Stereological study of the cerebral and cerebellar cortex following short time exposure to morphine in rats

Drug abuse has been claimed to cause the loss of neurons and reduction of volume in both the adult and developing brain. This study examined cortex volumes in cerebrum and cerebellum of male rats that were dependent on morphine using unbiased stereological counting methods and systematic random sampling technique. Our goal was to test whether short time exposure to morphine can affect the cortex volume in the cerebrum and cerebellum. In this study, 30 NMRI male rats (3 month old and 110.36 ± 1.7 g) were used and animals randomly divided into three groups. The first group received no drug, while the second group received saline, and the third group received morphine + saline. Animals in the second and third groups were treated with saline or with an increasing dose regimen of morphine (5-25 mg/kg, twice a day) subcutaneously for 5 days. After confirming that the animals show withdrawal symptoms (12 h after the last injection), animals were anesthetized with an intraperitoneal injection with phenobarbital and killed by intracardiac perfusion with formalin in phosphate buffer. Then, the cerebellum and the cerebrum were carefully removed from the skull and embedded in 7% agar solution. The unbiased stereological procedure known as the Cavalieri principle was used to estimate the volume of cortex in the cerebellum and cerebrum of each animal. There were no significant statistical differences in volume of the cortex in cerebellum and cerebrum between groups. It is concluded that morphine has not toxic effect on the neurons body in the cortex of cerebrum and cerebellum after its short exposure.