**1. Introduction**

The enteric nervous system (ENS), located in the wall of the bowel, is also known as the "second brain." The ENS exhibits a wide similarity to the brain, both structurally and functionally. Its neuronal structure is not cemented by collagen and Schwann cells but by glial astrocytes of the central nervous system (CNS). It has similar complex functions to the brain and contains various neurotransmitters [1]. The gastrointestinal system communicates with the brain through vagus nerve fibers and the gut-brain axis. The interaction between the CNS and ENS is known as the gut-brain axis. This axis is mainly regulated by gut microbiota and related neurotransmitters such as 5-hydroxytryptamine (5-HT), also known as serotonin [2]. The common features in terms of function between the ENS and the CNS are reflected in the context of disorder, in that gastrointestinal dysfunction may be seen in neurological diseases, and neurological dysfunction may become evident in gastrointestinal disease processes [3]. Painful abdominal cramping, nausea, and cyclical vomiting syndrome are related to childhood epilepsy, and also in adults, abdominal symptoms are usually associated with idiopathic complex partial or secondary generalized seizures [4]. The ketogenic diet has beneficial effects on intractable seizures, and has been shown to affect the gut microbiota [5]. The gut microbiota and the immune system are interrelated [6]. Gut bacteria balance affects the development of autoimmune disorders. For instance, changing the balance of *Firmicutes* and *Bacteroidetes* in gut microbiota may promote autoimmune disorders such as type 1 diabetes mellitus [7]. The balance in the gut microbiota is also linked to the pro- and anti-inflammatory immune responses [8]. There is a well-known relationship between autoimmune diseases and epileptogenesis, and this may explain the involvement of gut microbiota in the course of epilepsy. The incidence

of epilepsy differs between developed and developing countries, similarly to the differences observed in the gut microbiota [9]. Autoimmune diseases occur when the immune system exhibits redundant responses against the tissues of its own body. The etiology of autoimmune disease is still unclear, but some potential factors such as the environment, genetic predisposition, vaccines, an unbalanced diet, and immune disorders have been implicated [10, 11]. A large number of epilepsy cases have an autoimmune-related basis, and adjunctive immunotherapy has beneficial effects in such cases [12]. Some serum autoantibodies are also epileptogenic, and immunomodulatory therapy may attenuate the progression of some epilepsy syndromes [13]. In this context, gut microbiota-targeted therapy may be useful in the treatment of certain types of epilepsy syndromes by altering gut-related immunity and the gut-brain axis, which is also controlled by neurotransmitters. One case report stated that fecal microbiota transplantation cured refractory epilepsy in concomitant Crohn's disease [14].
