Genesis of morphologically identified neurons in the dorsal lateral geniculate nucleus of the cat.

Neurons in the dorsal lateral geniculate nucleus of the cat can be grouped into five morphological classes based on a variety of structural characteristics. These same structural characteristics can serve as morphological signatures for the three physiological classes (X, Y, W) of neurons found in this nucleus. The purpose of this study was to determine if a relationship exists between the birthdate of neurons within the dorsal lateral geniculate nucleus and the adult morphology of those neurons. Seven cats, each of which had received a single injection of 3H-thymidine, were studied. A total of 2,138 Golgi-impregnated neurons were identified in the dorsal lateral geniculate nuclei of these seven cats; 1,517 of these neurons were successfully resectioned and recovered, of which 385 (25%) were found to contain the 3H label. Neurons from each of the five morphological classes were labeled in each of the six animals that received a 3H-thymidine injection between embryonic day 24 (E24) and E28. Class 3 and class 5 neurons were labeled in a cat injected with 3H-thymidine on E30. These findings demonstrate that the development of the morphological class of a neuron in the dorsal lateral geniculate nucleus is independent of the time of its final cell division. Further, given the relationship that exists in the cat's dorsal lateral geniculate nucleus between neuronal structure and function, the present findings suggest that the different physiological classes of cells found in this nucleus undergo their final cell divisions throughout most of the period of neurogenesis except that the functional role of neurons born late in this period may be more restricted.