Neurobiology of fish under altered gravity conditions

Spatial Expression of Otolith Matrix Protein-1 and Otolin-1 in Normally and Kinetotically Swimming Fish

Kinetosis (motion sickness) has been repeatedly shown to affect some fish of a given clutch following the transition from 1g to microgravity or from hypergravity to 1g. This susceptibility to kinetosis may be correlated with irregular inner ear otolith growth. Otoliths are mainly composed of calcium carbonate and matrix proteins, which play an important role in the process of otolith mineralization. Here, we examine the morphology of otoliths and the expression pattern of the major otolith proteins OMP-1 and otolin-1 in a series of hypergravity experiments. In the utricle, OMP-1 is present in centripetal (medial) and centrifugal (lateral) regions of the meshwork area. In the saccule, OMP-1 was expressed within a dorsal and a ventral narrow band of the meshwork area opposite to the periphery of the sulcus acusticus. In normal animals, the spatial expression pattern of OMP-1 reaches more posteriorly in the centrifugal aspect and is considerably broader in the centripetal portion of the utricle compared to kinetotic animals. However, otolin-1 was not expressed in the utricule. In the saccule, no differences were observed for either gene when comparing normal and kinetotically behaving fish. The difference in the utricular OMP-1 expression pattern between normally and kinetotically swimming fish indicates a different otolith morphology and thus a different geometry of the otoliths resting on the corresponding sensory maculae. As the utricle is the endorgan responsible for sensing gravity, the aberrant morphology of the utricular otoliths, based on OMP-1 expression, likely leads to the observed kinetotic behavior.

The motivational component of withdrawal in opiate addiction: role of associative learning and aversive memory in opiate addiction from a behavioral, anatomical and functional perspective

A major challenge in current drug addiction research is not only to understand the immediate effects of drugs of abuse on brain operations, but also to define at the behavioral and neural levels how cognitive, emotional and motivational processes interact with drug use in order to lead to this psychopathological state which defines addiction. It is now clear that factors other than the direct effects of drugs of abuse are able to powerfully affect drug-seeking and drug-taking behaviors. In former opiate addicts, re-exposure to environmental situations previously paired with withdrawal is able to induce strong craving episodes. It has been proposed that these conditioned stimuli could be strongly involved in precipitating relapse in drug-taking behavior by re-activating the neurobiological circuits which are engaged in an unconditioned way by the withdrawal state itself, leading to a powerful aversive state relieved by drug consumption renewal. In the present review, we provide evidence from a neuropsychopharmacological viewpoint that environmental situations previously paired with the opiate withdrawal syndrome might be able to maintain drug-seeking motivation. Using behavioral models which allow assessment of the aversive and motivational properties of opiate withdrawal both in the unconditioned and conditioned situations, we have recently investigated using extensive mapping the neurobiological correlates which underlie acute withdrawal and the trace of its memory in the brain in terms of localization and neuronal population involved, with an anatomical and functional approach. Thus, on the basis of our results, and together with a number of data in the literature, we provide a functional model for the formation and retrieval of opiate withdrawal memories.