Marked differences in the number and type of synapses innervating the somata and primary dendrites of midbrain dopaminergic neurons, striatal cholinergic interneurons, and striatal spiny projection neurons in the rat.
Elucidating the link between cellular activity and goal-directed behavior requires a fuller understanding of the mechanisms underlying burst firing in midbrain dopaminergic neurons and those that suppress activity during aversive or non-rewarding events. We have characterized the afferent synaptic connections onto these neurons in the rat substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA), and compared these findings with cholinergic interneurons and spiny projection neurons in the striatum. We found that the average absolute number of synapses was three to three and one-half times greater onto the somata of dorsal striatal spiny projection neurons than onto the somata of dopaminergic neurons in the SNpc or dorsal striatal cholinergic interneurons. A similar comparison between populations of dopamine neurons revealed a two times greater number of somatic synapses on VTA dopaminergic neurons than SNpc dopaminergic neurons. The percentage of symmetrical, presumably inhibitory, synaptic inputs on somata was significantly higher on spiny projection neurons and cholinergic interneurons compared with SNpc dopaminergic neurons. Synaptic data on the primary dendrites yielded similar significant differences for the percentage of symmetrical synapses for VTA dopaminergic vs. striatal neurons. No differences in the absolute number or type of somatic synapses were evident for dopaminergic neurons in the SNpc of Wistar vs. Sprague-Dawley rat strains. These data from identified neurons are pivotal for interpreting their electrophysiological responses to afferent activity and for generating realistic computer models of neuronal networks of striatal and midbrain dopaminergic function.
Department of Anatomy, Otago School of Medical Sciences, and the Brain Health Research Centre, University of Otago, Dunedin, 9054, New Zealand.
Rachel J
RJ
Sizemore
Department of Anatomy, Otago School of Medical Sciences, and the Brain Health Research Centre, University of Otago, Dunedin, 9054, New Zealand.
Rong
R
Zhang
Department of Anatomy, Otago School of Medical Sciences, and the Brain Health Research Centre, University of Otago, Dunedin, 9054, New Zealand.
Naili
N
Lin
Department of Anatomy, Otago School of Medical Sciences, and the Brain Health Research Centre, University of Otago, Dunedin, 9054, New Zealand.
Liping
L
Goddard
Department of Anatomy, Otago School of Medical Sciences, and the Brain Health Research Centre, University of Otago, Dunedin, 9054, New Zealand.
Timothy
T
Wastney
Department of Anatomy, Otago School of Medical Sciences, and the Brain Health Research Centre, University of Otago, Dunedin, 9054, New Zealand.
Louise C
LC
Parr-Brownlie
Department of Anatomy, Otago School of Medical Sciences, and the Brain Health Research Centre, University of Otago, Dunedin, 9054, New Zealand.
John N J
JN
Reynolds
Department of Anatomy, Otago School of Medical Sciences, and the Brain Health Research Centre, University of Otago, Dunedin, 9054, New Zealand.
Dorothy E
DE
Oorschot
D000818:Animals; D059329:Cholinergic Neurons / Q000648:ultrastructure*; D003342:Corpus Striatum / Q000648:ultrastructure*; D003712:Dendrites / Q000648:ultrastructure*; D059290:Dopaminergic Neurons / Q000648:ultrastructure*; D007395:Interneurons / Q000648:ultrastructure; D008297:Male; D008636:Mesencephalon / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D013045:Species Specificity; D013569:Synapses / Q000648:ultrastructure*
RRID:AB_39024; RRID:AB_94647; dorsal striatum; substantia nigra pars compacta; synaptic innervation; transmission electron microscopy; ventral tegmental area