PubMed · 197344
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J N van der Molen. 1977. Automatic bucking potential source.. https://doi.org/10.1007/bf02458004
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A two-lever choice paradigm with concurrent variable interval schedules of reward was used to measure the growth in the subjective magnitude of reward as a function of current, by finding the adjustment in the stimulating current required to offset a given difference in the rates at which two rewards were received. Increasing current by a factor of 2 increased subjective reward magnitude by a factor ranging from as little as 3 to as much as 4,000. This range was about as great between electrodes within one rat as between electrodes and rats. In the light of earlier findings regarding the equivalent effects of increments is current and pulse frequency, these large differences cannot readily be explained by differing fiber densities at the site of stimulation. It is suggested that the medial forebrain bundle terminates in more than one spatio-temporal integration mechanism. The magnitude of the spatio-temporally integrated effect of a barrage of action potentials in the reward-relevant axons depends on which subset of reward-relevant axons is excited by the stimulation.
The effects of caffeine (10 mM) on depolarization-activated, calcium-independent outward K+ currents were investigated in isolated rat ventricular myocytes, using whole-cell clamping. The external solution contained CoCl2 2 mM and the internal solution contained ethylene glycol-bis(-aminoethyl ether) N,N,N',N'-tetraacetic acid 10 mM. Caffeine decreased the peak amplitude of the total current and the sustained plateau current. Caffeine did not modify the steady state inactivation curve, which was fitted by two Boltzmann functions. Caffeine blocked the tetraethylammonium-sensitive slowly activating and inactivating outward current by 32% and the 4-aminopyridine-sensitive rapidly activating and inactivating transient outward current by 19%. Caffeine did not modify the inactivation rate or the time course of the recovery from inactivation of the transient current. Ryanodine 10 microM did not modify any of the current components and the effect of caffeine was not modified by ryanodine pretreatment. The phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine 100 microM, did not modify the depolarization-activated calcium-independent outward currents.
Increasing the impulse activity of crustacean neurons for a few days causes long-lasting changes in transmitter release, which are termed 'long-term adaptation' (LTA) in previous studies. Both the amount of transmitter released at the beginning of a stimulus train, and synaptic fatigue during repetitive stimulation, are reduced. The present study examines the dependence of these synaptic changes on the frequency and number of impulses used to elicit LTA. Fatigue resistance develops consistently when crayfish phasic motor neurons are stimulated for 3 days with as few as 9,000 impulses per day, and occurs in response either to low frequency stimulation (0.2 or 0.5 Hz), or to stimulation in short bursts at a moderate average frequency (2.5 Hz). In contrast, the reduction in initial transmitter release does not appear consistently when the frequency and number of impulses are both low (9,000 impulses per day delivered at 0.2 Hz), but does occur at the moderate stimulus frequency (2.5 Hz) and when a larger number of impulses (18,000) are delivered at a low frequency (0.5 Hz). The data suggest that the two changes in synaptic transmission that comprise LTA have different stimulus requirements.