Effect of repeated immobilization on serotonin metabolism in different rat brain areas and on serum corticosterone

Abstract

The effect of daily repeated 10 min immobilization on the serotoninergic neurotransmission and serum corticosterone levels was studied. Male Lewis rats were immobilized for a 10 min period daily once or on 5 consecutive days. Serotoninergic neurotransmission was followed using differential in vivo pulse voltammetry with carbon fibre electrodes measuring extracellular 5-hydroxyindoleacetic acid (5-HIAA) levels. Recordings were performed in brain areas involved in the control of behaviour, mood, and stress response such as the frontal cortex, the hippocampal CA-3 and dentate gyrus, the striatum, and the raphe nuclei dorsalis (NRD) and medialis (MRN). The first immobilization resulted in an increase of the extracellular 5-HIAA levels in all areas under study, except the striatum where no reaction was observed. The major effect was recorded in the frontal cortex, showing an increase of about 400% as compared to control, which lasted for 3h after the end of the immobilization period. Beginning on day 2 in all areas, except the striatum, a consecutive habituation to the stressor seemed to occur, since the stress-induced increase in the voltammetric signal was found to be reduced after consecutive immobilization. Serum corticosterone levels were measured directly after a single and after 5 daily immobilization periods. After single immobilization the serum corticosterone level was found to be about 270 ng/ml. After the 5th immobilization about 300 ng/ml were detected. These differences were not found to be significant. In summary, our data indicate that the serotonin metabolism shows habituation in nearly all brain areas after repeated immobilization, though the corticosterone level at the end of the immobilization period was comparable after single and repeated immobilization.

Serotonin in the inferior colliculus fluctuates with behavioral state and environmental stimuli

“…Alternatively, voltammetric studies in other regions of the brain have measured extracellular 5-HIAA, which can potentially be used as an indicator of 5-HT's release, reuptake and then subsequent metabolism (Clement et al, 1998;Crespi et al, 1990;Houdouin et al, 1991). In the IC, however, we found that changes in the combined 5-HIAA+5-HT signal were not correlated with changes in the 5-HT signal during the recovery from anesthesia (Fig.3).…”

“…The restricted movement manipulation (N10) was modeled after restraint-stress paradigms that are known to influence extracellular 5-HT in other regions of the brain (Bowers et al, 2007;Clement et al, 1998). Mice were contained within a small, circular arena (7.5cm diameter) within their home cage.…”

“…A final behavioral manipulation assessed extracellular 5-HT in the IC during exposure to a stimulus designed to mimic restraint stress, because extracellular 5-HT in other regions of the brain change during exposure to stress paradigms (Clement et al, 1998;Mitsushima et al, 2006). Mice (N9) were restricted in a small circular arena within their home cage using a high-walled tube that slid down the recording tether to surround the animal.…”

“…Of the stimuli we presented, the two that did evoke significant increases in extracellular IC 5-HT were both potentially stressful. The restricted movement stimulus is a mild version of restraint, used to induce stress experimentally (Bowers et al, 2007;Clement et al, 1998). The broadband noise was relatively loud at 94dB and so could also have created stress in the mice (Day et al, 2009;Rex et al, 2005;Vitale et al, 2005).…”

“…In addition to behavioral transitions, the activity of some 5-HT-releasing neurons shows transient fluctuations with the presentation of simple environmental stimuli, like light and sound (Heym et al, 1982;Waterhouse et al, 2004). 5-HT release also varies in target regions during more complex behavioral paradigms or social interactions (Mas et al, 1995;Boutelle et al, 1990;Clement et al, 1998). As a result of both context-and region-specific influences on mechanisms that regulate 5-HT neurotransmission, 5-HT responses to a behavioral event can occur on a time course of minutes or less, with magnitudes and temporal profiles tailored to specific brain regions (Inoue et al, 1994;Pum et al, 2008).…”