Muscarinic presynaptic modulation in GABAergic pallidal synapses of the rat.
The external globus pallidus (GPe) is central for basal ganglia processing. It expresses muscarinic cholinergic receptors and receives cholinergic afferents from the pedunculopontine nuclei (PPN) and other regions. The role of these receptors and afferents is unknown. Muscarinic M1-type receptors are expressed by synapses from striatal projection neurons (SPNs). Because axons from SPNs project to the GPe, one hypothesis is that striatopallidal GABAergic terminals may be modulated by M1 receptors. Alternatively, some M1 receptors may be postsynaptic in some pallidal neurons. Evidence of muscarinic modulation in any of these elements would suggest that cholinergic afferents from the PPN, or other sources, could modulate the function of the GPe. In this study, we show this evidence using striatopallidal slice preparations: after field stimulation in the striatum, the cholinergic muscarinic receptor agonist muscarine significantly reduced the amplitude of inhibitory postsynaptic currents (IPSCs) from synapses that exhibited short-term synaptic facilitation. This inhibition was associated with significant increases in paired-pulse facilitation, and quantal content was proportional to IPSC amplitude. These actions were blocked by atropine, pirenzepine, and mamba toxin-7, suggesting that receptors involved were M1. In addition, we found that some pallidal neurons have functional postsynaptic M1 receptors. Moreover, some evoked IPSCs exhibited short-term depression and a different kind of modulation: they were indirectly modulated by muscarine via the activation of presynaptic cannabinoid CB1 receptors. Thus pallidal synapses presenting distinct forms of short-term plasticity were modulated differently.
Instituto de Fisiología Celular, División de Neurociencias, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Ricardo
R
Hernández-Martínez
Instituto de Fisiología Celular, División de Neurociencias, Universidad Nacional Autónoma de México, Mexico City, Mexico.
José J
JJ
Aceves
Instituto de Fisiología Celular, División de Neurociencias, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Pavel E
PE
Rueda-Orozco
Instituto de Fisiología Celular, División de Neurociencias, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Teresa
T
Hernández-Flores
Instituto de Fisiología Celular, División de Neurociencias, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Omar
O
Hernández-González
Instituto de Fisiología Celular, División de Neurociencias, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Dagoberto
D
Tapia
Instituto de Fisiología Celular, División de Neurociencias, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Elvira
E
Galarraga
Instituto de Fisiología Celular, División de Neurociencias, Universidad Nacional Autónoma de México, Mexico City, Mexico jbargas@ifc.unam.mx.
José
J
Bargas
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D059329:Cholinergic Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D005917:Globus Pallidus / Q000166:cytology / Q000502:physiology*; D053444:Inhibitory Postsynaptic Potentials; D036341:Intercellular Signaling Peptides and Proteins; D009116:Muscarine / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D010890:Pirenzepine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D043884:Receptor, Cannabinoid, CB1 / Q000378:metabolism; D043643:Receptor, Muscarinic M1 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology
D036341:Intercellular Signaling Peptides and Proteins; C496907:MT-7 mamba toxin; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D010455:Peptides; D043884:Receptor, Cannabinoid, CB1; D043643:Receptor, Muscarinic M1; D010890:Pirenzepine; D001285:Atropine; D009116:Muscarine
endocannabinoids; external globus pallidus; muscarinic receptors; pallidal synapses; presynaptic modulation