Fex

418 contain ordinary neurons that innervate the intrinsic cells of the corpora cardiaca (see below), causing them to release their product. More than 40 years ago, it was noted that different mNSC take up characteristic stains. Further, destruction of the cells affects a wide range of physiological processes (see later chapters), leading to the proposal that they produce a variety of hormones. This was confirmed through the use of immunohistochemistry, following purification of specific neurosecretory hormones. Also in the protocerebrum are two groups of lateral neurosecretory cells (l NSC) whose axons do not cross but travel to the corpus cardiacum of the same side. However, there is almost no information on their function.

The corpora cardiaca arise as invaginations of the foregut during embryogenesis at the same time as the stomatogastric nervous system and are, in fact, modified nerve ganglia. Though their main function is to store neurosecretion, many of their intrinsic cells also produce hormones. In some species, for example, the desert locust, the neurosecretory storage zone and glandular zone (zone of intrinsic cells) are distinct (Figure 13.4C-E); in others, the neurosecretory axons terminate among the intrinsic cells.

Neurosecretory cells are also found in all of the ventral ganglia, and their axons, which contain stainable droplets, can be traced to a series of segmental neurohemal organs, the perisympathetic organs adjacent to the unpaired ventral nerve. In addition, there are many reports of multipolar neurosecretory cell bodies lying on peripheral nerves innervating the heart, gut, etc. However, it should be noted that, for both the neurosecretory cells of the ventral ganglia and those associated with peripheral nerves, only rarely has experimental evidence for their function been obtained.

Many functions have been ascribed to neurosecretory hormones and the intrinsic hormones produced by the corpora cardiaca, but for relatively few of these is there good experimental evidence. Products of the m NSC include prothoracicotropic hormone (PTTH), which activates the molt glands (Chapter 21, Section 6.1); allatotropic and allatostatic hormones, whose primary function is to regulate the activity of the corpora allata (Chapter 19, Section 3.1.3 and Chapter 21, Section 6.1); diuretic hormone, which affects osmoregulation (Chapter 18, Section 5); ovarian ecdysiotropic hormone (OEH) (formerly egg development neurosecretory hormone) (Chapter 19, Section 3.1.3); ovulation- or oviposition-inducing hormone (Chapter 19, Sections 5 and 7.2); and testis ecdysiotropin (TE) (Chapter 19, Section 3.2). Bursicon, which is important in cuticular tanning (Chapter 11, Section 3.4), has been localized in the mNSC in some species, though is principally found in the abdominal ganglia from which it is released via abdominal perivisceral organs. Neurosecretion from the mNSC also affects behavior, though in many cases this is certainly an indirect action, and is important in protein synthesis. Eclosion hormone (EH), important in ecdysis (Chapter 21, Section 6.2), is produced by neurosecretory cells in the tritocerebrum. The intrinsic cells of the corpora cardiaca produce hyperglycemic and adipokinetic hormones (AKH) important in carbohydrate and lipid metabolism (Chapter 16, Sections 5.2 and 5.3) and hormones that stimulate heartbeat rate (Chapter 17, Section 3.2), gut peristalsis, and writhing movements of Malpighian tubules. It appears, however, that the mNSC may be involved in the elaboration of these materials because extracts of these cells exert similar, though less strong, effects on these processes. Neurosecretion from the subesophageal ganglion is, in cockroaches, synthesized and released regularly and controls the circadian rhythm of locomotor activity. In many female moths, pheromone biosynthesis activating neuropeptide (PBAN) (Section 4.1) is produced in three groups of neurosecretory cells in the subesophageal ganglion (in some species also other ventral ganglia). The PBAN synthesized in the subesophageal ganglion appears to be released via the corpora cardiaca. In

female pupae* of Bombyx, two large neurosecretory cells in the subesophageal ganglion produce a diapause hormone which promotes the development of eggs that enter diapause (see Chapter 22, Section 3.2.3). In Rhodnius, diuretic hormone is produced not by the cerebral neurosecretory cells but by the hindmost group of neurosecretory cells in the fused ganglion of the thoracic and first abdominal segments.

All neurosecretory factors characterized to date are peptides (sometimes glycosylated), an observation that is entirely in keeping with those from other animals. They range in molecular weight from the tens of thousands down to a thousand or less. Examples are bur-sicon (M.W. about 40,000), diuretic hormone (M.W. 1500-2000), OEH (6500), TE (2500), diapause hormone (2500), and AKH (a decapeptide). The PTTH of Drosophila is a glycosylated polypeptide (M.W. 66,000). Curiously, the moth Manduca sexta produces two forms of PTTH: the smaller form (M.W. 7000) comes from the mNSC, whereas the larger form (M.W. 28,000) is a product of the l NSC. The two forms have quite different structures, yet in larvae are about equally active.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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