Brain Neurosecretory Cells and their Hormones
Kopec was the very first to suggest the role of hormones in controlling metamorphosis. On the base of his experiments on the larval gypsy moth (Porthetria dispar) he observed that at a specific period the brain releases a substance into the blood which is essential for pupation and therefore for metamorphosis. His findings on the role of brain hormones in metamorphosis of insects was supported by consequent workers who found similar mechanisms in dissimilar insect groups. Large secretory nerve cells in the brain of the insects called neurosecretory nerves were as well identified as being responsible for affecting pupation. The secretion of these cells is known as activation hormone (AH) or brain hormone (BH). The activation hormone is comprised of proteins or Lipoproteins. The AH or BH after synthesis pass together the axons of these cells and end blindly into a pair of storage and release organs called the corpora cardiaca (CC), situated in the posterior brain. The CC releases the active hormone material termed as prothoracicotropic hormone (PTTH) which is a small polypeptide. This prothoracicotropic hormone acts on the prothoracic gland, causing it to secrete the moulting hormone known as 'ecdysone'.