Sympathoinhibitory pathway from caudal midline medulla  to RVLM is independent of baroreceptor reflex pathway

Potas, Jason R.; Dampney, R.A.L.

doi:10.1152/ajpregu.00559.2002

Cited by 12 publications

(7 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The hypothesis that inhibitory PS neurons exist within the midline medulla oblongata was suggested by Gebber and co‐workers (Morrison and Gebber, 1984; Barman and Gebber, 1989) based on correlation of baroactivated single units in the raphe with inhibition of sympathetic nerve discharge in cats. This hypothesis is also consistent with the sympathoinhibitory and hypotensive effects produced by stimulation within numerous midline medullary regions (McCall, 1988; Coleman and Dampney, 1998; Potas and Dampney, 2003).…”

supporting

confidence: 80%

GABAergic and glycinergic presympathetic neurons of rat medulla oblongata identified by retrograde transport of pseudorabies virus and in situ hybridization

Stornetta

McQuiston

2004

J of Comparative Neurology

View full text Add to dashboard Cite

Electron microscopy suggests that up to half the synaptic input to sympathetic preganglionic neurons (SPGNs) is GABAergic or glycinergic. A proportion of this input is suspected to originate from neurons located within the medulla oblongata. The present study provides definitive evidence for the existence of these supraspinal presympathetic (PS) neurons with inhibitory phenotypes. PS neurons were identified by retrograde trans-synaptic migration of pseudorabies virus (PRV) injected into the adrenal gland. GABAergic or glycinergic cell bodies were identified by the presence of glutamate decarboxylase (GAD)-67 mRNA or glycine transporter (GlyT)-2 mRNA detected with in situ hybridization (ISH). Neither GABAergic nor glycinergic PS neurons were tyrosine hydroxylase (TH)-immunoreactive (ir). GABAergic PS neurons were located within the ventral gigantocellular nucleus, gigantocellular nucleus alpha, and medial reticular formation, mostly medial to the TH-ir PS neurons. About 30% of GABAergic PS neurons were serotonergic cells located in the raphe pallidus (RPa) and parapyramidal region (PPyr). Glycinergic PS neurons had the same general distribution as the GABAergic cells, except that no glycinergic neurons were located in the RPa or PPyr and none were serotonergic. PRV immunohistochemistry combined with ISH for both GlyT2 and GAD-67 mRNAs showed that at least 63% of midline medulla GABAergic PS neurons were also glycinergic and 76% of glycinergic PS neurons were GABAergic. In conclusion, the rostral ventromedial medulla contains large numbers of GABAergic and glycinergic neurons that innervate adrenal gland SPGNs. Over half of these PS neurons may release both transmitters. The physiological role of this medullary inhibitory input remains to be explored.

show abstract

supporting

confidence: 80%

GABAergic and glycinergic presympathetic neurons of rat medulla oblongata identified by retrograde transport of pseudorabies virus and in situ hybridization

Stornetta

McQuiston

2004

J of Comparative Neurology

View full text Add to dashboard Cite

show abstract

“…In agreement with others (16,39,45), we have shown that microinjections of BIC or SR-95531 bilaterally into the rostral VLM of baroreceptor-innervated cats leads to an increase in SND and MAP as well as a loss of the cardiac-related rhythm in SND (S. M. Barman, G. L. Gebber, and H. S. Orer, unpublished observations).…”

Section: Resultssupporting

confidence: 92%

Role of ventrolateral medulla in generating the 10-Hz rhythm in sympathetic nerve discharge

Barman¹,

Gebber²

2007

American Journal of Physiology-Regulatory, Integrative and Comp

View full text Add to dashboard Cite

We recorded changes in right inferior cardiac and either left inferior cardiac or left vertebral sympathetic nerve discharge (SND) produced by unilateral microinjections of GABA-A and excitatory amino acid (EAA) receptor antagonists into the ventrolateral medulla (VLM) of urethane-anesthetized, baroreceptor-denervated cats. Unilateral microinjections of GABA-A receptor antagonists, SR-95531 or bicuculline, into single tracks in VLM anywhere between 1 and 5 mm rostral to the obex eliminated or markedly reduced 10-Hz power in SND on both sides of the body. Low-frequency components (<6 Hz) of SND were unaffected. Complete blockade of the 10-Hz rhythm occurred with a dose of SR-95531 as low as 6.25 pmol in a 50-nl volume. Unilateral microinjections of the nonselective EAA receptor antagonist, kynurenate (KYN; 7.5 nmol), into the caudal or rostral VLM significantly reduced, but did not eliminate, 10-Hz SND ipsilateral to the injection sites, while 10-Hz SND contralateral to the injection sites was not significantly changed. These observations suggest that 1) GABAergic transmission in VLM is critical for generation of the 10-Hz rhythm, 2) the caudal and rostral portions of VLM act together to generate the 10-Hz rhythm, and 3) 10-Hz rhythm generation depends, at least in part, on tonic or phasic excitatory drive to GABAergic interneurons in caudal VLM and presympathetic neurons in rostral VLM. The data also suggest that pathways interconnecting the two halves of the brain stem play an important role in promoting 10-Hz rhythm generation.

show abstract

“…Potential sources of arterial baroreflex-independent inhibitory input to the RVLM include the caudal midline medulla (58), paraventricular nucleus (PVN) of the hypothalamus (71), the CVLM (15,16,18,60), and GABA interneurons within the RVLM (19). The caudal midline medulla does not appear to be tonically active (58), and most studies suggest that sympathoinhibition from the PVN is related to decreased excitatory input from the PVN to RVLM and involves GABA within the PVN rather than the RVLM (29). Therefore any increase in GABAergic input to the RVLM would likely involve regions other than the PVN.…”

Section: Responses To Unilateral Activation Of the Rvlmmentioning

confidence: 99%

Pregnancy increases baroreflex-independent GABAergic inhibition of the RVLM in rats

Kvochina¹,

Hasser²,

Heesch³

2007

American Journal of Physiology-Regulatory, Integrative and Comp

View full text Add to dashboard Cite

ing baroreceptor unloading, sympathoexcitation is attenuated in nearterm pregnant compared with nonpregnant rats. Alterations in balance among different excitatory and inhibitory inputs within central autonomic pathways likely contribute to changes in regulation of sympathetic outflow in pregnancy. Both baroreflex-dependent and baroreflex-independent GABAergic inputs inhibit sympathoexcitatory neurons within rostral ventrolateral medulla (RVLM). The present experiments tested the hypothesis that influence of baroreflex-independent GABAergic inhibition of RVLM is greater in pregnant compared with nonpregnant rats. Afferent baroreceptor inputs were eliminated by bilateral sinoaortic denervation in inactin-anesthetized rats. In pregnant compared with nonpregnant rats, baseline mean arterial pressure (MAP) was lower (pregnant ϭ 75 Ϯ 6 mmHg, nonpregnant ϭ 115 Ϯ 7 mmHg) and heart rate was higher (pregnant ϭ 381 Ϯ 10 beats/min, nonpregnant ϭ 308 Ϯ 10 beats/min). Pressor and sympathoexcitatory [renal sympathetic nerve activity, (RSNA)] responses due to bilateral GABA A receptor blockade (bicuculline, 4 mM, 100 nl) of the RVLM were greater in pregnant rats (⌬MAP: pregnant ϭ 101 Ϯ 4 mmHg, nonpregnant ϭ 80 Ϯ 6 mmHg; ⌬RSNA: pregnant ϭ 182 Ϯ 23% control, nonpregnant ϭ 133 Ϯ 10% control). Unexpected transient sympathoexcitatory effects of angiotensin AT 1 receptor blockade in the RVLM were greater in pregnant rats. Although excitatory responses to bicuculline were attenuated by prior RVLM AT 1 receptor blockade in both groups, pressor responses to disinhibition of the RVLM remained augmented in pregnant rats. Increased influence of baroreflex-independent GABAergic inhibition in RVLM could contribute to suppressed sympathoexcitation during withdrawal of arterial baroreceptor input in pregnant animals. sympathetic nerve activity; brain stem; cardiovascular regulation; angiotensin II PREGNANCY IS CHARACTERIZED by increased blood volume and cardiac output, mild tachycardia, and decreased arterial blood pressure due to a significant decrease in total peripheral resistance (21, 47). Pregnant women and animals are more susceptible to orthostatic (3) and hemorrhagic hypotension (6,8). Although decreased vascular sensitivity to endogenous vasoconstrictors likely contributes to decreased compensatory responses (21), there is evidence that alterations in central nervous system (CNS) autonomic control mechanisms play a major role in regulation of sympathetic outflow and blood pressure during pregnancy.Attenuated arterial baroreflex control of heart rate (HR) has been reported in pregnant animals (5, 50) and women (28,49) and is partly due to suppression of the sympathetic component of the reflex. Direct assessment of arterial baroreflex control of renal sympathetic nerve activity (RSNA) in near-term pregnant rats (14, 43, 51) and rabbits (7, 54, 55) revealed that maximum baroreflex gain is decreased, largely due to an attenuated ability to increase RSNA above baseline levels in response to a hypotensive challenge. However, arterial baror...

show abstract

Sympathoinhibitory pathway from caudal midline medulla to RVLM is independent of baroreceptor reflex pathway

Cited by 12 publications

References 29 publications

GABAergic and glycinergic presympathetic neurons of rat medulla oblongata identified by retrograde transport of pseudorabies virus and in situ hybridization

GABAergic and glycinergic presympathetic neurons of rat medulla oblongata identified by retrograde transport of pseudorabies virus and in situ hybridization

Role of ventrolateral medulla in generating the 10-Hz rhythm in sympathetic nerve discharge

Pregnancy increases baroreflex-independent GABAergic inhibition of the RVLM in rats

Contact Info

Product

Resources

About