Social recognition memory requires two stages of protein synthesis in mice

Olfactory recognition memory was tested in adult male mice using a social discrimination task. The testing was conducted to begin to characterize the role of protein synthesis and the specific brain regions associated with activity in this task. Long-term olfactory recognition memory was blocked when the protein synthesis inhibitor anisomycin was injected 20 min before, immediately after, or 6 h after sampling. No effect was observed when anisomycin was administered 3 h or 18 h after sampling. Immunohistochemical analysis of Fos expression revealed that sampling-like exposure to a juvenile increased the activity of a subset of cells in the accessory olfactory bulb and the brain areas that are associated with it. Additionally, increased Fos expression was measured in the main olfactory bulb and the piriform cortex, whereas no signs of activation were seen in the cortical nucleus of the amygdala, all components of the main olfactory system. No increases in Fos immunoreactivity were observed after 4 h. Our data suggest that long-lasting olfactory recognition memory requires two stages of protein synthesis. The first stage takes place within 1-2 h and the second stage between 6-7 h after sampling. The first but not the second stage is paralleled by an increase in the number of Fos-immunoreactive cells in brain areas associated with both the main and accessory olfactory systems. It therefore appears that the role of the second stage of protein synthesis in recognition memory depends on the integrity of the first stage of protein synthesis.     

Non-specific effect of fear conditioning and specific effect of social defeat on social recognition memory performance in female rats

The so called "emotion learning" literature describes the ability of distressing and aversive unconditioned stimuli to classically condition a learned avoidance response. In order to investigate the impact of experience with noxious stimuli in one conditioning context on learning and memory performance in a separate, non-aversively motivated task, juvenile recognition ability was examined in adult female rats exposed previously to one of two environmental stressors. In particular, experimental adult rats were either socially defeated by exposure to an aggressive conspecific rat or fear conditioned using single or multiple pairings with footshock prior to performance of the social recognition task. Experiment 1 established that repeated exposure to a single juvenile resulted in social memory formation reflected in decreased social investigation from the first to the second exposure. Experiment 2 documented that both single and multiple pairings of an environment with footshock produced robust freezing behavior (90-95% suppression of activity). In addition, fear conditioning produced a non-specific 5-60% increase in social investigation time in both single and multiple-pairing fear conditioned groups which confounded the ability of the social recognition measure to assess effects of fear conditioning on learning and memory performance per se. In contrast, Experiment 3 documented that when social recognition memory performance was impaired to 85% of control levels by imposition of a 2 h delay, exposure to a social defeat stressor reinstated optimal social recognition memory performance. These findings suggest that the after effects of fear conditioning include non-specific alteration of social investigation whereas exposure to conspecific aggression enhances subsequent social recognition memory.     

Cytotoxic lesions of the hippocampus do not impair social recognition memory in socially housed rats

Socially housed mice with cytotoxic lesions of the hippocampus do not exhibit social recognition memory 30 min following exposure to a juvenile mouse, however the social recognition memory of singly housed rats is unimpaired. The present study tests the hypothesis that social housing of rats could render social recognition memory hippocampally dependent as seen for mice. Rats were housed with juveniles or with adults. Two social recognition one-animal tests paralleling those used with mice were carried out. Seven social discrimination two-animal tests were also given. Sham operated and hippocampally lesioned rats had normal social memory at 30 min whether socially housed for 24, 48 h, 7 or 8 days prior to testing. These findings support other results indicating the hippocampus proper is not required for normal social memory in rats. In a final experiment, rats socially housed in groups of three since weaning, were tested for 30 min and 24 h social memory. Unlike mice, rats socially housed throughout life exhibited social memory only at 30 min, but not at 24 h. Manipulations that extend social memory in rats may be required to render social memory hippocampally dependent or rats and mice may differ in the neural mediation of social memory.     

Social enrichment improves social recognition memory in male rats

The social environment is thought to have a strong impact on cognitive functions. In the present study, we investigated whether social enrichment could affect rats’ memory ability using the “Different Objects Task (DOT),” in which the levels of memory load could be modulated by changing the number of objects to be remembered. In addition, we applied the DOT to a social discrimination task using unfamiliar conspecific juveniles instead of objects. Animals were housed in one of the three different housing conditions after weaning [postnatal day (PND) 21]: social-separated (1 per cage), standard (3 per cage), or social-enriched (10 per cage) conditions. The object and social recognition tasks were conducted on PND 60. In the sample phase, the rats were allowed to explore a field in which 3, 4, or 5 different, unfamiliar stimuli (conspecific juveniles through a mesh or objects) were presented. In the test phase conducted after a 5-min delay, social-separated rats were able to discriminate the novel conspecific from the familiar ones only under the condition in which three different conspecifics were presented; social-enriched rats managed to recognize the novel conspecific even under the condition of five different conspecifics. On the other hand, in the object recognition task, both social-separated and social-enriched rats were able to discriminate the novel object from the familiar ones under the condition of five different objects. These results suggest that social enrichment can enhance social, but not object, memory span.     

Competition between two memory traces for long-term recognition memory

Previous studies investigating the processes which underlie memory consolidation focused almost exclusively on isolated learning events. Here I studied the competition of two similar memory traces for consolidation non-conditioned recognition memory in adult male C57BL/6JOlaHsd mice using the olfactory cues based social discrimination procedure. My results show that the interference phenomena that cause forgetting are time-dependent, and that retroactive interference can be discriminated from proactive interference. Furthermore, both types of interference can be suppressed by subcutaneous anisomycin treatment immediately after presentation of the interference stimulus. These findings imply that interference phenomena, which result from the competition of two similar memory traces for long-term recognition memory, are related to the progress of memory consolidation and linked to protein synthesis.     

Sensory and semantic factors in recognition memory for odors and graphic stimuli: elderly versus young persons

In four experiments, young (18-26 years, M = 21) and elderly (over 65 years, M = 72) people were compared for recognition memory of (a) graphic stimuli (faces of presidents and vice presidents, engineering symbols, and free forms) and (b) everyday odors. On graphic stimuli, the elderly consistently matched the young, but on odors the performance of the elderly was worse. Their poorer olfactory performance was observed after only 26 s, but became truly marked after 1 hr or more. Somewhere between 1 hr and 2 weeks, their odor performance fell to chance, but their graphic performance remained well above chance. Although the young did forget both graphic and odor materials progressively, their performance always stayed above chance over a 6-month period. Experiments 1 and 2 revealed that the elderly are less sensitive to odors than the young (with thresholds about 10-fold higher), which may explain, in part, their poorer olfactory memory performance. Knowledge that the subjects brought to the tasks by way of familiarity with and ability to name odors and faces played a positive role in recognition memory. Because of this positive role, together with the negative role played by verbal distraction, we conclude that odor recognition memory depends, perhaps heavily, on semantic processing. Impaired semantic processing may result even when odors are simply rendered desaturated, or pastel because of the weakening of olfactory sensitivity with aging.     

Neural correlates of olfactory learning: Critical role of centrifugal neuromodulation

The mammalian olfactory system is well established for its remarkable capability of undergoing experience-dependent plasticity. Although this process involves changes at multiple stages throughout the central olfactory pathway, even the early stages of processing, such as the olfactory bulb and piriform cortex, can display a high degree of plasticity. As in other sensory systems, this plasticity can be controlled by centrifugal inputs from brain regions known to be involved in attention and learning processes. Specifically, both the bulb and cortex receive heavy inputs from cholinergic, noradrenergic, and serotonergic modulatory systems. These neuromodulators are shown to have profound effects on both odor processing and odor memory by acting on both inhibitory local interneurons and output neurons in both regions.     

What a nostril knows: olfactory nerve-evoked AMPA responses increase while NMDA responses decrease at 24-h post-training for lateralized odor preference memory in neonate rat

Increased AMPA signaling is proposed to mediate long-term memory. Rat neonates acquire odor preferences in a single olfactory bulb if one nostril is occluded at training. Memory testing here confirmed that only trained bulbs support increased odor preference at 24 h. Olfactory nerve field potentials were tested at 24 h in slices from trained and untrained bulbs. A larger AMPA component and a smaller NMDA component characterized responses in the bulb receiving odor preference training. Field potential changes were not seen in a bulbar region separate from the lateral odor-encoding area. These results support models in which memory is mediated by increased olfactory nerve-mitral cell AMPA signaling, and memory stability is promoted by decreased NMDA-mediated signaling.     

The consolidation of object and context recognition memory involve different regions of the temporal lobe

These experiments investigated the involvement of several temporal lobe regions in consolidation of recognition memory. Anisomycin, a protein synthesis inhibitor, was infused into the hippocampus, perirhinal cortex, insular cortex, or basolateral amygdala of rats immediately after the sample phase of object or object-in-context recognition memory training. Anisomycin infused into perirhinal or insular cortices blocked long-term (24 h), but not short-term (90 min) object recognition memory. Infusions into the hippocampus or amygdala did not impair object recognition memory. Anisomycin infused into the hippocampus blocked long-term, but not short-term object-in-context recognition memory, whereas infusions administered into the perirhinal cortex, insular cortex, or amygdala did not affect object-in-context recognition memory. These results clearly indicate that distinct regions of the temporal lobe are differentially involved in long-term object and object-in-context recognition memory. Whereas perirhinal and insular cortices are required for consolidation of familiar objects, the hippocampus is necessary for consolidation of contextual information of recognition memory. Altogether, these results suggest that temporal lobe structures are differentially involved in recognition memory consolidation.     

Hippocampal c-fos is necessary for long-term memory of a socially transmitted food preference

The present article examined the requirement of hippocampal c-Fos for learning a socially transmitted food preference (STFP). We reported previously that expression of the c-Fos protein is increased in the dorsal and ventral hippocampus of rats trained on the STFP (Countryman, Orlowski, Brightwell, Oskowitz, & Colombo, 2005). Pretraining intrahippocampal antisense to the immediate early gene c-fos was administered to adult male Long-Evans rats to determine if c-fos expression is necessary for either short- or long-term memory for STFP. Guide cannulae were implanted bilaterally into the dorsal hippocampus. Antisense oligodeoxynucleotides (ODNs) were administered unilaterally either 6.5, 8.5, 10.5, or 12.5 h prior to STFP training while either sense ODNs or saline were infused into the opposite hemisphere. Immunocytochemistry was performed, and cells showing c-Fos immunoreactivity (ir) were counted from the antisense-treated hemisphere and compared to cell counts from the control hemisphere. The results indicated significant suppression of learning-induced c-Fos protein at the 8.5 and 10.5 infusion-train intervals. Additional rats were implanted with cannulae into the dorsal and ventral hippocampus, and antisense ODNs, sense ODNs, or saline were administered bilaterally 8.5h prior to training. Rats were tested immediately and 14 days after training. Rats in all groups showed a significant preference for the demonstrated food at the short-term memory test. At the long-term memory test, however, rats infused with c-fos antisense showed no preference for the demonstrated food whereas rats infused with either sense or saline maintained their preference. The present findings suggest that c-fos is necessary for consolidation of non-spatial hippocampal-dependent memory.     

Assessing the associative deficit of older adults in long-term and short-term/working memory

Older adults exhibit a deficit in associative long-term memory relative to younger adults. However, the literature is inconclusive regarding whether this deficit is attenuated in short-term/working memory. To elucidate the issue, three experiments assessed younger and older adults' item and interitem associative memory and the effects of several variables that might potentially contribute to the inconsistent pattern of results in previous studies. In Experiment 1, participants were tested on item and associative recognition memory with both long-term and short-term retention intervals in a single, continuous recognition paradigm. There was an associative deficit for older adults in the short-term and long-term intervals. Using only short-term intervals, Experiment 2 utilized mixed and blocked test designs to examine the effect of test event salience. Blocking the test did not attenuate the age-related associative deficit seen in the mixed test blocks. Finally, an age-related associative deficit was found in Experiment 3, under both sequential and simultaneous presentation conditions. Even while accounting for some methodological issues, the associative deficit of older adults is evident in short-term/working memory. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Bicuculline infusion into the accessory olfactory bulb facilitates the induction of maternal behavior in rats

The GABAA antagonist bicuculline, intracranially infused into the accessory olfactory bulb (AOB), facilitated the expression of maternal behavior (MB) in virgin Wistar female rats. Behavioral effects were observed 24 hours after infusion and were injection dependent. Pheromonal stimuli, generated by the pups, are thought to exert an inhibitory effect on vomeronasal nuclei involved in MB in virgin rats. The present study investigated the possibility that a decrement in AOB output, resulting from long-term compensatory synaptic changes to chronic bicuculline infusion, would facilitate the expression of MB. The implications of our findings for the mechanisms involved in the induction of MB and the maternal experience effect are discussed.     

Interspecific aggressiveness and reactivity in mouse-killing and nonkilling rats: Compared effects of olfactory bulb removal and raphe lesions

The experiments aimed at uncovering possible correlations between inter-specific aggressiveness and general and emotional responsiveness (appraised by means of the open-field technique) in the rat. Killer rats showed a higher level of emotional responsiveness than nonkillers. Removal of the olfactory bulbs induced an increased reactivity both in the rats which were converted into killers in those whose behavior toward mice remained unchanged. Destruction of the dorsal and medial nuclei of the raphé induced a clear hyperreactivity in most lesioned animals, but provoked initiation of mouse-killing behavior in only one-third. When produced in rats which had remained nonkillers following olfactory bulb removal, the raphé lesion clearly enhanced both the general and the emotional responsiveness; it provoked initiation of mouse-killing behavior in about 75% of the lesioned animals. The discussion bears on the correlations between interspecific aggressiveness and experimentally induced hyperreactivity in the rat.     

Stimulus-form effectsin recognition memory

In two experiments, recognition memory was tested using memorized lists of items containing from 2 to 32 nominal concepts. Stimulus form was manipulated by using the names of the items on word trials and outline drawings of the items on picture trials. In terms of an information processing stage model of recognition memory, stimulus form affected only an identification or encoding stage of processing. Subsequent memory-search, decision, and response processes were largely the same for all stimuli once the words or pictures were encoded. The results are consistent with the hypothesized role of stimulus form in processes underlying long-term recognition. However, our results are inconsistent with those of a number of studies involving stimulus-form effects in short-term recognition memory.     

The role of articulatory suppression in immediate false recognition

False memory for critical lures has been widely documented in long-term memory using the Deese/Roediger-McDermott paradigm. Recent evidence suggests that false memory effects can also be found in short-term memory (STM), supporting models that assume a strong relationship between short-term and long-term memory processes. However, no study has examined the role of articulatory suppression on immediate false memory, even though phono-articulatory factors are critically involved in STM performance and are an intrinsic part of all STM accounts. The current study proposes a novel paradigm to assess false memory effects in a STM task under both silent and articulatory suppression conditions. Using immediate serial recognition, in which participants had to judge whether two successive mixed lists of six associated and non-associated words were matched, we examined true recognition of matching lists and false recognition of mismatching lists comprising a critical lure or unrelated distractor in two experiments. Results from both experiments indicated reduced true recognition of matching lists and greater false serial recognition of mismatching lists comprising a critical lure under articulatory suppression relative to silence. These findings provide further support for some current models of verbal short-term memory, which posit a strong relationship between short-term and long-term memory processes.     

Noradrenergic control of odor recognition in a nonassociative olfactory learning task in the mouse

The present study examined the influence of pharmacological modulations of the locus coeruleus noradrenergic system on odor recognition in the mouse. Mice exposed to a nonrewarded olfactory stimulation (training) were able to memorize this odor and to discriminate it from a new odor in a recall test performed 15 min later. At longer delays (30 or 60 min), the familiar odor was no longer retained, and both stimuli were perceived as new ones. Following a post-training injection of the alpha(2)-adrenoceptor antagonist dexefaroxan, the familiar odor was still remembered 30 min after training. In contrast, both the alpha(2)-adrenoceptor agonist UK 14304 and the noradrenergic neurotoxin DSP-4 prevented the recognition of the familiar odor 15 min after the first exposure. Noradrenaline release in the olfactory bulb, assessed by measurement of the extracellular noradrenaline metabolite normetanephrine, was increased by 62% following dexefaroxan injection, and was decreased by 38%-44% after treatment with UK 14304 and DSP-4. Performance of mice in the recall test was reduced by a post-training injection of the beta-adrenoceptor antagonist propranolol or the alpha(1)-antagonist prazosin, thus implicating a role for beta- and alpha(1)-adrenoceptors in the facilitating effects of noradrenaline on short-term olfactory recognition in this model.     

The role of articulatory suppression in immediate false recognition

False memory for critical lures has been widely documented in long-term memory using the Deese/Roediger-McDermott paradigm. Recent evidence suggests that false memory effects can also be found in short-term memory (STM), supporting models that assume a strong relationship between short-term and long-term memory processes. However, no study has examined the role of articulatory suppression on immediate false memory, even though phono-articulatory factors are critically involved in STM performance and are an intrinsic part of all STM accounts. The current study proposes a novel paradigm to assess false memory effects in a STM task under both silent and articulatory suppression conditions. Using immediate serial recognition, in which participants had to judge whether two successive mixed lists of six associated and non-associated words were matched, we examined true recognition of matching lists and false recognition of mismatching lists comprising a critical lure or unrelated distractor in two experiments. Results from both experiments indicated reduced true recognition of matching lists and greater false serial recognition of mismatching lists comprising a critical lure under articulatory suppression relative to silence. These findings provide further support for some current models of verbal short-term memory, which posit a strong relationship between short-term and long-term memory processes.     

Muscarinic receptors activity in the perirhinal cortex and hippocampus has differential involvement in the formation of recognition memory

In this work we probed the effects of post-trial infusions of the muscarinic receptor antagonist scopolamine on object recognition memory formation. Scopolamine was infused bilaterally immediately after the sample phase in the perirhinal cortex or dorsal hippocampus and animals were tested for short-term (90 min) or long-term (24 h) memory. Results showed that scopolamine impaired short-term memory when injected in either the perirhinal cortex or hippocampus. Nevertheless, scopolamine disrupted long-term memory when administrated in the perirhinal cortex but not when applied in the hippocampus. Long-term memory was unaffected when scopolamine was infused 160 min after the sample phase or 90 min before test phase. Our data indicate that short-term recognition memory requires muscarinic receptors signaling in both the perirhinal cortex and hippocampus, whereas long-term recognition memory depends on muscarinic receptors in the perirhinal cortex but not hippocampus. These results support a differential involvement of muscarinic activity in these two medial temporal lobe structures in the formation of recognition memory.