AN ANATOMICAL AND IMMUNOCYTOCHEMICAL STUDY OF THE PRIMATE TEMPORAL AND FRONTAL CORTEX

Studies were carried out on the human and monkey temporal cortex, and, for comparison, the human frontal cortex. The neurons were studied by light and electron microscopy, and some of their immunocytochemical characteristics elucidated. Neurons in much of the left temporal cortex, apart from area 41, formed radial columns. This columnar organisation was most pronounced posteriorly and superiorly in the left hemisphere, so that anterior area 20 was the least columnar and area 42 the most. The right temporal cortex, on the other hand, showed little columnar organisation. Golgi studies showed a variety of pyramidal and non-pyramidal neurons with specific varieties typical of individual cortical layers. The ultrastructure of the adult and infant cortex was further investigated in well-fixed biopsy specimens. Neuronal profiles were classified by correlating their light microscopic features in semithin sections with their ultrastructural characteristics. Pyramidal cells had a prominent apical dendrite, and generally had a prominent small numbers of cytoplasmic organelles, except for numerous free ribosomes in some of the larger pyramidal cells of layers III-VI. Non-pyramidal cells lacked an apical dendrite, and were further classified, on size and ultrastructural characteristics, into several small, medium and large types. Human cortical neurons were typified by the absence of nuclear folds in the majority of neurons and a low number of axosomatic synapses. Large numbers of asymmetrical (perforated and non-perforated) and symmetrical synapses were, however, present in the neuropil. The same ultrastructural features of the adult cortex were also encountered in the infant, with certain exceptions: 1) Many of the infant neurons had less densely packed heterochromatin, but greater numbers of free ribosomes, compared with the adult. 2) Lipofuscin was absent from the infant neurons. 3) There was a total absence of myelinated fibres from the infant cortex. 4) Axosomatic synapses were commoner in the infant, although as in the adult, neuronal profiles were rarely seen with more than one or two synapses. 5) There were many more large diameter dendrites in the infant neuropil, compared with the adult. The distribution of various neurotransmitters or neuromodulators in the temporal cortex of the macaque monkey was also studied by a combination of immunocytochemistry and light and electron microscopy. GABAergic neurons were found in all cortical layers, but especially in layers II, IV and VI. They were all of non-pyramidal morphology, comprising small round cells, and bipolar or multipolar forms. Presumptive GABAergic axon terminals were also common. Peptidergic neurons were also found in all layers. They showed many morphological types, including some pyramidal cells. At the electron microscopic level, labelled antibody was associated with free ribosomes and the ribosomes associated with rough endoplasmic reticulum, but was absent from Golgi apparatus, mitochondria, and the cisternae of the rough endoplasmic reticulum. The postsynaptic membranes of labelled dendrites and dendritic spines were often densely labelled for peptides. These features of GABAergic and peptidergic neurons were also encountered in the adult and infant human cerebral cortex.

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• ONG WEI YI