By N. Tarok. Liberty University. 2018.
Pentazocine produces as much respiratory de- pentazocine in combination with alcohol or barbitu- pression as morphine but does not produce the same rates greatly enhances its sedative and respiratory de- degree of constipation or the biliary constriction ob- pressant effects order malegra dxt 130 mg with visa erectile dysfunction pumps side effects. Unlike morphine buy malegra dxt 130 mg on-line erectile dysfunction filthy frank, penta- Tolerance and Dependence zocine increases heart rate and blood pressure by re- Tolerance to the analgesic effects of pentazocine de- leasing norepinephrine. The onset of action occurs within approxi- Butorphanol (Stadol) is chemically related to levor- mately 15 minutes, and the half-life is 2 to 3 hours. As an opioid antagonist it is nearly 30 times as thus has a high ﬁrst-pass effect following oral administra- potent as pentazocine and has one-fortieth the potency tion; its half-life differs considerably from patient to pa- of naloxone. Its potency is 7 gation to glucuronides in the liver terminates the effects times that of morphine and 20 times that of pentazocine of pentazocine. It produces exci- Pentazocine is indicated for relief of moderate pain tatory effects and sedation and precipitates withdrawal in patients not receiving large doses of opioids. Although generally ad- used as premedication for anesthesia and as a supple- ministered parenterally because of its low bioavailabil- ment to surgical anesthesia. The nasal spray is Adverse Effects indicated for the relief of postoperative pain and mi- The most common side effect of pentazocine is se- graine headache. Nasal administration of butorphanol decreases the Respiratory depression and increased heart rate, body onset of action to 15 minutes and decreases the ﬁrst- temperature, and blood pressure accompany overdose. Naloxone is effective in reducing the respiratory de- Generally the patient sprays a set dose of 1 mg per hour pression but requires the use of higher doses than for for 2 hours. The convenience of such administration is a major 326 IV DRUGS AFFECTING THE CENTRAL NERVOUS SYSTEM advantage to patients requiring repeat dosing. The morphinelike, it does reduce the craving for morphine abuse potential following such administration has not and for the stimulant cocaine. Thus, buprenorphine is a been extensively studied, although it is thought to be potential new therapy for the treatment of addiction to small. Adverse effects, contraindications, and drug interac- Dezocine tions are similar to those for pentazocine and morphine. The onset of Nalbuphine activity and potency as an analgesic are comparable to Nalbuphine (Nubain) is a mixed agonist–antagonist that those of morphine. Although the drug requires glu- is similar in structure to both the antagonist naloxone curonidation during metabolism, patients with hepatic and the agonist oxymorphone. As an an- fects (analgesia, respiratory depression, sedation, and so tagonist, dezocine is more potent than pentazocine. As on) are similar to those produced by pentazocine, nal- an agonist, dezocine produces analgesia and respiratory buphine produces fewer psychotomimetic effects. It dif- depression (which is readily reversed by naloxone), but fers from pentazocine in that it has far greater antagonist unlike pentazocine, it has little if any effect on the car- than agonist effect. It is used Dezocine is indicated as an analgesic for moderate much as pentazocine is, that is, for moderate to severe to severe pain. Drug interactions and contraindications are Opioid Antagonists similar to those for pentazocine and morphine. Naloxone and naltrexone are pure opioid antagonists Buprenorphine synthesized by relatively minor changes in the morphine structure. Alteration of the substituent on the piperidine Buprenorphine (Temgesic) is a mixed agonist–antago- nitrogen from a methyl group to a longer side chain nist and a derivative of the naturally occurring opioid changes the drug from an agonist to an antagonist. Buprenorphine is highly lipophilic and is 25 to Opioid antagonists bind to the opioid receptor with 50 times more potent than morphine as an analgesic. The pure antagonists The sedation and respiratory depression it causes are block the effects of opioids at all opioid receptors. Its respiratory depressant effects are not for naloxone blockade of the -receptor versus the - readily reversed by naloxone. All opioid an- with high afﬁnity and only slowly dissociates from the tagonists will precipitate withdrawal in opioid-depend- receptor, which may explain the lack of naloxone rever- ent patients. Buprenorphine has more agonist than antagonist ef- Naloxone fects and is often considered a partial agonist rather than a mixed agonist–antagonist, although it precipi- Because of its fast onset (minutes), naloxone (Narcan) tates withdrawal in opioid-dependent patients.
Primate Behavioral Tasks A Animal squeezes handle B Animal touches two motor tips FIGURE 11 discount malegra dxt 130 mg with mastercard erectile dysfunction treatment by ayurveda. On the model buy malegra dxt 130 mg online impotence guilt, 1A the monkey had to open and close the hand piece for a variable number of trials. On the model 1B the money had to accurately place the tips of D1 and D2 onto the target and leave the digits in place during a random series of taps to the digits. Sensory representation abnormalities that parallel focal hand dystonia in primate model. The hand-piece was driven by a spring-loaded solenoid to provide a known force (80 g). When the vibration stopped, the monkey had to quickly release ﬁnger contact by extending the ﬁngers; then the hand piece automatically reopened. In the reaching task, the animal positioned its right, dominant hand in a hand mold, with the ﬁrst and second digits on two metal contacts with the forearm pronated. Each contact was 1 mm in diameter and positioned the two digits in an unnatural position. To receive an award, the animal was required to hold the hand in place for several hundred milliseconds before releasing. The animal was trained on a task that delivered 1000–200 µm taps to its ﬁngertips. When the animal placed the hand in the mold making electrical contact with the tips of the two motors on the pads of the thumb and index ﬁnger, then a series of stimuli were delivered to the index ﬁnger and the thumb with a change in the inter- tap interval time for a pair of taps, decreasing from 500 to 100 msec (See Figure 11. Speed of repetitions, number of repetitions, time of training, and accuracy of task performance (videotaped) and © 2005 by Taylor & Francis Group. After motor performance deteriorated by 50% in speed and accuracy, training continued at least another 2 weeks. The details of anesthesia, surgery and electrophysiological monitoring have been detailed in a variety of other studies and have been determined to meet the criteria for safe, animal care protocols for research. MAP 50 software109 was used to construct and measure the cortical representation and to measure the size of the cutaneous receptive ﬁelds. A food retrieval task (picking foot out of trays of graded size) was also rated for quality to conﬁrm that the movement disorder was conﬁned primarily to the target task. Following cortical mapping, anatomic dissec- tions were performed in the monkeys with analysis of the tissues for inﬂammatory cells, ﬁbroblasts and macrophages. In the monkey performing the reaching task, a dense microelectrode array was implanted in the left hemisphere, shortly before the full blown focal hand dystonia developed (right hand, D1, D2). Although the number of subjects was small, well over 100 d of data were gathered on motor accuracy and frequency of task performance, and 300–400 receptive ﬁelds were mapped. The clinical dependent variables included accuracy, speed and quality of task performance and food retrieval. For the electrophysiological data, the area of the topographical ﬁeld was mapped, the total area was calculated, the cortical distances between separate receptive ﬁelds was measured, the number of receptive ﬁelds were plotted per electrode penetration, the number of overlaps across adjacent digits and across glabrous and dorsal receptive ﬁelds were counted, and the circum- ference of the receptive ﬁelds were calculated. The Student t test was used to determine the signiﬁcance of differences between the trained animals and the controls. The decline in speed and accuracy of perfor- mance over time was analyzed using the Page Test for Trends. The presence of inﬂam- matory cells and ﬁbroblasts were described post anatomical dissection and immu- nochemical analysis but were not tested for signiﬁcance. The normal topography of the hand is characterized with one receptive ﬁeld per electrode penetration, small receptive ﬁelds (8. With training, the area of the representation increases in size while the receptive ﬁelds decrease in size and increase in speciﬁcity and density (Figure 11. Two owl monkeys performed the attended, repetitive, passive hand opening and closing task (1. Between 5–8 weeks of training, both monkeys sponta- © 2005 by Taylor & Francis Group. Normal Cortical Plasticity: Hand Effect of Sensory Training A1 Before differential A3 B1 Normal stimulation A2 After differential stimulation B2 Normal 1 mm Normal Representation A 1 cm B C 1 cm 1 mm FIGURE 11. In the normal Owl monkey, the hand is topo- graphically represented on the somatosensory cortex (A) with digit segments organized from distal to proximal and digit order represented medial to lateral for D1-D5 (B) with small receptive ﬁelds that have minimal overlap between digits (C). With attended, progressive tactile stimulation, the topographical representation increases in size (note change A1 to A2) with a shrinkage in the size of the receptive ﬁelds (A3) and an increase in density of the receptive ﬁelds on the trained digits (note change B1 to B2).
Attraction of a significant number of specific afferent axons from the host While these requirements are rigorous buy malegra dxt 130 mg overnight delivery impotence injections, the quantitative measurement of these characteristics may lend credence to exertion by the graft of a specific generic malegra dxt 130mg with mastercard loss of erectile dysfunction causes, defined role in the host, as opposed to a nonspecific or non-neuronal effect. For example, grafts into the striatum of dopamine-enriched tissue are intentionally ectopic, and do not appear to develop long-distance axonal growth despite the fact that embryonic dopaminergic axons are inherently capable of such growth. Thus, only some parallels may be noted between the two different regions, but issues of graft tissue survival and integration remain paramount for both. Second, the clinical situations to which hippocampal or cortical neural grafting may be applicable will be analyzed, in addition to potential graft sources and their © 2005 by CRC Press LLC limitations. Finally, the bridge between preclinical research and clinical usefulness and applicability will be discussed. Our hypothesis of cellular integration applies primarily to the goal of making a graft an integral part of synaptic circuitry within the brain. Cell survival, directly comparing the number of cells transplanted and those recovered in vivo at different postgrafting time points 2. Graft cell afferent connectivity with appropriate host axons Graft integration may be differentially analyzed for various cell types, including embryonic neurons and immature stem cells. Because the cells are postmitotic and committed after embryonic harvesting, the neurons retain the BrdU label permanently. For analysis purposes, the placement of micrografts (10,000 to 30,000 cells) is much more definitive than the use of larger but more therapeutic macrografts of >1 × 106 cells. The smaller number of cells within micrografts can be explicitly counted and tracked using © 2005 by CRC Press LLC Human Cell Sources Human Stem Cells Embryonic Allograft or Xenograft Cortex Neural Cell Cultured Lines Sterile Therapeutic Graft Effects Dissociation on Host Brain Host mossy fiber axons can innervate grafted neurons and form functional Transplantation synapses onto grafted cells. Graft axonal processes innervate host pyramidal cells and interneurons, leading to circuitry reconstruction and restoration of interneuron cell counts. Mossy fiber terminals can densely innervate graft and prevent aberrant mossy fiber sprouting Can grafts treat epilepsy in humans? First, cell sources include human or porcine embryonic cortex or hippocampus, various types of pro- genitor or stem cells, or cultured cell lines, most derived from neuronal tumors. After disso- ciation and transplantation, the fate of the transplanted cells can be assessed for synaptic integration within the host. In rodent models, therapeutic graft effects on the host include the formation of mossy fiber synapses onto grafted neurons, amelioration of postlesion interneu- ron loss, and prevention of aberrant mossy fiber sprouting. Whether grafts can ameliorate epilepsy remains to be analyzed in rodents and humans although the framework has been established. Unique labels form the critical basis for evaluation of graft integration within the host to unambiguously identify the grafted cells within the host. In normal or intact hosts and grafts performed late after lesions, only 18 to 30% of grafted hippocampal cells survived. However, at early time points following lesions, the degree of survival was much greater (60 to 80%), particularly in young adults. First, during development time when embryonic neurons are removed (at embryonic day 19), these cells have completed programmed migration along the radial glia into their respective layers. Therefore, after grafting, these cells show minimal specific migration to appropriate cell body layers, and most remain clumped within 0. This lack of capability for migration within the host requires more accurate placement of multiple grafts directly within the degenerated cell layer because only appropriately placed grafts of certain cell types show capacity for specific connectivity. We have termed this capability the axon guidance pathway, which for commissural connec- tions appears to be specific. There- fore grafts placed in most regions of the hippocampus can robustly send efferent © 2005 by CRC Press LLC fibers into the septum. These embryonic graft neuron axons demonstrate compe- tence to follow innate host axon guidance pathways and are not susceptible to inhibitory molecules such as myelin-associated glycoproteins along the host path- ways, unlike adult host axons. The locations of these axon guidance pathways in the host may be highly specific, requiring accurate placement of the grafts to achieve access. Afferents into the graft develop readily, particularly mossy fiber ingrowths, if the grafted cells are their natural target cells (i. Therefore, hippocampal stem cells with pyramidal neuronal phenotypes have also been analyzed as alternatives to embryonic cells. However, these cells show limited differentiation into neurons in vitro and in vivo, and may require conditioning with appropriate neurotrophic factors to enhance neuronal differentiation both prior to and after transplantation. Further, the milieu of the injured brain could adversely affect differentiation of stem cells into neurons as a result of inadequate positional cues.
In humans and most other primates buy malegra dxt 130mg without prescription erectile dysfunction treatment phoenix, many of the corticospinal projec- tions make direct contact to motor neurons cheap malegra dxt 130 mg otc impotence diabetes. Furthermore, these areas are reciprocally connected through cortico-cortical projections within and between the hemispheres. Although each area has been shown to be more specialized for certain functions, in general, overlapping functions are well distributed throughout the various hand representations. The anatomical and functional organization between motor areas provides the substrate for a mutually supportive relation among the multiple motor representations in the frontal cortex. This is consistent with imaging results that indicate that the nonprimary motor areas are recruited at a time when M1 is maxi- mally engaged during a complicated task or is compromised due to an infarction. Porter and Lemon (1995) consider the corticospinal tract, originating from the various motor cortices, as being involved in learning new motor skills, and not being restricted to just the execution of movements. It is this commonality of function between motor areas that supports the interpretation from imaging studies that when a major area contributing to the corticospinal tract is damaged, cortex associated with the remaining ﬁbers are able to compensate for the lost output and promote re- learning of motor function (i. As previously mentioned in this chapter, M1 was once considered to be relatively static, as Sherrington explained the ﬁnal common pathway of cortical output, indi- cating that its role is limited to the execution of movements directed or learned by association motor areas. This view has changed in light of new anatomical and physiological evidence of shared involvement of premotor areas. NEUROMODULATION OF CORTICAL ACTIVITY The previous sections of this chapter presented evidence that cortical plasticity is initiated by use-dependent activation, resulting in functional and structural changes in connectivity; and, that these changes are associated with acquiring new motor skills or behavioral strategies, not merely motor activity. Also, as stated previously, the process for initiating cortical plasticity in areas functionally linked to the damaged cortical tissue is facilitated by a process described as excitatory diaschi- sis. During this state of hyper-excitability, the cortex may become more receptive to novel, temporally associated inputs than under normal learning conditions in the intact brain. The monoamine neurotransmitters (norepinephrine, dopamine and serotonin) and acetylcholine, can have the effect of increasing the probability of synaptic excitation. They allow for sensory-motor adaptations to bio- logically signiﬁcant events and are thus related to motivational and attentional processes in learning. The monoamine neurotransmitters can directly inﬂuence cortical activity through ascending ﬁber tracts originating from the brainstem (nore- pinephrine from the locus coeruleus; serotonin from the raphe nucleus; and dopam- ine from the ventral tegmentum) or from the forebrain. Acetylcholine innervates the cortex from the nucleus basalis of Meynert in the basal forebrain. These cholinergic neurons in the forebrain can also be modiﬁed by norepinephrine and serotonin through the medial forebrain bundle. The drug that has received the most attention has been dexamphetamine (d- AMPH); this drug increases monoaminergic activity by enhancing release of neu- rotransmitters and blocking their re-uptake, thus prolonging post-synaptic excitation. It is believed that enhanced activity of the monoamine neuromodulators (norepi- nephrine, dopamine and serotonin) will create a favorable environment in the cortex for adaptive, synaptic plasticity as seen early after an infarct when the cortex is in a state of hyper-excitability. Many of the clinical studies have shown promising results,166,167 but the mechanisms by which d-AMPH mediate functional recovery are still being examined. Earlier animal studies have demonstrated that optimal recovery of motor function after cortical damage is enhanced by d-AMPH when it is paired with a related motor activity, and that improvement of motor function is mediated primarily through activation of the noradrenergic system. In addition to use- dependent strengthening of pre-existing connections, neural activity also leads to the release of neurotrophic factors that not only strengthens connections, but is also neuroprotective and induces neural sprouting and synaptogenesis. Amphetamine, as well as other drugs that stimulate noradrenergic activity, have been shown to increase neurotrophic factors in the brain. The neurotrophins bind to a low afﬁnity p75 receptor (a 75 kD glycoprotein receptor); each neurotrophin also binds to a high afﬁnity tyrosine kinase receptor (trk). There are three tyrosine kinase receptors that bind neurotrophins: trkA binds NGF; trkB binds BDNF and NT-4/5; and trkC binds NT-3. It has been found mostly in the cerebellum, hippocampus and © 2005 by Taylor & Francis Group. There was no loss of forelimb representation following a control injection of scrambled oligo- dexynucleotide that does not block BDNF synthesis. These results suggested that normal BDNF activity is necessary to maintain the functional integrity of cortical representations. There is also evidence to suggest that BDNF may be partially responsible for D-AMPH mediated recovery from stroke. As stated earlier in this section, previous animal studies have indicated that D-AMPH facilitates behavioral recovery mainly through noradrenergic activation. Recent studies have shown a relationship between noradrenergic activity and BDNF/trkB activity.
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