Sadahiro Maejima

Thalamic neuronal hyperactivity following transection of the spinothalamic tract in the cat: involvement ofN-methyl-d-aspartate receptor

Single neuron activities responding to peripheral stimuli with short latencies were recorded within the thalamic nucleus ventralis posterolateralis (VPL) after transection of the spinothalamic tract (STT) in the cat under alpha-chloralose anesthesia. The VPL neurons showed spontaneous and evoked hyperactivity after STT transection, which was revealed at 1-2 weeks. The spontaneous hyperactivity further progressed until 3-4 weeks. These hyperactivities were observed in core-area neurons as well as neurons found in the shell area, suggesting that some, if not many, of the N-methyl-D-aspartate (NMDA) receptor antagonist (MK-801, 4-16 mg; i.v.) attenuated both the spontaneous and evoked hyperactivity observed after STT transection. No such effects were demonstrated in sham-operated animals. These findings suggest that VPL neurons become hyperactive after STT transection through recruitment of NMDA receptors. The hyperactivity of VPL neurons may represent an important background process in the production of deafferentation pain induced by lesions involving the STT.

Preoperative determination of the level of spinal cord lesions from the killed end potential

To determine preoperatively the level of lesions in acute cervical cord injury, the killed end potential of the spinal cord was recorded with a pair of electrodes placed in the spinal epidural space, one initially being placed rostrally to the lesions for obtaining recordings and the other placed caudally to the lesions for stimulation. The level associated with the largest killed end potential was clearly determined without much difficulty, with sequential recordings on stepwise withdrawal of the recording electrode, in four of five cases investigated. In two cases subjected to surgery, the recording electrode left in place at the level associated with the largest killed end potential was found to be located at, or a few millimeters below, the center of the lesions. This demonstrates the preoperative localizing value of the killed end potential for determining the level of lesions responsible for myelopathy.

Responses of Raphe-Spinal Neurons to Stimulation of the Pontine Parabrachial Region Producing Behavioral Nociceptive Suppression in the Cat

Cholinergic stimulation of the pontine parabrachial region (PBR) produces behavioral nociceptive suppression in the awake cat. This report shows that electrical stimulation of both PBR sites (verified to be associated with behavioral nociceptive suppression on cholinergic stimulation) and the periaqueductal gray (PAG) excites raphe-spinal neurons which have been implicated in descending nociceptive suppression. Although several lines of evidence have strongly indicated that pathways from the PBR and PAG for nociceptive suppression are anatomically as well as neurochemically distinct, the results of the present study appear to suggest that certain components of the pathways from the PBR may be synergic in function with those from the PAG with regard to the activity of raphe-spinal neurons.

Neurosurgical trauma in Japan.

According to the statistics compiled by the Institute for Traffic Accident Research and Data Analysis, the total number of head trauma patients has stayed virtually the same for the last 10 years in Japan, although a fraction of people suffering minor head trauma has shown a trend to increase. The Japan Society of Neurotraumatology is in the process of establishing a guideline for head trauma management. No major difference is noted in surgical procedures selected by neurosurgeons in Japan as compared to those in other countries. It appears, however, that the ventriculostomy may be less frequently employed to control elevated intracranial pressure, and the jugular bulb venous oximetry is far more frequently employed to detect cerebral deoxygenation in Japan. There appear to be two obvious differences in selection of pharmacological therapies among neurosurgeons in Japan and those in other countries; neurosurgeons in Japan prefer glycerol to mannitol for osmotic control of intracranial pressure, and barbiturate to morphine as sedatives. Two drugs are currently available in Japan for promoting the recovery from disturbance of consciousness after head trauma: cytidine diphosphate choline (CDP)-choline (Nicholin, Takeda Chemical Industries, Ltd., Osaka) and protirelin tartrate (Hirtonin; thyrotropinreleasing hormone (TRH) analogue, Takeda). Another TRH analogue, NS-3 (montirelin hydrate), is currently submitted to the Ministry of Health and Welfare for approval. A multi-institutional controlled study to examine the efficacy of therapeutic hypothermia for head trauma management is now in progress in Japan. The Japan Neurotrauma Data Bank System was inaugurated 2 years ago, enabling joint statistical processing at 10 major neurotrauma centers. Utilizing such a system, more detailed analysis of head trauma management will be possible, and clinical trials will be conducted systematically and more promptly in future.

Dynamic changes in cytochrome oxidase activity in the rat somatosensory cortex following thalamocortical deafferentation

The changes in cytochrome oxidase (CYO) activity in the primary somatosensory cortex (SI) induced by unilateral lesions restricted to the posterior ventrobasal region of the thalamus were investigated by histochemical techniques and photometric semi-quantitation in the rat. The CYO activity decreased rapidly and dramatically in layer IV of the lesioned side, reaching its lowest level within 2 weeks, and remained depressed at 8 weeks post-lesion. Segmentations normally seen in layer IV corresponding to barrels remained absent. While less marked decreases were also noted in other layers, obvious recovery was subsequently observed, attaining levels comparable to those on the intact size at 6 or 8 weeks post-lesion. The persistent decrease in layer IV appears to reflect a reduced thalamocortical activation of the dendritic profiles and neuronal perikarya. The recovery in other layers may represent an increase in the resting level of the initially depressed neuronal activity near to the original levels. The persistent reduction of function in the inhibitory surround, which is normally activated by thalamocortical input, may contribute to the increase in CYO activity.

Meningeal chondrosarcomatous tumor associated with meningocytic differentiation

Most meningeal chondrosarcomatous tumors have been regarded as identical to similar tumors occurring elsewhere in the body. The neoplasm reported here, however, clearly demonstrated transitions between usual meningiomas and chondrosarcomatous tumors. The present case thus provides evidence in support of Cushings and Eisenhardts proposal that some meningeal chondrosarcomatous tumors are derived from meningeal cells and are histogenetically related to meningiomas.