Inhibitory influences on hypoglossal neural activity by stimulation of midpontine dorsal tegmentum in decerebrate cat

Premotor input to hypoglossal motoneurons from Kölliker-Fuse neurons in decerebrate cats

Experiments were performed in 18 paralysed, ventilated, decerebrate adult cats to characterise projections from the Kölliker-Fuse nucleus(KFN) to hypoglossal(HG) motoneurons. Efferent neural activity was recorded from the medial branch of both HG nerves, right recurrent laryngeal(RL) nerve, and C3 branch of the left phrenic nerve. Electrical stimulation(1 Hz, 1 msec pulse duration) of discrete areas within the KFN coordinates elicited a preferential, predominantly ipsilateral burst of HG action potentials with an average stimulus-response latency of 8 msec. Tonic stimulation(5-20 Hz) frequently produced considerable HG temporal summation and the appearance of phasic inspiratory HG activity. Injection of 40-100 nl kainic acid(6.37 mM) into the rostral pontine site with the lowest electrical threshold for HG activation elicited a prolonged tonic HG activation. Following kainate injection, the electrical stimulation threshold for HG excitation increased. Pressure injections of 5-100 nl of 2 mM N-methyl-D-aspartic acid (NMDA)and 2 mM(+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid hydrobromide(AMPA) into the KFN were associated with activation and/or suppression of HG motor output. The results indicate that HG motoneurons innervating protrusor tongue muscles receive a selective projection from the KFN that can be activated by glutamate receptors on KF neurons.

REM sleep pathways and anticholinesterase intoxication: a mechanism for nerve agent-induced, central respiratory failure

The mechanism of death following exposure to anticholinesterases, such as the highly toxic nerve agents soman and VX, and other organophosphate anticholinesterases such as the insecticide parathion, remains unclear, although evidence from nerve agent research suggests that death occurs by an atropine blockable respiratory failure mediated through mechanisms involving the central nervous system. It is proposed that REM sleep pathways, which can be triggered by acetylcholine accumulation in the pontomedullar reticular field, mediate respiratory failure through the inhibition of respiratory muscles. Cholinergic activation of REM sleep activities may also account for other physiological and behavioural effects that follow exposure to nerve agents. These include forebrain activation, which is associated with EEG desynchronization and seizures, locomotor depression with concomitant loss of righting reflex, and limb jerks and extensions. Pharmacologic evidence for atropine and clonidine protection against soman intoxication effects is entirely consistent with a scenario of cholinergic receptor activation in the pontomedullar reticular field.

Heart beat fluctuation during fictive locomotion in decerebrate cats: locomotor-cardiac coupling of central origin

Fictive locomotion was evoked by stimulation of the mesencephalic locomotor region (MLR) in immobilized, vagotomized and decerebrate cats. The coherence between heart beat fluctuation and efferent discharges of the hindlimb nerve was used to evaluate the strength of the coupling between the cardiac and locomotor rhythms during MLR-elicited fictive locomotion. This study demonstrated that there was a locomotor-cardiac coupling of central origin.

Descending inhibitory pathway responsible for simultaneous suppression of postural tone and respiration in decerebrate cats

The present study was performed in order to elucidate whether the suppressive effects on postural tone and respiration evoked by stimulation of the dorsal tegmental field (DTF) of the pons are relayed through the neurons in the ponto-medullary reticular formation. First, the DTF was functionally identified, and then a microelectrode was inserted into the caudal pontine and medullary reticular formation to investigate the distribution of the neurons monosynaptically activated by stimulation of the DTF. The monosynaptically activated neurons were distributed within the nucleus reticularis gigantocellularis (NRGc) in the caudal pons and medulla. The spinal cord (L1) was stimulated to study whether such monosynaptically activated neurons project to the spinal cord. Almost all the neurons monosynaptically activated by DTF stimulation were antidromically activated by spinal stimulation. This result indicates that the neurons in the NRGc activated monosynaptically by DTF stimulation send axons to the spinal cord. Tonic micro-stimulation was then delivered to the site in the NRGc, from which the monosynaptically driven units were recorded by DTF stimulation. The stimulation resulted in the parallel suppression of postural tone and respiration, similar to the suppressive effects elicited by DTF stimulation. The present study suggests the possible existence of a descending inhibitory pathway through the reticulospinal neurons in the NRGc responsible for parallel suppression of postural tone and respiration.

Coupling between respiratory and locomotor rhythms during fictive locomotion in decerebrate cats

Fictive locomotion of the hindlimb was evoked by stimulation of the mesencephalic locomotor region (MLR) in immobilized, decerebrate cats. Fictive respiration can also be obtained in such a preparation after bilateral vagotomy. A cross-correlation technique was used to evaluate the strength of the coupling between the locomotor and respiratory rhythms. This study demonstrated that there was a locomotor-respiratory coupling of central origin and the strength of the coupling varied depending on the level of end-tidal pCO2, reflecting the arterial CO2 tension.

Depression of diaphragmatic and external intercostal muscle activities elicited by stimulation of midpontine dorsal tegmentum in decerebrate cats

This paper describes the inhibitory influences on external intercostal muscle activity and diaphragmatic activity, evoked by stimulation of the dorsal tegmental field (DTF) of the pons in decerebrate cats. Stimulation of the DTF along the midline decreased both the diaphragmatic and the external intercostal activities. However, the inhibitory influences on the above two kinds of respiratory muscle activities were different in nature. Diaphragmatic activity, once suppressed by stimulation, recovered in spite of the continuation of stimulation. In contrast, DTF stimulation depressed tonic discharges of external intercostal muscle, and the depressed or abolished tonic discharges did not resume even after termination of stimulation. Rhythmic external intercostal muscle activity, synchronized with diaphragmatic activity, was also suppressed by DTF stimulation and the suppressed rhythmic activity seemed difficult to recover during stimulation, compared with the recovery process of the diaphragmatic activity.