Effects of alprazolam on cholecystokinin-tetrapeptide-induced panic and hypothalamic-pituitary-adrenal-axis activity: a placebo-controlled study

Cholecystokinin-tetrapeptide (CCK-4) induces panic attacks both in patients with panic disorder (PD) and healthy volunteers. It has been shown that panic elicited by CCK-4 is improved after treatment with antidepressants. Moreover, a reduction of CCK-4-induced panic has also been demonstrated after treatment with lorazepam in single subjects and after selective GABAergic treatment with vigabatrin. Although benzodiazepines are widely used as anxiolytics, no controlled study on the effects of benzodiazepines on CCK-4-induced panic symptoms is available so far. Therefore, we investigated the effects of alprazolam and placebo on CCK-4-induced panic symptoms in a double-blind, placebo-controlled study. A total of 30 healthy subjects were challenged with 50 microg CCK-4. Out of these 30 subjects, 26 showed a marked panic response to CCK-4. Subjects were rechallenged after a 7-day interval and treated with 1 mg alprazolam or placebo 1 h prior to the second CCK-4 challenge. Panic was assessed using the acute panic inventory (API) and a DSM-IV-derived panic symptom scale (PSS). Moreover, the number of reported symptoms and self-rated anxiety and arousal were recorded. We found a significant reduction of the API and PSS scores and of the number of reported symptoms compared to placebo. Moreover, compared to placebo the CCK-4-induced ACTH and cortisol release were significantly attenuated during the CCK-4 challenge after alprazolam treatment. However, also placebo treatment reduced CCK-4-induced anxiety and HPA-axis activation to a certain extent. In conclusion, our data show that alprazolam reduces CCK-4-induced panic, which supports the hypothesis of a possible interaction between the GABA and the CCK system.

Light and electron microscopic evidence for topographic and monosynaptic projections from neurons in the ventral medulla to noradrenergic dendrites in the rat locus coeruleus

Physiological studies have shown that afferents from the nucleus paragigantocellularis (PGi) in the rostral ventral medulla underlie the modulation of locus coeruleus (LC) activity by a variety of stimuli. However, there have been no anatomical demonstrations of a monosynaptic projection from neurons in the PGi to the LC. Thus, biotinylated dextran amine (BDA) was iontophoretically injected into the ventral medulla and single-tissue sections were processed for peroxidase localization of BDA and gold-silver labeling of tyrosine hydroxylase (TH). Discrete microinjections of BDA were placed into either the medial or lateral aspects of the ventral medulla. For medially placed injections, a medio-dorsal pathway to the LC was observed. This trajectory resulted in a predominant innervation of the ventral LC. Lateral injection placements yielded a fiber pathway that coursed more laterally within the medullo-pontine reticular formation and primarily innervated the dorsolateral LC. These light microscopic data suggested that neurons in the PGi use distinct pathways to innervate the LC and are topographically organized within this structure. Electron microscopic analyses of the LC region indicated that axon terminals originating from either subregion were equally likely to contact noradrenergic neurons in the LC. Approximately 57% and 62% of BDA-labeled terminals originating from the medial (n=150) or lateral (n=150) aspects of the ventral medulla, respectively, formed heterogeneous synaptic contacts (i.e., inhibitory- and excitatory-type) with dendrites containing TH. It is well known that the PGi is a functionally diverse region that is involved in sensory integration, autonomic regulation and pain modulation. It is also known that LC efferents are spatially organized with respect to their postsynaptic targets. Taken together, our findings that subdivisions of the ventral medulla topographically and monosynaptically innervate the LC suggest that regionally specific PGi neurons target subsets of LC neurons with efferent targets that may possess analogous functional correlates.