Classification of preganglionic neurones projecting into the cat cervical sympathetic trunk.

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SUMMARY1. The respiratory-related modulation of activity in neurones of the lumbar sympathetic outflow to skeletal muscle, skin and pelvic organs was investigated in anaesthetized, paralysed and artificially ventilated cats, using single-and multi-unit recordings. The activity of the neurones was analysed with respect to the phrenic nerve discharge under various experimental conditions.2. Neurones tentatively classified as muscle vasoconstrictor and visceral vasoconstrictor neurones exhibited two activity peaks, one caused by baroreceptor unloading during the declining phase of the second order blood pressure waves and a respiratory drive-dependent peak in parallel with inspiration. The two peaks were separated by depressions of activity in early inspiration and post-inspiration. After cutting vagus and buffer nerves the activity peak during inspiration remained and was followed and sometimes preceded by a depression of activity.3. The majority of the neurones tentatively classified as cutaneous vasoconstrictor neurones exhibited no respiratory modulation in their activity. Others exhibited an activity peak in expiration, an activity peak in inspiration, or a respiratory profile similar to that in muscle vasoconstrictor neurones. During increased respiratory drive (induced by hypercapnia) some neurones with unmodulated activity changed to an inspiratory or an expiratory pattern. Neurones discharging predominantly in inspiration projected preferentially to hairless skin.4. Neurones which were tentatively classified as sudomotor neurones discharged predominantly in early expiration. 5. Some preganglionic neurones which were tentatively classified as motilityregulating neurones discharged during expiration. The majority of these neurones disclosed no respiratory modulation of their activity.6. The study shows that different types of neurone of the lumbar sympathetic system exhibit distinct patterns of respiratory modulation in their activity. We conclude that the type and degree of central coupling between respiratory system and sympathetic nervous system may vary according to the destination of the sympathetic neurones.

Section: Discussionmentioning

confidence: 99%

Respiratory modulation of the activity in sympathetic neurones supplying muscle, skin and pelvic organs in the cat.

Boczek-Funcke

Häbler

Jänig

et al. 1992

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“…Experimental procedures, surgery and recording were the same as comprehensively described in a preceding paper (Boczek-Funcke et al 1992a). Briefly, sixteen adult cats were used which were anaesthetized with a-chloralose (initial dose 45 mg/kg i.P., additional doses 5-10 mg/kg i.v.)…”

Section: Methodsmentioning

confidence: 99%

“…Respiratory modulation of the activity is a prominent feature in some thoracic preganglionic neurones projecting into the CST (Preiss, Kirchner & Polosa, 1975;Boczek-Funcke et al 1992a). At least for cardiovascular neurones it may be due to synaptic interactions in the brainstem (McAllen, 1987;Richter & Spyer, 1990), whereby neurones involved in regulation of respiration affect those controlling the cardiovascular system (central component).…”

Section: Introductionmentioning

confidence: 99%

Respiratory‐related activity patterns in preganglionic neurones projecting into the cat cervical sympathetic trunk.

Boczek-Funcke

Dembowsky

Häbler

et al. 1992

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SUMMARY1. Activity in 233 single sympathetic preganglionic neurones that project to the superior cervical ganglion was analysed with respect to central components of respiration phrenicc nerve discharge) and to the afferent feedback generated by mechanical events occurring with ventilation in anaesthetized and artificially ventilated cats.2. The activity in ninety-one neurones was modulated during the respiratory cycle in two ways: directly by the central inspiratory drive, and indirectly by ventilationrelated blood pressure changes, acting via the systemic baroreceptors. The direct influence was prominent in vagotomized animals or those with a raised respiratory drive, and consisted of an inspiratory increase in activity and decreases of activity in early inspiration and postinspiration. The indirect influence (excitation due to baroreceptor unloading) usually dominated in normocapnic cats with intact vagus nerves. This population of neurones showed both similar reflex responses and a similar respiratory modulation of activity as postganglionic neurones supplying hindlimb skeletal muscle.3. Sixty-one neurones discharged exclusively, or almost exclusively, during central inspiration. This discharge pattern neither depended on the integrity of vagal nor baroreceptor afferents. The activity of these neurones was abolished during hyperventilation and enhanced during hypercapnia. In the latter state, a small activation was often seen in stage II expiration.4. In normocapnia the remainder of neurones (n = 81) exhibited no, or no pronounced, respiratory modulation of activity, except three neurones which showed a prominent expiratory pattern being of central and not of reflex origin. They were not a homogeneous population and included neurones exhibiting reflex responses similar to those of postganglionic neurones supplying hindlimb skin (n = 36), neurones responding to light (n = 4), and others (n = 41).5. It is concluded that distinct types of thoracic preganglionic neurone differ with t Present address: I. Physiologisches

“…Preliminary reports of this work have been published in abstract form (May & McAllen, 1990 (Boczek-Funcke et al 1992), and by the pressor response to noxious stimulation. For cats anaesthetized with Saffan, care was always taken to check that anaesthesia had stabilized to an adequate level with the current rate of infusion before the neuromuscular blocking agent was administered.…”

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confidence: 99%

Effects of preoptic warming on subretrofacial and cutaneous vasoconstrictor neurons in anaesthetized cats.

McAllen

May

1994

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1. Sympathetic and subretrofacial neuron responses to preoptic warming were studied in chloralose-or Saffan-anaesthetized, paralysed cats. 2. Warming a thermode in the preoptic region inhibited the activity of cutaneous vasoconstrictor fibres supplying hairy skin. Muscle vasoconstrictor fibre activity recorded at the same time was either unaffected or raised. 3. Small injections of sodium glutamate (5 nl, 0.1 M) were made into the region of the subretrofacial nucleus in the ventrolateral medulla. The part of that region where glutamate injections evoked brisk increases in cutaneous vasoconstrictor fibre activity was chosen for further study. 4. Extracellular single unit recordings were made in that area from seventy-seven subretrofacial neurons, which were identified by their barosensitivity (inhibition by carotid blind sac inflation). Forty-seven of them were antidromically activated by stimulation in the spinal cord. 5. The activity of twenty subretrofacial neurons (twelve proven bulbospinal) was significantly reduced by periods of preoptic warming. Cutaneous vasoconstrictor activity recorded at the same time also fell. Forty-nine subretrofacial neurons (thirty-five proven bulbospinal) were unaffected or excited by periods of preoptic warming that inhibited cutaneous vasoconstrictor fibres. The response of eight neurons was unclear. 6. No difference in either mean firing rate or axonal conduction velocity was found between neurons inhibited by preoptic warming and other subretrofacial neurons. 7. The subretrofacial neurons inhibited by warming were found intermingled with those unaffected or excited. Marked recording sites of warm-inhibited neurons were clustered around the ventromedial border of the subretrofacial nucleus. 8. In two cats, bilateral inhibition of subretrofacial neurons by surface application of 1 M glycine reduced cutaneous vasoconstrictor fibre activity to 32 and 44 % of control levels. 9. The results suggest that specific cutaneous vasoconstrictor premotor neurons exist in the subretrofacial nucleus. These apparently provide most of the background excitatory drive to cutaneous vasomotor neurons. Central warming stimuli may act, at least in part, by withdrawing that drive.The sympathetic nervous system is able to co-ordinate and convey highly differentiated patterns of activity to its various target organs. Even amongst the subgroup of postganglionic neurons that supply and constrict blood vessels there are clear functional differences. For example, sympathetic fibres which supply vessels in skeletal muscle are highly barosensitive and are excited by stimulation of either nociceptors or arterial chemoreceptors; those supplying hairy skin are much less barosensitive, and are inhibited by nociceptor or chemoreceptor stimuli (Jiinig, 1988 (Jainig, 1985(Jainig, , 1988. Preganglionic neurons also appear to be functionally specific, although on this point the evidence is less conclusive.Nevertheless, activity patterns characteristic of (e.g.) muscle or cutaneous vasoconstrictor neurons may be re...