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Despite their theoretical rationale, nicotinic alpha-7 acetylcholine (nα(7)) receptor agonists, have largely failed to demonstrate efficacy in placebo-controlled trials in schizophrenia. AVL-3288 is a nα(7) positive allosteric modulator (PAM), which is only active in the presence of the endogenous ligand (acetylcholine), and thus theoretically less likely to cause receptor desensitization. We evaluated the efficacy of AVL-3288 in a Phase 1b, randomized, double-blind, placebo-controlled, triple cross-over study. Twenty-four non-smoking, medicated, outpatients with schizophrenia or schizoaffective disorder and a Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) ≥62 were randomized. Each subject received 5 days of AVL-3288 (10, 30 mg) and placebo across three separate treatment weeks. The primary outcome measure was the RBANS total scale score, with auditory P50 evoked potential suppression the key target engagement biomarker. Secondary outcome measures include task-based fMRI (RISE task), mismatch negativity, the Scale for the Assessment of Negative Symptoms of Schizophrenia (SANS) and the Brief Psychiatric Rating Scale (BPRS). Twenty-four subjects were randomized and treated without any clinically significant treatment emergent adverse effects. Baseline RBANS (82 ± 17) and BPRS (41 ± 13) scores were consistent with moderate impairment. Primary outcomes were negative, with non-significant worsening for both active groups vs. placebo in the P50 and minimal between group changes on the RBANS. In conclusion, the results did not indicate efficacy of the compound, consistent with most prior results for the nα(7) target.

Serotonin reuptake inhibitors (SRIs), the first-line pharmacological treatment for obsessive-compulsive disorder (OCD), have two limitations: incomplete symptom relief and 2–3 months lag time before clinically meaningful improvement. New medications with faster onset are needed. As converging evidence suggests a role for the glutamate system in the pathophysiology of OCD, we tested whether a single dose of ketamine, a non-competitive N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, could achieve rapid anti-obsessional effects. In a randomized, double-blind, placebo-controlled, crossover design, drug-free OCD adults (n=15) with near-constant obsessions received two 40-min intravenous infusions, one of saline and one of ketamine (0.5 mg/kg), spaced at least 1-week apart. The OCD visual analog scale (OCD-VAS) and the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) were used to assess OCD symptoms. Unexpectedly, ketamine’s effects within the crossover design showed significant (p

Positron emission tomography (PET) and the high affinity D(2/3) radiotracer [(18)F]fallypride allow the assessment of D(2/3) receptor occupancy of antipsychotic drugs in striatal and extrastriatal brain regions. We measured regional occupancy attained across a range of clinical dosing by the partial D(2) agonist aripiprazole using these methods. Twenty-eight PET scans were acquired on the ECAT EXACT HR+ camera in 19 patients with schizophrenia or schizoaffective disorder. Daily aripiprazole doses ranged from 2 to 40 mg, with a minimum of 10 days on steady dose. Mean regional occupancies, a model-independent estimate of aripiprazole effect on pituitary binding, and PANSS ratings changes were evaluated. Occupancy levels were high across regions of interest, ranging from 71.6+/-5.5% at 2 mg/day to 96.8+/-5.3% at 40 mg/day. Occupancy levels were higher in extrastriatal than striatal regions. Pituitary measures of aripiprazole effect correlated with doses and were unrelated to prolactin levels, which remained within the normal range under medication. PANSS positive (but not negative) symptom improvement correlated with striatal but not extrastriatal occupancies. These data show, for the first time, D(2) occupancy by aripiprazole in treated patients with schizophrenia in extrastriatal as well as striatal regions, with high occupancy for all doses. We discuss possible explanations for higher extrastriatal than striatal occupancy. Correlations of ratings of clinical improvement with regional occupancy suggest that aripiprazole, as do other antipsychotics, benefits positive symptoms of schizophrenia most directly through its modulation of striatal rather than cortical or other extrastriatal dopamine activity.

A 40 base polymorphism of a variable number of tandem repeats (VNTR) has been described in the 3' untranslated region of the gene (SLC6A3) coding for the dopamine transporter (DAT). Despite being located in the untranslated region of the gene, this polymorphism has been associated with clinical phenotypes associated with dysregulation of dopamine transmission, such as attention deficit hyperactivity disorder and cocaine-induced paranoia. To examine the neurochemical phenotype associated with this polymorphism, we compared amphetamine-induced dopamine release (measured as displacement of the radiotracer [123I]IBZM) and DAT expression (measured with [123I]beta-CIT) in the striatum with Single Photon Computerized Emission Tomography (SPECT). Our sample included 59 subjects, 31 healthy controls and 29 patients with schizophrenia. No significant association was found between VNTR polymorphism and amphetamine-induced dopamine release or DAT density in the total sample, nor when each diagnostic group was considered separately. Thus, we did not replicate the findings of two previous studies, which had suggested that the 9 repeat allele was associated with either an increased or decreased DAT expression, albeit in different patient populations.

In vivo functional brain imaging, including global blood flow, regional cerebral blood flow (rCBF), measured with positron emission tomography (PET) and single photon emission computed tomography (SPECT), and regional cerebral metabolic rate (rCMR) measured with deoxyglucose PET, have been widely used in studies of psychiatric disorders. These studies have found modest differences and required large numbers of patients. Activation studies using rCBF or rCMR as indices of neuronal activity are more sensitive because patients act as their own control; however, findings localize regions of change but provide no data about specific neurotransmitter systems. After a general discussion of the role of neurotransmitter systems in neuropsychiatric disorders, an overview of the methodology of development and selection of radioligands for PET and SPECT is presented. Studies involving PET and SPECT ligand methods are reviewed and their findings summarized, including recent work demonstrating successive mutual modulation of neurotransmitter systems. Kinetic and equilibrium analysis modeling are reviewed. The emerging methodology of measuring neurotransmitter release on activation, both pharmacologically and by task performance, using ligand methods is reviewed and proposed as a promising new approach for studying psychiatric disorders.