Canadian journal of physiology and pharmacology
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Can. J. Physiol. Pharmacol. · Dec 1983
Inhibition of fast axonal transport in vitro by the local anesthetics prilocaine, mepivacaine, and bupivacaine.
The aim of the present study was to establish the concentrations of prilocaine, mepivacaine, and bupivacaine which are effective at blocking fast axonal transport, to determine whether prilocaine and mepivacaine offer a better prospect of dissociating conduction block and transport block in vivo than does lidocaine and whether bupivacaine offers a better prospect than etidocaine in the same context. Fast axonal transport of [3H]leucine-labeled proteins was studied in vitro in bullfrog spinal nerves and quantitated by liquid scintillation counting. Exposure of spinal nerves to 14 mM prilocaine reduced the quantity of 3H-labeled proteins which accumulated at a ligature by 86%, and exposure to 14 mM mepivacaine reduced it by 70%; 10 mM prilocaine reduced this same parameter by 54%, a degree of inhibition close to the 44% reduction caused by 14 mM lidocaine. ⋯ Bupivacaine reduced the accumulation of 3H-labeled proteins at the ligature by 49% at a 10 mM concentration (pH 6.2); its potency is close to that found for etidocaine in a previous study. Since prilocaine and mepivacaine are at least as potent as lidocaine as transport inhibitors and at blocking impulse conduction, these two anesthetics offer no advantage over lidocaine to achieve dissociation of conduction block from transport block in vivo. Bupivacaine appears to offer no advantage over etidocaine in the same context, as the two agents have a similar potency as local anesthetics and a similar potency as inhibitors of fast axonal transport.
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Can. J. Physiol. Pharmacol. · Jul 1983
Transfer of habituation between stimulation sites of the siphon withdrawal reflex in Aplysia californica.
Habituation of the siphon withdrawal reflex (SWR) can be evoked by iterative tactile stimuli presented to one of several sites, including the siphon and gill. The SWR evoked at an arbitrary "test" site did not habituate when stimuli were presented at 20-min intervals. However, there was a large decrease in the reflex evoked at the test site when the trial was preceded by 10 repetitive stimuli (interstimuli interval = 30 s) presented to the opposite "habituation" site. ⋯ Moreover, transfer of habituation occurred after the abdominal ganglion (central nervous system) was removed. There was little change in the magnitude of the control responses or transfer of habituation after deganglionation. Since transfer of habituation between stimulation sites of the SWR was similar to that reported previously for the gill withdrawal reflex, it was suggested that a common mechanism may underlie the two behaviors.
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Can. J. Physiol. Pharmacol. · Jul 1983
The gill withdrawal reflex is suppressed in sexually active Aplysia.
In Aplysia, the central nervous system and peripheral nervous system interact and form an integrated system that mediates adaptive gill withdrawal reflex behaviours evoked by tactile stimulation of the siphon. The central nervous system (CNS) exerts suppressive and facilitatory control over the peripheral nervous system (PNS) in the mediation of these behaviours. ⋯ In control animals, the evoked gill withdrawal reflex met a minimal response amplitude criterion, while in sexually active animals the reflex did not meet this criterion. At the neuronal level, the increased CNS suppressive control was manifested as a decrease in excitatory input to the central gill motor neurons.
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Effects of chest compressions on the pattern of breathing were studied in pentobarbital anaesthetized 9- to 11-day-old kittens before and after vagotomy. The chest was compressed by means of a micrometer at three levels (T1-4, T6-8, T9-11). In intact and vagotomized kittens, the group mean values of inspiratory time (tI), expiratory (tE) time, peak amplitude of the integrated phrenic activity (PHR) and its rate of rise (PHR/tI) during compressions were not different from those of the control breaths. ⋯ Nevertheless we cannot exclude contribution of extravagal receptors in control of tE. The tE effects could be masked by the increased variability of the control value in vagotomized kittens. The effects of chest compression on the integrated phrenic activity were mostly dependent on the intact vagal feedback.
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Can. J. Physiol. Pharmacol. · May 1980
Vasopressin increases the central nervous system suppressive control over gill reflex behaviours and associated neural activity in Aplysia.
Exposure of the abdominal ganglion of Aplysia to arginine vasopressin (10(-12) M) reduces the amplitude of the gill withdrawal reflex, accelerates its rate of habituation, and causes a concomitant decrease in the number of action potentials evoked in gill motor neuron L7. The effects of vasopressin on both the reflex and the concomitant neural activity evoked in L7 were completely reversible. Vasopressin did not affect the passive membrane properties of L7. The results indicate that a vertebrate neurohypophyseal hormone can affect behavioural responses as well as modify the synaptic efficacy of the reflex pathway.