Biomedical subjects

Kashif Parvez

Publications and source records attributed to Kashif Parvez.

5 recordsLinked to original sources

PubMed2006

Modulation of aerial respiratory behaviour in a pond snail.

Aerial respiratory in Lymnaea is driven by a three-neuron CPG whose sufficiency and necessity has been directly demonstrated. While this CPG is 'hard-wired' it displays a tremendous amount of plasticity. That is, it is possible by employing specific training procedures to alter how it functions in a specific hypoxic environment. Thus, it is possible to study directly the causal mechanisms of long-term memory formation, forgetting, and modulation of the memory at a single cell level. Thus, it is possible to use a relatively simple three-neuron CPG to study not only important questions concerning regulation of important homeostatic mechanisms but to also use it to study how learning and non-declarative memory are mediated at a cellular level.

Animals↗

PubMed2006

A context-specific single contingent-reinforcing stimulus boosts intermediate-term memory into long-term memory.

Following operant conditioning of aerial respiration in Lymnaea, memory forms. Depending on the training procedure either intermediate memory (ITM, < 3 h) or long-term memory (LTM, > 6 h) results. ITM is dependent on de novo protein synthesis whilst LTM is dependent on both transcription and de novo protein synthesis. LTM formation requires the soma of RPeD1 (one of the central pattern generator neurons) to be present. Following activation of a memory, it re-enters a labile state and undergoes a reconsolidation process to restabilize it. During reconsolidation, memory may be updated and/or changed. We add here another consequence of memory reactivation: a single contingent-reinforcing stimulus (SCRS), given in the same context as previous ITM training, boosts a residual memory trace to LTM. Separate cohorts of snails first received the ITM training procedure. In the cohort that received the SCRS 24 h after the last ITM training session, LTM was observed on the following day. LTM was not observed in cohorts that were: (i) given a single noncontingent stimulus; (ii) given the SCRS in a context other than the ITM training; (iii) given a 48-h gap between the last ITM training session and the context-specific SCRS; (iv) cooled immediately after the last ITM training session; (v) cooled immediately after the delivery of the context-specific SCRS; (vi) had the soma of RPeD1 ablated before the presentation of the context-specific SCRS; (vii) received a yoked control procedure. These data lead us to conclude that the context-specific SCRS reactivates a residual molecular memory trace in RPeD1 and boosts it into becoming the substrate for LTM.

Animals↗

PubMed2005

Boosting intermediate-term into long-term memory.

Aerial respiration in the pond snail Lymnaea stagnalis can be operantly conditioned. Depending on the specific training procedure used (i.e. a 0.5 h vs a 1.0 h interval between training sessions) either intermediate (ITM) or long-term memory (LTM) is formed. ITM, which persists for 2-3 h, is dependent only on de novo protein synthesis, whilst LTM persists for up to 4 weeks and is dependent on both transcription and de novo protein synthesis. We found that although the behavioural phenotype of ITM was not apparent 24 h after the last training session, a residual memory trace was present that serves as a foundation upon which a subsequent ITM-training-procedure builds on to form LTM (i.e. a "changed memory"). This residual memory trace could be perturbed by cooling, the behavioural process of context-specific extinction and by increasing the interval between the training procedures. Furthermore in preparations where the somata of RPeD1 (one of three interneurons in the central pattern generator required for aerial respiratory behavior) had been ablated before training, LTM could not be observed following a second bout of ITM-training. These data support the concept that a molecular memory trace is established as a consequence of ITM-training, which serves as a "permissive substrate", when the ITM memory is made active, sufficient to permit the necessary transcription and translation processes that are causal for LTM formation.

Analysis of Variance↗

PubMed2004

Memory, reconsolidation and extinction in Lymnaea require the soma of RPeD1.

The central pattern generator (CPG) that drives aerial respiratory behaviour in Lymnaea consists of 3 neurons. One of these, RPeD1--the cell that initiates activity in the circuit, plays an absolutely necessary role as a site for memory formation, memory reconsolidation, and extinction. Using an operant conditioning training procedure that results in a long-term non-declarative memory (LTM), we decrease the occurrence of aerial respiratory behaviour. Since snails can still breathe cutaneously learning this procedure is not harmful. Concomitant with behavioural memory are changes in the spiking activity of RPeD1. Going beyond neural correlates of memory we directly show that RPeD1 is a necessary site for LTM formation. Expanding on this finding we show that this neuron is also a necessary site for memory reconsolidation and 'Pavlovian' extinction. As far as we can determine, this is the first time a single neuron has been shown to be a necessary site for these different aspects memory. RPeD1 is thus a key neuron mediating different hierarchical aspects of memory. We are now in a position to determine the necessary neuronal, molecular and proteomic events in this neuron that are causal to memory formation, reconsolidation and extinction.

Animals↗

PubMed2003

A molluscan model system in the search for the engram.

A 3-neuron central pattern generator, whose sufficiency and necessity has been directly demonstrated, mediates aerial respiratory behaviour in the pond snail, Lymnaea stagnalis. This behaviour can be operantly conditioned, and this associative learning is consolidated into long-lasting memory. Depending on the operant conditioning training procedure used the learning can be consolidated into intermediate term (ITM) or long-term memory (LTM). ITM persists for only 2-3 h, whilst LTM persists for days to weeks. LTM is dependent on both altered gene activity and new protein synthesis while ITM is only dependent on new protein synthesis. We have now directly established that one of the 3-CPG neurons, RPeD1, is a site of LTM formation and storage. We did this by ablating the soma of RPeD1 and leaving behind a functional primary neurite capable of mediating the necessary synaptic interactions to drive aerial respiratory behaviour by the 3-neuron CPG. However, following soma ablation the neuronal circuit is only capable of mediating learning and ITM. LTM can no longer be demonstrated. However, if RPeD1's soma is ablated after LTM consolidation memory is still present. Thus the soma is not needed for the retention of LTM. Using a similar strategy it may be possible to block forgetting.

Animals↗