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Model neural networks and behavior

Determination of the dynamical structure of neural circuits--the general principles of how neural activity varies with time and manipulates information--is a prerequisite to understanding their computational function. Rhythmically active or oscillating neural circuits are particularly interesting dynamical structures, as rhythms and oscillations are a prominent feature of mammalian central nervous system electrophysiology. Coherent oscillations by networks of interneurons are observed in the vertebrate olfactory system and have recently been described in mammalian visual cortex. These interneuronal networks display oscillations in local field potential (LFP) and probability of producing action potentials that are highly correlated between subcircuits sharing the same stimulus features. Much less is known about the existence and importance of network oscillations in the higher centres of invertebrates. Here we report that a network of olfactory interneurons in the cerebral ganglion of the terrestrial mollusc Limax maximus also displays coherent oscillations in LFP which are modified by odour input. This dynamical structure could be central to the odour recognition and odour learning ability of Limax.

Odour-modulated collective network oscillations of olfactory interneurons in a terrestrial mollusc

The Biological Effects of Antidepressants on the Molluscs and Crustaceans: A Review

Oysters are permanently exposed to various microbes, and their defense system is continuously solicited to prevent accumulation of invading and pathogenic organisms. Therefore, impairment of the animal's defense system usually results in mass mortalities in cultured oyster stocks or increased bacterial loads in food products intended for human consumption. In the present study, experiments were conducted to examine the effects of stress on the juvenile oyster's resistance to the oyster pathogen Vibrio splendidus. Oysters (Crassostrea gigas) were challenged with a low dose of a pathogenic V. splendidus strain and subjected to a mechanical stress 3 days later. Both mortality and V. splendidus loads increased in stressed oysters, whereas they remained low in unstressed animals. Injection of noradrenaline or adrenocorticotropic hormone, two key components of the oyster neuroendocrine stress response system, also caused higher mortality and increased accumulation of V. splendidus in challenged oysters. These results suggest that the physiological changes imposed by stress, or stress hormones, influenced host-pathogen interactions in oysters and increased juvenile C. gigas vulnerability to Vibrio splendidus.

Stress and stress-induced neuroendocrine changes increase the susceptibility of juvenile oysters (Crassostrea gigas) to Vibrio splendidus.

The embryonic development of the catecholaminergic system of the pond snail, Lymnaea stagnalis, was investigated by using chromatographic and histochemical methods. High performance liquid chromatography suggested that dopamine was the only catecholamine present in significant concentrations throughout the embryonic development of Lymnaea. Dopamine first became detectable at about embryonic stage (E) 15 (15% of embryonic development) and then increased in amount during early development to reach about 120-140 fmol per animal by around E40. Dopamine content remained stable during mid-embryogenesis (E40-65), increased slowing for the next couple of days, and then increased rapidly to culminate at about 400 fmol per animal by hatching. The detection of aldehyde- and glyoxylate-induced fluorescence and of tyrosine hydroxylaselike immunoreactivity indicated that the first catecholaminergic cells appeared in the late trochophore or early veliger stage of embryonic development (E32-35). The paired perikarya of these transient apical catecholaminergic (TAC) neurons were located beneath the apical plate, remained outside of the central ganglia during embryogenesis, and no longer contained detectable catecholamines close to hatching. TAC neurons bore cilia on the ends of short processes that penetrated the overlying epithelium; their long processes branched repeatedly under the ciliated apical plate. Several smaller catecholaminergic cells first appeared in the anterior margin of the foot at a stage when the embryos began to metamorphose from the veliger form (E55). Similar bipolar cells later appeared in the tentacle and lips. The axons of all of these small peripheral cells projected centrally and terminated within the neuropil of different central ganglia. Central catecholaminergic neurons, including RPeD1, differentiated only after metamorphosis was complete (E75). Development of locomotor, respiratory, and feeding behaviors correlated with maturation of catecholaminergic neurons, as indicated by histology and chromatography.

Development of catecholaminergic neurons in the pond snail, Lymnaea stagnalis: I. Embryonic development of dopamine‐containing neurons and dopamine‐dependent behaviors

Neuronal perikarya of the procerebrum of Helix and Limax are generally naked and lie side by side. The cell mass contains large numbers of axosomatic and axoaxonic synapses represented by boutons of two types; dense core vesicles (800–1200 A, in diameter) being characteristic of the first type and clusters of electron lucent vesicles (500–800 A) of the second. Endings of the two types occur also in the terminal mass of the neuropile while the internal mass contains peculiar axonal enlargements filled with fine twisted tubuli. Axons containing dense core vesicles seem to correspond to varicose monoaminergic fibres detected by a fluorescent histochemical method.

The fine structure of the procerebrum of pulmonate molluscs, Helix and Limax.

Dopamine antagonists which affect the ergometrine-sensitive type of dopamine receptors produce characteristic motor disorders in a land snail,Helix pomatia L.

Effects of dopamine antagonists on snail locomotion

Es wurde gezeigt, dass im Procerebrum der Gastropoden axosomatische Synapsen von 2 Typen vorkommen. Diese Befunde sind ungewohnlich, da axosomatische Synapsen in anderen Teilen des Zentralnervensystems nicht existieren.

Axo-somatic synapses in procerebrum of gastropoda.

Каждая клетка исследованной группы #x043E;тсылает по аксонной ветви к периферическому депо и в синаптический нейропиль, а таюке имеет множество соматических отростков. Клетки получают богатый синаптический приток, тормозятся ацетилхолином и дофамином и стимулируются серотонином.

Study of neurosecretory cells of Helix pomatia by intracellular dye injection.

In the ascidian endostyle, all fluorescence due to serotonin is localized in the peripheral, iodine-binding area of the endostylar epithelium, which is homologous to the vertebrate thyroid. The amine appears to be stored in granule-containing cells which may correspond to the vertebrate calcitocytes.

D. A. Sakharov

Papers

The fine structure of the procerebrum of pulmonate molluscs, Helix and Limax.

Effects of dopamine antagonists on snail locomotion

Axo-somatic synapses in procerebrum of gastropoda.

Study of neurosecretory cells of Helix pomatia by intracellular dye injection.

Serotonin-containing cells in the ascidian endostyle