Characterising the neurobiology of CO2-induced anxiety in rodents using physiological pharmacological and psychological methodology

The induction of anxiety in normal human volunteers using either a 7.5% or 30% CO2 challenge induces reliable changes in physiological and psychological measures reflecting generalised anxiety disorder or panic disorder respectively. The Psychopharmacology Unit, University of Bristol has shown that 7.5% CO2 over a 20 min test session induces increases in heart rate and blood pressure as well as subjective ratings of fear and anxiety whilst decreasing subjective ratings of relaxed, when compared with breathing normal air. Studies using neuropsychological tests suggest that 7.5% CO2 alters the interpretation of emotionally relevant cues in normal volunteers. Pharmacological studies, using a range of anxiolytic drugs, have shown pharmacological efficacy but also revealed individual differences in terms of their effects on the cardiovascular parameters and subjective ratings of anxiety. In order to investigate the neurobiology of these pharmacological effects as well as more detailed characterisation of neural and neurochemical mediators of anxiety states, studies in animals are now required. CO2-inhalation offers an exciting new translational method to study the neurobiology of anxiety using animals because it induces an altered baseline state from which neural and neurochemical manipulations can be investigated. CO2 challenges have previous been used in rodents and induce changes in behaviour that reflect anxiety as well as activation of brain areas and systems associated with anxiety circuits, however, detailed translational experiments have yet to be undertaken. The current proposal will utilise the human volunteer data and derived hypotheses to study the basic biology of anxiety circuits and pharmacological effects of anxiolytic drugs using the CO2 challenge in rodents. The project will also investigate the potential of using CO2-inhalation to study the effects of altered anxiety state on cognitive function. The project as been broken down into four main objectives and will investigate the effects of CO2/inhalation on physiological and behavioural parameters in rodents. These studies will also measure changes in stress hormones and the ability of pharmacological agents to alter the CO2-induced responses compared with control responses under normal air. Project objectives 1. To investigate and compare the cardiovascular changes induced by a range of CO2 concentrations in rats to identify optimal parameters that induce equivalent changes to those obtained with 7.5% CO2 in human volunteers. 2. To examine the ability of CO2-inhalation to induce changes in behaviour that reflect increased anxiety using established animal models of anxiety such as elevated plus maze and open field arena. 3. To identify brain circuits mediating physiological and behavioural responses to CO2-inhalation using immediate early gene expression or 2-deoxyglucose utilisation experiments. 4. To utilise CO2-inhalation to test the effects of increased anxiety state of cognitive function using operant animal models of attention and negative affective state. The work will be performed within the Psychopharmacology Unit as part of the team carrying out CO2 experiments thus facilitating the transfer of knowledge between the clinical and pre-clinical researchers. Studies at Organon, will utilise their expertise in using radiotelemetry to record cardiovascular parameters as well supporting the ex vivo studies using 2-deoxyglucose (2DG) or immediate early gene activation. Following initial physiological and behavioural studies, the project will use CO2 to investigate the cognitive consequences associated with alterations in anxiety state.