Journal of neurophysiology
-
Modulation of sacral spinal dorsal horn neurons by the ventrolateral PAG was studied by extracellular recording combined with microiontophoretic applications of alpha-adrenergic agonists or antagonists. Bicuculline (BIC, 15 ng) microinjected into the ventrolateral PAG produced a consistent inhibition of the responses of nociceptive dorsal horn neurons. After PAG-BIC applications, the total number of spikes per heat stimulation period was significantly decreased to a mean of 37 +/- 19% (n = 8) of the pre-BIC control. ⋯ Activation of the alpha1 adrenoceptors by iontophoresis of methoxamine often led to a marked increase in the responses to kainic acid and, to a lesser extent, to NMDA iontophoresis or noxious heat. Together with previously reported work, the current experiments demonstrate that PAG neurons inhibit nociceptive dorsal horn neurons primarily through an indirect alpha2 adrenoceptor mechanism. In this same population of dorsal horn neurons, norepinephrine has a direct alpha1-mediated excitatory effect.
-
To characterize muscle synergy organization underlying multidirectional control of stance posture, electromyographic activity was recorded from 11 lower limb and trunk muscles of 7 healthy subjects while they were subjected to horizontal surface translations in 12 different, randomly presented directions. The latency and amplitude of muscle responses were quantified for each perturbation direction. Tuning curves for each muscle were examined to relate the amplitude of the muscle response to the direction of surface translation. ⋯ The results suggest that neither a simple reflex mechanism nor a fixed muscle synergy organization is adequate to explain the muscle activation patterns observed in this postural control task. Our results are consistent with a centrally mediated pattern of muscle latencies combined with peripheral influence on muscle magnitude. We suggest that a flexible continuum of muscle synergies that are modifiable in a task-dependent manner be used for equilibrium control in stance.
-
Neurons in the central nucleus of the inferior colliculus (ICc) typically respond with phase-locked discharges to low rates of sinusoidal amplitude-modulated (SAM) signals and fail to phase-lock to higher SAM rates. Previous studies have shown that comparable phase-locking to SAM occurs in the dorsal nucleus of the lateral lemniscus (DNLL) and medial superior olive (MSO) of the mustache bat. The studies of MSO and DNLL also showed that the restricted phase-locking to low SAM rates is created by the coincidence of phase-locked excitatory and inhibitory inputs that have slightly different latencies. ⋯ In none of the cells that we tested did the application of AP5 by itself, or in combination with bicuculline, cause an increase in the range of SAM rates that evoked phase-locking. These results illustrate that the same response property, phase-locking restricted to low SAM rates, is formed in more than one way in the auditory brain stem. In the MSO and DNLL, the mechanism is coincidence of phase-locked excitation and inhibition, whereas in ICc the same response feature is formed by a different but unknown mechanism.
-
Physiological survey of medullary raphe and magnocellular reticular neurons in the anesthetized rat.
The present study was designed to provide a detailed and quantitative description of the physiological characteristics of neurons in the medullary raphe magnus (RM) and adjacent nucleus reticularis magnocellularis (NRMC) under anesthetized conditions. The background discharge and noxious stimulus-evoked responses of RM and NRMC neurons were recorded in rats lightly anesthetized with isoflurane. All cells that were isolated successfully were studied. ⋯ Although many cells discharged too infrequently to be classified, units with physiological properties that were different from those described above were rare. In conclusion, most RM and NRMC cells belong to three nonserotonergic physiological cell classes that can be distinguished from each other by the consistency, not the magnitude, of their responses to repeated noxious thermal stimulation. Because most of the heat-evoked change in and cell discharge occurs after the conclusion of the initial motor withdrawal, ON and OFF cells are likely to principally modulate the response to subsequent noxious insults.
-
In the previous paper we have demonstrated, by means of field potential and extracellular unit recordings, that bicuculline-induced seizures, which include spike-wave (SW) or polyspike-wave (PSW) complexes, are initiated intracortically and survive ipsilateral thalamectomy. Here, we used multisite field potential and extracellular recordings to validate the patterns of cortical SW/PSW seizures in chronically implanted, behaving cats. To investigate the cellular patterns and excitability during spontaneously occurring and electrically elicited cortical seizures, we used single and dual intracellular recordings from regular-spiking (RS) and fast-rhythmic-bursting (FRB) cortical neurons, in conjunction with field potential recordings from neocortex and related thalamic nuclei, in cats maintained under ketamine-xylazine anesthesia. 1) Invariably, the spontaneous or electrically induced seizures were initiated within the cortex of both behaving and anesthetized animals. ⋯ The FRB neurons fired many more action potentials than RS cells during SW/PSW complexes. Averaged activities triggered by the spiky field potentials or by the steepest slope of depolarization in cortical neurons demonstrated similar relations between intracellular activities and field potentials during sleep and seizure epochs, the latter-being an exaggeration of the depolarizing and hyperpolarizing components of the slow sleep oscillation. 3) During the fast runs, RS cells were tonically depolarized and discharged single action potentials or spike doublets (usually with pronounced spike inactivation), whereas FRB cells discharged rhythmic spike bursts, time locked with the depth-negative field potentials. 4) Neuronal excitability, tested by depolarizing current pulses applied throughout the seizures and compared with pre- and postseizure epochs, showed a decreased number of evoked action potentials during both seizure components (SW/PSW complexes and fast runs), eventually leading to null responses during the postictal depression. 5) Data suggest that interconnected FRB neurons may play an important role in the initiation of cortical seizures. We discuss the similarities between the electrographic patterns described in this study and those found in different forms of clinical seizures.