By Y. Asam. Institute for Transpersonal Psychology. 2019.
Retrograde trophic signals have been shown to modulate neuronal growth trusted erectafil 20mg erectile dysfunction doctors in texas, survival buy 20mg erectafil erectile dysfunction drug stores, death buy erectafil 20mg visa impotence quotes, and the expression of neurotransmitters. It is now clear that neurotrophic factors can be provided by a number of sources including glial cells, afferent processes of neurons, muscle, and even by the extracellular matrix. Numerous biological events including neuronal growth, phe- notype (neurotransmitter) expression, and programmed cell death have been linked with retrograde neurotrophic factor signaling. Hence, there are many possible lines of study to explore the effects of neurotrophic factor gene therapy in relation to basic neural cell survival and function for the treatment of neurodegenerative disorders. From basic research, we have learned that if the brain is injured, these molecules can be released to play a signiﬁcant role in the recovery process. In addition to limiting the loss of neurons, neurotrophic factors can stimulate new outgrowth from the axons and dendrites, regulate axon branching, modulate neurotransmitter synthesis, and inﬂuence synapse formation. This inherit property of structural and functional change in neurons in response to environmental cues (like the release of neurotrophic factors) is referred to as plasticity. Many factors have been shown to have overlapping effects (primarily on development and survival) on subsets of neurons in the central and peripheral nervous system. It is now very clear that any given type of central or peripheral neuron needs a combination of factors, rather than a single neurotrophic factor to optimize survival and function. Therefore, decisions must be made regarding the most effective combinations of factors for the neurons/neurological disorder in question. The identiﬁcation and characterization of each neurotrophic molecule has been followed by the establishment of transgenic (knock-out) mice that do not produce that factor or the associated receptor components to help unravel the physiological function of these molecules and to assess their contribution to the survival of dif- ferent neuronal types. It should be pointed out, however, that we do not know if neurotrophic gene defects in humans are associated with any aspect of neurologi- cal dysfunction. Extensive research has focused on the beneﬁcial effects of delivering neu- rotrophic factors in the animal models of neurodegeneration and this research has set the foundation for a number of clinical trials (discussed later). The extent of the nervous system damage, the available concentration of neurotrophic factors, and the time at which the factor is released are key parameters in relation to the effective- ness of these molecules to rescue neurons from death. It should be realized that the precise roles of neurotrophic factors and their therapeutic potential in degenera- tion disorders remains to be elucidated. The in vivo method involves direct administration of the virus to the nervous system. For this approach, viral vectors are injected into speciﬁed locations of the brain or spinal cord. In the case of ex vivo gene transfer, new genes are ﬁrst introduced into cells in a tissue culture environment, and then the cells are stereotaxically transplanted into desired regions of the nervous system. The types of viruses and cells that have been used for gene delivery in the nervous system are shown in Figure 9. Now, viral vectors and cells are used together and certain combinations show real promise and beneﬁts over the gene and cell replace- ment procedures used just a few years ago. As each neurotrophic factor is identi- ﬁed, cells are genetically modiﬁed to secrete the factor and then tested in animal models for effects on neuronal survival and animal behavior (Table 9. The purpose of this section is to provide some examples of the streams of gene therapy used in the animal models for the neurodegenerative disorders described in this chapter. To model Alzheimer’s, animals are used that show cholinergic neuron loss, the formation of neuroﬁbrillary tangles plaques, or the generation of the amyloid pre- cursor protein. In mammals, transection of the ﬁmbria-fornix pathway (connection between the hippocampus and medial septum) produces signiﬁcant death (approx- imately 50%) of cholinergic neurons in the medial septum, paralleled by a loss of cholinergic inputs to the hippocampal formation. The possibility of supplying a neurotrophic factor to the brain via genetically engineered cells was ﬁrst demonstrated by Fred Gage and co-workers in 1988. In addition to gene therapy with neurotrophic factors, strategies that use regula- tory proteins of cell death have been examined. Antiapoptotic factors like Bcl-xL is one of three isoforms of Bcl-x that protects cells from the damaging effect of re- active oxygen molecules. These antiapoptotic factors are being evaluated by gene therapy in animal models of neural degeneration (see section on programmed cell death and neurodegeneration). This treatment results in a loss of dopamine and causes a circling behavior in the animals when they are given a dopamine agonist (e. The circling tendencies can be reduced when the enzyme tyrosine hydroxylase (rate-limiting enzyme for dopamine production) is made available to neurons in the striatum. Initial ex vivo gene therapy experiments in consideration of Parkinson’s used cell lines of ﬁbroblasts genetically modiﬁed in culture to express the gene for tyrosine hydroxylase. In this case, the function of the implanted ﬁbroblasts was monitored by observing reductions in the circling behavior of the recipient host rats. It should also be pointed out that ﬁbroblasts as well as other non-neuronal cell types do not make connections with the host brain circuitry but still produce strong functional effects when producing the transgene product. A primary drawback when using ﬁbroblast cell lines has been the continued expan- sion of the ﬁbroblast cell mass within the brain. To prevent tumor formation by these cell lines, the cells can be encapsulated by materials that allow for the exchange of the transgene product between the cells and the host tissue. Although we do not know why neurons that contain dopamine preferentially die in Parkinson’s, neurotrophic factors that enhance the survival and function of these dopamine neurons are the center of attention for gene therapy possibilities with the hope of preventing the death of these neurons. This molecule, discovered in the culture supernatants of a glial cell line by Leu-Fen Lin in the laboratory of Frank Collins in 1993 was shown to have potent effects on the survival of dopamine neurons. Host immune reactions to adenovirus and down-regulation of the viral promoters are common problems observed with adenoviral injections in the brain. Next generation Ad vectors will be designed to minimize the immune reac- tions and extend gene expression. It is a potent survival factor for motor neurons in the spinal cord and for Purkinje neurons in the cerebellum. Another technique to prevent neuronal degeneration has been to transplant support cells with fetal neurons. In this situation, referred to as a co-grafting strat- egy, the support cells assist with the survival of the transplanted neurons. The ﬁbroblasts not only help to maintain the population of trans- planted neurons but also help to reduce the need for large numbers of fetal cells when dissected from embryonic brains. Monkeys given an injection of quinolinic acid show features of neurodegeneration that are character- istic of Huntington’s disease. It should be noted that the vectors are designed to eliminate viral gene expres- sion to avoid cytotoxic and immunological effects. The exclusion of these genes, however, often reduces the efﬁciency and length of transgene expression. There are intense efforts to develop gene regulatory elements that offer cell-speciﬁc (spatial) expression and/or drug-dependent (temporal) expression of the desired therapeutic gene. Potential transgene promoter/regulatory elements to guide neuronal expression include the light neuroﬁlament subunit, a-tubulin, neuron-speciﬁc enolase, and tyrosine hydroxylase.
This also involves that they do not have a possibility to take the second self-control test and collect bonus points or to get an offered grade generic erectafil 20mg without prescription erectile dysfunction pills at walmart. If a student fails on this written examination cheap erectafil 20 mg otc erectile dysfunction doctor visit, it means that he/she does not get a signature and cannot take the Cell Biology Final Exam buy 20mg erectafil otc erectile dysfunction reviews. You have to read the relevant background information from your textbook and make the topic understandable to your fellow students. You should use the lecture material available at the cell biology website to make your presentation easy to follow. You are expected to be ready to present at least 10 slides of the lecture, from those that contain figures/pictures, rather than just explanatory text. Only exceptionally good presentations that clearly present good summaries of the lectures are awarded with 3 points. It is the professor / tutor in the seminar who alone decides the number of bonus points awarded, based on his/her own judgment. Including extra material obtained through the student’s own research in textbooks or the internet will be appreciated, but will not substitute for a clear and detailed knowledge of the lecture/textbook material. Labs: Completing all labs, and writing up the results and their interpretation in a lab log book on the spot is required. The average value of the lab bonus points is added to the exam points at the end of the semester. Only medical or official excuses are accepted, after showing the appropriate documents. After completing the lab, the lab tutor should sign on the cover of the log book, certifying your presence at the lab and sign separately for the acceptance of your work. You are eligible for this second signature only if you know what and why you did during the lab and what the result was. You should obtain these two signatures and the grade at the end of the lab and no later. This also involves that they do not have a possibility to take the second self-control test and collect bonus points or to get an offered grade. If a student fails on this written examination, it means that he or she does not get a signature and cannot take the Cell Biology Final Exam. Reading source for the lab and lab schedule: A Cell Biology lab manual written by the members of the department is provided in the Book Store (In Theoretical Building). Lab schedule: Small groups (subgroups) consist of 3-7 people for doing the various labs in a rotary system are formed in the first seminar. If you missed the first seminar you will be put into a subgroup where you fit and you should check your assignment with your fellow students. Lab questions will be included in the 2nd self-control test as well as in the Final Exam test, to approximately 10% of the total points. Accepting the grade means exemption from the final exam, so the accepted grade will be entered into the lecture book as the final grade. Signing the lecture book: The conditions for signing the lecture book are the following: (1) presence at, and acceptance of all the labs or passing the written lab exam, (2) presence at the seminars and (2) minimum 1 point for the presentation at the seminar (see above). Rules concerning repeaters: Attendance of labs is not compulsory if you had all the four labs accepted last year and your lecture book was signed. Your short presentation of last year does not have to be repeated if it scored 1 point or more, otherwise you have to redo it. These questions will include 5 brief descriptions of basic concepts, and 5 questions of yes/no type. The descriptions should contain 2 valuable and relevant facts/statements on the subject asked, for maximal score (2 points each; partial points may be considered). It is strongly recommended that the students themselves elaborate a few basic statements for each key-word during the semester, as part of their preparation and studying. Those earning below 14 points in part A fail the entire exam without regard to their score on part B, what will not be corrected and scored in this case. The score of a passed A test will be added to the score of part B, thus yielding 14-20% of the total exam points. Part B Part B is a complex test, including two short essays (2x10=20%), fill-in, short answer, multiple choice, relation analysis, sketch-recognition as well as simple choice and yes/no questions (50%). The lab questions are a section of the part B exam (to approximately 10% of the total test points). However, all bonuses and merits expire by next spring exam period except for Cell Biology lab points and bonus points for short presentations. Note that all parts have to be repeated on repeated exams, that is, cell biology written part B (including the lab questions), and cell biology written part A with less than 14 points. Important: The test/exam grade earned should reflect the true knowledge of the student. Rules for C-chance exams If the result of the written part of a C-chance exam is at least a pass (2) according to the rules pertaining to A- and B-chance exams, the grade of the C-chance exam will be what is to be offered based on the rules of the A- and B-chance exams. Part B of the written part of a C-chance exam will be scored even if the score of part A is less than 70%. If the result of a C-chance exam is a fail (the score of part A is less than 70% or the total exam score (calculated according to the rules pertaining to A- and B-chance exams) is below the passing level), the written part will be followed by an oral exam. In this case the grade of the C-chance exam will be determined by the result of the written test and the performance on the oral exam. User names and passwords will be given out at the first cell biology seminar during the first week of the semester. Exemptions: In order to get full exemption from the cellbiology course the student has to write an application to the Educational Office. Applications for exemptions from part of the courses are handled by the department. Year, Semester: 1 year/2st nd semester Number of teaching hours: Practical: 30 1st week: Practical: Organization of the course. The maximum percentage of allowable absences is 10 % which is a total of 2 out of the 15 weekly classes. Maximally, two language classes may be made up with another group and students have to ask for written permission (via e-mail) 24 hours in advance from the teacher whose class they would like to attend for a makeup because of the limited seats available. If the number of absences is more than two, the final signature is refused and the student must repeat the course. Students are required to bring the textbook or other study material given out for the course with them to each language class. If students’ behaviour or conduct does not meet the requirements of active participation, the teacher may evaluate their participation with a "minus" (-). If a student has 5 minuses, the signature may be refused due to the lack of active participation in classes. Testing, evaluation In each Hungarian language course, students must sit for 2 written language tests and a short minimal oral exam. A further minimum requirement is the knowledge of 200 words per semester announced on the first week. There is a (written or oral) word quiz in the first 5-10 minutes of the class, every week.
As gene therapy approaches are developed and reﬁned purchase erectafil in india erectile dysfunction bp meds, the outcome of gene therapy in the nervous system could be extremely effective generic 20mg erectafil with amex impotence herbal remedies. In this chapter purchase erectafil online pills erectile dysfunction medication otc, the key aspects of neural dysfunction associated with the promi- nent nervous system disorders are explained. A focus on the vectors and the cells used for gene delivery in animal models is provided. Numerous types of neurons specialized to receive, process, and transmit information via electrical impulses are primarily responsible for the functional characteristics of the nervous system (Fig. Neurons can be identiﬁed by their size, shape, development, and organization within the brain. Neurons work in networks and secrete neurotransmitters and other chemical messengers at sites of functional contact called synapses. At each synapse a region of the cell membrane in the presynaptic neuron is specialized for rapid secretion of one or more types of neurotransmitters. This area is closely apposed to a specialized region on the postsynaptic cell that contains the receptors for the neurotransmitter or other ligands. The binding of the neurotransmitter to the receptors triggers an electrical signal, the synaptic potential, in the postsynaptic cell (Fig. Information in the nervous system is thereby transmitted and pro- cessed by elaborate networks that generate a spectrum of electrical and chemical signals. The astrocyte processes are intimately associated with the neuronal cell bodies, dendrites, and nerve terminals. The myelin is wrapped around segments of axons and serves to accelerate the conduction of the electrical signals. There are 31 vertebral bones in the spinal column that house and protect the spinal cord. The individual nerves are made of sensory and motor ﬁbers that interface the peripheral parts of the body with the central nervous system (brain and spinal cord). Neurons are surrounded by astrocytes that ﬁll the interstices between neuronal cell bodies. Given the vast number and types of neurons and glial cells in the nervous system, one quickly realizes the potential for several neurological dysfunctions, depending on the cell type(s) affected. Illustration shows aspects of neurotransmitter release, receptor interaction, and generation of the electrical signal. All electrical signals arise from the action of various combinations of ion channel proteins that form aqueous pores through which ions traverse the membranes. When ion channels are open, ions move through the channels down their electrochemical gradients. Their net movement across the membrane constitutes a current that changes the membrane potential and generates an electrical signal. For the majority of neurological disorders, speciﬁc classes of neurons in the brain or spinal cord show selective vulnerability. Depending on the type of neuron/ neurotransmitter affected, changes will occur in behavior, memory, or movement. Loss of these neurons inﬂuences the normal function of the extrapyramidal system in the brain and results in rigidity and tremor of the limbs. Alzheimer’s isolates the hippocam- pus and regions of the cerebral cortex due to death of acetylcholine-rich neurons, causes dementia, and prevents the formation of new memory. Alternatively, when oligodendrocytes in the central nervous system are affected, problems develop with routine motor functions, and sensory deﬁcits become noticeable in individuals with multiple sclerosis. Although most lysosomal disorders result from defects in genes that code for lysosomal enzymes, some are caused by genes coding for transport proteins, protective proteins, or enzymes that process the lysosomal enzymes. In Huntington’s disease, a mutation (triplet repeat mutations) in chromosome 4 is linked with the death of neurons in a region of the brain called the caudate/putamen, a complex of inter- connected structures tuned to modulate motor activities. The identiﬁcation of un- stable triplet repeat mutations represents one of the great discoveries of human neurogenetics. Genetic linkages discussed later in this chapter have also been deter- mined for a small percentage of individuals with Alzheimer’s and Parkinson’s. We have identiﬁed various types of cytological and molecular changes in neurons that are associated with the death of neurons. Abnormal accumulations of ﬁlaments and altered pro- teins are recognized as primary features of neurons targeted in neurological dys- function. The accumulations may occur in the cytoplasm of the neuron or in the extracellular environment. In certain instances, the pattern of neuronal loss is dic- tated by how the neurons are connected to one another. Virtually all the subgroups of neurons lost in Alzheimer’s are found to be connected to regions of the cerebral cortex that show high levels of neuritic plaque formation—foci of degenerating processes and twisted arrays of cytoskeletal elements in the neurons referred to as neuroﬁbrillary tangles. What sets off the initial changes in neurons that lead to a cascade of cell death in speciﬁc areas and pathways of the nervous system? A number of molecular mech- anisms at different levels of neuronal function have been proposed. The factors are secreted from the target innervated by the neurons, taken up at the nerve terminals, and then transported over long distances to the cell body where they act to regulate neuronal functioning by a variety of signaling mechanisms (Fig. We now realize that neurotrophic factors bind to cell surface receptor proteins on the nerve terminals, become internalized (receptor-mediated endocytosis), and then move toward the cell body by the mechanism of retrograde axonal transport. Advances in the understanding of the structure of the receptors for neurotrophic factors indicate that they are similar to the receptors used by traditional growth factors and cytokines. The expression of the receptors for the neurotrophic factors is exclusively or predominantly in the nervous system, and, when activated, the factors display distinctive molecular actions. It was discovered and char- acterized in the 1950s by Rita Levi-Montalcini, Stanley Cohen, and Viktor Ham- burger and was the ﬁrst molecule to show potent nerve growth promoting activity on explants of neural tissue maintained in tissue culture. The neurotrophic factor ligand (supplied by a target tissue) binds to the receptor on the surface of the axon terminal. Promoters for glial ﬁbrillary acidic protein and myelin basic protein have been constructed to drive transgene expression in astrocytes and oligodendrocytes, respectively. A common inducible (temporal) transgene system uses tetracycline or tetracycline derivatives as con- trolled promoters. Neurons in the nervous system reside in a nondividing state and therefore potential virus vectors for gene therapy must be capable of infecting postmitotic cells. Lentiviruses (from the Latin word lentus meaning slow) cause slow chronic and progressive degenerative diseases of the nervous, hematopoietic, musculoskeletal, and immune systems. These viruses are the only retroviruses able to integrate into the chromo- somes of cells that are not mitotically active. The efﬁciency of gene transfer is high and reports indicate that lentiviral vectors injected into the adult rat brain stably transduce terminally differentiated cells in vivo, without a decrease in transgene expression or toxicity for at least 6 months in vivo. These genes and their products show homology throughout the animal kingdom from the nematode to the primates.