Alterations between high and low-avoidance lines of Hatano rats in learning behaviors, ultrasonic vocalizations, and histological characteristics in hippocampus and amygdala

Shuichi Chiba; Toru Okawara; Kotaro Kawakami; Ryo Ohta; Maiko Kawaguchi

doi:10.1016/j.physbeh.2021.113670

Alterations between high and low-avoidance lines of Hatano rats in learning behaviors, ultrasonic vocalizations, and histological characteristics in hippocampus and amygdala

Physiol Behav. 2022 Mar 1:245:113670. doi: 10.1016/j.physbeh.2021.113670. Epub 2021 Dec 8.

Authors

Shuichi Chiba¹, Toru Okawara², Kotaro Kawakami², Ryo Ohta³, Maiko Kawaguchi⁴

Affiliations

¹ Faculty of Veterinary Medicine, Okayama University of Science, 1-3 Ikoino-Oka, Imabari, Ehime 794-8555, Japan.
² School of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan.
³ Hatano Research Institute, Food and Drug Safety Center, 729-5 Ochiai, Hadano,Kanagawa 257-8523, Japan.
⁴ School of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan. Electronic address: maiko@meiji.ac.jp.

PMID: 34890592
DOI: 10.1016/j.physbeh.2021.113670

Abstract

Growing evidence supports interactions between anxiety and cognitive function. The primary object of this study was to elucidate whether high-avoidance (HAA) and low-avoidance (LAA) strains of Hatano rats are suitable for the analysis of interactions between the formation of long-term memory and emotional reactivity. The learning/memory ability of Hatano rats and their Sprague-Dawley (SD) ancestors was evaluated using contextual fear conditioning, Y-maze, and Barnes maze tests from 8 weeks of age. Ultrasonic vocalizations were recorded and analyzed during contextual fear conditioning. In a separate experiment, rat brains were sampled 90 min after the first context test and subjected to Nissl staining and c-fos immunostaining. The duration of freezing and number of 22 kHz ultrasonic vocalizations were decreased in LAA compared with HAA and SD rats during the first and second context tests of contextual fear conditioning. The HAA rats did not show preferences for quadrants during the Barnes maze probe test, whereas the SD and LAA rats spent significantly more time in the quadrant where the goals had been placed. There was no difference among the strains in short-term spatial memory as shown by the Y-maze test. Decreases were found in the number of c-fos⁺ cells as well as the volume of some hippocampal regions in the HAA rats compared to SD and LAA rats. By contrast, the volume of the basolateral amygdala was bigger in the HAA than the other strains. On the basis of the 22 kHz ultrasonic calls and literature regarding Syracuse rats, the possibility that emotional reactivity influences contextual memory in Hatano strains was discussed. This emotional difference may be derived from structural and/or functional divergence in the hippocampus and amygdala between the strains. The cause of strain-related differences in long-term spatial learning was difficult to elucidate because there are several possible explanations, including differences in memory and/or the interference of hyperactivity during the Barnes maze test.

Keywords: Barnes maze; Contextual fear conditioning; Hatano rats; Hippocampus; Spatial learning; Ultrasonic vocalization.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Amygdala
Animals
Avoidance Learning*
Hippocampus
Rats
Rats, Sprague-Dawley
Ultrasonics*
Vocalization, Animal