Abstract
The main thalamic afferentation of the prefrontal cortex (PFC) originates in the mediodorsal nucleus (MD). Although it is suggested that this pathway is affected in schizophrenia, there is a lack of functional and structural data regarding its synaptic organization. The scope of this study was to characterize the ultrastructural features of thalamocortical synapses formed by afferents from the MD by applying anterograde tract tracing, immunohistochemical detection of parvalbumin (PV, a probable marker of thalamocortical endings), and quantitative electron microscopic techniques to the PFC of the macaque monkey. Our findings indicate that anterogradely-labeled and PV-immunoreactive boutons exhibit similar ultrastructural properties, characterized by their larger size, higher incidence of release sites and a higher occurrence of mitochondria when compared to non-labeled, excitatory-like endings in the middle layers of the PFC. Although most of the contacts were made on spines in both cases, PV-immunopositive axon terminals apparently targeted dendritic shafts at about twice the frequency found for anterogradely-labeled afferents from the MD (20.5% and 9.5%, respectively). This result suggests diversity among thalamocortical and/or PV-immunoreactive axon terminals of the PFC. In accordance with studies in other cortical areas, our findings suggest that corollary discharge through the mediodorsal thalamocortical projection is also adapted to synaptic transmission with high efficacy and probably exhibits marked short-term temporal dynamics in the PFC.
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Abbreviations
- BDA:
-
Biotinylated dextrane amine
- EM:
-
Electron microscopic
- GABAergic:
-
Gamma aminobutyrate-containing
- MD:
-
Mediodorsal thalamic nucleus
- MDpc:
-
Mediodorsal thalamic nucleus, parvocellular part
- MRI:
-
Magnetic resonance imaging
- NL:
-
Non-labeled
- PB:
-
Phosphate buffer
- PBS:
-
Phosphate buffered saline
- PFC:
-
Prefrontal cortex
- PSD:
-
Postsynaptic density
- PV:
-
Parvalbumin
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Acknowledgements
This work was supported by National Institutes of Health Grants MH44866 (P.S.G.-R.) and MH38546 (P.S.G.-R.). Dr. E. Procyk’s help with the data analysis is highly appreciated. The authors are grateful for Klara Szigeti for her excellent technical assistance.
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P.S. Goldman-Rakic has died
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Negyessy, L., Goldman-Rakic, P.S. Morphometric characterization of synapses in the primate prefrontal cortex formed by afferents from the mediodorsal thalamic nucleus. Exp Brain Res 164, 148–154 (2005). https://doi.org/10.1007/s00221-005-2237-6
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DOI: https://doi.org/10.1007/s00221-005-2237-6