Nurturing nature

Mutant zebrafish exhibit different behaviours depending on the genetic background of the fish they were raised with

The effect of zinc deficiency on deoxyribonucleic acid synthesis in rat liver

The effect of a short-term (3-day) dietary zinc deficiency on DNA synthesis in regenerating rat liver was investigated, with particular attention being paid to the timing of the S-phase of synthesis. The findings indicated a significantly reduced (P<0,01) incorporation of 'H-thymidine into the DNA of animals receiving the zinc-deficient ration (0,3 µg/g) when compared with control animals which received 60 µg/g in their diet. Of special interest was the finding that a shift occurred in the timing of the peak of maximum incorporation, from 17½ hours postoperatively in the control animals to 25 hours postoperatively in the deficient animals. Thus, when comparisons were made between the incorporation data at the respective peaks of maximum DNA synthesis, the effect of zinc deficiency was considerably reduced (P<0,05), but not eliminated when compared with the data obtained at the same time postoperatively in both groups. The data highlight the need for studies concerning the effect of zinc deficiency on the incorporation of 'Hthymidine to be performed at the peak of maximum DNA synthesis for the respective treatments, and not, as is done at present, at the same time for all groups.S. Afr. Med. J., 48, 1697 (1974)

Autism-associated gene shank3 is necessary for social contagion in zebrafish

BACKGROUND: Animal models enable targeting autism-associated genes, such as the shank3 gene, to assess their impact on behavioural phenotypes. However, this is often limited to simple behaviours relevant for social interaction. Social contagion is a complex phenotype forming the basis of human empathic behaviour and involves attention to the behaviour of others for recognizing and sharing their emotional or affective state. Thus, it is a form of social communication, which constitutes the most common developmental impairment across autism spectrum disorders (ASD). METHODS: Here we describe the development of a zebrafish model that identifies the neurocognitive mechanisms by which shank3 mutation drives deficits in social contagion. We used a CRISPR-Cas9 technique to generate mutations to the shank3a gene, a zebrafish paralogue found to present greater orthology and functional conservation relative to the human gene. Mutants were first compared to wild types during a two-phase protocol that involves the observation of two conflicting states, distress and neutral, and the later recall and discrimination of others when no longer presenting such differences. Then, the whole-brain expression of different neuroplasticity markers was compared between genotypes and their contribution to cluster-specific phenotypic variation was assessed. RESULTS: The shank3 mutation markedly reduced social contagion via deficits in attention contributing to difficulties in recognising affective states. Also, the mutation changed the expression of neuronal plasticity genes. However, only downregulated neuroligins clustered with shank3a expression under a combined synaptogenesis component that contributed specifically to variation in attention. LIMITATIONS: While zebrafish are extremely useful in identifying the role of shank3 mutations to composite social behaviour, they are unlikely to represent the full complexity of socio-cognitive and communication deficits presented by human ASD pathology. Moreover, zebrafish cannot represent the scaling up of these deficits to higher-order empathic and prosocial phenotypes seen in humans. CONCLUSIONS: We demonstrate a causal link between the zebrafish orthologue of an ASD-associated gene and the attentional control of affect recognition and consequent social contagion. This models autistic affect-communication pathology in zebrafish and reveals a genetic attention-deficit mechanism, addressing the ongoing debate for such mechanisms accounting for emotion recognition difficulties in autistic individuals

Whole-brain mapping of socially isolated zebrafish reveals that lonely fish are not loners

The zebrafish was used to assess the impact of social isolation on behaviour and brain function. As in humans and other social species, early social deprivation reduced social preference in juvenile zebrafish. Whole-brain functional maps of anti-social isolated (lonely) fish were distinct from anti-social (loner) fish found in the normal population. These isolation-induced activity changes revealed profound disruption of neural activity in brain areas linked to social behaviour, social cue processing, and anxiety/stress. Several of the affected regions are modulated by serotonin, and we found that social preference in isolated fish could be rescued by acutely reducing serotonin levels

Plasma luteinizing hormone levels in ewes failing to exhibit oestrus during lactation and in ewes isolated from rams

Daar was geen betekenisvolle verskil in die peil van luteiniserende hormoon in die plasma van ooie wat geen oestrus gedurende laktasie getoon het nie en die tussen-estrus peil van ooie wat gereeld bronstig was. Die LH peil was beduidend laer by ooie wat van ramme afgesonder was as by soortgelyke, maar anestrus, ooie wat voortdurend by ramme geloop het. Die basale LH peil by ooie wat gereeld bronstig was, het relatief min gevarieer van dag tot dag, terwyl merkwaardigde skommelinge in die daaglikse monsters van ooie wat enstrus was, verkry is.SUMMARYThc plasme Level of ewes which did not exhibit oestrus during lactation was not significantly different from the inter-oestrus level of ewes showing regular oestrus. The LH level in the plasma of ewes kept isolated from rams was significantly lower than amongst similar, but anoestrous ewes continuously associated with rams. In ewes which were cycling regularly the basal LH level remained relatively constant from day to day during inter-oestrus, whereas in anoestrous ewes the daily samples showed considerable fluctuation

Crossover inhibition generates sustained visual responses in the inner retina

In daylight, the input to the retinal circuit is provided primarily by cone photoreceptors acting as band-pass filters, but the retinal output also contains neuronal populations transmitting sustained signals. Using in vivo imaging of genetically encoded calcium reporters, we investigated the circuits that generate these sustained channels within the inner retina of zebrafish. In OFF bipolar cells, sustained transmission was found to depend on crossover inhibition from the ON pathway through GABAergic amacrine cells. In ON bipolar cells, the amplitude of low-frequency signals was regulated by glycinergic amacrine cells, while GABAergic inhibition regulated the gain of band-pass signals. We also provide the first functional description of a subset of sustained ON bipolar cells in which synaptic activity was suppressed by fluctuations at frequencies above ∼0.2 Hz. These results map out the basic circuitry by which the inner retina generates sustained visual signals and describes a new function of crossover inhibition

Development of social behaviour in young zebrafish

Adult zebrafish are robustly social animals whereas larva is not. We designed an assay to determine at what stage of development zebrafish begin to interact with and prefer other fish. One week old zebrafish do not show significant social preference whereas most 3 weeks old zebrafish strongly prefer to remain in a compartment where they can view conspecifics. However, for some individuals, the presence of conspecifics drives avoidance instead of attraction. Social preference is dependent on vision and requires viewing fish of a similar age/size. In addition, over the same 1-3 weeks period larval zebrafish increasingly tend to coordinate their movements, a simple form of social interaction. Finally, social preference and coupled interactions are differentially modified by an NMDAR antagonist and acute exposure to ethanol, both of which are known to alter social behavior in adult zebrafish