d-Amphetamine enhances memory performance in rats with damage to the fimbria

Catecholaminergic based therapies for functional recovery after TBI

Among the many pathophysiologic consequences of traumatic brain injury are changes in catecholamines, including dopamine, epinephrine, and norepinephrine. In the context of TBI, dopamine is the one most extensively studied, though some research exploring epinephrine and norepinephrine have also been published. The purpose of this review is to summarize the evidence surrounding use of drugs that target the catecholaminergic system on pathophysiological and functional outcomes of TBI using published evidence from pre-clinical and clinical brain injury studies. Evidence of the effects of specific drugs that target catecholamines as agonists or antagonists will be discussed. Taken together, available evidence suggests that therapies targeting the catecholaminergic system may attenuate functional deficits after TBI. Notably, it is fairly common for TBI patients to be treated with catecholamine agonists for either physiological symptoms of TBI (e.g. altered cerebral perfusion pressures) or a co-occuring condition (e.g. shock), or cognitive symptoms (e.g. attentional and arousal deficits). Previous clinical trials are limited by methodological limitations, failure to replicate findings, challenges translating therapies to clinical practice, the complexity or lack of specificity of catecholamine receptors, as well as potentially counfounding effects of personal and genetic factors. Overall, there is a need for additional research evidence, along with a need for systematic dissemination of important study details and results as outlined in the common data elements published by the National Institute of Neurological Diseases and Stroke. Ultimately, a better understanding of catecholamines in the context of TBI may lead to therapeutic advancements. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Persistent cognitive dysfunction after traumatic brain injury: A dopamine hypothesis

Traumatic brain injury (TBI) represents a significant cause of death and disability in industrialized countries. Of particular importance to patients the chronic effect that TBI has on cognitive function. Therapeutic strategies have been difficult to evaluate because of the complexity of injuries and variety of patient presentations within a TBI population. However, pharmacotherapies targeting dopamine (DA) have consistently shown benefits in attention, behavioral outcome, executive function, and memory. Still it remains unclear what aspect of TBI pathology is targeted by DA therapies and what time-course of treatment is most beneficial for patient outcomes. Fortunately, ongoing research in animal models has begun to elucidate the pathophysiology of DA alterations after TBI. The purpose of this review is to discuss clinical and experimental research examining DAergic therapies after TBI, which will in turn elucidate the importance of DA for cognitive function/dysfunction after TBI as well as highlight the areas that require further study.

Place learning and object recognition by rats subjected to transection of the fimbria-fornix and/or ablation of the prefrontal cortex

The acquisition of a water maze-based allocentric place learning task and an exploration based object recognition task were studied in four groups of rats: animals in which the fimbria-fornix had been transected, rats who had received bilateral ablations of the anteromedial prefrontal cortex, animals in which both of these structures had been lesioned, and a sham operated control group. None of the groups showed impairments of object recognition. Ablations of the prefrontal cortex caused a mild impairment in the acquisition of the place learning task. The two fimbria-fornix transected groups exhibited a severe impairment during the acquisition of this task. All groups reached criterion level task performance eventually. All groups were subjected to a number of behavioural and pharmacological challenges in order to elucidate the neural and cognitive mechanisms of this behavioural recovery. During a no-platform session both the fimbria-fornix transected group and the prefrontally ablated group demonstrated a normal preference for the former platform position. The combined lesion group, however, failed to show a similar preference for this position. The outcome of the pharmacological challenges demonstrated that while the task performance of all four groups relied equally on catecholaminergic mediation, only the task solution of the fimbria-fornix transected group was significantly impaired by disturbance of the catecholaminergic systems. The data indicated a high likelihood that prefrontal cortical mechanisms contribute to the recovery of allocentric place learning after fimbria-fornix transections.

Place learning in scopolamine-treated rats: the roles of distal cues and catecholaminergic mediation

Experiments 1 and 2 tested the hypothesis that cholinergic receptor antagonists impair place learning in a water maze by interfering with the processing of distal, visual cues. Extramaze cues were offered to rats in the form of geometrical patterns arranged on the inner circumference of a curtain surrounding the water maze. In Experiment 1 the animals were offered both the distal cues and proximal cues in the form of pingpong balls in fixed positions on the surface of the water while only distal cues were present in Experiment 2. Animals were injected with either scopolamine (0.5 mg/kg body wt) or saline 20 min prior to the daily place learning sessions. Upon reaching criterion level performance the animals were tested on "rotation" sessions on which the distal cues were displaced. The outcome of such "rotations" demonstrated that-regardless of the presence or absence of proximal cues-scopolamine-treated rats relied at least as much as normal animals on the distal cues. The acquisition phase of both Experiments 1 and 2 demonstrated an almost complete lack of scopolamine-associated impairment in acquisition and performance of the place learning task. In Experiment 3 (when scopolamine was no longer administered) the subjects of Experiment 2 were exposed to a series of pharmacological "challenges" of their place learning performance and eventually to surgical ablation of the anteromedial prefrontal cortex. The outcome of the pharmacological challenges and the postoperative test of task performance demonstrated that the place learning performance of animals which had acquired the task under scopolamine was mediated by a neural substrate dissimilar to the substrate of task performance in normal animals. Rats acquiring the task while deprived of the cholinergic system demonstrated above-normal contributions to task mediation from catecholaminergic-probably dopaminergic-mechanisms and tentative results pointed to a "shift" toward prefrontal task mediation.

Cocaine enhances retention of avoidance conditioning in rats

The effects of post-training cocaine administration were tested on retention of a one-way active avoidance task in rats. A 5.0 mg/kg IP dose of cocaine enhanced retention of the avoidance task, in three separate experiments, as indicated by an increase in the number of avoidances made when animals were tested 24 h after training, while both a lower (2.5 mg/kg) and a higher (7.5 mg/kg) cocaine dose had no effect. Lidocaine (4-8 mg/kg) administered post-training did not reliably affect retention in the same task. Cocaine's ability to enhance retention depended on the interval between training and drug injection such that only cocaine administered directly after training enhanced retention the following day. The results show that post-training cocaine administration enhances retention of an active avoidance task in rats, and that this effect is probably independent of the anesthetic properties of the drug.

Effects of RU 52583, an alpha 2-antagonist, on memory in rats with excitotoxic damage to the septal area

The anti-amnesic action of RU 52583, an alpha 2-adrenergic receptor antagonist, was evaluated through performance of spatial tasks in a radial maze by rats with N-methyl-D-aspartic acid (NMDA) lesion of the medial septal (MS) nuclei. Memory performance of lesioned or sham-operated rats was evaluated by measuring reference memory as long-term maintenance of an acquired performance and working memory or memory for recent events. The lesion: a produced significant impairments of the animals' memory performance, b) significantly reduced the sodium-dependent high-affinity choline uptake in the hippocampal formation, and c) deeply disrupted cholinergic hippocampal theta waves. Oral administration of RU 52583 at 1 and 2 mg/kg (tested doses: 1-5 mg/kg) prior to performance of the task markedly reduced memory impairments, whereas idazoxan, another alpha 2-adrenergic receptor antagonist, had no effect at tested doses (2-5 mg/kg). Cholinergic drugs--arecoline at 0.1 and 1 mg/kg (tested doses: 0.05-1 mg/kg) and physostigmine at 0.02 and 0.1 mg/kg (tested doses: 1, 2, and 5 mg/kg)-administered intraperitoneally showed a tendency to alleviate memory deficits. The present results show that the alpha 2-adrenergic antagonist RU 52583 possesses cognition-enhancing properties in rats with damage to the septohippocampal system.

Place learning by fimbria-fornix transected rats in a modified water maze

The acquisition of a place learning task in a water maze modified from the "standard" setup by restriction of distal cues was tested in two groups of rats: (1) animals subjected to bilateral transection of the fimbria-fornix--a manipulation that renders the hippocampus dysfunctional--and (2) a sham operated control group. The fimbria-fornix transected animals acquired the task as quickly and to the same level of proficiency as the control group. Upon reaching criterion level performance all animals were tested on "rotation" sessions on which the distal cues were displaced. The outcome of such "rotations" demonstrated that both groups relied upon the distal cues for navigational purposes. Finally, the performance of all animals was "challenged" on two sessions by administration of d-amphetamine and scopolamine, respectively. The outcome of the pharmacological challenges demonstrated that the normal proficiency of place learning by the fimbria-fornix transected rats had been accomplished due to compensatory processes mediated at least partly by the catecholaminergic systems.

Cholinergic differentiation factor/leukemia inhibitory factor enhances functional effects of adrenal medulla grafts after hippocampal lesions in rats

We recently found that adrenal medulla grafts implanted into the hippocampus of rats survived for several months and significantly decreased the deficits produced by hippocampal lesions in the radial maze test [Jousselin-Hossaja et al. (1994) Neuroscience 59, 275-284]. These grafts contained choline acetyltransferase immunopositive chromaffin cells and received cholinergic innervation. In the experiments reported here, adrenal medulla grafts implanted in lesioned hippocampus were treated with cholinergic differentiation factor/leukemia inhibitory factor. In the presence of this factor, the number of chromaffin cells with cholinergic phenotypes increased as well as the beneficial effects of the grafts on the performances of rats in the radial maze. These results suggest that the functional effects of adrenal medulla grafted into the hippocampus set into play cholinergic mechanisms. The cholinergic differentiation factor/leukemia inhibitory factor may also have facilitated the survival and recovery of cholinergic neurons in the host tissue. However, due to the large range of action of this cytokine and the richness of the adrenal medulla contents, non cholinergic factors are also probably involved. Our results may help to elucidate the functions of the cholinergic differentiation factor/leukemia inhibitory factor since they provide the first indication that its intracerebral injection may have behavioral effects. Moreover, our data confirm the possibility of improving the efficiency of adrenal medulla implants in the central nervous system by appropriate treatments, not only by facilitating survival but also by selectively amplifying some potential factors of the graft. This might greatly enlarge the field of this grafting technique for analysing the normal functioning of the brain and for repairing it.

Effects of adrenal medulla grafts on memory capacities of rats after hippocampal lesions

Behavioral and immunocytochemical techniques were used to study the effects of adrenal medulla grafts implanted in hippocampus--after lesion of this structure--on the memory capacities of rats. Performances of the grafted rats in the radial maze test were significantly improved and, in some aspects, fully restored. On the other hand, grafts had no significant effects on a one-trial spatial recognition test and impaired object recognition. Immunocytochemical identification showed that the grafts contained chromaffin cells with a choline acetyltransferase stainings while, in parallel, phenylethanolamine-N-methyltransferase stainings seemed to be decreased. Cholinergic innervation was established between the graft and the host hippocampus. A likely interpretation of this complex pattern of results is that the functional effects of the grafts depended on the arousal level induced by the behavioral task. At the neurobiological level, these effects probably set into play an interaction between opioid, catecholaminergic and cholinergic factors. Our results may contribute to the clarification of the problem of specificity of functional effects of intracerebral grafts as well as the problem of hippocampal role in learning and memory.

Comparison of GM1 ganglioside, AGF2, and D-amphetamine as treatments for spatial reversal and place learning deficits following lesions of the neostriatum

These experiments tested the effectiveness of parenterally administered gangliosides and amphetamine as treatments for spatial learning deficits caused by bilateral lesions of the neostriatum. In Expt. 1, rats were tested postsurgically for 30 days on a shock-avoidance, spatial reversal task. Treatments of gangliosides (GM1 at 30 mg/kg, and AGF2 at 20 mg/kg and 30 mg/kg) and D-amphetamine (2 mg/kg) significantly decreased lesion-induced learning deficits on this task, while treatments of 10 mg/kg AGF2 and the combination of GM1 (30 mg/kg) and D-amphetamine (2 mg/kg) were ineffective. In Expt. 2, rats were given bilateral neostriatal lesions and treated with GM1 (30 mg/kg), AGF2 (20 mg/kg) or D-amphetamine (2 mg/kg) and tested postsurgically for 5 days on a place learning task in the Morris water maze. Only the GM1-treated rats showed a reduction in lesion-induced place learning deficits on this task. Since in both experiments, cell counts near the area of the lesion revealed no differences among any of the brain-damaged groups, it was suggested that the treatments exert their behavioral effects by biochemically activating spared neurons, independent of any ultimate effects they may have on neuronal survival.

Hemicholinium-3 impairs spatial learning and the deficit is reversed by cholinomimetics

The effects of hemicholinium-3 (HC-3) on spatial discrimination learning were studied. Rats were equipped with indwelling cannulae in the right lateral ventricle and, following recovery, were trained on a two platform spatial discrimination task in a water maze. In this task a visible escape platform remains in a fixed position in the pool during a single training session, whilst the location of an identical "float" (which affords no escape) is randomly varied. For each session the location of the fixed escape platform was changed and the rats were retrained to criterion following pretreatment either with artificial cerebrospinal fluid (CSF) or HC-3 (2.5, 5.0 micrograms/rat/ICV) 1 h before training. Each rat received every treatment according to a latin square design. The results showed that spatial learning was dose dependently impaired by HC-3, choice accuracy being reduced to chance levels by the higher dose. There was no evidence of motoric difficulty, as choice latencies were not significantly increased. Experiments were then conducted to test for reversal of the deficit using a range of psychotropic drugs. Rats were treated with CSF or HC-3 (5 micrograms/rat ICV) 60 min prior to testing and test drugs were injected 15 min before testing. Some doses of physostigmine (46-460 micrograms/kg/SC) and tetrahydroaminoacridine (THA) (2.2-10 mg/kg/SC) reversed the spatial learning deficit. The muscarinic agonists arecoline (0.046-1 mg/kg/SC), aceclidine (1-10 mg/kg/SC), oxotremorine (30-100 micrograms/kg/SC) and RS-86 (0.46, 1.0 microgram/kg/SC) were also effective. Pilocarpine (0.22-2.2 mg/kg/SC) showed marginal activity and isoarecoline (4.6-10 mg/kg/SC) was inactive. Nicotine (0.32, 1, 3.2 mg/kg/SC) and piracetam (10, 30, 100 mg/kg IP) were also inactive. The alpha 2 agonist, clonidine (46, 100 micrograms/kg SC) and the antagonist idazoxan (32, 100 micrograms/kg SC) were also inactive. Learning deficits were not reversed by haloperidol (20, 60 micrograms/kg), amphetamine (0.1, 0.46 mg/kg), the selective 5-HT1A agonist 8-OH-DPAT (30, 100 micrograms/kg) or by the benzodiazapine antagonist ZK-93426 (1, 3.2, 10 mg/kg). The results show that forebrain Ach depletion by HC-3 impairs spatial discrimination learning and these deficits are reversed by cholinesterase inhibitors and some muscarinic receptor agonists. Some degree of pharmacological selectivity is indicated by the failure of a range of other drugs to reverse the impairments.