Long-term memory formation in the chick requires mobilization of ryanodine-sensitive intracellular calcium stores

Role of lateral amygdala calstabin2 in regulation of fear memory

Calstabin2, also named FK506 binding protein 12.6 (FKBP12.6), is a subunit of ryanodine receptor subtype 2 (RyR2) macromolecular complex, an intracellular calcium channel. Studies from our and other's lab have shown that hippocampal calstabin2 regulates spatial memory. Calstabin2 and RyR2 are widely distributed in the brain, including the amygdala, a key brain area involved in the regulation of emotion including fear. Little is known about the role of calstabin2 in fear memory. Here, we found that genetic deletion of calstabin2 impaired long-term memory in cued fear conditioning test. Knockdown calstabin2 in the lateral amygdala (LA) by viral vector also impaired long-term cued fear memory expression. Furthermore, calstabin2 knockout reduced long-term potentiation (LTP) at both cortical and thalamic inputs to the LA. In conclusion, our present data indicate that calstabin2 in the LA plays a crucial role in the regulating of emotional memory.

The involvement of TRP channels in memory formation and task retrieval in a passive avoidance task in one-day old chicks

An increase in the intracellular Ca2+ level in neurons is one of the main steps in the memory formation cascade. The increase results from extracellular Ca2+ influx by activation of ionotropic glutamate receptors and release from intracellular stores by the stimulation of IP3 receptors (IP3Rs) via group I metabotropic glutamate receptors (mGluR1/5). Recent data indicate an additional mechanism resulting in Ca2+ influx into neurons, triggered by intracellular signals that are directly connected to the activation of group I mGluRs. This influx occurs through transient receptor potential (TRP) channels, which are permeable to Na+, K+ and, mainly, Ca2+. These channels are activated by increases in intracellular Ca2+, diacylglycerol (DAC) and inositol 1,4,5-triphosphate (IP3) level resulting from a group I mGluR activation. The aim of the present study was to investigate the participation of TRP channels, especially from TRPC and TRPV groups, in memory consolidation and reconsolidation and memory retrieval processes in a passive avoidance task in one-day old chicks. TRP channels were blocked by the injection of the unspecific channel modulators SKF 96365 (2.5 µl 30 µM/hemisphere) and 2-APB (2.5 µl 10 µM/hemisphere) directly into the intermediate medial mesopallium (IMM) region of the chick brain immediately after initial training or after a reminder. The inhibition of specific TRP channels (TRPV1, TRPV3 or TRPC3) was achieved by the application of selective antibodies. Our results demonstrate that the inhibition of TRP channels by the application of both modulators disrupted memory consolidation, resulting in permanent task amnesia. The inhibition of the TRPV1, TRPC3 and TRPV3 channels by specific antibodies resulted in similar amnesia. Moreover, the inhibition of TRP channels by SKF 96365 and 2-APB at different time points after initial training or after the reminder also resulted in amnesia, indicating the role of TRP channels in memory retrieval. The inhibition of calcium influx through these channels resulted in permanent memory disruption, which suggests that the calcium signal generated by TRP channels is crucial for memory formation and retrieval processes. For the first time, the important role of TRPV3 channels in memory formation was demonstrated.

The SERCA2: A Gatekeeper of Neuronal Calcium Homeostasis in the Brain

Calcium (Ca²⁺) ions are prominent cell signaling regulators that carry information for a variety of cellular processes and are critical for neuronal survival and function. Furthermore, Ca²⁺ acts as a prominent second messenger that modulates divergent intracellular cascades in the nerve cells. Therefore, nerve cells have developed intricate Ca²⁺ signaling pathways to couple the Ca²⁺ signal to their biochemical machinery. Notably, intracellular Ca²⁺ homeostasis greatly relies on the rapid redistribution of Ca²⁺ ions into the diverse subcellular organelles which serve as Ca²⁺ stores, including the endoplasmic reticulum (ER). It is well established that Ca²⁺ released into the neuronal cytoplasm is pumped back into the ER by the sarco-/ER Ca²⁺ ATPase 2 (SERCA2), a P-type ion-motive ATPase that resides on the ER membrane. Even though the SERCA2 is constitutively expressed in nerve cells, its precise role in brain physiology and pathophysiology is not well-characterized. Intriguingly, SERCA2-dependent Ca²⁺ dysregulation has been implicated in several disorders that affect cognitive function, including Darier's disease, schizophrenia, Alzheimer's disease, and cerebral ischemia. The current review summarizes knowledge on the expression pattern of the different SERCA2 isoforms in the nervous system, and further discusses evidence of SERCA2 dysregulation in various neuropsychiatric disorders. To the best of our knowledge, this is the first literature review that specifically highlights the critical role of the SERCA2 in the brain. Advancing knowledge on the role of SERCA2 in maintaining neuronal Ca²⁺ homeostasis may ultimately lead to the development of safer and more effective pharmacotherapies to combat debilitating neuropsychiatric disorders.

The role of intracellular calcium stores in synaptic plasticity and memory consolidation

Memory processing requires tightly controlled signalling cascades, many of which are dependent upon intracellular calcium (Ca(2+)). Despite this, most work investigating calcium signalling in memory formation has focused on plasma membrane channels and extracellular sources of Ca(2+). The intracellular Ca(2+) release channels, ryanodine receptors (RyRs) and inositol (1,4,5)-trisphosphate receptors (IP3Rs) have a significant capacity to regulate intracellular Ca(2+) signalling. Evidence at both cellular and behavioural levels implicates both RyRs and IP3Rs in synaptic plasticity and memory formation. Pharmacobehavioural experiments using young chicks trained on a single-trial discrimination avoidance task have been particularly useful by demonstrating that RyRs and IP3Rs have distinct roles in memory formation. RyR-dependent Ca(2+) release appears to aid the consolidation of labile memory into a persistent long-term memory trace. In contrast, IP3Rs are required during long-term memory. This review discusses various functions for RyRs and IP3Rs in memory processing, including neuro- and glio-transmitter release, dendritic spine remodelling, facilitating vasodilation, and the regulation of gene transcription and dendritic excitability. Altered Ca(2+) release from intracellular stores also has significant implications for neurodegenerative conditions.

Intracellular calcium chelation and pharmacological SERCA inhibition of Ca2+ pump in the insular cortex differentially affect taste aversive memory formation and retrieval

Variation in intracellular calcium concentration regulates the induction of long-term synaptic plasticity and is associated with a variety of memory/retrieval and learning paradigms. Accordingly, impaired calcium mobilization from internal deposits affects synaptic plasticity and cognition in the aged brain. During taste memory formation several proteins are modulated directly or indirectly by calcium, and recent evidence suggests the importance of calcium buffering and the role of intracellular calcium deposits during cognitive processes. Thus, the main goal of this research was to study the consequence of hampering changes in cytoplasmic calcium and inhibiting SERCA activity by BAPTA-AM and thapsigargin treatments, respectively, in the insular cortex during different stages of taste memory formation. Using conditioned taste aversion (CTA), we found differential effects of BAPTA-AM and thapsigargin infusions before and after gustatory stimulation, as well as during taste aversive memory consolidation; BAPTA-AM, but not thapsigargin, attenuates acquisition and/or consolidation of CTA, but neither compound affects taste aversive memory retrieval. These results point to the importance of intracellular calcium dynamics in the insular cortex during different stages of taste aversive memory formation.

Early calcium increase triggers the formation of olfactory long-term memory in honeybees

Background

Synaptic plasticity associated with an important wave of gene transcription and protein synthesis underlies long-term memory processes. Calcium (Ca²⁺) plays an important role in a variety of neuronal functions and indirect evidence suggests that it may be involved in synaptic plasticity and in the regulation of gene expression correlated to long-term memory formation. The aim of this study was to determine whether Ca²⁺ is necessary and sufficient for inducing long-term memory formation. A suitable model to address this question is the Pavlovian appetitive conditioning of the proboscis extension reflex in the honeybee Apis mellifera, in which animals learn to associate an odor with a sucrose reward.

Results

By modulating the intracellular Ca²⁺ concentration ([Ca²⁺]i) in the brain, we show that: (i) blocking [Ca²⁺]i increase during multiple-trial conditioning selectively impairs long-term memory performance; (ii) conversely, increasing [Ca²⁺]i during single-trial conditioning triggers long-term memory formation; and finally, (iii) as was the case for long-term memory produced by multiple-trial conditioning, enhancement of long-term memory performance induced by a [Ca²⁺]i increase depends on de novo protein synthesis.

Conclusion

Altogether our data suggest that during olfactory conditioning Ca²⁺ is both a necessary and a sufficient signal for the formation of protein-dependent long-term memory. Ca²⁺ therefore appears to act as a switch between short- and long-term storage of learned information.

Modelling the anxiety-depression continuum in chicks

The clinical syndromes of anxiety and depression are now thought to exist along a temporal continuum and this construct has been modelled in a preclinical setting in chicks separated from conspecifics. This research sought to further the validity of the chick anxiety-depression continuum model. Dose-response studies using two classes of anxiolytics (chlordiazepoxide: 2.5, 5.0, 10.0, 15.0 mg/kg, and clonidine: 0.1, 0.15, 0.2, 0.25 mg/kg) and three classes of antidepressants (imipramine: 1.0, 3.0, 10.0, 15.0 mg/kg, maprotoline: 2.5, 5.0, 10.0, 20.0 mg/kg and fluoxetine: 1.0, 5.0, 10.0, 20.0 mg/kg) showed an ability to detect anxiolytic activity of chlordiazepoxide, clonidine, imipramine and maprotoline in the anxiety-like phase of the model and to detect antidepressant effects of imipramine, maprotoline and fluoxetine in the depression-like phase of the model. In addition, blood plasma interleukin-6, a biomarker of stress, was found to be elevated in response to social-separation stress. Collectively, these findings further characterize the model as a simulation of the anxiety-depression continuum and begin to establish the paradigm as a high-utility adjuvant to rodent screening assays for putative anxiolytic and antidepressant compounds.

Inhibition of mGluR1 and IP3Rs impairs long-term memory formation in young chicks

Calcium (Ca(2+)) is involved in a myriad of cellular functions in the brain including synaptic plasticity. However, the role of intracellular Ca(2+) stores in memory processing remains poorly defined. The current study explored a role for glutamate-dependent intracellular Ca(2+) release in memory processing via blockade of metabotropic glutamate receptor subtype 1 (mGluR1) and inositol (1,4,5)-trisphosphate receptors (IP(3)Rs). Using a single-trial discrimination avoidance task developed for the young chick, administration of the specific and potent mGluR1 antagonist JNJ16259685 (500nM, immediately post-training, ic), or the IP(3)R antagonist Xestospongin C (5microM, immediately post-training, ic), impaired retention from 90min post-training. These findings are consistent with mGluR1 activating IP(3)Rs to release intracellular Ca(2+) required for long-term memory formation and have been interpreted within an LTP2 model. The consequences of different patterns of retention loss following ryanodine receptor (RyR) and IP(3)R inhibition are discussed.

Effect of gestational ethanol exposure on long-term memory formation in newborn chicks

Fetal alcohol syndrome (FAS), a condition occurring in some children of mothers who have consumed alcohol during pregnancy, is characterized by craniofacial malformations, and physical and mental retardation. It is significant that even children with history of gestational ethanol exposure but relatively unaffected overall IQ performance, often exhibit learning difficulties and behavioral problems, suggestive of impaired memory formation. Hence, the specific aim of this study was to examine memory formation in chicks exposed to ethanol during early gestation toward the understanding of neurobehavioral disturbances in FAS. Chicks were exposed to alcohol on gestational days 1-3 by injection of ethanol into the airspace of freshly fertilized eggs. The effects of prenatal ethanol on physical growth and development, and memory formation were studied. The one-trial passive avoidance learning paradigm in 1-day-old chicks was used to study memory formation in these chicks. It was observed that chick embryos exposed to 10% ethanol on gestational days 1-3 had significant reduction in all body parameters when compared with appropriate controls. Further, ethanol-exposed chick embryos had significantly impaired (P<.05) long-term memory (LTM) formation after training, though short-term or intermediate-term memory formation was unimpaired. Thus, the findings of the current study demonstrate the detrimental effects of ethanol exposure during early pregnancy on developing chick embryos in general and on memory formation in particular. Hence, it is suggested that impairment in LTM could be a fundamental mechanism for learning disorders and neurobehavioral abnormalities observed in FAS.

New perspectives on the mechanisms through which nitric oxide may affect learning and memory processes

Nitric oxide (NO) has been well established as a molecule necessary for memory consolidation. Interestingly, the majority of research has focused on only a single mechanism through which NO acts, namely the up-regulation of guanylate cyclase (GC). However, since NO and NO-derived reactive nitrogen species are capable of interacting with a broad array of enzymes, ion channels and receptors, a singular focus on GC appears short-sighted. Although NO inhibits the action of a number of molecules there are four, in addition to GC, which are up-regulated by the direct presence of NO, or NO-derived radicals, and implicated in memory processing. They are: cyclic nucleotide-gated channels; large conductance calcium-activated potassium channels; ryanodine receptor calcium release (RyR) channels; and the enzyme mono(ADP-ribosyl) transferase. This review presents evidence that not only are these four molecules worthy of investigation as GC-independent mechanisms through which NO may act, but that behavioural evidence already exists suggesting a relationship between NO and the RyR channel.

Pharmaco-behavioural evidence indicating a complex role for ryanodine receptor calcium release channels in memory processing for a passive avoidance task

Calcium signalling is an important process underlying neuronal function and consequently behaviour. The release of calcium from intracellular stores via the ryanodine receptor calcium release (RyR) channel has been implicated in both synaptic plasticity and to a limited extent in memory processing. While past investigations have suggested a role for RyR channels in long-term memory, the present study suggests their action is more complex. Using a single trial passive avoidance task developed for the day-old chick, it is proposed that RyR channels are necessary both prior to the expression of long-term memory and also in retrieval processes. Specifically, 5 mM dantrolene (a specific RyR channel blocker) resulted in a persistent retention loss from 40 min post-training while 10 nM dantrolene produced a transient retention loss centred at 40 min post-training. We speculate that in the context of memory formation, RyR channels may be activated by nitric oxide and in the context of memory retrieval may lead to the activation of large conductance calcium-activated potassium BK(Ca) channels which, when blocked by 50 nM iberiotoxin, also demonstrated a transient retention loss centred at 40 min post-training.

Zaprinast consolidates long-term memory when administered to neonate chicks trained using a weakly reinforced single trial passive avoidance task

A weakly reinforced variant of the single trial passive avoidance task developed for the day-old chick typically fails to consolidate long-term memory. However, administration of zaprinast, a phosphodiesterase (PDE) type 5 inhibitor, (ic; 10 microl/side) immediately post-training resulted in a dose-dependent increase in retention at test 180 min post-training. Further, 100 microM zaprinast resulted in high levels of retention at test 180 min post-training when administered from 10 min before training to 10 min after training. Finally, 100 microM zaprinast, when administered immediately post-training, resulted in the consolidation of long-term memory at a number of times of test extending as late as 24 h post-training. Inhibition of PDE type 5 is known to increase cellular cGMP levels. Previous investigations using a strongly reinforced variant of this task have suggested a role for cGMP in memory retrieval, we now postulate that cGMP is also necessary for memory formation in chicks trained using passive avoidance.

Local anesthetic procaine protects rat pheochromocytoma PC12 cells against beta-amyloid-induced neurotoxicity

Alzheimer's disease (AD) is the most common dementia occurring in elderly. We report herein the neuroprotective properties of procaine and other anesthetic agents against beta-amyloid-induced neurotoxicity. Procaine displayed strong neuroprotective properties against the amyloid peptide Abeta(1-42) and preserved Abeta(1-42)-induced ATP depletion on rat pheochromocytoma PC12 cells. Procaine also inhibited the neurotoxic effect that glutamate displayed on PC12 cells, suggesting that the reduction of glutamate-induced neurotoxicity may be the mechanism by which these compounds exert their 'antiamyloid' effects. In search of a mechanism of action we observed that procaine is a ligand for the sigma1 receptor, a protein which ligands have been shown to protect mitochondrial function and to exert antidepressant properties. Procaine binds also to muscarinic receptors but the true meaning of this feature needs to be clarified. In conclusion, these data suggest that procaine exerts neuroprotective properties and may serve either as a treatment for AD or as a starting point for the development of novel therapies for AD.

Characterization of the chick carrageenan response

The present study characterized carrageenan inflammatory nociception in the 7-day-old domestic chick. The time course effects of foot withdrawal latency to a thermal stimulus and edema were examined over a 6-h period following an intraplantar carrageenan (0.0-1.0%) injection. Carrageenan-induced hyperalgesia and edema had a similar course of action, enduring for approximately 6 h, with a peak effect at approximately 2 h post carrageenan injection. Carrageenan inflammation was produced in a robust concentration dependent manner. Carrageenan hyperalgesia was induced at all concentrations tested and no carrageenan concentration effects were discerned. In a subsequent series of experiments we challenged the carrageenan inflammation model with systemic administration of the opioid agonist morphine, the nonsteroidal anti-inflammatory drug naproxen or the steroidal antiinflammatory drug dexamethasone. Morphine produced a dose dependent attenuation of carrageenan hyperalgesia but had no effect upon carrageenan inflammation. Naproxen produced a moderate attenuation of carrageenan inflammation and hyperalgesia. Dexamethasone dramatically attenuated both carrageenan hyperalgesia and inflammation. Collectively, these experiments characterize the chick carrageenan response and demonstrate the potential of the chick carrageenan inflammation model as a less expensive adjunct model of inflammatory nociception.