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Quantitative and ultrastructural study of serotonin innervation of the globus pallidus in squirrel monkeys
Author(s) -
Eid Lara,
Champigny MarieFrance,
Parent André,
Parent Martin
Publication year - 2013
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/ejn.12164
Subject(s) - axon , globus pallidus , squirrel monkey , biology , anatomy , neuroscience , serotonin , axon terminal , neuron , neurotransmission , basal ganglia , synapse , central nervous system , receptor , biochemistry
The present immunohistochemical study was aimed at characterizing the serotonin (5‐ HT ) innervation of the internal ( GP i) and external ( GP e) pallidal segments in the squirrel monkey ( S aimiri sciureus ) with an antibody against the 5‐ HT transporter ( SERT ). At the light microscopic level, unbiased counts of SERT + axon varicosities showed that the density of innervation is similar in the GP i (0.57 ± 0.03 × 10 6 varicosities/mm 3 of tissue) and the GP e (0.60 ± 0.04 × 10 6 ), with the anterior half of both segments being more densely innervated than the posterior half. Dorsoventral and mediolateral decreasing gradients of SERT varicosities occur in both pallidal segments, but are statistically significant only in the GP i. The neuronal density being significantly greater in the GP e (3.41 ± 0.23 × 10 3 neurons/mm 3 ) than in the GP i (2.90 ± 0.11 × 103), the number of 5‐ HT axon varicosities per pallidal neuron was found to be superior in the GP i (201 ± 27) than in the GP e (156 ± 26). At the electron microscopic level, SERT + axon varicosities are comparable in size and vesicular content in GP i and GP e, where they establish mainly asynaptic contacts with unlabeled profiles. Less than 25% of SERT + varicosities display a synaptic specialization, which is of the symmetrical or asymmetrical type and occurs exclusively on pallidal dendrites. No SERT + axo‐axonic synapses are present, suggesting that 5‐ HT exerts its well‐established modulatory action upon various pallidal afferents mainly through diffuse transmission, whereas its direct control of pallidal neurons results from both volumic and synaptic release of the transmitter.