Enhanced acquisition of reversal training in a spatial learning task in rats treated with chronic nimodipine

Nimodipine levels were measured in blood and brain of rats implanted SC with sustained-release pellets of nimodipine (0, 10, 20, or 40 mg). Dose-dependent levels of nimodipine were detected in both plasma and brain. These results indicated the possible usefulness of these pellets in behavioral studies where long-term treatment is required. Therefore, the effects of chronic nimodipine, using 40-mg pellets, were examined on the performance of young, middle-aged, and aged rats in the Morris water maze. Following implantation of either nimodipine or placebo pellets, rats were trained for 6 days (three sessions/day) followed by 6 days of reversal training. During both initial and reversal training, every sixth trial was a probe trial. During initial training, there were clear age-related acquisition deficits in place training, with no effects of chronic nimodipine. Nimodipine did, however, enhance performance of rats during the first and second probe trials of reversal training. Time spent in the training quadrant by nimodipine-treated rats was approximately 30% longer on the first reversal probe and 35% longer on the second reversal probe than time spent in this quadrant by placebo-treated animals. These results indicate that chronic nimodipine enhances the performance of normal animals in reversal training on a spatial learning task.

Alteration of 5-HT1A receptor binding sites following chronic treatment with ipsapirone measured by quantitative autoradiography

Ipsapirone, a high-affinity ligand for the 5-hydroxytryptamine1A (5-HT1A) receptor subtype, has been shown to be a full agonist at presynaptic serotonergic sites and a partial agonist at postsynaptic sites. Several recent studies have examined the effects of chronic treatment with ipsapirone or other structurally related pyrimidinylpiperazine compounds, including buspirone and gepirone, on 5-HT1A binding sites with mixed results. Since the neural mechanism responsible for the anxiolytic and antidepressant properties of these compounds is currently uncertain, further investigation of this issue appeared warranted. [3H]8-hydroxy-2-(di-n-propylamino)-tetralin ([3H]8-OH-DPAT), a ligand specific for the 5-HT1A site, has been used successfully to label these sites using both membrane binding assays and autoradiography. Experiments were performed to determine whether chronic treatment with ipsapirone would differentially affect binding to 5-HT1A receptors at different brain sites. Rats were treated twice daily with ipsapirone (10 mg/kg i.p.) for 1 day or for 1, 2, or 3 weeks. Quantitative analyses were done of autoradiograms of in vitro [3H]8-OH-DPAT binding to selected brain regions. Binding in vehicle-treated rats was highest in the hippocampus, septal nucleus, interpeduncular nucleus, entorhinal cortex, and dorsal raphe nucleus. Following 3 weeks of treatment with ipsapirone, a large decline in binding was measured in the dorsal raphe nucleus. This decline was not seen with ipsapirone treatments for shorter periods. With the 3-week treatment, there were less robust declines in [3H]8-OH-DPAT binding in the entorhinal cortex and interpeduncular nucleus. Binding in the other brain regions analyzed was unaltered.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental spinal cord injury: effect of a calcium channel antagonist (nicardipine)

Variable benefits from the use of a number of calcium channel blockers in experimental spinal cord injury have been reported. To our knowledge, these agents have not been previously tested in a contusion model of cord injury in which neurological outcome is one of the critical outcome parameters. We carried out preliminary behavioral toxicity testing to identify a range of low, moderate, and high dosage levels of the calcium channel blocker, nicardipine; these dosage levels were to be used subsequently in formal testing. After laminectomy at T8 under general anesthesia in rats, a 10-g weight was dropped from a height of 5 cm onto the spinal cord. The animals were randomly assigned to four groups: control or one of three nicardipine treatment groups: (a) low dose (1 mg/kg, followed by a continuous 23-hour infusion of 0.5 mg/kg/hour), (b) moderate dose (10 mg/kg, followed by 5 mg/kg/hour for 23 hours, and (c) high dose (20 mg/kg, followed by 23-hour infusion of 10 mg/kg/hour). Functional recovery was tested over the course of 4 weeks with the Tarlov scale, the inclined plane, and a sensory-motor battery of tests (combined behavioral score). After sacrifice at 4 weeks, morphometric analysis of residual gray and white matter was performed at the epicenter of the spinal cord injury. Statistical analysis of the behavioral data failed to reveal any differences among the control or nicardipine treatment groups. The morphometric analysis similarly failed to show differences between the control and any treatment group.(ABSTRACT TRUNCATED AT 250 WORDS)