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  • Title: CNS control over gill reflex behaviors in Aplysia: satiation causes an increase in the suppressive control in older but not young animals.
    Author: Lukowiak K.
    Journal: J Neurobiol; 1980 Nov; 11(6):591-611. PubMed ID: 7441242.
    Abstract:
    The CNS and PNS interact and form an integrated system which mediates adaptive gill withdrawal reflex behaviors evoked by tactile stimulation of the siphon. The CNS exerts suppressive and facilitatory control over the PNS in the mediation of these behaviors. It was found that in Aplysia the CNS's supressive control over the PNS was significantly greater than in nonsatiated control animals. In the controls, the evoked gill reflex met a mimimal response amplitute criterion with the CNS and PNS present, while in the satiated group the reflex did not meet this criterion. In the control group, the relflex amplitute and the subsequent habituation were the same following removal of the CNS, while in satiated animals the reflex amplitude was larger and the rate of habituation slower with only the PNS intact. Satiation had no effect on young Aplysia since CNS control was not yet operable. It is thus of prime importance to take the "state" of the preparation into consideration in the analysis of the neural mechanisms that underlie adaptive gill reflex behaviors. The gill withdrawal reflex and its subsequent habituation evoked by repeated tactile stimulation of the siphon in Aplysia has been studied extensively in an attempt to gain an understanding of the neuronal mechanisms that underlie adaptive behavior (Jacklet and Lukowiak, 1975; Kandel, 1976). It has been found that the central (CNS) and peripheral(PNS) nervous systems in Aplysia interact and form an integrated system which normally mediates both the reflex and its subsequent habituation (Peretz, Jacklet, and Lukowaik, 1976; Lukowiak and Peretz, 1977). Further, it was found that in the integrated system the CNS exerted both suppressive and facilitatory control over the PNS in the mediation of gills reflex behaviors (Lukowiak, 1977a). Removal of only the CNS's suppressive control over the PNS, while leaving intact its facilitatory influence, resulted in a significant reduction in reflex latency, a significant increase in reflex amplitude, and a reflex that is resistant to habituation with repeated stimulation (Lukowiak, 1977a). In addition, it was found that an identifiable neuron, Ld9, could modulate the ability of the reflex to habituate (Lukowiak, 1979a). With induced tonic low-level activity in L9 the reflex evoked by repeated siphon stimulation did not habituate even though the synaptic decremental process which occurs in gill motor neurons such as L7 and accompanies gill reflex habituation (Castellucci et al., 1970) continued to occur. The neurons in abdominal ganglion, which by their activity exert control over the PNS and thus the reflex, have not yet been identified but it is known that these same neutrons apparently exert control over the synaptic input received by gill motor neurons such as L7 from the central sensory neurons (Byrne, Castellucci, and Kandel, 1974) as a result of siphon stimulation (Peretz and Lukowiak, 1975; Lukowiak and Peretz, 1980).
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