Light-dark decision making in snails: Do preceding light conditions matter?

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.

Frequency tuning of individual auditory receptors in female mosquitoes (Diptera, Culicidae).

The acoustic sensory organs in mosquitoes (Johnston organs) have been thoroughly studied; yet, to date, no data are available on the individual tuning properties of the numerous receptors that convert sound-induced vibrations into electrical signals. All previous measurements of frequency tuning in mosquitoes have been based on the acoustically evoked field potentials recorded from the entire Johnston organ. Here, we present evidence that individual receptors have various frequency tunings and that differently tuned receptors are unequally represented within the Johnston organ. We devised a positive feedback stimulation paradigm as a new and effective approach to test individual receptor properties. Alongside the glass microelectrode technique, the positive feedback stimulation paradigm has allowed us to obtain data on receptor tuning in females from three mosquito species: Anopheles messeae, Aedes excrucians and Culex pipiens pipiens. The existence of individually tuned auditory receptors implies that frequency analysis in mosquitoes may be possible.

[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.

The dependence of behavioral auditory thresholds on the delay of echo-like signals in noctuid moths (lepidoptera, noctuidae).

The auditory system of noctuoid moths capable to respond to ultrasounds has long been a model for anti-predator studies in neuroethology. Many moths avoid hunting bats by listening for their echolocation calls and taking evasive manoeuvres to escape predation. Besides these flight defences, certain tiger moths (Arctiidae) emit high-frequency clicks to jam the echolocator of an attacking bat. Another suggested function for ultrasonic audition in moths along with their capability to emit loud ultrasonic clicks was pulse echolocation. However, it seemed difficult to arrange sufficient temporal resolution in a simple invertebrate auditory system. Here we present an evidence of moth's capability to perceive an echo following its own click with a very short delay. The behavioral responses of moths to the acoustic pulses imitating echoes of their own clicks were investigated under conditions of tethered flight. It has been found that such echo-like stimulation evokes an increase in average emission rate of own acoustic signals in moths. Auditory thresholds were measured in two noctuid species (Enargia paleacea Esp. and Blepharita satura Schiff.) at stimulus delays 0.2, 0.3, 0.5 and 1 ms in relation to the respective moth clicks. Our findings reveal the ability of these moths to perceive echoes of their own signals, thus demonstrating potential possibility for use of pulse echolocation.

Higher-order control of the feeding network in Lymnaea.

A novel excitatory higher-order input (named Input-HO) to the feeding network of the pond snail, Lymnaea stagnalis, as well as a reliable procedure that makes it possible to initiate and maintain the Input-HO, are described. The Input-HO is primarily targeted to two bilaterally symmetrical pairs of extrabuccal projecting interneurons, the serotonergic Cerebral Giant Cells (CGCs or C1) and FMRFamidergic Pleural-Buccal cells (PlBs). Judging from the results of transection experiments, Input-HO originates in the paired cerebral ganglia where its left and right sources coexist. These sources discharge independently or, sometimes, one after the other. Both inputs project to the ipsilateral CGC/PlB only. In turn, the activity of PlB decreases the frequency of Input-HO bouts. We suggest that the Input-HO represents a prominent part of the mechanism controlling feeding behavior in Lymnaea.

Monitoring of neuroactive factors released from a pattern-generating network.

To detect neuroactive factors in biological fluids, we have previously elaborated a moveable biosensor, the preparation of isolated neuron penetrated with recording microelectrode. Here, we report that, in the pond snail, signals emanated from a central pattern generator (CPG) for feeding and detected by such biosensor correspond to long-term changes in motor output of the CPG as recorded from buccal nerves. The results suggest that combined recording from motor nerves, neurons in situ and the neuron-based biosensors may be a useful tool in studies of the mechanisms underlying network organisation.

[Comparative study of the rod and cone contributions to the generation of b-wave ERG and tectal evoked potential in the dark-adapted carp].

Amplitudes and peak latencies as functions of wave length and monochromatic light intensity were investigated for b-wave ERG and tectal evoked potentials (EP) in the dark-adapted carp (Cyprinus carpio L). It was found, that independently of light intensity b-wave action spectra had one maximum in the medium wave band, corresponding to rod sensitivity area. For tectal EP, similar action spectra with maximum in the middle-wave were seen at low light intensity only. The b-wave amplitude growth was significant for the whole band of light intensities, and these changes were accompanied with a slight decrease in peak latency (to 50-100 ms). Tectal EP amplitude increased when low-intensity light was changed for medium intensity light and did not considerably increase to brighter light stimuli. However, tectal EP time latency significantly decreased (to 100-200 ms) during light intensity increasing. This differences show that retinal rod system, which in responsible for ERG b-wave in darkness, is not a key factor in the generation of tectal EP.

[Retransmission of echo-like signals: methods and results of studies on nocturnal moths (Insecta)].

Studies of capability to echolocate in nocturnal moths using the method of echo-signal retransmission are described in detail. During retransmission the insect was presented not with the echo from some real object but with electronically generated echo-like signal which appears following the certain delay after insect's own acoustic signal. In that way the artificial echo from non-existent obstacle is produced. In the current study the delay was set to 0.5 ms that corresponds to a distance of about 8 cm from obstacle. At the same time there was no any single movement of any object near the flying insect therefore the activities of sensory systems other than auditory did not cause systematical influence on results obtained. Noctuid moths (Noctuidae, Lepidoptera) are acoustically active insects. They are capable of producing ultrasonic clicks during flight. The most typical response of a moth to the retransmission of echo-like stimuli is an activation of own clicks emission that is often accompanied with rise in click amplitude. Using the activation of emission as a criterion of moth's response to the echo-like stimulation we measured echolocational thresholds in three species: Amphipyra pyramidea (36 dB SPL), Enargia paleacea (31 dB SPL) and Blepharita satura (26 dB SPL). The ability to echolocate was also demonstrated in 20 species of subfamilies Catocalinae, Amphipyrinae, Cuculliinae, Hadeninae, Noctuinae, Heliothinae.

Phasic coordination between locomotor and respiratory rhythms in Lymnaea. Real behavior and computer simulation.

In the pond snail Lymnaea stagnalis, a firm phase-locked coupling of pneumostome movements to the locomotor cycle was observed during terrestrial locomotion, thus demonstrating that the coordination between locomotor and respiratory rhythms is a natural behavioral event in this animal. The results of computational modelling suggest a possible scheme of coordination between these motor rhythms which is based on inhibitory projection from the central pattern generator for locomotion to that for respiration. These findings allow the neuronal mechanisms underlying coordination of two rhythmic behaviors to be investigated.