Dopamine Induces Optical Changes in the Cichlid Fish Lens

The crystalline lens in the cichlid fish Aequidens pulcher undergoes a transformation of its optical properties every dawn and dusk as the eye adapts to changes in light conditions. During dusk the transformation result in an increase of the refractive power in the lens cortex, the outermost 40 percent. The change is thought to match the optical properties of the lens to the requirements of the retina. Using a short term in vitro lens culturing system together with optical measurements we here present data that confirm that the optical properties of the lens can change within hours and that dopamine influences the optical properties of the lens. Dopamine yields dose-dependent decrease of the refractive power in the lens cortex. The D1-agonist SKF-38393 induces a similar decrease of the refractive power in the cortex, while the D2-agonist quinpirole has no effect. The effect of dopamine can be blocked by using the D1-antagonist SCH 23390. Our results suggest that dopamine alone could be responsible for the light/dark adaptive optical changes in the lens, but the involvement of other signaling substances cannot be ruled out

Dogs can sense weak thermal radiation

The dog rhinarium (naked and often moist skin on the nose-tip) is prominent and richly innervated, suggesting a sensory function. Compared to nose-tips of herbivorous artio- and perissodactyla, carnivoran rhinaria are considerably colder. We hypothesized that this coldness makes the dog rhinarium particularly sensitive to radiating heat. We trained three dogs to distinguish between two distant objects based on radiating heat; the neutral object was about ambient temperature, the warm object was about the same surface temperature as a furry mammal. In addition, we employed functional magnetic resonance imaging on 13 awake dogs, comparing the responses to heat stimuli of about the same temperatures as in the behavioural experiment. The warm stimulus elicited increased neural response in the left somatosensory association cortex. Our results demonstrate a hitherto undiscovered sensory modality in a carnivoran species

Synthetic smooth muscle in the outer blood plexus of the rhinarium skin of Lemur catta L.

The skin of the lemur nose tip (rhinarium) has arterioles in the outer vascular plexus that are endowed with an unusual coat of smooth muscle cells. Comparison with the arterioles of the same area in a number of unrelated mammalians shows that the lemur pattern is unique. The vascular smooth muscle cells belong to the synthetic type. The function of synthetic smooth muscles around the terminal vessels in the lemur rhinarium is unclear but may have additional functions beyond regulation of vessel diameter

Osmotic Concentration of Zebrafish (Danio rerio) Body Fluids is Lower in Larvae than in Adults

We intended to perform optical and structural measurements on larval zebrafish eyes at 5 days post fertilization, that is, the earliest age at which zebrafish show visually guided behavior. However, excised larval crystalline lenses deteriorated quickly if immersed in a medium that gives good results with adult lenses from a variety of fish species. We suspected that the larvae have body fluids of lower osmolality and tested a medium with 240 mOsm, which is 75% of the established adult value of 320 mOsm. The optical quality of freshly excised and immersed lenses was used to judge the osmotic matches. In addition, we tested how well the shape of the eye is preserved in fixatives of different osmolalities. In both cases, 240 mOsm produced the best results. Immersed lenses performed better and the fixed eyes had a more natural shape. Our findings indicate that zebrafish body fluids have lower osmolality in larvae than in adults. This is probably due to an unfavorable body surface-to-volume ratio and incompletely developed regulatory mechanisms. Body fluid osmolality deviating from the adult value has to be taken into account in optical and histological work

The effect of dopamine is abolished by a D1-antagonist.

<p>(A) ΔBCD curves from 11 lens pairs where one lens was treated with dopamine and the other lens remained untreated are compared with ΔBCD curves from 10 lens pairs where one lens was treated with dopamine and the other lens with dopamine and the D1-antagonist SCH 23390. The curves are similar, indicating that the D1-antagonist abolished the effect of dopamine in the lens. The curves represent the mean ΔBCDs from 21 animals (Control: n = 11, D1 antagonist: n = 10). (B) The max-ΔBCDs and standard deviation. Both groups were similar with no statistically significant difference between them. This indicates that the D1-antagonist abolished the effect of dopamine. There was no significant (n.s) difference between the two groups (n = 21).</p

Dopamine and a D1-agonist induce similar changes in lens refractive power.

<p>(A) Mean ΔBCD curves from 31 lens pairs where one lens was treated with dopamine, D1-agonist, or D2-agonist, as well as pairs where both lenses were untreated (control). Treatment with the D1-agonist SKF-38393 induced an effect similar to that of dopamine in that BCD values increased in the lens cortex, BEP 0.60–0.95. Both treatments thus reduced the refractive power in the cortex compared to untreated lenses. The D2-agonist quinpirole had no effect. The curves represent the mean ΔBCDs from 31 animals (Control: n = 8, D1: n = 7, D2: n = 7, D: n = 9). (B) Max-ΔBCD values and standard deviation in the control and treatment groups. There was no significant (n.s) difference between max-BCD values from dopamine and D1-agonist treatments or between the control and D2-agonist. ** = Significance level 0.01%, *** = significance level 0.001% (n = 31).</p

Short-term culturing of teleost crystalline lenses combined with high-resolution optical measurements

Culturing whole lenses is a frequently used method for studying regulatory events on the lens in controlled environments. The evaluation methods used often fall under two categories, molecular or optical. The main benefit from optical measurements is that they directly detect changes in the lens’ main function, i.e. refracting light. However, these measurements often have rather low resolution or yield results open for subjective interpretation. Here we present a short-term crystalline lens culturing technique combined with a high-resolution optical measuring method. There are two main advantages of using teleost lenses compared to mammalian lenses. Teleost tissue generally has a higher tolerance than mammalian tissue with regard to temperature and nutrient fluctuations. Teleost lenses are structurally more robust and can be excised from the eye without disturbing form or function. The technique is developed for short-term culturing (3 h), however, the lenses appear viable for at least 24 h and longer culturing may be possible. The technique is resistant to small variations in osmolarity and yields quantitative datasets for further analyses and statistical treatment