Substance P attenuates and DAMGO potentiates amygdala glutamatergic neurotransmission within the ventral pallidum

The amygdala (AMG), nucleus accumbens (NA) and ventral pallidum (VP) influence goal-oriented behaviors. However, the nature of the interactions among these regions has not been well characterized. Anatomical studies indicate that excitatory amino acids are contained in VP inputs from the AMG, and th...

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Bibliographic Details
Published in:Brain research 1998-05, Vol.792 (2), p.193-206
Main Authors: Mitrovic, Igor, Celeste Napier, T
Format: Article
Language:English
Subjects:
Amygdala
Amygdala - cytology
Amygdala - drug effects
Amygdala - metabolism
Analgesics, Opioid - pharmacology
Animals
Biological and medical sciences
Biphenyl Compounds - pharmacology
Central nervous system
Central neurotransmission. Neuromudulation. Pathways and receptors
DAMGO
Electric Stimulation
Enkephalin, Ala-MePhe-Gly
Enkephalins - pharmacology
Evoked Potentials - drug effects
Evoked Potentials - physiology
Excitatory amino acid
Fundamental and applied biological sciences. Psychology
Globus Pallidus - cytology
Globus Pallidus - physiology
Glutamate
Glutamic Acid - physiology
Hypnotics and Sedatives - pharmacology
Male
Neuromodulation
Neurons - drug effects
Neurons - physiology
Neurotransmitter Agents - pharmacology
Nucleus accumbens
Nucleus Accumbens - cytology
Nucleus Accumbens - physiology
Opioid
Rats
Rats, Sprague-Dawley
Reaction Time - drug effects
Stimulation, Chemical
Substance P
Substance P - antagonists & inhibitors
Substance P - pharmacology
Synaptic Transmission - drug effects
Tachykinin
Ventral Pallidum
Vertebrates: nervous system and sense organs
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Summary:The amygdala (AMG), nucleus accumbens (NA) and ventral pallidum (VP) influence goal-oriented behaviors. However, the nature of the interactions among these regions has not been well characterized. Anatomical studies indicate that excitatory amino acids are contained in VP inputs from the AMG, and the NA is a primary source of VP substance P (SP) and opioids. The present study was designed to functionally characterize the NA and AMG projections to the VP, and to assess if opioids and SP can modulate AMG-mediated excitatory neurotransmission within the VP. To do so, extracellularly recorded electrophysiological responses of single VP neurons to electrical activation of VP afferents were monitored during microiontophoretic application of treatment ligands in chloral hydrate-anesthetized rats. The anatomically described glutamatergic inputs from the AMG, and SP inputs from the NA, were pharmacologically verified. It also was determined that even though iontophoretically applied SP increased the spontaneous activity of VP neurons, at ejection current levels that were below those necessary to produce this effect (termed sub-threshold), the tachykinin attenuated AMG stimulation-evoked glutamatergic neurotransmission. SP failed to modulate the excitations induced by iontophoretically applied glutamate suggesting that SP modulation of AMG-evoked excitations were mediated via a decrease in the pre-synaptic release of glutamate. Like SP, the effects of sub-threshold ejection currents of μ opioid agonist DAMGO on AMG-evoked responses were not predicted by the opioid's effects on spontaneous VP neuronal activity; DAMGO inhibited spontaneous firing but potentiated AMG-evoked glutamatergic neurotransmission. The opioid also potentiated effects of exogenous glutamate implying an interaction at a post-synaptic site. These results indicate that tachykinin and opioid neuropeptides contained in NA projection neurons can differentially modulate AMG glutamatergic inputs to the VP.
ISSN:0006-8993
1872-6240
DOI:10.1016/S0006-8993(98)00130-9