Effects of binge ethanol administration on the behavioral outcome of rats after lateral fluid percussion brain injury.

This study examined the effects of 4 weeks of binge ethanol administration (BEAn) on the behavioral outcome in rats after lateral fluid percussion (FP) brain injury. Rats were intragastrically given 7.5 mL/kg of either 40% ethanol in 5% glucose solution (3 g ethanol/kg; binge ethanol group), or 5% glucose solution (vehicle group), twice on Thursday and Friday of 3 consecutive weeks. Then rats from both groups were subjected to either lateral FP brain injury of moderate severity (1.8 atm) or to sham operation. Postinjury behavioral measurements revealed that brain injury caused significant spatial learning disability in both groups. There were no significant differences in mean search latencies in the sham animals between the vehicle and binge ethanol groups. On the other hand, the mean search latency of the binge ethanol group was significantly higher than that of the vehicle group in trial blocks 2 and 4. There were no significant differences in the target visits (expressed as mean zone difference [MZD]) during the probe trial between the injured animals of binge ethanol and vehicle groups. However, there was only a minor trend towards worsened MZD score in the binge-injured animals. Histologic analysis of injured animals from both injured ethanol and vehicle groups revealed similar extents of ipsilateral cortical and observable hippocampal damage. These results suggest that 4 weeks of binge ethanol treatment followed by ethanol intoxication at the time of injury worsens some aspects of the spatial learning ability of rats. This worsening is probably caused by subtle, undetectable morphologic damage by binge ethanol administration.

D-amphetamine facilitation of morris water task performance is blocked by eticlopride and correlated with increased dopamine synthesis in the prefrontal cortex.

The effect of posttraining D-amphetamine on Morris water task (MWT) performance was analyzed in this study by training rats using a single training trial per day procedure. In addition to acquisition latency, learning was assessed by a probe trial given 24 h after the last training trial. Rats given immediate post-trial D-amphetamine demonstrated improved performance over saline rats on both acquisition and the probe trial. An analysis of the mechanisms underlying facilitation revealed that eticlopride (a D2 antagonist) blocked D-amphetamine's facilitatory effects on the probe trial and dopamine synthesis was increased in the medial prefrontal cortex in the D-amphetamine group relative to controls. These results show that chronic administration of posttraining D-amphetamine facilitated MWT performance, and this facilitation may be mediated by the dopaminergic system and dopamine synthesis in the prefrontal cortex.

Three months of chronic ethanol administration and the behavioral outcome of rats after lateral fluid percussion brain injury.

This study examined the effects of 3 months of chronic ethanol administration (CEAn) on the behavioral outcome in rats after lateral fluid percussion (FP) brain injury. Rats were given either an ethanol liquid diet (ethanol diet groups) or a pair-fed isocaloric sucrose control diet (control diet groups) for 3 months. Then, rats from both diet groups were subjected to either lateral FP brain injury of moderate severity (1.8 atm) or to sham operation. Postinjury behavioral measurements revealed that brain injury caused significant spatial learning disability in both diet groups. There were no significant differences in spatial learning ability in the sham or brain-injured animals between the control and ethanol diets. However, a trend towards cognitive impairment in the sham animals and a trend towards reduced deficits in the brain-injured animals were observed in the ethanol diet group. Histologic analysis of injured animals from both diet groups revealed similar extents of ipsilateral cortical and hippocampal CA3 damage. These results, in general, suggest that 3 months of CEAn does not significantly alter the behavioral and morphologic outcome of experimental brain injury.

Effects of six weeks of chronic ethanol administration on the behavioral outcome of rats after lateral fluid percussion brain injury.

This study examined the effects of 6 weeks of chronic ethanol administration on the behavioral outcome in rats after lateral fluid percussion (FP) brain injury. Rats were given either an ethanol liquid diet (ethanol diet-groups) or a pair-fed isocaloric sucrose control diet (control diet groups) for 6 weeks. After 6 weeks, the ethanol diet was discontinued for the ethanol diet rats and they were then given the control sucrose diet for 2 days. During those 2 days, the rats were trained to perform a beam-walking task and subjected to either lateral FP brain injury of low to moderate severity (1.8 atm) or to sham operation. In both the control diet and the ethanol diet groups, lateral FP brain injury caused beam-walking impairment on days 1 and 2 and spatial learning disability on days 7 and 8 after brain injury. There were no significant differences in beam-walking performance and spatial learning disability between brain injured animals from the control and ethanol diet groups. However, a trend towards greater behavioral deficits was observed in brain injured animals in the ethanol diet group. Histologic analysis of both diet groups after behavioral assessment revealed comparable ipsilateral cortical damage and observable CA3 neuronal loss in the ipsilateral hippocampus. These results only suggest that chronic ethanol administration, longer than six weeks of administration, may worsen behavioral outcome following lateral FP brain injury. For more significant behavioral and/or morphological change to occur, we would suggest that the duration of chronic ethanol administration must be increased.

Olfactory cues and morphine-induced conditioned analgesia in rats.

In a Pavlovian conditioning procedure, rats were exposed to an odor conditioned stimulus (CS) and then were given morphine with its effect serving as the unconditioned stimulus (US). After four CS-US pairings, the CS was tested alone to assess the presence of an analgesic conditioned response (CR) using a hot-plate test. In Experiment 1a, two groups were conditioned by pairing either 10 mg/kg morphine or saline with an odor CS. In Experiment 1b, two groups were given an odor CS paired or unpaired with 10 mg/kg morphine. These results established that an odor cue can support a morphine-induced analgesic CR. Experiment 2 characterized the dose-effect curve (0, 3, 10, and 30 mg/kg morphine) using an odor conditioning procedure. The dose-effect curve showed an inverted U-shaped function, with the 10 mg/kg morphine group having significantly longer paw-lick latencies compared to all other groups. This finding contrasts with the monotonically ascending dose-effect curve for the analgesic unconditioned response (UR) to morphine.

Morphine-induced conditioned place preference in preweanling and adult rats.

The ability of morphine to support a conditioned place preference (CPP) in preweanling (18-22-day-old) and adult (70-90-day-old) rats was assessed. Prior to a 15-min compartment preference test, subjects received a saline-paired, 30-min exposure to a distinct compartment 2 h prior to receiving an injection of 1 or 5 mg/kg of morphine or saline, paired with a 30-min exposure to an alternate compartment for 4 consecutive days. Although overall activity levels differed substantially across age, preweanling and adult rats displayed similar patterns of activity during conditioning. Moreover, only adults exhibited a significant sex difference; females were more active than were males following an injection of 5 mg/kg of morphine. Both doses of morphine supported a comparable CPP in preweanlings and adults, and both ages exhibited relatively low activity levels while in the morphine-paired compartment. These similarities across age suggest that the CPP procedure may prove to be useful in elucidating the ontogeny of learning, memory, and stimulus selection in rats.

4-Hydroxynonenal, a product of lipid peroxidation, damages cholinergic neurons and impairs visuospatial memory in rats.

The mechanisms that underlie cholinergic neuronal degeneration in Alzheimer disease (AD) are unclear, but recent data suggest that oxidative stress plays a role. We report that 4-hydroxynonenal (HNE), an aldehydic product of lipid peroxidation, damages and kills basal forebrain cholinergic neurons when administered intraparenchymally. Examination of Nissl-stained brain sections following unilateral HNE infusion revealed widespread neuronal loss in basal forebrain ipsilateral to the injection, but not on the contralateral side. Levels of choline acetyltransferase activity and immunoreactivity in the ipsilateral basal forebrain and hippocampus were significantly reduced by 60-80% seven days following HNE administration. Performance in Morris water maze tasks of visuospatial memory was severely impaired in a dose-dependent manner seven days following bilateral administration of HNE. Bilateral infusion of FeCl2 (an inducer of membrane lipid peroxidation) into the basal forebrain caused neuron loss and decreased choline acetyltransferease immunoreactivity and deficits in visuospatial memory. Additionally, FeCl2 infusion increased HNE immunoreactivity, implicating HNE in iron-induced oxidative damage. Because recent studies have demonstrated HNE adducts in degenerating neurons in AD brain, the present findings suggest a role for HNE in damage to cholinergic neurons in AD.

Intradimensional transfer of duration matching-to-sample in pigeons with signals differing in color and location.

Duration matching-to-sample (MTS) was used to study the influence of signal attributes on temporal transfer in pigeons. Each of two groups was trained on two problems that involved 2 and 10 s duration samples that varied with respect to color and-or spatial location. For Group Color, signals were either a red or white light projected from the front wall. For Group Location, signals were a white light from either the front wall or the ceiling. Within each group, each combination of signal type (color or location) and duration was associated with a different choice stimulus, and one set of color choices always followed one signal type and a different set of color choices always followed the other signal type. Transfer tests involved a set of choices that had not previously been associated with the type of signal presented on that trial. Accuracy on transfer trials was very high in Group Color but at a chance level in Group Location, which indicates that temporal transfer occurs when signals emanate from the same location but not when signals emanate from different locations. These results are discussed in terms of other evidence of transfer of duration-MTS.

Conditioned place preference in 12-day-old Japanese quail.

Four experiments assessed the ability of 12-day-old Japanese quail to learn a conditioned place preference (CPP). In Experiment 1, immature quail learned to prefer a place paired with normal food over a place paired with tainted food. Experiment 2 indicated that this kind of learning can be achieved with as few as 2 days of training. It was discovered in Experiment 3 that place preferences can be established with exposure to only one hedonic event. Quail learned to prefer a chamber paired with either normal food or tainted food over a chamber that did not contain a hedonic stimulus. Experiment 4 successfully replicated the 2-day normal-food-induced place preference in the previous experiment, while also showing that mere context exposure is not sufficient to produce CPP.

Morris water maze deficits in rats following traumatic brain injury: lateral controlled cortical impact.

This experiment utilized a laterally placed controlled cortical impact model of traumatic brain injury (TBI) to assess changes on spatial learning and memory in the Morris water maze (MWM). Adult rats were subjected to one of two different levels of cortical injury, mild (1 mm) or moderate (2 mm) deformation, and subsequently tested for their ability to learn (acquisition) or remember (retention) a spatial task, 7 or 14 days after injury. Results revealed an injury-dependent deficit for experimental animals compared to sham-operated controls. Not only did the TBI result in longer escape latencies, but also significant deficits in search time and relative target visits. Although the moderately injured animals demonstrated significant histopathology in the cortex and hippocampus, mildly injured subjects demonstrated no obvious tissue destruction, but did manifest significant behavioral change. These results demonstrate that a laterally placed controlled cortical impact is capable of producing significant cognitive deficits on both acquisition and retention paradigms utilizing the MWM.

Impact of d-amphetamine on temporal estimation in pigeons tested with a production procedure.

The influence of d-amphetamine on timing in pigeons was examined with a production procedure. Birds were trained with a fixed time schedule in which food reinforcement was contingent on the first response made after a duration signal had appeared for 30 s. Probe tests involved trials in which the duration signal was extended to 90 s and reinforcement was omitted. In Experiment 1, 2.0 mg/kg d-amphetamine shifted peak responding to a duration shorter than that found with saline. In Experiment 2, the dose-response function for this drug effect was examined. A 0.3-mg/kg dose of d-amphetamine had no impact on performance, but a 1.0-mg/kg dose shifted the peak duration significantly relative to saline; a 2.0-mg/kg dose shifted the function even more. These results complement previous findings with rats tested with the peak procedure and pigeons tested with a discrimination procedure.

Lack of delayed effects of amphetamine, methoxamine, and prazosin (adrenergic drugs) on behavioral outcome after lateral fluid percussion brain injury in the rat.

This study examined the delayed effects of the administration of d-amphetamine, methoxamine (an alpha1-adrenergic receptor agonist), and prazosin (an alpha1-adrenergic receptor antagonist) on the behavioral outcome of lateral fluid-percussion (FP) brain injury. Rats trained to perform a beam-walking task were subjected to brain injury of moderate severity (2.1 to 2.2 atm). Twenty-four hours after injury, rats were treated with amphetamine, methoxamine, or prazosin at two or three different dose levels. Amphetamine-treated animals displayed no significant improvement in beam-walking ability either during or after drug intoxication (from days 3 to 5 after brain injury). Similarly, neither methoxamine nor prazosin significantly affected beam-walking ability during or after drug intoxication. Neither amphetamine treatment at three different doses nor treatment with methoxamine or prazosin at two different doses affected the spatial learning disabilities of brain-injured animals. These results suggest that (1) unlike amphetamine administration after sensorimotor cortex (SMC) ablation or contusion brain injury models, amphetamine administration at 24 h after concussive FP brain injury does not improve beam-walking performance; (2) unlike amphetamine administration 10 min after concussive FP brain injury amphetamine administration 24 h after injury does not improve cognitive function; and (3) unlike prazosin administration after SMC ablation brain injury, prazosin administration 24 h after concussive FP brain injury does not effect beam-walking performance.

Ontogenetic differences in retention of spatial learning tested with the Morris water maze.

Two experiments examined retention of spatial learning in rats using a Morris water maze. Retention was scored in terms of probe trial performance when the platform was removed. Latency to reach the platform location, percent of time in the quadrant that had contained the platform, and relative frequency of visits to the platform location were analyzed. Results of the first experiment showed that preweanlings and juveniles exhibited substantial forgetting at 3- and 7-day retention intervals. Forgetting in adults was much lower than that found in the younger animals, and no differences in amount of forgetting appeared between the 3- and 7-day retention intervals at any age. The second experiment showed that forgetting in juveniles was alleviated by a single training trial administered just prior to the probe trial. These results are discussed in terms of ontogenetic differences in memory processing and measurement issues pertinent to the Morris water maze test procedure.

Bacterial alkaloids mitigate seizure-induced hippocampal damage and spatial memory deficits.

Studies of human patients with temporal lobe epilepsy and animal models of epilepsy have established relationships between seizures, excitotoxic hippocampal damage, and memory impairment. We report that bacterial alkaloids, recently shown to mimic actions of neurotrophic factors in cell culture, attenuate seizure-induced damage to hippocampal neurons and memory impairment in adult rats when administered subcutaneously. Intrahippocampal administration of convulsant doses of kainic acid (KA) to adult rats resulted in degeneration of neurons in CA3, CA1, and hilus. Rats administered KA exhibited (24 h later) deficits in performance on both goal latency and probe trial tasks in Morris water maze (MWM) tests of visuospatial memory. Seizure-induced damage to hippocampal neurons was significantly reduced, to varying extents, in rats administered the bacterial alkaloids K252a, K252b, or staurosporine (daily injections of 4 micrograms/kg body weight) prior to KA administration. The KA-induced deficits in MWM goal latency performance were abrogated in rats administered K252a or K252b, and K252a and staurosporine completely prevented seizure-induced impairment on the MWM probe trial. The alkaloids did not suppress electroencephalographic seizure activity, suggesting a dissociation between synchronization of activity and synaptically mediated excitotoxic injury to hippocampal neurons. Each alkaloid caused an increase in levels of protein tyrosine phosphorylation as determined by Western blot analysis of hippocampal tissue. Our data indicate that these bacterial alkaloids have potent antiexcitotoxic activities which may have clinical utility in epilepsy and other disorders that involve excitotoxic damage.

Altered neuronal and microglial responses to excitotoxic and ischemic brain injury in mice lacking TNF receptors.

Brain injury, as occurs in stroke or head trauma, induces a dramatic increase in levels of tumor necrosis factor-alpha (TNF), but its role in brain injury response is unknown. We generated mice genetically deficient in TNF receptors (TNFR-KO) to determine the role of TNF in brain cell injury responses. Damage to neurons caused by focal cerebral ischemia and epileptic seizures was exacerbated in TNFR-KO mice, indicating that TNF serves a neuroprotective function. Oxidative stress was increased and levels of an antioxidant enzyme reduced in brain cells of TNFR-KO mice, indicating that TNF protects neurons by stimulating antioxidant pathways. Injury-induced microglial activation was suppressed in TNFR-KO mice, demonstrating a key role for TNF in injury-induced immune response. Drugs that target TNF signaling pathways may prove beneficial in treating stroke and traumatic brain injury.

Value transfer in a simultaneous discrimination appears to result from within-event pavlovian conditioning.

When pigeons acquire a simple simultaneous discrimination, some of the value acquired by the S+ transfers to the S-. The mechanism underlying this transfer of value was examined in three experiments. In Experiment 1, pigeons trained on two simultaneous discriminations (A + B- and C +/- D-) showed a preference for B over D. This preference was reduced, however, following the devaluation of A. In Experiment 2, when after the same original training, value was given to D, the pigeons' preference for C did not significantly increase. In Experiment 3, when both discriminations involved partial reinforcement (S +/-), A + C- training resulted in a preference for B over D, whereas B + D- training resulted in a preference for A over C. Thus, simultaneous discrimination training appears to result in bidirectional within-event conditioning involving the S+ and S-.

Validation of a single-day Morris Water Maze procedure used to assess cognitive deficits associated with brain damage.

This experiment was designed to validate a single-day Morris Water Maze procedure used to assess cognitive functioning in rats. Separate groups of randomly assigned rats received either bilateral or unilateral fimbria fornix transections, bilateral or unilateral cortical ablations, or a sham surgical control procedure. Subjects were tested 7 days postoperatively with a modified version of the Morris Water Maze procedure that requires only a single day of training. The results indicated that bilateral fimbria fornix transections severely disrupted acquisition. Unilateral fimbria fornix transections and bilateral and unilateral cortical lesions disrupted acquisition less severely but impaired subsequent test performance. In general, unilateral lesions of both types produced less severe deficits than bilateral lesions. The practical and analytical advantages of the single-day procedure are discussed.

Amphetamine affects the behavioral outcome of lateral fluid percussion brain injury in the rat.

This study examined the effects of (D)-amphetamine, methoxamine (an al-adrenergic receptor agonist), and prazosin (an al-adrenergic receptor antagonist) on the behavioral outcome of lateral fluid percussion brain injury. Rats trained to perform a beam walking task were subjected to brain injury of moderate severity (2.1-2.2 atm). At 10 min after injury, rats were treated with amphetamine, methoxamine or prazosin at two different dose levels. Amphetamine-treated animals displayed significantly lower impairment in beam walking ability from days 1 to 5 after brain injury. Neither methoxamine nor prazosin significantly affected the impairment in beam walking ability from day 1 to day 7 after injury. However, prazosin treatment at both dose levels increased the post-injury mortality and the incidences of failure to recovery from hemiplegia. Amphetamine-treatment at 4 mg/kg, but not at 2 mg/kg, improved the spatial learning abilities of the injured animals. Neither methoxamine nor prazosin affected the spatial learning abilities. These results indicate that amphetamine facilitated beam walking recovery and improved cognitive function after concussive fluid percussion injury. Although the methoxamine experiments suggest that the norepinephrine-α1-adrenergic receptor system may not be involved in the pathophysiology of fluid percussion brain injury, our results with amphetamine (beneficial effects) and prazosin (deleterious effects) and the results observed in other models of brain injury point out that further investigations are necessary to understand the role of a1-adrenergic receptors in brain injury.

Signal intensity and duration estimation in rats.

Rats were trained on a short (2-second) versus long (10-second) duration discrimination. The duration of an overhead light signaled which of two lever-press responses, left or right, would produce food reinforcement. After the rats had acquired the discrimination, probe tests were presented in which the light varied in intensity (bright or dim) and duration (values between 2 and 10 seconds). The results indicated that rats judged a bright light to be longer than a dim light of equal duration. Signal intensity has been shown to affect timing in humans and pigeons. The present results therefore extend the comparative generality of the effect to include rats as well.

Attention to uninformative features expressed by pigeons in a duration matching-to-sample task.

Pigeons were trained on a matching-to-sample task in which they had to respond to a different choice stimulus following the same durations (2 or 10 s) of two different signals. The duration signals consisted of a white light presented from the ceiling and a red light presented from the front wall. Subsequent test performance indicated that matching accuracy declined (1) when the set of choice stimuli following a duration signal differed from the set presented during training, and (2) when the color or location of the duration signal was changed from values used during training. These results are discussed in terms of attention to uninformative features of a visual stimulus.