Extinction of a conditioned emotional response: massed and distributed exposures.

Using the lick-suppression methodology of Jacobs, Buttrick & Kennedy (Pavlovian Journal of Biological Science, 23, 29-34, 1988), a conditioned emotional response (CER) was established in 24 rats using off-the-baseline pairings of a light (the conditional stimulus) and brief footshock (the unconditioned stimulus). Following conditioning, the rats were assigned to one of three extinction groups differing in whether they received massed or distributed off-the-baseline exposure to the conditional stimulus. The effects of differential treatment were assessed on-the-baseline on test days, when the extinction of the CER was monitored. Rats receiving a single, long exposure to the conditional stimulus showed greater resistance to extinction than the rats in the distributed groups. They also showed a difference pattern of CER extinction. The results were discussed and compared to similar studies that have explored the massed vs distributed dimension, both in CER and avoidance-extinction (using response prevention or flooding). The relation of animal studies to parallel human studies using exposure therapy was also discussed.

Characteristics of growth inhibition of Lactobacillus casei by 4-nitroquinoline-n-oxide.

The bacteriostatic action of 4-nitroquinoline-n-oxide (4-NQO) for Lactobacillus casei is substantially reversed by d-and l-cysteine, glutathione, and 2,2-dihydroxy-1,4-dithiolbutane (dithioerythritol). The action appears to involve a chemical reaction between carbon atom 4 of 4-NQO and nucleophilic centers, such as -SH groups, located on essential cell constituents. The evidence presented indicates that the protective effect of d- and l-cysteine, glutathione, and dithioerythritol against the action involves reactions between 4-NQO and -SH compounds.