Anxiety and panic: from human studies to animal research and back

Airjet and FG-7142-induced Fos expression differs in rats selectively bred for high and low anxiety-related behavior

We reported recently that two rat lines bred for either high (HAB) or low (LAB) anxiety-related behavior display differential Fos expression in restricted parts of the fear/anxiety circuitry when exposed to mild anxiety evoked in exploratory anxiety tests. Since different forms of anxiety are thought to activate different parts of the anxiety circuitry, we investigated now whether (1) an aversive stimulus which elicits escape behavior (airjet) and (2) the anxiogenic/panicogenic drug FG-7142 would reveal further differences in Fos expression as a marker of neuronal activation between HAB and LAB rats. Both airjet exposure and FG-7142 induced Fos expression in both lines in various anxiety-related brain areas. HAB rats, which displayed exaggerated escape responses during airjet exposure, exhibited increased Fos expression in brain areas including the hypothalamus, periaqueductal gray and locus coeruleus, as well as blunted Fos activation in the cingulate cortex in response to airjet and/or FG-7142. The results corroborate previous findings showing that trait anxiety affects neuronal excitability in hypothalamic and medial prefrontal areas. Furthermore, by using airjet as well as FG-7142, we now reveal that enhanced trait anxiety is also associated with neuronal hyperexcitability in the locus coeruleus and the periaqueductal gray, suggesting that investigation of an array of different anxiogenic stimuli is important for the detection of altered neuronal processing in trait anxiety.

Virtues and woes of AChE alternative splicing in stress-related neuropathologies

The ACh hydrolyzing enzyme acetylcholinesterase (AChE) is a combinatorial series of proteins with variant N and C termini generated from alternate promoter usage and 3' alternative splicing. Neuronal AChE variants show indistinguishable enzymatic activity yet differ in their expression, multimeric assembly and membrane-association patterns. Differentially induced under stress, they show distinct non-hydrolytic properties and interact with different protein partners. Recent findings suggest that transcriptional and post-transcriptional regulation of AChE pre-mRNA is a neuroprotection strategy but might involve long-term damage. Specifically, variant-specific causal involvement of AChE in the progression of both neurodegenerative diseases (e.g. Alzheimer's and Parkinson's diseases) and neuromuscular syndromes (e.g. myasthenia gravis) raises the possibility that future therapeutic drugs might target specific AChE variant(s) or the corresponding RNA transcripts.

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

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 tTA/tetO-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 molecular/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.

A review of the possible relevance of inositol and the phosphatidylinositol second messenger system (PI-cycle) to psychiatric disorders--focus on magnetic resonance spectroscopy (MRS) studies

Myo-inositol is an important part of the phosphatidylinositol second messenger system (PI-cycle). Abnormalities in nerve cell myo-inositol levels and/or PI-cycle regulation has been suggested as being involved in the pathophysiology and/or treatment of many psychiatric disorders including bipolar disorder, major depressive disorder, panic disorder, obsessive-compulsive disorder, eating disorders and schizophrenia. This review examines the metabolism and biochemical importance of myo-inositol and the PI-cycle. It relates this to the current in vivo evidence for myo-inositol and PI-cycle involvement in these psychiatric disorders, particularly focusing upon the magnetic resonance spectroscopy (MRS) findings in patient studies to date. From this review it is concluded that while the evidence suggests probable relevance to the pathophysiology and/or treatment of bipolar disorder, there is much less support for a significant role for the PI-cycle or myo-inositol in any other psychiatric disorder. More definitive investigation is required before PI-cycle dysfunction can be considered specific to bipolar disorder.