Locations and central projections of neurons associated with the retrocerebral neuroendocrine complex of the cockroach Periplaneta americana (L.)

Summary Retrograde diffusion and precipitation of Co²⁺ reveals in the ipsilateral pars lateralis (PL) and contralateral pars intercerebralis (PI) of the brain neurons that enter the corpus cardiacum (CC), and, possibly, the corpus allatum (CA) on each side. The PL group consists of 29.6±8.4 somata that fill. Of these, 5.6±0.6 exceed 25 m in diameter, 14.3±2.7 range from 15–25 m, and 9.6±7.6 are smaller than 15 m. After CoCl₂ was applied to the right CC-CA of two males, 239 and 265 somata in the left PI stained. Except for 16 ranging from 30–45 m and chiefly located anteriorly, a majority of these somata measured 10–25 m.The only somata revealed by staining whole brains with the performic acid-resorcin fuchsin method are neurosecretory cells 10–20 m in diameter located within the PI. In starved adult males there are 92.4±8.1 on the right, and 93.2±6.9 on the left. The largest somata in the PL group contain numerous granules that stain with paraldehyde fuchsin. These somata also fill with Co²⁺, and belong to neurosecretory cells that extend into the CC-CA.The cerebral distribution of branches from the PL group, and the relationship of these to the corpora pedunculata, central body, and arborizations from the PI decussation are described.