Botulinum toxin type A is a neurotoxic protein produced by the anaerobic bacterium Clostridium botulinum, and is one of the deadliest poisons in nature. The mechanism of action of BoNT/A involves the cleavage of the SNAP-25 protein, which plays a key role in the exocytosis of acetylcholine at the ends of axons, and consequently manifests its action in the occurrence of flaccid muscle paralysis. During the years of basic research, it was shown that the toxin not only acts on motor neurons, but also on sensory neurons and thus interferes with the transmission of pain signals, which as a result can have exceptional clinical significance. With controlled application in picomolar doses, the toxin is used in the treatment of conditions caused by muscle hyperactivity, such as cervical dystonia, strabismus, hyperhidrosis, but also in the treatment of chronic migraines. Numerous studies have been conducted investigating the additional possibilities of using BoNT/A for clinical purposes, among others in the therapy of chronic pain, the treatment of which has been a great challenge so far. The aim of this thesis was to examine the distribution of botulinum toxin in different regions of the brain after its application to the cisterna magna. The experiments were conducted on male Wistar rats at the Department of Pharmacology, Faculty of Medicine, University of Zagreb, in accordance with current regulations and the Animal Protection Act. After the initiation of 5 IU/kg BoNT/A into the cisterna magna, brain tissue samples were collected and prepared for immunohistochemical analysis. The presence of cleaved SNAP-25 protein was monitored as an indicator of the presence of toxins in different regions of the brain. The obtained results indicate the presence of toxins in the immediate vicinity of the initiation site, in the areas of the trigeminal nucleus of the caudalis and hippocampus, but also in distant regions of the brain. These findings require further research to explain the ways of toxin distribution to more distant areas and their significance for the action of the toxin, especially in the clinical setting.