X. Sinikar. Colby-Sawyer College.
Hickman antibody for axonal identiﬁcation; and labeling with anti-MAP-2 for dendrites and the cell body purchase doxycycline 100mg overnight delivery. This experiment indicates that polarity can also be achieved by geo- metric means alone (Stenger et al purchase doxycycline 100 mg otc. 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 doxycycline 100 mg generic. 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 discount doxycycline 200mg without prescription. 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. While this simulation dem- Building Minimalistic Hybrid Neuroelectric Devices 213 input - + E + I Figure 10. We speculate that two aspects of complexity may emerge upon examination of patterned neuronal circuits. First, synaptic connections may undergo long-term potentiation (LTP) or long-term depression (LTD), which require substantial and persistent postsynaptic activity (Juusola et al. Thus, LTP or LTD would cre- ate use-dependent alterations in synaptic strength to a¤ect information processing.
However safe doxycycline 100mg, pallidotomy decreases both reported that the H reﬂex was absent in 11 of 13 the rigidity and the amplitude of the M2 response patients 100 mg doxycycline. F waves Hreﬂex threshold F waves recorded in distal upper limb muscles (ﬁrst Recent investigations have shown that the threshold dorsal interosseus purchase doxycycline 100mg with visa, abductor pollicis brevis) occur for the soleus H reﬂex is increased in parkinsonian more frequently and have a longer duration and a patients(Kushnir 200 mg doxycycline with amex,Klein&Rabey,2001;Kushniretal. These ﬁndings have been observed lower than M wave threshold, but it was similar to, by many investigators (Abbruzzese et al. In lowing period of relative inhibition at 300–700 ms addition, the MEP produced by TMS activates cor- is decreased in parkinsonian patients (Olsen & Dia- tical neurones trans-synaptically, and is therefore mantopoulos,1967;Takamori,1967;Yap,1967),even affected by the excitability of corticospinal neurones in the early stages of the disease (Sabbahi et al. TheincreasedfacilitationoftheHreﬂexrecov- ery cycle disappears after successful thalamotomy Conclusions (Yap, 1967) and treatment by L-dopa (McLeod & Walsh, 1972). However, itation at 150–700 ms could result from decreased there is a concomitant decrease in the on-going post-activation depression at the Ia-motoneurone presynaptic inhibition of Ia terminals (see below) synapse,duetoadaptivechangesfollowingakinesia. They argued that this in parkinsonian patients is also inconsistent with disorder might not necessarily be detected by the increase in the F wave. However, this con- was recorded in distal upper limb muscles, which clusion was based on a comparison of electri- are the muscles most involved in the tremor. The cally and mechanically evoked reﬂexes as a mea- increased excitability of motoneurones of these sure of fusimotor drive, and the problems with this muscles could simply be due to the fact that they time-honoured but now discredited practice are were not truly at rest. As in the case of spasticity, it would be imprudent to discard completely the possibility that enhanced Fusimotor activity drive plays a role in parkinsonian rigidity. Clariﬁcation of in the limited data base, there was no evidence for this issue requires detailed studies under identical selective or disproportionate drive to spindle end- conditions of the responses of single spindle affer- ings in parkinsonian patients, and no evidence that ents in patients and control subjects. The apparent increase in spindle activity mentioned by Wallin, Hongell & Presynaptic inhibition of Ia terminals Hagbarth (1973) was probably due to the inability of parkinsonian patients to relax completely (Burke, Ia terminals to soleus motoneurones Hagbarth & Wallin, 1977). Evidence for decreased presynaptic inhibition of Ia terminals to soleus motoneurones has been found consistently using techniques studying speciﬁcally Stretch- vs. Indirect evidence for increased s drive was, how- Thus, in parkinsonian patients, the suppression of ever, claimed by Noth et al. No signiﬁcant relationship was While the electrically induced responses were simi- found between the reduction of presynaptic inhibi- lar in the two groups, the responses to stretch were tion assessed with either method and the rigidity in markedly reduced in parkinsonian patients. However, the increased femoral- that s stimulation in the cat reduces the sensitivity inducedfacilitationwassigniﬁcantlycorrelatedwith ofprimaryendingstosmall-amplitudestretches,the the degree of bradykinesia, before and after treat- authors suggested that this ﬁnding could result from ment with L-dopa (see p. Vibratory depression of a homonymous with respect to normal subjects (Obeso et al. After the blockade, the soleus H reﬂex was mous tendon activated reciprocal Ia inhibition from increased signiﬁcantly, thus revealing an exagger- pretibial ﬂexors, because vibration applied to the ated tonic inhibitory action from ﬂexor to extensor Achilles tendon spreads to these muscles (Ashby, muscles(Bathien&Rondot,1977;Obesoetal. The absence of a change in Interestingly, abnormal tonic reciprocal inhibition homonymous vibratory inhibition in parkinsonian was also decreased by L-dopa treatment, suggest- patients might then be explained by the increased ingthatadisorderofperipheralreciprocalinhibition reciprocal Ia inhibition that has been reported in might be involved in the pathophysiology of parkin- these patients (see below), a change that could off- sonian rigidity. However, here again, incon- not been obtained in 11 of 13 parkinsonian patients sistent results have been reported. Conclusions Transmission of reciprocal Ia inhibition to ankle extensors is tonically increased and the resulting Conclusions decreasedexcitabilityofsoleusmotoneuronesmight There are congruent arguments in favour of a explain why the soleus H reﬂex is not increased decrease in presynaptic inhibition of soleus Ia despite the decreased presynaptic inhibition of Ia terminals but this abnormality contributes only terminals. The increased reciprocal Ia inhibition marginally to the rigidity of ankle muscles. Incon- could be due to increased drive to ankle ﬂexors sistent results have been reported at wrist level. Alternatively, abnormal reticulospinal acti- intheearlystagesofthedisease,whereasthereplace- vation has been proposed (Delwaide, Pepin & ment of Ib inhibition by facilitation was observed in Maertens de Noordhout, 1993, see below). Correlation with treatment In denovopatientstreatedwithL-dopa,thedecrease Ib inhibition (and/or oligosynaptic in facilitation paralleled the reduction of the rigid- propriospinally mediated group I excitation) ity (Delwaide, Pepin & Maertens de Noordhout, 1991). High-frequency stimulation in the subthala- Decreased Ib inhibition mic nucleus (Potter¨ et al. The departures from normal values correlated with the Conclusions intensity of rigidity assessed by the Webster scale: There is little doubt that gastrocnemius medialis- increased rigidity was associated, ﬁrst, with a reduc- induced group I inhibition of soleus motoneurones tionofinhibitionand,inthemorerigidpatients,with is reduced in parkinsonian patients, and that it is facilitation replacing the normal inhibition. However, of the strong correlation between the decreased Ib interestingasthislatterﬁndingmaybe,itremainsan inhibition and the increased reciprocal Ia inhibition, open question whether the disorder affects primar- a common mechanism for these two abnormalities ily Ib inhibition or propriospinally mediated group I has been advanced (increased reticulospinal acti- facilitation. Evidence for increased group II excitation Inhibition tends to be replaced by facilitation, possi- The late group II, but not the early group I, deep blybecausefacilitatedgroupIexcitationoverwhelms peroneal facilitation of the quadriceps H reﬂex is theIbinhibition,withorwithoutdecreasedIbinhibi- larger in parkinsonian patients than in normal sub- tion (cf. The absence of increased peroneal- ulation, there is a signiﬁcant cell loss in the locus induced propriospinally mediated group I facilita- coeruleus, even in the early stages of the disease tion of the quadriceps H reﬂex (Simonetta-Moreau (German et al.
Her new doc- tor had just told them he was probably going to fuse her spine discount doxycycline 200 mg line. Not only do Group IV patients deny any life stress purchase doxycycline 200mg without a prescription, they deny any possibility of a relationship between their life and their health purchase 200mg doxycycline fast delivery. Of the twenty-nine patients in Group IV order 100 mg doxycycline with mastercard, twenty-one carried a diagnosis of a nonexistent disease. I was able to convince only four that they did not have the diagnosed disease (Florence in Chapter 10 was one of them). Seventeen of the twenty-one contin- ued to take medicines and to believe they had the diagnosed dis- ease (Sweet Ting in Chapter 8 was one of these). Symptoms Without Disease 89 Self-Awareness, Connection to Life, and Willingness to Explore Te method of grouping I used is not a diagnostic tool nor does it substitute for a thorough medical workup. Keep in mind that I cre- ated the groupings only after medical diagnoses had been excluded by extensive testing. Te groupings describe some characteristics of a special subset of patients who presented with symptoms but who did not have a demonstrable disease to explain them. Te method also does not predict the presence or absence of psychological or social stress. Although a patient readily admits to stress (Group I) and be- lieves the stress explains the symptoms, there still needs to be a medical evaluation to exclude likely diseases. Even though in these groupings I used the timing with which patients introduced social and psychological information (that is, in their ﬁrst or second vis- Table 11-1. Grouping of Patients with Symptoms Without Medical Disease Group Group Group Group I II III IV Level of self- Aware Aware Unaware Unaware awareness Level of Almost Un- Un- connection of Connected connected connected connected self to life Level of willingness to Willing Willing Willing Unwilling explore life 90 Symptoms of Unknown Origin its, or not at all), I do not mean to imply that all such patients have a psychological or social reason for their symptoms. Finding the real causative or triggering factors for any symptom takes collabo- ration between the physician and the patient. For patients who fall into Groups I, II, or even III, the collaborative eﬀort to trace causa- tion will likely be productive. For patients with the characteristics of Group IV, the eﬀort will be largely futile. Maybe future studies and research of this group of patients will lead to more productive approaches than I was able to ﬁnd. Although I did not test the idea systematically, I found this method for grouping by awareness and connectedness to life events also useful for patients with a deﬁned medical disease. Even though I did not subject the excluded seventy-two patients to detailed analysis, it was my experience that patients who fell into Groups I, II, or III were more amenable to examining their daily lives, even when there was a medical disease present. Tey were amenable to changing habits, making adjustments in their lives, and taking medications that the disease process required for maximum im- provement. For patients with the characteristics of Group IV, disease is a way of life whether it is objectively demonstrable or not. I believe, but cannot prove, that patients with the characteristics of Group IV will do more poorly with medical diseases than those in Groups I, II, or III. Some patients in Group IV use their diseases to manipu- late their families and friends. Tere were 165 previous surgi- Symptoms Without Disease 91 cal operations among the seventy-eight patients, an average of 2. One of the most telling aspects of this study is the number and nature of the false diagnoses carried by these patients. Table 11-2 lists the forty-two diagnoses that were not substantiated by fur- ther study. Aside from diverting the attention of patients from the real source of their problems, some of these labels are serious and harmful enough to be worthy of comment. Another patient was told the lipoma on her forearm was potentially malignant. Two patients were taking propylthiouracil for unsubstantiated hyperthyroidism.
Elec- trodeposition of metal nanowire arrays using nanochannel glass templates has been described previously (Nguyen et al discount doxycycline 200mg with amex. In this work cheap 200mg doxycycline with amex, arrays of uniform doxycycline 200mg visa, continu- ous nickel wires having diameter of 250 nm were fabricated doxycycline 200 mg cheap. In addition, nanotubes and nanowires of other metals, including platinum, copper, and cobalt, have been fabricated. Using similar electroplating methods, modiﬁed to account for the growth of metal wires with larger cross-sectional areas, arrays of nickel, copper, and plati- num microwires have been grown in both microchannel glass and nanochannel glass templates. Brieﬂy, the etched glass (hollow channels) is prepared for electrodepostion by coat- ing one surface with a thin layer of gold. The gold-coated channel glass is then attached to a gold Stimulation of Large Retinal Tissue Areas 33 Figure 2. Electrodeposition of metal within the hollow channels of the glass proceeds by immersing the sample in an electroplating solution and applying a voltage using a current-regulated power supply. High-quality deposition is observed when the growth rate is main- tained lower than that commonly used for electrodeposition of bulk metals. The limited growth rate is most likely due to reactant depletion in the channels because di¤usion-limited transfer of reactants down the high aspect-ratio channels is unable to maintain an optimum reactant concentration. Following electrodepostition, the piece is removed from the slide and both sides are ground and polished to a smooth ﬁnish. An optical photograph of a microelectrode array of nickel microwires electro- deposited in channel glass is shown in ﬁgure 2. Microelectronic Multiplexer Design for an Advanced IRP The silicon multiplexer discussed previously performs several operations in a sequen- tial order. During the ﬁrst step, an image frame is read onto the multiplexer, pixel- by-pixel, to each unit cell. Row-by-row, each unit cell samples the analog video input and stores the pixel value as a charge on a metal-oxide-semiconductor (MOS) capac- itor. A full ﬁeld is completed every sixtieth of a second in a manner compatible with the RS-170 television format (30 frames per second consisting of two ﬁelds per frame); this allows the use of the test prosthesis with standard video equipment. The digital electronics is of major im- portance because it generates the switching pulses that route image data into the unit cells. Without the on-chip digital electronics, a dozen or more clocks would have to be input to the device. That would make the cable through the eye wall much larger and more cumbersome. The use of IRFPA multiplexer technology greatly simpliﬁes the cable problems through the eye wall. After all the unit cells have been loaded with the pixel values for the current frame, the next step is to send a biphasic pulse to each unit cell, which in turn is modulated in proportion to the pixel value stored in each unit cell. The biphasic pulse ﬂows from an external source, through each unit cell, thus stimulating retinal neurons in a si- multaneous manner. This is an important feature of the design because it is a syn- chronistic action analogous to imaged photons stimulating photoreceptors in a normal retina. Finally, the electrodes are all connected to ground to prevent any pos- sible charge buildup at the electrode/neuron interface. There are several important considerations in designing a device that performs all these operations successfully. First, the multiplexer operation should be designed with Stimulation of Large Retinal Tissue Areas 35 Control logic Unit cells (80 x 40) Column MUX 3. Of course, the prosthetic test device moves image data in the direction opposite to that of a conventional imaging multiplexer; that is, the image moves onto the device rather than o¤ it, but otherwise the speciﬁ- cations are analogous. Another consideration is that each unit cell should store an individual pixel value and then use it to modulate the biphasic pulse that is input to the retinal tissue through the NCG. Note that the biphasic pulse and the image data are both generated o¤-chip. This allows greater ﬂexibility during human testing because any image sequence can be input and com- bined with any shape of biphasic pulse. Ancillary Electronics The operation of the test device during acute experiments is controlled and powered by external ancillary electronics (ﬁgure 2.