---
description: Discussion writing — section tags, annotated well-written example, and usage for scientific manuscripts.
name: writing-discussion-example
tags: [scitex-writer, scitex-package]
---

# Scientific Discussion — Section Tags and Example

Continuation of [33_writing-discussion.md](33_writing-discussion.md).

## Section Tags

Insert the following section tags (START and END) to annotate the revised text:
- [START of 1. Summarizing Key Findings] ... [END of 1. Summarizing Key Findings]
- [START of 2. Comparison with Previous Evidence] ... [END of 2. Comparison with Previous Evidence]
- [START of 3. Supporting Your Findings] ... [END of 3. Supporting Your Findings]
- [START of 4. Limitations] ... [END of 4. Limitations]
- [START of 5. Implications] ... [END of 5. Implications]

## Example (Well-written Discussion)

The following example demonstrates proper use of section tags. Note that the order of paragraphs may be exchangeable, and it is not always easy to allocate tags cleanly.

[START of 1. Summarizing Key Findings] We have generated a knockout mouse strain lacking the NMDAR1 subunit in the CA1 region of the hippocampus. These mice seem to grow normally and do not present obvious behavioral abnormalities. We have shown that the mutant mice lack NMDAR-mediated EPSCs and LTP in the CA1 region and are impaired in the hidden-platform version of the Morris water maze (a measure of spatial memory) but not in nonspatial learning tasks. Previously, it has been suggested that NMDA receptor-dependent LTP underlies the acquisition of new memories in the hippocampus (reviewed by4, 40). Our results provide a strong support for this view and makes it more specific: the NMDA receptor-dependent LTP in the CA1 region is crucially involved in the formation of certain types of memory. [END of 1. Summarizing Key Findings] [START of 4. Limitations] We cannot exclude the possibility that the NMDA receptor-dependent synaptic plasticity crucial for memory formation is LTD, given that the CA1-KO mice seem to lack NMDAR-dependent LTD. [END of 4. Limitations] [START of 3. Supporting Your Findings] However, we think that this is unlikely because spatial learning is apparently intact in knockout mice deficient in protein kinase A that lack CA1 LTD (Brandon et al. 1995). [END of 3. Supporting Your Findings]

[START of 2. Comparison with Previous Evidence] Previous work has used pharmacological and genetic tools to examine whether synaptic plasticity is the mechanism for memory formation. Although the evidence is consistent with this notion many issues have remained unresolved. For example, the most sophisticated pharmacological studies that have been done thus far are based on the infusion of NMDAR antagonists directly into the brain (39, 9). Since the infusion cannot be localized to a particular region (such as the CA1 region) with the exclusion of the rest of brain, it is not possible to determine the contribution of specific areas to memory formation. Moreover, it has been reported that NMDARs contribute substantially to the basal synaptic transmission in some areas of the neocortex (Hestrin 1996). Thus, the memory impairment could be explained at least in part by a defect in the computational ability of the neocortex rather than by an impairment in the synaptic plasticity within the hippocampus.
Several drawbacks also accompany the conventional gene knockout studies. In particular, the ubiquitous deletion of the gene may cause undesirable developmental and behavioral consequences. Our work circumvents these concerns because the deletion of the NMDAR1 subunit occurs in a restricted manner, only in the CA1 region. [END of 2. Comparison with Previous Evidence] [START of 3. Supporting Your Findings] We have not yet shown directly the precise developmental timing of the Cre/loxP recombination that deletes the NMDAR1 gene. However, an accompanying article (Tsien et al. 1996) in which we use the expression of beta-galactosidase as a reporter for the recombination shows that it occurs during the third postnatal week, about 2 weeks after the CA1 region of the hippocampus has completed its cellular organization and connections (44, 45, 52). Thus, it is likely that the NMDAR1 gene is also deleted at this time, providing a postnatal knockout of the gene and thus avoiding the developmental concerns. [END of 3. Supporting Your Findings]

[START of 4. Limitations] Consideration into the Mixed Genetic Background Another caveat associated with the behavioral studies done in gene knockout mice stems from the fact that ES cells from the mouse strain 129/Sv are commonly used to generate the mutant mice (reviewed by Gerlai 1996). The 129/Sv mice demonstrate behavioral defects such as the inability to perform the Morris water maze task (Gerlai 1996). Consequently, most behavioral studies with knockout mice have been carried out after crossing them to a behaviorally "normal" strain, such as C57BL/6. This of course causes animal-to-animal variations in the ability to perform a certain behavioral task, variation that is attributed to the difference in the genetic background. The problem is best resolved by using ES cells derived from a behaviorally normal strain, such as C57BL/6. Recently, ES cells from this strain that have an acceptable frequency of germline transmission have become available (Kawase et al. 1994; Kontgen et al. 1993; Ledermann and Burki 1991). In the current study, the genetic background issue has not been resolved completely. However, we avoided a major source of variation for the Morris water maze task by eliminating "floating" individuals from both the mutant and control groups (see Experimental Procedures). [END of 4. Limitations]

[START of 3. Supporting Your Findings] Gene Knockout Studies Point to a Pivotal Role of CA1 Synaptic Plasticity Previous studies examined the correlation between spatial memory and the site of hippocampal LTP (i.e., CA1, CA3, and dentate gyrus) by using a variety of conventional knockout mice (reviewed by Chen and Tonegawa 1997). These studies found a correlated impairment in Scc-CA1 LTP and spatial memory (but see Conquet et al. 1994). It is important to point out that the only exceptional case, namely that of the mGluR1 mutant mice, is complicated by the fact that two groups have generated and analyzed these mutants independently and have obtained opposing results (1, 13, 11). By contrast, it has been shown that impairments of mossy fiber-CA3 LTP (Huang et al. 1995) and perforant path-dentate LTP (Nosten-Bertrand et al. 1996) are not correlated with spatial memory deficit.
Our new evidence, while still correlational, is much stronger than that in the earlier reports because we have singled out the CA1 synapses as a site of plasticity impairment. What structural and functional features could explain this pivotal role of CA1 synapses as sites of plasticity underlying spatial memory? It is well known that the CA1 region is a crucial component of the "hippocampal formation" system that is involved in the acquisition of certain types of memory. In rodents, this system consists of several structures connected within a loop that encompasses the entorhinal cortex (EC), with inputs from higher sensory cortices; dentate gyrus (DG), with inputs from EC; CA3, with "external" inputs from EC and DG and "internal" inputs from CA3; CA1, with inputs from CA3 and EC; and subiculum (SUB), with inputs from CA1 and outputs to EC (33, 2). In lieu of the evidence currently available, it would seem that the minimal system required as a locus for memory acquisition would be the EC-CA3-CA1-SUB-EC loop. This is because first, the plasticity in the EC-DG and DG-CA3 synapses seems to be dispensable (25, 42); second, the direct EC-CA1 connection appears to be too weak to sustain the EC-CA1-SUB-EC loop as the locus for memory (Empson and Heinemann 1995); and third, the evidence presented in this article points to the special role of the CA3-CA1 synapses. [END of 3. Supporting Your Findings]

[START of 5. Implications] The plasticity of the EC-CA3 synapses has not been well studied, but our proposed scenario predicts that they are important in implementing the memory system. Most probably, both the EC-CA3 pathway and the EC-DG-CA3 pathway provide parallel inputs to the CA3 network during learning, and the CA3-CA3 synapses work as autoassociative memory devices, as has long been proposed (Marr 1971). Thus, it is desirable to generate a CA3 region-specific knockout of the NMDA receptor to allow direct examination of the contribution of these synapses to learning. [END of 5. Implications]

## Usage

Provide your discussion draft text below. The revision will be returned in a LaTeX code block with section tags.

``` tex
YOUR REVISED DISCUSSION
```

## Related

- [33_writing-discussion.md](33_writing-discussion.md) — role, aim, style/volume/miscellaneous rules, 5-section template
