Ndicates the 25th and 75th percentile. The solid and dashed lines within each box indicate the median and mean values, respectively. * significant difference from control and cannabis groups (P,0.007). doi:10.1371/journal.pone.0056438.g(MPTP) to Rhesus monkeys [61]. However, the type and/or concentration of exposure is likely to be important given that substantia nigra echogenicity was not corrected to lifetime stimulant use (number of occasions) in the current study and substantia nigra echogenicity in older patients with Parkinson’s disease does not significantly differ with exposure to pesticides, herbicides, paint, solvents, and heavy metals [24]. However, the latter substances cannot be readily linked mechanistically with changes in dopamine neurons induced by stimulants. Other factors that could have contributed to abnormal substantia nigra hyperechogenicity in stimulant 23727046 users are age and increased symptoms of depression. Individuals in the stimulant group were ,7 yrs older than subjects in the control and cannabis groups and drug users tended to exhibit more symptoms of depression than non-drug users. However, the contribution of these factors to substantia nigra hyperechogenicity in the stimulant group is likely to be minimal. The area of substantia nigra echogenicity does not vary between 20 to 50 yrs of age [58] and cannabis users exhibited normal substantia nigra morphology despite a tendency for a higher score on the Beck Depression Inventory-II. Substantia nigra hyperechogenicity could also be associated with personality traits in stimulant users. Individuals in the stimulant group had received 1 year less of education and Title Loaded From File substance-dependence is associated with impulsive behavior [62]. However, the contribution of personality traits to the result is likely to be small given that personality traits do not correlate with substantia nigra echogenicity in patients with Parkinson’s disease [24]. Furthermore, cannabis users exhibited normal substantia nigra morphology and lifetime initiation of cannabis use typically precedes stimulant use. In the current cohort of stimulant users, cannabis use commenced at age 1763 yrs whereas stimulant use commenced at age 2065 yrs (paired t-test, P,0.001). Substantia nigra morphology was also normal in 3 cannabis subjects withStimulant Drugs and Substantia Nigra Morphologyheavy cannabis use (.4 days per week) and signs of addictive behaviour (i.e. daily use).Appropriate blinding was not possible due to limited resources and personnel. Future studies will need a double-blind design to confirm the current findings.Ultrasound measurement validityIn the control group, the area of substantia nigra echogenicity (average: 0.176?.181 cm2; median: 0.175?.180 cm2) was higher than that reported previously (median: 0.11?.14 cm2) [24,34,58,63]. However, the 90th percentile (0.258 cm2) was similar to a Title Loaded From File previous study involving 301 healthy individuals (0.25 cm2) [58] and areas ranging from 0.28?.35 cm2 have been previously reported in healthy young adults [31]. The higher area of echogenicity in the current study is likely due to differences in the ultrasound manufacturer, transducer properties (1? MHz versus 2.5 MHz), greater propensity for the ultrasound beam to penetrate bone (97.5 versus 77?2 ) [24,52,53,58], and improvements in ultrasound resolution over time. Such factors did not contribute to the between group difference observed in the current study because all subjects were tested with a Philips i.Ndicates the 25th and 75th percentile. The solid and dashed lines within each box indicate the median and mean values, respectively. * significant difference from control and cannabis groups (P,0.007). doi:10.1371/journal.pone.0056438.g(MPTP) to Rhesus monkeys [61]. However, the type and/or concentration of exposure is likely to be important given that substantia nigra echogenicity was not corrected to lifetime stimulant use (number of occasions) in the current study and substantia nigra echogenicity in older patients with Parkinson’s disease does not significantly differ with exposure to pesticides, herbicides, paint, solvents, and heavy metals [24]. However, the latter substances cannot be readily linked mechanistically with changes in dopamine neurons induced by stimulants. Other factors that could have contributed to abnormal substantia nigra hyperechogenicity in stimulant 23727046 users are age and increased symptoms of depression. Individuals in the stimulant group were ,7 yrs older than subjects in the control and cannabis groups and drug users tended to exhibit more symptoms of depression than non-drug users. However, the contribution of these factors to substantia nigra hyperechogenicity in the stimulant group is likely to be minimal. The area of substantia nigra echogenicity does not vary between 20 to 50 yrs of age [58] and cannabis users exhibited normal substantia nigra morphology despite a tendency for a higher score on the Beck Depression Inventory-II. Substantia nigra hyperechogenicity could also be associated with personality traits in stimulant users. Individuals in the stimulant group had received 1 year less of education and substance-dependence is associated with impulsive behavior [62]. However, the contribution of personality traits to the result is likely to be small given that personality traits do not correlate with substantia nigra echogenicity in patients with Parkinson’s disease [24]. Furthermore, cannabis users exhibited normal substantia nigra morphology and lifetime initiation of cannabis use typically precedes stimulant use. In the current cohort of stimulant users, cannabis use commenced at age 1763 yrs whereas stimulant use commenced at age 2065 yrs (paired t-test, P,0.001). Substantia nigra morphology was also normal in 3 cannabis subjects withStimulant Drugs and Substantia Nigra Morphologyheavy cannabis use (.4 days per week) and signs of addictive behaviour (i.e. daily use).Appropriate blinding was not possible due to limited resources and personnel. Future studies will need a double-blind design to confirm the current findings.Ultrasound measurement validityIn the control group, the area of substantia nigra echogenicity (average: 0.176?.181 cm2; median: 0.175?.180 cm2) was higher than that reported previously (median: 0.11?.14 cm2) [24,34,58,63]. However, the 90th percentile (0.258 cm2) was similar to a previous study involving 301 healthy individuals (0.25 cm2) [58] and areas ranging from 0.28?.35 cm2 have been previously reported in healthy young adults [31]. The higher area of echogenicity in the current study is likely due to differences in the ultrasound manufacturer, transducer properties (1? MHz versus 2.5 MHz), greater propensity for the ultrasound beam to penetrate bone (97.5 versus 77?2 ) [24,52,53,58], and improvements in ultrasound resolution over time. Such factors did not contribute to the between group difference observed in the current study because all subjects were tested with a Philips i.
