Journal of neurophysiology
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1. Responses evoked by electrical stimulation of the olfactory nerve and olfactory tracts were analyzed in 46 output cells of the salamander olfactory bulb, in vivo. Labeling of several cells with horseradish peroxidase indicated that they were mitral and/or tufted neurons. ⋯ Full antidromic spikes were evoked prior to the period of inhibition and small antidromic spikes were evoked during the period. 4. The mean latencies of single evoked spikes or the first spikes of bursts decreased from 22 to 17 ms with increases in the intensity of nerve stimulation and from 7 to 6 ms with increases in the intensity of tract stimulation. Only decreases in orthodromic latency were significant at P less than or equal to 0.05, as determined by one-sided t tests between the means of responses subdivided according to response pattern and relative stimulus intensity.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. The CA1 region of rat hippocampal slices bathed in 8.5 mM interstitial K+ ([K+]o) exhibited spontaneous 20- to 90-s electrographic seizures at regular intervals of 1-8 min. In these same slices CA3 neurons generated spontaneous interictal bursts that propagated throughout the pyramidal cell subfields. ⋯ Thus, although the presence of interictal input from the CA3 region is required for CA1 seizure generation, it appears that electrographic seizures do not result from a change in the quality or quantity of interictal input to the CA1 region. 6. During the 30- to 60-s period leading to a seizure the excitability of CA1 pyramidal cells appeared to increase gradually. Over the interseizure interval both CA1 pyramidal cells and glia gradually depolarized, the intensity of interictal bursts recorded in the CA1 region increased, and the extracellular DC potential recorded in the CA1 cell layer drifted negative.(ABSTRACT TRUNCATED AT 400 WORDS)
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Comparative Study
Quantitative comparison of inhibition of visceral and cutaneous spinal nociceptive transmission from the midbrain and medulla in the rat.
1. The descending inhibition of neuronal responses by focal electrical stimulation or glutamate microinjections in the periaqueductal gray (PAG) or rostral ventromedial medulla (RVM) was quantitatively studied on 61 spinal neurons in halothane-N2O-anesthetized paralyzed rats. Thirty-six neurons were located in the medial L6-S1 spinal cord and were consistently and reproducibly excited by distension of the descending colon and rectum (75 mmHg). ⋯ Neuronal intensity coding to both graded heating of the hindfoot and graded colorectal distension was montonus and accelerating and could be expressed as linear stimulus-response functions (SRFs) in the temperature and pressure ranges studied (46-52 degrees C, 25-100 mmHg). Stimulation in the PAG modulated the SRFs differently than did stimulation in the RVM. Stimulation in the PAG decreased the slope of the SRFs without affecting the units' thresholds of response, thus influencing the gain control of both cutaneous and visceral nociception in the spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. The amplitudes of end-plate currents (EPCs) evoked by stimulating the nerve with frequencies ranging from 1 to 5 Hz and the amplitudes of miniature end-plate currents (MEPCs) gradually diminish if choline uptake is blocked by hemicholinium-3 (HC-3, 20 microM). This reduction of EPC amplitudes is predominantly of presynaptic origin, although an observed decrease in MEPC amplitudes suggests that some postsynaptic changes [due to direct action of HC-3 on acetylcholine (ACh) receptors or on open ACh channels] also occurs. 2. ⋯ Even with the choline uptake system intact, prolonged high-frequency stimulation leads to a gradual shortening of EPCs and, to a small extent, MEPCs. Shortening of EPCs appears to be mainly a result of a reduction of their quantal size. 5. It is estimated from the shortening of EPCs and the known EPC versus MEPC relationship that the reduction of the quantal sizes of nerve-evoked quanta probably contributes very significantly to synaptic depression that occurs during prolonged high-frequency nerve stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. The contribution of midline medullary bulbospinal neurons to descending inhibition from the locus coeruleus (LC) and the funicular trajectories of coeruleo- and raphe-spinal fibers mediating inhibition of spinal nociceptive transmission were examined in different experiments. Extracellular recordings of lumbar dorsal horn neurons were made in deeply pentobarbital-anesthetized, paralyzed rats. ⋯ The effects of ipsilateral and bilateral ventrolateral funiculus (VLF) lidocaine microinjections on spontaneous and heat-evoked unit activity were examined in other experiments. Spontaneous activity increased following ipsilateral VLF lidocaine microinjections for 13/18 units; decreases and no change in spontaneous activity were observed for three and two units, respectively. Heat-evoked unit activity was increased significantly following ipsilateral VLF lidocaine microinjections.(ABSTRACT TRUNCATED AT 400 WORDS)