Anatomy of Teleosts and elasmobranchs

Dissecting the localization of Tilapiatilapinevirus in the brain of the experimentally infected Nile tilapia, Oreochromisniloticus (L.)

“…Despite the fact that this study did not focus on functional study of the fish brain, basic science revealed that the brain is a central nervous system (CNS) that controls important living activities of the fish and different regions of the brain are responsible for different biological functions (Table 1) (Ferguson, 2006; Northcutt, 1981, 1995; Roberts & Ellis, 2012; Sado et al., 2020; Wullimann et al., 1996). Therefore, heavy viral infection (indicated by density of ISH signals) in particular brain regions may result in neurological cell damages and impairment of the brain function and thus possibly explain for abnormal behaviours observed in infected fish during the course of infection.…”

“…Indeed, based on literature, the teleost brain regions in the forebrain, midbrain and hindbrain are involved with specific physiological and behavioural outputs. Specifically, the forebrain contains the telencephalon and the diencephalon in which the telencephalon encompasses control of sensory and motor and cognitive tasks such as memory, learning and emotion (Table 1) (Northcutt, 1981, 1995; Roberts & Ellis, 2012; Sado et al., 2020). Heavy TiLV infection in this important brain part could thus result in some described signs such as lethargy, stoppage of schooling and swimming at the water surface.…”

“…With respect to the signs of loss of appetite and stoppage of eating, it is interesting that the intense TiLV signals were observed in the hypothalamus, which controls feeding behaviour, receives both olfactory and appetite information and appears to be able to control movement over the jaw muscles involved in feeding (Roberts & Ellis, 2012). The middle brain (mesencephalon) is the region particularly involved in the reception and coordination of optic nerve inputs, such as interpretation of motor and visual signals (Roberts & Ellis, 2012; Sado et al., 2020). Therefore, we speculate that TiLV infection and neuron damage in this area may be related to behavioural disorders of food and prey seeking, navigating around obstacles in the environment and avoidance of approaching objects.…”

“…Therefore, we speculate that TiLV infection and neuron damage in this area may be related to behavioural disorders of food and prey seeking, navigating around obstacles in the environment and avoidance of approaching objects. On the other hand, the cerebellum and medulla oblongata are located within the hindbrain (rhombencephalon) and are generally associated with the regulation of locomotion and balance stimuli and basal physiology (Roberts & Ellis, 2012; Sado et al., 2020). Therefore, it was possible that the strong densities of TiLV in these areas were linked with erratic swimming or loss of balance.…”

“…However, these findings were limited at suggesting that the brain is one of the target tissues for transcription and replication of the virus (Mugimba et al., 2020). In fact, the fish brain divides into different regions and each part is responsible for certain functions (Table 1) (Roberts & Ellis, 2012; Sado et al., 2020). Unfortunately, currently available data are unclear as to which part of the brain is affected and whether the possible injuries are linked to the brain function, as well as the possible route of viral entry into the brain.…”