Dendritic trees of neurones in the rat supraoptic nucleus.

The cytoarchitecture of the rat supraoptic nucleus was studied using the Golgi-Cox method with a neutral red or Cresyl violet counterstain to allow the limits of the nucleus to be determined accurately. A small number of stained neurones were seen in each of the brains sectioned but they were unevenly distributed in the supraoptic nucleus. There were more cells posteriorly and close to the optic tract. A minority of cells studied (a total of 4) were round (diameter approximately 20 micrograms) and multipolar and were interpreted as interneurones. The majority of stained cells studied (60) had oval cell bodies (mean long diameter 22.7 micrograms in coronal sections) with a single fine axon directed dorsally and medially and 1-3 heavier dendrites passing ventrally. Both cell bodies and dendrites of the major cell type showed spines and both dendrites and axons had some varicosities. The anatomy of the larger cell group (the presumed neurosecretory cells) is thus consistent with their having a substantial synaptic input and the presence of long dendrites (up to 205 micrograms) implies that caution is necessary in the interpretation of experiments where cell activity is monitored while active materials are placed near the cell bodies.