Examining face and construct validity of a noninvasive model of panic disorder in Lister-hooded rats

Rodent Brain Pathology, Audiogenic Epilepsy

The review presents data which provides evidence for the internal relationship between the stages of rodent audiogenic seizures and post-ictal catalepsy with the general pattern of animal reaction to the dangerous stimuli and/or situation. The wild run stage of audiogenic seizure fit could be regarded as an intense panic reaction, and this view found support in numerous experimental data. The phenomenon of audiogenic epilepsy probably attracted the attention of physiologists as rodents are extremely sensitive to dangerous sound stimuli. The seizure proneness in this group shares common physiological characteristics and depends on animal genotype. This concept could be the new platform for the study of epileptogenesis mechanisms.

Ultrasound of alternating frequencies and variable emotional impact evokes depressive syndrome in mice and rats

Emotional stress is primarily triggered by the cognitive processing of negative input; it is regarded as a serious pathogenetic factor of depression that is challenging to model in animals. While available stress paradigms achieve considerable face and construct validity in modelling depressive disorders, broader use of naturalistic stressors instead of the more prevalent models with artificial challenges inducing physical discomfort or pain may substantially contribute to the development of novel antidepressants. Here, we investigated whether a 3-week exposure of Wistar rats and Balb/c mice to unpredictably alternating frequencies of ultrasound between the ranges of 20-25 and 25-45kHz, which are known to correspond with an emotionally negative and with a neutral emotional state, respectively, for small rodents in nature, can induce behavioural and molecular depressive-like changes. Both rats and mice displayed decreased sucrose preference, elevated "despair" behaviour in a swim test, reduced locomotion and social exploration. Rats showed an increased expression of SERT and 5-HT2A receptor, a decreased expression of 5-HT1A receptor in the prefrontal cortex and hippocampus, diminished BDNF on gene and protein levels in the hippocampus. Fluoxetine, administered to rats at the dose of 10mg/kg, largely precluded behavioural depressive-like changes. Thus, the here applied paradigm of emotional stress is generating an experimental depressive state in rodents, which is not related to any physical stressors or pain. In essence, this ultrasound stress model, besides enhancing animal welfare, is likely to provide improved validity in the modelling of clinical depression and may help advance translational research and drug discovery for this disorder.

Central mechanisms regulating coordinated cardiovascular and respiratory function during stress and arousal

Actual or potentially threatening stimuli in the external environment (i.e., psychological stressors) trigger highly coordinated defensive behavioral responses that are accompanied by appropriate autonomic and respiratory changes. As discussed in this review, several brain regions and pathways have major roles in subserving the cardiovascular and respiratory responses to threatening stimuli, which may vary from relatively mild acute arousing stimuli to more prolonged life-threatening stimuli. One key region is the dorsomedial hypothalamus, which receives inputs from the cortex, amygdala, and other forebrain regions and which is critical for generating autonomic, respiratory, and neuroendocrine responses to psychological stressors. Recent studies suggest that the dorsomedial hypothalamus also receives an input from the dorsolateral column in the midbrain periaqueductal gray, which is another key region involved in the integration of stress-evoked cardiorespiratory responses. In addition, it has recently been shown that neurons in the midbrain colliculi can generate highly synchronized autonomic, respiratory, and somatomotor responses to visual, auditory, and somatosensory inputs. These collicular neurons may be part of a subcortical defense system that also includes the basal ganglia and which is well adapted to responding to threats that require an immediate stereotyped response that does not involve the cortex. The basal ganglia/colliculi system is phylogenetically ancient. In contrast, the defense system that includes the dorsomedial hypothalamus and cortex evolved at a later time, and appears to be better adapted to generating appropriate responses to more sustained threatening stimuli that involve cognitive appraisal.

In a rat model of panic, corticotropin responses to dorsal periaqueductal gray stimulation depend on physical exertion

Panic disorder patients are exquisitely and specifically sensitive to hypercapnia. The demonstration that carbon dioxide provokes panic in fear-unresponsive amygdala-calcified Urbach-Wiethe patients emphasizes that panic is not fear nor does it require the activation of the amygdala. This is consonant with increasing evidence suggesting that panic is mediated caudally at midbrain's dorsal periaqueductal gray matter (DPAG). Another startling feature of the apparently spontaneous clinical panic is the counterintuitive lack of increments in corticotropin, cortisol and prolactin, generally considered 'stress hormones'. Here we show that the stress hormones are not changed during DPAG-evoked panic when escape is prevented by stimulating the rat in a small compartment. Neither did the corticotropin increase when physical exertion was statistically adjusted to the same degree as non-stimulated controls, as measured by lactate plasma levels. Conversely, neuroendocrine responses to foot-shocks were independent from muscular effort. Data are consonant with DPAG mediation of panic attacks.

Sex differences in anxiety and emotional behavior

Research has elucidated causal links between stress exposure and the development of anxiety disorders, but due to the limited use of female or sex-comparative animal models, little is known about the mechanisms underlying sex differences in those disorders. This is despite an overwhelming wealth of evidence from the clinical literature that the prevalence of anxiety disorders is about twice as high in women compared to men, in addition to gender differences in severity and treatment efficacy. We here review human gender differences in generalized anxiety disorder, panic disorder, posttraumatic stress disorder and anxiety-relevant biological functions, discuss the limitations of classic conflict anxiety tests to measure naturally occurring sex differences in anxiety-like behaviors, describe sex-dependent manifestation of anxiety states after gestational, neonatal, or adolescent stressors, and present animal models of chronic anxiety states induced by acute or chronic stressors during adulthood. Potential mechanisms underlying sex differences in stress-related anxiety states include emerging evidence supporting the existence of two anatomically and functionally distinct serotonergic circuits that are related to the modulation of conflict anxiety and panic-like anxiety, respectively. We discuss how these serotonergic circuits may be controlled by reproductive steroid hormone-dependent modulation of crfr1 and crfr2 expression in the midbrain dorsal raphe nucleus and by estrous stage-dependent alterations of γ-aminobutyric acid (GABAergic) neurotransmission in the periaqueductal gray, ultimately leading to sex differences in emotional behavior.

Classical and novel approaches to the preclinical testing of anxiolytics: A critical evaluation

Over 80% of current anxiety studies employ one of the tests that were developed earlier than, or concurrently with the elevated plus-maze, i.e. before 1985. Considering 1985 as a historical reference point, we briefly review here 115 new tests and models of anxiety, the development of which was likely prompted by the poor predictive validity of classical tests as shown here by the comparison of preclinical and clinical findings with putative novel anxiolytics. The new approaches comprise major innovations to classical tests, the pre-test application of manipulations that mimic etiological factors of anxiety disorders, and entirely new approaches including anxiety disorder-specific tests. Thus, intensive test development over the last 27 years created a large pool of novel approaches. However, these are infrequently used and as such, their impact on anxiolytic drug development remains low. We suggest here that test/model development should step over the intensive phase when several new methods are proposed each year and should start selecting and establishing the methodologies that would successfully replace or complement classical tests. We propose here a novel strategy for improving the validity of anxiety testing that includes the retrospective analysis of the predictive validity of new procedures (as opposed to classical pharmacological validation), and a call for concerted international efforts at both the conceptual and practical levels. Similar endeavors proved recently successful with other psychiatric disorders.

The endocannabinoid system in the rat dorsolateral periaqueductal grey mediates fear-conditioned analgesia and controls fear expression in the presence of nociceptive tone

BACKGROUND AND PURPOSE

Endocannabinoids in the midbrain periaqueductal grey (PAG) modulate nociception and unconditioned stress-induced analgesia; however, their role in fear-conditioned analgesia (FCA) has not been examined. The present study examined the role of the endocannabinoid system in the dorsolateral (dl) PAG in formalin-evoked nociceptive behaviour, conditioned fear and FCA in rats.

EXPERIMENTAL APPROACH

Rats received intra-dlPAG administration of the CB(1) receptor antagonist/inverse agonist rimonabant, or vehicle, before re-exposure to a context paired 24 h previously with foot shock. Formalin-evoked nociceptive behaviour and fear-related behaviours (freezing and 22 kHz ultrasonic vocalization) were assessed. In a separate cohort, levels of endocannabinoids [2-arachidonoyl glycerol (2-AG) and N-arachidonoyl ethanolamide (anandamide; AEA)] and the related N-acylethanolamines (NAEs) [N-palmitoyl ethanolamide (PEA) and N-oleoyl ethanolamide (OEA)] were measured in dlPAG tissue following re-exposure to conditioned context in the presence or absence of formalin-evoked nociceptive tone.

KEY RESULTS

Re-exposure of rats to the context previously associated with foot shock resulted in FCA. Intra-dlPAG administration of rimonabant significantly attenuated FCA and fear-related behaviours expressed in the presence of nociceptive tone. Conditioned fear without formalin-evoked nociceptive tone was associated with increased levels of 2-AG, AEA, PEA and OEA in the dlPAG. FCA was specifically associated with an increase in AEA levels in the dlPAG.

CONCLUSIONS AND IMPLICATIONS

Conditioned fear to context mobilises endocannabinoids and NAEs in the dlPAG. These data support a role for endocannabinoids in the dlPAG in mediating the potent suppression of pain responding which occurs during exposure to conditioned aversive contexts.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

Further characterization of the prototypical nociceptin/orphanin FQ peptide receptor agonist Ro 64-6198 in rodent models of conflict anxiety and despair

RATIONALE

Ro 64-6198, the prototypical non-peptide nociceptin/orphanin FQ peptide (NOP) receptor agonist, has potent anxiolytic-like effects in several preclinical models and species. However the effects of Ro 64-6198 on distinctive anxiety-provoking conditions related to unconditioned conflict behavior as well as its role in despair-like behavior remain to be addressed.

OBJECTIVE

Here we examined the effects of Ro 64-6198 on unconditioned conflict anxiety using stimuli with different salience and on regulation of autonomic reactivity and compared these to the effects of benzodiazepine receptor agonists. We also addressed the potential effects of Ro 64-6198 on despair-like behavior.

MATERIALS AND METHODS

Ro 64-6198 (0.1 to 10 mg/kg i.p.) and either diazepam or chlordiazepoxide were tested in the Vogel conflict punished drinking test (VCT) in Sprague Dawley rats, in the social approach-avoidance (SAA) test in Lewis rats, in the novelty-induced hypophagia (NIH) in C57BL/6J mice, and in stress-induced hyperthermia in NMRI mice, as well as in the forced swim test (FST) in Sprague Dawley rats and the tail suspension test (TST) in C57BL/6J mice.

RESULTS

Ro 64-6198 (0.3 to 3 mg/kg) dose-dependently produced anxiolytic-like effects in the VCT, SAA, NIH, and SIH, similar to benzodiazepine receptor agonists. Ro 64-6198 did not alter immobility time in the FST and TST.

CONCLUSIONS

Ro 64-6198 produced marked anxiolytic-like effects in response to a variety of mild to strong anxiogenic stimuli, whereas it did not facilitate depression-related behaviors. This data extend previous literature suggesting that NOP receptors are a viable target for the treatment of anxiety disorders.

Current animal models of anxiety, anxiety disorders, and anxiolytic drugs

PURPOSE OF REVIEW

The perception that 'classical' anxiety tests are deficient was formulated in the mid-1990s. Recent clinical trials also demonstrate that the predictive power of such tests is low, which emphasizes the need for developing models of higher translational value. Several novel models are proposed each year. Here, we investigate their impact on anxiolytic-related studies performed in 2010 and 2011.

RECENT FINDINGS

Here, we depict as 'classical' all the tests that were developed at the same time as or earlier than the elevated plus-maze test. No test equaled its success in the subsequent decades; therefore, we consider it the endpoint of the period when the methodological bases of current laboratory research were laid down. Fourteen classical tests were employed in the investigated period, which were used in more than 80% of studies. Concurrently, 36 'nonclassical' tests were used and six novel tests were also proposed. These accounted for fewer than 20% of studies. 'Classical' tests were often performed under unconventional conditions that putatively increased their translational value. Taken together, half of the studies involved at least one innovative step. Yet, the new procedures were infrequently used. Out of the 36 'nonclassical' tests, only 11 were used more than once, while the amendments to 'classical tests' were almost entirely laboratory specific.

SUMMARY

Our analysis shows that there is a large interest in performing anxiety research innovatively. However, efforts are highly divergent and result in large numbers of poorly validated and infrequently used novel approaches. Thus, models with increased translational value still need to be developed.