Three-dimensional reconstruction of the basket cell of the human motor cortex

Abstract

The basket cell is a specialized interneuron of the human motor cortex which forms pericellular baskets around the soma of the pyramidal neurons ~. This cell appears to be spatially oriented in a specific manner within the motor cortex 3. The study of rapid Golgi preparations has suggested that the basket cell is a fiat neuron enclosed in its entirety within a narrow, by-and-large disc-shaped tissue volume oriented perpendicular to the pia mater and to the long axis of the precentral gyrus ~,4. The basket cell can be visualized in its entirety only in preparations cut in that particular plane; any change in the angle of view of this fiat neuron would change its morphological appearance. It has been postulated 5 that if this neuron were to be viewed 'in profile' or in preparations cut parallel to the long axis of the precentral gyrus it would have the appearance of a 'double-tufted' neuron. To pursue this suggestion we have devised a model lbr a 3-dimensional reconstruction of the cortical basket cell utilizing the computer and data (tomographic series of camera lucida drawings) obtained from microscopic observations of rapid Golgi preparations. Basket cells from layers If, upper Ill, lower Ill, IV and V were selected from rapid Golgi preparations (cut perpendicular to the pia and to the long axis of the precentral gyrus) of the motor cortex of a 2-month-old infant. A continuous camera lucida drawing was made of each selected neuron to illustrate its morphological appearance from that angle of view (Fig. 1). In addition, a series of separate camera lucida drawings was made of each neuron by setting the microscope at various subsequent depths, such as 0, 5, 10, 15... l~m from the surface of the preparation. At each of these depths only those axonic and dendritic components of the selected neuron which were in sharp focus were drawn. The number of steps (drawings) necessary to draw a complete neuron represents the thickness of the cell as well as that of its territory of distribution. The series of separate drawings of each neuron were reduced to numerical forms by reading the (×, y) coordinates of numerous points along the cell arborizations. These were entered into a computer file. The Dartmouth time-sharing system was used, the central processing system of which is a GE (Honeywell) 635 processor. The z value or depth of points read from each drawing were also entered. The computer