The Effect of Morphine Injection in Ca3 Area of Hippocampus on Spatial Learning and Memory in Male Rats

Learning is change of behavior based on experience, and memory is recalling the past events consciously or unconsciously. Learning and memory are of the higher functions in the brain that involve many regions in the central nervous system. Permanent synaptic morphological changes specially in hippocampus, are the basis of learning and memory that can be influence by many factors. In this study the effect of morphine injected in CA3 of hippocampus on spatial learning and memory in male rats was investigated.

In this experimental study 48 male rats were anaesthetized and cannula implanted bilaterally in CA3 area of hippocampus(AP = 3.5 from bregma, LA = ±3.8, DV = 2.7 from dura) using stereotaxic method. After recovery period (one week), rats were divided into six groups, including: control (only cannulated), Sham (received saline) and four other groups that received doses of 1, 5, 10 or 25 milligram of morphine in 1μl solation through cannula during 5 days. Each day, 30 minutes after injection, their spatial learning and memory in morris water maze were evaluated. Throughout the experiments, animals were treated according to the suggested international ethical guidelines for the care of laboratory animals.

Results showed that 5, 10 and 25 milligram cause of morphine can delay in time and distance toward the hidden platform in four days. However, in fifth day all doses of morphine caused animals to spend fewer time and distance in trigger region.

This study indicates that morphine injection in CA3 of hippocampus caused impairment on spatial learning and memory.