Presynaptic and postsynaptic relations of μ-opioid receptors to γ- aminobutyric acid-immunoreactive and medullary-projecting periaqueductal gray neurons

Kathryn G. Commons, Sue Aicher, Lee Ming Kow, Donald W. Pfaff

Research output: Contribution to journalArticle

58 Citations (Scopus)

Abstract

The ventrolateral portion of the periaqueductal gray (PAG) is one brain region in which ligands of the μ-opioid receptor (MOR) produce analgesia. In the PAG, MOR ligands are thought to act primarily on inhibitory [e.g., γ- aminobutyric acidergic (GABAergic)] neurons to disinhibit PAG output rather than directly on medullary-projecting PAG neurons. In this study, the ultrastructural localization of MOR immunolabeling was examined with respect to either GABAergic PAG neurons or PAG projection neurons that were labeled retrogradely from the rostral ventromedial medulla. Immunoreactivity for MOR and GABA often coexisted within dendrites. Dual-labeled profiles accounted for subpopulations of dendrites containing immunoreactivity for either MOR (65 of 145 dendrites; 45%) or GABA (65 of 183 dendrites; 35%). In addition, nearly half of PAG neuronal profiles (148 of 344 profiles) that were labeled retrogradely from the ventromedial medulla contained MOR immunoreactivity. MOR was distributed equally among retrogradely labeled neuronal profiles in the lateral and ventrolateral columns of the caudal PAG. With respect to the presynaptic distribution of MOR, approximately half of MOR-immunolabeled axon terminals (35 of 69 terminals) also contained GABA. Some MOR and GABA dual- immunolabeled axon terminals contacted unlabeled dendrites (11 of 35 terminals), whereas others contacted GABA-immunoreactive dendrites (15 of 35 terminals). Furthermore, axon terminals synapsing on medullary-projecting PAG neurons sometimes contained immunoreactivity for MOR. These data support the model that MOR ligands can act by inhibiting GABAergic neurons, but they also provide evidence that MOR ligands may act directly on PAG output neurons. In addition, MOR at presynaptic sites could affect both GABAergic neurons and output neurons. Thus, the disinhibitory model represents only partially the potential mechanisms by which MOR ligands can modulate output of the PAG. (C) 2000 Wiley-Liss, Inc.

Original languageEnglish (US)
Pages (from-to)532-542
Number of pages11
JournalJournal of Comparative Neurology
Volume419
Issue number4
DOIs
StatePublished - Apr 17 2000
Externally publishedYes

Fingerprint

Aminobutyrates
Periaqueductal Gray
Opioid Receptors
Neurons
Dendrites
gamma-Aminobutyric Acid
GABAergic Neurons
Ligands
Presynaptic Terminals
Analgesia

Keywords

  • Analgesia
  • Enkephalin
  • Mesencephalon
  • Morphine
  • Pain

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Presynaptic and postsynaptic relations of μ-opioid receptors to γ- aminobutyric acid-immunoreactive and medullary-projecting periaqueductal gray neurons. / Commons, Kathryn G.; Aicher, Sue; Kow, Lee Ming; Pfaff, Donald W.

In: Journal of Comparative Neurology, Vol. 419, No. 4, 17.04.2000, p. 532-542.

Research output: Contribution to journalArticle

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abstract = "The ventrolateral portion of the periaqueductal gray (PAG) is one brain region in which ligands of the μ-opioid receptor (MOR) produce analgesia. In the PAG, MOR ligands are thought to act primarily on inhibitory [e.g., γ- aminobutyric acidergic (GABAergic)] neurons to disinhibit PAG output rather than directly on medullary-projecting PAG neurons. In this study, the ultrastructural localization of MOR immunolabeling was examined with respect to either GABAergic PAG neurons or PAG projection neurons that were labeled retrogradely from the rostral ventromedial medulla. Immunoreactivity for MOR and GABA often coexisted within dendrites. Dual-labeled profiles accounted for subpopulations of dendrites containing immunoreactivity for either MOR (65 of 145 dendrites; 45{\%}) or GABA (65 of 183 dendrites; 35{\%}). In addition, nearly half of PAG neuronal profiles (148 of 344 profiles) that were labeled retrogradely from the ventromedial medulla contained MOR immunoreactivity. MOR was distributed equally among retrogradely labeled neuronal profiles in the lateral and ventrolateral columns of the caudal PAG. With respect to the presynaptic distribution of MOR, approximately half of MOR-immunolabeled axon terminals (35 of 69 terminals) also contained GABA. Some MOR and GABA dual- immunolabeled axon terminals contacted unlabeled dendrites (11 of 35 terminals), whereas others contacted GABA-immunoreactive dendrites (15 of 35 terminals). Furthermore, axon terminals synapsing on medullary-projecting PAG neurons sometimes contained immunoreactivity for MOR. These data support the model that MOR ligands can act by inhibiting GABAergic neurons, but they also provide evidence that MOR ligands may act directly on PAG output neurons. In addition, MOR at presynaptic sites could affect both GABAergic neurons and output neurons. Thus, the disinhibitory model represents only partially the potential mechanisms by which MOR ligands can modulate output of the PAG. (C) 2000 Wiley-Liss, Inc.",
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N2 - The ventrolateral portion of the periaqueductal gray (PAG) is one brain region in which ligands of the μ-opioid receptor (MOR) produce analgesia. In the PAG, MOR ligands are thought to act primarily on inhibitory [e.g., γ- aminobutyric acidergic (GABAergic)] neurons to disinhibit PAG output rather than directly on medullary-projecting PAG neurons. In this study, the ultrastructural localization of MOR immunolabeling was examined with respect to either GABAergic PAG neurons or PAG projection neurons that were labeled retrogradely from the rostral ventromedial medulla. Immunoreactivity for MOR and GABA often coexisted within dendrites. Dual-labeled profiles accounted for subpopulations of dendrites containing immunoreactivity for either MOR (65 of 145 dendrites; 45%) or GABA (65 of 183 dendrites; 35%). In addition, nearly half of PAG neuronal profiles (148 of 344 profiles) that were labeled retrogradely from the ventromedial medulla contained MOR immunoreactivity. MOR was distributed equally among retrogradely labeled neuronal profiles in the lateral and ventrolateral columns of the caudal PAG. With respect to the presynaptic distribution of MOR, approximately half of MOR-immunolabeled axon terminals (35 of 69 terminals) also contained GABA. Some MOR and GABA dual- immunolabeled axon terminals contacted unlabeled dendrites (11 of 35 terminals), whereas others contacted GABA-immunoreactive dendrites (15 of 35 terminals). Furthermore, axon terminals synapsing on medullary-projecting PAG neurons sometimes contained immunoreactivity for MOR. These data support the model that MOR ligands can act by inhibiting GABAergic neurons, but they also provide evidence that MOR ligands may act directly on PAG output neurons. In addition, MOR at presynaptic sites could affect both GABAergic neurons and output neurons. Thus, the disinhibitory model represents only partially the potential mechanisms by which MOR ligands can modulate output of the PAG. (C) 2000 Wiley-Liss, Inc.

AB - The ventrolateral portion of the periaqueductal gray (PAG) is one brain region in which ligands of the μ-opioid receptor (MOR) produce analgesia. In the PAG, MOR ligands are thought to act primarily on inhibitory [e.g., γ- aminobutyric acidergic (GABAergic)] neurons to disinhibit PAG output rather than directly on medullary-projecting PAG neurons. In this study, the ultrastructural localization of MOR immunolabeling was examined with respect to either GABAergic PAG neurons or PAG projection neurons that were labeled retrogradely from the rostral ventromedial medulla. Immunoreactivity for MOR and GABA often coexisted within dendrites. Dual-labeled profiles accounted for subpopulations of dendrites containing immunoreactivity for either MOR (65 of 145 dendrites; 45%) or GABA (65 of 183 dendrites; 35%). In addition, nearly half of PAG neuronal profiles (148 of 344 profiles) that were labeled retrogradely from the ventromedial medulla contained MOR immunoreactivity. MOR was distributed equally among retrogradely labeled neuronal profiles in the lateral and ventrolateral columns of the caudal PAG. With respect to the presynaptic distribution of MOR, approximately half of MOR-immunolabeled axon terminals (35 of 69 terminals) also contained GABA. Some MOR and GABA dual- immunolabeled axon terminals contacted unlabeled dendrites (11 of 35 terminals), whereas others contacted GABA-immunoreactive dendrites (15 of 35 terminals). Furthermore, axon terminals synapsing on medullary-projecting PAG neurons sometimes contained immunoreactivity for MOR. These data support the model that MOR ligands can act by inhibiting GABAergic neurons, but they also provide evidence that MOR ligands may act directly on PAG output neurons. In addition, MOR at presynaptic sites could affect both GABAergic neurons and output neurons. Thus, the disinhibitory model represents only partially the potential mechanisms by which MOR ligands can modulate output of the PAG. (C) 2000 Wiley-Liss, Inc.

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