Topographical analysis of reactive zinc in the central nervous system of adult zebrafish (Danio rerio).

Reactive zinc (Zn) is crucial for neuronal signaling and is largely distributed within presynaptic vesicles of some axon terminals of distinct vertebrates. However, the distribution of reactive Zn throughout the central nervous system (CNS) is not fully explored. We performed a topographical study of CNS structures containing reactive Zn in the adult zebrafish (Danio rerio). Slices of CNS from zebrafish were stained by Neo-Timm and/or cresyl violet. The Zn specificity of Neo-Timm was evaluated with Zn chelants, N,N,N',N'-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), sodium diethyldithiocarbamate (DEDTC), Zn sulfide washing solution, and hydrochloric acid (HCl). Unfixed slices were also immersed in the fluorescent Zn probe (zinpyr-1). Yellow-to-brown-to-black granules were revealed by Neo-Timm in the zebrafish CNS. Telencephalon exhibited slightly stained regions, while rhombencephalic structures showed high levels of staining. Although stained granules were found on the cell bodies, rhombencephalic structures showed a neuropil staining profile. The TPEN produced a mild reduction in Neo-Timm staining, while HCl and mainly DEDTC abolished the staining, indicating a large Zn content. This result was also confirmed by the application of a Zn probe. The present topographical study revealed reactive Zn throughout the CNS in adult zebrafish that should be considered in future investigation of Zn in the brain on a larger scale.

Evaluation of spontaneous recovery of behavioral and brain injury profiles in zebrafish after hypoxia.

Cerebral hypoxia-ischemia can lead to motor and sensory impairments which can be dependent on the extent of infarcted regions. Since a better understanding of the neurochemical mechanisms involved in this injury is needed, the use of zebrafish as a cerebral hypoxia model has become quite promising because it could improve the knowledge about hypoxia-ischemia. In the current study, we aimed to investigate the spontaneous recovery of brain and behavioral impairments induced by hypoxia in adult zebrafish. Brain injury levels were analyzed by spectrophotometric measurement of mitochondrial dehydrogenase activity by staining with 2,3,5-triphenyltetrazolium chloride, and behavioral profiles were assessed by the open tank test. The induction of hypoxia substantially decreased mitochondrial activity in the brain and impaired behavior. The spontaneous recovery of fish subjected to hypoxia was assessed after 1, 3, 6, 24, and 48h under normoxia. The quantification of brain injury levels showed a significant increase until 24h after hypoxia, but after 48h this effect was completely reversed. Regarding behavioral parameters, we verified that locomotor activity and vertical exploration were impaired by hypoxia and these effects were reversed after 3h under normoxia. Taken together, these results show that zebrafish exhibited transient cerebral and behavioral impairments when submitted to hypoxia, and 1h under normoxic conditions was insufficient to reverse both effects. Therefore, our data help to elucidate the time window of spontaneous recovery in zebrafish after hypoxia and also the behavioral phenotypes involved in this phenomenon.

Behavioral effects of taurine pretreatment in zebrafish acutely exposed to ethanol.

Taurine (TAU) is an amino sulfonic acid that plays protective roles against neurochemical impairments induced by ethanol (EtOH). Mounting evidence shows the applicability of zebrafish for evaluating locomotor parameters and anxiety-like behavioral phenotypes after EtOH exposure in a large scale manner. In this study, we assess the effects of TAU pretreatment on the behavior of zebrafish in the open tank after acute 1% EtOH (v/v) exposure (20 and 60 min of duration) and on brain alcohol contents. The exposure for 20 min exerted significant anxiolytic effects, which were prevented by 42, 150, and 400 mg/L TAU. Conversely, the 60-min condition induced depressant/sedative effects, in which the changes on vertical activity were associated to modifications on the exploratory profile. Although all TAU concentrations kept locomotor parameters at basal levels, 150 mg/L TAU, did not prevent the impairment on vertical activity of EtOH[60]. Despite the higher brain EtOH content detected in the 60-min exposure, 42, 150, and 400 mg/L TAU attenuated the increase of alcohol content in EtOH[60] group. In conclusion, our data suggest that both protocols of acute EtOH exposure induce significant changes in the spatio-temporal behavior of zebrafish and that TAU may exert a preventive role by antagonizing the effects induced by EtOH possibly due to its neuromodulatory role and also by decreasing brain EtOH levels. The hormetic dose-response of TAU on vertical exploration suggests a complex interaction between TAU and EtOH in the central nervous system.