By V. Rhobar. Stanford University.
Neural networks that formed were predominantly in parallel quality 20 mg erectafil ayurvedic treatment erectile dysfunction kerala, linear tracks over the columns of electrodes cheap 20 mg erectafil with amex coke causes erectile dysfunction. The Biotic/Abiotic Interface 225 Poly-D-Lysine Substrate Poly-D-Lysine with Basement Membrane Matrix Figure 11. The panels on the far left show hippocampal neurons grown on glass coated with poly-d-lysine in the absence (top) and in combination with basement membrane matrix (bottom). Note that in the presence of basement membrane, neuronal clusters appear more frequently and a modest degree of process fasciculation occurs. The middle panels show phenotypic development of neuronal processes on these two substrates. Dendritic processes are la- beled with the dendrite selective marker MAP2 shown, while axons are labeled with the axon-selective marker, GAP43. In the third panel are dissociated hippocampal neurons cultured onto multisite electrode arrays. Note that in the presence of basement membrane, a much greater degree of clustering of neurons and fasciculation of their processes occurs. Polyornithine PO Structurally very similar to PDL, but (PO) H N H O unbranched cationic polymer, with peptide 2 bonds. NH CH2CH2CH2C C n Polyethyleneimine PEI Branched cationic polymer with no (PEI) CH2CH2NH2 carboxylic group, thus more positively NH CH CH N CH CH charged. Basement Contains: Extracellular matrix extracted from EHS membrane (BM) Laminin 56% mouse tumor. Similar in structure, Collagen IV 31% composition, physical property, and Entactin 8% functional characteristics to in vivo BM. Heparan sulfate proteoglycan Matrix metalloproteinases Growth factors: EGF, bFGF, NGF, PDGF, IGF-1, TFG-b Table 11. Both nerve cell bodies and their processes were predominantly attached to the linear tracts of poly-d-lysine, with minimal crossing of processes across the 50-mm gap between electrode pads and leads. Impact of Surface Composition on Electrophysiological Signaling of Neurons Our most recent work has addressed the impact of surface composition on the elec- trophysiological properties of neurons, with the long-term intent of manipulating the excitability of neurons that would interface with the electrodes of a neural prosthesis. Our initial data indicate that the morphologies induced by di¤erent substrates are associated with di¤erent electrophysiological phenotypes (see ﬁgure 11. It is important to note that the di¤erences in electrophysiological phe- notype are not due to changes in neuronal viability because neurons cultured on titanium nitride-silicon nitride multisite electrode arrays coated with poly-d-lysine exhibit markers of viability comparable to that of neurons cultured onto similarly coated glass coverslips (see ﬁgure 11. Electro- physiological recordings are derived from the same dissociated hippocampal neuron culture on a polyethy- leneimine (PEI)-coated multisite electrode array at days 15 (1) and 18 (2). The continuously ﬁring cell has a wider and delayed histo- gram, while the histograms of the bursting cells get narrower with shorter burst durations. The gray-scale correlation matrices plot the cross-correlation indices of all the active electrodes in that particular multisite electrode array, so that each pair of electrodes has two small squares coding their indices (one above the midline and one below). The culture medium was collected following speciﬁed days from hippocampal neuron cultures plated onto glass or multisite electrode arrays and analyzed for lactate dehydrogenase (LDH) content in the culture medium. LDH is a stable cytoplasmic enzyme expressed in all cells, including neurons. It is rap- idly released into the cell culture supernatant upon damage to the plasma membrane. The spectophotomet- ric results are translated to nanograms per milliliter by interpolation on a standard reference curve and normalized to the cell plating density. Both multisite electrode array cultures and control cultures show similar aging patterns: initially high LDH release into the medium as a result of the initial damage at seed- ing, followed by low level of LDH release for 10 days, and aging followed by a modest rise in LDH release likely due to related oxidative damage to the plasma membrane after 20 days in culture, which occurs in the absence of antioxidants. The Biotic/Abiotic Interface 231 nonspecific cell attachment or repulsion group cell adhesion molecule (CAM) R artificial surface anchoring group cell R nonspecific R R R R R cell binding R R R R R R R R cell artificial surface artificial surface cell R R R R R repulsion neural cell integration selective cell attachment artificial surface artificial surface Figure 11. Sur- face chemistries can be designed to promote selective cell attachment, prohibit nonspeciﬁc cell binding, and prevent inﬂammation through cell repulsion chemistry to thwart activation of the inﬂammatory response in glial cells. Integration of the neural component with the artiﬁcial surface of the neuroprosthesis could be achieved by speciﬁc recognition between either an nCAM sequence or receptors selectively expressed on speciﬁc neuron populations (shown as bars). Although much of the electrophysiological testing of interfaces to date has been completed using hippocampal slices (which remain physiologically viable for 12–18 hr), we also have begun using hippocampal slice cultures to test the long-term viabil- ity of the neuron/silicon interface. 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 incubator (Gholmieh et al.
This indicates that we may be able to control synaptic development by controlling the cell growth parameters and surface geometry order 20 mg erectafil with visa impotence after 50. Another important issue is how to orient the neurons once they are placed in the correct position cheap 20 mg erectafil mastercard erectile dysfunction juice drink. Much like an electronic transistor, not only the construction but the orientation of the device is critical for function. Banker and Cowan (1977) showed that the longest neurite from a developing embryonic neuron would become the axon. Hickman antibody for axonal identiﬁcation; and labeling with anti-MAP-2 for dendrites and the cell body. This experiment indicates that polarity can also be achieved by geo- metric means alone (Stenger et al. The accurate spatial placement of a neuronal cell network allows a wide spectrum of circuit and fabrication technology to be applied to the detection of signals trans- mitted within the network. We have also developed an electronic interface to a microelectrode chip and have successfully tested it by recording electrical activity from single unpatterned hippocampal neurons using metal microelectrodes (Jung et al. The neurons were grown on a silicon nitride (Si3N4)-coated microelectrode, and the signals were recorded from gold microelectrodes in serum-free media. This demonstrates that we can culture the cells in a deﬁned media on the Si3N4 surface and record the signals, and that the electronic interface can process and display the electrophysiological sig- nals. The results demonstrate that the signals produced by the mammalian cells are strong enough to be picked up by the electrodes, and the signal-to-noise ratio can approach that achieved with patch-clamp electrophysiology. This result demonstrates the feasibility of using the sensor to evaluate drug candi- dates if we can establish the modes of cell-cell communication that could be moni- tored as an indicator of cell function. Modeling Cell-Cell Communication We believe that there will be di¤erent modes of operation of the system based on the number and location of synapses, which will permit the fabrication of neuroelectric devices with distinct input-output relationships. To address this question, preliminary simulations of simple two-neuron circuits were made using the neural modeling pro- gram GENESIS (Wilson et al. In these models, the interaction between an excitatory and an inhibitory neuron was simulated. For the sake of simplicity, both current injection and voltage mea- surements were performed at the soma of each neuron, as represented by the micro- electrodes in ﬁgure 10. We typically ran the modeling experiments using current injection on both neurons. Building Minimalistic Hybrid Neuroelectric Devices 211 current voltage injection measurement electrode electrode I I - 1 2 - pA Neuron 1 pA Neuron 2 Current Current 400 400 0 0 100 200 300 400 msec 100 200 300 400 msec Figure 10. A B input A +5V input B V out I + - E Vin output - Dual Neuron Circuit Corresponding Transistor "Inverter" Circuit Equivalent Key: : stimulationsite : recording site : synapse I: inhibitory neuron E: excitatory neuron Figure 10. With appropriately chosen stimuli, this simple circuit can produce distinctive behavior, as demonstrated by the simulation e¤orts in ﬁgure 10. For example, a constant stimulation train ap- plied at input B would be gated based on the state of input A. Stimulation of input A would inhibit the transmission of excitation, whereas the lack of stimulation of input A would permit the propagation of excitability. The behavior of this circuit model is similar to that of a simple transistor-logic circuit where the state of the transistor gate inﬂuences circuit output (ﬁgure 10. Furthermore, this circuit model is the core element of a circuit to explain directional selectivity in the mammalian retina 212 James J. The synaptic connection from L1 to R1 is inhibitory and is set at a weight of 600. For 100 ms, cell R1 received no somatic current input and then a constant pulse soma input of 0. Cell L1 received a similar pulse, which started later and lasted for 200 ms. With a stimulus moving in the nonpreferred direction (A to B), the inhibition decreases the excitability of the post- synaptic excitatory neuron, whereas in the preferred direction, excitation passes freely (Anton et al. In the experiment we employed two neurons (the top is L1 and the bottom is R1) with standard sodium (Na) and potassium (K) channels and linked the two cells with an inhibitory connection from the cell L1 to the cell R1. The simulation was done in GENESIS using simple Hodgkins dynamics with the following results: Cell L1 turns on 50 ms after R1 and, after a delay, inhibits the output of cell R1.
ETHICAL ISSUES An example of an N-of-one design in an ide- alised setting would be to answer the question of At present buy erectafil 20mg amex erectile dysfunction purple pill, available drugs to treat AD are symp- whether or not a patient on a cognitive-enhancing tomatic buy erectafil 20 mg fast delivery erectile dysfunction yoga exercises. Several agents are currently approved agent, such as a cholinesterase inhibitor, is still and before enrolling patients in any clinical trial, responding to drug. This question is an impor- disclosure and discussion of these agents with the tant one since AD patients continue to decline patient and their caregiver is necessary. After one or two years on tion, vitamin E and selegiline have been reported treatment, the clinician is faced with the decision to delay the time to endpoints in moderately as to whether or not to continue treatment. The results of the vitamin an idealised version, a patient could be blindly E study also need to be discussed with patients crossed over to placebo to examine for a with- before enrolling them in clinical trials since the drawal effect. If the patient was on a symp- use of both cholinesterase inhibitors and vitamin tomatic treatment and continuing to respond, a E is currently the standard of care in the US. This manoeuvre could then regarding the ethics of placebo-controlled tri- be followed by blindly restarting the patient on als. Arch Neurol (1976) 33: on studies or by demonstrating equivalence of 217–18. In addition, patients are free to not enter hypoxia in senile dementia and other abiotrophies. Necropsy evidence of central cholinergic deﬁcits cern that comparator studies may result in the in senile dementia. George-Hyslop PH, Tanzi RE, Polinsky PJ, agent and the true effect size in the approved et al. Gene dose of apolipoprotein E type 4 allele and a placebo-controlled trial. Allgem Z Psychiatr-Gerich Med man R, Bick KL, Sisodia SS, eds, Alzheimer Dis- (1907) 64: 146–8. The associa- disease: a case–control study of an Italian popu- tion between quantitative measures of dementia lation. A double-blind, heimer and morbus Pic: a genetic, clinical, and placebo-controlled multicenter study of tacrine for patho-anatomical study. Philadelphia: Lippincott Williams Patterns of decline in the Lewy body variant & Wilkins (1999) 188–203. Growdon JH, Locascio JJ, Corkin S, Gomez- Rossor MN, eds, The Dementias Boston: Butter- Isla T, Hyman BT. Arch Validation of clinical diagnostic criteria for Alz- Neurol (1999) 56: 303–8. Acta Neuropathol (1987) 75: ease: development of cytoskeletal changes and 8–15. Perry R, Irving D, Blessed G, Fairbairn A, Per- controlled trial of donepezil in patients with ry E. LAVORI 1Western Psychiatric Institute and Clinic, Pittsburgh, PA 15213, USA 2VA Medical Center, Menlo Park, CA 94025 2539, USA INTRODUCTION speciﬁed and explained in manualised format. Treatment training and adherence measures are Anxiety disorders are the most prevalent psychi- available. These methodological advances mean atric conditions in the community with a life- that studies of the efﬁcacy of new interventions time community prevalence of 20–30%. Recent researchers are now turning their attention to studies suggest some forms of anxiety are asso- studies that test these interventions in the commu- ciated with early mortality. Many who suffer nity settings where they will be used, and in clin- from anxiety disorders have other serious medical ical contexts (such as maintenance of response) problems, such as depression, pulmonary disease, that go beyond the phase of acute illness that is cardiovascular illness and neurological condi- the focus of most efﬁcacy studies. Prevalent and debilitating, anxiety disor- in focus, new methodological problems appear. Clinical trials are needed to establish designing such studies, often known as effec- efﬁcacy of promising interventions and to deter- tiveness studies, have been described in the mine the best ways to deliver efﬁcacious treat- literature. Methods for conducting efﬁcacy trials in anx- ological issues pertaining to effectiveness stud- iety disorders have evolved over the past few ies of anxiety disorders. Reliable diagnostic instruments and features of these disorders and consider the prob- symptom severity scales have been developed lems they create for study questions and study and tested.