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Although predictions from the past about the future have been of major interest to current neuroscience, how past and present behavioral experience interacts at the level of a single neuron remains largely unknown. Using the pond snail Lymnaea stagnalis we found that recent experience of terrestrial locomotion (exercise) results in a long-term increase in the firing rate of serotonergic pedal (PeA) neurons. Isolation from the CNS preserved the "memory" about previous motor activity in the neurons even after the animals rested for two hours in deep water after the exercise. In contrast, in the CNS, no difference in the firing rate between the control and "exercise-rested" (ER) neurons was seen. ER snails, when placed again on a surface to exercise, nevertheless showed faster locomotor arousal. The difference in the firing rate between the control and ER isolated neurons disappeared when the neurons were placed in the microenvironment of their home ganglia. It is likely that an increased content of dopamine in the CNS masks an increased excitation of PeA neurons after rest: the dopamine receptor antagonist sulpiride produced sustained excitation in PeA neurons from ER snails but not in the control. Therefore, our data suggest the involvement of two mechanisms in the interplay of past and present experiences at the cellular level: intrinsic neuronal changes in the biophysical properties of the cell membrane and extrinsic modulatory environment of the ganglia.

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We have recently demonstrated that preceding motor activity can facilitate decision-making not only in humans and mammals but also in molluscs.5 In the behavioral paradigm used, snails Lymnaea stagnalis were removed from their natural environment (water) and placed in a dry, asymmetrically lit arena from which they had to decide which way to go in order to reach an aquatic environment. One possible explanation of the observed effects of preceding motor activity was that it could affect the snail's memory of light conditions that corresponded to its previous aquatic habitat. Here we report experimental results discarding this hypothesis. We suggest that preceding intense locomotion is likely to facilitate decision-making by increasing the level of confidence.

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This study demonstrates that injection of the serotonin precursor 5-HTP causes substantial changes in the behavioral state, fighting behavior and ability to establish winner-loser relationships in male crickets (Gryllus bimaculatus). The characteristic features of 5-HTP-treated crickets include an elevated posture, enhanced general activity, longer duration of fighting, enhanced rival singing and a decreased ability to produce a clear fight loser. In addition, 5-HTP-treated males showed a slightly delayed latency to spread their mandibles, a decreased number of attacks and an equal potential to win in comparison to controls (physiological solution-treated males). The obtained results imply a significant role for serotonin in the regulation of social status-related behaviors in G. bimaculatus. Specifically, these data indicate that a decrease in serotonergic activity may be functionally important for the control of loser behavior and that some behavioral features of dominant male crickets are likely to be connected with the activation of the serotonergic system.

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The central pattern generator (CPG) is defined as a set of neurons involved in joint production of patterned motor output. The roundtable discussion on the CPG was a part of the 5th All-Russian Conference on Animal Behavior (Moscow, Nov. 21, 2012). The discussion centred on three core themes: 1) the mechanisms of the organization and reconfiguration of pattern generating neuronal ensembles, 2) extrapolations that extend the CPG concept beyond the motor systems, and 3) evolutionary and developmental aspects of CPG.

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NO-producing neuron exhibited an excitatory response to the decrease in NO concentration, which was induced by NO synthase inhibitor N-nitro-L-arginine or specific NO acceptor 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. Addition of NO donors to the medium inhibits neuronal activity. The excitatory effects of N-nitro-L-arginine and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide were preserved, while the inhibitory action of NO donors significantly decreased after isolation of the neuron. These findings indicate that NO regulates activity of these neurons by the negative feedback mechanism. This regulation includes the following complementary mechanisms: (1) endogenous mechanism of cell self-activation in response to the decrease in NO concentration; and (2) exogenous mechanism of cell-mediated inhibition in response to NO excess.

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We examined the effects of selective serotonin depletion and opioid ligands on social rank and related escape behavior of the cricket Gryllus bimaculatus. Establishment of social rank in a pair of males affected their escape reactions. Losers showed a lower and dominants a higher percentage of jumps in response to tactile cercal stimulation than before a fight. The serotonin-depleting drug alpha-methyltryptophan (AMTP) caused an activation of the escape reactivity in socially naive crickets. AMTP-treated animals also showed a lower ability to become dominants. With an initial 51.6+/- 3.6% of wins in the AMTP group, the percentage decreased to 26+/-1.6% on day 5 after injection. The opiate receptor antagonist naloxone affected fight and escape similarly as AMTP. In contrast to naloxone, the opioid agonist [d-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin decreased escape responsiveness to cercal stimulation in naive and subordinate crickets. We suggest that serotonergic and opioid systems are involved in the dominance induced depression of escape behavior.

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1. In hot plate experiments, the pulmonate land snail Cepaea nemoralis displays a biphasic passive/active avoidance behaviour composed of retraction and subsequent searching mediated by antagonistic muscular systems. The switch, between the behaviours, is under neuronal control. 2. Leu- and met-enkephalin, as well as FMRFamide-antiserum, attenuated the retraction response and potentiated the searching behaviour. Opposite effects were achieved by injection of antisera to the enkephalins. 3. Both retraction and searching behaviours were potentiated by 5-HT. Methysergide antagonized the effects of the enkephalins on the searching behaviour. 4. We conclude that endogenous opioids act antagonistic to FMRFamide in the neuronally controlled switch between passive and active avoidance behaviour.

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