Delivery of agmatine after the establishment of fentanyl self-administration
Time course of fentanyl self-administration for mice receiving i.c.v. treatments of saline (A) or agmatine (10 nmol/ 5 μL) (B) given after fentanyl self-administration has been established on day 8 and every 2 days for 14 days. The arrow on the graph denotes the first injection. Responses represent lever presses on one of two bars. The first bar (active lever) delivers 70 μL of fentanyl (10 μg/mL) (triangles). Pressing the control lever results in no reward and is indicative of non-specific activity (circles). Only mice meeting inclusion criteria were tested (ratio of 2 or greater compared to control lever presses and that the mice had to lever press for fentanyl a minimum of 10 times per session for 3 days; 75% of mice met this criteria). Mice did not alter active lever responding in response to agmatine i.c.v. injections. (C) Analysis of the AUC for the groups in A and B show that animals that received repeated ICV saline continued to discriminated between the control (1st bar, left to right) and the active (2nd bar) levers. The mice that received repeated agmatine after establishment of self-administration behavior also continued to discriminate between control (3rd bar) and active (4th bar) levers suggesting that this injection schedule of agmatine does not reverse the maintenance of fentanyl self-administration (*signifies difference in responding between the respective control and active lever within experimental group ANOVA, F(3,32); p < 0.05). N=9 mice per group.