Effects of Lesions in the Parabrachial Nucleus on the Mechanisms for Central and Reflex Termination of Inspiration in the Cat

109

SUMMARY1. In cats under pentobarbitone anaesthesia the effects of focal temperature changes of the 'chemoceptive' areas on the ventral surface of medulla, described by Loescheke and his associates, were studied with respect to tidal volume, VT, tidal variation in efferent phrenic activity, PhrT, and respiratory rate. The cats were either paralysed and ventilated at various constant PA, co and Pa,O2 levels, or breathing spontaneously. It was confirmed that focal bilateral cooling of the intermediate, 'I(S)', areascaused rapid depression of respiration even at constant artificial ventilation. In normocapnic and normoxic conditions apnoea usually ensued at brain surface temperatures of 20-22 "C.3. The effects were graded along continuous temperature-response curves with enhancements of ventilation above and depression below normal body temperature.4. The strongest effects on VT and PhrT were obtained from the I(s) areas with no or only small effects on inspiratory or expiratory timing in the vagotomized animal. The Hering-Breuer inflation reflex and its effects on timing and amplitudes were not affected by cooling this area.5. Focal cooling of the caudal or the rostral 'chemoceptive' areas, 'C(L)' and 'R(M)' areas, caused smaller effects on VT and PhrT but produced significant effects on respiratory rate even after vagotomy.6. The effects of focal cooling of these areas could be mimicked by topical application of procaine solution which has been shown not to penetrate deeper than 100 pm from the surface. suggesting an additive type of interaction between the input from the peripheral chemoreceptors and that from the central (C02, H+) sensing structures whether the latter was altered by changing Peo2 or by focal temperature changes on the I(s) areas.9. In contrast to these effects of hypoxia and stimulation of the carotid sinus nerves the reflex increase of inspiratory activity caused by lung deflation or by electrical stimulation of the glossopharyngeal nerve distal to the carotid sinus nerves was C02 dependent. These reflex effects decreased with focal cooling of the I(s) areas as with hypocapnia, suggesting a mainly multiplicative or 'gain-changing' type of interaction with the central chemoceptive drive. 10. The close similarities in effect of focal cooling and of hypocapnia on the different respiratory parameters even during constant artificial ventilation indicate that focal temperature changes of the I(s) areas intervene effectively with the normal ventilatory response to CO2 without changing the chemical or physical environment of those neural structures in the brain stem which set respiratory pattern.

“…An approximate indication of the 'vagal contribution' to inspiratory 'off-switch' (Euler & Trippenbach, 1976) Phro-Phrc (rel. units) VT eq (ml.)…”

Section: Timingmentioning

confidence: 99%

Section: Effects Of Topical Applicadion Of Procainementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Graded changes in central chemoreceptor input by local temperature changes on the ventral surface of medulla

Cherniack

Euler

Homma

et al. 1979

109

“…For the injured nervous system in man instability of rhythm leading to death is associated with lesions of the brain stem (Plum, 1970). Low decerebration (Lumsden, 1923;Stella, 1938), or bilateral lesions in the region of the nucleus parabrachialis, can cause prolonged periods of inspiratory 'apneusis' (Sears, 1977) in cats, rabbits and other mammalian species, but with intact vagi the rhythm is maintained through the reflex action (Breuer-Hering reflex) of the pulmonary stretch receptors (Euler, Martilla, Remmers & Trippenbach, 1976). Although infant breathing is episodic, particularly during REM sleep (Bryan & Bryan, 1979), it is essentially stable and following each apnoeic pause there is spontaneous resumption of the rhythm.…”

Section: Introductionmentioning

confidence: 99%

The effects of opiates on the respiratory activity of thoracic motoneurones in the anaesthetized and decerebrate rabbit.

Howard¹,

Sears²

1991

“…Lesion studies have suggested that profound changes in respiration are organized within the pons and these observations led to schemes involving the description of pneumotaxic and apneustic centres within those pontine structures (see for example Euler, Martilla, Remmers & St John, 1972;Trippenbach, 1976). Anatomical tracing studies show that the pons, and particularly the parabrachial complex, is a target for descending inputs from the forebrain, hypothalamus, midbrain and cerebellum and also indirectly for reflex afferent inputs that arise from pulmonary and airway receptors, etc.…”

mentioning

confidence: 99%

Cardiovascular and respiratory effects of stimulation of cell bodies of the parabrachial nuclei in the anaesthetized rat.

Lara

Parkes

Silva-Carvhalo

et al. 1994

113

1. In order to assess the importance of the parabrachial nuclei in modulating cardiorespiratory activity, electric current or microinjections of glutamate were used to stimulate discrete regions of the parabrachial nuclei in anaesthetized rats. 2. Stimulation of cell bodies in the medial region of the parabrachial nuclei and in the Kolliker-Fuse nuclei, caused an expiratory facilitatory response. This consisted mainly of a decrease in respiratory rate as measured by observing phrenic nerve activity. 3. Stimulation of cell bodies in the lateral region of the parabrachial nuclei caused an inspiratory facilitatory response. This consisted mainly of an increase in respiratory rate. 4. At the majority of sites (16 out of 20) where changes in respiratory rate were elicited by glutamate injection or electrical stimulation an increase in blood pressure was observed. The coexistence of increases in blood pressure and heart rate indicates the presence of inhibition of the heart rate component of the baroreflex and/or an increase in cardiac sympathetic drive. 5. The expiratory facilitatory response was not evoked reflexly by the rise in blood pressure since it was still present after administration of guanethidine, which abolished the rise in blood pressure. 6. The interactions between the parabrachial nuclei and the medullary respiratory complex in eliciting these changes are discussed.