Processing in the Central Nervous System

The extreme sensitivity of the receptor neurons is combined with a most efficient processing of their responses by the central nervous system. Via the axons of the receptor neurons the nerve impulses are conducted to the antennal lobe, the first synaptic station of the central olfactory pathway in insects. The axons of the pheromone receptor neurons terminate on local interneurons and projection neurons (PN) of the macroglomerular complex (MGC) (Hildebrand 1996). The silk moth has 

000 bombykol receptor neurons per antenna (Steinbrecht 1970) and 34 projection neurons connecting the MGC with higher centres of the central nervous system (Kanzaki et al. 2003). Since there are also 17,000 bombykal receptors the messages of at least 1000 (in the hawk moth Manduca sexta up to 10,000) receptor neurons finally converge to one projection neuron. 

With a load of 10 g of bombykol /f.p. (10 ° g/f-p.) 40% (80%) of the males responded with wing vibration (at 21°C). At these loads we foundX, = 0.0145 (0.1545) spikes/s (from Tab. 2 in Kaissling and Priesner, 1970). For a convergence of 17,000 receptor neurons we find from Eq. 3.3 and with/ = 0.0855 spikes/s a signal-to-noise ratio of 3 (31). This shows that the processing in the CNS works near the theoretical limit. 

Finally it should be mentioned that the bombykol concentration in air at the 40% (80%) behavioural threshold was 3,000 (30,000) pheromone molecules/ml of air, at an airstream velocity of 57 cm/s. Interestingly these moths with 17,000 receptor neu-rons/antenna are almost as sensitive as a dog for (other) odorants (1000 molecules/ml). 

For linguistic improvements I thank Dr. Ann Biederman-Thorson, Oxford. 

---

In summary, complete examination of CSF, including basic biochemical analysis and qualitative cytology with the determination of specific CSF proteins and isoelectric focusing, provides very sensitive diagnostic imformation concerning serous inflammatory processes in the central nervous system, including diseases of autoimmune origin such as multiple sclerosis. 

Duggan AW, Fleetwood-Walker SM. Opioids and sensory processing in the central nervous system. In Handbook of Experimental Pharmacology, Vol. 104. Berlin Springer-Verlag, 1993 731-771. 

Also affects concentrations of neurotransmitters. Interferes with biochemical processes in the central nervous system involving calcium. 

Collectively, these histopathological studies suggested that an inflammatory process in the central nervous system (CNS) is involved in the pathogenesis of HAM/TSP. 

FIGURE 3.22 West Nile virus. Immunostaining of flaviviral antigens in neurons and neuronal processes in the central nervous system from an immunosuppressed patient who died of West Nile virus encephalitis. (Flavivirus-hyperimmune mouse ascitic fluid naphthol fast red substrate with hematoxylin counterstain original magnification x40.)... 

Involvement of the nitric oxide pathway in nociceptive processes in the central nervous system in rats... 

Cleavage sites are shown in red in Figure 23.10. In the anterior pituitary, cleavage generates ACTH and / -lipotropin, and further processing in the central nervous system yields endorphin and enkephalin, among other products. 

The use of acetylenic compounds as suicide inhibitors can be illustrated in the case of 7-acetylenic GABA. y-Aminobutyric acid (GABA), an inhibitory neurotransmitter amino acid, modulates various physiological and pathophysiological processes in the central nervous system. Therefore, elevation of brain GABA levels may be beneficial in the treatment of convulsive disease (epilepsy)... 

In the insect, the scent bouquet causes a specific stimulation pattern at the sensory neurons, which is then processed in the central nervous system into an unambiguous reaction and eventually leads to a characteristic response by the insect. 

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. 

Prostaglandins are a group of lipid autacoids known as eicosanoids. They are produced from membrane phospholipids and found in almost every tissue and body fluid. They are involved in a number of physiological processes including inflammation, smooth muscle tone and gastrointestinal secretion. In the central nervous system they have been reported to produce both excitation and inhibition of neuronal activity. 

Enterochromaffin cells are interspersed with mucosal cells mainly in the stomach and small intestine. In the blood, serotonin is present at high concentrations in platelets, which take up serotonin from the plasma by an active transport process. Serotonin is released on platelet activation. In the central nervous system, serotonin serves as a transmitter. The main serotonin-containing neurons are those clustered in form of the Raphe nuclei. Serotonin exerts its biological effects through the activation of specific receptors. Most of them are G-protein coupled receptors (GPCRs) and belong to the 5-HTr, 5-HT2-, 5-HT4-, 5-HTs-, 5-HT6-, 5-HT7-receptor subfamilies. The 5-HT3-receptor is a ligand-operated ion channel. 

Neuropathic pain is defined as spontaneous pain and hypersensitivity to pain associated with damage to or pathologic changes in the peripheral nervous system as in painful diabetic peripheral neuropathy (DPN), acquired immunodeficiency syndrome (AIDS), polyneuropathy, post-herpetic neuralgia (PHN) or pain originating in the central nervous system (CNS), that which occurs with spinal cord injury, multiple sclerosis, and stroke. Functional pain, a relatively newer concept, is pain sensitivity due to an abnormal processing or function of the central nervous system in response to normal stimuli. Several conditions considered to have this abnormal sensitivity or hyperresponsiveness include fibromyalgia and irritable bowel syndrome. 

Microglia, in contrast, serve as macrophages in the central nervous system. They are relatively inactive during normal conditions, but rapidly proliferate during inflammatory or degenerative processes. 

---