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  • 1
    Electronic Resource
    Electronic Resource
    A persistent sodium current contributes to oscillatory activity in heart interneurons of the medicinal leech (1994)
    Springer
    Journal of comparative physiology 175 (1994), S. 781-789 
    Details
    ISSN: 1432-1351
    Keywords: Tetraethylammonium ; Single-electrode voltage-clamp ; Plateaus ; Leech ; Oscillation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract 1. Normal activity in bilateral pairs of heart interneurons, from ganglia 3 or 4, in the medicinal leech (Hirudo medicinalis) is antiphasic due to their reciprocally inhibitory connections. However, Ca+-free Co+-containing salines lead to synchronous oscillations in these neurons. 2. Internal TEA+ allows expression of full plateaus during Co++ induced oscillations in heart interneurons; these plateaus are not blocked by Cs+. Similar plateaus are also observed with internal TEA+ alone, but under these conditions activity in heart interneurons from ganglia 3 or 4 is antiphasic. 3. Plateaus in heart interneurons induced by Co++ and internal TEA+ involve a conductance increase. 4. A voltage-dependent inward current, IP, showing little inactivation, was isolated using single-electrode voltageclamp in heart interneurons. This current is carried at least in part by Na+; the current is reduced when external Na+ is reduced and is carried by Li+ when substituted for Na+. 5. Calcium channel blockers such as La3+ and Co++ block neither the TEA+ induced plateaus nor IP, suggesting that Na+ is not using Ca++ channels. Moreover, IP is enhanced by Ca++-free Co++-containing salines. Thus, IP is correlated with the TEA+- and Co++-induced plateau behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00191850
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  • 2
    Electronic Resource
    Electronic Resource
    Motor pattern switching in the heartbeat pattern generator of the medicinal leech: membrane properties and lack of synaptic interaction in switch interneurons (1999)
    Springer
    Journal of comparative physiology 184 (1999), S. 311-324 
    Details
    ISSN: 1432-1351
    Keywords: Key words Motor pattern switching ; Dynamic clamp ; Single-electrode voltage clamp ; Leech
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The motor program for heartbeat in the medicinal leech is produced by a central pattern generator that regularly switches between two alternative coordination states. A pair of switch heart interneurons reciprocally alternate between rhythmically active and inactive states to effect these switches. During spontaneous switches in the activity state of switch interneurons, there was no correlation between the duration of a particular activity state and beat period, indicating that the timing networks for the switch cycle and the beat cycle are relatively independent. Simultaneous recordings from two switch heart interneurons showed that a perturbation in the electrical activity of one does not influence switching of the other and that there is no synaptic interaction between them. Using voltage clamp, we characterized an L-like Ca2+ current (measured as Ba2+ currents), inactivating and non-inactivating K+ currents, a persistent Na+ current, and a hyperpolarization-activated inward current in switch interneurons. Dynamic clamp experiments show that “subtraction” of an artificial switch leak conductance (described previously by Gramoll et al. 1994) from a switch interneuron when it is in the inactive state causes it to display activity associated with the active state. We discuss how the switch leak conductance may interact with the intrinsic currents of switch interneurons to control their activity state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003590050329
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