Ventral tegmental area of the rabbit brain: a developmental Golgi study.

The ventral tegmental area (VTA) of the rabbit mesencephalon was examined with Golgi-Cox impregnation at neonatal (days 3-21 of age) and young adult (6-12 months of age) stages of development. Neurons in the dorsal midline were small, with sparsely-branched, vertically-oriented dendrites. Neurons in the ventral midline were medium-sized, oval cells with sparse, vertically-oriented dendrites, and multipolar cells with more abundant diffusely-oriented dendrites. Neurons in the medial zone of the VTA, between the midline and the exiting III nerve fibers, were oval in shape, medium in size, and possessed vertical dendritic arborizations of greater size and extent of branching than those in the dorsal midline. Lateral neurons, found among III nerve fibers, were medium-sized and possessed dendritic trees that were specifically oriented in a vertical or horizontal plane, or were diffusely-branched with more abundant arborizations than their specifically oriented counterpart. Very small neurons with short, single branches were scattered among all regions of the VTA. The major cell types showed a similar pattern of dendritic maturation. At 3-9 days of age, the dendrites were generally short, spiny and poorly branched. From days 9-21, the branches increased in number and length, spines were lost, and these neurons rapidly approached adult size and form. The neurons of VTA appear isodendritic in form, and developed in a pattern consistent with other areas of reticular formation, suggesting that VTA may be part of the reticular core of the brain stem.(ABSTRACT TRUNCATED AT 250 WORDS)