Summary
Neurons in opossum somatic sensory-motor (SSM) cortex were studied to define some features of their normal ultrastructure and to identify the morphology and location of cortical cells that can be activated at short latencies by peripheral stimulation. Pyramidal neurons are characterized by rather triangular perikarya containing a relatively low density of cytoplasmic organelles and receiving few synaptic contacts on their somata and proximal dendrites. Synaptic contacts in this location are always of the ‘flat-symmetrical’ variety. The dendrites of pyramidal cells are densely laden with spines, and most of these postsynaptic elements receive ‘round-asymmetrical’ contacts. Some non-pyramidal neurons with beaded dendrites contain a high density of cytoplasmic organelles and receive both types of synaptic contact on their cell bodies. The dendrites of these neurons rarely bear spines. Many cortical neurons have electron-opaque satellite cells in close apposition to their perikaryal plasmalemma. Thus, the constituent neurons follow the same general rules of synaptic organization as equivalent cells in other mammals. To study these neurons, a technique was developed for the intracellular injection of Procion brown and horseradish peroxidase, because these substances are visible in both the light and electron microscope. Procion brown injection into single cortical neurons produces a vigorous response from a small number of glial cells that leads to partial phagocytosis in only a few hours after the injection. This response was not seen following HRP injections, and HRP-filled neurons could be studied at both the light and EM levels. Serial reconstruction of the cell body region of four pyramidal neurons showed that they received an average of 48 flat-symmetrical contacts per cell. Cells responding with a short latency to peripheral stimulation were all located in layer III of SSM cortex. We conclude that the basal dendrites of layer III pyramidal cells form one target of thalamic fibres in this cortex.
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Christensen, B.N., Ebner, F.F. The synaptic architecture of neurons in opossum somatic sensory-motor cortex: A combined anatomical and physiological study. J Neurocytol 7, 39–60 (1978). https://doi.org/10.1007/BF01213459
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DOI: https://doi.org/10.1007/BF01213459