By Z. Volkar. Ramapo College of New Jersey.
Either route would be expected to depend upon excitatory glutamatergic synapses and NMDA receptor activation cheap 100mg voveran sr free shipping spasms multiple sclerosis,79 and indeed proven 100 mg voveran sr muscle relaxant reversals, blocking NMDA receptors at the time of adult whisker trimming prevents WPP. Hence, with adult cortex the WPP paradigm generates Hebbian potentiation and competitive inhibition in at least the ﬁrst four layers of the barrel cortex. Several studies have analyzed with different techniques, the activity-based syn- aptic plasticity that occurs readily without tissue damage, in adult cortex as readily as in immature brains. Using 2-deoxyglucose autoradiography, several studies have documented the expansion of the cortical activation pattern of a single whisker after several weeks of trimming all but one whisker. These changes are also reﬂected in the levels of cytochrome oxidase histochemical staining in the barrels appropriate to the trimmed (higher CO) and untrimmed (lower CO) whiskers. Using chronic intrinsic signal optical imaging Frostig and colleagues showed that adult rats left in their home cage after plucking all but one whisker exhibited a similar spatial expansion and increased magnitude of cortical activation, but as little as four minutes per week of free exploration led to a contraction of the cortical activation locus and a reduction in peak signal. MOLECULAR MECHANISMS AFFECTED BY SENSORY DEPRIVATION As a result of these clear demonstrations that early postnatal whisker removal modiﬁes the normal development and function of the barrel cortex, it is important to understand how the reduced postnatal sensory activity becomes translated into © 2005 by Taylor & Francis Group. There are changes in layer IV barrel cells whose principal whiskers have been trimmed for a longer or a shorter time if deprivation starts on the day of birth, but as reviewed above, a number of studies converge on the conclusion that the greatest damage is done to the intrinsic intra-cortical circuits that transfer information from layer IV to layers II/III. Effects of Sensory Deprivation on Excitatory Neurotransmission The generation of receptive ﬁelds in barrel cortex neurons has been intensively studied and is heavily dependent upon excitatory glutamatergic circuits. In summary, excitatory projection neurons in VPM thalamic barreloids are dominated by inputs from a single whisker, but respond weakly to a number of other whiskers, especially in the awake animal. The excitatory barrel neurons project almost exclusively to layers II/III above the barrel and into the septa surrounding the barrel. The septal and supragranular (layer II/III) neurons are modulated by direct projections from the POm thalamic nucleus and by inputs from the contralateral hemisphere. The septal and supragranular cells, in turn, generate extensive horizontal excitatory circuits that link the single whisker dominated barrel columns together and integrate the inputs from the entire ensemble of whiskers on the contralateral face with those from the ipsilateral whiskers. P2 is within a few days of when thalamocortical synapses stop exhibiting robust LTP in layer IV of the barrel cortex,23 and before cortical cells can be induced to show robust responses to sensory stimulation (usually PND6-7,10). However, partial sensory deprivation early in life prevents whisker pairing plasticity at maturity in layers II/III, but not in layer IV123 and also prevents other forms of potentiation in adolescent (35 day) rats. In the same preparations the responses to test/conditioning whisker stimuli from 30 to 200 msec did not show changes in intracortical inhibition. Effects of Sensory Deprivation on Inhibitory Neurotransmission Activity-based cortical excitation leading to plasticity can only take place when inhibitory processes do not block the ability of excitation to enhance synaptic strength. SD plasticity in the barrel cortex is blocked when all activity is suppressed by the release of a GABA receptor agonist, muscimol, onto the surface of the cortex. One result of sensory manipulations is to produce a decrease in GABAa receptor beta2 and beta3 receptor subunit immunoreactivity after whisker follicle damage, but not after neonatal or adult whisker trimming. Akhtar and Land147 made an important (but as yet unexplained) observation that cells in the neonatal sensory deprived barrels failed, at maturity, to show activity-induced up- and down- regulation of glutamic acid decarboxylase (GAD), the synthetic enzyme for GABA. In these studies, SD was also induced by C-row or all but C-row trimming for 5–10 weeks starting at PNDo (neonatal) or PND60 (adult), but without a recovery period after either starting age. The effect of early, partial sensory deprivation in these cases was that GABA mechanisms appear to develop to a certain level of efﬁcacy after deprivation, but at the same time are incapable of responding appropriately to changes in activity levels when the system was challenged later in life. A ﬁnal set of experiments conﬁrmed this deﬁcit when neonatal deprived animals had their whiskers trimmed for 6 weeks, allowed to regrow and stabilize for two months, then row C was retrimmed for six weeks as adults before assaying the GAD levels. The row C whisker barrels showed GAD staining as expected for normal animals (no reduction), an effect that is most easily interpreted as abnormal GAD regulation because of the early deprivation producing a permanent deﬁciency in ability to adjust GAD levels based on activity. Micheva and Beaulieu118,119 found bilateral changes in layer IV GABAergic circuitry after neonatal whisker plucking, combined with an increase number of GABA-positive axon terminals on dendritic spines (GABA-positive spine synapses are rare except in layer IV barrels, and even there are only a small percentage of the total). Welker and his colleagues recently reported that 24 h of whisker stimu- © 2005 by Taylor & Francis Group. Subtle, but potentially important effects of trimming whiskers have been described affecting the develop- ment of trigeminal nuclei after whisker trimming for 60 d with no recovery period. Cytochrome oxidase staining and levels of glutamatic acid decar- boxylase reﬂect the history of low levels of activity in the VPM nucleus of the thalamus after long term sensory deprivation,149 but when thalamic plasticity was tested after trimming whiskers in a checkerboard pattern, predictable changes were again produced in the cortex, but there were no changes detected in the receptive ﬁeld or other response properties assayed in the thalamus. SD interferes with circuit development such that the deprived cortex never undergoes the last stage of development leading to normal behavior using the deprived cortex.
Prenatal testing is available to families in which a retardation are seen in all individuals affected with genetic change has been identified cheap 100mg voveran sr spasms gums. People with the same Resources genetic change can have a wide range of medical prob- PERIODICALS lems with varying degrees of severity purchase voveran sr 100 mg line back spasms 5 weeks pregnant. In WEBSITES either case, people who have the genetic change have a “Entry 304050: Corpus callosum, agenesis of, with chorioreti- 50% chance to pass the altered gene on to each of their nal abnormality. Since the gene is dominant, passing on one GALE ENCYCLOPEDIA OF GENETIC DISORDERS 41 ulation of development. The protein is active in many cell KEY TERMS types and directs cells to their proper place in the embryo. Seventy to 75% of Alagille syndrome probands Amniocentesis—A procedure performed at 16-18 have had an identifiable change within this gene. There are a vari- the fluid can be used for a variety of tests to obtain ety of other molecular changes in the gene that have been information about genetic disorders and other detected by sequencing the gene. It is possible that there are other genes that Chorionic villus sampling (CVS)—A procedure cause the disease in these families. The condition affects males for chromosome abnormalities or other genetic and females equally. Hemivertebra—A disorder in which one side or Signs and symptoms half of a vertebra fails to form. Liver manifestations Proband—The person in the family who is affected by a genetic disorder and who brings the One of the most common and most serious symp- family to the attention of a health care provider. Liver disease occurs in 90-100% of patients and often leads to growth Second-degree relative—Aunts, uncles, nieces, delay or failure as a result of malnutrition. Because there nephews, grandparents, grandchildren and half is a reduction in the number of bile ducts in the liver, siblings are second-degree relatives. These indi- there are elevated bile acids in the blood and an arrest of viduals have one fourth of their genes in common. This results in jaundice, Spina bifida occulta—The failure of vertebrae to pruritus (severe skin itching), and xanthomas (raised nod- close into the neural tube without nerves protrud- ules on the skin, especially at skin creases or areas of fric- ing. Some patients have mild or no liver problems, while others have progressive liver failure. This means Heart defects and murmurs have been noted in 85- that different people with the condition may experience 95% of patients with Alagille syndrome. One mon type of defect is pulmonary artery stenosis, although explanation for this is that different changes in the gene other types of defects also occur. However, even in families that all have the same genetic change, complex and severe heart defects occur and are one of the different features and degrees of severity can occur. In more common causes of mortality in patients with addition, the condition is not fully penetrant. Eye manifestations Changes in a gene called the Jagged1 (Jag1) gene on An important diagnostic feature of Alagille syn- the short arm of chromosome 20 have been shown to be drome is a particular eye finding called posterior embry- the underlying defect in many patients. This is an anterior chamber defect of the eye encodes a cell surface protein that plays a role in the reg- caused by a prominent, centrally positioned Schwalbe 42 GALE ENCYCLOPEDIA OF GENETIC DISORDERS ring. This feature can be seen through a split lamp exam- blood tests for renal function, an ophthalmologic exami- ination and does not affect vision. Since 56-90% of nation, and an examination of facial features are impor- patients have this or other changes in the eye, including tant diagnostic tools. A careful family history is also retinal pigmentary changes, an eye examination can aid important in diagnosis. A particular finding called a butterfly vertebra is Once a diagnosis has been made in an individual, the associated with Alagille syndrome. The term butterfly parents should undergo an evaluation for subtle features vertebra refers to the appearance of the space around the of the condition. If a parent is diagnosed, then evaluation vertebrae due to clefting or disruption of formation of a for appropriate extended family members would be vertebra. A correct diagnosis is important since there are associated with this radiological finding. The frequency other syndromes that exhibit similar liver disease, heart of butterfly vertebrae in this syndrome is uncertain, defects, and eye findings.
These sacculations may be seen in a plain radi- ograph of the abdomen when the large bowel is distended and appear as incomplete septa projecting into the gas shadow discount 100mg voveran sr otc back spasms 40 weeks pregnant. The radiograph of dis- tended small intestine buy voveran sr 100 mg line spasms after hemorrhoidectomy, in contrast, characteristically has complete trans- verse lines across the bowel shadow due to the transverse mucosal folds of the valvulae conniventes. Peritoneal attachments The transverse colon and sigmoid are completely peritonealized (the former being readily identiﬁed by its attachment to the greater omentum). The ascending and descending colon have no mesocolon but adhere directly to the posterior abdominal wall (although exceptionally the ascending colon has a mesocolon). The caecum may or may not be com- pletely peritonealized, and the appendix, although usually free within its own mesentery, occasionally lies extraperitoneally behind caecum and ascending colon or adheres to the posterior wall of these structures. The rectum is extraperitoneal on its posterior aspect in its upper third, posteriorly and laterally in its middle third and completely in its lower third as it sinks below the pelvic peritoneum. The appendix The appendix arises from the posteromedial aspect of the caecum about 1in (2. In the fetus it is a direct outpouching of the caecum, but differential overgrowth of the lateral caecal wall results in its medial displacement. The position of the appendix is extremely variable—more so than that of any other organ (Fig. The appendix is usually quite free in this position although occasionally it lies beneath the peritoneal covering of the caecum. If the appendix is very long, it may actually extend behind the ascending 80 The abdomen and pelvis Fig. In about 20% of cases, the appendix lies just below the caecum or else hangs down into the pelvis. Less commonly, it passes in front of or behind the terminal ileum, or lies in front of the caecum or in the right paracolic gutter. Along appendix has been known to ulcerate into the duodenum or per- forate into the left paracolic gutter. The mesentery of the appendix, containing the appendicular branch of the ileocolic artery, descends behind the ileum as a triangular fold (Fig. Another peritoneal sheet, the ileocaecal fold, passes to the appendix or to the base of the caecum from the front of the ileum. The ileocaecal fold is termed the bloodless fold of Treves although, in fact, it often contains a vessel and, if cut, proves far from bloodless. Clinical features 1The lumen of the appendix is relatively wide in the infant and is fre- The gastrointestinal tract 81 quently completely obliterated in the elderly. Since obstruction of the lumen is the usual precipitating cause of acute appendicitis it is not unnat- ural, therefore, that appendicitis should be uncommon at the two extremes of life. It runs ﬁrst in the edge of the appendicular mesentery and then, distally, along the wall of the appendix. Acute infection of the appendix may result in thrombosis of this artery with rapid development of gangrene and subsequent perforation. This is in contrast to acute cholecystitis, where the rich collateral vascular supply from the liver bed ensures the rarity of gangrene of the gall-bladder even if the cystic artery becomes thrombosed. The caecum is delivered into the wound and, if the appendix is not immediately visible, it is located by tracing the taeniae coli along the caecum— they fuse at the base of the appendix. When the caecum is extraperitoneal it may be difﬁcult to bring the appendix up into the incision; this is facilitated by ﬁrst mobiliz- ing the caecum by incising the almost avascular peritoneum along its lateral and inferior borders. The appendix mesentery, containing the appendicular vessels, is ﬁrmly tied and divided, the appendix base tied, the appendix removed and its stump invaginated into the caecum. It commences anterior to the third segment of the sacrum and ends at the level of the apex of the prostate or at the lower quarter of the vagina, where it leads into the anal canal. The rectum is straight in lower mammals (hence its name) but is curved in man to ﬁt into the sacral hollow. Moreover, it presents a series of three lateral inﬂexions, capped by the valves of Houston, projecting left, right and left from above downwards. They must be visualized in carrying out a rectal examination, they provide the key to the local spread of rectal growths and they are important in operative removal of the rectum.