Intravenous reproductive and developmental toxicity studies of cimadronate (YM175), a novel bisphosphonate, in rats and rabbits.

Cimadronate (YM175) is a novel bisphosphonate with potent inhibitory activity on bone resorption under development for the treatment of tumor-induced hypercalcemia, metastatic bone disease and osteoporosis. We conducted intravenous reproductive toxicity and teratology studies (Segment I, II and III) of this compound in rats and teratology study in rabbits. The test compound was dissolved in physiological saline, which was also given as the vehicle control. Rats were administered at a dosage of 0.06, 0.16 and 0.62 mg/kg/day in the male Segment I study. Dose levels in the other studies in rats including the female Segment I were 0.16, 0.31 and 0.62 mg/kg/day. In the Segment I study, no treatment-related abnormalities were observed in reproductive parameters or fetuses. In the Segment II study, slightly retarded fetal ossification was noted at 0.31 mg/kg/day or more, but the incidence of malformation did not increase. In the Segment III study, death of the dams and abnormal tooth growth of offspring were observed at 0.16 mg/kg/day or more. Further Segment III study showed that the no toxic effect level was 0.003 mg/kg/day. In the rabbit teratology study, dose levels were 0.01, 0.025 or 0.05 mg/kg/day. No toxic effects on pregnant females or their litters were observed at up to 0.05 mg/kg/day.

Role of cyclic AMP dependent protein kinase in cannabinoid receptor modulation of potassium "A-current" in cultured rat hippocampal neurons.

Cannabinoid receptor agonists have been previously shown to enhance a potassium A-current (IA) in cultured rat hippocampal neurons. This effect has been further demonstrated to be dependent on G-protein linkage to adenylyl cyclase and levels of intracellular cyclic AMP (cAMP). The present study extends this analysis to the involvement of cAMP-dependent protein kinase (PKA) in this cascade. Specific activators and inhibitors of PKA were shown to have differential effects on the voltage dependence of IA. Specific activators of PKA produced a negative shift in voltage dependence of IA, whereas PKA inhibitors produced a positive shift in IA voltage dependence, the latter similar to that effected by the cannabinoid agonist WIN 55,212-2. Although the negative shift in IA induced by PKA stimulation could be reversed by PKA inhibitors, the positive shift produced by the PKA inhibitors alone was only 50-60% of the cannabinoid-produced shift in IA voltage dependence. This partial effect of PKA inhibition was confirmed by biochemical assays in the same cultured neurons that showed a similar 50-60% decrement in in vitro protein phosphorylation produced by PKA inhibitors. Results are discussed in terms of a diffusible second messenger linkage of the cannabinoid receptor to the A-current channel via the role of protein phosphorylation in modulation of IA.

Firing patterns of nucleus accumbens neurons during cocaine self-administration in rats.

The firing patterns of neurons in the nucleus accumbens (NA) were recorded in rats trained to self-administer cocaine via response contingent intravenous drug infusions. Recordings were obtained from permanently implanted multiple electrode arrays (8 microwires) inserted bilaterally into the NA and/or ventral striatum (NA-VS) in animals exhibiting stable responding (inter-infusion intervals, INT) during test sessions consisting of 16-30 drug delivery episodes. Electronically isolated and identified NA-VS neurons showed distinct patterns of phasic increases in firing relative to the occurrence of the reinforced lever press. Two particular firing patterns, however, were repeatedly encountered in different animals. In one type, a marked increase was observed in discharge following response contingent drug delivery. A second firing pattern showed two distinct temporally separated brief firing peaks (bursts), one immediately prior to the initiation of responding, and the other a brief discharge commencing within 200 ms after the initiation of drug delivery. The time between firing peaks was found to be modifiable by changing the response/reward (FR) ratio for drug delivery. A third finding was that the correlates of the self-administration response were not solely the result of drug infusion since, (1) phasic firing increases were not observed when the drug was delivered non-contingently during the same session and, (2) the emergence of patterns was frequently delayed within the session until after drug self-administration behavior stabilized at regular INTs. The findings are discussed in terms of the significance of NA-VS neuron firing correlates for the initiation and maintenance of cocaine self-administration.