Cytology and synaptology of the lateral reticular nucleus of the cat.

The organization of lateral reticular nucleus (LRN) of the cat was investigated using electron microscopy and Golgi techniques. Golgi-Cox preparations revealed that the LRN consists of allodendritic and, especially, isodendritic neurons. The latter have been associated with neural centres that have important roles integrating signals from distant sources. Several forms of spines were identified with the Golgi method, and their ultrastructural correlates were determined. Somatic spines resembled stubby protrusions, while dendritic spines, where were usually observed on distal dendrites, appeared as pedunculated spines, racemose appendages and spine-crowned appendages. Ultrastructural examination of this nuclease revealed various synaptic relationships. The majority of the synaptic terminals were small (1.5--2.5 micrometer in diameter), contained round vesicles and usually contacted dendrites and spines. Other small terminals contained pleomorphic vesicles and contacted distal dendrites and spines. Large terminals (greater than 2.5 micrometer in diameter) with round or pleomorphic vesicles contacted the somata or proximal dendrites. Three types of "synaptic configurations," which consisted of discrete aggregations of neuronal processes invested by astrocytic lamellae, were also identified. These structural arrangements likely provide a basis for the integration of inputs to the LRN from spinal and supraspinal centres.