Anatomy and fine structure of nerves associated with the corpus allatum and foregut musculature of Periplaneta americana (L.) (Dictyoptera : Blattidae)

Abstract

The ultrastructure of nerves associated with the corpus allatum (CA) of Periplaneta americana (Dictyoptera : Blattidae) is described, and estimates of the numbers of neurons they contain is presented. The nerves examined include the nervi corporis cardiaci 1 and 2 (NCC 1, 2), the nervi corporis allati 1, the anterior and posterior branches of nervus corporis allati 2 (NCA 2), the allatal commissure (AC), and the postallatals (PN). These nerves have the ultrastructural appearance of neurohormone release sites, suggesting that much of the retrocerebral complex functions as a diffuse neurohemal organ. NCC 1 contains about 600 axons, roughly 90% of which are less than 1 μm in diameter, while NCC 2 comprises about 75 that are 0.6–3.8 μm wide. AC consists of 12–14 neurosecretory axons, 6–7 apparently crossing from the NCA 2 and CA on each side. Synaptoids with 2 kinds of granules, presumably neurosecretory, occur on CA cells within the parenchyma, and adjacent to invaginated pockets of basement lamella at the gland's periphery. This suggests that neurochemical mediators are released at both sites. Most of the PN axons have electron-opaque granules 100–200 nm in diameter. These axons form multiple synapses on foregut muscles, and the synapses contain 93 ± 17.7 nm ( x ± S. D. ) electron-opaque granules, and 48.4 ± 7.2 nm electron-lucent vesicles.