Acetylcholine and posttraumatic stress disorder.

Field: Neuroscience (Life Sciences)

Posttraumatic Stress Disorder (PTSD) is a psychiatric condition that can develop following exposure to a traumatic event involving actual or threatened death or serious injury. Responses include intense fear, helplessness or horror. Symptoms are characterised into clusters, described as re-experiencing, avoidance, and arousal. These symptoms, which are also evident in other conditions, have been associated with dysfunctions in the central acetylcholinergic system. Benefits from administering acetylcholinesterase inhibitors (AChEI) to people suffering these symptoms have been demonstrated. Donepezil hydrochloride, a reversible inhibitor of the enzyme acetylcholinesterase, is used in the treatment of conditions with difficulties in cognitive function, but has not been used in PTSD. \nThe aim of this thesis was to determine (1) whether there was a difference in the ACh system in people with PTSD and (2) whether administration of an AChEI would change the symtomatology. \nIDEX (I¹ ² ³ iododexetimide) has been useful in imaging muscarinic-ACh receptors using Single Photon Emission Computerised Tomography (SPECT) and was utilised to investigate whether cholinergic activity in PTSD is altered. One hundred and sixty eight potential subjects were screened and eleven PTSD subjects were enrolled in the IDEX SPECT study. Three healthy non-PTSD control subjects also completed the study. Due to technical complications only the data obtained from eight PTSD and two control subjects was available for analysis. Imaging data for 2 further healthy non-PTSD control subjects were obtained from another study. Sixteen subjects were enrolled in the donepezil open label study (assessed at baseline, Week 2, 6 and 10). Nine PTSD subjects completed the 10-week trial and seven withdrew prematurely (at or after Week 2) due to side effects or a worsening of PTSD symptoms. \nFor the IDEX SPECT study, a voxel-by-voxel statistical analysis of the PTSD subject group versus the control group showed both areas of reduced and increased IDEX uptake. Significant clusters in the PTSD group with a reduced IDEX uptake centred around the bilateral hippocampus, left insula and right precuneus, while increased IDEX uptake appeared in the caudate head. \nFor the donepezil study, in the per-protocol analysis (including only the 9 subjects that completed the protocol), all psychological assessments revealed a difference between the totals obtained at the Week 10 visit compared to those at the Baseline visit and the improvement was in the order of 51%. The intention-to-treat analysis (including all 16 subjects), a repeated measures Analysis of Variance (ANOVA) with a mixed models approach showed that all psychological measures demonstrated statistically significant benefits of the treatment. All subjects who completed the protocol recounted considerable improvement in their overall PTSD symptom profile, which covered symptoms in each of the three clusters. \nThe results of the IDEX SPECT study suggest that alterations in ACh binding in PTSD are evident and may begin to explain a part of the altered cognitive symptomatology apparent in this condition. The pilot open label donepezil trial provided some preliminary evidence that treatment with an AChEI can lessen the intrusions and distress associated with traumatic memories in people with PTSD.