Neural Encoding of Olfactory Recognition Memory

Abstract

Abstract. Our work with both sheep and mouse models has revealed many of the neural substrates and signalling pathways involved in olfactory recognition memory in the main olfactory system. A distributed neural system is required for initial memory formation and its short-term retention-the olfactory bulb, piriform and entorhinal cortices and hippocampus. Following memory consolidation, after 8 h or so, only the olfactory bulb and piriform cortex appear to be important for effective recall. Similarly, whereas the glutamate-NMDA/AMPA receptor-nitric oxide (NO)-cyclic GMP signalling pathway is important for memory formation it is not involved in recall post-consolidation. Here, within the olfactory bulb, up-regulation of class 1 metabotropic glutamate receptors appears to maintain the enhanced sensitivity at the mitral to granule cell synapses required for effective memory recall. Recently we have investigated whether fluctuating sex hormone levels during the oestrous cycle modulate olfactory recognition memory and the different neural substrates and signalling pathways involved. These studies have used two robust models of social olfactory memory in the mouse which either involve social or non social odours (habituation-dishabituation and social transmission of food preference tasks). In both cases significant improvement of learning retention occurs when original learning takes place during the proestrus phase of the ovarian cycle. This is probably the result of oestrogen changes at this time since transgenic mice lacking functional expression of oestrogen receptors (ERα and ERβ, the two main oestrogen receptor sub-types) have shown problems in social recognition. Therefore, oestrogen appears to act at the level of the olfactory bulb by modulating both noradrenaline and the glutamate/NO signalling pathway. Key words: Olfactory bulb, Olfactory memory, Olfactory recognition, Social learning, Nitric oxide (NO), Oestrous cycle, Sheep, Mouse, Social transmission of food preference (J. Reprod. Dev. 51: [547][548][549][550][551][552][553][554][555][556][557][558] 2005) or several decades, olfactory learning has been used as a model for the study of memory. This is not only because mammalian olfactory learning shows a number of features common to the human declarative memory system one-trial learning, rapid encoding, long lasting memories and a high capacity for information storage-but also because olfactory memory models represent a relatively simple form of learning and the olfactory system has well characterised pathways and structural organisation which offers many advantages in defining how processing occurs at a systems level. This makes it feasible to study plasticity at all levels in the system, from the initial sensory detection of odourant molecules at the level of the olfactory receptors righ t thr ough to high er cortical processing.There are many different forms of olfactory learning and memory in diverse behavioural contexts involving different mechanisms within the olfactory system. Olfactory learning ...

Differential Effects of Estrogen Receptor Alpha and Beta Specific Agonists on Social Learning of Food Preferences in Female Mice

“…DA has been shown to be involved in social learning, as studies in mice have found that dopamine acting on the D1 but not the D2 dopamine receptor mediates the STFP (Choleris et al, in preparation). Mesocorticolimbic DA projections innervate many of the areas known to be involved in the STFP, such as the hippocampal region, the orbitofrontal cortex, and the amygdala (eg Bunsey and Eichenbaum, 1995;Alvarez et al, 2001;Sánchez-Andrade et al, 2005;Ross et al, 2005;Wang et al, 2007). The dopaminergic system is modulated by estrogens, both through increasing the release of DA (McDermott et al, 1994;Liu and Xie, 2004) and through decreasing the expression and activity of the DA transporter, which eliminates DA from the extracellular space (Karakaya et al, 2007).…”

“…It was recently shown that the estrous cycle can affect the memory of an STFP (as reported in Sánchez-Andrade et al, 2005). When tested 24 h after interacting with a demonstrator, only mice in proestrus showed a socially acquired preference (Sánchez-Andrade et al, 2005).…”

“…It was recently shown that the estrous cycle can affect the memory of an STFP (as reported in Sánchez-Andrade et al, 2005). When tested 24 h after interacting with a demonstrator, only mice in proestrus showed a socially acquired preference (Sánchez-Andrade et al, 2005). Additionally, we have recently shown that, when tested immediately, the preference for the demonstrated food lasted 1.5-2.5 times longer in diestrus and proestrus females than in estrus and ovariectomized mice (Choleris et al, in preparation).…”

Maternal responsiveness and maternal selectivity in domestic sheep and goats: The two facets of maternal attachment

“…While during lamb memory formation, extensive immediately early genes activation was found throughout the olfactory processing network, it appears that only few brain structures are engaged in retrieval of lamb memory once consolidated. During the early stages of memory consolidation, piriform and entorhinal cortices show significant expression of activation markers, while retrieval of more consolidated memory (7 days postpartum) leads to an enhanced activation of frontal and orbitofrontal cortices (Keller et al, 2004a(Keller et al, ,b, 2005Sanchez-Andrade et al, 2005). Thus, consolidation processes induce time-dependent reorganization in the network engaged in lamb recognition.…”

Olfactory cues are sufficient to elicit social approach behaviors but not social transmission of food preference in C57BL/6J mice

“…The food preference is subsequently measured in a choice test for consumption of the novel flavored food that the demonstrator ate versus a second, completely novel flavored food. Originally developed as a memory task [23,54], STFP may be used without a temporal delay between the interaction session and the choice session, to measure aspects of social communication between conspecifics [39,53]. Successful development of the food preference requires the subject mouse to interact with, and gather relevant olfactory and taste cues from, a conspecific.…”