Perioral Stimuli Research Articles

Determinants of rebound burst responses in rat cerebellar nuclear neurons to physiological stimuli.

Cerebellar Purkinje cells project GABAergic inhibitory input to neurons of the deep cerebellar nuclei (DCN) that generate a rebound increase in firing, but the specific patterns of input that might elicit a rebound response have not been established. We used recordings of Purkinje cell firing obtained during perioral whisker stimulation in vivo to create a physiological stimulus template to activate Purkinje cell afferents in vitro. DCN cell bursts were evoked by the stimulus pattern but not in relation to the perioral whisker stimulus, complex spikes or regular patterns within the Purkinje cell record. Reverse correlation revealed that bursts were triggered by an elevation-pause pattern of Purkinje cell firing, with pause duration a key factor in burst generation. Our data identify for the first time a physiological pattern of Purkinje cell input that can be encoded by the generation of rebound bursts in DCN cells. The end result of signal processing in cerebellar cortex is encoded in the output of Purkinje cells that project inhibitory input to deep cerebellar nuclear (DCN) neurons. DCN cells can respond to a period of inhibition in vitro with a rebound burst of firing, yet the optimal physiological pattern of Purkinje cell input that might evoke a rebound burst is unknown. The current study used spike trains recorded from rat Purkinje cells in response to perioral stimuli in vivo to create a physiological pattern to stimulate Purkinje cell axons in vitro. The perioral stimulus-evoked Purkinje cell firing pattern proved to be virtually ineffective in evoking a rebound burst despite the ability to reliably evoke rebounds using a traditional brief 100Hz stimulus. Similarly, neither complex spike firing nor Purkinje cell patterns identified by CV2 analysis were reliably associated with rebound bursts. Reverse correlation revealed that the optimal Purkinje cell input to evoke a rebound burst was a sequential increase in mean firing rate of at least 30Hz above baseline over 250ms followed by a reduction of 40-60Hz below baseline for up to 500ms. The most important factor was the duration of a pause in Purkinje cell firing that allowed DCN cells to recover from a state of net inhibitory influence. These data indicate that physiological patterns of Purkinje cell firing can elicit rebound bursts in DCN cells in vitro, with pauses in Purkinje cell firing rate acting as a key stimulus for DCN cell rebound responses.

Electromyographic evidence for a digastric reflex evoked by perioral stimuli in humans

summary Electromyographic recordings (EMGs) were made using skin surface electrodes placed over the anterior digastric muscle in seven subjects. In every case, short bursts of electrical stimuli to the upper lip produced a response in the EMG that had a minimum latency of 62.0 ± 10.8 ms (mean ± SD). By contrast, no responses were seen when single pulse stimuli were applied. In 6/7 subjects, the minimum stimulation intensity that produced the reflex was described as being sharp or painful. In three additional experiments, single motor units were recorded within the digastric muscle using needle electrodes. In two of these experiments, there was evidence of reflex activity 60–110 ms after the application of painful electrical stimuli to the lip. These findings confirm that perioral stimuli can evoke a digastric reflex in humans and suggest that this reflex requires the summation that results from successive volleys of impulses in a large number of nociceptive afferent neurones.

Electromyographic evidence for a digastric reflex evoked by perioral stimuli in humans.

Electromyographic recordings (EMGs) were made using skin surface electrodes placed over the anterior digastric muscle in seven subjects. In every case, short bursts of electrical stimuli to the upper lip produced a response in the EMG that had a minimum latency of 62.0 +/- 10.8 ms (mean +/- SD). By contrast, no responses were seen when single pulse stimuli were applied. In 6/7 subjects, the minimum stimulation intensity that produced the reflex was described as being sharp or painful. In three additional experiments, single motor units were recorded within the digastric muscle using needle electrodes. In two of these experiments, there was evidence of reflex activity 60-110 ms after the application of painful electrical stimuli to the lip. These findings confirm that perioral stimuli can evoke a digastric reflex in humans and suggest that this reflex requires the summation that results from successive volleys of impulses in a large number of nociceptive afferent neurones.

Endogenous AVP systems regulate oral behavior in the rat fetus: neuropeptide systems as ontogenetic adaptations.

Pharmacological manipulation of V1 receptors in rostral and caudal brain regions alters perioral responsiveness in the E20 rat fetus. Blockade of caudal V1 receptors or activation of rostral V1 receptors reduces fetal responsiveness to perioral cutaneous stimulation. Activation of caudal V1 receptors or blockade of rostral V1 receptors increases fetal responsiveness to perioral stimulation, including oral capture and grasping of an artificial nipple. These results suggest that V1 receptor-containing neurons regulate perioral responsiveness in the E20 rat fetus and that the 2 populations of neurons exhibit functional differences. The caudal part of the arginine8-vasopressin (AVP) system increases whereas the rostral part decreases responsiveness to different types of perioral stimuli. The neuropeptide AVP may affect suckling behavior immediately after birth by regulating perioral sensory responsiveness.

The effects of inhibitory controls triggered by heterotopic noxious stimuli on a jaw reflex evoked by perioral stimuli in man

Electromyographic recordings (EMGs) were made from the active masseter muscle of the inhibitory reflex evoked by application of electrical stimuli to the skin of the upper lip in 11 human subjects. In control sequences, the reflex had a mean latency and duration of 41 ± 1.7 and 44 ± 2.6 ms, respectively. The magnitude of the reflex (measured by integration of the EMG) was significantly reduced by the application of cold (3 °C) or hot (47–48 °C) but not warm (38–46 ° C) water to a hand or foot. The strongest stimuli (3 or 48 °C) produced mean reductions of the reflex magnitude in the range of 62–85%. These effects occurred regardless of whether the background activity in the masseter was raised or lowered during the application of the thermal stimuli. Thus, activity in nociceptive nerves from widespread areas of the body can modulate jaw reflexes in man by exerting an influence on the reflex pathway at a point before the motor neurones. This may involve the system of ‘diffuse noxious inhibitory controls’, which have been shown to depress limb flexion reflexes and neuronal activity in the spinal dorsal horn and trigeminal nuclear complex.

Effects of dopamine and kappa opioid receptors on fetal responsiveness to perioral stimuli

Opioid ligands or drugs that act on dopaminergic pathways effect changes in the motor behavior of near-term rat fetuses. In this study, selective manipulation of kappa opioid and D1 DA receptors was used to investigate opioid and dopamine involvement in mediating the behavioral effects of milk infusion. Milk reduced expression of the fetal facial wiping response to a tactile probe, and this effect was blocked by the kappa antagonist nor-binaltorphimine as well as the D1 antagonist SCH-23390. Administration of either the kappa agonist U50,488 or the D1 agonist SKF-38393 mimicked the effects of milk and reduced fetal responsiveness to the probe in the absence of milk infusion. Administration of nor-binaltorphimine reversed the effects of SKF-38393 and resulted in a high incidence of the wiping response. However, administration of SCH-23390 did not reverse the low incidence of facial wiping induced by U50,488. These findings suggest that milk modulates activity at dopamine receptors, which in turn promotes activity at kappa receptors of the opioid system to bring about changes in cutaneous responsiveness in the fetal rat.

A comparison of reflex depressions of activity in jaw-closing muscles evoked by intra- and peri-oral stimuli in man

The effects on activity in the masseter muscle of applying electrical stimuli to discrete areas within the mouth or on peri-oral skin were studied electromyographically in 8 subjects. In all subjects, the intra-oral stimuli produced two phases of depressed masseteric activity with mean latencies of 14ms and 47 ms. By contrast, this shorter latency response was generally not obtained with peri-oral stimuli: responses evoked from vermilion-border skin had an intermediate latency (mean 25 ms) and consisted of either one or two periods of depressed activity, while the responses to stimulation of the hairy skin of the lip generally consisted of a single phase of depressed activity, the time course of which was similar to the later phase produced by intra-oral stimuli (mean latency, 48 ms). These findings were consistently obtained with both single and short trains of electrical stimuli and contrast with reports that intra- and peri-oral stimuli produce similar reflexes. The finding that the short-latency reflex depression of masseteric activity could be evoked only by stimulating nerves supplying intra-oral tissues is consistent with the notion that this reflex may play a role in functions such as mastication, and indeed may indicate that the reflex exists specifically for such a purpose.

Trigeminal orosensation and ingestive behavior in the rat.

A deafferentation procedure was used to examine the contributions of trigeminal orosensation to the control of ingestive behavior in the rat. The procedure removed somatosensory input from the mouth, sparing olfaction, lingual taste, and vibrissae inputs as well as proprioceptive afferents from and efferents to the jaw muscles. Rats with sections of tongue or jaw muscle efferents served as oromotor controls. Bilateral trigeminal orosensory deafferentation was followed by an array of effects on ingestive behavior whose magnitudes were proportional to the extent of the deafferentation. The "trigeminal syndrome" includes a disruption of food and water intake (aphagia, adipsia), impairments in the sensorimotor control of eating and drinking, decreased responsiveness to food and water, and a reduction in the level of body weight regulation. Trigeminal deafferentation spared elementary ingestive movement patterns (biting, licking, chewing) but disrupted their control by the perioral stimuli, which normally elicit them, so that eating and drinking sequences were either aborted or inefficient. Deficits in food intake varied with the sensory properties of the diet. Recovery of intake took place along a palatability gradient, and recovery of water intake paralleled that of dry food. The chronically reduced body weight was caused by a persistent hypophagia and reflects reduced responsiveness to food. These findings suggest a considerable degree of overlap in the neural mechanisms mediating the sensorimotor and motivational control of intake in the rat.

Modulation of alpha and gamma trigeminal motoneurons by various peripheral stimuli

The effect of various peripheral stimuli was tested on masseter and digastric reflex activity and on cells identified as masseter and temporalis alpha or gamma motoneurons or as digastric motoneurons. Low-intensity intraoral and perioral stimuli were particularly effective for digastric activation, but this activation could be modulated by a tonic ascending facilitatory influence from trigeminal (V) nucleus caudalis. When used as conditioning stimuli, these stimuli produced a short-lasting facilitation of digastric reflex and motoneuron activity. The facilitation was often followed by a prolonged inhibitory phase to which presynaptic regulatory mechanisms may contribute. In contrast to their excitatory effects on digastric activity, the stimuli largely produced a concomitant inhibition of both alpha and gamma and temporalis motoneurons. However, tooth tap in particular had powerful excitatory effects as well. In some masseter motoneurons a monosynaptic excitation was indicated with this stimulus, and peripherally induced coactivation of alphas and gammas was also noted. Sometimes a complex sequence of excitatory and inhibitory events was produced, and their possible mechanisms and significance are discussed.