By F. Tippler. University of Tennessee, Chattanooga. 2018.
It acts only in the bloodstream because even after destruction of all the invaders that elicited the its large molecular size prevents its movement or trans- original cytotoxic activity buy rogaine 2 60 ml prostate cancer 9 out of 10 gleason. It activates complement to pecially important in killing body cells that have been in- destroy microorganisms order 60 ml rogaine 2 overnight delivery androgen female hormones. Cytotoxic T cells also play a role in body fluids and readily enters body tissues. It is in- the destruction of transplanted organs and delayed hyper- volved in parasitic infections and hypersensitivity re- sensitivity reactions. IgE sensitizes mast An additional type of T cells, called suppressor cells, which then release histamine and other chemical T cells, has been postulated to exist and to function by mediators that cause bronchoconstriction, edema, ur- stopping the immune response (ie, decreasing the ac- ticaria, and other manifestations of allergic reactions. This activity is considered impor- of IgE is stimulated by T lymphocytes and interleukins tant in preventing further tissue damage. Small in autoimmune disorders, suppressor T cell function is amounts of IgE are present in the serum of nonallergic impaired and extensive tissue damage may result. They also regulate the intensity and duration of in the bone marrow), and migrate to the spleen, lymph the immune response by stimulating or inhibiting the acti- nodes, or other lymphoid tissue. In lymphoid tissue, the vation, proliferation, and/or differentiation of various cells cells may be dormant until exposed to an antigen. In re- and by regulating the secretion of antibodies or other cy- sponse to an antigen and IL-2 from helper T cells, B cells tokines. Although the hematopoietic cytokines described in- multiply rapidly, enlarge, and differentiate into plasma clude the immune system cytokines, the emphasis here is on cells, which then produce antibodies (immunoglobulins those that affect immune cells. Immunoglobulins are secreted formed by activated macrophages enter the bone marrow, into lymph and transported to the bloodstream for circula- where they induce the synthesis and release of other cytokines 636 SECTION 7 DRUGS AFFECTING HEMATOPOIESIS AND THE IMMUNE SYSTEM Macrophage Antigen ILs 1, 6, 11, 12 IL8 G-CSF, GM-CSF, TNF alpha M-CSF, TNF RBCs ILs 1, 6, 8, 10, 12, 15 IFNs alpha and beta WBCs TNF alpha Stem cell Neutrophils Platelets Resting TH cell Activated TH cell ILs 4, 10 IL2 ILs 3, 6, 7 ILs 3, 4, 10 ILs 3, 5 ILs 2, 12, 15 GM-CSF Antigen Resting TH cells B cell IL12 Stem cells Activated B cell TC cells ILs 2, 4, 5, 13 IFN gamma ILs 3, 4, 10, 13 IFN alpha and beta Natural TNF beta Eosinophils killer cells RBCs WBCs Platelets Mast cells B cells IL 6 Macrophages Plasma cells Antibodies (Ig G, M, A, E, D) Figure 42–2 Macrophage and T cell cytokines, their target cells, and the products of target cells. IL, interleukin; IFN, interferon; TNF, tumor necrosis factor; TH, helper T cell; TC, cytotoxic T cells; CSF, colony- stimulating factor. CHAPTER 42 PHYSIOLOGY OF THE HEMATOPOIETIC AND IMMUNE SYSTEMS 637 that activate resting stem cells to produce more granulocytes crease over approximately 6 months as maternal antibodies and monocyte–macrophages. Although the infant does start producing and monocytes leave the bone marrow and enter the circulat- IgG, the rate of production is lower than the rate of break- ing blood in approximately 3 days. Cell-mediated immunity is Cytokine binding to target cells elicits wide-ranging ef- probably completely functional at birth. In general, the Immune Function in Older Adults cytokines secreted by antigen-activated lymphocytes can af- fect the activity of most cells involved in the immune re- Both humoral and cell-mediated immune functions decline sponse. As a result, a network of interacting cells is age, which may account for the greater frequency of auto- activated. Lymphocytes are less Some cytokines enhance macrophage activity by two main able to proliferate in response to antigenic stimulation, and mechanisms. First, they cause macrophages to accumulate in a relative state of immunodeficiency prevails. With T lym- damaged tissues by delaying or stopping macrophage migra- phocytes, function is impaired, and the numbers in periph- tion from the area. Some cytokines, especially includes decreased activity of helper T cells. With B lym- IL-2, directly stimulate helper T cells and enhance their anti- phocytes, the numbers probably do not decrease, but the antigenic activity. They also enhance the antiantigenic activity cells are less able to form antibodies in response to antigens. Interleukins 4, 5, and 6 are espe- Abnormal antibody production results from impaired func- cially important in B-cell activities. In addition, older adults Tumor necrosis factors (TNF) are produced by activated have increased blood levels of antibodies against their own macrophages and other cells and act on many immune and tissues (autoantibodies). They participate in the inflamma- Impaired immune mechanisms have several implications tory response and cause hemorrhagic necrosis in several for clinicians who care for elderly patients, including the types of tumor cells. TNF-alpha is structurally the same following: as cachectin, a substance associated with debilitation and • Older adults are more likely to contract infections and weight loss in patients with cancer. When an infection develops in INFLUENCE IMMUNE FUNCTION older adults, signs and symptoms (eg, fever and drainage) may be absent or less pronounced than in younger Age adults. Thus, achieving protective antibody titers may re- During the first few months of gestation, the fetal immune quire higher doses of immunizing antigens in older system is deficient in antibody production and phagocytic adults than in younger adults. During the last trimester, the fetal immune system • Older adults often exhibit a less intense positive reac- may be able to respond to infectious antigens, such as cy- tion in skin tests for tuberculosis (indicating a decreased tomegalovirus, rubella virus, and Toxoplasma. In the placenta, maternal blood and fetal blood Nutritional Status are separated only by a layer of specialized cells called tro- phoblasts.
Silicon nitride ﬁlms approximately 1500 A˚ thick were deposited using the plasma-enhanced chemical vapor deposition (PECVD) technique buy rogaine 2 60 ml without a prescription prostate warning signs. Electrical char- acterization using a VLSI electronic probing station showed excellent insulation ca- pability and electrical isolation generic rogaine 2 60 ml overnight delivery prostate cancer robotic surgery, with less than a 1. Experimental testing with acutely prepared rat hippocampal slices consistently demonstrated evoked extracellular ﬁeld potentials with signal-to-noise ratios greater than 10:1. Additional mask designs that incorporate several key modiﬁcations have been suc- cessfully completed and fabricated. Berger and colleagues resized to 30-mm diameters, a size approaching the diameter of a single neuron cell body. Combined with smaller center-to-center distances between pads, the smaller pad size will allow higher density arrays for greater spatial resolution when interfac- ing with a given brain region, and thus better monitoring and control of that region. Second, several new layouts have included di¤erent distributions of stimulation- recording pads that geometrically map several subregions of the hippocampus (ﬁgure 12. This represents the beginnings of a group of interface devices that will o¤er monitoring and control capabilities with respect to di¤erent subregions of the hippo- campus, and ultimately other brain structures as well. In addition, more recent de- signs have utilized gold as the stimulation-recording electrode material to allow higher injection current densities during stimulation. Electrical characterization of the most recent generation of conformal neural probe arrays indicates, despite the higher density of electrodes, less than a 4. Biocompatibility and Long-Term Viability Many of the problems with respect to biocompatibility and long-term viability can- not be fully identiﬁed until the working prototypes of multielectrode arrays described earlier have been developed to the point that they can be tested through long-term implantation in animals. Nonetheless, we have begun to consider these issues and to develop research strategies to address them. One of the key obstacles will be main- taining close contact between the electrode sites of the interface device and the target neurons over time. We have begun investigating organic compounds that could be used to coat the surface of the interface device to increase its biocompatibility and thus promote outgrowth of neuronal processes from the host tissue and increase their adhesion to the interface materials. Poly-d-lysine and laminin are known to be particularly e¤ective in promoting ad- hesion of dissociated neuron cultures (cultures prepared from neonatal brain; neu- rons are prepared as a suspension and then allowed to adhere, redevelop processes, and reconnect into a network) onto inorganic materials (Stenger et al. Poly-d-lysine and laminin were applied to the surface of the conformal arrays shown in ﬁgure 12. When dissociated hippocampal neurons were prepared on the surface of the array, the adhesion of cells and the extension of their processes were restricted to the treated regions; that is, hippocampal neurons were attracted, attached, and proliferated synaptic connections almost exclusively in parallel, linear tracks over the columns of electrodes (see chapter 11). Although this represents only an initial step in addressing the issues of biocompatibility, it is A Neural Prosthesis for Hippocampal Memory Function 269 Figure 12. Berger and colleagues through approaches such as these that we anticipate ﬁnding solutions to biocompati- bility problems. Although much of the electrophysiological testing of interfaces to date has been completed using acutely prepared hippocampal slices (which remain physiologically viable for 12–18 hr), we also have begun using hippocampal slice cultures to test the long-term viability of the neuron/silicon interface (Gholmieh et al. The latter preparations involve placing slices of hippocampus on a semipermeable membrane in contact with tissue culture media, and maintaining them long-term in a culture incu- bator (Stoppini et al. Slice cultures can be prepared directly onto multisite electrode arrays, which then can be taken out the incubator and tested periodically to examine the robustness of the electrophysiological interaction with the hippocam- pal tissue. Preliminary ﬁndings have revealed that bidirectional communication re- mains viable for at least several weeks, although we have yet to systematically test long-term functionality. The main point to be made here is that novel preparations like the slice culture will provide highly useful platforms for identifying and resolving viability issues. Conclusions The goal of this chapter was to bring into focus what we believe will be one of the premier thrusts of the emerging ﬁeld of neural engineering: to develop implantable neural prostheses that can coexist and bidirectionally communicate with living brain tissue and thus substitute for a cognitive function lost as a result of damage and/or disease (ﬁgure 12. Because of progress in neuroscience, molecular biology, bio- medical engineering, computer science, electrical engineering, and materials science, it is now reasonable to begin deﬁning the combined theoretical and experimental pathways required to achieve this end. We have described here major progress on four of the essential requirements for an implantable neural prosthesis, achieved through a series of experimental and modeling studies using the hippocampus: bio- logically realistic neuron models that can e¤ectively replace the functional properties of hippocampal cells, the concatenation of the neuron model dynamics into neural networks that can solve a pattern recognition problem of cognitive and neurological relevance, the implementation of biologically realistic neural network models in VLSI for miniaturization, and the development of silicon-based multisite electrode arrays that provide bidirectional communication with living neural tissue. This progress does not constitute a set of ﬁnal solutions to these four requirements. Additional work is needed on nonlinear models of neuron dynamics, both with re- spect to characterization of higher-order nonlinearities and particularly cross-input nonlinearities. All neurons receive inputs from more than one other source, and interactions among separate inputs most likely result in nonlinearities speciﬁc to A Neural Prosthesis for Hippocampal Memory Function 271 Figure 12.
From the biological point of view cheap rogaine 2 60 ml without prescription prostate oncology specialists, the complexity of the phenomena involved is es- sentially the same whether we consider a real rogaine 2 60 ml lowest price prostate cancer va disability compensation, isolated neuron or a network of artiﬁ- cial neurons. This idea stimulated the search for a representation incorporating the properties of a real neural network (G. Over the past few years, much headway has been made in the mathematical description of a real biological 132 G. The hierarchical organization of biological structural units from the cellular to the organismal levels (cell organelles, nuclei, neurons, synapses, neural groups, nervous tissue, and cerebral organs), naturally suggested a hierarchical representa- tion of a system. However, the hierarchical aspect of the corresponding functional organization is far from evident. The novel three-dimensional representation of a biological system that one of us has proposed (G. Chauvet, 1996a), with axes for space scales, time scales, and structural units, allows visualization of the coupling between the structural and functional organizations. This representation is based es- sentially on the determination of the time scales of the dynamic systems describing physiological functions. This functional hierarchy is useful for determining the phys- iological functions associated with nervous structures. In the case of real neural net- works, there are at least two physiological functions: the propagation of membrane potential on a time scale on the order of milliseconds, and the modiﬁcation of synap- tic e‰cacy on a time scale on the order of seconds or even hours. Thus, the func- tional order has its origin in a functional hierarchy that is evidently a manifestation of molecular mechanisms. Typically, the artiﬁcial neural networks generally studied have several neuron layers. The structure-function rela- tionship is more evident in this representation than in any other one. The hierarchical network is fundamentally di¤erent and, in particular, possesses speciﬁc emergent properties, that is, properties that appear at a higher level in a new structure. An im- Inputs Outputs (behaviors) Sensory Hierarchical Motor neurons circuit neurons Figure 7. Properties emerge from a lower level and appear at a higher level inside a new structure. This new structure is called a functional unit if, and only if, it has a speciﬁc function. Mathematical Modeling of Neuromimetic Circuits 133 portant advantage of the hierarchical representation is that it o¤ers a rigorous ap- proach to the notion of a functional unit that may now be deﬁned as a structural unit with a speciﬁc function at a higher level of organization (G. The functional unit, possessing its own time scale, incorporates a new function that can be derived mathematically from the lower levels of organization in a biological system. For example, a neuromimetic circuit may be considered as a functional unit. Hierarchical Representation of a Biological Theory of Functional Organization Functional Interactions In the course of our work on physiological models, ranging from the molecular to the organismal levels (G. Chauvet, 1996b), some novel ideas speciﬁc to the study of biology have been introduced, in particular the concepts of nonsymmetric and non- local functional interactions in hierarchical space. These basic concepts emerged from a bottom-up approach to living systems; that is, from a systematic study of iso- lated physiological functions, followed by the integration of these functions at the level of the organism. A signiﬁcant consequence of this theory is that living organ- isms can be given not only a double organizational representation that is simultane- ously structural and functional but also a double mathematical representation that is simultaneously geometric and topological. We may compare it to a mathematical function in the sense that the action of one structure on another results in a certain product. The physiological function would then be the action (the application, in mathematical terms) and the product would be the result of the function (the value of the function, in mathematical terms) that is often identiﬁed with the physiological function itself. Although this deﬁnition is general, it is unfortunately not operational. It is relatively easy to describe particular physiological functions such as vision, di- gestion, memorization, and so on, but it is far more di‰cult to give an operational deﬁnition of a physiological function in general. One possibility may be to deﬁne a physiological function in terms of a combinatorial set of functional interactions between structures. Such functional interactions are evidently speciﬁc since they de- scribe the action (whatever its nature) of one structure on another or, more precisely, the action of a source on a sink, after the action has undergone a transformation in the source.
A major criterion for diagnosing later sodium benzoate is occasionally used as a respiratory stimulant ADHD is a previous diagnosis of childhood ADHD buy 60 ml rogaine 2 with amex mens health pdf. Central nervous system stimulants cause cardiac stimulation and thus are contraindicated in clients with cardiovascular dis- TYPES OF STIMULANTS orders (eg rogaine 2 60 ml free shipping prostate cancer survival rate, angina, dysrhythmias, hypertension) that are likely to be aggravated by the drugs. They also are contraindicated Most CNS stimulants act by facilitating initiation and trans- in clients with anxiety or agitation, glaucoma, or hyper- mission of nerve impulses that excite other cells. They are usually contraindicated in clients with a somewhat selective in their actions at lower doses but tend to history of drug abuse. The major groups are amphetamines and related drugs, analeptics, and xanthines. Amphetamines increase the amounts of norepinephrine, INDIVIDUAL CENTRAL NERVOUS dopamine, and possibly serotonin in the brain, thereby pro- SYSTEM STIMULANTS ducing mood elevation or euphoria, increasing mental alert- ness and capacity for work, decreasing fatigue and drowsiness, Individual drugs are described below; dosages are listed in and prolonging wakefulness. Larger doses, however, produce Drugs at a Glance: Central Nervous System Stimulants. Overdoses can produce convulsions Amphetamines and Related Drugs and psychotic behavior. Amphetamines also stimulate the sympathetic nervous system, resulting in increased heart Amphetamine, dextroamphetamine (Dexedrine), and meth- rate and blood pressure, pupil dilation (mydriasis), slowed amphetamine (Desoxyn) are closely related drugs that share gastrointestinal motility, and other symptoms. They are more drugs reduce behavioral symptoms and may improve cognitive important as drugs of abuse than as therapeutic agents. Methylphenidate (Ritalin) is chemically related to am- Amphetamines are Schedule II drugs under the Controlled phetamines and produces similar actions and adverse effects. Substances Act and have a high potential for drug abuse and It is well absorbed with oral administration. These plasma levels occur in about 2 hours with immediate-release drugs are widely sold on the street and commonly abused (see tablets and about 5 hours with extended-release tablets. Amphetamine-related drugs (methylphenidate and dexme- Most of a dose is metabolized in the liver and excreted in urine. It is well absorbed with Analeptics are infrequently used (see doxapram and oral administration and reaches peak plasma levels in 1 to modafinil, below). Xanthines stimulate the cerebral cortex, increasing mental alertness and decreasing drowsiness and fatigue. Other effects include myocardial stimulation with increased cardiac output Analeptics and heart rate, diuresis, and increased secretion of pepsin and hydrochloric acid. Large doses can impair mental and physi- Doxapram (Dopram) is occasionally used by anesthesiolo- cal functions by producing restlessness, nervousness, anxiety, gists and pulmonary specialists as a respiratory stimulant. Although it increases tidal volume and respiratory rate, it also increases oxygen consumption and carbon dioxide production. Limitations include a short duration of action (5 to 10 minutes Indications for Use after a single intravenous [IV] dose) and therapeutic dosages near or overlapping those that produce convulsions. Endotra- Amphetamines and methylphenidate are used in the treatment cheal intubation and mechanical ventilation are safer and more of narcolepsy and ADHD. Dexmethylphenidate is indicated effective in relieving respiratory depression from depressant only for ADHD. Its ability to promote wakefulness is similar to that in nonprescription analgesics and stimulants that promote of amphetamines and methylphenidate, but its mechanism of wakefulness (eg, No-Doz). Like other CNS stimulants, it also has CHAPTER 16 CENTRAL NERVOUS SYSTEM STIMULANTS 253 Drugs at a Glance: Central Nervous System Stimulants Routes and Dosage Ranges Generic/Trade Name Indications for Use Adults Children Amphetamines Amphetamine Narcolepsy Narcolepsy: PO 5–60 mg/d in divided Narcolepsy: >6 y: PO 5 mg/d initially, ADHD doses increase by 5 mg/wk to effective dose ADHD: 3–5 y: PO 2. Usual dose, 15–25 mg daily, in 2 divided doses Amphetamine mixture (Adderall) ADHD Narcolepsy: PO 10 mg daily initially, >6y: ADHD, PO 5 mg 1–2 times daily, Narcolepsy increase if necessary increased if necessary Amphetamine-Related Drugs Dexmethylphenidate (Focalin) ADHD PO 2. Dosage not established for children Dosage should be reduced by 50% <16 years of age with severe hepatic impairment. Steady-state concentrations are reached in 2 to 4 days and half-life with chronic use is about 15 hours. Caffeine has numerous pharmacologic actions, including CNS Modaﬁnil is not recommended for patients with a history of stimulation, diuresis, hyperglycemia, cardiac stimulation, left ventricular hypertrophy or ischemic changes on electro- coronary and peripheral vasodilation, cerebrovascular vascon- cardiograms. Adverse effects include anxiety, chest pain, striction, skeletal muscle stimulation, increased secretion of dizziness, dyspnea, dysrhythmias, headache, nausea, nervous- gastric acid and pepsin, and bronchodilation from relaxation of ness, and palpitations. In low to moderate amounts, caffeine in- decreased effects of cyclosporine and oral contraceptives and creases alertness and capacity for work and decreases fatigue. Dosage should be reduced by 50% with se- agitation, diarrhea, insomnia, irritability, nausea, nervousness, 254 SECTION 2 DRUGS AFFECTING THE CENTRAL NERVOUS SYSTEM premature ventricular contractions, hyperactivity and restless- beverages is determined by the particular coffee bean or tea ness, tachycardia, tremors, and vomiting.
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