Journal of neurophysiology
-
Clinical Trial Controlled Clinical Trial
Characteristics of temporal summation of second pain sensations elicited by brief contact of glabrous skin by a preheated thermode.
Temporal summation of sensory intensity was investigated in normal subjects using novel methods of thermal stimulation. A Peltier thermode was heated and then applied in a series of brief (700 ms) contacts to different sites on the glabrous skin of either hand. Repetitive contacts on the thenar or hypothenar eminence, at interstimulus intervals (ISIs) of 3 s, progressively increased the perceived intensity of a thermal sensation that followed each contact at an onset latency > 2 s. ⋯ Evidence that temporal summation of sensory intensity during series of brief contacts relies on central integration, rather than a sensitization of peripheral receptors, was obtained using two approaches. In the first, a moderate degree of temporal summation was observed during alternating stimulation of adjacent but nonoverlapping skin sites at 0.33 Hz. Second, temporal summation was significantly attenuated by prior administration of dextromethorphan, a N-methyl-D-aspartate receptor antagonist.
-
These experiments were designed to examine the effects of inactivating separately each of the major cerebellar nuclear regions in cats on the execution and retention of a previously learned, operantly conditioned volitional forelimb movement. The experiments test the postulates that the cerebellar nuclei, and particularly the interposed nuclei, contribute substantially to the spatial and temporal features of the interjoint coordination required to execute the task and that the engram necessary for the retention of this task is not located in any one of the cerebellar nuclei. All cats were trained to perform a task in which they were required to reach for and grasp a vertical bar at the sound of a tone and move the bar to a reward zone through a template consisting of two straight grooves in the shape of an inverted "L." After the task was learned, the effects of inactivating separately each nuclear region (the fastigial, interposed, and dentate nuclei) using muscimol microinjections were determined. ⋯ These data suggest that the cerebellum plays an important role in regulating the consistent, stereotypic organization of complex goal-directed movements, including the temporal correlation among joint angle velocities. The data also indicate that the retention of the task is not dependent on any of the individual cerebellar nuclear regions. Consequently, these structures are unlikely to be critical storage sites for the engram established during the learning of this task.
-
Comparative Study
Spinal strychnine alters response properties of nociceptive-specific neurons in rat medial thalamus.
Experiments in both conscious and anesthetized animals indicate that intrathecal (i.t.) strychnine (STR; glycine receptor antagonist) produces acute, reversible allodynia, as evidenced by inappropriate behavioral and autonomic responses to cutaneous tactile stimuli. Although STR is known to produce disinhibition of afferent input to the spinal cord, changes in spinal reflexes cannot fully explain the complex behaviors observed following i.t. STR. ⋯ The ability of NS cells in medial thalamus to respond to tactile input after i.t. STR suggests that the STR lowers the threshold of nociceptive neurons that project directly and/or indirectly to medial thalamus. These observations suggest that ascending nociceptive pathways and medial thalamic structures contribute to the expression of STR-dependent allodynia.
-
The modulatory effects of electrical and chemical (glutamate) stimulation in the rostral ventromedial medulla (RVM) on spinal nociceptive transmission and a spinal nociceptive reflex were studied in rats. Electrical stimulation at a total 86 sites in the RVM in the medial raphe nuclei (n = 54) and adjacent gigantocellular areas (n = 32) produced biphasic (facilitatory and inhibitory, n = 43) or only inhibitory (n = 43) modulation of the tail-flick (TF) reflex. At these 43 biphasic sites in the RVM, facilitation of the TF reflex was produced at low intensities of stimulation (5-25 microA) and inhibition was produced at greater intensities of stimulation (50-200 microA). ⋯ The spinal pathways conveying descending facilitatory and inhibitory influences were found to be different. Descending facilitatory influences on the TF reflex were conveyed in ventral/ventrolateral funiculi, whereas inhibitory influences were conveyed in dorsolateral funiculi. The results indicate that descending inhibitory and facilitatory influences can be simultaneously engaged throughout the RVM, including nucleus raphe magnus, and that such influences are conveyed in different spinal funiculi.
-
The dorsal root potential (DRP) was measured on the lumbar dorsal roots of urethan anesthetized rats and evoked by stimulation of five separate inputs. In some experiments, the dorsal cord potential was recorded simultaneously. Stimulation of the L3 dorsal root produced a DRP on the L2 dorsal root containing the six components observed in the cat including the prolonged negative wave (DRP V of Lloyd 1952). ⋯ Convergence of input from LT sural, and gastrocnemius nerves and cortex was observed. Spike-triggered averaging was used to examine the relationship between the ongoing discharge of superficial dorsal horn neurons and the spontaneous DRP. The discharge of 81% of LT responsive cells was correlated with the DRP.