Abstract: Objective To compare pineal gland injury models established using para-chlorophenylalanine (PCPA), electrical stimulation stress, and PCPA plus electrical stimulation, to evaluate the structure and function changes of the pineal gland, and to establish a simple and effective method of pineal gland injury model with short modeling time. Methods Forty rats were adaptively reared for 1 week and randomly divided into blank control, PCPA, electrical stimulation, and PCPA + electrical stimulation groups. The control group was left untreated. The PCPA group was intraperitoneally injected with PCPA 450 mg/kg for 2 consecutive days. The electric stimulation group was given a shuttle box with electric stimulation (voltage 30 V, current 0.8 A, stimulation time 30 s, interval 30 s, 60 cycles) for 5 consecutive days. The rats in the PCPA + electrical stimulation group were given electrical stimulation plus PCPA on the 4th day. The operation was the same as before. The rats in each group were tested for open field activities, elevated plus maze and other behaviors, pentobarbital sodium for sleep and other indicators. ELISA was performed to detect serum melatonin (MT) levels, and the pathological structure of the pineal gland was observed under a microscope. Results The total distance and average speed of the rats in the three experimental groups were significantly lower than those of the rats in the control group (P < 0.01), and the central area time of the PCPA and PCPA + electrical stimulation groups was significantly higher than that of the control group (P < 0.05). The open arm number was significantly higher in the PCPA + electrical stimulation group than that the control group (P < 0.05), and the open arm time ratios of the PCPA and PCPA + electrical stimulation groups were significantly higher than that of the control group (P < 0.05). The latency period to falling asleep in the PCPA group was significantly higher than that in the control group (P < 0.05). The serum MT levels in the three experimental groups were significantly lower than that of the control group (P < 0.01). In the PCPA group, the pineal gland cells were disorderly arranged, nuclear pyknosis was evident, the number of cells was significantly reduced, and vacuolar degeneration was increased. In the electrical stimulation group, the pineal gland cells were disorderly arranged, nuclear pyknosis was evident, the number of cells was slightly reduced, and vacuolar degeneration was slightly increased. In the PCPA + electrical stimulation group, the pineal gland cells were disorderly arranged, nuclear pyknosis was evident, the number of cells was significantly reduced, and vacuolar degeneration was increased. Conclusion Different degrees of damage to the pineal gland in rats can be caused by three different methods of making model, which can provide reference for making different pineal gland injury models.

Key words: Pineal gland, Circadian rhythm, Melatonin, Pathology, Rats