A combined study of behavior and Fos expression in limbic structures after re-testing Wistar rats in the elevated plus-maze

Abstract

The elevated plus-maze is an animal model used to study anxiety. In a second session, rats show a reduction in the exploratory behavior even when the two sessions are separated by intervals as large as 7 days. The aim of the present study was to investigate whether the reduction in the exploratory behavior is maintained after intervals larger than 7 days. Additionally, we aimed at investigating eventual correlations between behaviors in the plus-maze and activation of limbic structures as measured by Fos protein expression after the second session. Rats were tested for 5 min in the elevated plus-maze and re-tested 3, 9 or 33 days later. Other groups were tested only once. The rat brains were processed for immunohistochemical detection of Fos protein. The results show a decrease in the open arms exploration in the second trial with intervals of 3, 9 and 33 days. The expression of Fos protein in the piriform cortex, septal nucleus and paraventricular hypothalamic nucleus in the groups tested with intervals of 9 and 33 days were statistically different from the other groups. The alterations observed in exploratory behavior in the second session in the plus-maze did not correlate with Fos expression. In conclusion, although the specific test conditions were sufficient to evoke behavioral alterations in exploration in the elevated plus-maze, they were enough to induce significant Fos protein expression in piriform cortex, septal nucleus and thalamic and hypothalamic paraventricular nuclei but not in other areas such as dorsomedial nucleus of the hypothalamus and amygdala nuclei, known to be also active participants in circuits controlling fear and anxiety.

Brain regional differences in social encounter-induced Fos expression in male and female rats after post-weaning social isolation

“…Male rats were not tested in that study, and we know of no previous studies that examine sex differences in activation of PIR during social interaction. Activation of the piriform cortex has also been shown to be produced by exposure to the elevated plus maze, suggesting sensitivity to anxiogenic stimuli (Galvis-Alonso et al, 2010), and social interaction is often used as a test of anxiety (Seth and File, 2003).…”

Yohimbine anxiogenesis in the elevated plus maze requires hindbrain noradrenergic neurons that target the anterior ventrolateral bed nucleus of the stria terminalis

“…For example, maze-experienced rats display significantly more neuronal cFos activation within the ventral mPFC, BLA and central amygdala after EPMZ re-testing compared with cFos activation displayed by maze-na € õve rats after initial testing (Albrechet-Souza et al, 2008;Albrechet-Souza & Brandao, 2010). It has been suggested that the reduced exploratory behavior and open arm activities displayed by rats during maze re-exposure is indicative of learned avoidance, and can be used to assess memory acquisition and retention (Bertoglio & Carobrez, 2000, 2004Albrechet-Souza & Brandao, 2010;Galvis-Alonsoa et al, 2010). In the present study, DSAP lesions had no significant impact on the development of avoidance learning that presumably underlies the qualitative shift in emotional state suggested by behavioral changes between Test 1 and Test 2.…”

“…In a second experiment, we examined whether loss of vlBST‐projecting NA neurons alters the pronounced effect of prior maze experience to alter maze behavior during a subsequent test, a phenomenon observed previously in non‐lesioned rats (File et al ., , ; Treit et al ., ; Bertoglio & Carobrez, , ; Albrechet‐Souza & Brandao, ). It has been suggested that the reduced exploratory behavior and open arm activities displayed by rats during maze re‐exposure is indicative of learned avoidance, and can be used to assess memory acquisition and retention (Bertoglio & Carobrez, , ; Albrechet‐Souza & Brandao, ; Galvis‐Alonsoa et al ., ). Therefore, we sought to determine whether vlBST‐projecting NA neurons participate in this process of emotional learning and memory.…”

Intra-amygdala microinjections of chlorpheniramine impair memory formation or memory retrieval in anxiety- and fear-mediated models

“…A prior maze trial provides a baseline for the acquisition and retention of memories because experience-dependent behavioral changes can be observed (GALVIS-ALONSO et al, 2010). We have shown the histaminergic system participation via H 1 receptors on emotional memory modulation, using a Trial1/Trial 2 (T1/T2) protocol in an EPM test (GIANLORENÇO et al, 2012;SERAFIM et al, 2012;.…”