Involvement of the K⁺‐Cl⁻ co‐transporter KCC2 in the sensitization to morphine‐induced hyperlocomotion under chronic treatment with zolpidem in the mesolimbic system

Abstract

Benzodiazepines are commonly used as sedatives, sleeping aids, and anti-anxiety drugs. However, chronic treatment with benzodiazepines is known to induce dependence, which is considered related to neuroplastic changes in the mesolimbic system. This study investigated the involvement of K + -Cl À cotransporter 2 (KCC2) in the sensitization to morphine-induced hyperlocomotion after chronic treatment with zolpidem [a selective agonist of c-aminobutyric acid A-type receptor (GABA A R) a1 subunit]. In this study, chronic treatment with zolpidem enhanced morphine-induced hyperlocomotion, which is accompanied by the up-regulation of KCC2 in the limbic forebrain. We also found that chronic treatment with zolpidem induced the down-regulation of protein phosphatase-1 (PP-1) as well as the up-regulation of phosphorylated protein kinase C c (pPKCc). Furthermore, PP-1 directly associated with KCC2 and pPKCc, whereas pPKCc did not associate with KCC2. On the other hand, pre-treatment with furosemide (a KCC2 inhibitor) suppressed the enhancing effects of zolpidem on morphine-induced hyperlocomotion. These results suggest that the mesolimbic dopaminergic system could be amenable to neuroplastic change through a pPKCc-PP-1-KCC2 pathway by chronic treatment with zolpidem. Keywords: benzodiazepine, drug dependence, KCC2, morphine, nucleus accumbens, zolpidem. Benzodiazepines are used as sedatives, sleeping aids, and anti-anxiety drugs. However, the long-term use of benzodiazepines induces psychological and physiological dependence. Psychological dependence is considered to accompany the neuroplastic changes in the dopaminergic system which projects from the ventral tegmental area to the nucleus accumbens, and activation of the mesolimbic dopaminergic system induces the rewarding effects and sensitization to locomotor activity induced by opioids and psychostimulants Narita et al. 2003Narita et al. , 2004Narita et al. , 2006Fukakusa et al. 2008). On the other hand, even though benzodiazepines induce psychological dependence without increasing the release of dopamine (Invernizzi et al. 1991), the mechanisms by which benzodiazepines induce psychological dependence are not fully understood. c-aminobutyric acid A-type receptor (GABA A R) consists of a five-subunit complex (2 a, 2 b, and 1 c subunit), containing Cl À channels, and the activation of GABA A R by GABA results in an increase in Cl À influx. Benzodiazepines bind to the benzodiazepine receptor that is located on GABA A R between a and c subunits. The activation of GABA A R containing a1 subunit is associated with sleeping, sedation, abuse potential, and anti-epilepsia.

Implication of mGlu5 receptor in the enhancement of morphine-induced hyperlocomotion under chronic treatment with zolpidem

“…It has been reported that zolpidem suppresses the lomotor activity in mice (Heldt and Ressler, 2010). Furthermore, we suggested that single administration of zolpidem did not affect morphine-induced hyperlocomotion (Shibasaki et al, 2013a). Taken together, it is important that chronic treatment with zolpidem enhanced the morphine-induced hyperlocomotion via up-regulation of mGlu 5 receptor.…”

“…The locomotor activity of mice was measured by an ambulometer (ANB-M20, O'Hara, Co., Ltd., Tokyo, Japan) as described previously (Shibasaki et al, 2013a). Briefly, a male ICR mouse was placed in a tilting-type round activity cage of 20 cm in diameter and 19 cm in height.…”

“…Accumulating evidence suggests that the rewarding effects and behavioral sensitization induced by psychostimulants may be accompanied by long-lasting neural plasticity that may participate in structural modifications in the dopaminergic neuronal system (Shibasaki et al, 2011). On the other hand, even though benzodiazepines induce psychological dependence without increasing the release of dopamine (Invernizzi et al, 1991;Shibasaki et al, 2013a), the mechanisms by which benzodiazepines induce psychological dependence are not fully understood.…”

“…Especially, it is reported that 30 mg/kg of zolpidem for 4 days or 10 days has been used for physical dependence study (Mirza and Nielsen, 2006;Perrault et al, 1992). Moreover, our recent study demonstrated that chronic treatment with zolpidem enhanced morphine-induced hyperlocomotion by increasing dopamine response through the up-regulation of KCC2 in the limbic forebrain (Shibasaki et al, 2013a). It has been reported that GABA A receptors might be involved in the acquisition of morphine-induced sensitization (Zarrindast et al, 2007).…”

“…The increase in Ca 2 þ influx from either extracellular or intracellular sources and the production of DAG are essential elements for the stimulation of various forms of protein kinase C (PKC). Our recent report suggested that chronic treatment with zolpidem induced the up-regulation of phosphorylated-PKCγ (Shibasaki et al, 2013a).…”