Carlo Musio

Photobehaviour of Hydra (Cnidaria, Hydrozoa) and correlated mechanisms: a case of extraocular photosensitivity.

The morpho-functional organization correlated to photosensitivity in Cnidaria is that of ocelli and extraocular photoreception. Several examples of the second type of organization are reported. The photosensitivity of the cnidarian Hydra is of the extraocular (neural or dermal) type. The effects of photic stimulation (applied according to various experimental protocols: steady condition; step stimulus; single, twin, or repetitive pulses; different polarities and chromaticities of steady, step and pulse stimulation and different phases of pulse application) on the modulation of various bioelectric events linked to the periodic behaviour of the animal are reviewed. The mechanisms correlated with the photobehaviour of Hydra, as well as the problems still open on the molecular mechanisms of phototransduction, are discussed.

The Neural Net of Hydra and the Modulation of Its Periodic Activity

One of the main problems in the cybernetic approach to the nervous system is that of dealing with the processing of the information coming from the outside environment. This information is furnished in order to shape the behavioural activity of an organism. The problem is faced when considering the information processing of all organisms of the animal kingdom, from the more simple ones to the higher cognitive processes of man. The first organism of the zoological scale in which a nervous system is encountered is Hydra, a freshwater Cnidarian. In the organisms of the lower phylum Porifera, isolated neuron cells are scattered, not interconnected in a system, and act as local input-output units.

The photobiology of Hydra's periodic activity

Hydra’s response to a light pulse is a phase shift of the state of bioelectric activity correlated with the periodic shortening-elongation behaviour. The direction and absolute value of a phase shift depend on intensity, direction, application phase (along the periodic activity state), and wavelength of the light pulse. Repetitive pulses entrain the behavioural cycle. The period of the behavioural cycle depends on intensity and wavelength of steady background illumination; however, the light effect is not exerted isotropically along all the phases of the behavioural cycle. Inferences are drawn on light influence on the behaviour pacemaking mechanism. By using polyclonal antibodies against squid rhodopsin, an opsin-like protein has been identified in the ectodermal layer, presumably in sensory cells.

EXPLAN — a programming language for complex visual stimuli presentation

Visual cognition research requires the flexible use of structured spatial patterns, characterized by various space and time parameters, which may be administered as visual stimuli. Dealing with this kind of study, we developed a special-purpose programming language and implemented a compiler to build executable programs. The language allows the presentation of stimuli, their space coordinates, persistency values, sequence, kinematic parameters, space-time proximity with other visual stimuli, determination of their modification according to external interaction, generation of subliminal stimuli, monitoring of different subject reactions, automatic reporting of stimulus presentation, and reaction monitoring. Such a language has been successfully utilized in a visual perception research.

Nitric oxide signaling pathways at neural level in invertebrates: Functional implications in cnidarians

Nitric oxide (NO) is a small molecule with unconventional properties. It is found in organisms throughout the phylogenetic scale, from fungi to mammals, in which it acts as an intercellular messenger of main physiological events, or even as an intracellular messenger in invertebrates. In both vertebrates and invertebrates, NO is involved in many processes, regulated in part by cyclic guanosine monophosphate (cGMP), and reacts with different oxygen molecular species. The presence of NO in the early-diverging metazoan phylum of Cnidaria, of which Hydra represents the first known species having a nervous system, supports a role of this molecule as an ancestral neural messenger with physiological roles that remain to be largely elucidated. Therefore, our novel findings on the presence of NO in Hydra are here integrated in such a comparative frame.

Non-linearity of the interactions between bottom-up and top-down signals in multistable visual perception

SummaryBoth bottom-up sensory information and top-down influences contribute to the perception processes. We studied the perceptual alternations of a multistable ambiguous pattern. We observed that it is possible to interfere on the process of the perception alternance by means of subliminal visual stimuli, which either contrast or second the previous perception. We investigated also the effect of the top-down volitional factor on the perceptual alternation. By using a combination of such top-down factor and bottom-up stimulation, we ascertained that a non-linear type of interaction occurs between the two above factors.

Molecular and functional diversity of visual pigments: clues from the photosensitive opsin–like proteins of the animal model Hydra

The primary event of vision is the absorption of photons by photosensitive pigments, which triggers the transduction process producing the visual excitation. Although animal eyes and eyeless photoreceptive systems developed along several levels of molecular, morphological and functional complexity, image–forming rhodopsin family appears ubiquous along visual systems. Moreover, all Metazoa have supplementary extraocular photoreceptors that regulate their temporal physiology. The investigation of novel non-visual photopigments exerting extraretinal photoreception is a challenging field in vision research. To study molecular and functional differences between these pigment families, we propose the cnidarian Hydra, the first metazoan owning a nervous system, as a powerful tool of investigation. Hydra shows only an extraocular photoreception lacking classic visual structures. Our findings provide the first evidence in a phylogenetically old species of both image– and non–image–forming opsins, giving new insights on the molecular biology of Hydra photoreception and on comparative physiology of visual pigments.

Application of the patch‐clamp technique to photoreceptor cells of the crayfish Orconectes limosus

Abstract This paper describes a method to obtain isolated photoreceptors by means of enzymatic and mechanical dissociation of the whole retina of Orconectes limosus and the application of patch‐clamp technique to these dissociated ommatidia. Several gigaseals and single‐channel currents were recorded, demonstrating the validity and suitability of the experimental protocol. The data reported provide a new element in the ≪single photoreceptor approach≫ to the study of phototransduction mechanisms in invertebrates. These results add another animal model to the few currently described in literature, in which the application of gigaseal techniques to isolated cells has proved useful in the study of ion channels gating.