Storage and erasure of behavioural experiences at the single neuron level.

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.

[The central pattern generators].

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.

Electrical activity of no-producing neuron depends on NO level.

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.

Effects of met-enkephalin on electrical coupling between identified neurons in the pulmonate snails, Helix and Lymnaea.

1. The effects of met-enkephalin on electrical coupling between molluscan neurons have been investigated using the isolated brains of Helix pomatia and Lymnaea stagnalis. 2. In the presence of both serotonin and met-enkephalin, non-rectifying electrical coupling is strongly facilitated between identified respiratory neurons in Helix, whilst coupling between putative, serotonin-containing, ciliomotoneurons in Lymnaea is facilitated by met-enkephalin alone. 3. Facilitation of coupling by met-enkephalin is weaker in the strongly coupled neurons, VD1/RPaD2 of Lymnaea. 4. These data suggest that met-enkephalin can modulate different groups of electrically coupled cells and may be involved in coordination of motor patterns.

Interaction of serotonin and leu-enkephalin on the habituating central neurons of Helix pomatia L. in situ and in vitro.

1. Habituating neurons (a, b and c) of Helix pomatia reacted to the serotonin (10(-5)-10(-4)M) with depolarization evoking oscillatory waves and burst firing at the range of -35 to -55 MP values. 2. Isolated habituating cells were hyperpolarized by serotonin and failed to generate membrane oscillation or bursting pattern. 3. Only the isolated habituating neurons reacted to the application of leu-enkephalin (10(-5)-10(-4)M) by depolarization. 4. Neither membrane oscillation nor burst firing were evoked by leu-enkephalin. 5. On the cells a, b and c leu-enkephalin modulated the serotonin effect through cyclic 3',5'-AMP system both in situ and in vitro. 6. The membrane oscillation and burst firing of the habituating cells are connected to the regulation of various rhythmic processes including pneumostoma movements.