Mapping a mouse limbic seizure susceptibility locus on chromosome 10.

PURPOSE: Mapping seizure susceptibility loci in mice provides a framework for identifying potentially novel candidate genes for human epilepsy. Using C57BL/6J × A/J chromosome substitution strains (CSS), we previously identified a locus on mouse chromosome 10 (Ch10) conferring susceptibility to pilocarpine, a muscarinic cholinergic agonist that models human temporal lobe epilepsy by inducing initial limbic seizures and status epilepticus (status), followed by hippocampal cell loss and delayed-onset chronic spontaneous limbic seizures. Herein we report further genetic mapping of pilocarpine quantitative trait loci (QTLs) on Ch10. METHODS: Seventy-nine Ch10 F(2) mice were used to map QTLs for duration of partial status epilepticus and the highest stage reached in response to pilocarpine. Based on those results we created interval-specific congenic lines to confirm and extend the results, using sequential rounds of breeding selectively by genotype to isolate segments of A/J Ch10 genome on a B6 background. KEY FINDINGS: Analysis of Ch10 F(2) genotypes and seizure susceptibility phenotypes identified significant, overlapping QTLs for duration of partial status and severity of pilocarpine-induced seizures on distal Ch10. Interval-specific Ch10 congenics containing the susceptibility locus on distal Ch10 also demonstrated susceptibility to pilocarpine-induced seizures, confirming results from the F(2) mapping population and strongly supporting the presence of a QTL between rs13480781 (117.6 Mb) and rs13480832 (127.7 Mb). SIGNIFICANCE: QTL mapping can identify loci that make a quantitative contribution to a trait, and eventually identify the causative DNA-sequence polymorphisms. We have mapped a locus on mouse Ch10 for pilocarpine-induced limbic seizures. Novel candidate genes identified in mice can be investigated in functional studies and tested for their role in human epilepsy.

The kappa-opioid receptor antagonist nor-BNI inhibits cocaine and amphetamine, but not cannabinoid (WIN 52212-2), abstinence-induced withdrawal in planarians: an instance of 'pharmacologic congruence'.

The broad applicability of receptor theory to diverse species, from invertebrates to mammals, provides evidence for the evolution in complexity of pharmacologic receptor diversification and of receptor-effector signal transduction mechanisms. However, pre-mammalian species have less receptor subtype differentiation, and thus, might share signal transduction pathways to a greater extent than do mammals, a phenomenon that we term 'pharmacologic congruence'. We have demonstrated previously that the lowest species considered to have a centralized nervous system, planarians, display both abstinence-induced and antagonist-precipitated withdrawal signs, indicative of the development of physical dependence. We report here: (1) amphetamine abstinence-induced withdrawal, and (2) the attenuation of cocaine and amphetamine, but not cannabinoid agonist (WIN 52212-2), abstinence-induced withdrawal by the opioid receptor antagonist naloxone and by the selective kappa-opioid receptor subtype antagonist nor-BNI (nor-Binaltorphimine), but not by the selective mu-opioid or the delta-opioid receptor subtype antagonists CTAP (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2)) and naltrindole. These results provide evidence that the withdrawal from cocaine and amphetamine, but not cannabinoids, in planarians is mediated through a common nor-BNI-sensitive (kappa-opioid receptor-like) pathway.

Withdrawal-like behavior in planarians is dependent on drug exposure duration.

Planarians display a concentration-related reduction in locomotor activity following their spontaneous withdrawal from opioids, cannabinoids, stimulants and benzodiazepines. This suggests that planarians display a withdrawal-like behavior that can be quantified as a reduction in locomotor activity. Because withdrawal-like behavior in previous studies has been quantified only following the cessation of a 60-min drug exposure, it is unclear whether the withdrawal response varies with drug exposure duration. Therefore, the goal of this study is to determine if the duration of drug exposure (0, 5, 15, 30, 45, 60min and 24h) to three different drugs - methamphetamine, cocaine and caffeine - affects the magnitude of withdrawal-like behavior (i.e., reduced locomotor activity) in planarians. Experiments revealed that methamphetamine (10microM) produced significant withdrawal-like behavior regardless of the exposure time (P<0.05). An exposure time of only 5min resulted in a significant reduction in locomotor activity. The peak effect, although occurring following a 24-h exposure, was only slightly greater than that caused by a 30-min exposure. For cocaine (10microM), a longer exposure time (15min) was required for the manifestation of significant withdrawal-like behavior. The peak cocaine effect was observed following a 24-h exposure. Caffeine (10microM) did not produce significant changes in locomotor activity during withdrawal or alter locomotor activity during acute exposure. The present results suggest that the magnitude of withdrawal-like behavior in planarians is dependent on both the duration and type of drug exposure, and that planarians do not display withdrawal to caffeine.