Developmentally different onset ofα1- andα2-adrenergic responses in the neonatal rat dorsal motor nucleus of the vagus in vitro

Fukuda, Atsuo; Nabekura, Junichi; Ito, Chitose; ́n, Carlos R. Plata-Salama; Osuga, Yutaka

doi:10.1016/0006-8993(89)91170-0

Cited by 7 publications

(2 citation statements)

References 13 publications

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“…Another explanation for the absence of NA-mimetic effects of clonidine and guanfacine is the possible immaturity (in terms of number, distribution, structure, responsiveness or combination of all the above) of the medullary a2-receptors at birth. Developmentally different onsets of°x l-and a2-adrenergic responses have been reported for neurons in the dorsal motor nucleus of the vagus (Fukuda, Nabekura, Ito, Plata-Salaman & Oomura, 1989). Our results show that the use of antagonists points to the existence of differences between al-and a2-responses (NA-induced decreases in RF are blocked by a2-but not a1-antagonists) but that some x2-agonists were not efficient.…”

Section: Maturity Of Adrenoceptors At Birthsupporting

confidence: 54%

Noradrenergic modulation of the medullary respiratory rhythm generator in the newborn rat: an in vitro study.

Errchidi

Monteau

Hilaire

1991

The Journal of Physiology

125

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SUMMARY1. Superfused brain stem-spinal cord preparations of newborn rats, which continue to show a rhythmic respiratory activity in vitro, were used to analyse the mechanisms whereby the A5 noradrenergic area modulates the activity of the medullary respiratory rhythm generator in the newborn.2. In preparations including the pons (ponto-medullary preparations), noradrenaline (NA, 25-100,IM) added to the bathing medium either increased (n = 29/50) or decreased (n = 21/50) the respiratory frequency and elicited a tonic discharge in the cervical ventral roots in 50 % of the experiments. Double-bath experiments showed that the increases in respiratory frequency were due to NA acting on the pons, whereas the decreases in respiratory frequency were due to NA acting on the medulla. The NA-induced increases in respiratory frequency were attributed to inhibition of A5 neurons by NA and therefore to withdrawal of A5 inhibition on the medullary rhythm respiratory generator. The NA-induced decreases in respiratory frequency seemed to mimic the effects of endogenous NA on the A5 medullary targets.3. Noradrenaline-induced tonic activity (i) could be induced after elimination of the pons but not on isolated spinal cord, (ii) could be elicited by al-but not a2-agonists, (iii) could be blocked by al-but not x2-antagonists. The tonic activity therefore originated from activation of a, receptors located in the medulla but its importance in respiratory function is doubtful. 4. In medullary preparations (elimination of the pons by transection), the effects of NA agonists and antagonists on respiratory frequency were analysed. Significant decreases in respiratory frequency were induced by NA, adrenaline, phenylephrine and a-methyl-NA, but not by the agonists classified as a2 (clonidine and guanfacine), a, (6-fluoro-NA) and , (isoprenaline). Since yohimbine, idazoxan and piperoxane (a2 antagonists) blocked the NA-induced decreases in respiratory frequency whereas prazosin (a, -antagonist) did not, it is postulated that ac2-receptors may be involved in modulating respiratory frequency.5. Stimulation, lesion and NA microejection experiments showed the complexity of the mechanisms mediating NA-induced changes in respiratory activity but IS 9166 S. ERRCHIDI, R. MIONTE4 U AND G. HILAIRE suggested that the main site of NA action is located in the rostral ventrolateral medulla, where electrical stimulations triggered inspiration prematurely, lesions suppressed the NA-induced decrease in respiratory frequency, and localized application of NA led to an immediate decrease in the respiratory frequency.6. To conclude, the A5 noradrenergic modulation of the medullary respiratory rhythm generator may be relayed by x2-adrenoceptors located within the rostral ventrolateral medulla. Discrepancies between the respiratory effects elicited by NA and a2-agonists raise the question as to whether these drugs are actually potent agonists, or whether the adrenoceptors are functionally mature at birth.

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Section: Maturity Of Adrenoceptors At Birthsupporting

confidence: 54%

Noradrenergic modulation of the medullary respiratory rhythm generator in the newborn rat: an in vitro study.

Errchidi

Monteau

Hilaire

1991

The Journal of Physiology

125

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“…These effects of NE at a 2 , b 1 , and a 1 receptors are consistent with those that have been reported in other in vivo and in vitro studies of various brain structures (Rogawski & Aghajanian, 1980a-c;Van der Maelen & Aghajanian, 1980Egan et al, 1983;Williams et al, 1985;Yoshimura et al, 1985;Ma & Dun, 1985;Wilson & Leon, 1988;Fukuda et al, 1989;Coulter et al, 1990). The present observation that activation of b 1 receptors suppressed the responses of SC cells is somewhat surprising in view of the results of previous studies.…”

Section: Relation Of Present Results To Previous Findings In Scsupporting

confidence: 90%

Effects of norepinephrine on the activity of visual neurons in the superior colliculus of the hamster

1999

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Single-unit recording and micropressure ejection techniques were used to test the effects of norepinephrine (NE) on the responses of neurons in the superficial layers (the stratum griseum superficiale and stratum opticum) of the hamster's superior colliculus (SC). Application of NE suppressed visually evoked responses by -30% in 75% of 40 neurons tested and produced > or = 30% augmentation of responses in only 5%. The decrement in response strength was mimicked by application of the alpha2 adrenoceptor agonist, p-aminoclonidine, the nonspecific beta agonist, isoproterenol, and the beta1 agonist, dobutamine. These agents had similar effects on responses evoked by electrical stimulation of the optic chiasm and visual cortex. The alpha1 agonist, methoxamine, augmented the light-evoked responses of 53% of 49 SC cells by > or = 30%, but had little effect on responses evoked by electrical stimulation of optic chiasm or visual cortex. The effects of adrenergic agonists upon the glutamate-evoked responses of SC cells that were synaptically "isolated" by concurrent application of Mg2+ were similar to those obtained during visual stimulation. Analysis of effects of NE on visually evoked and background activity indicated that application of this amine did not significantly enhance signal-to-noise ratios for most superficial layer SC neurons, and signal-to-noise ratios were in some cases reduced. These results indicate that NE acts primarily through alpha2 and beta1 receptors to suppress the visual responses of SC neurons. Activation of either of these receptors reduces the responses of SC neurons to either of their two major visual inputs as well as to direct stimulation by glutamate, and it would thus appear that these effects are primarily postsynaptic.

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Norepinephrine activates potassium conductance in neurons of the turtle cerebral cortex

Blanton

Kriegstein

1992

Brain Research

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Developmentally different onset ofα1- andα2-adrenergic responses in the neonatal rat dorsal motor nucleus of the vagus in vitro

Cited by 7 publications

References 13 publications

Noradrenergic modulation of the medullary respiratory rhythm generator in the newborn rat: an in vitro study.

Noradrenergic modulation of the medullary respiratory rhythm generator in the newborn rat: an in vitro study.

Effects of norepinephrine on the activity of visual neurons in the superior colliculus of the hamster

Norepinephrine activates potassium conductance in neurons of the turtle cerebral cortex

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