['To investigate whether cannabinoid receptor 1 (CB1R) is involved in nerve growth in endometriosis-associated ectopic cyst.', 'The effect of CB1R agonist and antagonist on the expression of pan-neuronal marker protein gene product (PGP) 9.5 in ectopic cyst was examined by immunofluorescence and Western blot in endometriosis model of 18 rats.', 'Immunofluorescence revealed that PGP 9.5 was expressed in the nerve fibers and was mainly distributed in the cyst hilum. Western blot revealed that the protein density of either PGP 9.5 (2 week: 0.38 ± 0.05; 4 week: 0.63 ± 0.03; 8 week: 0.80 ± 0.07, P < 0.01) or CB1R (2 week: 0.48 ± 0.04; 4 week: 0.68 ± 0.01; 8 week: 0.80 ± 0.03, P < 0.01) in the ectopic cyst increased with cyst size. In addition, compared to control group (0.75 ± 0.01), PGP 9.5 expression in the ectopic cyst was promoted by CB1R agonist ACPA (0.81 ± 0.01, P < 0.05), and inhibited by CB1R antagonist AM251 (0.67 ± 0.03, P < 0.01).'] Does [ Cannabinoid receptor 1 control nerve growth in ectopic cyst in a rat endometriosis model ]?