By S. Ashton. Bismarck State College. 2018.
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Edited by Roy Webster Copyright & 2001 John Wiley & Sons Ltd ISBN: Hardback 0-471-97819-1 Paperback 0-471-98586-4 Electronic 0-470-84657-7 21 Pain and nalgesia A. DICKENSON INTRODUCTION The mechanisms of pain and the ability to control pain may vary in different pain states. This is of particular importance in consideration of a rational basis for the treatment of both inflammatory and neuropathic pain where the damage to tissue and nerve leads to alterations in both the peripheral and central mechanisms of pain signalling. In respect of existing drug therapies, this plasticity, the ability of the system to change in the face of a particular pain syndrome, explains the effectiveness of NSAIDs in inflammatory conditions and yet is also responsible for some of the limitations in the effectiveness of opioids in neuropathic pain. For many years, the neurobiological basis for understanding the causes and improving the treatment of pain states remained somewhat unclear. Fortunately, the development of a number of animal models of inflammation and nerve injury, produced by mani- pulation of either peripheral tissue or nerves, has greatly aided our understanding of the mechanisms of pain and realised many examples of this plasticity. Over the past two decades our knowledge of the pharmacology of pain and analgesia has made enormous strides so that whereas 25 years ago we had a rudimentary idea that morphine worked somewhere in the nervous system we can now recite the complete amino-acid sequence of the four opioid receptors. In parallel with advances in the opioid pharmacology a bewildering list of interacting mediators, transmitters and receptors, some peripheral, some central and some located at both sites, has been established as parts of the initiation and conception of pain. In recent years, further progress has been made in our understanding of both acute and chronic pain mechanisms that can be largely attributed to advancements in molecular biology and genomic techniques, as well as the use of animals. This has fundamentally altered our understanding of the pathophysiology of pain mechanisms, allowed us to explore new targets for pain relief and has led to the hope of development of novel analgesics. Unfortunately, despite this progress, the management of pain remains a major clinical concern and is still inadequate in many cases and a significant problem even to this day. Not only does it bring undesirable sensations, it can often impair the quality of living for many if not effectively treated. In broad terms, pain can be divided into two categories, acute and chronic, which differ in their aetiology, mechanisms and pathophysiology.
Contained in the admits light and protects the inner eye posterior chamber is a structure called the from foreign particles and organisms cheap tadapox 80mg with visa. The vessels purchase 80 mg tadapox amex, it is richly supplied with nerve aqueous humor escapes from the posteri- cells purchase tadapox 80 mg visa. Connected to the cornea and com- or chamber through the pupil into a space pletely covering the eyeball except for the lying between the iris and cornea called part covered by the cornea is a ﬁbrous the anterior chamber order tadapox 80mg visa, which lies between membrane called the sclera discount tadapox 80mg with visa. The aqueous forms the white part of the eye and has humor then drains from the eye into the primary function of supporting and lymph channels and into the venous sys- protecting the eye and maintaining eye tem through a sievelike structure called shape. Lining the exposed area of the scle- the canal of Schlemm (trabecular network), ra and inner eyelid is a sensitive mem- which is located at the junction of the iris brane called the conjunctiva. The balance between the underneath the sclera and also surround- amount of aqueous humor produced and 123 124 CHAPTER 4 CONDITIONS OF THE EYE AND BLINDNESS Muscle Chorid Retina Conjunctiva Ciliary muscle Iris Aqueous humor Fovea Cornea (Macular area) Pupil Optic nerve Lens Optic disc Vitreous Anterior chamber humor Posterior chamber Canal of Schlemm Sclera Figure 4–1 The Eye. This space is ﬁlled with a jelly- cornea and a structure located directly like, translucent substance called the behind the iris called the lens. The lens is vitreous humor, which helps to maintain a small transparent disk enclosed in a the form and shape of the eyeball. Attachments around At the very back of the eye is the inner- the circumference of the lens, called ciliary most coat of the eye, the retina. The reti- muscles, automatically contract or ex- na contains two layers, a pigmented layer pand, changing the shape of the lens from that is ﬁxed to the choroid and an inner fat to thin or vice versa in response to the layer that contains special light-sensitive proximity or distance of an object being cells called rods and cones. The changing shape of the lens Rods are involved with detecting light permits the eye to focus for near or far and dark as well as shape and movement vision, a process called accommodation. Rods contain iary muscles relax, thinning and ﬂatten- a derivative of vitamin A, rhodopsin, a ing the lens. To focus on objects close by, highly light-sensitive substance that breaks Measuring Vision 125 down rapidly when exposed to light. This of best vision and to measure the need for chemical process causes a reaction that corrective lenses. A standard test of visu- activates the rods so that the eye adjusts, al acuity is the Snellen test. Lines are Cones are involved primarily in daylight identiﬁed according to the distance from and color vision as well as in the percep- which they can be read by individuals tion of sharp visual detail. For example, cones are located in a spot on the retina individuals with normal visual acuity can called the macula. The macula is the area read the top line of the chart at 200 feet of clearest central vision. When taking macula, the fovea, contains no rods and is the Snellen test, individuals view the the area where vision is clearest in good Snellen chart at the equivalent of 20 feet light. This are expressed as a fraction, the numerator area is sometimes called the blind spot denoting the equivalent distance from the because it does not contain light-sensitive chart at which the individual being test- cells. Light rays pass through the cornea, ed views the chart (20 feet) and the enter the pupil, pass through the lens, and denominator denoting the distance from register on the retina. Sensory cells of the the chart at which a person with normal retina receive light stimuli and convert vision would be able to read the same line. These elec- Consequently, a visual acuity of 20/100 trical impulses are then transmitted to the means that the individual being tested can optic nerve, which carries them to the see at 20 feet what a person with normal occipital lobe of the brain, where they are visual acuity could see at 100 feet, indicat- interpreted. On the other hand, a result of nerves from each eye combine at the base 20/10 would indicate that the individual of the brain just in front of the brain stem being tested has better-than-normal visu- to form the optic chiasm. At this point half al acuity, since he or she can see at 20 feet of the nerve tracts from each eye cross what individuals with normal visual acu- over to the opposite side of the brain. Depth perception area that individuals can see without turn- requires that the brain receive input from ing the head or moving the eyes. The portion of the visual ﬁeld Peripheral vision (side vision) is meas- detected by both eyes is called the binoc- ured by a curved device called a perimeter. Visual acuity is deﬁned as the sharp- Central vision (vision in the center of the ness of the visual image perceived. Visual visual ﬁeld) is tested with the individual acuity tests are used to measure the level looking at a tangent screen on which a test 126 CHAPTER 4 CONDITIONS OF THE EYE AND BLINDNESS object is systematically moved across the Severe visual impairment can be deﬁned screen. Individuals’ ability to see the as the inability to read ordinary newsprint object at certain points is then mapped, even with the aid of glasses (Lighthouse, outlining their central ﬁeld of vision. When deviations of vision are great enough to cause total loss of light percep- tion, the term blindness is used. Many TYPES OF VISUAL IMPAIRMENTS individuals, however, have some usable vision if they use special aids or devices to When any deviation from normal perform most tasks. When ordinary glass- vision exists, individuals are considered to es, contact lenses, medical treatment, and/ have a visual impairment.
As follicles mature buy tadapox 80mg cheap, oocytes will also mature by ered with densely ciliated projections generic 80 mg tadapox amex, which facilitate entering meiosis tadapox 80mg otc, which produces the proper number of ovum uptake and movement through this region buy tadapox 80 mg on line. The isthmus is located at the uterotubal junction and has a narrow lumen surrounded The Primordial Follicle Contains an by smooth muscle order tadapox 80mg visa. It has sphincter-like properties and can Oocyte Arrested in Meiosis serve as a barrier to the passage of germ cells. The oviducts transport the germ cells in two directions: sperm ascend to- Female germ cells develop in the embryonic yolk sac and ward the ampulla and the zygote descends toward the migrate to the genital ridge where they participate in the uterus. This requires coordination between smooth muscle development of the ovary (Table 38. Without germ contraction, ciliary movement, and fluid secretion, all of cells, the ovary does not develop. Oogonia undergo mi- The uterus is situated between the urinary bladder and tosis only during the prenatal period. On each upper side, an oviduct opens into the uter- contain a finite number of oocytes, estimated to be about 1 ine lumen, and on the lower side, the uterus connects to the million. The puberty, only 200,000 oocytes remain; by age 30, only outer part is the myometrium, composed of multiple layers 26,000 remain; and by the time of menopause, the ovaries of smooth muscle. The inner part, lining the lumen of the are essentially devoid of oocytes. The stroma is permeated by spiral arteries and con- sis, to prepare for the production of a haploid ovum), become tains much connective tissue. The epithelial layer is inter- arrested in prophase of the first meiotic division, and remain rupted by uterine glands, which also penetrate the stromal arrested in that phase until they either die or grow into ma- layer and are lined by columnar secretory cells. The primordial follicle provides an environment for the developing fetus, and (Fig. When pregranulosa The cervix (neck) is a narrow muscular canal that con- cells surround the oocyte, a basement membrane develops, nects the vagina and the body (corpus) of the uterus. The cervix has numerous glands with a colum- A Graafian Follicle Is the Final Stage of nar epithelium that produces mucus under the control of Follicle Development estradiol. As more and more estradiol is produced during the follicular phase of the cycle, the cervical mucus changes Folliculogenesis (also called follicular development) is the from a scanty viscous material to a profuse watery and process by which follicles develop and mature (see Fig. Follicles are in one of the following physiological of the spinnbarkeit can be tested by touching it with a piece states: resting, growing, degenerating, or ready to ovulate. The mucus can form a thread During each menstrual cycle, the ovaries produce a group up to 6 cm under the influence of elevated estradiol. If a of growing follicles of which most will fail to grow to ma- drop of the cervical mucus is placed on a slide and allowed turity and will undergo follicular atresia (death) at some to dry, it will form a typical ferning pattern when under the stage of development. It is lined by several layers of epithelium that change Primordial follicles are generally considered the non- histologically during the menstrual cycle. When estradiol growing resting pool of follicles, which gets progressively levels are low, as during the prepubertal or post- depleted throughout life; by the time of menopause, the menopausal periods, the vaginal epithelium is thin and the ovaries are essentially devoid of all follicles. Primordial fol- secretions are scanty, resulting in a dry and infection-sus- licles are located in the ovarian cortex (peripheral regions ceptible area. Estradiol induces proliferation and cornifi- of the ovary) beneath the tunica albuginea. The theca externa remains fibroblastic constant rate throughout fetal, juvenile, prepubertal, and and provides structural support to the developing follicle. Once primary follicles leave the resting pool, Development beyond the primary follicle is go- they are committed to further development or atresia. Most nadotropin-dependent, begins at puberty, and continues in become atretic, and typically only one fully developed fol- a cyclic manner throughout the reproductive years. The conversion from primordial to pri- follicle continues to grow, theca layers expand, and fluid- mary follicles is believed to be independent of pituitary go- filled spaces or antra begin to develop around the granulosa nadotropins. This early antral stage of follicle development is re- resting to a growing pool is unknown; it could be pro- ferred to as the tertiary follicular stage (see Fig. The grammed by the cell genome or influenced by local ovarian critical hormone responsible for progression from the pre- growth regulators. Mitosis of the granulosa The first sign that a primordial follicle is entering the cells is stimulated by FSH. As the number of granulosa cells growth phase is a morphological change of the flattened increases, the production of estrogens, the binding capac- pregranulosa cells into cuboidal granulosa cells. The ity for FSH, the size of the follicle, and the volume of the cuboidal granulosa cells proliferate to form a single contin- follicular fluid all increase significantly. At this stage, a glassy membrane, the zona the follicle and forming a large 2- to 2.
Nevertheless generic 80mg tadapox free shipping, it is evident that these neurons are a crucial component of the network of monoamine influences on the limbic system and that they 184 NEUROTRANSMITTERS generic tadapox 80 mg visa, DRUGS AND BRAIN FUNCTION are capable of both short- and long-term adaptive changes that will influence emotion generic tadapox 80 mg mastercard, motivation tadapox 80mg, cognition and many other aspects of behaviour buy generic tadapox 80mg line. Aston-Jones, G, Rajkowski, J, Kubiak, P and Alexinsky, T (1994) Locus coeruleus neurons in monkey are selectively activated by attended cues in a vigilance task. Bonisch, H, Hammermann, R and Bruss, M (1998) Role of protein kinase C and second messengers in regulation of the norepinephrine transporter. Cederbaum, JM and Aghajanian, GK (1976) Noradrenergic neurons of the locus coeruleus: inhibition by epinephrine and activation by the alpha-antagonist piperoxane. Fassio, A, Bonanno, G, Fontana, G, Usai, C, Marchi, M and Raiteri, M (1996) Role of external and internal calcium on heterocarrier-mediated transmitter release. Fillenz, M (1993) Short-term control of transmitter synthesis in central catecholaminergic neurones. Harley, CW (1987) A role for norepinephrine in arousal, emotion and learning: limbic modulation by norepinephrine and the Kety hypothesis. Hieble, JP, Bondinell, WE and Ruffolo, RR (1995) Alpha- and beta-adrenoceptors: from the gene to the clinic. Kumar, SC and Vrana, KE (1996) Intricate regulation of tyrosine hydroxylase activity and gene expression. McCormick, DA, Pape, HC and Williamson, A (1991) Actions of norepinephrine in the cerebral cortex and thalamus: implications for function of the central noradrenergic system. McQuade, R and Stanford, SC (2000) A microdialysis study of the noradrenergic response in rat frontal cortex and hypothalamus to a conditioned cue for aversive, naturalistic environmental stimuli. Neff, NH and Costa, E (1966) The influence of monoamine oxidase inhibition on catecholamine synthesis. Pacholczyk, T, Blakely, RD and Amara, SG (1991) Expression cloning of a cocaine- and antidepressant-sensitive human noradrenaline transporter. Papadopoulos, GC and Parnavelas, JG (1991) Monoamine systems in the cerebral cortex: evidence for anatomical specificity. Povlock, SL and Amara, SG (1997) The structure and function of norepinephrine, dopamine and serotonin transporters. In Neurotransmitter Transporters: Structure, Function, and Regulation (Ed. Rajkowski, J, Kubiak, P, Ivanova, S and Aston-Jones, G (1998) State-related activity, reactivity of locus coeruleus neurons in behaving monkeys. Russ, H, Staust, K, Martel, R, Gliess, M and Schomig, E (1996) The extracellular transporter for monoamine transmitters exists in cells derived from human central nervous system glia. In Neurotransmitter Transporters: Structure, Function, and Regulation (Ed. Stanford, SC (1999) SSRI-induced changes in catecholaminergic transmission. In Selective Serotonin Reuptake Inhibitors (SSRIs): Past, Present and Future (Ed. Stanford, SC and Salmon, P (1992) b-Adrenoceptors and resistance to stress: old problems and new possibilities. Zigmond, RE, Schwarzschild, MA and Rittenhouse, AR (1989) Acute regulation of tyrosine hydroxylase by nerve activity and by neurotransmitters via phosphorylation. Edited by Roy Webster Copyright & 2001 John Wiley & Sons Ltd ISBN: Hardback 0-471-97819-1 Paperback 0-471-98586-4 Electronic 0-470-84657-7 9 5-H ydroxytryptam ine S. STANFORD INTRODUCTION The idoleamine, 5-hydroxytryptamine (5-HT), like the catecholamines, dopamine and noradrenaline, is found in both the periphery and the brain. This chapter will concentrate on the aspects of 5-HT transmission which have made the greatest advances in recent years, particularly those for which some important and interesting questions remain unanswered. Although this material will obviously focus on 5-HT in the brain, the neurochemical mechanisms that regulate 5-HT transmission, such as its synthesis and inactivation, will apply generally to 5-HT-containing cells in the periphery (e. All these processes, together with some well-known drugs that affect them, are summarised in Fig. DISTRIBUTION IN THE CNS As with the other monoamines, the distribution of 5-HT-releasing neurons in the brain was first characterised in the 1960s using the Falck±Hillarp histochemical technique whereby 5-HT is converted to a compound that is fluorescent under ultra-violet light. This showed that the cell bodies of 5-HT neurons aggregate around the midline of the upper brainstem, forming distinct clusters (or nuclei) (Fig. Since then, 5-HT neurons have been found in the noradrenergic locus coeruleus and the area postrema as well. Yet, despite this relatively restricted distribution of cell bodies, their processes project more or less throughout the whole neuraxis.
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