By F. Kippler. University of California, Santa Barbara. 2018.
These behaviours order 100 mg extra super cialis mastercard erectile dysfunction young men, and consequently those in humans cheap extra super cialis 100mg mastercard erectile dysfunction treatment mumbai, were attributed to the depletion of neuronal vesicular stores of monoamines and the reduction in monoamine transmission caused by this drug. In fact, these patients, when given iproniazid, could become quite disruptive and this action was regarded as an undesirable side-effect! However, its beneficial effects in depression were soon recognised and it was regarded as the first effective antidepressant drug. Studies of peripheral sympathetic neurons, later extended to noradrenergic neurons in the brain, showed that iproniazid irreversibly inhibits the catalytic enzyme, monoamine oxidase (MAO). Because only cytoplasmic monoamines are accessible to MAO, inhibition of this enzyme first increases the concentration of the pool of soluble transmitter but this leads to a secondary increase in the stores of vesicle-bound transmitter: i. Reserpine blocks vesicular uptake of monoamines which, as a consequence, leak from the storage vesicles into the cytosol. Although these monoamines would normally be metabolised by MAO, they are conserved when a MAO inhibitor (MAOI) is present, and so co-administration of reserpine and a MAOI leads to accumulation of monoamines in the neuronal cytosol. It is now known that, when the concentration of cytoplasmic monoamines is increased in this way, they are exported to the synapse on membrane-bound monoamine trans- porters. The ensuing increase in monoamine transmission, despite the depletion of the vesicular pool, presumably accounts for the effects of iproniazid on the behaviour of reserpine-pretreated rats. In 1958, another agent, imipramine, was discovered by chance to have beneficial effects in depression. Drawing all this evidence together, Schildkraut (1965) concluded that depression was caused by a functional deficit of noradrenergic transmission in the brain. He also thought that the rebound depression and fatigue, which are experienced after the arousing effects of amphetamine have worn off, were due to depletion of neuronal stores of noradrenaline. To this day, there is controversy over whether or not amphetamine has a beneficial effect in depression. One suggested that there is a malfunction of neurons which release 5-HT (Coppen 1967). Another proposed that a deficit in both noradrenergic and serotonergic transmission is to blame (Maas 1975). Others have argued that an imbalance in the functional output of these two systems is the key factor (Ricci and Wellman 1990). However, they all share a common theme: that disruption of some aspect of monoaminergic transmission in the brain is a causal factor in depression. It is remarkable that, although this theory is often challenged, it has not yet been replaced by a validated alternative and, to this day, central noradrenergic and/or serotonergic systems are primary targets for all established antidepressant drugs. THE NEUROBIOLOGY OF DEPRESSION Attempts to find the cause(s) of depression have adopted two main approaches. One is to lookfor the neurobiological basis of depression in human subjects and animal models of this condition. The second is to investigate the pharmacology of established antidepressant agents to see whether they consistently augment some, and ideally the same, neurobiological targets in the brain. HUMAN STUDIES The objective of these studies is to find a neurochemical marker for depression. For obvious reasons, the majority has looked for changes that might affect monoamine function and so the following sections concentrate on these neurotransmitters. The changes indicated are based on the most frequently published findings. For instance, it is not at all certain that neurochemical changes in the plasma or urine give any reliable indication of what is happening in the brain. Measurements in post-mortem brain tissue do not have this problem but the unavoidable delay in collecting tissue samples intro- duces another. Confirmation of the diagnostic status of the subjects is often difficult (especially retrospectively) and any drug treatments they had taken could distort the results. So far, evidence for abnormal peripheral (Elliott 1992) or central (Horton 1992) monoamine function in depression is equivocal, and no consistent biochemical markers have emerged to provide a firm linkbetween the two (Table 20. One widely cited finding is that subjects who have attempted violent suicide form a neurochemically distinct group because the concentration of the 5-HT metabolite, 5-HIAA, in their CSF is lower than normal, suggesting that a deficit in 5-HT release is associated with suicide DEPRESSION 429 (Asberg, Traskman and Thoren 1976). However, this abnormality is now believed to be associated with a deficit in control of behavioural impulsivity, rather than depression. Evidence for a linkbetween monoaminergic transmission and the therapeutic effects of antidepressant agents is more convincing. Depletion of noradrenaline stores (achieved by administration of the noradrenaline synthesis inhibitor, a-methyl-p-tyrosine) causes a resurgence of depression in patients who are in remission following treatment with antidepressants that selectively target noradrenergic neurons.
They are then involved in the distribution of the chromo- Although cilia and flagella appear to be extensions of the cell somes during cellular reproduction buy 100mg extra super cialis visa erectile dysfunction in cyclists. Mature muscle and nerve membrane order 100 mg extra super cialis visa erectile dysfunction treatment mumbai, they are actually cytoplasmic projections from the in- cells lack centrosomes, and thus cannot divide. These projections contain cytoplasm and sup- portive microtubules bounded by the cell membrane (fig. Vacuoles Cilia and flagella should not be confused with microvilli or with Vacuoles (vak′yoo-o¯lz) are membranous sacs of various sizes that stereocilia, both of which are specializations of cell membranes. They are formed when a Cilia (sil′e-a˘) are numerous short projections from the ex- portion of the cell membrane invaginates and pinches off during posed border of certain cells (fig. Vacuolation is initiated either by pinocytosis (pin″o˘- spersed with mucus-secreting goblet cells. There is always a film si-to′sis), in which cells take in minute droplets of liquid through of mucus on the free surface of ciliated cells. Ciliated cells line the cell membrane, or by phagocytosis (fag″o˘-si-to′sis), in which the lumina (hollow portions) of sections of the respiratory and re- the cell membrane engulfs solid particles (fig. The function of the cilia is to move the mucus may contain liquid or solid materials that were previously outside and any adherent material toward the exterior of the body. Flagella (fla˘-jel′a˘) are similar to cilia in basic microtubular structure (see fig. The only example of a flagellated cell in humans is the sperm vacuole: L. Cytology © The McGraw−Hill Anatomy, Sixth Edition of the Body Companies, 2001 62 Unit 3 Microscopic Structure of the Body Fluid-filled Cell Fluid vesicle membrane Nucleolus Nucleus Cytoplasm (a) Pinocytosis Particle Vesicle Cell membrane Phagocytized particle Nucleolus Nucleus (b) Phagocytosis FIGURE 3. Cytology © The McGraw−Hill Anatomy, Sixth Edition of the Body Companies, 2001 Chapter 3 Cytology 63 Flagellar or ciliary membrane Cell membrane (a) Cilia Debris Goblet cell Flagellum FIGURE 3. Nucleoli (noo-kle′o˘-li) are small, nonmembra- arrangement of their microtubules. As ribosomes are formed, they migrate through the nuclear membrane into the cytoplasm. It is the genetic material of the cell and consists Cell Nucleus principally of protein and DNA molecules. When a cell begins to divide, the chromatin shortens and thickens into The spherical nucleus is usually located near the center of the rod-shaped structures called chromosomes (kro′mo˘-so¯mz) cell (fig. Each chromosome carries thousands the genetic material that determines cellular structure and con- of genes that determine the structure and function of a cell. Certain cells, however, such as skeletal muscle cells, are multinucleated. The long skele- Knowledge Check tal muscle fibers contain so much cytoplasm that several govern- 9. Describe the composition and specializations of the cell ing centers are necessary. These cells are limited to certain types of ability of the cell membrane. Describe the various kinds of movements across the cell (nuclear envelope) (fig. Describe the structure and function of the following cyto- cleolemma cisterna (sis-ter′na). Minute nuclear pores are lo- plasmic organelles: rough endoplasmic reticulum, Golgi cated along the nuclear membrane. Cytology © The McGraw−Hill Anatomy, Sixth Edition of the Body Companies, 2001 64 Unit 3 Microscopic Structure of the Body Nuclear pore Nuclear membrane Nucleolus Outer layer Nucleolemma Nucleus cisterna Inner layer (a) Chromatin (b) FIGURE 3. Cytology © The McGraw−Hill Anatomy, Sixth Edition of the Body Companies, 2001 Chapter 3 Cytology 65 CELL CYCLE A cell cycle consists of growth, synthesis, and mitosis. Synthesis is the production of DNA and RNA to regulate cellular activity. Mi- tosis is the division of the nucleus and cytoplasm of a cell that re- sults in the formation of two daughter cells.
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