Involvement of the histaminergic system on appetitive learning and its interaction with haloperidol in goldfish

From land to water: "Sunken" T-maze for associated learning in cichlid fish

The study introduced and evaluated learning paradigms for Maylandia callainos cichlids using a modified version of the rodent T-maze, filled with tank water (the "sunken" modification). Both male and female fish underwent training in two distinct conditioning paradigms. Firstly, simple operant conditioning involved placing a food reward in either the right or left compartment. Cichlids demonstrated the ability to purposefully find the bait within 6 days of training, with a persistent place preference lasting up to 6 days. Additionally, the learning dynamics varied with sex: female cichlids exhibited reduction in latency to visit the target compartment and consume the bait, along with a decrease in the number of errors 3 and 4 days earlier than males, respectively. Secondly, visually-cued operant conditioning was conducted, with a food reward exclusively placed in the yellow compartment, randomly positioned on the left or right side of the maze during each training session. Visual learning persisted for 10 days until reaction time improvement plateaued. Color preference disappeared after 4 consecutive check-ups, with no sex-related interference. For further validation of visually-cued operant conditioning paradigm, drugs MK-801 (dizocilpine) and caffeine, known to affect performance in learning tasks, were administered intraperitoneally. Chronic MK-801 (0.17 mg/kg) impaired maze learning, resulting in no color preference development. Conversely, caffeine administration enhanced test performance, increasing precision in fish. This developed paradigm offers a viable approach for studying learning and memory and presents an effective alternative to rodent-based drug screening tools, exhibiting good face and predictive validity.

Parameters of rewards on choice behavior in Siamese fighting fish (Betta splendens)

Five experiments were conducted with Siamese fighting fish (Betta splendens) to investigate how choices in a T-maze were affected by parameters of a social reward (aggression display to another male): presence or absence, amount, delay and distance traveled. Bettas showed a preference for the side associated with the presence of another male rather than the side associated with nothing (Exp 1), a greater length of time of the reward (Exp 2) and shorter delay (Exp 3). The animals were indifferent when one side offered a longer delay to a longer reward time compared with a shorter delay to a shorter reward time (Exp 4). What was most surprising, however, was that fish preferred to choose the side that was associated with swimming a greater distance to reach an opponent male (Exp 5). These experiments demonstrate that, while some parameters of a visual reward affect behavior in predictable ways (greater amount, shorter delay), the complex motivations underlying inter-male aggression can produce what appear to be paradoxical results.

The goldfish (Carassius auratus) as a model for neuroendocrine signaling

Goldfish (Carassius auratus) are excellent model organisms for the neuroendocrine signaling and the regulation of reproduction in vertebrates. Goldfish also serve as useful model organisms in numerous other fields. In contrast to mammals, teleost fish do not have a median eminence; the anterior pituitary is innervated by numerous neuronal cell types and thus, pituitary hormone release is directly regulated. Here we briefly describe the neuroendocrine control of luteinizing hormone. Stimulation by gonadotropin-releasing hormone and a multitude of classical neurotransmitters and neuropeptides is opposed by the potent inhibitory actions of dopamine. The stimulatory actions of gamma-aminobutyric acid and serotonin are also discussed. We will focus on the development of a cDNA microarray composed of carp and goldfish sequences which has allowed us to examine neurotransmitter-regulated gene expression in the neuroendocrine brain and to investigate potential genomic interactions between these key neurotransmitter systems. We observed that isotocin (fish homologue of oxytocin) and activins are regulated by multiple neurotransmitters, which is discussed in light of their roles in reproduction in other species. We have also found that many novel and uncharacterized goldfish expressed sequence tags in the brain are also regulated by neurotransmitters. Their sites of production and whether they play a role in neuroendocrine signaling and control of reproduction remain to be determined. The transcriptomic tools developed to study reproduction could also be used to advance our understanding of neuroendocrine-immune interactions and the relationship between growth and food intake in fish.