Effects of Electrical Stimulation of Raphe Magnus on Locomotion and Selected Cognitive Abilities in Rats

Serotonin (5-HT) in the brain is involved in the regulation of various emotional states and behaviors. Most serotonergic neurons are located in the raphe nuclei. The raphe magnus (RMg) is one of the raphe nuclei and belongs to the caudal raphe complex. The primary goal of our research was to examine the effects of chronic, repeated electrical stimulation of the RMg on rats' motility over a period of 15 days. During the research, 35 rats were used; 21 rats underwent electrical stimulation of the RMg (RMg-ST), while 14 rats were included in the control group (RMg-Sham). In addition, we aimed to evaluate the effects of electrical stimulation in the RMg-ST group as well as the naïve procedure in the RMg-Sham group on anxiety-related behaviors and spatial memory on selected days 30 min after the end of stimulation. We found that rats in the RMg-ST group were characterized by considerably higher locomotor activity than animals in the RMg-Sham group over a 15-day stimulation period. Stimulated animals were less anxious during the elevated plus maze on the 4th and 5th days of stimulation and demonstrated improved memory performance during the Morris water maze conducted between the 9th and 12th days of stimulation in comparison to the control animals. Furthermore, in both behavioral tests, rats' motility when subjected to the RMg electrical stimulation was much higher than in control rats. On the last day of the 15-day stimulation period, rats were sacrificed, and their brains were collected. Brain immunofluorescent analysis revealed an increase in the number of 5-HT-positive cells in the RMg-ST group and altered activity of c-Fos-positive cells in selected brain structures connected with locomotion (secondary motor cortex), anxiety (arcuate nucleus of the hypothalamus), and spatial memory (dentate gyrus) after stimulation in comparison to the results in the RMg-Sham group. These findings suggest that locomotion may be strictly dependent on the RMg neuronal projections, and electrical stimulation of the structure influences cognitive behaviors.