G Walasek

Effects of partial lesion of dorsal hippocampal afferent and GM1 ganglioside treatment on conditioned emotional response and hippocampal afferent markers in rats

Acquisition of the conditioned emotional response (CER) in 32 male hooded rats previously learned to press a bar for food and divided into four groups was studied. Two groups received electrolytic lesions of the dorsal hippocampal afferent and were thereafter injected either with GM1 ganglioside (30 mg/kg daily) or with buffer. Two remaining groups were sham operated and similarly injected. The partial hippocampal deafferentation evoked immediate enhancement of bar presses rate which persisted during the 2-week period of testing. CER training undertaken 2 days after surgical procedures appeared unsuccessful, whereas similar training with a cue of different modality initiated a week later resulted in acquisition of conditioned suppression of bar presses in all groups. Toward the end of training the conditioned suppression was more pronounced in lesioned than in control rats. The GM1 injections attenuated the conditioned suppression in control rats, presumably due to an antinociceptive role of ganglioside treatment. Behavioural training did not change the normal distribution pattern in cholinergic and serotonergic hippocampal afferent markers showing dorso-ventral gradient along longitudinal axis. The lesion-induced decrease pattern was also not affected. However, in contrast to previous findings in non-trained animals, the GM1 treatment was not effective in protecting against degenerative changes in the hippocampus of trained rats.

Effects of stimulus modality on the shuttle activity in rats.

Shuttle activity during repeated presentation of irrelevant auditory (white band noise) and visual (darkness) stimuli was studied in 32 male Möll-Wistar rats. The subjects were randomly divided into two groups. In Group ND the auditory stimulus was used in the first habituation session, and the visual stimulus in the second habituation session. The opposite sequence of stimuli was applied in Group DN. House light was used as a background stimulus in both groups of subjects. The rate of crossing from one compartment to the other was markedly enhanced by noise, regardless of the position of the auditory stimulus in the sessions sequence. A clear decrease of response rate was caused by noise termination, whereas neither darkness offset nor onset changed the relatively high and stable rate of responding. The results of this study provided convincing evidence of the energizing influence of the irrelevant auditory cue on the shuttle activity in rats. Moreover, these findings showed that a habituation procedure provides an efficient tool to analyze pure unconditional features of the to-be-conditioned stimuli, and to foresee several response modifications during further conditioning.