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Barvni vid metuljev je ključen za ustrezno prepoznavo cvetja za prehranjevanje, za uspešno prepoznavo partnerjev ter plenilcev in na koncu primernih odlagališč jajčec. Predpostavili smo, da je delovanje fotoreceptorjev plastično in nastavljivo z intrinzičnim sproščanjem nevromodulatorjev. Z uporabo elektrofizioloških znotrajceličnih meritev smo najprej določili nabor fotoreceptorjev, ki sestavljajo mozaik v mrežnici trikromatskih in tetrakromatskih vrst metuljev. Na barvni vid smo poizkusili vplivati preko aplikacije agonistov in antagonistov oktopaminergičnega in histaminergičnega sistema. Vpliv oktopamina in njegovega antagonista epinastina na receptorski signal smo vrednotili preko sprememb v stopnji neposredne sinaptične oponence med fotoreceptorji. Ta je posledica delovanja inhibitornih interfotoreceptornih povezav v lamini in meduli metuljev. Med tem ko oktopamin na spektralno občutljivost ni imel vpliva, so imele celice, tretirane z epinastinom povišano inhibicijo oponentne enote. Še večji vpliv na oponenco je imela aplikacija blokatorjev histaminergičnih kloridnih kanalov. Z uspešno aplikacijo antagonistov oktopamina smo pokazali, da je barvni vid metuljev na najzgodnejši stopnji uravnan z nevromodulatorji, z uspešno blokado histaminergičnih kanalov pa smo razvili metodo za analitično preučevanje barvne oponence med fotoreceptorji. The colour vision of butterflies is crucial for the proper identification of foraging flowers, for the successful identification of mates and predators, and ultimately for the suitable oviposition sites. We hypothesized that photoreceptor activity is plastic and adjustable by intrinsic neuromodulator release. Using electrophysiological intracellular measurements, we first determined the set of photoreceptors that make up the mosaic in the retina of trichromatic and tetrachromatic butterfly species. We attempted to influence colour vision through the application of agonists and antagonists of the octopaminergic and histaminergic systems. The effect of octopamine and its antagonist epinastine on the receptor signal was evaluated through changes in the degree of direct synaptic opponency between photoreceptors. This is due to the action of inhibitory interphotoreceptor connections in the lamina and medulla of butterflies. While octopamine had no effect on spectral sensitivity, epinastine-treated cells had increased inhibition of the opponent unit. The effect on opponency was even greater when histaminergic chloride channel blockers were applied. By successful application of octopamine antagonists, we have shown that colour vision in butterflies is regulated by neuromodulators at the earliest stage, and by successful blockade of histaminergic channels, we have developed a method for analytically studying colour opponency between photoreceptors.

The eyes of nymphalid butterflies, investigated with incident illumination, show colourful facet reflection patterns—the eye shine—which is uniform or heterogeneous, dependent on the species. Facet colours suggest that the ommatidia contain different sets of photoreceptors and screening pigments, but how the colours and the cell characteristics are associated has not been clearly established. Here, we analyse the retinae of two nymphalids, Apatura ilia , which has a uniform eyeshine, and Charaxes jasius, a species with a heterogeneous eye shine, using single-cell recordings, spectroscopy and optical pupillometry. Apatura has UV-, blue- and green-sensitive photoreceptors, allocated into three ommatidial types. The UV- and blue-sensitive cells are long visual fibres (LVFs), receiving opponent input from the green-sensitive short visual fibres (SVFs). Charaxes has an expanded set of photoreceptors, allocated into three additional, red-reflecting ommatidial types. All red ommatidia contain green-sensitive LVFs, receiving opponent input from red receptors. In both species, the SVFs do not receive any opponent input. The simple retina of Apatura with three ommatidial types and two colour-opponent channels can support trichromatic vision. Charaxes has six ommatidial types and three colour-opponent channels. Its expanded receptor set can support tetrachromatic vision. This article is part of the theme issue ‘Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods’.

In many butterflies, the ancestral trichromatic insect colour vision, based on UV-, blue- and green-sensitive photoreceptors, is extended with red-sensitive cells. Physiological evidence for red receptors has been missing in nymphalid butterflies, although some species can discriminate red hues well. In eight species from genera Archaeoprepona, Argynnis, Charaxes, Danaus, Melitaea, Morpho, Heliconius and Speyeria , we found a novel class of green-sensitive photoreceptors that have hyperpolarizing responses to stimulation with red light. These green-positive, red-negative (G+R–) cells are allocated to positions R1/2, normally occupied by UV and blue-sensitive cells. Spectral sensitivity, polarization sensitivity and temporal dynamics suggest that the red opponent units (R–) are the basal photoreceptors R9, interacting with R1/2 in the same ommatidia via direct inhibitory synapses. We found the G+R– cells exclusively in butterflies with red-shining ommatidia, which contain longitudinal screening pigments. The implementation of the red colour channel with R9 is different from pierid and papilionid butterflies, where cells R5–8 are the red receptors. The nymphalid red-green opponent channel and the potential for tetrachromacy seem to have been switched on several times during evolution, balancing between the cost of neural processing and the value of extended colour information.

MSc (Pharmacology), North-West University, Potchefstroom Campus Obsessive-compulsive disorder (OCD)1 is a chronic and debilitating neuropsychiatric condition affecting 1 – 3% of the world population. The condition is characterized by two main symptom cohorts namely recurrent, distressing and intrusive thoughts (obsessions) and seemingly purposeless rigid and repetitive behaviors (compulsions). Furthermore, OCD patients present with notable cognitive rigidity and behavioral inflexibility. This is characterized by deficits in reward and punishment feedback processing which are regulated by dopaminergic and serotonergic neurotransmission. In addition, OCD causes remarkable distress and severely impairs almost every aspect of an individual’s life. Although chronic high-dose selective serotonin reuptake inhibitor (SSRI)2 intervention is regarded as the first-line pharmacological treatment for OCD, 40 – 60% of patients remain symptomatic and full remission is usually not achieved. Over the preceding decades, rodent models of OCD have helped us to further our understanding of the disorder and its treatment. However, these are characterized by noteworthy limitations for example, they are exceptionally time-consuming and expensive and have a low-throughput capacity. In this regard, zebrafish (Danio rerio) have emerged as an alternative framework for the pre-clinical study of neurobehavioral disorders. The most important advantages of applying zebrafish include 1) their broad homology to rodent and human neurobiology, presenting with almost fully conserved dopaminergic and serotonergic systems, 2) their highly social nature which enables them to shoal and seek out conspecifics (same species fish), 3) their ability to clearly distinguish between colors, which facilitates color-dependent learning, and 4) their sophisticated sensory, motor and motivational systems that are well-suited for experiments into associative learning. As such, the present investigation was conceptualized to provide a foundation for establishing a novel, high-throughput screening test for anti-compulsive drug action using zebrafish as a model organism by exploiting their natural reward-seeking behavior such as elevated motivational drive to engage in social interaction in a cue-reward contingency learning paradigm. Considering the current theories describing the roles of dopamine and serotonin in OCD, we aimed to induce compulsive-like persistence with the dopaminergic agonist, apomorphine, and further investigated if such persistence, if present, would be reversed by chronic escitalopram, an SSRI. Seven groups of zebrafish (n = 6 per group) were exposed for 24 days (1 hour per day) to either control (normal tank water), apomorphine (50 or 100 𝜇g/L), escitalopram (500 or 1000 𝜇g/L) or a combination 1 obsessive-compulsive disorder 2 selective serotonin reuptake inhibitor (A100/E500 or A100/E1000 𝜇g/L). Cue-reward learning was assessed over three phases i.e. Phase 1 (contingency learning), Phase 2 (dissociative testing), and Phase 3 (re-associative testing). We demonstrate that 1) sight of social conspecifics is an inadequate reinforcer of contingency learning under circumstances of motivational conflict, 2) dopaminergic and serotonergic intervention lessens the importance of an aversive stimulus, increasing the motivational valence of social reward, 3) while serotonergic intervention maintains reward-directed behavior, high-dose dopaminergic intervention bolsters cue-directed responses and 4) high-dose escitalopram reverses apomorphine-induced behavioral inflexibility. The results reported here are supportive of current dopamine-serotonin opponency theories and confirm that zebrafish may be a potentially useful species in which to emulate compulsive-like behaviors. Although compulsive-like persistence toward habitual, cue-directed behavior was not induced by either dose of apomorphine, fish exposed to high-dose apomorphine present with behavior more akin to behavioral inflexibility compared to their counterparts in all other exposure groups. This was reversed by chronic high, but not lower dose escitalopram, a finding that is supportive of current dopamine-serotonin opponency theory. The apparent aversion demonstrated by drug-naive subjects to the color red was unexpected and has complicated the interpretation of our results. Indeed, it is likely that the use of a more-preferred color in this population may have yielded a more robust result, a possibility that we will investigate in future. In conclusion, typical theories of neurotransmitter involvement in OCD1 for example imbalanced crosstalk between dopamine and serotonin amongst others, provides a useful background for investigating compulsive-like behaviors in animals. Not only do the findings presented here confirm the viability of zebrafish as a model species in which to study the neurobiological and cognitive processes underlying dopamine-serotonin interactions under circumstances of motivational conflict, it also provides valuable direction for future endeavors toward the development of a novel screening framework that is sensitive for anti-compulsive drug action. Masters

Cognitive flexibility, shown to be impaired in patients presenting with compulsions, is dependent on balanced dopaminergic and serotonergic interaction. Towards the development of a zebrafish (Danio rerio) screening test for anti-compulsive drug action, we manipulated social reward appraisal under different contexts by means of dopaminergic (apomorphine) and serotonergic (escitalopram) intervention. Seven groups of zebrafish (n = 6 per group) were exposed for 24 days (1 h per day) to either control (normal tank water), apomorphine (50 or 100 μg/L), escitalopram (500 or 1000 μg/L) or a combination (A100/E500 or A100/E1000 μg/L). Contextual reward appraisal was assessed over three phases i.e. Phase 1 (contingency association), Phase 2 (dissociative testing), and Phase 3 (re-associative testing). We demonstrate that 1) sight of social conspecifics is an inadequate motivational reinforcer under circumstances of motivational conflict, 2) dopaminergic and serotonergic intervention lessens the importance of an aversive stimulus, increasing the motivational valence of social reward, 3) while serotoninergic intervention maintains reward directed behavior, high-dose dopaminergic intervention bolsters cue-directed responses and 4) high-dose escitalopram reversed apomorphine-induced behavioral inflexibility. The results reported here are supportive of current dopamine-serotonin opponency theories and confirm the zebrafish as a potentially useful species in which to investigate compulsive-like behaviors.

While studies of human color vision have made enormous strides, an overarching rationale for the circular sense of color relationships generated by two classes of color opponent neurons and three cone types is still lacking. Here we suggest that color circularity, color opponency and trichromacy may have arisen, at least in part, because of the geometrical requirements needed to unambiguously distinguish all possible spectrally different regions on a plane.