Chronic hyperammonemia causes a hypoglutamatergic and hyperGABAergic metabolic state associated with neurobehavioral abnormalities in zebrafish larvae

Chronic hyperammonemia is a common condition affecting individuals with inherited urea cycle disorders resulting in progressive cognitive impairment and behavioral abnormalities. Altered neurotransmission has been proposed as major source of neuronal dysfunction during chronic hyperammonemia, but the molecular pathomechanism has remained incompletely understood. Here we show that chronic exposure to ammonium acetate induces locomotor dysfunction and abnormal feeding behavior in zebrafish larvae, indicative for an impairment of higher brain functions. Biochemically, chronically elevated ammonium concentrations cause enhanced activity of glutamate decarboxylase isoforms GAD1 and GAD2 with increased formation of GABA and concomitant depletion of glutamate, ultimately leading to a dysfunctional hypoglutamatergic and hyperGABAergic metabolic state. Moreover, elevated GABA concentrations are accompanied by increased expression of GABA_A receptor subunits alpha-1, gamma-2 and delta, supporting the notion of an increased GABA tone in chronic hyperammonemia. Propionate oxidation as major anaplerotic reaction sufficiently compensates for the transamination-dependent withdrawal of 2-oxoglutarate, thereby preventing bioenergetic dysfunction under chronic hyperammonemic conditions. Thus, our study extends the hypothesis of alterations in the glutamatergic and GABAergic system being an important pathophysiological factor causing neurobehavioral impairment in chronic hyperammonemia. Given that zebrafish larvae have already been successfully used for high-throughput identification of novel compounds to treat inherited neurological diseases, the reported zebrafish model should be considered an important tool for systematic drug screening targeting altered glutamatergic and GABAergic metabolism under chronic hyperammonemic conditions in the future.

DIY Automated Feeding and Motion Recording System for the Analysis of Fish Behavior

Fish species such as medaka or zebrafish are widely used as animal models to study physiology, disease development, and treatment efficacy. They are also used to study the rapidly growing field of behavior research, such as social interactions, anxiety, and the influence of environmental factors. Here we describe an automated experimental setup allowing the recording of general locomotor activity in combination with a food-on-demand system. It can simply be built with some basic electronic knowledge. Our setup enables the recording of locomotor and feeding activity of several fish for long-term studies, excluding disturbing external influences. A description of the automated recording system is given, as well as examples of recordings to illustrate its applicability for the study of fish behavior. The construction manual and operation instructions can be downloaded for free.