Neurons In Nucleus Reticularis Gigantocellularis Research Articles

Multimodal Sensory Responses of Nucleus Reticularis Gigantocellularis and the Responses' Relation to Cortical and Motor Activation

The connectivity of large neurons of the nucleus reticularis gigantocellularis (NRGc) in the medullary reticular formation potentially allows both for the integration of stimuli, in several modalities, that would demand immediate action, and for coordinated activation of cortical and motoric activity. We have simultaneously recorded cortical local field potentials, neck muscle electromyograph (EMG), and the neural activity of medullary NRGc neurons in unrestrained, unanesthetized rats to determine whether the activity of the NRGc is consistent with the modulation of general arousal. We observed excitatory responses of individual NRGc neurons to all modalities tested: tactile, visual, auditory, vestibular, and olfactory. Excitation was directly linked to increases in neck muscle EMG amplitude and corresponded with increases in the power of fast oscillations (30 to 80 Hz) of cortical activity and decreases in the power of slow oscillations (2 to 8 Hz). Because these reticular formation neurons can respond to broad ranges of stimuli with increased firing rates associated with the initiation of behavioral responses, we infer that they are part of an elementary "first responder" CNS arousal mechanism.

Further Characterization of Nociception-Related and Arterial Pressure-Related Neuronal Responses in the Nucleus Reticularis Gigantocellularis of the Rat.

The present study was undertaken to further characterize the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata in the central processing of nociceptive and cardiovascular signals, and its modulation by met-enkephalin. In Sprague-Dawley rats anesthetized with pentobarbital sodium, we found that all 125 spontaneously active NRGC neurons that responded to noxious stimuli (tail clamp) also exhibited arterial pressure-relatedness. Forty neurons additionally manifested cardiac periodicity that persisted even during nociceptive responses. While maintaining their cardiovascular responsive characteristics, the nociception-related NRGC neuronal activity was blocked, naloxone-reversibly (0.5 mg/kg, i.v.), by morphine (5 mg/kg, i.v.). Microiontophoretically applied met-enkephalin suppressed the responsiveness of NRGC neurons to individually delivered tail clamp or transient hypertension induced by phenylephrine (5 &mgr;g/kg, i.v.). Interestingly, in NRGC neurons that manifested both nociception and arterial pressure relatedness, the preferential reduction in the response to noxious stimuli upon simultaneous elevation in systemic arterial pressure was reversed to one that favored nociception in the presence of met-enkephalin. All actions of met-enkephalin were discernibly blocked by the opioid receptor antagonist, naloxone. Our results suggest that individual NRGC neurons may participate in the processing of both nociceptive and cardiovascular information, or in the coordination of the necessary circulatory supports during nociception. In addition, neuropeptides such as met-enkephalin may exert differential modulation on neuronal responsiveness according to the prevailing physiologic status of the animal. They also showed that NRGC may be a central integrator for pain and cardiovascular-related functions. Copyright 1996 S. Karger AG, Basel

Responses to vertical vestibular stimulation of neurons in the nucleus reticularis gigantocellularis in rabbits.

1. Because the nucleus reticularis gigantocellularis (NRGc) receives a substantial descending projection from the caudal vestibular nuclei, we used extracellular single-unit recording combined with natural vestibular stimulation to examine the possible peripheral origins of the vestibularly modulated activity of caudal NRGc neurons located within 500 microns of the midline. Chloralose-urethan anesthetized rabbits were stimulated with an exponential "step" and/or static head-tilt stimulus, as well as sinusoidal rotation about the longitudinal or interaural axes providing various combinations of roll or pitch, respectively. Recording sites were reconstructed from electrolytic lesions confirmed histologically. 2. More than 85% of the 151 neurons, in the medial aspect of the caudal NRGc, responded to vertical vestibular stimulation. Ninety-six percent of these responded to rotation onto the contralateral side (beta responses). Only a few also responded to horizontal stimulation. Seventy-eight percent of the neurons that responded to vestibular stimulation responded during static roll-tilt. One-half of these neurons also responded transiently to the change in head position during exponential "step" stimulation, suggesting input mediated by otolith and semicircular canal receptors or tonic-phasic otolith neurons. 3. Seventy-five percent of the responsive neurons had a "null plane." The planes of stimulation resulting in maximal responses, for cells that responded to static stimulation, were distributed throughout 150 degrees in both roll and pitch quadrants. Five of these cells responded only transiently during exponential "step" stimulation and responded maximally when stimulated in the plane of one of the vertical semicircular canals. 4. The phase of the response of the 25% of medial NRGc neurons that lacked "null planes" gradually shifted approximately 180 degrees during sinusoidal vestibular stimulation as the plane of stimulation was shifted about the vertical axis. These neurons likely received convergent input with differing spatial and temporal properties. 5. The activity of neurons in the medial aspect of the caudal NRGc of rabbits was modulated by both otolithic macular and vertical semicircular canal receptor stimulation. This vestibular information may be important for controlling the intensity of the muscle activity in muscles such as neck muscles where the load on the muscle is affected by the position of the head with respect to gravity. Some of these neurons may also shift muscle function from an agonist to an antagonist as the direction of head tilt changes.

Modulation by angiotensin III of nociception-related and arterial pressure-related neuronal responsiveness in the nucleus reticularis gigantocellularis of the rat.

We evaluated possible modulation by angiotensin III (AIII) of the interactive effect of noxious stimuli and elevation in systemic arterial pressure on the responsiveness of neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Combined extracellular single-neuron recording and microiontophoresis were carried out on male, adult Sprague-Dawley rats anesthetized with pentobarbital sodium. The responsiveness of NRGC neurons to nociception (tail clamp) and/or transient hypertension elicited by phenylephrine (5 micrograms/kg, i.v.), in the absence or presence of AIII, was used as the experimental index. Microiontophoretic application of the heptapeptide suppressed the responses of spontaneously active NRGC neurons to individually delivered nociception or hypertension. Interestingly, the preferential reduction in responsiveness to tail clamp upon simultaneous elevation in arterial pressure was reversed to one that favored nociception in the presence of AIII. These actions of the heptapeptide appeared to be receptor-specific, since they were discernibly blocked by its selective antagonist, Ile7-angiotensin III. Our results reveal that neuropeptides such as AIII may differentially modulate neuronal responsiveness according to the prevailing physiologic input(s) to the central nervous system of the animal.

Interaction between neuronal responses to nociception and hypertension in the nucleus reticularis gigantocellularis of the rat

We evaluated the interactive effects of noxious stimuli and elevation in systemic arterial pressure on the responsiveness of spontaneously active neurons in the nucleus reticularis gigantocellularis (NRGC) of male, adult Sprague-Dawley rats anesthetized with pentobarbital sodium. In NRGC neurons that responded to both nociception (tail clamp) and transient hypertension elicited by phenylephrine (5 μg/kg, i.v.), the responsiveness to tail clamp was reduced upon simultaneous elevation in arterial pressure. This preferential response pattern did not appear to be affected by the level of anesthesia, since it was demonstrated in animals that were maintained by hourly bolus supplements or continuous infusion of pentobarbital sodium. These data offer a feasible cellular explanation for the documented correlation between elevated nociceptive threshold and hypertension. They also showed that NRGC may be a central integrator for the processing of nociceptive and cardiovascular information.

Passive biophysical membrane properties of nucleus reticularis gigantocellularis neurons in brain slices from the rat

This study employed intracellular recording coupled with the current clamp technique to characterize the passive biophysical membrane properties of neurons in the nucleus reticularis gigantocellularis (NRGC) of brain slices from adult, male Sprague-Dawley rats. We found that NRGC neurons possessed highly depolarized transmembrane potentials (−22.9 ± 0.6 mV, n = 189). The 29 NRGC neurons that received further evaluation showed that they could be separated into two clusters, with significantly different membrane input resistances (3.51 ± 0.89 vs 77.50 ± 8.82 M Ω ) and membrane time constants (0.56 ± 0.05 vs 1.27 ± 0.12 ms). These membrane properties, which resembled qualitatively those we observed previously in cats in vivo, will form the basis for further evaluation of the ionic mechanisms that may underlie the actions of pharmacologic agents on the NRGC neurons.

Passive electrical properties of spontaneously active neurons in the nucleus reticularis gigantocellularis of the cat

We evaluated in chloralose-urethane anesthetized cats the passive electrical properties of 25 spontaneously active neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Compared to other mammalian brain regions, these reticular cells in general possessed higher input resistance, shorter membrane time constant and first equalizing time constant, and longer somatodendritic electrotonic length factor. It is discussed that, by providing a synaptic machinery for quick and sensitive response to afferent inputs and an efficacious interplay between temporal and spatial summation, these electrical membrane properties may account for the spontaneous and irregular discharge pattern characteristic of the NRGC neurons.

Arterial pressure- and cardiac rhythm-related single-neuron activities in the nucleus reticularis gigantocellularis of the rat

This communication presents an analysis of 531 extracellularly recorded spontaneously active nucleus reticularis gigantocellularis (NRGC) single-neurons in pentobarbital anesthetized rats, with particular reference to their cardiovascular-related activities. Fifty-nine percent of the gigantocellular neurons evaluated had temporal relationship with induced or spontaneous arterial pressure fluctuations. Twenty-eight percent of the NRGC neurons manifested definite discharge patterns and periodicity with reference to the cardiac cycle. It is discussed that these gigantocellular neurons may serve as a primary component of the cardiovascular regulatory mechanism. Alternatively, they may coordinate the necessary circulatory support for activities varying from respiration to somatomotor functions or sleep-wakefulness.

Intracellular potential of medullary reticular neurons during sleep and wakefulness

Intracellular records were obtained in the chronic cat from neurons of the nucleus reticularis gigantocellularis (NGC) during naturally occurring sleep and wakefulness. When wakefulness and quiet sleep was compared with active sleep, the membrane potential level of NGC neurons gradually decreased; a depolarized membrane potential was maintained tonically and selectively throughout active sleep. These data support the concept that NGC neurons assist in the generation of somatic atonia during active sleep and suggest that this state-dependent inhibitory function may be controlled by the nucleus pontis oralis as part of the general phenomenon of reticular response reversal.

Interactions between nucleus centrum medianum and gigantocellular nociceptive neurons

Cells in nucleus reticularis gigantocellularis (NGC) and nucleus centrum medianum (CM) are known to respond to tooth pulp stimulation, which is a nociceptive trigeminal stimulus. We examined the effect of stimulation of CM on this class of neurons in NGC. Thirty-nine percent of the 57 neurons tested were antidromically activated by stimulation of the ipsilateral CM, while 28% of the 40 neurons tested were antidromically activated from the contralateral CM. In addition, the spontaneous activity of seven NGC neurons was altered by stimulation of the ipsilateral CM, while five cells were affected by stimulation of the contralateral CM. These data suggest a complex and reciprocal interaction between neurons in NGC and CM.

Neuronal receptive field properties in feline nucleus reticularis gigantocellularis

Nucleus reticularis gigantocellularis (NGC) has been shown, using both behavioral and physiological techniques, to be involved in the processing of nociceptive information. However, previous studies of the receptive fields of NGC neurons have utilized only innocuous stimuli. Thus, while neurons in NGC may play an important role in nociception, the receptive field properties of these cells remain to be defined. This investigation was designed to determine the receptive field properties of neurons in NGC using nociceptive and innocuous stimuli. Receptive fields were determined for 127 neurons in NGC. Eighty-seven percent of the NGC neurons studied responded exclusively to noxious stimuli, while 13% also responded to innocuous stimuli. None of the neurons studied responded exclusively to innocuous stimuli. The receptive fields of most NGC neurons (63%) were large, discontinuous, and bilaterally symmetrical. Eighty-one percent of NGC neurons received convergent inputs from both spinal and trigeminal systems. These receptive field properties differ from those previously reported using only innocuous stimulation

The reduced responsiveness of neurones in nucleus reticularis gigantocellularis following their excitation by peripheral nerve stimulation.

1. Post-stimulus histograms of neuronal activity, constructed from extracellular recordings in decerebrate, decerebellate cats, have been used to investigate the responsiveness of neurons in nucleus reticularis gigantocellularis following their excitation by a peripheral nerve stimulus. 2. The response to a testing stimulus applied to a peripheral nerve was depressed following the response to a conditioning stimulus applied to the same or a different peripheral nerve. This reduction in responsiveness was maximal within 50 msec of the peak of the response to the conditioning stimulus. Response latencies to the testing stimulus were increased during the period of reduced responsiveness. 3. Responsiveness to a peripheral nerve stimulus was also reduced following a spontaneous or an antidromically evoked spike, but this effect was weaker and much shorter-lasting than that following a nerve-evoked spike. Thus, the reduced responsiveness cannot be solely due to phenomena which are an inevitable consequence of an action potential in the neurone. 4. In spontaneously firing neurones, the duration of the reduced responsiveness to a testing stimulus generally outlasted the depression of spontaneous activity which often followed an excitation evoked by a peripheral nerve conditioning stimulus. 5. The reduction in responsiveness to a testing stimulus applied to the same nerve as the conditioning stimulus was greater and longer-lasting than that to a testing stimulus applied to a different nerve. 6. When stimuli were applied to one nerve at a relatively high rate, the neurone became much less responsive to that input, but simultaneously became more responsive to low rate stimulation of other nerves. 7. It is concluded that the greater part of the reduced responsiveness is due to events occurring on the input pathway to a reticular neurone, or possibly in the region of the afferent endings on its dendrites. These processes may allow selective changes in responsiveness to different inputs, and enable the units to act as novelty detectors.