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Biomedical subjects

N C Christopher

Publications and source records attributed to N C Christopher.

At least 19 recordsLinked to original sources
PubMed2001

Persistent behavioral consequences of neonatal chlorpyrifos exposure in rats.

Chlorpyrifos (CPF) is a widely used insecticides which has been shown to alter brain cell development. The current project was conducted to determine whether there are persistent behavioral effects of early [1 mg/kg/day postnatal days (PNDs) 1-4] or late (5 mg/kg/day PNDs 11-14) postnatal CPF exposure in rats. We tested spontaneous alternation in a T-maze, locomotor activity in the Figure-8 apparatus and learning in the 16-arm radial maze, throughout adolescence and into adulthood. Exposure during either neonatal period elicited significant long-term effects on cognitive behavior. In the radial-arm maze, as has been seen previously, control male performed more accurately than control females. Early postnatal CPF exposure reversed this effect. With exposure on PNDs 1-4, females in the CPF group showed a reduction in working and reference memory errors in the radial maze, reducing their error rate to that seen in control males; in contrast, CPF-exposed males exhibited an increase in errors during the initial stages of training. When animals were exposed on PNDs 11-14 and then tested in adolescence and adulthood, males showed a significant slowing of response latency in the T-maze and the rate of habituation in the Figure-8 apparatus was slowed in both sexes. When females were challenged acutely with the muscarinic antagonist, scopolamine, they did not show reference memory impairment, whereas controls did; these results suggest that adaptations occur after CPF exposure that lead to loss of muscarinic cholinergic control of reference memory. No such changes were seen with a nicotinic cholinergic antagonist (mecamylamine). These results indicate that early neonatal exposure to CPF induces long-term changes in cognitive performance that, in keeping with the neurochemical changes seen previously, are distinctly gender-selective. Additional defects may be revealed by similar strategies that subject the animals to acute challenges, thus uncovering the adaptive mechanisms that maintain basal performance.

Animals↗
PubMed2001

Curling iron-related injuries presenting to U.S. emergency departments.

OBJECTIVE: To describe curling iron-related injuries reported to the National Electronic Injury Surveillance System (NEISS) between January 1, 1992, and December 31, 1996. METHODS: The authors retrospectively reviewed data from NEISS, a weighted probability sample of emergency departments (EDs) developed to monitor consumer product-related injuries. The information reported includes patient demographics, injury diagnosis, body part injured, incident locale, patient disposition, and a brief narrative description. The authors reviewed the narrative in the hair care products category and abstracted records indicating the injury was caused by contact with a curling iron. Also analyzed were the design features of commonly available curling irons purchased from national discount department stores. RESULTS: There were an estimated 105,081 hair care product-related injuries in the five-year period, of which 82,151 (78%) involved a curling iron. Seventy percent of injuries were to females. The patient's median age was 8 years (range 1 month to 96 years). The most commonly occurring injury was thermal burns (97%; 79,912/82,151). Ninety-eight percent of the injuries occurred in the home and 99% of the patients were discharged home from the ED. In patients <4 years old, 56% of burns occurred by grabbing or touching, while in those > or =10 years the burns occurred by contact while in use. In the older group 69% of burns were of the cornea. Most curling irons use small amounts of power, yet there are no standards for temperature settings or control. The cylinder containing the heating element is mostly exposed, and many irons do not have a power switch. CONCLUSIONS: The most common injury resulting from curling irons is thermal burns. The mechanisms and patterns of injury in developmentally distinct age groups suggest that many of these injuries could be prevented by public education and the re-engineering of curling irons.

Adolescent↗
PubMed1999

Ventral hippocampal ibotenic acid lesions block chronic nicotine-induced spatial working memory improvement in rats.

Chronic nicotine infusions have been found to significantly improve working memory performance in the radial-arm maze. This effect is blocked by co-infusions of the nicotinic antagonist mecamylamine. Acute nicotine injections also improve working memory performance in the radial-arm maze. This effect is also blocked by mecamylamine co-administration. Recent local infusions studies have demonstrated the importance of the ventral hippocampus for nicotinic involvement in memory. Local infusions of mecamylamine, DHbetaE or MLA impair working memory performance on the radial-arm maze. The current study was conducted to determine the importance of the ventral hippocampus for the chronic effects of nicotine. Rats were trained on the working memory task in an eight-arm radial maze. After acquisition they underwent either infusions of ibotenic acid lesions or vehicle infusions and received subcutaneous implants of osmotic minipumps that delivered either nicotine at a dose of 5 mg kg-1 day-1 or vehicle in a 2x2 design. The rats then were given 2 days of recovery and were tested on the radial-arm maze three times per week for the next 4 weeks. As seen in previous studies, in the sham lesioned group nicotine infusions caused a significant improvement in choice accuracy. In contrast no nicotine-induced improvement was seen in the rats after ibotenic acid lesions of the ventral hippocampus. The effect of nicotine was blocked even though this lesion did not cause a deficit in performance. Previous work showed that chronic nicotine infusion still caused a significant improvement in working memory performance in the radial-arm maze after knife-cut lesions of the fimbria-fornix carrying the septo-hippocampal cholinergic innervation. Thus it appears that it is the postsynaptic nicotinic receptors in the ventral hippocampus which are critically important for the expression of the chronic nicotine induced working memory improvement.

Animals↗
PubMed1998

Nicotine-dizocilpine interactions and working and reference memory performance of rats in the radial-arm maze.

Both nicotinic cholinergic and NMDA glutaminergic systems are important for memory function. Nicotine has been found repeatedly to significantly improve working memory performance in the radial-arm maze. The NMDA antagonist dizocilpine has been found to impair working memory performance. There is neuropharmacological evidence that these two systems are functionally related. Nicotine is potent at releasing many transmitters including glutamate. The current study was conducted to examine the interaction of nicotinic and NMDA systems with regard to working and reference memory. Rats were trained on a working/reference procedure on a 16-arm radial maze. After acquisition, they were administered nicotine (0, 0.2, and 0.4 mg/kg) and dizocilpine (0, 100, and 200 microg/kg) alone or in combination in a repeated measures, counterbalanced design. As seen previously, nicotine at a dose of 0.2 mg/kg caused a significant improvement in working but not reference memory performance in the radial-arm maze. The 200 microg/kg dose of dizocilpine made the rats nonresponsive on the maze so that choice accuracy could not be assessed. The 100 microg/kg dose of dizocilpine caused significant impairments in both working and reference memory. The 0.4 mg/kg dose of nicotine significantly attenuated the dizocilpine-induced deficit in both working and reference memory. NMDA blockade impairs working and reference memory and blocks the expression of the working memory improvement caused by 0.2 mg/kg of nicotine. However, a higher dose of 0.4 mg/kg of nicotine is effective at attenuating the dizocilpine-induced deficit, even though this dose alone is not effective in improving performance. A second study examined the effects of a lower dose range of dizocilpine. Comensurately smaller memory impairments were seen with lower doses of dizocilpine down to 12.5 microg/kg, which did not produce any significant effects on memory performance or response latency. Nicotine had a more modest effect in attenuating the smaller deficits caused by these lower doses of dizocilpine. These studies provide evidence for important interactions between nicotinic and NMDA systems with regard to memory function.

Animals↗
PubMed1998

Paramedic judgment of the need for trauma team activation for pediatric patients.

OBJECTIVE: To determine the value of paramedic judgment in determining the need for trauma team activation (TA) for pediatric blunt trauma patients. METHODS: A prospective, observational study was conducted at the ED of Children's Hospital Medical Center of Akron between July 12, 1996, and February 28, 1997, in cooperation with Akron Fire Department emergency medical technician-paramedics (EMT-Ps). The ED provides on-line and off-line medical control for pediatric transports. Patients with minor or no identifiable injuries are released at the scene with the instructions to see a physician. The remainder are transported to the ED. The decision for TTA is based on ED trauma protocols as well as emergency physician judgment of injury severity in combination with the judgment of the treating paramedic. During the study, EMT-Ps were asked (before physician input) whether, based solely on their judgment, a patient needed TTA. Patients 0-14 years old who were involved in motor vehicle crashes, bike crashes, or falls from a height of >10 feet were included in the study. TTA was defined as necessary if the patient was admitted to the intensive care unit (ICU) or operating room (OR) for nonorthopedic surgical procedures. Out-of-hospital, ED, and hospital records were reviewed. Coroners' records as well as medical records of all trauma admissions during the study period were reviewed to ensure that the patients released at the scene were not mistriaged. RESULTS: One hundred ninety-two patients met study criteria. Eighty-five patients (44%) were transported to the ED, of whom 12 had TTA. EMT-Ps requested TTA for 10 of these patients, and 2 patients had TTA per ED trauma protocol. Two of the patients who were judged by EMT-Ps to need TTA were admitted to the ICU/OR, and neither of the patients identified by ED trauma protocol to require TTA were admitted to the ICU/OR. Two initially stable patients who did not have TTA deteriorated after arrival to the ED. Both were admitted to the ICU. The sensitivity and specificity of paramedic judgment of the need for TTA for pediatric blunt trauma patients were 50% (95% CI 9.2-90.8) and 87.7% (95% CI 78.0-93.6), respectively. The positive and negative predictive values were 16.7% (95% CI 2.9-49.1) and 97.3% (95% CI 89.6-99.5). None of the patients released at the scene was mistriaged based on the review of the coroners' and trauma admission records. CONCLUSION: Results of this investigation indicate that a small percentage of pediatric blunt trauma patients require TTA. EMT-P judgment alone of the need for TTA for pediatric blunt trauma patients is not sufficiently sensitive to be of clinical use. The low sensitivity is explained by the deterioration in the clinical condition of 2 initially stable patients. The paramedic disposition decisions from the scene were always accurate. Nontransport by emergency medical services (EMS) may be acceptable in some uninjured pediatric trauma patients. Injured pediatric trauma patients who appear to be stable may deteriorate shortly after injury. However, if a pediatric patient appears injured, transport from the scene and examination by a trauma specialist are needed. Finally, the role of paramedic judgment must be further defined by larger studies with urban, rural, and suburban EMS systems before it can be used as a sole predictor of TTA.

Adolescent↗
PubMed1997

Chronic nicotinic agonist and antagonist effects on T-maze alternation.

A variety of studies have found that nicotine improves working memory function. However, other studies have either not found improvements or have found nicotine-induced deficits. The demands of the particular memory test may be critical for the expression of the nicotine effects. In several studies, we have found that chronic nicotine administration improves working memory performance in the radial arm maze. Chronic mecamylamine coadministration reversed this effect. The current study was conducted to determine the effects of chronic nicotine and mecamylamine on choice accuracy in a T-maze spatial alternation task. The same dose and duration of nicotine administration that we have previously found to significantly improve choice accuracy in the radial-arm maze was not effective in altering T-maze spatial alternation. The critical difference in task demands may be the presence with T-maze alternation of proactive interference. During a session, a choice alternative repeatedly changes valence from correct to incorrect and back again. In contrast, with the radial-arm maze as run in our studies, in a session the valence of an arm only changes once from correct to incorrect. Previous work with nicotine effects on spatial alternation in an operant task found evidence that nicotine increased the negative effect of proactive interference on performance. In the current study, chronic mecamylamine caused a significant deficit in T-maze spatial alternation. This same dose did not produce a deficit in the radial-arm maze and, in fact, caused an improvement during the first week of administration.

Animals↗
PubMed1997

Is binding to nicotinic acetylcholine and dopamine receptors related to working memory in rats?

Nicotinic acetylcholine (ACh) and dopamine (DA) receptor activation has been found to be important for working memory. The regional distribution of these receptors in the brain has been well characterized. However, the relationship of the region-specific nicotinic ACh and DA binding density to memory performance has not been well assessed. In the current studies the relationship of receptor binding and memory function was examined. Receptor binding and memory performance were assessed in rats in three types of conditions: 1) chronic nicotine and mecamylamine vs. vehicle infusion; 2) lesions of the fimbria-fornix or medial basalocortical projection vs. sham lesions; and 3) 2-year-old aged rats vs. 3-month-old young adult rats. Nicotinic ACh receptors were labeled by [3H]N-methyl-carbamylcholine ([3H]MCC), D1 receptors by [3H]SCH 23390, and D2 receptors by [125I]iodosulpiride. Working memory was assessed using the radial-arm maze and T-maze delayed spatial alternation tasks. Chronic nicotine infusion substantially increased nicotinic receptor binding in a variety of brain areas and significantly improved working memory performance in the radial-arm maze. However, nicotinic receptor binding did not correlate well with memory performance. The nicotinic antagonist mecamylamine did not block nicotine-induced increased nicotinic binding, but it did block nicotine-induced memory improvement. Aged rats relative to young adults showed both a decrease in nicotinic binding and impaired memory performance. However, chronic effects of nicotine on nicotinic receptor binding and memory performance did not correlate in the aged rats. Nicotine also increased nicotinic receptor binding in the aged rats in brain areas except for the VTA, but did not improve memory performance. Lesions of the medial basalocortical projection or the fimbria-fornix did not cause significant changes in nicotinic binding in their target fields, but they did cause significant deficits in memory performance. Finally, there were no significant correlations of nicotinic binding in any brain region and memory performance. DA receptor binding was not altered by chronic nicotine or mecamylamine infusion, fimbria-fornix lesions, medial basalocortical lesions, or in aged rats. However, DA receptor binding did correlate with memory performance. There was a positive correlation of T-maze accuracy and D1 receptor binding in the frontal cortex and a negative correlation of T-maze accuracy and D1 receptor binding in the VTA and dentate gyrus. In contrast, a positive correlation was seen between radial-arm maze accuracy and D1 receptor binding in the VTA. Radial-arm maze accuracy was positively correlated with D2 receptor binding in the striatum and dentate gyrus. There are significant relationships between the extent of DA receptor binding and working memory, but relationship between nicotinic ACh receptor binding density and memory is weak.

Animals↗
PubMed1997

Pain management in the emergency department: patterns of analgesic utilization.

OBJECTIVE: To compare the use of analgesia in children to adults in 3 different emergency department (ED) settings. METHODS: Forty adult and 40 pediatric ED charts were randomly selected for review at each of 3 institutions: an academic medical center with separate pediatric and adult EDs (SEP ED), a community academic medical center with a combined adult and pediatric ED (COMB ED), and a community hospital with a combined ED (COMTY ED). All patients presenting to the EDs from July 1993 to June 1994 within 12 hours of an isolated long bone fracture were eligible for inclusion. Data were collected on demographics, training of providers, analgesic use and dosing in the ED and on discharge, and time from triage to analgesic use. RESULTS: The mean pediatric and adult ages were 8.7 and 38.3 years, respectively. Overall, 152/240 (63%) patients received some form of analgesia in the ED, with the COMTY ED (41/80; 51%) offering significantly less analgesia than the COMB ED (58/80; 73%), but not the SEP ED (53/80; 66%). Pediatric patients (64/120; 53%) received significantly less analgesia in the ED than adult patients (88/120; 73%). This difference was significant at the COMB ED (pediatric 23/40; 58% vs adult 35/40; 88%) and COMTY ED (pediatric 15/40; 38% vs adult 26/40; 65%), but not at the SEP ED (pediatric 26/40; 65% vs adult 27/40; 68%). 195/240 (81%) patients received discharge pain medication. There were no differences between pediatric (93/120; 78%) and adult (102/120; 85%) discharge analgesic prescribing practices. Although there was no difference in appropriateness of analgesic doses in the ED, pediatric patients (20/74; 27%) were more likely than adult patients (3/88; 3%) to receive inadequate doses of analgesics on discharge from the ED. CONCLUSIONS: ED analgesia continues to be used less frequently in the pediatric compared with the adult population. Inadequate dosing of discharge analgesic medication in children is a significant problem. Patterns of analgesic utilization may differ in different types of ED settings.

Academic Medical Centers↗
PubMed1996

Prenatal nicotine effects on memory in rats: pharmacological and behavioral challenges.

Cigarette smoking during pregnancy has been shown in a variety of studies to be associated with cognitive deficits in the children. Nicotine administration to rats during gestation has been found to cause subtle cognitive effects in the offspring. Some individual differences in cognitive impairment may be related to prenatal nicotine effects on noradrenergic (NE) systems. In the current study, 10 Sprague-Dawley rat dams were infused with approximately 2 mg/kg/day of nicotine ditartrate via osmotic minipumps and 10 control dams were exposed to vehicle-containing minipumps from gestational day (GD) 4-20. Starting on postnatal day (PND) 50, the offspring were tested for T-maze rewarded spatial alternation with intertrial intervals of 0, 10, 20, or 40 s. There was a sex- and delay-dependent effect of prenatal nicotine exposure on T-maze alternation. Nicotine-exposed males showed a significant deficit at the 0 s delay. In radial-arm maze (RAM) acquisition training there were no significant nicotine effects. However, significant nicotine-related effects were seen with subsequent behavioral and pharmacological challenges in the RAM. Changing the RAM testing location to an identical maze in a different room elicited a significant choice accuracy deficit in the prenatal nicotine-exposed rats compared with controls. Acute nicotine challenge did not cause any differential effects in the prenatal nicotine and control groups. During the isoproterenol (beta-NE agonist) challenge phase there appeared a significant facilitation of choice accuracy and speeding of response in the prenatal nicotine exposure group which was not seen in the control group. The alpha-NE agonist phenylpropanolamine caused a significant deficit in control females but not in the females prenatally exposed to nicotine. No differential effects of the alpha-NE antagonist phenoxybenzamine were seen in the prenatal nicotine and control groups. Throughout RAM testing there was a significant sex effect with males having better choice accuracy than females. These results demonstrate that the persisting cognitive effects of prenatal exposure to 2 mg/kg/day cause subtle effects in cognitive performance which can be elicited with behavioral and pharmacological challenge. These results also support previous studies suggesting the involvement of NE systems in persisting effects of prenatal nicotine exposure.

Animals↗
PubMed1995

Triphenyl phosphite-induced impairment of spatial alternation learning.

Triphenyl phosphite (TPP) is a weak acetylcholinesterase inhibitor and a type II organophosphorus compound-induced delayed neurotoxic agent. The current study examined the cognitive effects of a single 250 mg/kg ip dose of TPP administered to either 3-mo- or 1-yr-old male Sprague-Dawley rats. Starting 4 d after TPP administration, the rats began training on a T-maze spatial alternation task for food reinforcement. Over five sessions of acquisition training, the TPP-treated rats showed significantly lower alternation scores than controls. There was no difference in spatial alternation performance in the first session, when both groups were performing at near-chance levels. In sessions 2-5, the controls improved dramatically to an average of 85.3 +/- 3.2% correct, while the TPP-treated rats did not significantly change, with 69.7 +/- 3.1 percent correct. During sessions 2 and 3 there was a significant TPP treatment-related deficit. This TPP-induced choice accuracy deficit was persistent in that it was seen well after the acute exposure. With continued training the TPP-exposed rats were able to learn the task as well as controls. There were no significant TPP effects on response latency. These data show that acute TPP administration has persistent effects of impairing T-maze learning that do not appear to result from effects on motor function.

Aging↗
PubMed1995

Childhood injuries and the importance of documentation in the emergency department.

The purpose of this study is 1) to evaluate the extent to which documentation of the medical record is completed for dependent children who present for evaluation of an acute injury, and 2) to examine the factors that favorably or adversely influence completion of the medical record. The emergency department (ED) ledgers of 669 children less than nine years of age were reviewed, including 172 (25.7%) who presented for evaluation of an acute injury. Each of the latter charts was examined for basic demographic data, as well as information about injury type and mechanism, ED provider, and involvement of social services personnel. The ledgers were further examined to determine completeness of chart documentation in several relevant areas, including the circumstances and characteristics of the acute injury, pertinent past medical history, and course of management and referral while in the ED. Each of 15 individual documentation variables was assigned a score of either zero (incompletely/not addressed or documented) or one (completely addressed or documented). The 15 individual scores were equally weighted and summed, resulting in a total documentation score ranging from zero (failure to address or document any of the 15 variables) to 15 (all variables completely addressed/documented). The mechanisms of injury included falls from height (48.3%), direct blunt impact other than falls (26.7%), penetrating injury (6.4%), burn (5.2%), and ingestion (8.1%). Seventeen patients (9.9%) were admitted for primarily medical, and one (0.6%) for primarily social, indications; one patient died as a result of his injuries.(ABSTRACT TRUNCATED AT 250 WORDS)

Child↗
PubMed1994

Working memory performance and cholinergic effects in the ventral tegmental area and substantia nigra.

The nicotinic antagonist mecamylamine has been found to impair working memory performance in the radial-arm maze (RAM) after s.c. or i.c.v. administration. Mecamylamine has important interactions with dopaminergic (DA) systems. Mecamylamine-induced memory deficits in the RAM are potentiated by the D2 antagonist raclopride and reversed by the D2 agonist quinpirole. The nicotinic agonist nicotine has been found to improve working memory performance in the RAM after s.c. or i.c.v. administration. Nicotine-induced memory improvement in the RAM is potentiated by the D2 agonist quinpirole. The midbrain DA nuclei, the substantia nigra (SN) and the ventral tegmental area (VTA) have relatively dense concentrations of nicotinic receptors which may be critical sites of action for mecamylamine and nicotine. In the current study, the effects of mecamylamine (1, 3.3 and 10 micrograms/side) infusions into the SN (n = 12) and VTA (n = 13) on working memory in the radial-arm maze were examined in adult female Sprague-Dawley rats. The 10-micrograms/side dose of mecamylamine significantly impaired radial-arm maze working memory performance when infused into either the SN or VTA. No significant effects of mecamylamine on response latency were seen. The nicotinic agonists cytisine (0.1, 0.33 and 1.0 microgram/side) and nicotine (0.3, 1.0 and 3.3 micrograms/side) were administered in a counterbalanced order. The high dose of cytisine (1 microgram/side) nearly caused a significant deficit in choice accuracy. Nicotine slightly depressed choice accuracy but not significantly in this study. The interaction of nicotine and mecamylamine was then studied. A dose of 1.0 microgram/side of nicotine caused a significant decrease in choice accuracy. Interestingly, this was significantly reversed by a 3.3-micrograms/side dose of mecamylamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1993

Sertraline attenuates hyperphagia in rats following nicotine withdrawal.

Chronic nicotine administration can decrease food consumption and body weight. Abrupt withdrawal from nicotine can cause the reverse effect, hyperphagia and rapid weight gain. In the current study, the efficacy of sertraline, a serotonin reuptake inhibitor, on nicotine withdrawal-induced hyperphagia and rapid weight gain was assessed in rats. Sertraline was found to be effective in reversing the increase in feeding that occurred after withdrawal from chronic nicotine administration. Sertraline caused a dose-related decrease in food consumption in control rats not given nicotine. Doses of 5 and 10 mg/kg/day caused significant decreases while 2.5 mg/kg/day caused a slight though nonsignificant decrease in food consumption. Rats in which nicotine was abruptly withdrawn after 3 weeks of administration showed a significant increase in food consumption relative to controls. This increase was eliminated by the high dose of sertraline (10 mg/kg/day), but not by the lower two doses (2.5 and 5 mg/kg/day). Water consumption was affected in a similar fashion. Body weight gain was also affected by sertraline. During the first week after nicotine withdrawal, rats rapidly gained weight, but sertraline attenuated this. The 10-mg/kg dose of sertraline significantly attenuated the nicotine withdrawal-induced weight gain. These results suggest that sertraline can counteract the hyperphagia and rapid weight gain associated with nicotine withdrawal, and might therefore be a useful adjunct to smoking cessation.

1-Naphthylamine↗
PubMed1993

Chronic nicotine reverses working memory deficits caused by lesions of the fimbria or medial basalocortical projection.

Nicotine has been found in a variety of studies to improve performance in memory tasks. This study was conducted to determine if chronic nicotine administration is useful in counteracting the working memory deficits seen after lesions of the fimbria or the medial basalocortical projection. Rats were trained to asymptotic performance on a working memory version of the radial-arm maze. Then, they were given knife cut lesions of the fimbria or the medial basalocortical projection or underwent sham surgeries. At the time of surgery, rats in each treatment group were implanted with either nicotine-containing or placebo glass and Silastic pellets. Rats with fimbria or basalocortical lesions showed a significant decline in working memory performance. Chronic nicotine significantly improved choice accuracy in both lesioned and unlesioned rats. Nicotine treatment restored performance of the lesioned rats to control levels. These data show that in addition to improving memory performance in normal rats, nicotine can counteract lesion-induced memory impairments. Nicotine also may be useful for treatment of disease-related memory impairments such as seen in Alzheimer's disease.

Animals↗
PubMed1992

Persistence of chronic nicotine-induced cognitive facilitation.

Nicotine has been found in a variety of species and behavioral paradigms to improve memory performance. The beneficial effect of nicotine has been seen after both acute and chronic administration. Interestingly, improved performance has been seen 24 h after acute injection and for at least 2 weeks after chronic administration. However, it is not clear from previous studies whether the persistence of the improved performance represents a true carryover of the drug effect or is due to the behavioral experience while under nicotine's effect. The current study was conducted to determine whether the facilitating effect of nicotine on learning and memory performance could be seen after withdrawal even if there was no behavioral training during the period of chronic nicotine administration. Rats were administered nicotine chronically for 3 weeks but were not tested during that time. Starting 1 week after withdrawal they were trained on a working memory paradigm in an eight-arm radial maze. The nicotine-treated rats started out at control-like levels of performance, but showed significantly faster learning as detected by three different measures of choice accuracy. By the final phase of testing the control subjects had caught up with the nicotine-treated rats. After the acquisition phase, acute challenges with the nicotinic and muscarinic antagonists, mecamylamine and scopolamine, did not elicit any differential effects in the nicotine-treated and control groups. The current study demonstrated that nicotine-induced cognitive facilitation persists for at least 4 weeks after withdrawal and does not depend upon behavioral test experience under the influence of the drug. The mechanism for this persisting effect is not currently understood.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Sialylation and human neutrophil killing of group C Neisseria meningitidis.

This study describes the association of lipooligosaccharide (LOS) and capsule sialylation with the survival of 25 serogroup C meningococcal strains in phagocytosis assays. Eleven strains isolated from children were of diverse protein serotypes or were nontypeable; 14 were serotype 2b:P1.2 and were isolated from children during or immediately after a focal epidemic in Texas. Degree of endogenous LOS sialylation and amount of sialic acid capsule were associated with each other and with susceptibility to killing by neutrophils for the non-2b:P1.2 strains. The 2b:P1.2 strains as a group had significantly greater survival in the presence of neutrophils than did the non-2b:P1.2 strains. The susceptibility of these strains to killing by neutrophils was not associated with endogenous LOS sialylation or amount of capsule. These data suggest that many virulent strains evade neutrophil killing, either by sialylation or another mechanism. Evasion of neutrophil killing might enhance a strain's epidemic potential.

Child, Preschool↗