Effect of hashish on vigilance performance

Alterations to pre-pulse inhibition (PPI) in chronic cannabis users are secondary to sustained attention deficits

RATIONALE

Given the hypothesised association between cannabis use and schizophrenia, and the well documented alterations in pre-pulse inhibition (PPI) that are observed in schizophrenia, it is of interest to examine the effects of cannabis use on PPI.

OBJECTIVE

The objective of the study was to use novel methodology for the measurement and characterisation of attentional modulation of PPI, in order to examine the nature of PPI in chronic cannabis users.

METHODS

PPI was measured in 34 chronic cannabis users (who were otherwise healthy) and 32 healthy controls, across a range of startling stimulus intensities, during two attention set conditions, one in which they were instructed to attend to the auditory stimuli and one in which they were instructed to ignore the auditory stimuli and focus on a visual task. Curves of best fit were fitted to the startle magnitudes, across the stimulus intensities. A number of reflex parameters were extracted from these logistic functions, each of which reflects a different characteristic of the startle response.

RESULTS

Cannabis users failed to show attentional modulation of any of the reflex parameters and showed altered PPI, relative to controls, but only when they were instructed to sustain attention to the auditory stimuli.

CONCLUSION

Cannabis users showed an attention-dependant alteration in PPI, which appeared to reflect a deficit in sustain attention, and which was different to that which has been observed in schizophrenia using the same methodology.

The Effect of Recent Stimulant Use on Sustained Attention in HIV-Infected Adults

Evidence suggests that stimulant use may exacerbate the deleterious cognitive effects of HIV, and that it has similar neuropathological consequences. In the current study, we examined the effect of recent stimulant use on sustained attention in adults infected with HIV. The sample consisted of 23 non-drug users and 17 stimulant users (cocaine and/or methamphetamine), all who were HIV-positive. Drug use was determined via urine toxicology. Sustained attention was assessed with the Conners' Continuous Performance Task--second edition (CPT-II). Groups were compared on overall performance variables, as well as patterns of performance across time. Compared to the non-drug users, stimulant users showed a gradual increase in reaction time variability and omission errors. Stimulant users' scores indicated impaired vigilance relative to an age and gender-matched normative sample. The groups were equivalent on other measures of attention, global neuropsychological functioning, mood, and demographic variables. The results indicate that recent stimulant use among HIV-infected adults adversely affects sustained attention.

Anxiolytic-like properties of the anandamide transport inhibitor AM404

The endocannabinoids anandamide and 2-arachidonoyglycerol (2-AG) may contribute to the regulation of mood and emotion. In this study, we investigated the impact of the endocannabinoid transport inhibitor AM404 on three rat models of anxiety: elevated plus maze, defensive withdrawal and separation-induced ultrasonic vocalizations. AM404 (1-5 mg kg(-1), intraperitoneal (i.p.)) exerted dose-dependent anxiolytic-like effects in the three models. These behavioral effects were associated with increased levels of anandamide, but not 2-AG, in the prefrontal cortex and were prevented by the CB(1) cannabinoid antagonist rimonabant (SR141716A), suggesting that they were dependent on anandamide-mediated activation of CB(1) cannabinoid receptors. We also evaluated whether AM404 might influence motivation (in the conditioned place preference (CPP) test), sensory reactivity (acoustic startle reflex) and sensorimotor gating (prepulse inhibition (PPI) of the startle reflex). In the CPP test, AM404 (1.25-10 mg kg(-1), i.p.) elicited rewarding effects in rats housed under enriched conditions, but not in rats kept in standard cages. Moreover, AM404 did not alter reactivity to sensory stimuli or cause overt perceptual distortion, as suggested by its lack of effect on startle or PPI of startle. These results support a role of anandamide in the regulation of emotion and point to the anandamide transport system as a potential target for anxiolytic drugs.

EFFECT OF POLYDRUG ABUSE ON SUSTAINED ATTENTION, VISUOGRAPHIC FUNCTION, AND REACTION TIME

The present study consists of two parts. In the first part 23 polydrug abusers and a control group of 33 from United Arab Emirates were tested for visuographic functions using the Benton Visual Retention Test. In the second part 14 polydrug abusers and a group control subjects were tested for sustained attention and reaction time. Analysis suggested that polydrug use affects visuographic function and sustained attention adversely but has no effect on reaction time. The later result was explained in terms of indiscriminate responses by substance abusers.