Concurrent muscarinic and beta-adrenergic blockade in rats impairs place-learning in a water maze and retention of inhibitory avoidance

Propranolol attenuates the establishment of conditioned context aversions: differential effects compared to MK-801 in an animal model of anticipatory nausea and vomiting

Cancer patients often experience anticipatory nausea and vomiting (ANV) due to Pavlovian conditioning. Both N-methyl-D-aspartate and beta-adrenergic receptors are known to mediate memory formation, but their role in the development of ANV remains unclear. This study used a conditioned context aversion (CCA) paradigm, an animal model for ANV, to assess whether administration of the beta-adrenergic receptor antagonist propranolol or the N-methyl-D-aspartate receptor antagonist MK-801 immediately after CCA training has an effect on the later expression of CCA in CD1 male mice. In experiment 1, three groups were injected with lithium chloride (LiCl) to induce aversion in a novel context, resulting in CCA. A control group was injected with sodium chloride (NaCl). Following conditioning, two of the LiCl-treated groups received different doses of MK-801 (0.05 or 0.2 mg/kg), while the remaining LiCl-treated and NaCl-treated groups received a second NaCl injection. In experiment 2, two groups were injected with LiCl, and one group was injected with NaCl. After conditioning, one of the LiCl-treated groups received a propranolol injection (10 mg/kg). The remaining LiCl-treated and NaCl-treated groups received NaCl injections. Water consumption was measured in all groups 72 h later within the conditioning context. Postconditioning administration of propranolol, but not MK-801, attenuated CCA, as revealed by similar levels of water consumption in animals that received LiCl and propranolol relative to NaCl-treated animals. These findings suggest that beta-adrenergic receptor activation is crucial for the development of CCA. Therefore, propranolol may represent a novel therapeutic approach for cancer patients at high risk of ANV.

Acetylcholine and noradrenaline differentially regulate hippocampus-dependent spatial learning and memory

Severe loss of cholinergic neurons in the basal forebrain nuclei and of noradrenergic neurons in the locus coeruleus are almost invariant histopathological hallmarks of Alzheimer's disease. However, the role of these transmitter systems in the spectrum of cognitive dysfunctions typical of the disease is still unclear, nor is it yet fully known whether do these systems interact and how. Selective ablation of either neuronal population, or both of them combined, were produced in developing animals to investigate their respective and/or concurrent contribution to spatial learning and memory, known to be severely affected in Alzheimer's disease. Single or double lesions were created in 4-8 days old rats by bilateral intraventricular infusion of two selective immunotoxins. At about 16 weeks of age, the animals underwent behavioural tests specifically designed to evaluate reference and working memory abilities, and their brains were later processed for quantitative morphological analyses. Animals with lesion to either system alone showed no significant reference memory deficits which, by contrast, were evident in the double-lesioned subjects. These animals could not adopt an efficient search strategy on a given testing day and were unable to transfer all relevant information to the next day, suggesting deficits in acquisition, storage and/or recall. Only animals with single noradrenergic or double lesions exhibited impaired working memory. Interestingly, ablation of cholinergic afferents to the hippocampus stimulated a robust ingrowth of thick fibres from the superior cervical ganglion which, however, did not appear to have contributed to the observed cognitive performance. Ascending cholinergic and noradrenergic afferents to the hippocampus and neocortex appear to be primarily involved in the regulation of different cognitive domains, but they may functionally interact, mainly at hippocampal level, for sustaining normal learning and memory. Moreover, these transmitter systems are likely to compensate for each other, but apparently not via ingrowing sympathetic fibres.

Neurophysiological contributors to advantageous risk-taking: an experimental psychopharmacological investigation

The ability to learn from experience is critical for determining when to take risks and when to play it safe. However, we know little about how within-person state changes, such as an individual's degree of neurophysiological arousal, may impact the ability to learn which risks are most likely to fail vs succeed. To test this, we used a randomized, double-blind, placebo-controlled design to pharmacologically manipulate neurophysiological arousal and assess its causal impact on risk-related learning and performance. Eighty-seven adults (45% female, Mage = 20.1 ± 1.46 years) took either propranolol (n = 42), a beta-adrenergic receptor blocker that attenuates sympathetic nervous system-related signaling, or a placebo (n = 45). Participants then completed the Balloon Emotional Learning Task, a risk-taking task wherein experiential learning is necessary for task success. We found that individuals on propranolol, relative to placebo, earned fewer points on the task, suggesting that they were less effective risk-takers. This effect was mediated by the fact that those on propranolol made less optimal decisions in the final phase of the task on trials with the greatest opportunity for advantageous risk-taking. These findings highlight that neurophysiological arousal supports risk-related learning and, in turn, more advantageous decision-making and optimal behavior under conditions of risk.

Differential effects of post-training scopolamine on spatial and non-spatial learning tasks in mice

Muscarinic antagonist scopolamine has been extensively used to model amnesia in lab rodents, but most studies have focused on the effects of pre-training scopolamine administration. Here, we examined post-training scopolamine administration in C57BL/6JRj mice. Learning was assessed in three different procedures: odour discrimination in a digging paradigm, visual discrimination in a touchscreen-based setup, and spatial learning in the Morris water maze. Scopolamine administration affected performance in the odour discrimination task. More specifically, scopolamine decreased perseverance, which facilitated reversal learning. Similar results were obtained in the visual discrimination task, but scopolamine did not affect performance in the spatial learning task. It is unlikely that these results can be explained by non-memory-related cognitive effects (e.g., attention), non-cognitive behaviours (e.g., locomotor activity) or peripheral side-effects (e.g., mydriasis). They likely relate to the various neuropharmacological actions of scopolamine.

Complex noradrenergic dysfunction in Alzheimer's disease: Low norepinephrine input is not always to blame

The locus coeruleus-noradrenergic (LC-NA) system supplies the cerebral cortex with norepinephrine, a key modulator of cognition. Neurodegeneration of the LC is an early hallmark of Alzheimer's disease (AD). In this article, we analyze current literature to understand whether NA degeneration in AD simply leads to a loss of norepinephrine input to the cortex. With reported adaptive changes in the LC-NA system at the anatomical, cellular, and molecular levels in AD, existing evidence support a seemingly sustained level of extracellular NE in the cortex, at least at early stages of the long course of AD. We postulate that loss of the integrity of the NA system, rather than mere loss of NE input, is a key contributor to AD pathogenesis. A thorough understanding of NA dysfunction in AD has a large impact on both our comprehension and treatment of this devastating disease.

Noradrenergic dysfunction in Alzheimer's disease

The brain noradrenergic system supplies the neurotransmitter norepinephrine throughout the brain via widespread efferent projections, and plays a pivotal role in modulating cognitive activities in the cortex. Profound noradrenergic degeneration in Alzheimer's disease (AD) patients has been observed for decades, with recent research suggesting that the locus coeruleus (where noradrenergic neurons are mainly located) is a predominant site where AD-related pathology begins. Mounting evidence indicates that the loss of noradrenergic innervation greatly exacerbates AD pathogenesis and progression, although the precise roles of noradrenergic components in AD pathogenesis remain unclear. The aim of this review is to summarize current findings on noradrenergic dysfunction in AD, as well as to point out deficiencies in our knowledge where more research is needed.

Estrogen levels modify scopolamine-induced amnesia in gonadally intact rats

Previous studies suggested that estrogen plays a role in cognitive function by modulating the cholinergic transmission. However, most of the studies dealing with this subject have been conducted using ovariectomized rats. In the present study we evaluated the effects of physiological and supra-physiological variation of estrogen levels on scopolamine-induced amnesia in gonadally intact female rats. We used the plus-maze discriminative avoidance task (PMDAT) in order to evaluate anxiety levels and motor activity concomitantly to the memory performance. In experiment 1, female Wistar rats in each estrous cycle phase received scopolamine (1 mg/kg) or saline i.p. 20 min before the training session in the PMDAT. In experiment 2, rats in diestrus received estradiol valerate (1 mg/kg) or sesame oil i.m., and scopolamine (1 mg/kg) or saline i.p., 45 min and 20 min before the training, respectively. In experiment 3, rats in diestrus received scopolamine (1 mg/kg) or saline i.p. 20 min before the training, and estradiol valerate (1 mg/kg) or sesame oil i.m. immediately after the training session. In all experiments, a test session was performed 24 h later. The main results showed that: (1) scopolamine impaired retrieval and induced anxiolytic and hyperlocomotor effects in all experiments; (2) this cholinergic antagonist impaired acquisition only in animals in diestrus; (3) acute administration of estradiol valerate prevented the learning impairment induced by scopolamine and (4) interfered with memory consolidation process. The results suggest that endogenous variations in estrogen levels across the estrous cycle modulate some aspects of memory mediated by the cholinergic system. Indeed, specifically in diestrus, a stage with low estrogen levels, the impairment produced by scopolamine on the acquisition was counteracted by exogenous administration of the hormone, whereas the posttraining treatment potentiated the negative effects of scopolamine during the consolidation phase of memory.

Systemic vaccination with anti-oligomeric monoclonal antibodies improves cognitive function by reducing Aβ deposition and tau pathology in 3xTg-AD mice

Alzheimer's disease (AD) is a devastating disorder that is clinically characterized by a comprehensive cognitive decline. Accumulation of the amyloid-beta (Aβ) peptide plays a pivotal role in the pathogenesis of AD. In AD, the conversion of Aβ from a physiological soluble monomeric form into insoluble fibrillar conformation is an important event. The most toxic form of Aβ is oligomers, which is the intermediate step during the conversion of monomeric form to fibrillar form. There are at least two types of oligomers: oligomers that are immunologically related to fibrils and those that are not. In transgenic AD animal models, both active and passive anti-Aβ immunotherapies improve cognitive function and clear the parenchymal accumulation of amyloid plaques in the brain. In this report we studied effect of immunotherapy of two sequence-independent non-fibrillar oligomer specific monoclonal antibodies on the cognitive function, amyloid load and tau pathology in 3xTg-AD mice. Anti-oligomeric monoclonal antibodies significantly reduce the amyloid load and improve the cognition. The clearance of amyloid load was significantly correlated with reduced tau hyperphosphorylation and improvement in cognition. These results demonstrate that systemic immunotherapy using oligomer-specific monoclonal antibodies effectively attenuates behavioral and pathological impairments in 3xTg-AD mice. These findings demonstrate the potential of using oligomer specific monoclonal antibodies as a therapeutic approach to prevent and treat Alzheimer's disease.

Nonhuman amyloid oligomer epitope reduces Alzheimer's-like neuropathology in 3xTg-AD transgenic mice

Accumulation of beta-amyloid (Aβ) is an important pathological event in Alzheimer's disease (AD). It is now well known that vaccination against fibrillar Aβ prevents amyloid accumulation and preserves cognitive function in transgenic mouse models. To study the effect of vaccination against generic oligomer epitopes, Aβ oligomers, islet amyloid polypeptide oligomers, random peptide oligomer (3A), and Aβ fibrils were used to vaccinate 3xTg-AD, which develop a progressive accumulation of plaques and cognitive impairment. Subcutaneous administration of these antigens markedly reduced total plaque load (Aβ burden) and improved cognitive function in the 3xTg-AD mouse brains as compared to controls. We demonstrated that vaccination with this nonhuman amyloid oligomer generated high titers of specifically antibodies recognizing Aβ oligomers, which in turn inhibited accumulation of Aβ pathology in mice. In addition to amyloid plaques, another hallmark of AD is tau pathology. It was found that there was a significant decline in the level of hyper-phosphorylated tau following vaccination. We have previously shown that immunization with 3A peptide improves cognitive function and clears amyloid plaques in Tg2576 mice, which provides a novel strategy of AD therapy. Here, we have shown that vaccination with 3A peptide in 3xTg-AD mice not only clears amyloid plaques but also extensively clears abnormal tau in brain.

A double blind, placebo-controlled study of the effects of post-retrieval propranolol on reconsolidation of memory for craving and cue reactivity in cocaine dependent humans

RATIONALE/OBJECTIVES

This study examined the effects of propranolol vs. placebo, administered immediately after a "retrieval" session of cocaine cue exposure (CCE), on craving and physiological responses occurring 24 h later during a subsequent "test" session of CCE. It was hypothesized that compared to placebo-treated cocaine-dependent (CD) individuals, propranolol-treated CD individuals would evidence attenuated craving and physiological reactivity during the test session. Secondarily, it was expected that group differences identified in the test session would be evident at a 1-week follow-up CCE session. Exploratory analyses of treatment effects on cocaine use were also performed at follow-up.

METHODS

CD participants received either 40 mg propranolol or placebo immediately following a "retrieval" CCE session. The next day, participants received a "test" session of CCE that was identical to the "retrieval" session except no medication was administered. Participants underwent a "follow-up" CCE session 1 week later. Craving and other reactivity measures were obtained at multiple time points during the CCE sessions.

RESULTS

Propranolol- vs. placebo-treated participants evidenced significantly greater attenuation of craving and cardiovascular reactivity during the test session. Analysis of the follow-up CCE session data did not reveal any group differences. Although there was no evidence of treatment effects on cocaine use during follow-up, this study was insufficiently powered to rigorously evaluate differential cocaine use.

CONCLUSIONS

This double-blind, placebo-controlled laboratory study provides the first evidence that propranolol administration following CCE may modulate memories for learning processes that subserve cocaine craving/cue reactivity in CD humans. Alternative interpretations of the findings were considered, and implications of the results for treatment were noted.

Targeting plasticity with vagus nerve stimulation to treat neurological disease

Pathological neural activity in a variety of neurological disorders could be treated by directing plasticity to specifically renormalize aberrant neural circuits, thereby restoring normal function. Brief bursts of acetylcholine and norepinephrine can enhance the neural plasticity associated with coincident events. Vagus nerve stimulation (VNS) represents a safe and effective means to trigger the release of these neuromodulators with a high degree of temporal control. VNS-event pairing can generate highly specific and long-lasting plasticity in sensory and motor cortex. Based on the capacity to drive specific changes in neural circuitry, VNS paired with experience has been successful in effectively ameliorating animal models of chronic tinnitus, stroke, and posttraumatic stress disorder. Targeted plasticity therapy utilizing VNS is currently being translated to humans to treat chronic tinnitus and improve motor recovery after stroke. This chapter will discuss the current progress of VNS paired with experience to drive specific plasticity to treat these neurological disorders and will evaluate additional future applications of targeted plasticity therapy.

Vaccination with a non-human random sequence amyloid oligomer mimic results in improved cognitive function and reduced plaque deposition and micro hemorrhage in Tg2576 mice

Background

It is well established that vaccination of humans and transgenic animals against fibrillar Aβ prevents amyloid accumulation in plaques and preserves cognitive function in transgenic mouse models. However, autoimmune side effects have halted the development of vaccines based on full length human Aβ. Further development of an effective vaccine depends on overcoming these side effects while maintaining an effective immune response.

Results

We have previously reported that the immune response to amyloid oligomers is largely directed against generic epitopes that are common to amyloid oligomers of many different proteins and independent of a specific amino acid sequence. Here we have examined whether we can exploit this generic immune response to develop a vaccine that targets amyloid oligomers using a non-human random sequence amyloid oligomer. In order to study the effect of vaccination against generic oligomer epitopes, a random sequence oligomer (3A) was selected as it forms oligomers that react with the oligomer specific A11 antibody. Oligomer mimics from 3A peptide, Aβ, islet amyloid polypeptide (IAPP), and Aβ fibrils were used to vaccinate Tg2576 mice, which develop a progressive accumulation of plaques and cognitive impairment. Vaccination with the 3A random sequence antigen was just as effective as vaccination with the other antigens in improving cognitive function and reducing total plaque load (Aβ burden) in the Tg2576 mouse brains, but was associated with a much lower incidence of micro hemorrhage than Aβ antigens.

Conclusion

These results shows that the amyloid Aβ sequence is not necessary to produce a protective immune response that specifically targets generic amyloid oligomers. Using a non-human, random sequence antigen may facilitate the development of a vaccine that avoids autoimmune side effects.

Glucocorticoid-cholinergic interactions in the dorsal striatum in memory consolidation of inhibitory avoidance training

Extensive evidence indicates that glucocorticoid hormones act in a variety of brain regions to enhance the consolidation of memory of emotionally motivated training experiences. We previously reported that corticosterone, the major glucocorticoid in the rat, administered into the dorsal striatum immediately after inhibitory avoidance training dose-dependently enhances memory consolidation of this training. There is also abundant evidence that the intrinsic cholinergic system of the dorsal striatum is importantly involved in memory consolidation of inhibitory avoidance training. However, it is presently unknown whether these two neuromodulatory systems interact within the dorsal striatum in the formation of long-term memory. To address this issue, we first investigated in male Wistar rats whether the muscarinic receptor agonist oxotremorine administered into the dorsal striatum immediately after inhibitory avoidance training enhances 48 h retention of the training. Subsequently, we examined whether an attenuation of glucocorticoid signaling by either a systemic administration of the corticosterone-synthesis inhibitor metyrapone or an intra-striatal infusion of the glucocorticoid receptor (GR) antagonist RU 38486 would block the memory enhancement induced by oxotremorine. Our findings indicate that oxotremorine dose-dependently enhanced 48 h retention latencies, but that the administration of either metyrapone or RU 38486 prevented the memory-enhancing effect of oxotremorine. In the last experiment, corticosterone was infused into the dorsal striatum together with the muscarinic receptor antagonist scopolamine immediately after inhibitory avoidance training. Scopolamine blocked the enhancing effect of corticosterone on 48 h retention performance. These findings indicate that there are mutual interactions between glucocorticoids and the striatal cholinergic system in enhancing the consolidation of memory of inhibitory avoidance training.

Scopolamine administration modulates muscarinic, nicotinic and NMDA receptor systems

Studies on the effect of scopolamine on memory are abundant but so far only regulation of the muscarinic receptor (M1) has been reported. We hypothesized that levels of other cholinergic brain receptors as the nicotinic receptors and the N-methyl-D-aspartate (NMDA) receptor, known to be involved in memory formation, would be modified by scopolamine administration.

C57BL/6J mice were used for the experiments and divided into four groups. Two groups were given scopolamine 1 mg/kg i.p. (the first group was trained and the second group untrained) in the multiple T-maze (MTM), a paradigm for evaluation of spatial memory. Likewise, vehicle-treated mice were trained or untrained thus serving as controls. Hippocampal levels of M1, nicotinic receptor alpha 4 (Nic4) and 7 (Nic7) and subunit NR1containing complexes were determined by immunoblotting on blue native gel electrophoresis.

Vehicle-treated trained mice learned the task and showed memory retrieval on day 8, while scopolamine-treatment led to significant impairment of performance in the MTM. At the day of retrieval, hippocampal levels for M1, Nic7 and NR1 were higher in the scopolamine treated groups than in vehicle-treated groups.

The concerted action, i.e. the pattern of four brain receptor complexes regulated by the anticholinergic compound scopolamine, is shown. Insight into probable action mechanisms of scopolamine at the brain receptor complex level in the hippocampus is provided. Scopolamine treatment is a standard approach to test cognitive enhancers and other psychoactive compounds in pharmacological studies and therefore knowledge on mechanisms is of pivotal interest.

Stress-dependent impairment of passive-avoidance memory by propranolol or naloxone

Previous work has shown that the effect of opioid-receptor blockade on memory modulation is critically dependent upon the intensity of stress. The current study determined the effect of adrenergic-receptor blockade on memory modulation under varied levels of stress and then compared the effect of adrenergic-receptor blockade under intense stress to that of a) opioid-receptor blockade and b) concurrent opioid- and adrenergic-receptor blockade. In the first experiment, the β-adrenergic-receptor blocker propranolol impaired retention in the passive-avoidance procedure when administered immediately after exposure to intense stress (passive-avoidance training followed by swim stress) but not mild stress (passive-avoidance training alone). In the second experiment, while separate administration of either propranolol or the opioid-receptor blocker naloxone immediately after exposure to intense stress impaired retention, the combined administration of propranolol and naloxone failed to do so. These findings demonstrate that the effect of β-adrenergic-receptor blockade or opioid-receptor blockade on memory modulation in the passive-avoidance procedure is dependent upon the intensity of stress, and suggest that concurrent inactivation of endogenous adrenergic- and opioid-based memory modulation systems under stressful conditions is protective of memory.

Involvement of the cholinergic system in conditioning and perceptual memory

The cholinergic systems play a pivotal role in learning and memory, and have been the centre of attention when it comes to diseases containing cognitive deficits. It is therefore not surprising, that the cholinergic transmitter system has experienced detailed examination of its role in numerous behavioural situations not least with the perspective that cognition may be rescued with appropriate cholinergic 'boosters'. Here we reviewed the literature on (i) cholinergic lesions, (ii) pharmacological intervention of muscarinic or nicotinic system, or (iii) genetic deletion of selective receptor subtypes with respect to sensory discrimination and conditioning procedures. We consider visual, auditory, olfactory and somatosensory processing first before discussing more complex tasks such as startle responses, latent inhibition, negative patterning, eye blink and fear conditioning, and passive avoidance paradigms. An overarching reoccurring theme is that lesions of the cholinergic projection neurones of the basal forebrain impact negatively on acquisition learning in these paradigms and blockade of muscarinic (and to a lesser extent nicotinic) receptors in the target structures produce similar behavioural deficits. While these pertain mainly to impairments in acquisition learning, some rare cases extend to memory consolidation. Such single case observations warranted replication and more in-depth studies. Intriguingly, receptor blockade or receptor gene knockout repeatedly produced contradictory results (for example in fear conditioning) and combined studies, in which genetically altered mice are pharmacological manipulated, are so far missing. However, they are desperately needed to clarify underlying reasons for these contradictions. Consistently, stimulation of either muscarinic (mainly M(1)) or nicotinic (predominantly α7) receptors was beneficial for learning and memory formation across all paradigms supporting the notion that research into the development and mechanisms of novel and better cholinomimetics may prove useful in the treatment of neurodegenerative or psychiatric disorders with cognitive endophenotypes.

Components of lemon essential oil attenuate dementia induced by scopolamine

The anti-dementia effects of s-limonene and s-perillyl alcohol were observed using the passive avoidance test (PA) and the open field habituation test (OFH). These lemon essential oils showed strong ability to improve memory impaired by scopolamine; however, s-perillyl alcohol relieved the deficit of associative memory in PA only, and did not improve non-associative memory significantly in OFH. Analysis of neurotransmitter concentration in some brain regions on the test day showed that dopamine concentration of the vehicle/scopolamine group was significantly lower than that of the vehicle/vehicle group, but this phenomenon was reversed when s-limonene or s-perillyl alcohol were administered before the injection of scopolamine. Simultaneously, we found that these two lemon essential oil components could inhibit acetylcholinesterase activity in vitro using the Ellman method.

Treatment with a C5aR antagonist decreases pathology and enhances behavioral performance in murine models of Alzheimer's disease

Alzheimer's disease (AD) is an age-related dementia, characterized by amyloid plaques, neurofibrillary tangles, neuroinflammation, and neuronal loss in the brain. Components of the complement system, known to produce a local inflammatory reaction, are associated with the plaques and tangles in AD brain, and thus a role for complement-mediated inflammation in the acceleration or progression of disease has been proposed. A complement activation product, C5a, is known to recruit and activate microglia and astrocytes in vitro by activation of a G protein-coupled cell-surface C5aR. Here, oral delivery of a cyclic hexapeptide C5a receptor antagonist (PMX205) for 2-3 mo resulted in substantial reduction of pathological markers such as fibrillar amyloid deposits (49-62%) and activated glia (42-68%) in two mouse models of AD. The reduction in pathology was correlated with improvements in a passive avoidance behavioral task in Tg2576 mice. In 3xTg mice, PMX205 also significantly reduced hyperphosphorylated tau (69%). These data provide the first evidence that inhibition of a proinflammatory receptor-mediated function of the complement cascade (i.e., C5aR) can interfere with neuroinflammation and neurodegeneration in AD rodent models, suggesting a novel therapeutic target for reducing pathology and improving cognitive function in human AD patients.

A dose-response study of the effects of pre-test administration of beta-adrenergic receptor antagonist propranolol on the learning of active place avoidance, a spatial cognition task, in rats

The involvement of various neurotransmitter receptors in the brain in the regulation of spatial behavior is a focus of interest for many cognitive neuroscientists. Active allothetic place avoidance (AAPA) task have been demonstrated to require spatial mapping and cognitive coordination and is highly dependent upon hippocampus. The present study was designed to evaluate the role of beta-adrenergic receptors in the modulation of locomotor and spatial behavior in this task. Four doses of centrally active beta-adrenergic antagonist propranolol (5, 20, 25 and 30 mg/kg) were administered intraperitoneally 30 min prior to testing in the place avoidance task. Four daily sessions were pursued, each lasting 20 min. A dose of 25 mg/kg was found to induce a deficit in spatial behavior (measured by number of entrances into the shock sector) without altering locomotion; lower doses were without effect. The highest dose (30 mg/kg) impaired both locomotion and avoidance behavior. The results suggest that beta-adrenoceptors are involved in the regulation of behavior in the place avoidance task and that it is possible to dissociate the effect of propranolol on the spatial performance and locomotion in the AAPA using dose-selection.

Combined but not individual administration of beta-adrenergic and serotonergic antagonists impairs water maze acquisition in the rat

This study examined the effects of serotonergic depletion and beta-adrenergic antagonism on performance in both visible platform and hidden platform versions of the water maze task. Male Long-Evans rats received systemic injections of p-chlorophenylalanine (500 mg/kg x 2) to deplete serotonin, or propranolol (20 or 40 mg/kg) to antagonize beta-adrenergic receptors. Some rats received treatments in combination. To separate strategies learning from spatial learning, half of the rats underwent Morris' water maze strategies pretraining before drug administration and spatial training. Individual depletion of serotonin or antagonism of beta-adrenergic receptors caused few or no impairments in either naive or pretrained rats in either version of the task. In contrast, combined depletion of serotonin and antagonism of beta-adrenergic receptors impaired naive rats in the visible platform task and impaired both naive and strategies-pretrained rats in the hidden platform task, and also caused sensorimotor impairments. This is the first finding of a 'global' water maze task/sensorimotor impairment with combined administration of two agents that, at the high doses that were given individually, produced few or no impairments. The data imply that (1) serotonergic and beta-adrenergic systems may interact in a manner that is important for adaptive behavior; (2) impairments in these systems found in Alzheimer patients may be important for their cognitive and behavioral impairments; and (3) the approach used here can model aspects of the cognitive and behavioral impairments in Alzheimer disease.

Combined administration of subthreshold doses of the nitric oxide inhibitor, nitro-L-arginine, and muscarinic receptor antagonist, scopolamine, impairs complex maze learning in rats

Traditionally, research into the neurobiological mechanisms of age-related memory impairments has focused on single neurotransmitter systems. As normal and abnormal age-related declines in memory function probably involve alterations in more than one system, a more effective approach for elucidating underlying neurobiological changes and resulting impairments may be to evaluate the roles of multiple systems simultaneously. This study evaluated the interaction of the cholinergic and nitric oxide systems in rats on acquisition in the 14-unit T-maze. This task requires learning a series of turns to avoid foot shock, and most likely reflects procedural learning. Administration of scopolamine (0.1 mg/kg) or N-nitro-L-arginine methyl ester (30 mg/kg) alone did not impair acquisition, whereas administration of the same doses in combination increased both the latency to complete the maze and number of errors committed. These data suggest that manipulation of learning and memory processes with multiple compounds potentially offers a clinically relevant paradigm for investigating cognitive function in normal and abnormal aging.

Hormonal and monoamine signaling during reinforcement of hippocampal long-term potentiation and memory retrieval

Recently it was shown that holeboard training can reinforce, i.e., transform early-LTP into late-LTP in the dentate gyrus during the initial formation of a long-term spatial reference memory in rats. The consolidation of LTP as well as of the reference memory was dependent on protein synthesis. We have now investigated the transmitter systems involved in this reinforcement and found that LTP-consolidation and memory retrieval were dependent on beta-adrenergic, dopaminergic, and mineralocorticoid receptor (MR) activation, whereas glucocorticoid receptors (GRs) were not involved. Blockade of the beta-adrenergic signaling pathway significantly increased the number of reference memory errors compared with MR and dopamine receptor inhibition. In addition, beta-adrenergic blockade impaired the working memory. Therefore, we suggest that beta-adrenergic receptor activation is the main signaling system required for the retrieval of spatial memory. In addition, other modulatory interactions such as dopaminergic as well as MR systems are involved. This result points to specific roles of different modulatory systems during the retrieval of specific components of spatial memory. The data provide evidence for similar integrative interactions between different signaling systems during cellular memory processes.

NMDA receptor antagonists antagonize the facilitatory effects of post-training intra-basolateral amygdala NMDA and physostigmine on passive avoidance learning

In the present study, the effects of post-training intra-basolateral amygdala (BLA) injection of an N-methyl-d-aspartate (NMDA) receptor agonist and competitive or noncompetitive antagonists, on memory retention of passive avoidance learning was measured in the presence and absence of physostigmine in rats. Intra-BLA administration of lower doses of NMDA (10(-5) and 10(-4) microg/rat) did not affect memory retention, although higher doses of the drug (10(-3), 10(-2) and 10(-1) microg/rat) increased memory retention. The greatest response was obtained with 10(-1) microg/rat of the drug. The different doses of the competitive NMDA receptor antagonist DL-AP5 (1, 3.2 and 10 microg/rat) and noncompetitive NMDA receptor antagonist MK-801 (0.5, 1 and 2 microg/rat) decreased memory retention in rats dose dependently. Both competitive and noncompetitive NMDA receptor antagonists reduced the effect of NMDA (10(-2) microg/rat). In another series of experiments, intra-BLA injection of physostigmine (2, 3 and 4 microg/rat) improved memory retention. Post-training co-administration of lower doses of NMDA (10(-5) and 10(-4) microg/rat) and physostigmine (1 microg/rat), doses which were ineffective when given alone, significantly improved the retention latency. The competitive and noncompetitive NMDA receptor antagonists, DL-AP5 and MK-801, decreased the effect of physostigmine (2 microg/rat). Atropine decreased memory retention by itself and potentiated the response to DL-AP5 and MK-801. It may be concluded that amygdalar NMDA receptor mechanisms interact with cholinergic systems in the modulation of memory.

Effects of Galantamine, a Nicotinic Allosteric Potentiating Ligand, on Nicotine-Induced Catecholamine Release in Hippocampus and Nucleus Accumbens of Rats

Galantamine, a drug for treatment of Alzheimer's disease, is a novel cholinergic agent with a dual mode of action that inhibits acetylcholinesterase and allosterically modulates nicotinic cholinergic receptors (nAChRs). Nicotine stimulates catecholamine secretion, inducing hippocampal norepinephrine (NE) release, and improves memory consolidation. Thus, the effect of galantamine on nicotine-induced hippocampal NE secretion was investigated. This was compared with the effect of galantamine on nicotine-induced dopamine (DA) release within the nucleus accumbens of the same rat. Nicotine (0.025-0.09 mg/kg i.v.) dose dependently increased NE and DA levels in microdialysates from the hippocampus and nucleus accumbens, respectively, of freely moving rats. Pretreatment with galantamine (3.0 mg/kg s.c.) 3 h before nicotine either potentiated NE responses to doses of nicotine that were ineffective alone (0.025-0.045 mg/kg) or significantly enhanced (0.065 mg/kg) NE responses, whereas galantamine was ineffective when administered 2 or 4 h before nicotine. In contrast to its effects on NE, galantamine did not alter accumbal DA responses to any dose of nicotine. These selective effects of galantamine on nicotine-stimulated NE secretion may reflect differences in local neural circuits that use nAChRs to modulate hippocampal NE versus accumbal DA release.

Enhanced retention in the passive-avoidance task by 5-HT(1A) receptor blockade is not associated with increased activity of the central nucleus of the amygdala

The effect of blockade of 5-HT1A receptors was investigated on (1). retention in a mildly aversive passive-avoidance task, and (2). spontaneous single-unit activity of central nucleus of the amygdala (CeA) neurons, a brain site implicated in modulation of retention. Systemic administration of the selective 5-HT1A antagonist NAN-190 immediately after training markedly-and dose-dependently-facilitated retention in the passive-avoidance task; enhanced retention was time-dependent and was not attributable to variations in wattages of shock received by animals. Systemic administration of NAN-190 had mixed effects on spontaneous single-unit activity of CeA neurons recorded extracellularly in vivo; microiontophoretic application of 5-HT, in contrast, consistently and potently suppressed CeA activity. The present findings-that 5-HT1A receptor blockade by NAN-190 (1). enhances retention in the passive-avoidance task, and (2). does not consistently increase spontaneous neuronal activity of the CeA-provide evidence that a serotonergic system tonically inhibits modulation of retention in the passive-avoidance task through activation of the 5-HT1A receptor subtype at brain sites located outside the CeA.

Combined beta-adrenergic and cholinergic antagonism produces behavioral and cognitive impairments in the water maze: implications for Alzheimer disease and pharmacotherapy with beta-adrenergic antagonists

This study examined the effects of beta-adrenergic and muscarinic blockade on spatial learning and strategy use in the water maze. Male Long-Evans rats received systemic injections of propranolol (PRO; 10 or 20 mg/kg) or scopolamine (SCO; 0.3 or 1.0 mg/kg) either singly or in combination. To separate strategies learning from spatial learning approximately half of the rats underwent water maze strategies pretraining prior to drug administration and spatial training. PRO did not impair performance in any group. SCO impaired naive but not pretrained rats. PRO and SCO given together in high doses impaired all aspects of behavior in both naive and pretrained rats, and caused sensorimotor disturbances in some groups. PRO (10 mg/kg) and SCO (0.3 mg/kg) together caused a specific spatial reversal learning impairment in pretrained rats without causing strategies impairments or sensorimotor disturbances. Nadolol administered with SCO failed to produce the same impairments as PRO, suggesting that PRO produced its effects by acting on central nervous system sites. These results point to a greater than additive impairing effect of PRO and SCO on adaptive behavior, and a specific role for beta-adrenergic and cholinergic systems working in conjunction in spatial learning. They also suggest that some of the behavioral and cognitive impairments seen in Alzheimer patients or patients receiving pharmacotherapy with beta-adrenergic antagonists in which cholinergic activity is also compromised may result from the combined impairment of beta-adrenergic and cholinergic systems.

Differential involvement of nucleus accumbens shell and core subregions in maternal memory in postpartum female rats

Maternal memory refers to the long-term retention of maternal responsiveness as a consequence of animals' prior experiences with their young. This study examined the relative roles of 2 subregions of the nucleus accumbens (NA; shell and core) in maternal memory in rats. NA shell lesions either before or immediately after a short experience significantly disrupted maternal memory, but lesions after a 24-hr maternal experience had no effect. NA core lesions had no significant impact on maternal memory. Cycloheximide (a protein synthesis inhibitor) at a high dose (25 micrograms/microliter) infused in the NA shell immediately after 1 hr of maternal experience also significantly disrupted maternal memory, whereas infusions in the medial preoptic area had no effect. It was concluded that the NA shell, but not the NA core, is involved in the consolidation of maternal memory.

Serotonin, locomotion, exploration, and place recall in the rat

Intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT) led to a 90% reduction of the 5-hydroxytryptamine (5-HT) reuptake site. Behavioural symptoms were studied early (45 to 93 h) as well as late (11 to 14 days) in the postoperative period. Forty-five hours postoperatively, recall of a place navigation task in a water maze was clearly impaired in 5,7-DHT-treated animals. This impairment had disappeared by the fifth postoperative session. During the early test period, injection of scopolamine (0.5 mg/kg) or d-amphetamine (3.0 mg/kg) did not affect place recall of the vehicle-treated control group. In contrast, 5,7-DHT-treated animals were impaired by administration of scopolamine, but not d-amphetamine. During the late test period, the place recall of both groups was affected by scopolamine, but only the performance of the 5,7-DHT lesioned animals was sensitive to d-amphetamine. Locomotion was not severely affected at any time after 5,7-DHT treatment. The vertical hole-board test indicated that the exploratory activities of the animals were relatively unaffected by 5,7-DHT when measured 48 h postoperatively. At 14 days postsurgery, the 5,7-DHT-treated animals demonstrated an impaired habituation of the exploratory behaviour.

Cholinergic modulation of memory in the basolateral amygdala involves activation of both m1 and m2 receptors

Muscarinic cholinergic activation is a critical component of basolateral amygdala (BLA)-mediated modulation of memory consolidation. The receptor(s) mediating this activation during consolidation have not been elucidated. This study investigated the roles of muscarinic subtype 1 (m1) and subtype 2 (m2) receptors in memory enhancement, by post-training intra-BLA infusions of the non-selective muscarinic agonist oxotremorine. Rats received intra-BLA infusions of either oxotremorine alone (10 microg in 0.2 microl per side), oxotremorine together with the selective m1 antagonist telenzipine (1.7, 5.0, 17 or 50 nmol/side), oxotremorine with the selective m2 antagonist methoctramine (1.7, 5.0, 17 or 50 nmol/side), oxotremorine with a combination of the above doses of telenzipine and methoctramine, or only vehicle, immediately after inhibitory avoidance training. Performance on a 48-hour retention test was significantly enhanced in oxotremorine-treated rats relative to vehicle-infused controls. Intra-BLA co-infusion of oxotremorine with either telenzipine (5, 17 or 50 nmol/side) or methoctramine (17 or 50 nmol/side) blocked the oxotremorine-induced enhancement. Combinations of these antagonists did not act additively to block memory enhancement by oxotremorine. These findings indicate that modulation of memory consolidation induced by cholinergic influences within the BLA requires activation of both m1 and m2 receptor synapses. Plausible mechanisms for m1- and m2-mediated influences on BLA circuitry are discussed.

Phthalic acid amygdalopetal lesion of the nucleus basalis magnocellularis induces reversible memory deficits in rats

The basolateral amygdala (BLA) is extensively implicated in emotional learning and memory. The current study investigated the contribution of cholinergic afferents to the BLA from the nucleus basalis magnocellularis in influencing aversive learning and memory. Sprague-Dawley rats were given permanent unilateral phthalic acid (300 ng) lesions of the nucleus basalis magnocellularis and were chronically implanted with cannulas aimed at the ipsilateral BLA. Lesioned rats showed a pronounced inhibitory avoidance task retention deficit that was attenuated by acute posttraining infusions of the muscarinic cholinergic agonist oxotremorine (4 ng) or the indirect agonist physostigmine (1 microg) into the BLA. Continuous multiple-trial inhibitory avoidance training and testing revealed that lesioned rats have a mild acquisition deficit, requiring approximately 1 additional shock to reach the criterion, and a pronounced consolidation deficit as indicated by a shorter latency to enter the shock compartment on the retention test. Because lesioned rats did not differ from sham-operated controls in performance on a spatial water maze task or in shock sensitivity, it is not likely that the memory impairments produced by the phthalic acid lesions are due to any general sensory or motor deficits. These findings suggest that the dense cholinergic projection from the nucleus basalis magnocellularis to the BLA is involved in both the acquisition and the consolidation of the aversive inhibitory avoidance task.

Light and electron microscopic study of cholinergic and noradrenergic elements in the basolateral nucleus of the rat amygdala: evidence for interactions between the two systems

Pharmacological studies have suggested that the cholinergic (ACh) and noradrenergic (NA) systems in the amygdala (AM) play an important role in learning and memory storage and that the two systems interact to modulate memory storage. To obtain anatomical evidence for the interaction, the organization of the ACh and NA fibers in rat AM was investigated by immunocytochemistry for choline acetyltransferase (ChAT) and dopamine-beta-hydroxylase (DBH) in conjunction with light, confocal laser scanning, and electron microscopy (LM, CLSM, and TEM, respectively). LM showed that the ChAT immunoreactivity was densest in the basolateral nucleus (BL), whereas the DBH immunoreactivity was densest in the posterior BL. CLSM demonstrated that the ChAT-immunoreactive profiles in the BL were frequently located in juxtaposition to the DBH-immunoreactive axons. The TEM observations were as follows: The majority of the synapses formed by ChAT-immunoreactive terminals were symmetric, but DBH-immunoreactive axons formed both asymmetric and symmetric synapses. The ChAT-immunoreactive terminals usually established the symmetric synaptic contacts with the DBH-immunoreactive terminals and varicosities. The DBH-immunoreactive terminals formed the asymmetric synapses with the ChAT-immunoreactive dendrites of the intrinsic neurons within the AM. The results provide anatomical substrates for mnemonic functions of the ACh and NA systems and for the interactions between the two systems in the AM.

Impaired memory consolidation in rats produced with beta-adrenergic blockade

Despite abundant evidence that systemic administration of adrenergic drugs and hormones can produce retrograde memory enhancement, the literature contains no clear demonstration that postlearning systemic administration of adrenergic antagonists produces retrograde amnesia. Here we demonstrate retrograde amnesia for a stressful learning task (a spatial water maze) with systemic administration of the beta-adrenergic antagonist propranolol (5 mg/kg). The amnesic effect of the drug depended on the degree of learning in the subjects: Propranolol caused a robust retrograde amnesia in "good learners," but did not significantly affect memory in "poor learners." The findings provide critical additional support for the hypothesis that postlearning adrenergic activation modulates memory consolidation processes after emotionally stressful events and help explain previous failures to detect memory impairment after systemic administration of adrenergic blocking drugs.

Glucocorticoid enhancement of memory consolidation in the rat is blocked by muscarinic receptor antagonism in the basolateral amygdala

Glucocorticoid-induced memory enhancement is known to depend on beta-adrenoceptor activation in the basolateral amygdala (BLA). Additionally, inactivation of muscarinic cholinergic receptors in the rat amygdala blocks memory enhancement induced by concurrent beta-adrenergic activation. Together, these findings suggest that glucocorticoid-induced modulation of memory consolidation requires cholinergic as well as adrenergic activation in the BLA. Two experiments investigated this issue. The first experiment examined whether blockade of muscarinic cholinergic receptors in the BLA with atropine alters the memory-enhancing effects of the systemically administered glucocorticoid dexamethasone. Dexamethasone (0.3, 1.0 or 3.0 mg/kg, s.c.) administered to rats immediately after inhibitory avoidance training produced dose-dependent enhancement of 48-h retention. Concurrent bilateral infusions of the muscarinic cholinergic antagonist atropine (0.5 microg in 0.2 microL per side) into the BLA blocked the memory enhancement. The second experiment investigated whether the BLA is a locus of interaction between glucocorticoid and muscarinic activation. The specific glucocorticoid receptor (GR or type II) agonist RU 28362 (1.0, 3.0 or 10 ng) was infused into the BLA either alone or together with atropine immediately after training. The GR agonist produced dose-dependent memory enhancement and atropine blocked the memory enhancement. These findings indicate that muscarinic cholinergic activation within the BLA is critical for enabling glucocorticoid enhancement of memory consolidation and that enhancement of memory induced by GR activation in the BLA requires cholinergic activation within the BLA.

Coactivation of beta-adrenergic and cholinergic receptors enhances the induction of long-term potentiation and synergistically activates mitogen-activated protein kinase in the hippocampal CA1 region

Interactions between noradrenergic and cholinergic receptor signaling may be important in some forms of learning. To investigate whether noradrenergic and cholinergic receptor interactions regulate forms of synaptic plasticity thought to be involved in memory formation, we examined the effects of concurrent beta-adrenergic and cholinergic receptor activation on the induction of long-term potentiation (LTP) in the hippocampal CA1 region. Low concentrations of the beta-adrenergic receptor agonist isoproterenol (ISO) and the cholinergic receptor agonist carbachol had no effect on the induction of LTP by a brief train of 5 Hz stimulation when applied individually but dramatically facilitated LTP induction when coapplied. Although carbachol did not enhance ISO-induced increases in cAMP, coapplication of ISO and carbachol synergistically activated p42 mitogen-activated protein kinase (p42 MAPK). This suggests that concurrent beta-adrenergic and cholinergic receptor activation enhances LTP induction by activating MAPK and not by additive or synergistic effects on adenylyl cyclase. Consistent with this, blocking MAPK activation with MEK inhibitors suppressed the facilitation of LTP induction produced by concurrent beta-adrenergic and cholinergic receptor activation. Although MEK inhibitors also suppressed the induction of LTP by a stronger 5 Hz stimulation protocol that induced LTP in the absence of ISO and carbachol, they had no effect on LTP induced by high-frequency synaptic stimulation or low-frequency synaptic stimulation paired with postsynaptic depolarization. Our results indicate that MAPK activation has an important, modulatory role in the induction of LTP and suggest that coactivation of noradrenergic and cholinergic receptors regulates LTP induction via convergent effects on MAPK.

Chronic propranolol induces deficits in retention but not acquisition performance in the water maze in mice

Agents that alter adrenergic receptors, such as "beta-blockers," also alter memory storage. However, reports suggest that beta-adrenergic receptor antagonists, such as propranolol, have conflicting behavioral effects with acute vs chronic dosing. This study was designed to evaluate the effects of chronic propranolol on retention for a spatial learning task. Adult male ICR mice were given daily injections of propranolol (2, 4, 8, or 12 mg/kg ip) or 0. 9% NaCl for 15 days prior to, and during, trials in a Morris water maze. Mice received five massed acquisition (escape) trials in each of three daily sessions, followed by a single 60-s probe trial on the fourth day. The location of the submerged platform was constant for each animal over acquisition trials, but varied across animals; starting position varied across trials. A 5 (dose) x 3 (trial blocks) mixed factorial ANOVA for escape time yielded a significant trial blocks effect only (p <.001), showing performance improving over sessions. Time spent in the target quadrant on the probe trial was shorter under all doses of propranolol when compared to vehicle group (all p <.001), indicating poorer retention of prior platform location. This effect, however, was not dose-related. Swim speed was not significantly affected by propranolol. These data demonstrate that chronic dosing with propranolol can impair retention of spatial learning, which cannot be attributed to reduced arousal or motor function.

Effects of D-cycloserine, a positive modulator of N-methyl-D-aspartate receptors, and ST 587, a putative alpha-1 adrenergic agonist, individually and in combination, on the non-delayed and delayed foraging behaviour of rats assessed in the radial arm maze

The present study investigated whether alpha-1 adrenergic and glutamatergic N-methyl-D-aspartate (NMDA) receptor-mediated mechanisms interact in memory processes, by examining the effects of individual and combined systemic administration of ST 587, a putative alpha-1 agonist, and D-cycloserine (DCS), a partial agonist at the glycine-B binding site of the NMDA receptor, on the performance of rats in non-delayed and delayed (4-6 h) foraging behaviour in the radial arm maze task, using the delayed non-matching to sample (DNMTS) version. The results indicated that DCS (5.0 mg/kg) decreased working memory errors, i.e. the number of re-entries into the previously visited arms during the sampling phase. In addition, both ST 587 (100 microg/kg) and DCS (10 mg/kg), when administered alone 30 min before a sampling phase, improved retention of this task as reflected by the increased number of correct choices before the first error during the retention phase. The combined administration of ST 587 and DCS, however, did not lead to better retention in the DNMTS task compared with the administration of each of the drugs alone. Combinations of sub-threshold doses of ST 587 (50 or 75 microg/kg) and DCS (5.0 or 7.5 mg/kg) also did not improve retention in this task. DCS (5.0 or 7.5 mg/kg) increased activity as indicated by the increased number of arm entries in a given time during the sampling phase. These findings suggest that the systemic administration of a positive modulator of the NMDA receptor facilitates hippocampal-dependent memory functions, but that these effects are not enhanced by combined administration with an alpha-1 agonist, even though the alpha-1 agonist is effective when given alone. The results support the idea that NMDA receptors modulate both mnemonic and non-mnemonic functions in the brain.

Central alpha1-adrenoceptors: their role in the modulation of attention and memory formation

Adrenoceptors presently are classified into three main subclasses: alpha1-, alpha2-, and beta-receptors, each with three (perhaps more) subtypes. All three alpha1-adrenoceptor subtypes are present in rat brain. The purpose of this review is to assess the role of alpha1-adrenoceptors in the modulation of synaptic transmission and plasticity, as well as their ability to modulate higher cerebral functions, such as attentional and memory processes. However, since there are no truly subtype-specific agonists or antagonists available at present, it is virtually impossible to allocate a particular central effect to one or other of the subtypes. The activation of alpha1-adrenoceptors reduces the firing probability and glutamate release in the cornu ammonis of the hippocampus. Alpha1-Adrenoceptors may flexibly modulate weak and strong activation of the pyramidal neurones in the neocortex. Alpha1-Adrenoceptors play only a minor role in the modulation of long-term potentiation in the hippocampus, and may influence many brain functions also via non-neuronal mechanisms. since glial cells can express alpha1-adrenoceptors. At the behavioural level, the activation of alpha1-adrenoceptors promotes vigilance and influences working memory and behavioural activation, while having only a minor role in the modulation of long-term memory.

Role of vasopressin in learning and memory in the hippocampus

The involvement of arginine8-vasopressin (VP) in learning and memory in the hippocampus is examined in mice using a discriminative learning task. Bilateral dorsal hippocampal lesion blocks the enhancing effect of intracerebroventricular (i.c.v.) injection of VP on retrieval and relearning processes. An additional study showed that immunoneutralization of dorsal hippocampal endogenous VP inhibited the facilitating effect of i.c.v. injection of VP, suggesting that hippocampus is essential for the expression of VP's behavioral effects. Using in situ microinjection, a greater sensitivity of the ventral part of the hippocampus to the memory enhancing effects of VP has been reported. This effect is mediated by vasopressin V1 type receptors and oxytocin receptors. Then, we examined the effects on behavior of VP applied to the ventral hippocampus, in relation to the time of treatment during learning. When the animals have no previous information about the task to learn, a deleterious effect of VP appears (pre-first session treatment). Regarding memory consolidation, the effects of VP may depend upon the previous level of performance acquired by the animals since, when injected after the first learning session, the peptide slightly delayed performance, whereas when the injection took place after the second learning session, it enhanced learning. Concerning memory retrieval, the effects of VP depend on the quality of the previously stored information. The fact that VP did not generate the same behavioral effects when the treatment was performed at the beginning or in the middle of the learning processes, suggests that mnemonic context is an important factor in understanding the effect of VP on memory in the ventral hippocampus. Finally, the role of hippocampal adrenergic receptors in the enhancing VP effects on memory retrieval has been examined. The facilitatory effects of VP seem to depend upon the functional state of both alpha- and beta-adrenergic receptors, but further studies will be necessary to clarify the role played by each receptor type in retrieval processes, and to determine the relationships that might exist between them.

Chronic administration of propranolol impairs inhibitory avoidance retention in mice

Adrenergic systems are importantly involved in memory storage processes. As such, agents that alter adrenergic receptors, such as "beta-blockers," also alter memory storage. However, the anxiety literature cautions that beta-adrenergic receptor antagonists, such as propranolol, may have different behavioral effects with acute vs chronic dosing. The effects of chronic propranolol specifically on memory modulation are unknown. This study was designed to evaluate the effects of chronic propranolol on retention for an aversive task, in which there is endogenous adrenergic activation. Adult male ICR mice were given daily injections of one of four doses of propranolol (2, 4, 8, and 12 mg/kg) or 0.9% NaCl vehicle for 15 days prior to, and continuing during, behavioral tests of exploration and retention. Exploratory behavior, as an index of anxiety level, was measured in a conventional elevated plus-maze, whereas retention of an aversive experience was measured in a step-through inhibitory avoidance apparatus. Sensitivity to aversive footshock was also evaluated. Compared to controls, propranolol-treated mice showed a dose-dependent decrease in retention for the inhibitory avoidance task, but no effect on anxiety on the plus-maze or on footshock sensitivity. Taken together with results from previous studies, it is apparent that propranolol can have different behavioral effects when administered acutely vs chronically, and its chronic effects significantly impair memory storage processes. Since these drugs are typically used chronically, and often in older adults, they could contribute to functional memory impairments.

The effects of T-588, a novel cognitive enhancer, on noradrenaline uptake and release in rat cerebral cortical slices

Previously, we reported that (R)-(-)-1-(benzo[b]thiophen-5-yl)-2-[2-(N,N-diethylamino)-ethoxy]e thanol hydrochloride (T-588), a novel cognitive enhancer, stimulated noradrenaline (NA) release from rat cerebral cortical slices. In this study, we investigated the effects of T-588 on NA uptake and release, compared to the effects of desipramine, a blocker of the NA carrier on the plasma membrane. Both T-588 and desipramine caused dose-dependent inhibition of [3H]NA uptake into the slices. Addition of 3 mM T-588 stimulated [3H]NA release from the prelabeled slices even in the presence of 10 microM desipramine, which inhibited NA uptake completely. Tyramine, which accelerates NA carrier-mediated release, also stimulated [3H]NA release, and tyramine-stimulated release was inhibited by desipramine. These findings indicated that T-588-stimulated NA release was not mediated by 1) inhibition of reuptake or 2) reverse transport mediated by NA carriers. Reserpine, which interacts with the intracellular vesicular transport system, increased [3H]NA efflux from slices. High K+-, not T-588-, stimulated [3H]NA release was shifted upward by reserpine. These findings suggest that T-588 evokes NA release by a mechanism similar to that induced by reserpine. T-588 might act as a cognitive enhancer via neurotransmitter release in the brain.

Stimulation of alpha-1 adrenergic receptors facilitates spatial learning in rats

The present experiments were designed to examine the effects of alpha-1 adrenergic stimulation and inhibition on memory encoding and to investigate whether the alpha-1 adrenergic and muscarinic cholinergic systems interact in the regulation of spatial navigation behavior in the Morris water maze test and we also studied the effects of D-cycloserine, a partial agonist at the glycine binding site on the N-methyl-D-aspartate (NMDA) receptor complex, on the performance of scopolamine-treated rats in this task. Pre-training subcutaneous administration of St-587 (a putative alpha-1 agonist) at 1000 micrograms kg-1 or 1500 micrograms kg-1 improved water maze navigation to a hidden platform. Prazosin (an alpha-1 antagonist), 300-2000 micrograms kg-1, did not significantly impair the spatial navigation performance. Pre-training administration of prazosin 1000 micrograms kg-1, but not 300 micrograms kg-1, slightly potentiated the deficit in water maze navigation seen after scopolamine (200 micrograms kg-1, pre-training intraperitoneal injection). Pre-training administration of St-587 at a dose 1500 micrograms kg-1, but not 500 micrograms kg-1, slightly ameliorated the scopolamine-induced (200 micrograms kg-1) impairment in performance of rats. Pre-training administration of prazosin at doses 300 or 1000 micrograms kg-1 or St-587 at doses 500 micrograms kg-1 or 1500 micrograms kg-1 did not have any significant influence on the scopolamine-induced (200 micrograms kg-1) increase of swimming speed. Furthermore, D-cycloserine at the dose of 300 micrograms kg-1 but not 1000 or 3000 micrograms kg-1 reversed the scopolamine (200 micrograms kg-1)-induced deficit in acquisition of the water maze task but not the increase in motor output (increased swimming speed). These results indicate that the stimulation of alpha-1 adrenoceptors may facilitate the encoding of new information. These findings suggest that alpha-1 adrenergic mechanisms do not participate or at least are not the most critical part of the noradrenergic system in the interaction between noradrenaline and muscarinic receptors in the modulation of learning and memory. In addition, these results suggest that D-cycloserine may be effective in alleviating states of central cholinergic hypofunction.

Minor role for alpha1-adrenoceptors in the facilitation of induction and early maintenance of long-term potentiation in the CA1 field of the hippocampus

The influences of noradrenaline on the modulation of learning and memory functions, as well as synaptic plasticity, e.g., long-term potentiation (LTP), via beta-adrenoceptors are well documented, whereas the role of alpha1-adrenoceptors has not been studied extensively. Therefore, the effects of alpha1-agonists (ST 587 and methoxamine) on the induction of LTP were examined in the CA1 area of the hippocampus in vitro. Submaximal LTP in extracellular excitatory postsynaptic potentials (EPSP) was induced with theta burst stimulation using 4 bursts. The effects of a beta-agonist, isoproterenol, on synaptic potentiation were studied as a comparison in this preparation. At a concentration of 1 microM, ST 587 slightly increased the magnitude of potentiation in EPSPs (measured 30 min after stimulation) compared to a control pathway potentiated 30 min before drug infusion, whereas a lower concentration (0.3 microM) was not effective. Methoxamine did not induce any increase in the amount of submaximal LTP at concentrations of 0.3, 1.0, or 3.0 microM. Isoproterenol (1.5 microM) increased the amount of LTP when measured 30 min after stimulation, and also transiently increased synaptic transmission, measured both in the slope and amplitude of the field EPSP in the prepotentiated control pathway. Thus, the present results indicate that (1) alpha1-adrenoceptors have only a minor role in hippocampal synaptic plasticity in the CA1 area, but (2) the synaptic plasticity in the CA1 area of the hippocampus assessed by induction and early maintenance of LTP in vitro can be modulated through beta-adrenoceptors.

Epinephrine effects on memory are not dependent on hepatic glucose release

Epinephrine released or administered soon after a given training task modulates memory processes. Since epinephrine does not readily cross the blood-brain barrier, studies have suggested that some of the central effects of epinephrine might be mediated by peripheral release of glucose. These experiments examined the involvement of blood glucose levels in the posttraining effects of peripherally administered epinephrine. The effects of the administration of epinephrine (25 and 625 microg/kg) [corrected] on memory of an inhibitory avoidance task were evaluated in fed and fasted rats (depleted glycogen stores in liver). Blood glucose levels after the task in each group were also measured. Female Wistar rats were divided in two groups. Fed and 48-h-fasted animals were submitted to the inhibitory avoidance task and received i.p. epinephrine or saline immediately after training. The test session was carried out 48 h after training. Epinephrine (25 or 625 microg/kg) [corrected] caused an increased glycemia in fed rats, but no effect was observed in fasted animals. Administration of epinephrine 25 microg/kg [corrected] induced a facilitation of memory, while epinephrine 625 microg/kg [corrected] impaired retention (either in fasted or in fed animals). There was no relation between increased glycemia induced by epinephrine and its effects on memory, since this drug presented its classical effects independently of the previous state of the animal (fed or fasted). The results of the present study suggest that the effects of systemic released or administered epinephrine on memory processes are not dependent on hepatic glucose release.

Noradrenergic suppression of synaptic transmission may influence cortical signal-to-noise ratio

Norepinephrine has been proposed to influence signal-to-noise ratio within cortical structures, but the exact cellular mechanisms underlying this influence have not been described in detail. Here we present data on a cellular effect of norepinephrine that could contribute to the influence on signal-to-noise ratio. In brain slice preparations of the rat piriform (olfactory) cortex, perfusion of norepinephrine causes a dose-dependent suppression of excitatory synaptic potentials in the layer containing synapses among pyramidal cells in the cortex (layer Ib), while having a weaker effect on synaptic potentials in the afferent fiber layer (layer Ia). Effects of norepinephrine were similar in dose-response characteristics and laminar selectivity to the effects of the cholinergic agonist carbachol, and combined perfusion of both agonists caused effects similar to an equivalent concentration of a single agonist. In a computational model of the piriform cortex, we have analyzed the effect of noradrenergic suppression of synaptic transmission on signal-to-noise ratio. The selective suppression of excitatory intrinsic connectivity decreases the background activity of modeled neurons relative to the activity of neurons receiving direct afferent input. This can be interpreted as an increase in signal-to-noise ratio, but the term noise does not accurately characterize activity dependent on the intrinsic spread of excitation, which would more accurately be described as interpretation or retrieval. Increases in levels of norepinephrine mediated by locus coeruleus activity appear to enhance the influence of extrinsic input on cortical representations, allowing a pulse of norepinephrine in an arousing context to mediate formation of memories with a strong influence of environmental variables.

Working memory failure by combined blockade of muscarinic and beta-adrenergic transmission in the rat hippocampus

INTRAHIPPOCAMPAL administration of the muscarinic acetylcholine receptor antagonist scopolamine at a dose of 3.2 micrograms/side significantly increased the number of errors (attempts to pass through two incorrect panels of the three panel-gates at four choice points) in the working memory task with a three-panel runway setup, whereas 0.32 microgram/side scopolamine did not affect working memory errors. The beta-adrenoceptor antagonist propranolol (10 mg/kg, i.p.) had no effect on working memory error, but it produced a significant increase in working memory errors when administered in combination with intrahippocampal scopolamine at the behaviourally ineffective dose (0.32 microgram/side). The increase in working memory errors induced by intrahippocampal administration of 0.32 microgram/side scopolamine to rats treated with 10 mg/kg propranolol was decreased by concurrent injection of the cholinesterase inhibitor physostigmine (3.2 micrograms/side). D-Cycloserine (the partial agonist at the glycine bindings site on the NMDA receptor/channel complex) at a dose of 10 micrograms/side reduced the increase in working memory errors induced by intrahippocampal 0.32 microgram/side scopolamine combined with 10 mg/kg propranolol. These results suggest that neural mechanisms regulated cooperatively by hippocampal muscarinic and beta-adrenergic transmission underlie working memory performance, and that modification of NMDA function contributes to such interactive regulation of working memory processes in the hippocampus.