Elevated cholecystokininergic tone constitutes an important molecular/neuronal mechanism for the expression of anxiety in the mouse

Abstract

Cholecystokinin (CCK), one of the most abundant neuropeptides in the brain, plays an important role in anxiogenesis through the activation of CCK receptor-2 (CCKR-2). Accumulating evidence, however, has suggested this role depends on endogenous CCKergic ''tone,'' which is largely determined by the expression level of the CCKR-2. Using the tTA͞tetO-inducible transgenic (tg) approach, we show here that overexpression of the CCKR-2 in neurons of the forebrain significantly increases CCKR-2 binding capacity in tg mice compared with their littermate controls. Interestingly, these tg mice consistently exhibit increased fear responses, which are generally interpreted as anxiety-like behaviors in the rodent, in a battery of behavioral tests, which represented conflict situations or delivered stress to the subjects. The inhibition of transgene expression with doxycycline treatment completely diminished both increased receptor-binding activity and all behavioral phenotypes. Furthermore, treatment of tg mice with diazepam significantly attenuated these anxiety-like behaviors. Our results directly demonstrate that the elevated CCKergic tone via overexpression of the CCKR-2 in the brain may constitute an underlying molecular͞ neuronal mechanism for the expression of anxiety. In addition, our study has validated a robust genetic anxiety model in the mouse in terms of their face, constructive, and predictive validity.behaviors ͉ transgenic mouse

CCKergic System, Hypothalamus-Pituitary-Adrenal (HPA) Axis, and Early-Life Stress (ELS)

“…1A). The expression pattern of the CCKR-2 transgene (data not shown) was the same as both the pattern of the tTA expression and the CCKR-2 transgene expression reported in our previous study [101]. …”

“…Virtually, the CCKergic system has long been recognized as an anxiogenic factor for the animals [98], and this effect has been well validated in human populations as well [89,99,100]. Our recent study also showed that overexpression of CCKR2 in neurons of the forebrain of mice significantly enhanced ALBs [101]. At the same time, some candidate genes that are linked to ADs are also associated with HPA axis activity.…”

“…In this study, by using our previously engineered inducible forebrain-specific CCKR-2 transgenic (IF-CCKR-2 tg) mice [101], we demonstrated that the elevated CCKergic tone in the brain significantly facilitated the effect of AT on the impairment of the glucocorticoid negative feedback inhibition in response to a novel acute stressor during the adult stage in the mouse, providing direct evidence that reveals a molecular basis for this co-effect.…”

“…The procedures for the generation of IF-CCKR-2 tg (simply dtg) mice were described in our previous publication [101]. Briefly, we used the tTA/tetO-inducible gene expression system to produce these dtg mice.…”

The CCK-system underpins novelty-seeking behavior in the rat: Gene expression and pharmacological analyses

“…The CCKA receptor (recently termed CCK-1R) is expressed at relatively low levels, while the CCKB receptor (or CCK-2R) is densely distributed in the forebrain regions. There is general agreement about the influence of CCK-2R in generating anxiety-like behaviors and emotional responsiveness (Bradwejn et al, 1991;Van Megen, 1996;Farook et al, 2001;Chen et al, 2006). However, the anxiolytic profile of CCK-2R antagonists has been questioned (Griebel, 1999) thus raising serious concerns about the therapeutic potential of targeting the CCK system (Abelson, 1995).…”