Involvement of cholinergic and GABAergic systems in the reversal of memory disruption by NS-105, a cognition enhancer

GABAB Receptors and Cognitive Processing in Health and Disease

GABA_B receptors are implicated in numerous central nervous system-based behaviours and mechanisms, including cognitive processing in preclinical animal models. Homeostatic changes in the expression and function of these receptors across brain structures have been found to affect cognitive processing. Numerous preclinical studies have focused on the role of GABA_B receptors in learning, memory and cognition per se with some interesting, although sometimes contradictory, findings. The majority of the existing clinical literature focuses on alterations in GABA_B receptor function in conditions and disorders whose main symptomatology includes deficits in cognitive processing. The aim of this chapter is to delineate the role of GABA_B receptors in cognitive processes in health and disease of animal models and human clinical populations. More specifically, this review aims to present literature on the role of GABA_B receptors in animal models with cognitive deficits, especially those of learning and memory. Further, it aims to capture the progress and advances of research studies on the effects of GABA_B receptor compounds in neurodevelopmental and neurodegenerative conditions with cognitive dysfunctions. The neurodevelopmental conditions covered include autism spectrum disorders, fragile X syndrome and Down's syndrome and the neurodegenerative conditions discussed are Alzheimer's disease, epilepsy and autoimmune anti-GABA_B encephalitis. Although some findings are contradictory, results indicate a possible therapeutic role of GABA_B receptor compounds for the treatment of cognitive dysfunction and learning/memory impairments for some of these conditions, especially in neurodegeneration. Moreover, future research efforts should aim to develop selective GABA_B receptor compounds with minimal, if any, side effects.

Fasoracetam in adolescents with ADHD and glutamatergic gene network variants disrupting mGluR neurotransmitter signaling

The glutamatergic neurotransmitter system may play an important role in attention-deficit hyperactivity disorder (ADHD). This 5-week, open-label, single-blind, placebo-controlled study reports the safety, pharmacokinetics and responsiveness of the metabotropic glutamate receptor (mGluR) activator fasoracetam (NFC-1), in 30 adolescents, age 12-17 years with ADHD, harboring mutations in mGluR network genes. Mutation status was double-blinded. A single-dose pharmacokinetic profiling from 50-800 mg was followed by a single-blind placebo at week 1 and subsequent symptom-driven dose advancement up to 400 mg BID for 4 weeks. NFC-1 treatment resulted in significant improvement. Mean Clinical Global Impressions-Improvement (CGI-I) and Severity (CGI-S) scores were, respectively, 3.79 at baseline vs. 2.33 at week 5 (P < 0.001) and 4.83 at baseline vs. 3.86 at week 5 (P < 0.001). Parental Vanderbilt scores showed significant improvement for subjects with mGluR Tier 1 variants (P < 0.035). There were no differences in the incidence of adverse events between placebo week and weeks on active drug. The trial is registered at https://clinicaltrials.gov/ct2/show/study/NCT02286817 .

A Study of Fasoracetam's Solid State Forms: A Potential Anti-Alzheimer Pharmaceutical

Different solid state forms of the research chemical fasoracetam, which counters the effects of Alzheimer's disease, have been subjected to a thermal and structural analysis. Single crystals were obtained from solution evaporation and from the melt. Single-crystal X-ray analyses of the crystals show the existence of 2 hydrated and 1 non-hydrated crystalline form of fasoracetam. Under ambient conditions, the hydrate form I is found to be the most stable form, showing a melting point of 57C. This low melting point, combined with possible water losses could cause problems when formulating the hydrated form and impact the storage conditions of the compound.

Basal Forebrain Cholinergic System and Memory

Basal forebrain cholinergic neurons constitute a way station for many ascending and descending pathways. These cholinergic neurons have a role in eliciting cortical activation and arousal. It is well established that they are mainly involved in cognitive processes requiring increased levels of arousal, attentive states and/or cortical activation with desynchronized activity in the EEG. These cholinergic neurons are modulated by several afferents of different neurotransmitter systems. Of particular importance within the cortical targets of basal forebrain neurons is the hippocampal cortex. The septohippocampal pathway is a bidirectional pathway constituting the main septal efferent system, which is widely known to be implicated in every memory process investigated. The present work aims to review the main neurotransmitter systems involved in modulating cognitive processes related to learning and memory through modulation of basal forebrain neurons.

ADHD & Pharmacotherapy: Past, Present and Future: A Review of the Changing Landscape of Drug Therapy for Attention Deficit Hyperactivity Disorder

Attention deficit hyperactivity disorder (ADHD) is the most common neurobiological disorder in children, with a prevalence of ~6-7%^1,2 that has remained stable for decades². The social and economic burden associated with patients³, families, and broader systems (healthcare/educational) is substantial, with the annual economic impact of ADHD exceed $30 billion in the US alone⁴. Efficacy of pharmacotherapy in treating ADHD symptoms has generally been considerable with at least ¾ of individuals benefitting from pharmacotherapy, typically in the form of stimulants⁵. In this review, we begin by briefly reviewing the history of pharmacotherapy in relation to ADHD, before focusing (primarily) on the state-of-the-field on themes such as biophysiology, pharmacokinetics, and pharmacogenomics. We conclude with a summary of emerging clinical and research studies, particularly the potential role for precision therapy in matching ADHD patients and drug types.

NMDA receptor blockers prevents the facilitatory effects of post-training intra-dorsal hippocampal NMDA and physostigmine on memory retention of passive avoidance learning in rats

In the present study, the effects of post-training intra-dorsal hippocampal (intra-CA1) 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-CA1 administration of lower doses of the NMDA receptor agonist NMDA (10(-5) and 10(-4) microg/rat) did not affect memory retention, although the 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-CA1 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. In conclusion, it seems that both NMDA and cholinergic systems not only play a part in the modulation of memory in the dorsal hippocampus of rats but also have demonstrated a complex interaction as well.

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.

Therapeutic potential of positive AMPA modulators and their relationship to AMPA receptor subunits. A review of preclinical data

BACKGROUND

Positive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) modulators enhance glutamate transmission via the AMPA receptor by altering the rate of desensitization; alone they have no intrinsic activity. They are the only class of compounds known that may pharmacologically separate AMPA subtypes.

OBJECTIVE

This manuscript will review preclinical work on positive AMPA modulators, with clinical examples where relevant.

RESULTS

The activity of these compounds appears to be determined by the AMPA receptor subunit composition. Studies have shown that splice variant and/or subunit combinations change the desensitization rate of this receptor. Also, these subunits are heterogeneously expressed across the central nervous system. Therefore, the functional outcome of different positive AMPA modulators could indeed be different. The origins of this pharmacological class come from hippocampal long-term potentiation studies, so quite naturally they were first studied in models of short- and long-term memory (e.g., delayed match to sample, maze performance). In general, these agents were procognitive. However, more recent work with different chemical classes has suggested additional therapeutic effects in models of schizophrenia (e.g., amphetamine locomotor activity), depression (e.g., forced swim test), neuroprotection (e.g., NMDA agonist lesions) and Parkinson's disease (e.g., 6-hydroxydopamine lesion).

CONCLUSIONS

In conclusion, positive modulation of AMPA may offer numerous therapeutic avenues for central nervous system drug discovery.

Effect of antidepressants on GABA(B) receptor function and subunit expression in rat hippocampus

Laboratory and clinical studies suggest that depression is associated with changes in the hippocampus and that this brain region is a major target for antidepressant drugs. Given the data suggesting that GABA(B) receptor antagonists display antidepressant properties, the present study was undertaken to assess the effect of antidepressant administration on GABA(B) receptors in the rat hippocampus to determine whether changes in this regional receptor system may play a role in the response to these agents. Rats were administered (i.p.) the monoamine oxidase inhibitors tranylcypromine (10mg/kg) or phenelzine (10mg/kg), the tricyclic antidepressant desipramine (15 mg/kg), or fluoxetine (5mg/kg), a selective serotonin re-uptake inhibitor, once daily for seven consecutive days. Two hours following the last drug treatment the hippocampal tissue was prepared for defining the distribution and quantity of GABA(B) receptor subunits using in situ hybridization and for assessing GABA(B) receptor function by quantifying baclofen-stimulated [(35)S]-GTPgammaS binding. All of these antidepressants selectively increased the expression of the GABA(B(1a)) subunit in hippocampus, having no consistent effect on the expression of GABA(B(1b)) or GABA(B(2)). Moreover, except for fluoxetine, these treatments increased GABA(B) receptor function in this brain region. The results indicate that an enhancement in the production of hippocampal GABA(B(1a)) subunits may be a component of the response to antidepressants, supporting a possible role for this receptor in the symptoms of depression and the treatment of this condition.

Parafascicular electrical stimulation attenuates nucleus basalis magnocellularis lesion-induced active avoidance retention deficit

Previous experiments from our laboratory showed that retention of two-way active avoidance learning is improved by post-training intracranial electrical stimulation (ICS) of the parafascicular nucleus (PF) and impaired by pre-training electrolytic lesions of the nucleus basalis magnocellularis (NBM). The question investigated here was whether post-training PF ICS is able to attenuate the active avoidance retention deficit observed in rats lesioned pre-training in the NBM. To this goal, the following experimental design was used: rats bilaterally lesioned in the NBM and stimulated in the PF, rats lesioned in the NBM, rats stimulated in the PF, control rats implanted in the PF, and sham-operated rats were first trained in a shuttle-box for a single 30-trial session and tested again following two successive retention intervals (24 h and 11 days). The results showed that: (1) NBM lesions impaired the 11-day performance without affecting either the acquisition or the 24-h retention of the avoidance learning; (2) PF ICS treatment in unlesioned rats improved performance in both retention sessions only when the stimulation was applied in the posterior region of the nucleus; and (3) stimulation of the posterior PF compensated the 11-day retention impairment induced by NBM lesions. These results are discussed in relation to the interaction of arousal systems in the modulation of cognitive processes.

Effects of intrahippocampal injection of GABAergic drugs on memory retention of passive avoidance learning in rats

The effect of post-training intrahippocampal injection of gamma-aminobutyric acid (GABA) receptor agonists and antagonists, immediately after a training session on memory retention of passive avoidance learning in rats, was measured in the presence and absence of physostigmine. Post-training treatments were carried out in all the experiments. The different doses of the GABAA receptor agonist muscimol (2, 4 and 6 microg/rat) decreased memory retention in rats dose-dependently. The higher response was obtained with 6 microg/rat of the drug. When the GABAA receptor antagonist bicuculline (0.5, 1, 2 and 4 microg/rat) was administered, only one dose of the drug (1 microg/rat) increased memory retention; however, the antagonist reduced the effect of muscimol. The GABAB receptor agonist, baclofen (0.25, 0.5, 1 and 2 microg/rat) also reduced memory retention in the animals. Intrahippocampal injection of lower doses of the GABAB receptor antagonist CGP35348 (P-[3-aminopropyl]-p-diethoxymethyl-phosphinic acid) (2.5, 5, 10 microg/rat) did not effect memory retention, although the higher doses of the drug (25 and 50 microg/rat) decreased memory retention. The doses of antagonist (2.5, 5 and 10 microg/rat), which did not elicit any response alone, reduced the effect of baclofen. The inhibitory response of CGP35348 was also decreased by bicuculline. In another series of experiments, physostigmine improved memory retention. The GABA receptor agonists, muscimol and baclofen, as well as the GABA receptor antagonists bicuculline and CGP35348, decreased the effect of physostigmine. Atropine decreased memory retention by itself and potentiated the response of muscimol and baclofen. It is concluded that GABAA and GABAB receptor activation may be involved in the impairment of memory retention.

Pyrrolidone derivatives

The pyrrolidone (2-oxopyrrolidine) family of chemicals has been the subject of research for more than three decades. Experimental and clinical work first focused on their so-called nootropic effects; later came the possibilities for neuroprotection after stroke and use as antiepileptic agents. Piracetam, the first of the class, was developed by pioneering research by C Giurgea in the late 1960s, and it was he who coined the term "nootropic", to mean enhancement of learning and memory. The term is sometimes extended to include other actions such as neuroprotection. These properties, together with the lack of other generally adverse psychopharmacological actions (eg, sedation, analgesia, or motor or behavioural changes), distinguish the pyrrolidones from other psychoactive drug classes. The mechanisms of action of these drugs are still not fully established; indeed, different compounds in this class may have different modes of action. Interest in this drug class has recently been reawakened by the licensing of levetiracetam as a potentially major new antiepileptic drug and of piracetam for its antimyoclonic action and effects after stroke and in mild cognitive impairment. Other drugs in this class are currently at an advanced stage of development, and the renewal of interest in this therapeutic area is likely to mean not only that more pyrrolidones will enter clinical practice in the next few years but also that the clinical indications of drugs already licensed will widen.

Nootropic and anxiolytic activity of saponins of Albizzia lebbeck leaves

The effect of saponin containing, n-butanolic fraction (BF), extracted from dried leaves of Albizzia lebbeck, was studied on cognitive behavior and anxiety in albino mice. The elevated plus maze was used for assessment of both nootropic and anxiolytic activity. The nootropic activity was evaluated by recording the effect of BF (0, 10, 25, and 50 mg/kg) on the transfer latency, whereas anxiolytic activity was assessed by studying its effect on the duration of occupancy in the closed arm. Results showed significant improvement in the retention ability of the normal and amnesic mice as compared to their respective controls. Animals treated with BF (25 mg/kg) spent more time in the open arm in a dose-dependent manner. The BF was without any significant effect on motor coordination. However, it significantly inhibited passivity and hypothermia induced by baclofen (10 mg/kg), a GABA(B) agonist. The data emanated in the present study suggests involvement of gamma-aminobutyric acid (GABA) in the nootropic and anxiolytic activity of saponins obtained from A. lebbeck.

Role of metabotropic glutamate receptor subclasses in modulation of adenylyl cyclase activity by a nootropic NS-105

The involvement of metabotropic glutamate (mGlu) receptors in the modulatory actions of a novel cognition enhancer, (+)-5-oxo-D-prolinepiperidinamide monohydrate (NS-105), on adenylyl cyclase activity in rat cerebrocortical membranes and primary neuronal cultures was investigated using selective antagonists and antisense oligodeoxynucleotides for mGlu receptor subclasses. In rat cerebrocortical membranes, the inhibitory action of NS-105 (0.1 microM) on forskolin-stimulated cAMP formation was blocked by a group II mGlu receptor antagonist, (+/-)-alpha-ethylglutamic acid, and by a group III antagonist, (+)-2-amino-2-methyl-4-phosphonobutanoic acid (MAP-4), but not by a group I antagonist, (+/-)-1-aminoindan-1,5-dicarboxylic acid (AIDA), whereas the facilitation of cAMP formation by NS-105 (1 microM) in pertussis toxin-pretreated membranes was abolished by AIDA but not by (+/-)-alpha-ethylglutamic acid or MAP-4. In primary cultured neurons of mouse cerebral cortex, the inhibitory action of NS-105 on adenylyl cyclase activity disappeared after treatment with antisense oligodeoxynucleotides for group II (mGlu(2) and mGlu(3) receptors) and group III (mGlu(4) and mGlu(7) receptors) but not group I (mGlu(5) receptor) mGlu receptor subclasses. These findings suggest that the inhibitory action of NS-105 on adenylyl cyclase activity is mediated through group II and group III mGlu receptor subclasses while the facilitatory action is dependent on the group I mGlu receptor subclass.