Journal of neurophysiology
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1. To examine further the ability of different classes of nociceptive and nonnociceptive primary afferent neurons to induce c-fos expression in central neurons, fos-like immunoreactivity was examined in the medullary dorsal horn (laminae I-IV) of the rat after facial application of a range of warming and cooling thermal stimuli. Urethan-anesthetized rats received 15 30-s thermal pulses (53, 50, 47, 41, 25, or 10 degrees C) applied to the vibrissal pad over a period of 30 min and were perfused 2 h after the end of stimulation. 2. ⋯ The results also provide evidence that neurons that receive input from C polymodal nociceptors are present in both laminae I and II, as are neurons that receive input from low-threshold cold receptors. Neurons that receive input from high-threshold cold receptors, but not from low-threshold cold receptors, appear to be located preferentially in lamina I. The shape of the curve relating fos-LI labeling to stimulus temperature in the warming direction is consistent with the expected pattern of recruitment of primary afferent nociceptors.
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1. The present study evaluates the necessity of the ventroposterior medial thalamic nucleus (VPM) for discrimination of the intensity of noxious heating, innocuous cooling, and innocuous tactile (airpuff) stimulation of the maxillary skin. 2. Two rhesus monkeys were trained to detect small differences (< 1.0 degrees C) in the intensity of noxious heat (near 46 degrees C) and innocuous cold (near 30 degrees C) as well as differences in the force of an airpuff applied to the skin over the maxilla. ⋯ Monitoring of adjacent microelectrodes revealed that although activity ventral to the injection sites was blocked, activity in medial thalamic nuclei, implicated in nociceptive processing, was probably not altered by these injections. 5. These data suggest that VPM is important for the perception of noxious and innocuous thermal stimuli as well as for the perception of tactile stimuli. However, considering the ineffectiveness of small single microinjections of lidocaine, it appears that some critical proportion of VPM must be inactivated to disrupt thermal or tactile discrimination, possibly because of overlapping receptive field properties of neurons in different areas of the nucleus.
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1. In vitro slices of frontal neocortex were prepared from rat pups at various ages after birth: postnatal days (PN) 3-5, 6-8, and 9-14. Using whole-cell patch-clamp techniques, both spontaneous and evoked excitatory postsynaptic currents (EPSCs) were recorded from voltage-clamped layer II-III pyramidal neurons. ⋯ These results indicate that the basic kinetic properties of mEPSCs are present by PN 3-5 and do not change significantly over the first two postnatal weeks. NMDA receptor activation contributes to mEPSCs and sensitivity to Mg2+ appears as early as PN 3-5. Unitary EPSCs resemble mEPSCs, but a late NMDA receptor-mediated component appears in EPSCs as stimulus intensity is increased.(ABSTRACT TRUNCATED AT 400 WORDS)