Studies on the Hexapod Nervous System. Iv. A Cytological and Cytochemical Study of Neurons and Their Inclusions in the Brain of a Cockroach Periplaneta Americana (L.)

A variety of cytological and cytochemical staining reactions has been applied in a study of neuronal inclusions in the brain of the American cockroach. Three types of cytoplasmic inclusions, which exist in addition to mitochondria, ribosomes, and the Golgi apparatus, are characterized. For discussion purposes these are called A-cell NSM, beta-, and delta-granules. 2. The cytochemical staining reactions used indicate that A-cell NSM is a cystine- or cysteine-rich phospholipoprotein. 3. Perikaryal inclusions which stain intensely with PAS, SBB, CPM, and AF, but which are not stained blue-black with CAHP, occur in the majority of neurons. These are called beta-granules. Despite similarities in stainability, there is a possibility that these inclusions are not all of one type. They clearly differ from the Golgi apparatus, and it is also highly unlikely that they are "typical" mitochondria. The cytochemical data suggest that beta-granules contain a lipid or glycolipid which is either not predominantly phospholipid, or from which phospholipid has been removed during fixation. The fact that they are rendered relatively resistant to lipid solvents by formalin fixation indicates chemical association with a protein. 4. Delta-granules occur as single, conspicuous inclusions within the perikarya of certain of the smaller neurons. Unlike beta-granules, they stain green with AF. They appear to consist of a lipoprotein or glycolipoprotein which contains phospholipid. 5. The Golgi apparatus consists of sudanophilic crescent-shaped or spheroidal "externa" frequently closely associated with variably sudanophilic "interna" which may contain beta-granules. The "mottled" appearance of nerve cells which have been stained to demonstrate RNA appears to be due to the unstained Golgi spheroids. 6. The limitations of staining reactions as criteria for categorizing cytoplasmic inclusions, and the significance of cytomorphological features as indices of neurosecretory activity are discussed.