Pascal Steullet

Redox Dysregulation Affects the Ventral But Not Dorsal Hippocampus: Impairment of Parvalbumin Neurons, Gamma Oscillations, and Related Behaviors

Elevated oxidative stress and alteration in antioxidant systems, including glutathione (GSH) decrease, are observed in schizophrenia. Genetic and functional data indicate that impaired GSH synthesis represents a susceptibility factor for the disorder. Here, we show that a genetically compromised GSH synthesis affects the morphological and functional integrity of hippocampal parvalbumin-immunoreactive (PV-IR) interneurons, known to be affected in schizophrenia. A GSH deficit causes a selective decrease of PV-IR interneurons in CA3 and dendate gyrus (DG) of the ventral but not dorsal hippocampus and a concomitant reduction of β/γ oscillations. Impairment of PV-IR interneurons emerges at the end of adolescence/early adulthood as oxidative stress increases or cumulates selectively in CA3 and DG of the ventral hippocampus. Such redox dysregulation alters stress and emotion-related behaviors but leaves spatial abilities intact, indicating functional disruption of the ventral but not dorsal hippocampus. Thus, a GSH deficit affects PV-IR interneurons integrity and neuronal synchrony in a region- and time-specific manner, leading to behavioral phenotypes related to psychiatric disorders.

The sensory basis of feeding behaviour in the Caribbean spiny lobster, Panulirus argus

A complex nervous system enables spiny lobsters to have a rich behavioural repertoire. The present paper discusses the ways in which the sensory systems of the Caribbean spiny lobster, Panulirus argus, particularly its chemosensory systems, are involved in feeding behaviour. It addresses the neural mechanisms of three aspects of their food-finding ability: detection, identification, and discrimination of natural food odours; the effect of learning on responses to food odours; the mechanisms by which spiny lobsters orient to odours from a distance under natural flow conditions. It demonstrates that the olfactory organ of spiny lobsters might use acrossneuron response patterns in discriminating odour quality; that the hedonic value of food can be modified by experience, including associative and nonassociative conditioning; that spiny lobsters can readily orient to distant odour sources; and that both chemo- and mechanosensory antennular input are important in this behaviour. Either aesthetasc or nonaesthetasc chemosensory pathways can be used in identifying odour quality, mediating learned behaviours, and permitting orientation to the source of distant odours. Studying the neuroethology of feeding behaviour helps us understand how spiny lobsters are adapted to living in complex and variable environments.

Functional units of a compound nose: Aesthetasc sensilla house similar populations of olfactory receptor neurons on the crustacean antennule

The lateral flagellum of the antennule of the spiny lobster Panulirus argus houses more than 1,000 morphologically similar olfactory sensilla, called aesthetascs. By using a high‐resolution activity labeling technique that depends on entry of agmatine into olfactory receptor neurons (ORNs) through cation channels during odor stimulation, we examined the distribution of different functional types of ORNs within and across mature aesthetascs. A significant number of ORNs in mature aesthetascs are labeled with agmatine during stimulation by single odorants, including adenosine‐5`‐monophosphate, ammonium chloride, cysteine, glycine, proline, and taurine. The percentage of ORNs per aesthetasc that was agmatine labeled during odor stimulation averaged 0.5–1.6% for single compounds and 4.6% for a 33‐component mimic of oyster tissue. For most antennules and antennular regions studied, the percentage of agmatine‐labeled ORNs by stimulation with single or complex odorants was statistically homogeneous across most or all aesthetascs. The extent of heterogeneity among mature aesthetascs was correlated with their age: extensive heterogeneity was observed only in the distal part of the flagellum containing the oldest aesthetascs and their ORNs. Thus, it appears that over most of the length of the aesthetasc‐bearing region of the lateral flagellum, different and distinct functional types of aesthetascs do not exist. Rather, aesthetascs appear to be repetitive morphological and functional units in olfactory coding. However, because odor sensitivity of ORNs can change with the age of an aesthetasc, some development‐related functional heterogeneity exists among aesthetascs. J. Comp. Neurol. 418:270–280, 2000.

Why Do Animals Have So Many Receptors? The Role of Multiple Chemosensors in Animal Perception

Many animals have an abundance and diverse assortment of peripheral sensors, both across and within sensory modalities. Multiple sensors offer many functional advantages to an animal’s ability to perceive and respond to environmental signals. Advantages include extending the ability to detect and determine the spatial distribution of stimuli, improving the range and accuracy of discrimination among stimuli of different types and intensities, increasing behavioral sensitivity to stimuli, ensuring continued sensory capabilities when the probability of damage or other loss of function to some sensors is high, maintaining sensory function over the entire sensory surface during development and growth, and increasing the richness of behavioral output to sensory stimulation. In this paper, we use the crustacean chemosensory system as the primary example to discuss these functions of multiple sensors. These principles may be applicable to the function of autonomous robots and should be considered in their design.

Identification of vertebrate volatiles stimulating olfactory receptors on tarsus I of the tick Amblyomma variegatum Fabricius (Ixodidae)

Gas chromatography-coupled electrophysiological recordings (GC-EL) from olfactory sensilla within the capsule of Hallers organ of the tick Amblyomma variegatum indicate the presence of a number of stimulants in rabbit and bovine odours, and in steer skin wash. Some of these stimulants were fully identified by gas chromatography-mass spectrometry analysis and by matching electrophysiological activity of synthetic analogues as: 1) hexanal, 2-heptenal, nonanal, furfural, benzaldehyde, and 2-hydroxybenzaldehyde (in all extracts); 2) heptanal, 2-, 3-, and 4-methylbenzaldehyde, and γ-valerolactone (only in bovine and rabbit odour). Careful examination of the electrophysiological responses permit characterization of 6 receptor types: 1) a benzaldehyde receptor, 2) a 2-hydroxybenzaldehyde receptor, 3) three types of receptors responding differently to aliphatic aldehydes, and 4) a lactone receptor.

Perception of breath components by the tropical bont tick, Amblyomma variegatum Fabricius (Ixodidae)

SummaryWall-pore olfactory sensilla located in the capsule of Hallers organ on the tarsus of Amblyomma variegatum ticks bear cells responding to vertebrate breath: one of these sensilla contains a CO2-excited receptor and a second sensillum has a CO2- inhibited receptor. Each of these antagonistic CO2-receptors, which display typical phasic-tonic responses, monitors a different CO2-concentration range. The CO2-inhibited receptor is very sensitive to small concentration changes between 0 and ca. 0.2%, but variations of 0.01% around ambient (ca. 0.04%) induce the strongest frequency modulation of this receptor. An increase of just 0.001–0.002% (10–20 ppm) above a zero CO2-level already inhibits this receptor. By contrast, the CO2-excited receptor is not so sensitive to small CO2 shifts around ambient, but best monitors changes in CO2 concentrations above 0.1%. This receptor is characterized by a steep dose-response curve and a fast inactivation even at high CO2-concentrations (>2%). In a wind-tunnel, Amblyomma variegatum is activated from the resting state and attracted by CO2 concentrations of 0.04 to ca. 1%, which corresponds to the sensitivity range of its CO2-receptors. The task of perceiving the whole concentration range to which this tick is attracted would thus appear to be divided between two receptors, one sensitive to small changes around ambient and the other sensitive to the higher concentrations normally encountered when approaching a vertebrate host.

High-resolution functional labeling of vertebrate and invertebrate olfactory receptor neurons using agmatine, a channel-permeant cation

Methods are described for odor-stimulated labeling of olfactory receptor neurons (ORNs) of the freshwater zebrafish Danio rerio and the marine spiny lobster Panulirus argus. Permeation of a cationic molecule, 1-amino-4-guanidobutane ( = agmatine, AGB), through ion channels following odor stimulation, and its detection by an anti-AGB antibody, allow labeling of odor-stimulated ORNs. Parameters adjusted to optimize activity-dependent labeling included labeling medium ionic composition, stimulation times, and AGB concentration. For lobsters, 7% of ORNs were labeled by a complex odor, oyster mixture, under optimal conditions, which was stimulation for 5 s per min for 60 min with 20 mM AGB in artificial seawater with reduced sodium and calcium concentrations. AGB was a weak odorant for lobsters; it elicited only a small electrophysiological response from ORNs and labeled < 1% of the ORNs during stimulation with AGB in the absence of odors. For the zebrafish, stimulation for 10 s per min for 10 min with 5 mM AGB plus odorant (L-glutamine) in fish Ringers solution was the optimal labeling condition, resulting in labeling of 17% of the olfactory epithelial area. Approximately 6% of the olfactory epithelium was labeled during stimulation with a control stimulus, AGB alone. This labeling by AGB alone suggests it is an olfactory stimulus for zebrafish; a conclusion supported by electrophysiological recordings. We used electrophysiological assays and channel blockers to examine, for each species, potential ion channels for entry of AGB into ORNs. These results show that AGB can be used as an activity-dependent label for chemoreceptor neurons of diverse phyla living in a range of environmental conditions.

Coding of blend ratios of binary mixtures by olfactory neurons in the Florida spiny lobster, Panulirus argus.

Abstract The aim of this study was to investigate quality coding of blend ratios of binary mixtures by olfactory receptor cells in the spiny lobster. Three odorants (adenosine-5′-monophosphate, l-glutamate, and taurine) at 0.1–100 μmolu200a·u200al−1 and seven blend ratios of each of their binary mixtures at a total concentration of 100 μmolu200a·u200al−1 were used. The olfactory cells recorded (nu2009=u200948) evoked across-neuron patterns for single odorants that were well separated from each other. Across-neuron patterns varied with stimulus concentration but less than with stimulus type. Blend ratios of the three mixtures evoked across-neuron patterns that were orderly placed within a continuum between those elicited by the components. Mixture interactions, defined as a lack of independent effects by a mixtures components, occurred in 25, 24 and 37% of responses to blend ratios of glutamate/taurine, adenosine-5′-monophosphate/taurine, and glutamate/adenosine-5′-monophosphate, respectively. These mixture interactions did not have a large enough effect on the across-neuron patterns for the mixtures such they would be novel relative to those of the single components. These results suggest that despite mixture interactions the quality of individual compounds is not lost when mixed. This corroborates behavioral studies showing that spiny lobsters have the ability to elementally process odor mixtures.

Structural plasticity in the olfactory system of adult spiny lobsters: postembryonic development permits life-long growth, turnover, and regeneration

Caribbean spiny lobsters (Panulirus argus) rely on their sense of olfaction for many behaviours. Growth of their olfactory systems, and maintenance of olfactory function, is ensured by structural change that occurs continuously throughout life. In this paper, we review recent studies on postembryonic development in the olfactory system of P. argus and several other decapod species. Major structural change occurs in both the peripheral and central olfactory systems; it includes addition and loss of olfactory receptor neurons (ORNs), aesthetasc and other sensilla, and interneurons associated with the olfactory lobes of the brain. From these studies it is clear that continuous growth and turnover of olfactory tissue is a normal process in decapod crustaceans. In addition, we describe for the first time mechanisms that enable the peripheral olfactory system of spiny lobsters to regenerate after injury. We monitored the regeneration of olfactory tissue usingin vivo incorporation of the cell proliferation marker 5- bromo-2′-deoxyuridine (BrdU). Our results show that regeneration after partial antennular amputation, which reduces the length of the antennule and thereby the number of ORNs, occurs as a result of upregulation of the normal mode of ORN addition and down-regulation of loss. In contrast, localized injury to aesthetasc sensilla, which causes the associated ORNs to degenerate but does not reduce antennular length, is followed by local regeneration of olfactory tissue.

Comparison of turnover in the olfactory organ of early juvenile stage and adult Caribbean spiny lobsters.

Proliferation and turnover of neurons occurs in the olfactory systems of many animals. In this study, we examined developmental changes in turnover in the olfactory organ of the Caribbean spiny lobster Panulirus argus by examining two life-history stages-early juveniles and young adults. Turnover was compared using external morphology of the olfactory organ before and after molting to determine addition and loss of aesthetascs and other chemosensilla, and BrdU labeling to identify newly proliferated cells. The number of olfactory receptor neurons (ORNs) innervating each aesthetasc increased only slightly over development, but there was a net increase of olfactory sensory units (i.e. aesthetascs and their ORNs) at each molt. This increase was similar in early juveniles and young adults when expressed as absolute number of ORNs neurons but greater in early juveniles when expressed as a proportion of existing ORNs. The net increase in olfactory sensory units in early juveniles is due solely to addition, since virtually no aesthetascs are lost. In contrast, the net increase in olfactory sensory units in adults reflects addition of new units accompanied by considerable loss of old units. These developmental changes result in expansive enlargement of the olfactory organ without turnover in early juveniles, and a more modest growth combined with continuous turnover and replenishment of ORNs in adults.