Memory Reconsolidation Mediates the Updating of Hippocampal Memory Content

The retrieval or reactivation of a memory places it into a labile state, requiring a process of reconsolidation to restabilize it. This retrieval-induced plasticity is a potential mechanism for the modification of the existing memory. Following previous data supportive of a functional role for memory reconsolidation in the modification of memory strength, here I show that hippocampal memory reconsolidation also supports the updating of contextual memory content. Using a procedure that separates the learning of pure context from footshock-motivated contextual fear learning, I demonstrate doubly dissociable hippocampal mechanisms of initial context learning and subsequent updating of the neutral contextual representation to incorporate the footshock. Contextual memory consolidation was dependent upon BDNF expression in the dorsal hippocampus, whereas the footshock modification of the contextual representation required the expression of Zif268. These mechanisms match those previously shown to be selectively involved in hippocampal memory consolidation and reconsolidation, respectively. Moreover, memory reactivation is a necessary step in modifying memory content, as inhibition of hippocampal synaptic protein degradation also prevented the footshock-mediated memory modification. Finally, dorsal hippocampal knockdown of Zif268 impaired the reconsolidation of the pure contextual memory only under conditions of weak context memory training, as well as failing to disrupt contextual freezing when a strong contextual fear memory is reactivated by further conditioning. Therefore, an adaptive function of the reactivation and reconsolidation process is to enable the updating of memory content

Perspectives of healthcare providers on the nutritional management of patients on haemodialysis in Australia: An interview study

Objective To describe the perspectives of healthcare providers on the nutritional management of patients on haemodialysis, which may inform strategies for improving patient-centred nutritional care. Design Face-to-face semistructured interviews were conducted until data saturation, and thematic analysis based on principles of grounded theory. Setting 21 haemodialysis centres across Australia. Participants 42 haemodialysis clinicians (nephrologists and nephrology trainees (15), nurses (12) and dietitians (15)) were purposively sampled to obtain a range of demographic characteristics and clinical experiences. Results Six themes were identified: responding to changing clinical status (individualising strategies to patient needs, prioritising acute events, adapting guidelines), integrating patient circumstances (assimilating life priorities, access and affordability), delineating specialty roles in collaborative structures (shared and cohesive care, pivotal role of dietary expertise, facilitating access to nutritional care, perpetuating conflicting advice and patient confusion, devaluing nutritional specialty), empowerment for behaviour change (enabling comprehension of complexities, building autonomy and ownership, developing self-efficacy through engagement, tailoring self-management strategies), initiating and sustaining motivation (encountering motivational hurdles, empathy for confronting life changes, fostering non-judgemental relationships, emphasising symptomatic and tangible benefits, harnessing support networks), and organisational and staffing barriers (staffing shortfalls, readdressing system inefficiencies). Conclusions Organisational support with collaborative multidisciplinary teams and individualised patient care were seen as necessary for developing positive patient-clinician relationships, delivering consistent nutrition advice, and building and sustaining patient motivation to enable change in dietary behaviour. Improving service delivery and developing and delivering targeted, multifaceted self-management interventions may enhance current nutritional management of patients on haemodialysis

Memory reconsolidation in aversive and appetitive settings

Memory reconsolidation has been observed across species and in a number of behavioral paradigms. The majority of memory reconsolidation studies have been carried out in Pavlovian fear conditioning and other aversive memory settings, with potential implications for the treatment of post-traumatic stress disorder. However, there is a growing literature on memory reconsolidation in appetitive reward-related memory paradigms, including translational models of drug addiction. While there appears to be substantial similarity in the basic phenomenon and underlying mechanisms of memory reconsolidation across unconditioned stimulus valence, there are also notable discrepancies. These arise both when comparing aversive to appetitive paradigms and also across different paradigms within the same valence of memory. We review the demonstration of memory reconsolidation across different aversive and appetitive memory paradigms, the commonalities and differences in underlying mechanisms and the conditions under which each memory undergoes reconsolidation. We focus particularly on whether principles derived from the aversive literature are applicable to appetitive settings, and also whether the expanding literature in appetitive paradigms is informative for fear memory reconsolidation

Dopamine D1-like receptor signalling in the hippocampus and amygdala modulates the acquisition of contextual fear conditioning

RATIONALE: Dopamine D1-like receptor signalling is involved in contextual fear conditioning, but the brain regions involved and its role in other contextual fear memory processes remain unclear. OBJECTIVES: The objective of this study was to investigate (1) the effects of SCH 23390, a dopamine D1/D5 receptor antagonist, on contextual fear memory encoding, retrieval and reconsolidation, and (2) if the effects of SCH 23390 on conditioning involve the dorsal hippocampus (DH) and/or basolateral amygdala (BLA). METHODS: Rats were used to examine the effects of systemically administering SCH 23390 on the acquisition, consolidation, retrieval and reconsolidation of contextual fear memory, and on locomotor activity and shock sensitivity. We also determined the effects of MK-801, an NMDA receptor antagonist, on contextual fear memory reconsolidation. The effects of infusing SCH 23390 locally into DH or BLA on contextual fear conditioning and locomotor activity were also examined. RESULTS: Systemic administration of SCH 23390 impaired contextual fear conditioning but had no effects on fear memory consolidation, retrieval or reconsolidation. MK-801 was found to impair reconsolidation, suggesting that the behavioural parameters used allowed for the pharmacological disruption of memory reconsolidation. The effects of SCH 23390 on conditioning were unlikely the result of any lasting drug effects on locomotor activity at memory test or any acute drug effects on shock sensitivity during conditioning. SCH 23390 infused into either DH or BLA impaired contextual fear conditioning and decreased locomotor activity. CONCLUSIONS: These findings suggest that dopamine D1-like receptor signalling in DH and BLA contributes to the acquisition of contextual fear memory