Increased anxiety and impaired spatial memory in young adult rats following adolescent exposure to methylone

• Methylone treatment during adolescence increased adult anxiety.
• Changes in such anxiety were dependent on sex and treatment age.
• Adolescent methylone treatment disrupted adult detection of a brightness change.
• Disrupted detection ability suggested impaired spatial memory.

This study investigated the possibility that treatment of adolescent rats with the substituted cathinone, 3,4-methylenedioxymethcathinone (methylone), might result in heightened anxiety and/or impaired memory during early adulthood, as has been shown for other designer drugs. For 10 consecutive days from 35 days after birth (PND35-44, early adolescence) or 45 days after birth (PND45-54, late adolescence), male and female PVG/c rats were administered saline or 8.0 mg/kg methylone via intraperitoneal injection. When 90 days old (early adulthood), their anxiety-related behavior was recorded in an open field and a light/dark box. Acoustic startle amplitude was also measured as well as their spatial memory which was determined by their ability to detect which arm of a Y maze had changed in brightness between an acquisition and a retention trial. Previously methylone-treated rats showed increased anxiety-related behavior only in the open field as reflected in decreased ambulation, and increased corner occupancy and defecation. In the latter two cases, the increases depended on the age of treatment. Also, for defecation, only male rats were affected. In addition, methylone-treated rats displayed signs of impaired spatial memory, independent of anxiety, through their reduced ability to detect a novel changed Y-maze arm. The results of the study suggested some possible consequences in adulthood of methylone use during adolescence. There were also several examples of female rats exhibiting higher overall frequencies of activity and anxiety-related responding than males that were consistent with them being the more active and less anxious of the two sexes.