Assessment of club drug use in a treatment-seeking sample of individuals with marijuana dependence

Club drug use is becoming increasingly popular in the United States and has been associated with chronic psychiatric symptoms and neuropsychological abnormalities. Patterns of club drug use and characteristics of club drug users are not homogeneous. Thus, treatment-seeking marijuana-dependent individuals may have a differential pattern of club drug use. Baseline assessments collected from 55 individuals participating in a pharmacological treatment study for marijuana dependence were examined. Individuals completed a 16-item self-report questionnaire assessing club drugs used, frequency and patterns of use, problems associated with use, and reasons for use. Subjects were primarily male (87.3%) and Caucasian (81.8%), with a mean age of 32.1 (+/-9.1 years). As expected, a large number of individuals had used ecstasy (75%). However, LSD and methamphetamine use was also reported by many users (82.5% and 47.5% respectively), with many individuals reporting the use of more than one club drug. Notably, 31.6% of individuals reported tolerance to club drugs. These results emphasize the significant co-occurrence of club drug use in marijuana-dependent individuals. This appears to be the first study to report on club drug use in treatment-seeking marijuana-dependent individuals. Clinical implications and directions for future research are discussed.     

Loss of otolith function with age is associated with increased postural sway measures

Loss of balance and increased fall risk is a common problem associated with aging. Changes in vestibular function occur with aging but the contribution of reduced vestibular otolith function to fall risk remains unknown. We examined a population of 151 healthy individuals (aged 21–93) for both balance (sway measures) and ocular counter-rolling (OCR) function. We assessed balance function with eyes open and closed on a firm surface, eyes open and closed on a foam surface and OCR during ±20 degree roll tilt at 0.005 Hz. Subjects demonstrated a significant age-related reduction in OCR and increase in postural sway. The effect of age on OCR was greater in females than males. The reduction in OCR was strongly correlated with the mediolateral measures of sway with eyes closed. This correlation was also present in the elderly group alone, suggesting that aging alone does not account for this effect. OCR decreased linearly with age and at a greater rate in females than males. This loss of vestibular otolith-ocular function is associated with increased mediolateral measures of sway which have been shown to be related to increased risk of falls. These data suggest a role for loss of otolith function in contributing to fall risk in the elderly. Further prospective, longitudinal studies are necessary to confirm these findings.     

Positive allosteric modulation of α7 neuronal nicotinic acetylcholine receptors: lack of cytotoxicity in PC12 cells and rat primary cortical neurons

Background and purpose:

α7-Nicotinic acetylcholine receptors (α7 nAChRs) play an important role in cognitive function. Positive allosteric modulators (PAMs) amplify effects of α7 nAChR agonist and could provide an approach for treatment of cognitive deficits in neuropsychiatric diseases. PAMs can either predominantly affect the apparent peak current response (type I) or increase both the apparent peak current response and duration of channel opening, due to prolonged desensitization (type II). The delay of receptor desensitization by type II PAMs raises the possibility of Ca²⁺-induced toxicity through prolonged activation of α7 nAChRs. The present study addresses whether type I and II PAMs exhibit different cytotoxicity profiles.

Experimental approach:

The present studies evaluated cytotoxic effects of type I PAM [N-(4-chlorophenyl)]-α-[(4-chloro-phenyl)-aminomethylene]-3-methyl-5-isoxazoleacet-amide (CCMI) and type II PAM 1-[5-chloro-2,4-dimethoxy-phenyl]-3-[5-methyl-isoxazol-3-yl]-urea (PNU-120596), or 4-[5-(4chloro-phenyl)-2-methyl-3-propionyl-pyrrol-1-yl]-benzenesulphonamide (A-867744). The studies used cultures of PC12 cells and primary cultures of rat cortical neuronal cells.

Key results:

Our results showed that neither type I nor type II PAMs had any detrimental effect on cell integrity or cell viability. In particular, type II PAMs did not affect neuron number and neurite outgrowth under conditions when α7 nAChR activity was measured by Ca²⁺ influx and extracellular signal-regulated kinases 1 and 2 phosphorylation, following exposure to α7 nAChR agonists.

Conclusions and implications:

This study demonstrated that both type I and type II α7 nAChR selective PAMs, although exhibiting differential electrophysiological profiles, did not exert cytotoxic effects in cells endogenously expressing α7 nAChRs.     

Identification of the substrate binding region of vesicular monoamine transporter-2 (VMAT-2) using iodoaminoflisopolol as a novel photoprobe

Monoamines, such as serotonin, dopamine, and norepinephrine, are sequestered into synaptic vesicles by specific transporters (vesicular monoamine transporter-2; VMAT2) using energy from an electrochemical proton gradient across the vesicle membranes. Based on our previous studies using photoaffinity-labeling techniques in characterizing the VMAT2-specific ligands ketanserin and tetrabenazine, this study describes the synthesis and characterization of a fluorenone-based compound, iodoaminoflisopolol (IAmF), as a photoprobe to identify the substrate binding site(s) of VMAT2. Using vesicles prepared from rat VMAT2 containing recombinant baculovirus-infected Sf9 cells, we show the inhibition of [3H]5-hydroxytryptamine (5-HT) uptake and [3H]dihydrotetrabenazine (TBZOH) binding by aminoflisopolol and iodoaminoflisopolol. The interaction of [125I]IAmF with VMAT2 is highly dependent on the presence of ATP and an intact proton gradient. We report a simple and novel method to distinguish between a ligand and substrate using classic compounds such as [3H]5-HT and [3H]TBZOH by incubating the compound with the vesicles followed by washes with isotonic and hypotonic solutions. Using this method, we confirm the characterization of IAmF as a novel VMAT2 substrate. Sf9 vesicles expressing VMAT2 show reserpine- and tetrabenazine-protectable photolabeling by [125I]IAmF. [125I]IAmF photolabeling of recombinant VMAT2, expressed in SH-SY5Y cells with an engineered thrombin site between transmembranes 6 and 7, followed by thrombin digestion, retained photolabel in a 22-kDa fragment, indicating that iodoaminoflisopolol binds to the C-terminal half of the VMAT2 molecule. Thus, IAmF possesses a unique combination of VMAT2 substrate properties and a photoprobe and is, therefore, useful to identify the substrate binding site of the vesicular transporter.