Hiromasa Iwakiri

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%).

Stimulus effects of the medial pontine reticular formation and the mesencephalic locomotor region upon medullary reticulospinal neurons in acute decerebrate cats

In acute decerebrate cats, medial pontine reticular formation (mPRF) and the mesencephalic locomotor region (MLR) were stimulated and their stimulus effects upon 250 medullary reticulospinal neurons (RSNs) were studied. One hundred and twenty-six RSNs were mono- and disynaptically activated. From the response patterns of the RSNs, they were divided into the mPRF-activated RSNs (n = 67) and the MLR-activated RSNs (n = 59). The former group of RSNs was located in the nucleus reticularis gigantocellularis (NRGc), while the latter group of RSNs was distributed in both the NRGc and the nucleus reticularis magnocellularis (NRMc). The activity of MLR-excited 12 RSNs was suppressed with the preceding mPRF stimulation. These RSNs were mainly located in the NRMc. Most mPRF-excited RSNs increased their discharge rates during mPRF-evoked suppression of postural muscle tone, and most MLR-excited RSNs increased their discharge rates during MLR-evoked locomotion. With mPRF stimulation, MLR-evoked locomotion was suppressed with cessation of MLR-excited RSNs activity. These results suggest that mPRF stimulation suppresses the activity of the locomotor rhythm generating system at the levels of not only the spinal cord but also the medullary output cells.

Pontine-induced generalized suppression of postural muscle tone in a reflexively standing acute decerebrate cat

In a reflexively standing acute decerebrate cat, the pontine tegmentum was electrically stimulated and the effects on postural muscle tone and locomotor movements evoked by stimulation of the mesencephalic locomotor region (MLR) were studied. A stimulating microelectrode was placed systematically at 1-mm increments throughout the pons (H - 2 to H - 10) at levels ranging from P0.0 to P6.5 dorsoventrally and mediolaterally from LR0 to L4 or R4. Another stimulating microelectrode was placed in the physiologically identified MLR. Stimuli delivered to the dorsomedial regions of the pontine tegmentum (P3 to P4, LR1.5 to 2.5, H - 4 to H - 6) resulted in simultaneous and bilateral suppression of tonic activities in the neck, lumbar back, forelimb and hindlimb muscles. The pontine inhibitory sites corresponded to the medial area of the central tegmental field (FTC) and the central area of the gigantocellular tegmental field (FTG), bilaterally. Effects of pontine induced suppression on those muscles were stimulus frequency and stimulus intensity-dependent and the effects persisted even after termination of the stimulation. With concomitant pontine stimulation, MLR-evoked locomotor movements were suppressed along with prolongation of the forelimb and hindlimb step cycles.

Follicular Dendritic Cell Tumor of the Cervical Lymph Node

Follicular dendritic cell (FDC) tumor is an uncommon sarcoma, which occurs in lymph nodes or in extranodal sites. A 61-year-old female was referred to our hospital because of a nontender mass on her neck. The mass was surgically removed and initially diagnosed as a metastasis of malignant fibrous histiocytoma (MFH). Because the subsequent progress was inconsistent with the common prognosis of a patient with MFH, the possibility of FDC tumor was taken into consideration. Immunohistological studies for FDC antigens, such as CD21 and CD35, led to final diagnosis. It is suggested that FDC tumor should be included in the diagnostic considerations when a spindle cell tumor is present in a lymph node.

Multi-segmental and generalized suppression of postural muscle tone evoked by stimulating the dorsal tegmental field and the medial pontine reticular formation in acute decerebrate cats

In acute decerebrate cat, stimulation of the dorsal tegmental field (DTF) of the caudal pons along its midline and the medial pontine reticular formation (mPRF) evokes generalized suppression of postural muscle tone. In this study, the effects of stimulation of the DTF area were compared with those evoked by stimulating the mPRF unilaterally or bilaterally. By stimulating the mPRF bilaterally, simultaneous suppression of tonic activities in the neck, lumbar back, forelimb and hindlimb muscles, bilaterally, was evoked as that evoked by stimulating the DTF area alone.

Extracellular levels of serotonin in the medial pontine reticular formation in acute decerebrate cats with a microdialysis technique.

Extracellular levels of serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) were measured in the medial pontine reticular formation of acute decerebrate cats. The mean basal levels of 5-HT and 5-HIAA were 26 fmol/20 microliters and 15 pmol/20 microliters. Perfusion of the dialysis probe with high K+ and Ca(2+)-free Ringer solution for 60 min resulted in 4.8-8.5 x increase and 25-48% decrease in the extracellular levels of 5-HT, respectively, in comparison to the basal 5-HT levels. Perfusion with TTX-added Ringer solution for 60 min resulted in a consistent decrease in the extracellular levels of 5-HT.