Smoking cessation strategies in vascular surgery

Tobacco abuse is a highly prevalent modifiable risk factor in vascular surgery patient populations. Despite the known benefits of smoking cessation, quitting smoking is difficult for most patients. Physician advice to stop smoking can help, though more intensive or multifactorial interventions have greater impact. Smoking cessation initiatives based in vascular clinics are feasible, although currently there is significant variation in physician delivery of smoking cessation interventions. Vascular surgeons are optimally poised to be able to capitalize on the "teachable moment" of the vascular procedure to encourage smoking cessation. Concise and effective smoking cessation strategies include standardized physician "very brief advice" (a standardized advice delivery developed and validated by the National Health Service), referral to telephone counseling, and prescription of pharmacotherapy, all of which are best utilized together. This review will discuss different smoking cessation strategies, as well as their inclusion in multicenter trials designed to study delivery of smoking cessation interventions in vascular surgery patients.

Outcomes of carotid endarterectomy versus stenting in comparable medical risk patients

OBJECTIVE

In medically high-risk patients the choice between carotid artery stenting (CAS) and carotid endarterectomy (CEA) can be difficult. The purpose of this study was to compare risk-stratified outcomes of CAS and CEA.

METHODS

Patients who underwent isolated primary CEA (n = 11,336) or primary CAS (n = 544) at 29 centers in the Vascular Study Group of New England were analyzed (2003-2013); patients with previous ipsilateral CEA or CAS, or concomitant coronary artery bypass graft were excluded. A medical risk score based on predicted 5-year mortality was developed for each patient using a Cox proportional hazards model. Patients in the highest risk score quartile were termed high-risk (vs normal-risk for the other three quartiles). Medically high-risk patients had a 5-year survival of 65% and comprised 23% of CEA and 25% of CAS patients. Risk-stratified outcomes were compared within neurologically symptomatic and asymptomatic patients.

RESULTS

Among asymptomatic patients, rates of in-hospital stroke and/or death were not different between CAS and CEA in normal and high-risk cohorts, ranging from 0.7% in normal-risk CEA patients to 1.6% in high-risk CAS patients. In symptomatic patients, significantly worse outcomes were seen with CAS compared with CEA in normal-risk and high-risk patients. Normal-risk symptomatic patients had a stroke or death rate of 1.3% with CEA, but 5.2% with CAS (P < .01). In high-risk symptomatic patients, the stroke or death rate was 1.5% with CEA and 9.3% with CAS (P < .01). No significant differences were seen between asymptomatic CEA and CAS within risk strata across secondary outcome measures of stroke, death, or myocardial infarction, and ipsilateral stroke, major stroke, or death. However, symptomatic high-risk CAS patients had significantly greater rates of all secondary outcomes compared with CEA except death, and symptomatic normal-risk CAS patients had only significantly greater rates of death and stroke, death, or myocardial infarction.

CONCLUSIONS

In the Vascular Study Group of New England, asymptomatic normal- and high-risk patients do equally well after CEA or CAS. However, normal- and high-risk symptomatic patients have substantially worse outcomes with CAS compared with CEA. High medical risk alone might be an insufficient indication for CAS in symptomatic patients.

Cost-effectiveness of guidelines for insertion of inferior vena cava filters in high-risk trauma patients

BACKGROUND

Inferior vena cava filters (IVCFs) can prevent pulmonary embolism (PE); however, indications for use vary. The Eastern Association for the Surgery of Trauma (EAST) 2002 guidelines suggest prophylactic IVCF use in high-risk patients, but the American College of Chest Physicians (ACCP) 2008 guidelines do not. This analysis compares cost-effectiveness of prophylactic vs therapeutic retrievable IVCF placement in high-risk trauma patients.

METHODS

Markov modeling was used to determine incremental cost-effectiveness of these guidelines in dollars per quality-adjusted life-years (QALYs) during hospitalization and long-term follow-up. Our population was 46-year-old trauma patients at high risk for venous thromboembolism (VTE) by EAST criteria to whom either the EAST (prophylactic IVCF) or ACCP (no prophylactic IVCF) guidelines were applied. The analysis assumed the societal perspective over a lifetime. For base case and sensitivity analyses, probabilities and utilities were obtained from published literature and costs calculated from Centers for Medicare & Medicaid Services fee schedules, the Healthcare Cost & Utilization Project database, and Red Book wholesale drug prices for 2007. For data unavailable from the literature, similarities to other populations were used to make assumptions.

RESULTS

In base case analysis, prophylactic IVCFs were more costly ($37,700 vs $37,300) and less effective (by 0.139 QALYs) than therapeutic IVCFs. In sensitivity analysis, the EAST strategy of prophylactic filter placement would become the preferred strategy in individuals never having a filter, with either an annual probability of VTE of ≥ 9.6% (base case, 5.9%), or a very high annual probability of anticoagulation complications of ≥ 24.3% (base case, 2.5%). The EAST strategy would also be favored if the annual probability of venous insufficiency was <7.69% (base case, 13.9%) after filter removal or <1.90% with a retained filter (base case, 14.1%). In initial hospitalization only, EAST guidelines were more costly by $2988 and slightly more effective by .0008 QALY, resulting in an incremental cost-effectiveness ratio of $383,638/QALY.

CONCLUSIONS

Analysis suggests prophylactic IVC filters are not cost-effective in high-risk trauma patients. The magnitude of this result is primarily dependent on probabilities of long-term sequelae (venous thromboembolism, bleeding complications). Even in the initial hospitalization, however, prophylactic IVCF costs for the additional quality-adjusted life years gained did not justify use.

Identification of maze learning-associated genes in rat hippocampus by cDNA microarray

Long-term memory formation requires de novo RNA and protein synthesis. To assess gene-expression changes associated with learning and memory processes, we used cDNA microarray to analyze hippocampal gene expression in male Fischer-344 rats following training in a multiunit T-maze. Here, we report the identification of 28 clones (18 known genes and 10 ESTs) for which expression increased after the maze learning. Some of the known genes appear to be involved in Ca2+ signaling, Ras activation, kinase cascades, and extracellular matrix (ECM) function, which may regulate neural transmission, synaptic plasticity, and neurogenesis. The gene-expression profile presented here provides the groundwork for future, more focused research to elucidate the contribution of these genes in learning and memory processes.

Involvement of dopamine D(2) receptors in complex maze learning and acetylcholine release in ventral hippocampus of rats

In the current study we focus on the involvement of dopamine D(2) receptors in the ventral hippocampus in memory performance and acetylcholine release. Using the aversively motivated 14-unit T-maze (Stone maze) the injection of raclopride, a D(2) receptor antagonist, into the ventral hippocampus (8 microg/kg) was found to impair memory performance. Co-injection of quinpirole, a D(2) receptor agonist (8 microg/kg), overcame the impairment in performance. Microdialysis study revealed that quinpirole infusion (10-500 microM) into the ventral hippocampus stimulated acetylcholine release in a dose-dependent manner, and systemic injection of quinpirole (0.5 mg/kg, i.p.) also stimulated acetylcholine release in the ventral hippocampus. Infusion of eticlopride, another D(2) receptor antagonist, into the ventral hippocampus suppressed acetylcholine release in the hippocampus induced by systemic injection of quinpirole. Taken together, we suggest that D(2) receptors in the ventral hippocampus are involved in memory performance, possibly through the regulation of acetylcholine.

Hemodynamic changes during aging associated with cerebral blood flow and impaired cognitive function

This study investigates the age associated changes in hemorheological properties and cerebral blood flow. Partial correlations indicate that part of the age-dependent decrease in flow velocities can be attributed to a hemorheological decrement resulting in part from enhanced oxidative stress in the aged. A possible link with Alzheimer's pathology is suggested by the augmented hemorheological impairment resulting from in vitro incubation of red cells with amyloids. These results suggest that in aging, oxidative stress as well as amyloids may influence the fluid properties of blood, resulting in a potential decrement in blood flow and oxygen delivery to the brain. Animal intervention studies further demonstrate that altered hemorheological properties of blood can actually influence cognitive function. The relationships shown to exist between hemorheology, blood flow, amyloids, oxidative stress, and cognitive function suggest that these factors may be one of the mechanisms operating in the complex etiology of Alzheimer's disease.

Maze learning impairment is associated with stress hemopoiesis induced by chronic treatment of aged rats with human recombinant erythropoietin

Mean cell volume (MCV) of erythrocytes has been reported to increase with age in humans, and to be negatively correlated with memory performance in humans and rats. We evaluated hematological changes in 21-mo old male Fischer 344 rats undergoing a 3-mo twice weekly subcutaneous injection of human recombinant erythropoietin (EPO). A baseline hematocrit (HCT) was obtained initially and repeated at monthly intervals to determine the effectiveness of EPO treatment. At 24-mo of age and after 3 mo EPO treatment, the rats were tested for their ability to learn a 14-unit T maze. Following maze testing, blood was drawn for hematologic analyses, including HCT, MCV, maximum swollen cell volume (MCVS), mean cell transit time (MCTT), and the membrane shear modulus of elasticity (G), the latter a derived measure of the relative elasticity of the red cell membrane. After 1 mo EPO treatment, HCT significantly increased compared to saline-injected controls. After 2 mo treatment, HCT began to decline but remained elevated above baseline levels even after 3 mo treatment. After 3 mo EPO treatment, MCV was significantly lower in EPO-treated rats compared to controls. These changes imply altered hemopoiesis to produce cells which undergo shrinkage associated with accelerated cellular aging. The lower MCV would have predicted a shorter MCTT which instead was unchanged. This observation suggested the presence of an additional factor contributing to the MCTT. The G, which measures the membrane contribution to deformability, very significantly increased with EPO treatment. This finding indicates an increased contribution of membrane properties to the MCTT after EPO treatment, which cancels the expected decrease in MCTT for smaller cells. After 3 mo of EPO treatment, aged rats exhibited significantly impaired maze learning compared to controls. A relationship between, changes in erythrocyte membrane properties and impaired function was indicated by a significant correlation (r=0.67, p <0.04) between G and errors in the 14-unit T-maze. These findings suggest that stress-induced erythropoiesis produces accelerated aging in the red blood cell population that may have functional implications (i.e., impaired learning ability).

Age-associated memory impairment. Assessing the role of nitric oxide

Several neurotransmitter systems have been investigated to assess hypothesized mechanisms underlying the decline in recent memory abilities in normal aging and in Alzheimer's disease. Examining the performance of F344 rats in a 14-unit T-maze (Stone maze), we have focused on the muscarinic cholinergic (mACh) and the N-methyl-D-aspartate (NMDA) glutamate (Glu) systems and their interactions. Maze learning is impaired by antagonists to mACh or NMDA receptors. We have also shown that stimulation of mACh receptors can overcome a maze learning deficit induced by NMDA blockade, and stimulation of the NMDA receptor can overcome a similar blockade of mACh receptors. No consistent evidence in rats has been produced from our laboratory to reveal significant age-related declines in mACh or NMDA receptor binding in the hippocampus (HC), a brain region that is greatly involved in processing of recent memory. Thus, we have directed attention to the possibility of a common signal transduction pathway, the nitric oxide (NO) system. Activated by calcium influx through the NMDA receptor, NO is hypothesized to be a retrograde messenger that enhances presynaptic Glu release. Maze learning can be impaired by inhibiting the synthetic enzyme for NO, nitric oxide synthase (NOS), or enhanced by stimulating NO release. However, we have found no age-related loss of NOS-containing HC neurons or fibers in rats. Additionally, other laboratories have reported no evidence of an age-related loss of HC NOS activity. In a microdialysis study we have found preliminary evidence of reduced NO production following NMDA stimulation. We are currently working to identify the parameters of this phenomenon as well as testing various strategies for safely stimulating the NO system to improve memory function in aged rats.

Behavioral assessment of the senescence-accelerated mouse (SAM P8 and R1)

Senescence-accelerated mice (SAM P8 and R1) were behaviorally assessed in a cross-sectional study at 4 and 15 months of age. Behavioral measures included memory (place discrimination and repeated acquisition in a water maze), sensorimotor performance (turning in an alley, traversing bridges, wire rod hanging, and falls from a wire screen), psychomotor performance (open-field exploration), and emotionality (entries in a plus maze, grooming, and defecation in a plus maze and in an open field). In the water maze, aged P8 mice were impaired in place discrimination and in repeated acquisition tasks, demonstrating evidence of an age-related decline in spatial memory processing abilities. The demonstration of this impairment, however, was complicated by noncognitive factors, such as the tendency of many older P8 mice to float. Sensorimotor skill impairment was accelerated with age in P8 mice, but not in R1 mice, and this impairment was present despite the lack of age-related changes in body weight in P8 mice. Although P8 and R1 mice were not different in general activity at old age, P8 mice were substantially more hyperactive in an open field and in the plus maze than R1 mice when compared at young age. Independent of age, P8 mice demonstrated a reduction of anxiety-like behavior in the plus maze. Taken as a whole, the data suggest that although age-related behavioral alterations occur in the P8 mice, some of these changes are evident at 4 months of age. Thus, the behavioral abnormalities that exist not only represent an accelerated aging phenomenon but may also be considered a developmental pathology.

Combined stimulation of the glycine and polyamine sites of the NMDA receptor attenuates NMDA blockade-induced learning deficits of rats in a 14-unit T-maze

The present study examined the effects of multi-site activation of the glycine and polyamine sites of the NMDA receptor on memory formation in rats learning a 14-unit T-maze task. The competitive NMDA receptor antagonist, (+/-)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP, 9 mg/kg), was used to impair learning. The objectives were two-fold: (1) to investigate the effects of independent stimulation of the strychnine-insensitive glycine site or the polyamine site; (2) to investigate the effects of simultaneous activation of these two sites. Male, Fischer-344 rats were pretrained to a criterion of 13 out of 15 shock avoidances in a straight runway, and 24 h later were trained in a 14-unit T-maze that also required shock avoidance. Prior to maze training, rats received intraperitoneal (i.p.) injections of saline, saline plus CPP, CPP plus the glycine agonist, D-cycloserine (DCS, 30 or 40 mg/kg), CPP plus the polyamine agonist, spermine (SPM, 2.5 or 5 mg/kg), or CPP plus a combination of DCS (7.5 mg/kg) and SPM (0.625 mg/kg). Individual administration of either DCS or SPM attenuated the CPP-induced maze learning impairment in a dose-dependent manner. However, the combined treatment with both DCS and SPM completely reversed the learning deficit at doses five-fold less than either drug given alone. These findings provide additional evidence that the glycine and polyamine modulatory sites of the NMDA receptor are involved in memory formation. Furthermore, the potent synergistic effect resulting from combined activation of the glycine and polyamine sites would suggest a stronger interaction between these two sites than previously considered, and might provide new therapeutic approaches for enhancing glutamatergic function.

Phenserine, a novel acetylcholinesterase inhibitor, attenuates impaired learning of rats in a 14-unit T-maze induced by blockade of the N-methyl-D-aspartate receptor

The present study evaluated the interaction of the glutamatergic and acetylcholinergic systems in memory formation, with an overall emphasis on developing multi-system approaches for treating age-related cognitive decline and Alzheimer' s disease. Specifically, we used a 14-unit T-maze to investigate whether phenserine (PHEN), a long-acting acetylcholinesterase inhibitor, could overcome a learning deficit in rats induced by the NMDA receptor antagonist, 3-(+/-) 2-carboxypiperzin-4-yl) propyl phosphonic acid (CPP). Prior to drug treatment, 3-month-old male Fischer-344 rats were trained to criterion (13 of 15 shock avoidances) in a straight runway. Twenty-four hours later, rats were given i.p. injections of saline (SAL), CPP (9 mg/kg) + SAL or CPP + PHEN (0.25, 0.5 or 0.75 mg/kg) and received 15 massed training trials in a 14-unit T-maze. CPP significantly increased the number of errors made in the maze relative to controls, and phenserine significantly reduced the number of errors made relative to rats receiving CPP only, with the lowest dose being the most effective. These results provide further support of phenserine's potent, cognitive-enhancing properties, and suggest that combined modulation of glutamatergic and acetylcholinergic systems may be of potential benefit in developing new pharmacotherapies for Alzheimer's disease and age-related cognitive decline.

Intracerebroventricular injection of N omega-nitro-L-arginine in rats impairs learning in a 14-unit T-maze

We investigated whether intracerebroventricular (i.c.v.) infusion of the nitric oxide synthase inhibitor, Nomega-nitro-L-arginine (N-Arg), impairs learning in male Sprague-Dawley rats (2-3 months old) in a 14-unit T-maze. Rats were pretrained in one-way active avoidance to a criterion of 13/15 avoidances of foot shock in a straight runway. The next day, rats received i.c.v. injections of either artificial cerebrospinal fluid (aCSF) as controls or N-Arg (12 microg or 15 microg) 30 min before training in the 14-unit T-maze. The learning contingency was to negotiate each of 5 segments within 10 s to avoid footshock during 15 trials. Performance variables included errors (deviations from the correct pathway), runtime from start to goal, and shock frequency and duration. Compared to controls, the number of errors over the last 10 trials was higher in rats receiving 15 microg N-Arg and over the last 5 trials for those given 12 microg. Runtime, shock frequency and duration were increased in both N-Arg groups. The N-Arg-induced (15 microg i.c.v.) impairment could be attenuated when the nitric oxide donor, sodium nitroprusside (1 mg/kg), was administered intraperitoneally 1 min prior to maze learning. In a retention test, rats were treated with either aCSF or 15 microg N-Arg i.c.v. 30 min before being retested in the maze 7-10 d following acquisition training. Under these conditions, maze performance was not significantly affected. These results confirmed previous findings that inhibition of nitric oxide synthase impairs acquisition but not retention. Moreover, the N-Arg-induced learning impairment does not appear to be related to noncognitive aspects of performance.

Impaired learning in rats in a 14-unit T-maze by 7-nitroindazole, a neuronal nitric oxide synthase inhibitor, is attenuated by the nitric oxide donor, molsidomine

In previous experiments, it was demonstrated that systemic or central administration of the nitric oxide synthase (NO synthase) inhibitor, NG-nitro-L-arginine (N-Arg), produced dose-dependent learning impairments in rats in a 14-unit T-maze; and that sodium nitroprusside, a NO donor, could attenuate the impairment. Since N-Arg is not specific for neuronal NO synthase and produces hypertension, it is possible that effects on the cardiovasculature may have contributed to the impaired maze performance. In the present experiment, we have investigated the maze performance of 3-4 months old male Fischer-344 rats following treatment with 7-nitroindazole, a NO synthase inhibitor that is selective for neuronal NO synthase and does not produce hypertension. In addition, we examined the effects of the NO donor, molsidomine, which is much longer acting than sodium nitroprusside. Rats were pretrained to avoid footshock in a straight runway and received training in a 14-unit T-maze 24 h later. In an initial dose-response study, rats received intraperitoneal (i.p.) injections of either 7-nitroindazole (25, 50, or 65 mg/kg) or peanut oil 30 min prior to maze training. 7-nitroindazole produced significant, dose-dependent maze acquisition deficits, with 65 mg/kg producing the greatest learning impairment. This dose of 7-nitroindazole had no significant effect on systolic blood pressure. Following the dose-response study, rats were given i.p. injections of either 7-nitroindazole (70 mg/kg) plus saline, 7-nitroindazole (70 mg/kg) plus the NO donor, molsidomine (2 or 4 mg/kg), or peanut oil plus saline as controls. Both doses of molsidomine significantly attenuated the learning deficit induced by 7-nitroindazole relative to controls. These findings represent the first evidence that impaired learning produced by inhibition of neuronal NO synthase can be overcome by systemic administration of a NO donor.

Learning in a 14-unit T-maze is impaired in rats following systemic treatment with N omega-nitro-L-arginine

We examined whether inhibition of nitric oxide synthase (NO synthase) impairs learning in male Fischer-344 rats (9 mo) in a shock-motivated 14-unit T-maze. Rats were pretrained in one-way active avoidance of foot shock to a criterion of 13/15 avoidances in a straight runway. The next day, rats received intraperitoneal (i.p.) injections of 0.9% NaCl as controls or Nomega-nitro-L-arginine (N-Arg: 3.0. 4.5, or 6.0 mg/kg) to inhibit NO synthase 30 min before maze training. During 15 trials, rats were required to negotiate each of 5 segments within 10 s to avoid footshock. Performance variables included errors (deviations from the correct pathway), runtime from start to goal, shock frequency and duration. N-Arg treatment impaired performance on all variables in a dose-dependent manner. Specifically, only the 6 mg/kg N-Arg dose significantly increased errors compared to controls over the last 10 trials but not the first 5 trials. Controls and rats treated with 3 or 4.5 mg/kg N-Arg were retested in the maze 7-10 days following training, with half receiving N-Arg (6 mg/kg i.p.) 30 min in advance. In this retention test, maze performance was not significantly affected; thus, these results indicated that NO synthase inhibition primarily impaired acquisition without impacting upon noncognitive aspects of performance. This conclusion was further reinforced by the demonstration that 6 mg/kg N-Arg did not significantly affect sensorimotor performance in a rotarod task. When rats were treated with sodium nitroprusside, an NO donor, at 1 min, but not 30 min, prior to training, the N-Arg induced impairment (6 or 8 mg/kg i.p.) in maze learning was significantly attenuated.

An assessment of behavioral aging in the Mongolian gerbil

Male Mongolian gerbils (Meriones unguiculatus) 14-54 months old (n = 77) were evaluated in a battery of psychomotor (open field, locomotor, and runwheel activity, rotorod performance) and learning (one-way active avoidance in a straight runway and in 14-unit T-maze performance) tests. Body weight and seizure activity were also monitored. According to linear regression analysis, runwheel activity decreased with age; and the number of errors in the 14-unit T-maze increased as a function of age (ps < 0.05). None of the other behavioral measures or body weight were significantly correlated with age. This gerbil strain (Tumblebrook Farms; West Brookfield, MA) tended to be very prone to seizures with 64% of the gerbils experiencing at least one seizure while being tested. Seizures tended to occur when the gerbil was exposed to a novel situation (e.g., initial weighing, placement on the rotorod). An age-related decline in some aspects of psychomotor and learning performance was observed, suggesting the gerbil as an additional mammalian model of aging. The high incidence of seizure activity presented a complicating and confounding variable to the interpretation of the results of the behavioral tests used in the present study. Interventions to control seizure activity (e.g., systematic, controlled breeding; adaptation to apparati) in this model will likely increase its viability as a mammalian model of aging.

Effect of age and caloric restriction on cutaneous wound closure in rats and monkeys

Cutaneous wounds close more slowly in rats and monkeys as age increases. Caloric restriction of 40% in rats and 30% in monkeys did not significantly affect healing rates, although it did exert a trend toward faster closure. Similarly, voluntary exercise did not significantly alter healing rates in rats. Thus, impaired wound healing appears to be a generalized physiological manifestation of aging, but its possible amelioration by "anti-aging" interventions remains to be established.

Cognitive enhancement. New strategies for stimulating cholinergic, glutamatergic, and nitric oxide systems

The development of treatments for AD is being pursued along many diverse lines. While the ACh hypothesis has generated abundant development efforts, little clinical progress has been achieved to date. Recent efforts aimed at developing more potent, more specific, and safer ChE inhibitors appear to offer greater potential for therapeutic success than achieved to date. Treatments aimed at the NMDA Glu system lag much further behind in their development. Progress in this area must be tempered by the potential for glutamate excitotoxicity mediated through this neurotransmitter system. Development of indirect agonists operating at the glycine and polyamine modulatory sites on the NMDA receptor might offer the safest alternative to applying more direct agonists. While a great degree of interest had been generated by the reports of NO involvement in signal transduction through the NMDA system, this area of research has been complicated by conflicting reports regarding NO involvement in learning and LTP. Moreover, the interaction of drugs acting on NOS with the vascular effects mediated by eNOS has also complicated development of drugs that act specifically on the neural actions of NO. This area will continue to receive extensive research attention; but similar to the development of Glu agonists, attention must be given to the potential neurotoxic effects of overstimulating this system. Perhaps targeting other presynaptic mechanisms that effect glutamate release might be a safer strategy to pursue. Considerable progress has been made over the last two decades in identifying the genetic and neural mechanisms involved in AD. Progress in developing treatments will remain highly correlated with this effort, and with basic research geared to comprehending how memories are formed and why neurons degenerate and regenerate.

Effects of aging and chronic nimodipine on hippocampal binding of [3H]CGS 19755

Previous studies have suggested that aging is associated with impaired behavioral performance and with decrements of N-methyl-D-aspartate (NMDA) receptors in the rat hippo-campus. Other studies have indicated that chronic treatment with nimodipine, a Ca2+ channel antagonist, prevents the age-related decline in performance by rats in behavioral tasks. Therefore, we tested whether nimodipine altered binding of [3H]CGS 19755 to hippocampal NMDA receptors in rats whose performance on a 14-unit T maze had been tested previously (14). No significant age difference was observed in [3H]CGS 19755 binding in hippocampi from old Fischer-344 rats (27 months) as compared with mature but not senescent rats (9 months); however, old rats that received chronic treatment with a low dose of nimodipine (20 mg pellets implanted subcutaneously twice during 70 days of treatment) showed higher levels of binding. A high dose of nimodipine (40 mg pellets implanted by the same route and at the same times as the low dose) was without effect on [3H]CGS 19755 binding, although aged rats given this treatment performed better in the maze than rats that received no nimodipine or the low dose. In a second experiment comparing hippocampi of young (4 months) and old (24 months) rats, saturation studies confirmed the lack of an age difference in [3H]CGS 19755 binding. The findings suggest that neither the age-related decline in maze performance nor the enhancement of behavior by nimodipine depend upon changes in hippocampal NMDA receptors.

Utilization of the rat as a model of mammalian aging: impact of pathology on behavior

Because pathology is concomitant to aging in rat strains, extraneous variance can be added to studies of aging at all levels of analysis. Thus, several gerontologists have made recent requests for characterization of pathology in aging studies including not only investigators' reports of diseases commonly observed (e.g., Sendai virus) and the occurrence of prevalent age-related lesions (e.g., nephropathy, leukemia, radiculoneuropathy) in rodent colonies, but also how specific disease processes might impact on the variable of interest in their investigation. Reported here are simple techniques (e.g., physical examination, necropsy to identify lesions, hematocrit, Wright stain) used routinely by our laboratory to screen for the presence of age-related disease in studies using Fischer 344 and Wistar rats. Routine health screening by physical examination and blood testing in our studies has allowed us either to eliminate moribund rats or to assess whether deficient performance was related to health status when these animals had been included in behavioral investigations. Additional health screens (e.g., antibodies for specific tumors) need to be developed. Investigators should be encouraged to utilize existing techniques, such as those reported here, and new technologies either to screen moribund animals from studies or to demonstrate that the pathology observed does or does not impact on the variable under investigation.

In vivo assessment of striatal dopamine release in the aged male Fischer 344 rat

A microdialysis probe was implanted into the striatum of young (4- to 5-month-old) and aged (26- to 27-month-old) Fischer 344 male rats to assess age-related alterations in striatal dopamine (DA) release. Basal levels of DA and the magnitude of DA response evoked by 50 mM and 100 mM high potassium (K+) in aged rats were similar to those in young rats. Furthermore, K(+)-evoked DA release did not correlate with motor performance within either age group. In contrast, amphetamine (250 microM) evoked-DA release of aged rats was significantly lower than that of young rats. Moreover, the enhancement of K(+)-evoked DA release by oxotremorine (500 microM) was significantly attenuated in aged rats. These results indicate that a putative DA release mechanism and its cholinergic modulation of the aged striatum are impaired.

Maze learning in aged rats is enhanced by phenserine, a novel anticholinesterase

A new generation of cholinesterase inhibitors is expected to overcome some limitations of the therapeutic use of anticholinesterases. Phenserine is a long-acting and selective inhibitor of acetylcholinesterase with a preferential brain uptake. We have assessed the effects of chronic phenserine tartrate treatment on performance of aged Fischer-344 rats in the 14-unit T-maze. Phenserine (1-3 mg kg-1, i.p.) treatment for 5 days significantly reduced the number of errors made in the Stone maze. Other performance variables were also improved. No side effects were noted across 5 days treatment at doses of 1-2 mg kg-1. Phenserine can therefore improve the performance of aged rats in this complex maze task without producing obvious side effects.

Relationship of hematological variables to learning performance in aged Fischer-344 rats

The relationship between hematological variables and the ability to perform behaviorally in two learning tests was evaluated in male F344 rats aged 22-24 months. Rats were screened for ability to meet criterion for learning one-way active avoidance in a straight runway task. Rats failing to meet criterion were given no further testing and were assigned to Group 1 (G1). Rats meeting criterion were tested in a 14-unit T-maze (2 days, 10 trials/day). Failure to negotiate the T-maze within 600 s on any three trials resulted in assignment to Group 2 (G2) with no further testing. Rats successfully completing both tasks constituted Group 3 (G3). Trunk blood was collected following behavioral testing and was assayed to determine red blood cell count (RBC), hematocrit (HCT), hemoglobin (HGB), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), white blood cell count (WBC), bands (BND), polymorphs (POLY), lymphocytes (LYM), monocytes (MON), and eosinophils (EOS). The combined G1/G2 group had significantly lower RBC, HCT, HGB, and EOS but significantly higher MCV and MCH than G3 rats. Correlation analysis revealed a positive relationship of group membership (i.e., learning test completion) to RBC, HCT, HGB, and EOS, but a negative correlation of group membership to MCH. No significant correlation emerged between any hematological characteristic and performance in either behavioral task. These results suggest that a simple blood test to determine HCT may be a useful screen for removal of moribund rats from aging studies attempting to control for effects of health on behavioral performance in rodent models.

Spermidine potentiates dizocilpine-induced impairment of learning performance by rats in a 14-unit T-maze

The NMDA receptor, a ligand-gated ion channel complex, has been reported to be involved in memory processes. Learning is impaired following administration of dizocilpine, a non-competitive antagonist of the NMDA receptor. Polyamines, such as spermine and spermidine, interact with the NMDA receptor to enhance binding of dizocilpine, which blocks the ion channel. The present study assessed action of polyamines as modulators of learning via NMDA receptor activation. Dizocilpine (0.05 mg/kg) was given i.p. before maze learning, at a dose that produced a slight, nonsignificant impairment of maze learning. Pretreatment with 80 mg/kg but not 15 or 40 mg/kg spermidine (i.p.) before dizocilpine impaired maze learning compared to saline controls. Administration of 80 mg/kg spermidine without dizocilpine did not impair maze learning. The results are consistent with the view that systemic injection of a polyamine can modulate learning processes involving the NMDA receptor.

Thrombosis of parietal, but not striate, cortex impairs acquisition of a 14-unit T-maze in the rat

We evaluated parietal cortex (PCTX) involvement in learning a shock-motivated, 14-unit T-maize in young F344 rats. In Experiment 1, each rat was placed into a stereotaxic instrument, and the scalp was retracted before either the photosensitive dye, rose bengal, or saline (CON) was provided via a jugular catheter. After 60 s, halogen lamps were used to illuminate the cranium bilaterally over PCTX for 40 min to activate the dye and generate a thrombus in dye-injected rats. Active avoidance pretraining in a straight runway occurred 12 days after surgery. Each rat was provided acquisition (ACQ) trials in the 14-unit T-maze 24-h later. The PCTX rats were impaired relative to CON in errors, run time, alternation errors, and shock frequency measures in the 14-unit T-maze, but not in shock duration. The thrombosis extended to areas comprising anteromedial and posterior PCTX, and also into the striate cortex (SCTX). In Experiment 2, rats were divided into four groups: a PCTX group that received bilateral illumination; PCTX+SCTX and SCTX groups that were illuminated at midline; and a CON group that received the surgery and either dye or illumination. Only PCTX differed from CON, with maze performance similar to Experiment 1. The thrombosis for the PCTX group in Experiment 2 was confined to anteromedial and posterior PCTX. Thus, PCTX, but not SCTX, was implicated in ACQ of this maze task, suggesting that PCTX might be involved in the robust age-related impairments in ACQ previously observed.

New pharmacological strategies for cognitive enhancement using a rat model of age-related memory impairment

We have developed the Stone maze paradigm for use as a rat model of memory impairment observed in normal aging and in Alzheimer's disease. Evidence produced thus far clearly implicates both the cholinergic and glutamatergic systems in acquisition performance in this complex maze task. Although results have been very inconsistent regarding the cognitive enhancing abilities of cholinomimetics for use in Alzheimer's disease, new classes of cholinesterase inhibitors may offer greater therapeutic efficacy. The use of glycine and polyamine agonists appears to be a viable strategy for positive modulation of the NMDA receptor. In addition, an approach that combines stimulation both of cholinergic and glutamatergic systems may have greater potential than agonism of either separately. Manipulation of signal transduction events might also have potential for cognitive enhancement. The influx of Ca2+ through the NMDA receptor stimulates production of NO via the action of NOS. By using NARG to block NOS activity, we have demonstrated in rats that NO production appears to influence learning in the Stone maze. We are currently exploring the age-related changes in NOS activity in specific brain regions of rats to determine if loss in the NO generating system is related to age-related memory impairment observed in the Stone maze. In addition, we are exploring pharmacological strategies for inducing NO production; however, because of the potential neurotoxicity for NO overstimulation, this strategy will present some obstacles. The identification of NO as a simple molecule serving vital physiological functions but representing potential for neurotoxicity presents an important unifying area for neurobiological investigations searching for mechanisms of normal brain aging and of age-related neuropathology, as observed in Alzheimer's disease.

Behavioral assessment of aging in male Fischer 344 and brown Norway rat strains and their F1 hybrid

Male Fischer-344 (F344) and Brown Norway (BN) rats 7-, 13-, and 24-month-old and their F344 x BN hybrid (F1) 7-, 13-, 24- and 31-month-old were tested in a behavioral battery (15-min and 24-h locomotor activity, inclined screen, rod suspension, rotorod, shock-motivated learning in a straight runway and 14-unit T maze). Necropsy was performed 3 days later and the results rated for pathology (i.e., severity of lesions observed). Age-related performance declines were observed in all behavioral tests except 15-min locomotor activity. Strain effects were observed in 15-min (BN more active than F344 and F1) and 24-h locomotor activity test (F344 more active than BN and F1 strains); rotorod performance (F344 fell more than BN and F1); and in all measures [errors (E), runtime (RT)], shock frequency (SF), and duration (SD)] in the 14-unit T maze (F344 worse than BN, BN worse than F1). T maze performance of 31-month-old F1 rats was deficient in RT, SD, and SF but E performance was equivalent to that of 7-month-old F1 rats. In a second experiment, only 7- and 31-month-old F1 rats were tested in the 14-unit T maze and the results obtained in Experiment 1 were replicated. Gross necropsy revealed age and strain effects in the number of lesions observed and the mean ratings of pathology. The 24-month-old F344 rats exhibited the greatest number of lesions and had the highest ratings (generally observed as chronic nephrosis and enlarged spleens characteristic of mononuclear cell leukemia). BN rats exhibited a high incidence of hydronephrosis at all age levels. While experiencing less obvious pathology, F1 rats experienced a significant number of lesions in the 31-month-old group. Pathology ratings correlated with behavioral performance but only for a few tests (e.g., SD and RT in 14 unit T maze in 24-month-old F344). Thus, behavioral performance declined with age and the battery of tests differentiated between the strains tested (in general, F344 worse than BN; BN worse than F1). The correlation of pathology ratings at gross necropsy with behavior did not appear to be systematic, suggesting that morbidity was not responsible for the age-related performance declines. However, more extensive evaluation of the relationship of age-related changes in health status to behavior with larger samples of rats is suggested.

Rodent models of memory dysfunction in Alzheimer's disease and normal aging: moving beyond the cholinergic hypothesis

The Stone maze paradigm has been developed for use as a rat model of memory impairment observed in normal aging and in Alzheimer's disease. Results from several studies have demonstrated the involvement of both cholinergic and glutamatergic systems in acquisition performance in this complex maze task. Although results of clinical studies on the cognitive enhancing abilities of cholinomimetics for treatment of memory impairment in Alzheimer's disease have been inconsistent, new classes of cholinesterase inhibitors offer greater potential for therapeutic efficacy. The physostigimine derivative, phenserine, appears to have marked efficacy for improving learning performance of aged rats or of young rats treated with scopolamine in the Stone maze. Declines in markers of glutamatergic neurotransmission in Alzheimer's disease and in normal aging suggest that pharmacological manipulation of this system might also prove beneficial for cognitive enhancement. Treatment with glycine and/or polyamine agonists is suggested as a strategy for activating the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. In addition, the use of combined pharmacological activation of cholinergic and glutamatergic systems is suggested. Manipulation of signal transduction events should also be considered as a strategy for cognitive enhancement. The influx of Ca2+ through the channel formed by the NMDA receptor stimulates the production of the oxyradical, nitric oxide (NO*), via the action of nitric oxide synthase (NOS). Compounds that inhibit NOS activity impair acquisition in the Stone maze, suggesting an involvement of NO*. Thus, strategies for inducing NO* production to enhance cognitive performance may be beneficial. Because of the potential neurotoxicity for NO*, this strategy is not straightforward. Although many new directions beyond the cholinergic hypothesis can be suggested, each has its potential benefits which must be weighed against its risks. Nonetheless, an important unifying area for neurobiological research examining mechanisms of normal brain aging and of age-related neuropathology, as observed in Alzheimer's disease, might emerge from the identification of NO* as a simple molecule serving vital physiological functions but representing potential for neurotoxicity.

Chronic nimodipine treatment in aged rats: analysis of motor and cognitive effects and muscarinic-induced striatal dopamine release

Nimodipine is a calcium channel blocker reported to have beneficial effects on treatment of ischemic damage as well as the potential for retarding aspects of brain and behavioral aging when provided chronically to rats. We treated aged male F-344 rats (24 months) with nimodipine in SC pellets in the following doses: 0 (controls), 20 mg (low-dose), or 40 mg (high-dose) replenished after 6 weeks. After 3 months of treatment, surviving rats and a group of young controls (6 months) were tested in a behavioral battery involving exploratory activity in an open field and in a runwheel cage as well as motor abilities required for remaining on an inclined screen, suspended from a wire, and balanced on a rotorod. Rats were also pretrained for one-way active avoidance in a straight runway before being trained in a 14-unit T maze. During 20 trials rats were required to negotiate each of 5 maze segments within 10 s to avoid foot shock (0.8 mA). Nimodipine treatment produced no significant effects on body weight, food intake, or survival of aged rats. Analysis of behavioral results indicated significant age-related decline in performance of all tasks except in open-field behavior. Nimodipine treatment had no significant effects on behavioral performance of aged rats except in maze learning. Rats on the high-dose regimen performed significantly better than aged controls in the maze. The results indicate that chronic nimodipine treatment of aged rats had no toxic effects and might be beneficial for preventing age-related decline in learning performance.

Impaired acquisition in a 14-unit T-maze following medial septal lesions in rats is correlated with lesion size and hippocampal acetylcholinesterase staining

Septohippocampal cholinergic system involvement in acquisition of an aversively motivated 14-unit T-maze was evaluated in 4-month-old male Fischer-344 rats. Each rat was assigned to one of two groups that received either a bilateral electrolytic lesion to the medial septal area (MSA) or a sham operation. One week after surgery, each rat began pretraining in one-way active avoidance (footshock = 0.8 mA) consisting of 10 trials per day on each of 3 consecutive days. Criterion for successful completion of pretraining was 8/10 avoidances on the third day. On the day following completion of pretraining, each rat received 10 trials in a shock-motivated 14-unit T-maze. The performance requirement was to move through each of five maze segments within 10 s to avoid footshock (0.8 mA). A second 10-trial session was provided 24 h later. Performance measures included errors, alternation errors, runtime, shock frequency, and duration. Following maze training, each rat was sacrificed, and formalin-fixed brains were frozen for histology, which included procedures for thionin Nissl and acetylcholinesterase (AChE) staining. MSA-lesioned rats were observed to be significantly impaired on all measures of maze performance compared to sham-operated controls. Densitometric analysis of hippocampal AChE staining revealed a 30% reduction in relative AChE staining of MSA-lesioned rats compared to sham-operated controls. Lesion size was observed to be highly positively correlated with maze errors. A negative correlation of mean error score with density of AChE staining was observed for MSA-lesioned rats, but not for sham-operated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Phenserine: a physostigmine derivative that is a long-acting inhibitor of cholinesterase and demonstrates a wide dose range for attenuating a scopolamine-induced learning impairment of rats in a 14-unit T-maze

Phenserine ((-)-N-phenylcarbamoyl eseroline), a carbamate analog of physostigmine (Phy), is a long-acting inhibitor of cholinesterase. We have assessed the potential clinical value of phenserine for cholinomimetic therapy of cognitive impairments associated with aging and Alzheimer's disease by evaluating its duration of in vivo activity against rat plasma acetylcholinesterase (AChE) and its effect on attenuating a scopolamine-induced impairment in learning performance of young rats in a shock-motivated 14-unit T-maze. Phenserine achieved maximum AChE inhibition of 73.5% at 5 min and maintained a high and relatively constant inhibition for more than 8 h. For analysis of effects on learning performance, 69, 3-month-old male Fischer-344 rats were pretrained in a straight runway to avoid electric footshock. On the following day, each animal received 15 trials in the 14-unit T-maze. Sixty minutes prior to the maze training, each rat received the first IP injection of either vehicle (Tween 80, ethanol and 0.9% NaCl) or phenserine at 1.5, 3.0, 4.0, 5.0, 7.5, or 10.0 mg/kg. Then 30 min prior to the training, each animal received a second IP injection of either 0.9% NaCl or scopolamine hydrochloride (0.75 mg/kg; SCOP). Compared to the vehicle-SCOP group, all but the 7.5 mg/kg dose of phenserine significantly ameliorated error performance, runtime, shock frequency and shock duration in SCOP-treated rats at the final block of three trials. Appearing to have a long effect and a wide therapeutic window, phenserine deserves further study as a cognitive enhancer.

The long-acting cholinesterase inhibitor heptyl-physostigmine attenuates the scopolamine-induced learning impairment of rats in a 14-unit T-maze

Heptyl-physostigmine (heptyl-Phy), a new carbamate derivative of physostigmine (Phy), has been assessed for potential clinical value by evaluating its in vitro activity against human erythrocyte acetylcholinesterase (AChE) and plasma butyrylcholinesterase (BChE), its duration of in vivo activity against rat plasma AChE, and its effects on attenuating a scopolamine-induced impairment in learning performance of young rats in a 14-unit T-maze. Heptyl-Phy demonstrated potent cholinesterase inhibition, with activity similar to that of Phy against AChE, IC50 values 21.7 +/- 2.0 nM and 27.9 +/- 2.4 nM, respectively, and significantly greater than that of Phy against BChE, IC50 values 5.0 +/- 0.1 nM and 16.0 +/- 2.9 nM, respectively. Heptyl-Phy achieved maximum AChE inhibition of 92.5% at 60 min and maintained a high and relatively constant inhibition for more than 8 h. For analysis of effects on learning performance, heptyl-Phy at 1.0, 1.5, 2.0 or 3.0 mg/kg, or vehicle was administered i.p. to 52 3-month-old male Fischer-344 rats 60 min prior to maze training. Thirty minutes prior to training, each animal received either 0.9% NaCl or scopolamine hydrochloride (0.75 mg/kg). Only a 2.0 mg/kg dose of heptyl-Phy significantly reduced the number of errors in scopolamine-treated rats. The other doses did not improve any aspect of maze performance. Although the therapeutic window of heptyl-Phy did not appear wide enough for clinical use, the longer duration of action of heptyl-Phy would appear beneficial.

Reduced density of NMDA receptors and increased sensitivity to dizocilpine-induced learning impairment in aged rats

About 20 min prior to training in a shock-motivated 14-unit T-maze, young (3-4 months) and aged (24-25 months) male Fischer-344 rats were given s.c. injections of either saline or dizocilpine (MK-801, 0.02 or 0.04 mg/kg), a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor. The aged rats showed a dose-dependent impairment in maze performance. Deficiencies were manifested as increases in errors, in runtime from start to goal, and in the number and duration of shocks received. In contrast, young rats exhibited no detrimental effects of dizocilpine on maze performance. Analysis of [3H]glutamate binding in these rats revealed a marked age-related decline in NMDA receptor binding in hippocampus. A significant correlation was observed between errors in the maze and hippocampal [3H]-glutamate binding, but the correlation was positive, i.e., rats that made the most errors had the highest level of NMDA receptor binding. Thus, compared to young rats, aged rats were more sensitive to the behavioral effects of NMDA receptor antagonism and they showed a hippocampal loss of [3H]glutamate in binding, which may be related to the increased sensitivity to dizocilpine. The positive correlation between poor maze performance and NMDA receptor binding suggests that the behaviors assessed involve complex interactions between NMDA receptors and other neuronal systems in the hippocampus.

Complex maze performance in young and aged rats: response to glucose treatment and relationship to blood insulin and glucose

In aged rats and humans, impaired glucose regulation has been correlated with poor memory performance, and glucose treatment can result in improved performance. We tested this glucose hypothesis with rats in a 14-unit T-maze that has provided robust evidence of age-related performance decline. Aged (24-25 month) and young (6-7 month) male F-344 rats were pretrained for one-way active avoidance before receiving complex maze training (4 daily trials over 5 days) with the contingency of moving through each of 5 segments to avoid footshock. Ten min before daily training, aged rats received either saline or glucose in doses of 10, 100, or 500 mg/kg IP, while young rats received saline. Significant (ps less than 0.05) age-related increases in errors, runtime, and shock duration were observed. Glucose treatment had no significant effect on the number of maze errors committed; however, performance variables such as runtime and shock duration appeared to be reduced in rats receiving glucose. About 4-6 weeks later, a sample of these rats was fasted overnight, injected IP with glucose (150 mg/kg), and bled at various postinjection intervals to obtain estimates of blood glucose and insulin levels. Significant correlations (ps less than 0.05) were observed between maze errors and baseline glucose levels, r(21) = -.62, and peak glucose response, r(19) = .49. However; within the aged group, significant correlations (ps less than 0.01) with maze errors emerged only for baseline glucose, r(13) = -.69, and peak insulin response, r(13) = -.65. Thus, regulation of insulin, but not glucose, appeared related to learning abilities among aged rats.(ABSTRACT TRUNCATED AT 250 WORDS)

NMDA receptor channel antagonism by dizocilpine (MK-801) impairs performance of rats in aversively motivated complex maze tasks

To determine the involvement of the N-methyl-D-aspartate (NMDA) receptor in shock-motivated complex maze performance, the drug dizocilpine (DIZO; a.k.a. MK-801) was administered a) to naive, 3-month-old male F-344 rats prior to acquisition (AQ) in the 14-unit T-maze (Experiment 1), and b) to well-trained 11-month-old male F-344 rats prior to testing in a delayed-matching-to-sample (DMTS) task in the detour maze (Experiment 2). For Experiment 1, rats first were pretrained in a straight runway on one-way active avoidance (13/15 correct avoidances) for a maximum of 30 trials. On the following day, either DIZO 0.025 (n = 8), 0.05 (n = 8), 0.1 (n = 8), mg/kg, or saline (SAL; n = 15) was administered subcutaneously (SC) 20 min prior to 15 AQ trials in the shock-motivated 14-unit T-maze. The highest dose disrupted all measures of maze performance including errors, alternation errors, runtime, shock duration and frequency, but also produced marked motor ataxia. The 0.05-mg/kg group displayed significant impairment in AQ of this task but only on the cognitive measures, errors and alternation errors, and the 0.025-mg/kg group was impaired on the alternation measure only. One week later, the 15 SAL rats were divided into 2 groups and tested on retention with either SAL or 0.05 mg/kg DIZO. No effects on maze performance were observed. For Experiment 2, after receiving extensive pretraining in the shock-motivated detour maze, 7 rats were exposed to a novel sequence of 4 problems (P) during each of 7 daily sessions. Performance was evaluated 20 min after SC injection of either DIZO--0.025, 0.05, 0.125 mg/kg, or SAL. The 0.125-mg/kg dose caused extreme motor ataxia which precluded testing during that session. The 0.05-mg/kg but not the 0.025-mg/kg dose significantly disrupted performance on both error and trials to criterion measures. Both problem and interaction effects were significant. Disruption was most evident on two specific problems, those involving a side change from the first to second detour. Also, rats had more difficulty switching sides from problem to problem (few errors on P-1 and most on P-4), suggesting proactive interference effects. In sum, DIZO was observed to significantly disrupt performance in both mazes in a dose-related manner similar to effects observed in previous studies following administration of the anticholinergic drug scopolamine. For the 14-unit T-maze, the present results simulate age-related deficits previously found in acquisition of that task.

Acetyl-1-carnitine. 2: Effects on learning and memory performance of aged rats in simple and complex mazes

Acetyl-1-carnitine (AC) was administered via drinking water for six months to one group (OLD-AC) of male F-344 rats beginning at 16 months of age, while another group (OLD-CON) of rats was given water only during that period. The rats were maintained on this treatment throughout behavioral testing, which began at 22 months of age. Performance of the OLD-AC and OLD-CON rats was compared to that of young control (YG-CON) rats on the following set of tasks: spontaneous alternation in the arms of a T-maze, two-choice simultaneous discrimination in the stem of a T-maze, rewarded alternation in the arms of a T-maze, spatial discrimination and reversal on a circular platform, spatial working memory in the radial 8-arm maze, long-term memory in the 14-unit T-maze, and for preference of the light or dark chamber of a two-compartment box. AC improved the long-term memory performance in the split-stem T-maze and on the circular platform but had no discernable effects on performance of aged rats in the other tasks. Possible reasons for the selectivity of this agent's action on behavior are suggested.

Acetyl-1-carnitine. 1: Effects on mortality, pathology and sensory-motor performance in aging rats

Three different test sites assessed the effects of acetyl-1-carnitine (AC) on age-related changes in general health, sensory-motor skills, learning, and memory. Two groups of rats began the experiments at 16 months of age. One group (OLD-AC) was given AC, 75 mg/kg/day, beginning at 16 months. The other group (OLD-CON) was treated identically except it was not given the drug. Beginning at 22 months of age, these rats and a group of young (3-4 months old) rats (YG-CON) were given a series of sensory-motor tasks. AC decreased mortality, and had no reliable effect on body weight, fluid intake, or the general health of the rats. These data indicate that a chronic dose of AC does not interfere with food and water intake, and may increase longevity. An age-related decline of performance occurred in most of the sensory-motor tasks; locomotor activity was reduced in a novel environment and in a runwheel, and the ability to prevent falling was reduced in tests on a taut wire, rotorod, inclined screen, and several types of elevated bridges. An age-related decline of performance did not occur in grooming, or in the latency to initiate several different behaviors. AC had no effect on performance in any sensory-motor task. These data indicate that the improvements produced by AC in some tests of spatial memory may be due to the effects of AC on cognitive abilities rather than on sensory-motor skills.

Complex maze performance in rats: effects of noradrenergic depletion and cholinergic blockade

Noradrenergic (NA) involvement in acquisition (AQ) and retention (RET) of a shock-motivated 14-unit T-maze after intraperitoneal (ip) administration of DSP4, a neurotoxin that depletes forebrain NA, was evaluated in 2 experiments using 3-month-old male F-344 rats. Depletion of cortical NA level in DSP4-treated rats was verified by neurochemical assay and by latency to postdecapitation clonus reflex. In Experiment 1, DSP4 (50 mg/kg ip) rats did not differ from saline-treated (SAL) rats on any measure of maze performance (errors, alternation errors, run time, shock duration, or shock frequency) during AQ (DSP4 2 weeks prior to testing) nor during a RET test 2-3 weeks later (DSP4 immediately after the last AQ trial or 1 week after AQ). In Experiment 2, DSP4 and scopolamine (SCOP), a cholinergic (ACh) antagonist, were administered in combination to test for an NA-ACh interaction. DSP4 (50 mg/kg ip 2 weeks prior to AQ) again had no effect on AQ performance nor did DSP4 interact with either dose of SCOP (0.25 or 0.5 mg/kg ip 30 min prior to AQ) to further impair performance. Similar to previous studies SCOP impaired all measures of maze performance except shock duration. These experiments provide further evidence for involvement of ACh systems in the learning of this task and in the age-related impairments previously observed, but they suggest that central NA systems may not be involved directly or interactively with ACh systems required for efficient performance in this maze.

Complex maze performance in rats: Effects of noradrenergic depletion and cholinergic blockade

Noradrenergic (NA) involvement in acquisition (AQ) and retention (RET) of a shock-motivated 14-unit T-maze after intraperitoneal (ip) administration of DSP4, a neurotoxin that depletes forebrain NA, was evaluated in 2 experiments using 3-month-old male F-344 rats. Depletion of cortical NA level in DSP4-treated rats was verified by neurochemical assay and by latency to postdecapitation clonus reflex. In Experiment 1, DSP4 (50 mg/kg ip) rats did not differ from saline-treated (SAL) rats on any measure of maze performance (errors, alternation errors, run time, shock duration, or shock frequency) during AQ (DSP4 2 weeks prior to testing) nor during a RET test 2-3 weeks later (DSP4 immediately after the last AQ trial or 1 week after AQ). In Experiment 2, DSP4 and scopolamine (SCOP), a cholinergic (ACh) antagonist, were administered in combination to test for an NA-ACh interaction. DSP4 (50 mg/kg ip 2 weeks prior to AQ) again had no effect on AQ performance nor did DSP4 interact with either dose of SCOP (0.25 or 0.5 mg/kg ip 30 min prior to AQ) to further impair performance. Similar to previous studies SCOP impaired all measures of maze performance except shock duration. These experiments provide further evidence for involvement of ACh systems in the learning of this task and in the age-related impairments previously observed, but they suggest that central NA systems may not be involved directly or interactively with ACh systems required for efficient performance in this maze.

Comparison of retention performance between young rats with fimbria-fornix lesions and aged rats in a 14-unit T-maze

Young (3-months) and aged (24-months) male F-344 rats were pretrained in one-way active avoidance in a straight runway for 3 days. Then two 10-trial daily sessions were given in a 14-unit T-maze in which the response requirement was to negotiate each of 5 maze segments within 10 s to avoid footshock. One day or one week after acquisition, bilateral electrolytic lesions were made in the fimbria-fornix of young rats (1-day lesion or 1-week lesion). Corresponding sham operations were made for remaining young rats (1-day sham or 1-week sham). Aged animals did not receive any surgical treatment. One week after surgery, a 10-trial retention test was conducted to assess the lesion effects on retention and to manipulate the interval between acquisition and lesions. Aged animals were tested in the maze 1 week after acquisition. Results revealed that rats with fimbria-fornix lesions exhibited significant impairment compared to sham-operated groups on all retention performance measures including errors, runtime, number of shocks, duration of shock, and alternation errors. The number of errors and alternation errors of lesioned animals were still higher than those of sham-operated animals at the second half of the retention test, whereas other non-cognitive measures for lesioned animals recovered to control levels. The interval between acquisition training and lesions had no influence on retention performance. Although performance of aged rats during acquisition and retention trials was significantly worse than that of young controls and lesioned animals, a similar recovery pattern during retention testing was found for young rats with fimbria-fornix lesions and aged rats, i.e. both groups showed significant declines in non-cognitive measures with less decline in cognitive measures. These results suggest that the fimbria-fornix is partially involved in retention of 14-unit T-maze performance and that the age-related retention deficit observed in this task may be related to impaired transmission through this pathway.

Retention of maze performance inversely correlates with N-methyl-D-aspartate receptor number in hippocampus and frontal neocortex in the rat

The N-methyl-D-aspartate (NMDA) receptor may play a critical role in learning and memory. In the present study, a significant correlation was found between the number of NMDA-displaceable, Na+-independent L-[3H]glutamate binding sites in the hippocampus and neocortex of young rats and the mean number of errors during retention, but not acquisition, in a 14-unit T-maze.

Retention of maze performance inversely correlates with N-methyl-D-aspartate receptor number in hippocampus and frontal neocortex in the rat

The N-methyl-D-aspartate (NMDA) receptor may play a critical role in learning and memory. In the present study, a significant correlation was found between the number of NMDA-displaceable, Na+-independent L-[3H]glutamate binding sites in the hippocampus and neocortex of young rats and the mean number of errors during retention, but not acquisition, in a 14-unit T-maze.

Age-related impairment in complex maze learning in rats: relationship to neophobia and cholinergic antagonism

Scopolamine was utilized to assess cholinergic muscarinic blockade on the performance of young (3 months) and aged (23 months) male F-344 rats in a 14-unit T-maze task. Prior to training, a portion of each age group received a gustatory neophobia test (percent consumption of a novel sucrose solution) to assess involvement of norepinephrine systems implicated in age-related impairments of rats in other memory tasks. All rats were pretrained in one-way active avoidance (1.0 mA) on 3 consecutive days. Rats meeting criterion (8/10 avoidances on last day) began maze training the next day consisting of 10 trials on 2 consecutive days. The task required the rat to negotiate each of 5 maze segments within 10 sec to avoid scrambled footshock (1.0 mA). Rats received an intraperitoneal injection of either scopolamine hydrochloride (0.5 mg/kg or 0.75 mg/kg) or saline vehicle 30 min prior to maze testing. Consistent with past reports, aged rats were more neophobic (i.e., consumed less sucrose) than were young rats, but the degree of neophobia was not significantly correlated with maze error performance in either age group. Also consistent with previous studies, aged rats were significantly impaired, compared to young counterparts, in all maze performance measures including errors, alternation errors, runtime, and shock frequency and duration. Significant scopolamine-induced deficits were observed in both age groups, but only in errors and alternation strategy. No age by drug interaction was manifested in any performance measure indicating that scopolamine impaired learning of young and aged rats equivalently.(ABSTRACT TRUNCATED AT 250 WORDS)

Scopolamine in rats impairs acquisition but not retention in a 14-unit T-maze

To follow up a previous report noting that scopolamine impaired acquisition performance of young rats in a shock-motivated 14-unit T-maze, the present study assessed the effects of muscarinic antagonism on retention aspects of the same task. The broader objective was to further the investigation of possible defects in cholinergic neurotransmission that might underlie the age-related impairments previously observed in this task. Young (3-month) male F-344 rats were given preliminary training to criterion in one-way active avoidance in a straight runway. Then on the first day of complex maze training, each rat received 5 acquisition (AQ) trials followed by a second 10-trial retention (RET) session conducted the following day. Subjects were assigned to one of eight groups receiving an intraperitoneal injection of either scopolamine hydrochloride (1.0 mg/kg) or saline as follows: (a) 30 min prior to training on the first day (PRE-AQ); (b) 30 min prior to training on both the first and second day (PRE-AQ-RET); (c) immediately after completing the trial on the first day (POST-AQ); (d) 30 min prior to testing on the second day (PRE-RET). Dependent measures included errors, alternation errors, run time, number of shocks, and total shock received. On the first day of maze training, all performance measures except for alternation errors were significantly higher for the two acquisition groups (PRE-AQ and PRE-AQ-RET) compared to all other groups which did not differ significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Co-dergocrine, cerebral glucose utilization and maze performance in middle-aged rats

The objective of this study was to determine the effect of co-dergocrine in rats on local cerebral glucose utilization and performance in a complex T-maze. Middle-aged (12-16 months) male Fischer-344 rats were given injections of co-dergocrine (3 or 10 mg/kg, IP) 35 min before behavioral testing or the administration of 2-deoxy-D-[1-14C]glucose ([14C]DG), a radiotracer for local cerebral glucose utilization (LCGU). Both doses stimulated LCGU in the locus ceruleus and median raphe nucleus and in subcortical structures associated with learning and memory (hippocampus and subiculum). The higher dose also stimulated LCGU in motor areas (caudate-putamen, globus pallidus, internal capsule). In contrast, co-dergocrine decreased LCGU in the frontal cortex. Poorer performance in a complex maze (increased shocks, errors and run time) was observed in middle-aged as compared with younger animals (3 months). Acute co-dergocrine treatment did not improve performance of middle-aged rats in this task. Thus, in the present experimental paradigm employing single dose administration, co-dergocrine's stimulation of LCGU was not associated with an alteration of maze performance in age-matched animals.

Dietary restriction benefits learning and motor performance of aged mice

Female C3B10RF1 mice maintained on either a control (approximately 95 kcal/week) or restricted (approximately 55 kcal/week) diet since weaning were tested in a behavioral battery at 11 to 15 or 31 to 35 months of age (middle-aged vs. aged). Age-related declines observed among control groups in tests of motor coordination (rotorod) and learning (complex maze) were prevented by the restriction regime. In addition, diet restriction increased locomotor activity in a runwheel cage among mice of both ages but did not affect exploratory activity in a novel arena.

Scopolamine impairs learning performance of rats in a 14-unit T-maze

To assess involvement of muscarinic cholinergic systems in performance of a shock-motivated 14-unit T-maze task, 3-month old Fischer-344 rats were given an IP injection of scopolamine (0.1, 0.3, 1.0 or 3.0 mg/kg), methylscopolamine (1.0 mg/kg), or saline 30 min prior to maze training on 2 consecutive days. Scopolamine, but not methylscopolamine, impaired all components of acquisition performance. Measures of error performance, run time, shock duration, and number of shocks received were significantly increased but only at the 1.0 and 3.0 mg/kg scopolamine doses. The cognitive component of the task, measured by error performance, appeared most affected. Cognitive performance deficits observed following scopolamine administration in the present study resembled age-related impairments in rats and mice previously observed in this task. The cholinergic hypothesis of geriatric memory dysfunction appears to be implicated by these findings; however, the degree to which memory systems are involved remains unclear. Other performance variables such as discriminative control of stimuli or mechanisms of attention are implicated and discussed.

Effects of inescapable shock on maze performance as a function of age in mice

The hypothesis was investigated that aged animals receiving an experimental treatment of inescapable shock would suffer greater deficits in swim T-maze performance than either their younger shocked counterparts or their age-matched nonshocked controls. Three age groups of male C57BL/6J mice were studied: (a) young-mature (8-9 mo); (b) middle-aged (15-16 mo); and (c) aged (26-27 mo). Equal numbers (n = 16) from each age group were assigned to either a treatment group, which received 3 days of inescapable shock (6 sec, 200 microA) during a 60-min session on a variable time schedule (VI-60 sec), or a control group, which was placed inside the apparatus for an equal amount of time. Beginning 24 hr after the last shock session, swim maze training consisted of 10 daily trials over 5 consecutive sessions. The hypothesis was partially confirmed with respect to the latency to swim to the choice-point of the T-maze. Only the aged treatment group demonstrated significantly impaired performance. With respect to the measure of learning (percent correct responses) in the alternation task, inescapable shock significantly impaired performance; however, the effect was a weak one and there was no evidence of differential impairment across age.