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Substance P depolarizes striatal projection neurons and facilitates their glutamatergic inputs
Author(s) -
Blomeley Craig,
Bracci Enrico
Publication year - 2008
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2007.148965
Subject(s) - glutamatergic , neuroscience , medium spiny neuron , excitatory postsynaptic potential , chemistry , glutamate receptor , agonist , gabaergic , striatum , receptor , biology , inhibitory postsynaptic potential , dopamine , biochemistry
The striatum is the main basal ganglia input nucleus, receiving extensive glutamatergic inputs from cortex and thalamus. Medium spiny striatal projection neurons (MSNs) are GABAergic, and their axon collaterals synapse on other MSNs. Approximately 50% of MSNs corelease substance P (SP), but how this neurotransmitter controls MSN activity is poorly understood. We used whole‐cell recordings to investigate how SP affects MSNs and their glutamatergic inputs. SP elicited slow depolarizations in 47/90 MSNs, which persisted in the presence of tetrodotoxin (TTX). SP responses were mimicked by the NK1 receptor agonist [Sar9,Met(O 2 )11]‐substance P (SSP), and fully blocked by the NK1 receptor antagonists L‐732,138, or extracellular zinc. When intracellular chloride was altered, the polarity of SP responses depended on the sign of the chloride driving force. In voltage‐clamp, SP‐induced currents reversed around −68 mV and displayed marked inward rectification. These data indicate that SP increased a ClC‐2‐type chloride conductance in MSNs, acting through NK1 receptors. SP also strongly increased glutamatergic responses in 49/89 MSNs. Facilitation of glutamatergic responses (which was observed both in MSNs directly affected by SP and in non‐affected ones) was reduced by application of L‐732,138, and fully blocked by coapplication of L‐732,138 and SB222200 (an NK3 receptor antagonists), showing that both NK1 and NK3 receptors were involved. SP‐induced facilitation of glutamatergic responses was accompanied by a marked decrease in paired‐pulse ratio, indicating a presynaptic mechanism of action. These data provide an electrophysiological correlate for the anatomically known connections between SP‐positive MSN terminals and the dendrites and somata of other MSNs.