Apomorphine-susceptible and apomorphine-unsusceptible Wistar rats differ in novelty-induced changes in hippocampal dynorphin B expression and two-way active avoidance: a new key in the search for the role of the hippocampal-accumbens axis.

The present study examines two characteristic traits of the hippocampus in apomorphine-susceptible (APO-SUS) and apomorphine-unsusceptible (APO-UNSUS) Wistar rat lines. Since hippocampal mossy fibers contain among others dynorphin B as transmitter, a radioimmunoassay was used to analyze the hippocampal dynorphin B expression in response to novelty in these lines. Dynorphin B expression at the end of the baseline condition was greater in APO-SUS rats than in APO-UNSUS rats, while exposure to novelty decreased and increased the dynorphin B expression in APO-SUS and APO-UNSUS rats, respectively. These interline differences in dynorphin B expression could be due to (a) an interline difference in the size of the mossy fiber terminal fields, (b) an interline difference in the regulation of the firing rate of mossy fibers by corticosteroids, and/or (c) an interline difference in the release of corticosteroids in response to novelty. Since the size of the mossy fiber infra/intrapyramidal terminal field is inversely related to two-way active avoidance performance, APO-SUS and APO-UNSUS rats (n = 9 per line) were given this task: APO-UNSUS rats performed much better than APO-SUS rats. It is concluded that the neurochemical and behavioural function of the hippocampus significantly differs between lines. Given the already known interline differences in the function of the nucleus accumbens, the present results provide a new avenue in search for the functional relationship between the hippocampus and the nucleus accumbens.

Effective streptokinase treatment of blocked catheters in pigs and sheep.

Sheep and pigs with chronic silastic catheters with a partial blockage of the catheter were treated locally with streptokinase. After one week of treatment all affected catheters were patent again for many weeks. In sheep it proved necessary to use the enzyme treatment as a maintenance tool by contrast with pigs. This treatment may reduce the number of animals used in long-term trials requiring vascular access.

The effect of anchor residue modifications on the stability of major histocompatibility complex class I-peptide interactions.

Anchor residues in peptides determine the specificity of binding to major histocompatibility complex class I molecules through interactions of their side chains with pockets in the peptide-binding groove. We have compared the kinetics of association of a Sendai virus nucleoprotein-derived peptide (FAPGNYPAL, termed SV9) with H-2Kb class I molecules, and the same peptide iodinated on the anchor residue tyrosine (125I-SV9). Even though the association rates were too rapid for direct measurements, competition studies indicated that they were similar for SV9 and 125I-SV9. To measure the binding of non-radioactive SV9 directly, SV9 was tritiated (3H-SV9). 3H-SV9 remained stably associated with H-2Kb molecules, whereas 125I-SV9 dissociated in a temperature-dependent fashion. Thus, modifications on anchor residues do not necessarily have to affect the specificity and association kinetics of peptide binding to class I molecules but can affect the stability of the resulting class I-peptide interaction. The dissociation of peptides with modified and, more generally, suboptimal anchor residue side chains may explain the presence of empty class I molecules and free class I heavy chains at the cell surface.