinal segment with a width less than 1 mm.

Pontine microinjection of carbachol and critical zone for inducing postural atonia in reflexively standing decerebrate cats.

Pontine carbachol injection sites critically related to the induction of postural atonia were explored in reflexively standing acute decerebrate cats. Carbachol (4.0 micrograms/0.25 microliter) and atropine (2.0 micrograms/0.25 microliter) were focally injected into the pontomedullary reticular formation, and their effects on hindlimb extensor muscle tone were studied. The effective carbachol injection sites were concentrated in the region between P 1.5 and P 3.5, H -3.0 and H -5.0, and LR 1.2 and LR 2.5 (Horsley-Clarke coordinates). The effective sites corresponded to the dorsomedial part of both the nucleus reticularis pontis oralis (NRPo) and the rostral portion of the nucleus reticularis pontis caudalis (NRPc). The mean latency to the beginning of carbachol-induced postural atonia was about 90 s (92 +/- 28 s; n = 24).

Synaptic mechanisms acting on lumbar motoneurons during postural augmentation induced by serotonin injection into the rostral pontine reticular formation in decerebrate cats

Intrapontine microinjections of serotonin in acutely decerebrated cats resulted in the bilateral augmentation of the postural muscle tone of the hindlimbs. Optimal injection sites were located in the dorsomedial part of the rostral pontine reticular formation corresponding to the nucleus reticularis ponds oralis (NRPo). In this study, attempts were made to elucidate the cellular basis for the serotoninergically induced augmentation of postural muscle tone by recording the electromyographic (EMG) activity of hindlimb extensor muscles, the monosynaptic reflex responses evoked by electrical stimulation of group Ia muscle afferent fibres and the membrane potentials of hindlimb alpha-motoneurons (MNs). Serotonin injections resulted not only in the augmentation of the EMG activity of gastrocnemius soleus muscles, but also in the restoration of EMG suppression, which was induced by previous injection of carbachol into the NRPo. Extensor and flexor monosynaptic reflex responses were facilitated by serotonin injections into the NRPo. Such reflex facilitation was not induced by serotonin injections into the mesencephalic or the medullary reticular formation. Intrapontine serotonin injections resulted in membrane depolarization of extensor and flexor MNs with decreases in input resistance and rheobase. Spontaneous depolarizing synaptic potentials (EPSPs) increased in both frequency and amplitude. Peak voltage of Ia monosynaptic EPSPs also increased. Serotonin injections which followed carbachol injections resulted in membrane depolarization of MNs along with an increase in the frequency of spontaneous EPSPs and a decrease in carbachol-induced inhibitory postsynaptic potentials. Following pontine carbachol injections, antidromic and orthodromic responses in MNs were suppressed. Discharges of MNs evoked by intracellular current injections were also suppressed, but were restored following serotonin injections. These results indicate that postsynaptic excitation, presynaptic facilitation and disinhibition (withdrawal of postsynaptic inhibition) simultaneously act on the hindlimb MNs during serotonin-induced postural augmentation and restoration.

Chapter 18 The behaviour of lateral vestibular neurons during walk, trot and gallop in acute precollicular decerebrate cats

During controlled locomotion in acute decerebrate cats, discharge characteristics of 90 Deiters neurons were analysed. Representative Deiters neurons changed their discharge from a tonic pattern (loco-motor-unrelated) during slow walk to a phasic pattern (locomotor-related) during fast walk. Bursting discharge of these units was phase-locked with the bursting EMG activity of either the left or the right hindlimb extensor muscle. During trot, the same Deiters neurons discharged twice in a single step cycle, and each bursting discharge was phase-locked with the bursting EMG activity of the left and the right hindlimb extensor muscles. During gallop, in which bursting EMG activities of bilateral hindlimb muscles appeared more or less in phase, such bursting discharges of the Deiters neurons fused each other, thus being phase-locked with the bursting EMG activity. There were also activities of Deiters neurons recruited at each transitional phase of locomotion from slow walk to fast walk, fast walk to trot and trot to gallop. These recruited Deiters neurons either changed their discharge patterns in a sequence as described above or maintained a tonic pattern with an increase in the firing frequency in relation to the changes in the pattern of locomotion.