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The peri-stimulus time histogram (upper left panel: PSTH) was summed over all frequencies of presentation viagra 25mg with amex erectile dysfunction 27. Both PSTH examples demonstrate sustained firing in response to the entire 500 msec stimulus train purchase 25mg viagra with mastercard erectile dysfunction fpnotebook. In this panel, the thicker blue line shows the vector strength calculated for the driving frequency. Vector strength at a given frequency indicates the power at that frequency normalized by the power over all frequencies (i. In both examples, the vector strength shows tuning surrounding a peak at the vibrissa fundamental resonance frequency, as seen by comparison of the blue and gray curves. Consistent with trigeminal recordings, these recordings demonstrate sharper tuning using a measure of tem- poral fidelity than of mean firing rate. This finding also demonstrates that the increased neural tuning measured with vector strength is not an artifact of an increased firing rate. The example in the lower frame shows no mean firing rate frequency tuning around the FRF (top panel), despite precise temporal tuning (vector strength tuning). Estimates of expected vector strength for Poisson spike trains with equal mean firing rates at each frequency are also shown (mean +- std. These measures provide some evidence for frequency doubling in the convergence of signals within SI, a finding predicted by the velocity sensitivity of the vibrissa sensory system. Smaller panels In the smaller panels, cycle histograms (upper right panels within the 4 panel grid) taken at the fundamental resonance frequency are also shown (black line), and demonstrate clear modulation at the cycle length that is not apparent in Poisson control spike trains (blue line, mean +- std. The autocorrelograms (lower right panels) and spike traces (lower left panels) identify these recordings as coming from single fast spiking unit recordings. The peri-stimulus time histogram (upper left panel: PSTH) was summed over all frequencies of presentation. Both PSTH examples demonstrate sustained firing in response to the entire 500 msec stimulus train. SUMMARY AND HUMAN IMPLICATIONS In this chapter we proposed a vibrissa resonance hypothesis in which we suggested that the biomechanical properties of the vibrissae facilitate the detection of small amplitude high-frequency stimuli and the discrimination of frequency-specific stim- uli. In support of this hypothesis, we described recent evidence demonstrating that vibrissa resonance amplifies small amplitude high-frequency inputs such that signals that would not otherwise drive neural activity in peripheral or SI neurons are able to evoke significant neural responses. This amplification of sensory input could greatly facilitate high-frequency stimulus detection. Further, the presence of vibrissa resonance generates frequency tuning in somatosensory neurons and a frequency map and system of isofrequency columns in SI (and, presumably, in other central somatotopic maps). This neural representation suggests that a place code may be engaged in the vibrissa sensory system. The velocity sensitivity of the system and the presence of higher harmonics may affect the quality and precision of transduction within this place code: further studies are required to assess both factors. In addition to discussing enhanced detection achieved through signal amplifi- cation and place coding through the resonance tuning map, we also described two different ways that vibrissa resonance may create or impact temporal coding in the vibrissa sensory system. Vibrissa resonance amplification requires ~ tens of milliseconds to evolve, and as a product of this delay, relatively greater frequency- tuning is observed in later temporal epochs. This finding led to the hypothesis that initial neural activity, occurring in the epoch ~0–25 msec after stimulus onset, may encode vibrissa position and/or the initial contact of a vibrissa, while later sustained activity may represent frequency information. We also presented several examples of fine temporal following of sensory input on a millisecond time scale in trigeminal and cortical neurons and presented evidence for the hypothesis that frequency doubling should occur through a volley principle present in the vibrissa sensory system. Under controlled stimulus presentation conditions, vibrissae generate signals that are well positioned to amplify and selectively filter frequency information. Further, in the anesthetized animal, these signals are transduced into complementary patterns of neural activity. While this kind of characterization has been the first step in the elucidation of several fundamental principles of sensory encoding (e. The predominance of the resonance effects described here suggest that even if resonance does not enhance perception, the behaving animal must compensate for the impact that resonance has on incoming sensory information. As discussed in Section IV, active manipulation of whisking velocity and damping in the follicle © 2005 by Taylor & Francis Group. Dynamic regulation of frequency dependent pro- cessing, on the millisecond to second timescale likely plays a role. While humans obviously do not possess vibrissae, there are several potential connections between the principles discussed here and our understanding of human tactile perception. One important parallel is the study of how biomechanical properties of the human body impact the perception of vibratory stimuli. Cochlea-like devices applied to the skin can successfully relay auditory stim- uli. A great deal of modern human tactile perception is mediated through haptic probes — for example, the perception of the texture of a writing surface through contact of a pen or pencil tip.

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H owever safe viagra 50 mg erectile dysfunction how common, after several days of therapy buy 50 mg viagra with mastercard erectile dysfunction treatment supplements, the renal blood flow is usually no different from that before The vasodilation produced by hydralazine (Apresoline) drug use. Its the release of nitric oxide, which acts on the vascular pharmacological actions are largely confined to vascular sm ooth m uscle to cause relaxation. In addition, hy- smooth muscle and occur predominantly on the arterial dralazine m ay produce vasodilation by activating K side of the circulation; venous capacitance is much less channels. Because cardiovascular reflexes and venous ca- pacitance are not affected by hydralazine, postural hy- Absorption, M etabolism, and Excretion potension is not a clinical concern. Hydralazine treat- ment does, however, result in an increase in cardiac H ydralazine is well absorbed (65–90% ) after oral ad- output. Its peak antihypertensive effect occurs in fects of a reflex increase in sympathetic stimulation of the about 1 hour, and its duration of action is about 6 hours. These effects limit the hypotensive usefulness of hydroxylation, with subsequent glucuronide conjuga- hydralazine to such an extent that it is rarely used alone. H ydralazine exhibits a first-pass effect in that a large part of an orally adm inistered dose Clinical Uses is m etabolized before the drug reaches the system ic cir- culation. The first-pass m etabolism occurs in the intes- H ydralazine is generally reserved for m oderately hy- tinal m ucosa (m ostly N-acetylation) and the liver. The pertensive am bulatory patients whose blood pressure is prim ary excretory route is through renal elim ination, not well controlled either by diuretics or by drugs that and about 80% of an oral dose appears in the urine interfere with the sym pathetic nervous system. The triple com bina- pear to be a m ajor therapeutic concern, the potential for tion of a diuretic, -blocker, and hydralazine constitutes interactions with other drugs that also bind to plasm a a unique hem odynam ic approach to the treatm ent of hy- proteins does exist. The plasm a half-life of hydralazine pertension, since three of the chief determ inants of in patients with norm al renal function is 1. The hem odynam ic effects of m inoxidil are generally A lthough hydralazine is available for intravenous sim ilar to those of hydralazine, with the noteworthy ex- adm inistration and has been used in the past for hyper- ception that a greater decrease in peripheral vascular tensive em ergencies, it is not generally em ployed for resistance and consequently a larger reduction in blood this purpose. M inoxidil pro- jection is relatively slow, and its actions are som ewhat duces no im portant changes in either renal blood flow unpredictable in com parison with those of several other or glom erular filtration rate. O rthostasis Adverse Effects and other side effects of sym pathetic blockade are M ost side effects associated with hydralazine adm inis- therefore not a problem. A s with hydralazine, there is a tration are due to vasodilation and the reflex hem ody- significant increase in cardiac output that is secondary nam ic changes that occur in response to vasodilation. M ore serious stantially reduce the effectiveness of m inoxidil when it m anifestations include m yocardial ischem ia and heart is used alone. W hen adm inistered chronically in high doses, hy- dralazine m ay produce a rheum atoidlike state that Clinical Uses when fully developed, resem bles dissem inated lupus The m ajor indications for the use of m inoxidil are erythem atosus. Com prom ises in renal function do not prolong M inoxidil (Loniten) is an orally effective vasodilator. It either the plasm a or the therapeutic half-life of m inoxi- is m ore potent and longer acting than hydralazine and dil, and therefore, it seem s to be particularly im portant does not accum ulate significantly in patients with renal for hypertensive patients with chronic renal failure. It depends on in vivo m etabolism by he- patic enzym es to produce an active m etabolite, m inoxi- Adverse Effects dil sulfate. M inoxidil sulfate activates potassium chan- Signs of toxicity com m on to vasodilator therapy in gen- nels, resulting in hyperpolarization of vascular sm ooth eral also occur with m inoxidil; they are attributable to m uscle and relaxation of the blood vessel. These include headache, nasal congestion, Absorption, M etabolism, and Excretion tachycardia, and palpitations. These effects do not have Peak concentrations of m inoxidil in the blood occur 1 great clinical im portance, since m inoxidil is alm ost al- hour after oral adm inistration, although the therapeutic ways adm inistered in com bination with a -blocker, effect m ay take 2 or m ore hours to m anifest. A m ore probably related to the tim e it takes to convert m inoxi- troublesom e side effect, particularly in wom en, is the dil to m inoxidil sulfate. The antihypertensive action af- growth of body hair, possibly due to a direct stim ulation ter an oral dose of m inoxidil lasts 12 to 24 hours. The of the growth and m aturation of cells that form hair long duration of action allows the drug to be adm inis- shafts. A pparently, m inoxidil activates a specific gene tered only once or twice a day, a regim en that m ay be that regulates hair shaft protein. Interestingly, the therapeutic ular side effect has been capitalized upon, and m inoxi- half-life is considerably longer than the plasm a half-life. The ultimate disposition of minoxidil depends prima- D iazoxide (H yperstat) is chem ically sim ilar to the thi- rily on hepatic metabolism and only slightly on renal ex- azide diuretics. The ripheral vascular resistance, leads to severe retention of m echanism by which diazoxide relaxes vascular sm ooth Na and water. Since tolerance to diazoxide can de- m uscle is related to its ability to activate potassium velop rapidly, it is frequently adm inistered in conjunc- channels and produce a hyperpolarization of the cell tion with a diuretic. Adverse Effects Absorption, M etabolism, and Excretion Since diazoxide is not often used for long-term treat- D iazoxide lowers blood pressure within 3 to 5 m inutes m ent, toxicities associated with chronic use are rare. The after rapid intravenous injection, and its duration of ac- chief concern is the side effects associated with the in- tion m ay be 4 to 12 hours. Interestingly, if diazoxide is creased workload on the heart, which m ay precipitate either injected slowly or infused its hypotensive action m yocardial ischem ia and Na and water retention. This is believed to be due to a rapid and These undesirable effects can be controlled by concur- extensive binding of the drug to plasm a proteins. The plasm a half-life is therefore prolonged in diabetics, so if the drug is used for several days, blood patients with chronic renal failure.

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