[Correlation between the analgesic effect by thalamic relay nucleus stimulation and somatosensory evoked potentials recorded from thalamus].

Electric stimulation of the thalamic sensory relay nucleus (Vc) has an analgesic effect on deafferentation pain, however, the analgesic effect differs from patient to patient. Electrode position and state of the substrate stimulated are considered important factors influencing the analgesic effect. In order to determine the best position for the stimulating electrodes, we recorded somatosensory evoked potentials (SEPs) from stimulating electrodes implanted in the Vc and compared thalamic SEPs with the analgesic effect of Vc stimulation. The subjects were thirteen patients with deafferentation pain, four patients with thalamic lesions, seven patients with suprathalamic lesions and two patients with infrathalamic lesions. We inserted the electrode array into the Vc stereotactically, and fixed it so that stimulation-induced paresthesia would cover the painful frea. The electrode array consisted of the four contact points of four electrodes spaced at 2 mm intervals within 10 mm from the tip. Using bipolar combinations of the four electrodes (twelve combinations in all), we stimulated the Vc for about half an hour with each combination. We then rated the degree (%) of analgesia as 100% when pain disappeared and 0% when there was no change. Thalamic SEPs elicited after stimulation of the contralateral median nerve were recorded from all four contact points simultaneously. The latencies, amplitudes and recorded positions of large early positive components (P1) followed by large negative components (N1) with latencies between 10 and 20 msec were then analyzed and compared with the best electrode combination for optimal pain relief and with the degree of analgesia.(ABSTRACT TRUNCATED AT 250 WORDS)

[Responsiveness of brain tumors to chemotherapeutic agents in the subrenal capsule assay].

The 6-day subrenal capsule assay was used to determine chemotherapeutic sensitivities of brain tumors. Twenty-nine brain tumors were obtained at the time of surgical resection. A minced tumor fragment (1-mm cube) was implanted under the renal capsule of 5- to 8- week-old normal female ddY mice. Each fragment was measured at two diameters using ocular micrometer unit (10 omu = 1.0 mm). The animals were randomized, usually 5 to 7 per group, and treated with anticancer drugs on day 1 through 5. On day 6, the mice were killed. The kidney was exteriorized and the tumor was again measured. The change in tumor size was obtained for each animal by ratio of the final tumor size/the initial tumor size. Sensitivities of tumors to anticancer agents were determined by comparing differences in mean values of the change in tumor size between control and treated group. Twenty-seven out of 29 specimens (93%) were submitted to evaluable assay. The response rate of 11 malignant gliomas (grade 3 and 4) was 44% and that to anticancer drugs tested were as follow: 5-FU 78%, ACNU and CPA 50%, VCR 40%, CDDP 36%. The response rate of 3 medulloblastomas was 36%: MTX 67%, CPA 50%, ACNU and CDDP 33%. That of two low-grade gliomas (grade 2) was 29%, while that of 4 malignant brain tumors (2 metastasis, chordoma, malignant fibrous histiocytoma) was 60%. Four neurinomas and 3 meningiomas were not sensitive to Tamoxifen and none were determined for estrogen receptor. In histological analysis, the transplanted tumor retained similar characteristics to the original tumor in the cases of neurinomas, meningiomas and some gliomas. Lymphocytic infiltration was observed in many cases. In the cases of metastasis (adenocarcinomas), considerable mesenchymation and lymphocytic infiltration was observed, tumor cells were reduced in number with poor preservation. Clinical response in 9 cases treated with sensitive drugs were 1 complete response, 2 partial response, 5 stable and 1 progressive disease in CT examination. The subrenal capsule assay is therefore considered to be very useful for determining suitable chemotherapeutic agents for brain tumors.