Journal of neurophysiology
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Whole cell current- and voltage-clamp recording techniques were employed in a rat thalamocortical slice preparation to characterize corticothalamic stimulation-evoked responses in thalamic neurons. Three types of corticothalamic stimulation-evoked responses were observed in thalamic neurons. Of thalamic neurons, 57% responded to corticothalamic stimulation with purely excitatory synaptic responses, whereas 27% had inhibitory synaptic responses and 16% had mixed excitatory/inhibitory responses. ⋯ Corticothalamic feedback onto thalamic relay neurons activated diverse responses due to differing relative activation of NRT and "feedforward" inhibitory responses. These multiple in vitro corticothalamic responses differ from responses encountered in other in vitro thalamic preparations lacking a synaptically connected neocortex, but are similar to results evident in thalamic neurons in response to cortical stimulation in vivo. In addition, the thalamocortical 3- to 6-Hz frequency preference was conserved, suggesting that many factors critical for this emergent property of the thalamocortical system are maintained in vitro.
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Sound onsets are salient and behaviorally relevant, and most auditory neurons discharge spikes locked to such transients. The acoustic parameters of sound onsets that shape such onset responses are unknown. In this paper is analyzed the timing of spikes of single neurons in the primary auditory cortex of barbiturate-anesthetized cats to the onsets of tone bursts. ⋯ Minimum SD increased nonlinearly with increasing Lmin. These findings suggest a peripheral origin of S and a peripheral establishment of latency-acceleration/rate of change of peak pressure functions. Because of the striking similarity in the shapes of such functions across the neuronal pool, sound onsets will produce orderly and predictable spatiotemporal patterns of first-spike timing, which could be used to instantaneously track rapid transients and to represent transient features by partly scale-invariant temporal codes.
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To investigate the spinal processing of cutaneous pruritic and algesic stimuli, single-unit recordings were made from wide-dynamic-range-type lumbar spinal dorsal horn neurons in pentobarbital-sodium-anesthetized rats. Neuronal responses were recorded to mechanical and noxious thermal stimuli, as well as to microinjection (1 microl) of histamine (0.01-10% = 9 x 10(-1)-9 x 10(-4) M), capsaicin (0.1% = 3.3 x 10(-3) M), or other algesic chemicals into skin within the receptive field via intracutaneously placed needles. Most (84%) of the 89 neurons responded to intracutaneous (i.c.) microinjection of histamine with a brief phasic discharge followed by an afterdischarge of variable (s to min) duration. ⋯ The mean response to 80% ethanol was significantly smaller than to 0.1% capsaicin. All units tested also responded to topical application of mustard oil (50%) and i.c. serotonin (30 microg). The results are discussed in terms of theories that attempt to reconcile psychophysical and clinical observations of pain and itch sensation.
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Responses of cutaneous nociceptors to natural stimuli, particularly mechanical and heat stimuli, have been well documented. Although nociceptors are excited by noxious cold stimuli, there have been few studies of their stimulus-response functions for cold stimuli over a wide range of stimulus temperatures. Furthermore, the proportion of nociceptors excited by noxious cold is not clear. ⋯ It is concluded that the proportion of cutaneous A delta-nociceptors excited by noxious cold stimuli has been underestimated in previous studies. All nociceptors were excited by stimulus temperatures <0 degrees C and encoded the intensity of cold stimuli. It is therefore likely that cutaneous A delta-nociceptors contribute to the sensation of cold pain, particularly pain produced by stimulus temperatures <0 degrees C.
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Comparative Study
Properties of unitary IPSCs in hippocampal pyramidal cells originating from different types of interneurons in young rats.
Whole cell recordings were used in hippocampal slices of young rats to examine unitary inhibitory postsynaptic currents (uIPSCs) evoked in CA1 pyramidal cells at room temperature. Loose cell-attached stimulation was applied to activate single interneurons of different subtypes located in stratum oriens (OR), near stratum pyramidale (PYR), and at the border of stratum radiatum and lacunosum-moleculare (LM). uIPSCs evoked by stimulation of PYR and OR interneurons had similar onset latency, rise time, peak amplitude, and decay. In contrast, uIPSCs elicited by activation of LM interneurons were significantly smaller in amplitude and had a slower time course. ⋯ A small, but not significant, paired pulse depression (90.8 +/- 4.0%) was found when the first uIPSC was larger than the mean of all first uIPSCs. Our results indicate that these different subtypes of hippocampal interneurons generate Cl(-)-mediated GABA(A) uIPSCs. uIPSCs originating from different types of interneurons may have heterogeneous properties and may be subject to tonic presynaptic inhibition via heterosynaptic GABA(B) receptors. These results suggest a specialization of function for inhibitory interneurons and point to complex presynaptic modulation of interneuron function.