BetaCCM but not physostigmine enhancement of memory retrieval depends on emotional processes in mice

Bilateral Olfactory Mucosa Damage Induces the Disappearance of Olfactory Glomerulus and Reduces the Expression of Extrasynaptic α5GABAARs in the Hippocampus in Early Postnatal Sprague Dawley Rats

Chloroform-induced olfactory mucosal degeneration has been reported in adult rats following gavage. We used fixed-point chloroform infusions on different postnatal days (PNDs) to investigate the effects of early olfactory bilateral deprivation on the main olfactory bulbs in Sprague Dawley rats. The experimental groups included rats infused with chloroform (5 μl) or saline (sham, 5 μl) on PNDs 3 and 8, and rats not receiving infusions (control) (n = 6 in all groups). Rats receiving chloroform on PND 3 showed significant hypoevolutism when compared to those in other groups (P < 0.05). There was a complete disappearance and a significant reduction in the size of olfactory glomeruli in the PND 3 and 8 groups, respectively, when compared to the respective sham groups. Rats receiving chloroform on PND 3 had significant memory impairment (P < 0.01) and increased levels of learned helplessness (P < 0.05), as measured using the Morris water maze and tail suspension tests, respectively. GABA_A receptor alpha5 subunit (α5GABA_AR) expression in hippocampal neurons was significantly lower in rats receiving chloroform on PND 3 than in rats in other groups (P < 0.01), as measured using immunohistochemistry and polymerase chain reaction. There was thus a critical period for the preservation of regenerative ability in olfactory receptor neurons, during which damage and olfactory deprivation led to altered rhinencephalon structure and disappearance of olfactory glomeruli, which induced hypoevolutism. Olfactory deprivation after the critical period had no significant effect on olfactory receptor neuron regeneration, leading to reduced developmental and behavioral effects in Sprague Dawley rats.

Overexpression of Protein Kinase Mζ in the Prelimbic Cortex Enhances the Formation of Long-Term Fear Memory

Neuroplasticity in the prefrontal cortex (PFC) after fear conditioning has been suggested to regulate the formation and expression of fear memory. Protein kinase Mζ (PKMζ), an isoform of protein kinase C with persistent activity, is involved in the formation and maintenance of memory. However, less is known about the role of PKMζ in the PFC in the formation of fear memory. We investigated whether the overexpression of PKMζ enhances the formation of auditory fear memory in rats. We found that microinfusion of lentiviral vector-expressing PKMζ into the prelimbic cortex (PrL) selectively enhanced the expression of PKMζ without influencing the expression of other isoforms of PKC. The overexpression of PKMζ in the PrL enhanced the formation of long-term fear memory without affecting short-term fear memory, whereas the overexpression of PKMζ in the infralimbic cortex had no effect on either short-term or long-term fear memory. The overexpression of PKMζ in the PrL had no effect on anxiety-like behavior or locomotor activity. We also found that PKMζ overexpression potentiated the fear conditioning-induced increase in the membrane levels of glutamate subunit 2 of AMPA receptors in the PrL. These results demonstrate that the overexpression of PKMζ in the PrL but not infralimbic cortex selectively enhanced the formation of long-term fear memory, and PKMζ in the PrL may be involved in the formation of fear memory.

Combined effects of acute stress and amphetamine on serial memory retrieval pattern in mice

INTRODUCTION

This study investigated the dose-effect of amphetamine on contextual serial (contextual serial discrimination (CSD)) and serial (serial discrimination (SD)) memory in acutely stressed versus nonstressed C57 Bl/6 Jico mice.

MATERIALS AND METHODS

Memory was first evaluated in nonstress condition. Mice learned two consecutive discriminations (D1 and D2) in a four-hole board involving either distinct (CSD) or identical (SD) internal contextual cues. All mice received i.p. injections of vehicle before acquisition and vehicle or amphetamine 20 min before the memory retrieval phase occurring 24 h after acquisition.

RESULTS

Results showed that: (1) vehicle group expressed in both tasks a similar memory retrieval pattern, D2 being better retrieved than D1; (2) 2 mg/kg amphetamine significantly enhanced D1 but not D2 performance in both tasks, whereas 4 mg/kg amphetamine enhanced D2 but not D1 retrieval. Thus, amphetamine more specifically modulates serial order memory retrieval in a context-independent manner. In a further step, we studied the effect of an acute stress (electric foot shocks 5 min before retrieval) specifically on D1 performance of the CSD task in 2 mg/kg amphetamine-treated mice. Immediately after testing, blood was sampled to measure plasma corticosterone levels. Results showed that acute stress significantly improved D1 performance in vehicles but blocked the memory-enhancing effect of 2 mg/kg amphetamine, as compared to the nonstress condition. However, statistical analysis failed to evidence a significant interaction between treatments and conditions (stress vs nonstress) on corticosterone levels, contrary to another vigilance-enhancing drug, modafinil (Béracochéa, Psychopharmacology 196:1-13, 2008).

Improvement of contextual memory by S 24795 in aged mice: comparison with memantine

RESULTS

In comparison with 5-month-old mice, 18- to 19-month-old mice exhibited a severe and specific memory impairment in a contextual serial discrimination (CSD) task involving the learning and remembering of two successive spatial discriminations carried out on two distinct floors. This impairment was specific, as spatial memory, simultaneously tested on a simple discrimination (SD) task, was not affected in these aged mice. This deficit was completely reversed by 9-day per os administration of S 24795, a partial agonist of alpha 7 nicotinic receptors, at either 0.3 or 1.0 mg/kg. Memantine, an NMDA receptor antagonist, also had a memory-enhancing effect at a dose of 3.0 mg/kg, but not at 0.3 mg/kg.

CONCLUSIONS

The memory-enhancing effect of S 24795 was due to a strong enhancement of contextual memory as indicated by a decrease in interference rate, whereas memantine enhanced spatial/semantic memory. S 24795 was more effective than memantine and also appears to be more specific to flexible forms of memory, one of the first cognitive domains (i.e. episodic memory) affected in Alzheimer's disease.

Stress modulation of the memory retrograde-enhancing effects of the awakening drug modafinil in mice

PURPOSE

This study investigated the dose-effect relationship of modafinil administration on contextual memory processes, in parallel with the measurements of plasma corticosterone levels in acutely stressed mice.

MATERIALS AND METHODS

Memory was first evaluated in normal (nonstressed) mice either in contextual (CSD) or spatial (SSD) tasks. Thus, C57 Bl/6 Jico mice learned two consecutive discriminations (D1 and D2) in a four-hole board. The discriminations occurred on either distinct (CSD) or identical (SSD) floors (internal contextual cues). All mice received a vehicle intraperitoneal injection before learning and were injected 24 h later (20 min before the test session) either with vehicle or modafinil.

RESULTS

Results showed that modafinil-treated mice behaved similarly as vehicles in the spatial SSD task, whereas in contrast, memory of the first-learned discrimination (D1) in the CSD task was enhanced by a 32- but not a 16-mg/kg modafinil dose. Hence, we studied the effect of a pretest acute stress (electric footshocks) specifically on D1 performance in modafinil-treated subjects. Immediately after behavioral testing, blood was sampled to measure plasma corticosterone levels.

CONCLUSIONS

Results showed that: (1) stress significantly improved performance in vehicles, (2) stress decreased the efficiency threshold of modafinil, as performance was enhanced at the low dose (16 mg/kg), whereas this enhancement was obtained for the high dose (32 mg/kg) under nonstress conditions, (3) the performance was impaired at the high (32 mg/kg) dose, and (4) modafinil significantly reduced the magnitude of the stress-induced corticosterone secretion, mainly at the dose of 32 mg/kg.

Improvement of episodic contextual memory by S 18986 in middle-aged mice: comparison with donepezil

INTRODUCTION

This study compared the effects of S 18986, a positive allosteric modulator of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors, to those of donepezil a cholinesterase inhibitor on memory impairments induced by ageing in a contextual serial discrimination (CSD) task in middle-aged mice.

MATERIALS AND METHODS

The CSD task involved the learning of two consecutive discriminations in a four-hole board, each performed on two different floors. This model has been developed to study simultaneously different forms of memory in mice (i.e., episodic-like vs semantic-like forms of memory). We showed that placebo-middle-aged mice (14-15 months old) and placebo-aged subjects (19-20 months old) exhibited a severe memory deficit for the first but not the second discrimination, which was due to an increase in interference, as compared with placebo-treated young mice (5 months old). Middle-aged mice were given (9 days) per os administration of either donepezil, S 18986, or placebo.

RESULTS AND DISCUSSION

Both 0.3 mg/kg donepezil and 0.1 mg/kg S 18986 reversed the deficit of middle-aged mice through a significant increase in contextually correct responses and in parallel a tendency to reduce interfering responses.

CONCLUSION

Overall, S 18986 emerges as having a beneficial impact on contextual memory processes in middle-aged mice.