Regulation of striatal serotonin release by the lateral habenula-dorsal raphe pathway in the rat as demonstrated by in vivo microdialysis: role of excitatory amino acids and GABA

Striatal extracellular levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were monitored with the microdialysis technique during electrical stimulation of the lateral habenula-dorsal raphe (LHb-NRD) pathway in halothane anaesthetized rats. A new double-loop probe, with an improved recovery factor, was implanted into the head of the caudate-putamen and perfused with Ringer solution containing 1 microM of the 5-HT uptake blocker indalpine. Samples were collected every 15 min and analyzed with HPLC coupled to fluorimetric detection. Low frequency stimulation of the LHb (1.5 and 3 Hz, 0.5 mA) produced no detectable changes in striatal indole levels, whereas 15 Hz stimulation induced a 70% increase in 5-HT release. This effect was most likely mediated by a direct LHb-NRD link, since it persisted after ibotenic acid lesions of the interpeduncular nucleus (which is the major projection area for the medial habenular nucleus), but was completely abolished after transection of the fasciculus retroflexus, which carries the axons of the LHb-NRD pathway. The possible identity of the transmitter operating in the LHb-NRD pathway was investigated by NRD injections of kynurenic acid, a potent blocker of excitatory amino acid transmission, and by NRD injections of the GABA antagonist bicuculline. Kynurenic acid (300 nl, 50 mM) did not by itself induce any detectable changes in spontaneous indole output, but completely blocked the effect of LHb stimulation. Injection of bicuculline (300 nl, 2 mM) increased the striatal 5-HT output by about 70%, and potentiated the effect of LHb stimulation by a further 50%. In none of the experiments performed in this study were there any significant changes in striatal 5-HIAA output. These data are compatible with the idea that excitatory amino acids in the LHb-NRD pathway are involved in the regulation of striatal 5-HT release, and that this influence is modulated by GABAergic synaptic activity at the level of the NRD.     

Tumor growth delay and cell survival after treatment with irradiation and vinblastine

The interaction of irradiation and vinblastine was investigated in a solid rat rhabdomyosarcoma. Growth delay of the tumor and cell survival by an in vitro assay were the endpoints measured. Vinblastine was administered at a dose of 1.5 mg/kg body weight at different time intervals before or after doses of 10 and 20 Gy of X-rays. Excess growth delay, i.e., the difference between observed growth delay for the combined radio-chemotherapy treatment and the sum of growth delays of individual treatments, was observed when vinblastine was administered at intervals of 1 to 12 days after or 2 to 8 days before the radiation doses.The clonogenic capacity of cells from tumors treated in vivo was messed using an in vitro survival assay. Cell survival data as a function of time after treatment with either vinblastine, a dose of 10 Gy of X-rays, or a dose of 10 Gy followed after 1 day by vinblastine were collected. The radiation treatment resulted in surviving fractions which remained constant up to 6 days after treatment. The effectiveness of vinblastine and of the combined treatments could be assessed 2 or 3 days after the drug application. The fractions of surviving cells determined after combined therapy were not significantly different from the fractions expected on the basis of simple multiplication of the fractions of surviving cells of individual treatments. This indicates that for a 1 day interval tumor growth delay observed after a dose of 10 Gy of X-rays followed by vinblastine correlates with a simple additional effect of the two individual treatments.     

Evaluation of non-invasive techniques to assess vasoconstriction in healthy volunteers using methoxamine as a probe drug

Non-invasive methods for assessment of the vascular effects of antimigraine drugs were evaluated with respect to their utility, variability and sensitivity in a double-blind, placebo-controlled, three-period crossover study in six healthy volunteers using an intravenous vasoconstrictor, methoxamine, as a probe drug. Changes in the internal diameter of the brachial and radial arteries were measured using ultrasound which had low between-day and within-day coefficients of variation. Peak systolic velocity (PSV), time-averaged velocity (TAV), total flow, resistance (RI) and pulsatility indices (PI) were measured by Doppler from one arterial wave form. Whilst PSV and TAV increased with methoxamine, because of bradycardia, changes in PI and RI were difficult to interpret. An automatic oscillametric cuff, a mercury-in-silastic strain gauge method and the "Finapres", finger arterial blood pressure monitor were used to follow changes in systolic blood pressure (SBP). The strain gauge technique underestimated arm SBP compared to the oscillometric method but clearly showed drug-related increases whilst the Finapres did not reflect changes in blood pressure detected by the other methods.     

Growth pattern of tumor xenografts in wistar rats after treatment with cyclophosphamide,total lymphoid irradiation and/or cyclosporin A

Wistar rats treated with cyclophosphamide, total lymphoid irradiation (TLI and/or cyclosporin A (CSA) develop a state of immune suppression permitting the growth of tumor xenografts. Experiments were carried out on this newly developed model to investigate the growth patterns of a mouse osteosarcoma and a human colon adenocarcinoma. The combination of cyclophosphamide and CSA permitted a limited period of growth of the mouse osteosarcoma with a tumor take rate of 66%. No takes were observed with the human adenocarcinoma. The combination of cyclophosphamide and TLI resulted in a period of immunosuppression followed by recovery of the immune status. During the period of immunosuppression, tumor xenografts showed a 100% take rate. The most efficient immunosuppression was achieved by a combination of cyclophosphamide, TLI and CSA administered on alternate days. Wistar rats subjected to this treatment showed prolonged tolerance to mouse osteosarcoma and human adenocarcinoma xenografts. There was no alteration in the tumor doubling time or histological morphology of the xenografts in the adapted host as compared with those in the donor tumors. The tumor growth curve showed a pattern of of initial growth, a period of stagnation, followed by a steady but slower growth phase. The significance of the results and the advantages of the rat model described in this paper for human tumor xenotransplantation are discussed.