Central nervous system of insects

Imidacloprid or l-[(6-chloro-3-pyridyl methyl]-N-nitro-2-imidazol idinimine Neonicotinoid Systemic uptake by plant and further distributed through the leaves, acts through central nervous system of insects Control of sucking insects, termites, biting insects 11-16... 

The most fundamental studies on their mode of action have been those of Narahashi who worked with giant fibre preparations. He proposed that pyrethroids modify axonal conduction within the central nervous system of insects by altering the permeability of the nerve membrane to sodium and potassium ions (Narahashi, 1965 1974 1976 Burt and Goodchild, 1977 Clements and May, 1977). 

The chemical mediators in the central nervous system of insects are far from completely explored, but acetylcholine (ACh) and octopamine (2.35) play important roles. The neurotransmitter at insect ganglia is acetylcholine, but that at the neuromuscular junction is not acetylcholine but L-glutamic acid (Usherwood and Machili, 1968), and for this neurotransmitter, no selective antagonist has yet been found. The receptors for the neurotransmitters are well protected by selectively permeable membranes. 

Ommochromes belong to the naturally occurring pigments present in many members of the animal kingdom mainly in insects. Their presence in the central nervous system of the silkworm Bombyx mori was proved by using cellulose and silica stationary phases. The Rp values of standards and the isolated pigments are compiled in Tables 2.107 and 2.108. 

Ma P. W. K., Roelofs W. L. and Jurenka R. A. (1996) Characterization of PBAN and PB AN-encoding gene neuropeptides in the central nervous system of the com earworm moth, Helicoverpa zea. J. Insect Physiol. 42, 257-266. 

Tips A., Paemen L., Schoofs L., Ma M. and Blackburn M. (1993) Co-localization of locustamyotropin- and pheromone biosynthesis activating neuropeptide-like immunoreactivity in the central nervous system of five insect species. Comp. Biochem. Physiol. 106A, 195-207. 

The modes of action of different alkaloids are diverse. For example, nicotine binds to and affects nicotinic acetylcholine receptors and shows toxicity. A recent molecular 3D model suggests that both acetylcholine and nicotine bind to the same pocket formed in a nicotinic acetylcholine receptor.15 Morphine binds to and activates opioid receptors, transmembrane-spanning G protein-coupled receptors, in the central nervous system of humans.16 Caffeine, which is structurally similar to adenine, inhibits cyclic AMP phosphodiesterase activity and inhibits the degradation of cAMP, thus exerting a toxic effect on insects 17 in human beings, binding of caffeine to the adenosine A2A receptor induces wakefulness.18 Atropine binds to muscarinic acetylcholine receptors, competing with acetylcholine, and blocks neurotransmission.1... 

Proctolin appears to potentiate synaptic transmission in the central nervous system of the cockroach P. americana (37). Bursts of spike activity in the ventral nerve cord of this insect were elicited by mechanical stimulation of the cereal organs. In the presence of micromolar proctolin, the peak frequency and the duration of bursts were slowly, but significantly, increased. Carbacol, by comparison, caused an immediate enhancement of spontaneous activity, but potentiation of bursts was not observed. Thus, it was concluded that proctolin might function as a neuromodulator in the terminal ganglion. 

Gamma-aminobutyric acid (GABA) is an inhibitory transmitter substance in the central nervous system of both insects and higher animals. However, there are subtle differences in the properties of the GABA-receptor complex between these two groups of animals. 

The sensitivity of pheromone perception in bark beetles appears to be generally typical of the very high sensitivity shown by many insects to their pheromones (Seabrook, 1978 Payne, 1979 see also Mustaparta, Chapter 2). In general, beetles have a lower threshold for their own pheromonal components than to other terpenes and related compounds (Mustaparta et al., 1979 Dickens, 1981). In I. pini, receptor cells specialized for pheromone perception respond minimally, if at all, to host compounds, and vice versa (Mustaparta et al., 1979,1980). However, the behavioral interruption of the response of I. pini to (- )ipsdienol by a few percent of (+ )ipsdienol or by ipsenol must be due to processing in the central nervous system of the insect and not to any interaction of compounds at the antennal receptor sites. Similarly, the synergistic effect of a pheromone blend is due to central integration. 

Verhaert, P, De Loof, A. (1986) Substances resembling peptides of the vertebrate gonadotropin system occur in the central nervous system of Periplaneta americana L. Immunocytological and some biological evidence. Insect Biochem, 16, 191-197... 

Hohensee S, Bleiss W, Duch C (2008) Correlative electron and confocal microscopy assessment of synapse localization in the central nervous system of an insect. J Neurosci Meth 168 64-70... 

The pyrethrins possess the most desirable combination of high biological activity coupled with low mammalian toxicity. The synthetic pyrethroids have been improved over the pyrethrins to achieve a thousand fold increase in activity with even lower mammalian toxicity (Naumann, 1990a Henrick, 1995). The pyrethrins and pyrethroids are considered to act on almost all parts of the nervous system of insects in their primary mode of action. They are speculated to act stereospecifically to block sodium channels in excitable nerve membranes in several parts of the insect nervous system to rapidly produce loss of coordinated movement, periods of convulsive activity and ultimate paralysis (Ruigt, 1985). The pyrethrins which produce repetitive discharges in the peripheral and central nervous system are classified as Type I pyrethroids. Type II pyrethroids (most modem synthetics) block the action potentials without inducing repetitive after discharges (Soderlund and Bloomquist, 1989 Henrick, 1995). 

Mode of Motion. Nicotine, anabasine, and imidocloprid affect the ganglia of the insect central nervous system, faciUtating transsynaptic conduction at low concentrations and blocking conduction at higher levels. The extent of ionisation of the nicotinoids plays an important role in both their penetration through the ionic barrier of the nerve sheath to the site of action and in their interaction with the site of action, which is befleved to be the acetylcholine receptor protein. There is a marked similarity in dimensions between acetylcholine and the nicotinium ion. 

Broadly speaking herbivorous animals (guinea-pig excepted) show cardiac symptoms and carnivores develop central nervous system convulsions or depression with omnivores both heart and central nervous system may be affected. Cold-blooded vertebrates are usually less sensitive to fluoroacetate, but frogs are more sensitive in summer than in winter.2 Fish appear to be insensitive to fluoroacetate dissolved in water.3 Insects are easily killed by fluoroacetate, and the use of sodium fluoroacetate as a systemic insecticide is described on p. 182. 

Lummis SCR, Buckingham SD, Rauh JJ, et al. 1990. Blocking actions of heptachlor at an insect central nervous system GABA receptor. Proc R Soc Lond [Biol] 240 97-106. 

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