Effect of cholinergic neurotransmission modulation on visual spatial paired associate learning in healthy human adults

The Granular Retrosplenial Cortex Is Necessary in Male Rats for Object-Location Associative Learning and Memory, But Not Spatial Working Memory or Visual Discrimination and Reversal, in the Touchscreen Operant Chamber

The retrosplenial cortex (RSC) is a hub of diverse afferent and efferent projections thought to be involved in associative learning. RSC shows early pathology in mild cognitive impairment and Alzheimer's disease (AD), which impairs associative learning. To understand and develop therapies for diseases such as AD, animal models are essential. Given the importance of human RSC in object-location associative learning and the success of object-location associative paradigms in human studies and in the clinic, it would be of considerable value to establish a translational model of object-location learning for the rodent. For this reason, we sought to test the role of RSC in object-location learning in male rats using the object-location paired-associates learning (PAL) touchscreen task. First, increased cFos immunoreactivity was observed in granular RSC following PAL training when compared with extended pretraining controls. Following this, RSC lesions following PAL acquisition were used to explore the necessity of the RSC in object-location associative learning and memory and two tasks involving only one modality: trial-unique nonmatching-to-location for spatial working memory and pairwise visual discrimination/reversal. RSC lesions impaired both memory for learned paired-associates and learning of new object-location associations but did not affect performance in either the spatial or visual single-modality tasks. These findings provide evidence that RSC is necessary for object-location learning and less so for learning and memory involving the individual modalities therein.

Back to the Future of Neuropsychopharmacology

Disappointments in translating preclinical findings into clinical efficacy have triggered a number of changes in neuroscience drug discovery ranging from investments diverted to other therapeutic areas to reduced reliance on efficacy claims derived from preclinical models. In this chapter, we argue that there are several existing examples that teach us on what needs to be done to improve the success rate. We advocate the reverse engineering approach that shifts the focus from preclinical efforts to "model" human disease states to pharmacodynamic activity as a common denominator in the journey to translate clinically validated phenomena to preclinical level and then back to humans. Combined with the research rigor, openness, and transparency, this reverse engineering approach is well set to bring new effective and safe medications to patients in need.

Cerebral activity manipulation of low-frequency repetitive transcranial magnetic stimulation in post-stroke patients with cognitive impairment

OBJECTIVE

The aim of this study was to evaluate the therapeutic effect of low-frequency repetitive transcranial magnetic stimulation (rTMS) on post-stroke cognitive impairment (PSCI).

METHODS

Thirty-six PSCI patients were randomly divided into treatment and control groups of equal size. Both groups were pre-treated with conventional cognitive rehabilitation training. Subsequently, the treatment group was exposed to 1 Hz low-frequency repetitive transcranial magnetic stimulations for 8 weeks, with 5 days per week. Meanwhile, the control group was treated with placebo stimulations. Patients were evaluated via the LOTCA scale assessments and changes in P300 latencies and amplitudes before and after 8 weeks of treatment.

RESULTS

Before treatment, there were no significant differences between the two groups in LOTCA scores, P300 latencies, and amplitudes (P > 0.05). After treatment, LOTCA scores for both groups improved (P < 0.05), and those of the treatment group were higher than those of the control (P < 0.05). For both groups, P300 latencies were not only shortened but also had greater amplitudes (P < 0.05), and those for the treatment group were significantly shorter and larger than those of the control (P < 0.05).

CONCLUSION

As a therapy, rTMS improved cognitive function in PSCI patients, possibly via regulation of neural electrical activity of the cerebral cortex.

Pre-treatment hippocampal functioning impacts context renewal for cholinergic modulated exposure therapy

Our recent trial demonstrated individuals suffering from social anxiety with performance-related concerns who received virtual reality exposure augmented with scopolamine, a cholinergic antagonist, experienced significantly less post-treatment context renewal (CX) than placebo (Craske et al., 2019). The purpose of the present investigation was to determine who specifically benefits from scopolamine by examining hippocampal (HPC) functioning as a moderator of treatment response (Placebo n = 15, SCOP 0.5 mg n = 15, SCOP 0.6 mg n = 15). Skin conductance response to conditional stimulus (SCR-to-CS) termination suggested a dose-response relationship for enhanced HPC functioning individuals, wherein individuals receiving scopolamine demonstrated less fear at CX. In addition, SCR-to-CS onset indicated reduced fear at CX for impaired HPC individuals receiving SCOP 0.5 mg and SCOP 0.6 mg relative to Placebo. Our findings, however, lacked consistency across measures. Scopolamine remains a promising agent and additional research required to further understand its effects.

Effects of a novel M4 muscarinic positive allosteric modulator on behavior and cognitive deficits relevant to Alzheimer's disease and schizophrenia in rhesus monkey

Alzheimer's disease (AD) is a profoundly debilitating neurodegenerative disorder characterized most notably by progressive cognitive decline, but also agitation and behavioral disturbances that are extremely disruptive to patient and caregiver. Current pharmacological treatments for these symptoms have limited efficacy and significant side effects. We have recently reported the discovery of Compound 24, an M4 positive allosteric modulator (PAM) that is potent, highly selective, and devoid of cholinergic-like side effects in rats. In order to further evaluate the translatability of the effects of compound 24 in primates, here we describe the effect of Compound 24 on three behavioral and cognition assays in rhesus monkeys, the stimulant induced motor activity (SIMA) assay, the object retrieval detour task (ORD), and the visuo-spatial paired-associates learning (vsPAL) task. As far as we know, this is the first such characterization of an M4 PAM in non-human primate. Compound 24 and the clinical standard olanzapine attenuated amphetamine induced hyperactivity to a similar degree. In addition, Compound 24 demonstrated procognitive effects in scopolamine-impaired ORD and vsPAL, and these effects were of similar magnitude to donepezil. These findings suggest that M4 PAMs may be beneficial to diseases such as Alzheimer's disease and schizophrenia, which are marked by behavioral disturbances as well as deficits in cognitive function.

Cholinergic Modulation of Exposure Disrupts Hippocampal Processes and Augments Extinction: Proof-of-Concept Study With Social Anxiety Disorder

BACKGROUND

In rodents, context specificity of Pavlovian extinction is attenuated by manipulations that impair hippocampal function, including systemic administration of scopolamine, a muscarinic-cholinergic receptor antagonist. Context renewal translates into return of fear following exposure therapy to feared situations. We evaluated the effectiveness of scopolamine for attenuating context renewal of phobic fear in humans.

METHODS

A total of 60 participants (35 female, 22 male, 1 transgender, 2 undeclared) with social anxiety disorder and fear of public speaking were randomized to placebo, 0.5 mg scopolamine, or 0.6 mg scopolamine. They completed seven exposure sessions in an exposure context and subsequently tested in the exposure context (extinction retest) versus a different context (context renewal test), which were counterbalanced. Testing 1 month later occurred in the exposure context (long-term extinction retest). Fear measures included skin conductance and self-reported distress during speeches. Hippocampus-dependent cognitive tasks were completed as well.

RESULTS

Scopolamine augmented extinction across exposure sessions on skin conductance response and skin conductance level. Lower skin conductance response at context renewal in scopolamine groups relative to the placebo group was constrained to simple effects and complicated by unexpected outcomes within placebo and on self-reported fear. Scopolamine led to lower skin conductance response at long-term extinction retest. Scopolamine impaired performance on a cognitive task of hippocampal function.

CONCLUSIONS

Noninvasive and well-tolerated scopolamine impaired hippocampal processes and augmented extinction during exposure. Drug-free effects persisted 1 month later. Findings at context renewal were limited and suggestive only. Further investigation is warranted with varying scopolamine dosages.

Regulation of Cognitive Processing by Hippocampal Cholinergic Tone

Cholinergic dysfunction has been associated with cognitive abnormalities in a variety of neurodegenerative and neuropsychiatric diseases. Here we tested how information processing is regulated by cholinergic tone in genetically modified mice targeting the vesicular acetylcholine transporter (VAChT), a protein required for acetylcholine release. We measured long-term potentiation of Schaffer collateral-CA1 synapses in vivo and assessed information processing by using a mouse touchscreen version of paired associates learning task (PAL). Acquisition of information in the mouse PAL task correlated to levels of hippocampal VAChT, suggesting a critical role for cholinergic tone. Accordingly, synaptic plasticity in the hippocampus in vivo was disturbed, but not completely abolished, by decreased hippocampal cholinergic signaling. Disrupted forebrain cholinergic signaling also affected working memory, a result reproduced by selectively decreasing VAChT in the hippocampus. In contrast, spatial memory was relatively preserved, whereas reversal spatial memory was sensitive to decreased hippocampal cholinergic signaling. This work provides a refined roadmap of how synaptically secreted acetylcholine influences distinct behaviors and suggests that distinct forms of cognitive processing may be regulated in different ways by cholinergic activity.

Nicotinic alpha 7 receptor agonists EVP-6124 and BMS-933043, attenuate scopolamine-induced deficits in visuo-spatial paired associates learning

Agonists at the nicotinic acetylcholine alpha 7 receptor (nAChR α7) subtype have the potential to treat cognitive deficits in patients with Alzheimer’s disease (AD) or schizophrenia. Visuo-spatial paired associates learning (vsPAL) is a task that has been shown to reliably predict conversion from mild cognitive impairment to AD in humans and can also be performed by nonhuman primates. Reversal of scopolamine-induced impairment of vsPAL performance may represent a translational approach for the development of nAChR α7 agonists. The present study investigated the effect of treatment with the acetylcholinesterase inhibitor, donepezil, or three nAChR α7 agonists, BMS-933043, EVP-6124 and RG3487, on vsPAL performance in scopolamine-treated cynomolgus monkeys. Scopolamine administration impaired vsPAL performance accuracy in a dose- and difficulty- dependent manner. The impairment of eventual accuracy, a measure of visuo-spatial learning during the task, was significantly ameliorated by treatment with donepezil (0.3 mg/kg, i.m.), EVP-6124 (0.01 mg/kg, i.m.) or BMS-933043 (0.03, 0.1 and 0.3 mg/kg, i.m.). Both nAChR α7 agonists showed inverted-U shaped dose-effect relationships with EVP-6124 effective at a single dose only whereas BMS-933043 was effective across at least a 10 fold dose/exposure range. RG3487 was not efficacious in this paradigm at the dose range examined (0.03–1 mg/kg, i.m.). These results are the first demonstration that the nAChR α7 agonists, EVP-6124 and BMS-933043, can ameliorate scopolamine-induced cognitive deficits in nonhuman primates performing the vsPAL task.

No Acute Effects of Choline Bitartrate Food Supplements on Memory in Healthy, Young, Human Adults

Choline is a dietary component and precursor of acetylcholine, a crucial neurotransmitter for memory-related brain functions. In two double-blind, placebo-controlled cross-over experiments, we investigated whether the food supplement choline bitartrate improved declarative memory and working memory in healthy, young students one to two hours after supplementation. In experiment 1, 28 participants performed a visuospatial working memory task. In experiment 2, 26 participants performed a declarative picture memorization task. In experiment 3, 40 participants performed a verbal working memory task in addition to the visuospatial working memory and declarative picture task. All tasks were conducted approximately 60 minutes after the ingestion of 2.0–2.5g of either choline bitartrate or placebo. We found that choline did not significantly enhance memory performance during any of the tasks. The null hypothesis that choline does not improve memory performance as compared to placebo was strongly supported by Bayesian statistics. These results are in contrast with animal studies suggesting that choline supplementation boosts memory performance and learning. We conclude that choline likely has no acute effects on cholinergic memory functions in healthy human participants.

Spatial sequence memory and spatial error monitoring in the Groton Maze Learning Task (GMLT): A validation study of GMLT sub-measures in healthy children

The stepping-stone variant of the hidden pathway maze learning (HPML) task paradigm has been extensively used to investigate cognitive functions in neuropsychology and neuropharmacology. Previous studies have used total error across trials, as well as rule-break errors and learning errors, to define spatial memory and/or executive function in healthy and impaired adults and children. However, the construct validity of performance measures on HPML tasks has not been established in healthy children. To assess the construct validity of measures of exploratory and rule-break errors on the Groton Maze Learning Task (GMLT) measures of spatial sequence memory (Corsi Blocks Task) and spatial error monitoring (Continuous Paired Associate Learning; CPAL) were used. The results indicate that Corsi span predicted GMLT spatial sequence memory and CPAL accuracy predicted GMLT spatial error monitoring. The construct validity of the GMLT as a measure of spatial memory and executive function are discussed with regard to prior research using HPML tasks in neuropsychological contexts.

The development of associate learning in school age children

Associate learning is fundamental to the acquisition of knowledge and plays a critical role in the everyday functioning of the developing child, though the developmental course is still unclear. This study investigated the development of visual associate learning in 125 school age children using the Continuous Paired Associate Learning task. As hypothesized, younger children made more errors than older children across all memory loads and evidenced decreased learning efficiency as memory load increased. Results suggest that age-related differences in performance largely reflect continued development of executive function in the context of relatively developed memory processes.

SSP-002392, a new 5-HT4 receptor agonist, dose-dependently reverses scopolamine-induced learning and memory impairments in C57Bl/6 mice

5-HT4 receptors (5-HT4R) are suggested to affect learning and memory processes. Earlier studies have shown that animals treated with 5-HT4R agonists, often with limited selectivity, show improved learning and memory with retention memory often being assessed immediately after or within 24 h after the last training session. In this study, we characterized the effect of pre-training treatment with the selective 5-HT4R agonist SSP-002392 on memory acquisition and the associated long-term memory retrieval in animal models of impaired cognition. Pre-training treatment with SSP-002392 (0.3 mg/kg, 1.5 mg/kg and 7.5 mg/kg p.o.) dose-dependently inhibited the cognitive deficits induced by scopolamine (0.5 mg/kg s.c.) in two different behavioral tasks: passive avoidance and Morris water maze. In the Morris water maze, spatial learning was significantly improved after treatment with SSP-002392 translating in an accelerated and more efficient localization of the hidden platform compared to scopolamine-treated controls. Moreover, retention memory was assessed 24 h (passive avoidance) and 72 h (Morris water maze) after the last training session of cognitive-impaired animals and this was significantly improved in animals treated with SSP-002392 prior to the training sessions. Furthermore, the effects of SSP-002392 were comparable to galanthamine hydrobromide. We conclude that SSP-002392 has potential as a memory-enhancing compound.