Multiphasic On/Off Pheromone Signalling in Moths as Neural Correlates of a Search Strategy

Insects and robots searching for odour sources in turbulent plumes face the same problem: the random nature of mixing causes fluctuations and intermittency in perception. Pheromone-tracking male moths appear to deal with discontinuous flows of information by surging upwind, upon sensing a pheromone patch, and casting crosswind, upon losing the plume. Using a combination of neurophysiological recordings, computational modelling and experiments with a cyborg, we propose a neuronal mechanism that promotes a behavioural switch between surge and casting. We show how multiphasic On/Off pheromone-sensitive neurons may guide action selection based on signalling presence or loss of the pheromone. A Hodgkin-Huxley-type neuron model with a small-conductance calcium-activated potassium (SK) channel reproduces physiological On/Off responses. Using this model as a command neuron and the antennae of tethered moths as pheromone sensors, we demonstrate the efficiency of multiphasic patterning in driving a robotic searcher toward the source. Taken together, our results suggest that multiphasic On/Off responses may mediate olfactory navigation and that SK channels may account for these responses.     

Reassessment of the vocal repertoire of a nest-building gladiator frog,Boana pardalis (Anura,Hylidae, Cophomantinae): implications for its diagnosis within the B. faber species group

In this study, we re-describe the advertisement and territorial calls of Boana pardalis, carry out an acoustic comparison between the studied species and the other congeners of the B. faber group, and report for the first time the tympanic amplexus for the studied species. The advertisement call of B. pardalis can be used to supplement its diagnosis in the B. faber group based on temporal call traits, e.g. emission rate and emission pattern, as well as the call envelope.     

Regulatory factors produced by lymphocytes. I. The occurrence of multiple alpha-lymphotoxins associated with ribonuclease activity.

Supernatant fluids of mitogen-activated human tonsil lymphocytes contain large amounts of a factor toxic to mouse L cells. This substance, with a m.w. of 80,000 +/- 5,000 daltons, is called alpha-lymphotoxin (alpha-LT), to differentiate it from another toxin elaborated by mitogen activated human blood lymphocytes, called beta-lymphotoxin (beta-LT), which differs from alpha-LT in size (45,000 +/- 5,000 daltons), antigenicity, and stability. Further purification of alpha-LT by sequential phosphocellulose and DEAE-cellulose chromatography and polyacrylamide gel electrophoresis (PAGE) identifies a series of cytotoxins differing in ion exchange characteristics and electrophoretic mobilities. The three PAGE fractions (PAGE Ia, Ib and II), recovered in 2, 4.6, and 21% yield from the starting serum-free culture supernatant, represent purifications of 24-, 24- and 1851-fold, respectively. Each cytotoxic fraction has a ribonuclease activity. Comparison of RNase and mouse L cell cytotoxic activities of the three alpha-LT fractions shows that both activities for all three fractions have a similar temperature stability pattern and that both are similarly inhibited by DNA, single strand forms better than double strands, by glycerol in 5 to 20% concentration, and by protein denaturing reagents. These observations suggest, but do not prove, that mouse L cell toxicity and RNase activity are mediated by the same substance, which appears to occur in multiple or isozymic forms.     

Interactions between Males of the Lizard Liolaemus tenuis: Roles of Familiarity and Memory

For territorial organisms, recognition of familiar individuals can reduce the frequency and intensity of aggressive encounters (‘dear enemy’ phenomenon), stabilize social systems, and reduce the cost of territory maintenance. Here, we investigated the behavioural events displayed during contests between familiar and unfamiliar individuals in the lizard Liolaemus tenuis (Liolaemidae), a species in which males are territorial. The behaviours recorded were attack, warning, evasion, and submission, and the latencies to the first aggressive (attack or warning) behaviour. Additionally, we assessed the ability of individuals to remember a familiar conspecific after a period without social interaction. Individual males reduced and delayed aggressive behaviour directed towards socially familiar individuals compared with unfamiliar ones. These results suggest that males distinguished between familiar and unfamiliar conspecific males and are in agreement with the ‘dear enemy’ phenomenon. Other behaviours were similar in the contests between familiar and unfamiliar individuals. Recognition of familiar conspecifics was lost after 20 d without social interactions. This may be relevant for interactions with floater males or with neighbours that lose their territory and subsequently attempt to fight for their ex‐neighbour's territory.     

A comparison of structure-activity relationships within alpha-MSH on melanophores of Anolis carolinensis and Rana pipiens

We have compared the structure-function relationship of the tridecapeptide alpha-melanocyte stimulating hormone (alpha-MSH) on the melanophores of the lizard Anolis carolinensis and the frog Rana pipiens by determining the melanosome-dispersing potency of 15 shorter peptide sequences and 8 substituted alpha-MSH analogues. Major differences were found between the lizard and the frog in their response to alpha-MSH peptide fragments and analogues. In Anolis, the sequence Ser-Tyr-Ser- is not as important for the pigmentary response as in Rana since alpha-MSH-(4-13) was nearly as potent (89%) as alpha-MSH-(1-13) (100%), whereas in Rana alpha-MSH-(4-13) potency was reduced to 7.5%. In addition, loss of potency due to removal of residues Pro and Val was more marked in Rana (alpha-MSH-(1-11) = 0.1%) than in Anolis (alpha-MSH-(1-11) = 1%), suggesting that this C-terminal sequence is necessary for pigmentary activity in the frog melanophore. These results together with those of other peptide fragments and analogues have led us to define the minimal pigmentary sequence of alpha-MSH as alpha-MSH-(4-12) in Anolis in contrast to alpha-MSH-(1-13) in Rana. This suggests that Anolis and Rana alpha-MSH receptors recognise different message amino acids of the alpha-MSH peptide sequence even though the final response (melanosome dispersion) is the same.     

Fluxes of h and k in corn roots : characterization and stoichiometries using ion-selective microelectrodes

We report here on an experimental system that utilizes ion-selective microelectrodes to measure the electrochemical potential gradients for H⁺ and K⁺ ions within the unstirred layer near the root surface of both intact 4-day-old corn seedlings and corn root segments. Analysis of the steady state H⁺ and K⁺ electrochemical potential gradients provided a simultaneous measure of the fluxes crossing a localized region of the root surface. Net K⁺ influx values obtained by this method were compared with unidirectional K⁺ (⁸⁶Rb⁺) influx kinetic data; at any particular K⁺ concentration, similar values were obtained by either technique. The ionspecific microelectrode system was then used to investigate the association between net H⁺ efflux and net K⁺ influx. Although the computed H⁺:K⁺ stoichiometry is dependent upon the choice of diffusion coefficients, the values obtained were extremely variable, and net K⁺ influx rarely appeared to be charge-balanced by H⁺ efflux. In contrast to earlier studies, we found the cortical membrane potential to be highly K⁺ sensitive within the micromolar K⁺ concentration range. Simultaneous measurements of membrane potential and K⁺ influx, as a function of K⁺ concentration, revealed similar K_m values for the depolarization of the potential (K_m 6-9 micromolar K⁺) and net K⁺ influx (K_m 4-7 micromolar K⁺). These data suggest that K⁺ may enter corn roots via a K⁺-H⁺ cotransport system rather than a K⁺/H⁺ antiporter.