Opioids and anxiety

The opioid system plays a crucial role in the neural modulation of anxiety. The involvement of opioid ligands and receptors in physiological and dysfunctional forms of anxiety is supported by findings from a wide range of preclinical and clinical studies, including clinical trials, experimental research, and neuroimaging, genetic, and epidemiological data. In this review we provide a summary of studies from a variety of research disciplines to elucidate the role of the opioid system in the neurobiology of anxiety. First, we report data from preclinical studies using animal models to examine the modulatory role of central opioid system on defensive responses conducive to fear and anxiety. Second, we summarize the human literature providing evidence that clinical and experimental human studies are consistent with preclinical models. The implication of these data is that activation of the opioid system leads to anxiolytic responses both in healthy subjects and in patients suffering from anxiety disorders. The role of opioids in suppressing anxiety may serve as an adaptive mechanism, collocated in the general framework of opioid neurotransmission blunting acute negative and distressing affective responses.

Brain imaging studies in human addicts

Addiction provides fertile ground for the application of the tools of functional neuroimaging. They can be divided into studies of neural activity and neurotransmitter function. Using the former, both opiates and stimulants cause a global decrease in brain metabolism. Against this background, acute doses have still been shown to produce relative increases in brain activation in specific regions, e.g., anterior cingulate, thalamus, and amygdala. These are also regions frequently found with cue-exposure paradigms. Our own work on cue-exposure has shown that heroin-related stimuli provoke activation of the anterior cingulate and orbitofrontal regions. Brain metabolism has also been shown to increase in drug withdrawal from alcohol and cocaine. Neurotransmitter studies have shown that in alcohol dependence, GABA(A)-benzodiazepine (GABA-BDZ) receptors are reduced in a number of brain regions and suggest that there may be 'capacity within the system' in some benzodiazepine functions, but tolerance to others, e.g., time asleep. Finally, 11C-Ro15-4513 offers new opportunities for imaging the GABA-BDZ system.

N1'-fluoroethyl-naltrindole (BU97001) and N1'-fluoroethyl-(14-formylamino)-naltrindole (BU97018) potential delta-opioid receptor PET ligands

The properties of two prospective positron emission tomography (PET) ligands for the delta-opioid receptor, N1'-fluoroethyl-naltrindole (BU97001) and N1'-fluoroethyl-(14-formylamino)-naltrindole (BU97018) were investigated. Both were antagonists in the mouse vas deferens, and showed high affinity and selectivity, 1.81 nM and 3.09 nM respectively. [3H]BU97001 binding to rat whole brain was also of high affinity, K(D) of 0.42 nM of and B(MAX) of 59.95 fmol mg of protein(-1). In autoradiographic studies, it was found to bind to brain areas previously shown to be associated with the delta-opioid receptor and good correlations were found to exist with naltrindole and DPDPE. BU97018 and especially BU97001 appear to show good potential as delta-opioid receptor PET ligands with the incorporation of 18F.