Journal of neurophysiology
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1. The effects of repetitive stimulation of primary afferents in lumbar dorsal roots on synaptic transmission in the dorsal horn (DH) were studied in a rat spinal cord slice-dorsal root ganglion (DRG)-peripheral nerve trunk preparation by the use of intracellular recording from neurons (n = 115) of the spinal dorsal horn (depth 147 +/- 139, mean +/- SD). All DH neurons were excited synaptically by electrical stimulation of the dorsal root or the peripheral nerve trunk. ⋯ A test of other, adjacent primary afferents revealed that these synapses in the neurons in the superficial laminae had not undergone potentiation. This "synaptic specificity" of post-wind-up potentiation suggested that the mechanism for the induction of stimulation-dependent changes in the excitability of the DH neuron is presynaptic to the recorded-from neuron. 4. In a concentration of 0.5 microM and higher, tetrodotoxin (TTX) applied to sensory neurons selectively blocked action potentials in large myelinated primary afferents.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. The antimasking effects of olivocochlear (OC) efferent feedback were studied in anesthetized or decerebrate cats by comparing responses of single auditory-nerve fibers (ANFs) to tone bursts in continuous masking noise seen with and without addition of a moderate-level contralateral noise known to activate the OC reflex. Responses were measured as a function of tone-burst intensity, tone-burst frequency, and masker intensity and were analyzed so as to allow quantitative estimates of the detectability of the tone bursts against the noise background. 2. ⋯ In quiet, the effects are predominately suppressive and are restricted to stimuli at frequencies near a fiber's CF and at intensities within its dynamic range. In continuous background noise, the OC reflex can enhance the responses to transient stimuli. Such effects are seen throughout the fiber's response area.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. Both electrical and chemical stimulation of the midbrain periaqueductal gray matter (PAG) inhibit baroreflex vagal bradycardia (BVB). The present study was designed to determine the target site of this inhibition about which little is known. ⋯ In addition, unitary recordings revealed that ADN-evoked unitary responses of neurons in the NA region were suppressed by PAG stimulation, whereas NTS baroreceptor neurons, either ADN responsive or nonresponsive, were scarcely inhibited by PAG stimulation. 5. These findings suggest that the PAG inhibited BVB mainly at the vagal preganglionic cell level and not at the NTS interneuron level. The conclusion is in harmony with our previous reports that the target site of hypothalamic inhibition of BVB in rats is also the preganglionic neurons and that hypothalamic inhibition of BVB is mediated predominantly by the PAG.
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1. Most quantitative examinations of nociception are performed with thermal or mechanical stimuli. Because nociceptive processing mechanisms may depend on the modality of the stimuli, comparable studies on chemonociception are necessary. 2. ⋯ The discriminatory capacity of WDR and NS neurons was reduced in the highest concentration range (75-100% CO2). The proportion of NS neurons significantly discriminating between these intensities tended to be higher compared with WDR neurons when stimuli were applied with long ISIs (120 s). 5. To examine the effects of the duration of the ISI, identical test sequences were performed with ISIs of 30 and 120 s. (ABSTRACT TRUNCATED AT 400 WORDS)
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1. The effects of olivocochlear (OC) feedback on signal processing in the cochlea were studied by comparing responses seen with and without a contralateral noise or by comparing responses seen before and after cutting the OC bundle (OCB). Adding and subtracting a contralateral noise is a convenient, reversible way of changing the level of OC feedback; however, it fully reveals only the contribution of the contralaterally responsive efferent fibers. ⋯ Present evidence suggests that all these antimasking effects can be explained on the basis of activation of the medial OC fibers to the outer hair cells. By suppressing responses to continuous noise backgrounds, the OC reflex may enhance responses to transient masked stimuli by decreasing the level of adaptation in auditory nerve fibers. Such effects of the OC reflex should improve discrimination of transient signals presented in a continuous noise background.