Neuropeptides I: classification, synthesis and co-localization with classical neurotransmitters
Bibliographic record
Abstract
Many chemical messengers regulate neural activity, including neurotransmitters (Chapter 5), steroid hormones (Chapter 9) and peptide hormones (Chapter 10). This chapter, and Chapter 12, examines how the class of chemical messengers termed neuropeptides regulates neural activity. The topic of neuropeptides is now an extensive one and we divide the coverage into two parts. This chapter will describe the classification and synthesis of neuropeptides and their co-localization with classical neurotransmitters. Chapter 12 examines the functions of neuropeptides in the brain and neuroendocrine system. Classification of neuropeptides The realization that neuropeptides can act as neurotransmitters took place after the discovery of most of the “classical,” or small molecule, neurotransmitters, such as NE, glutamate and ACh. Perhaps the simplest and obvious difference between these two classes of neurotransmitter is the size of the molecules; neuropeptides range in size from 2 to at least 40 amino acids, whereas a molecule such as NE is derived from a single amino acid (tyrosine) (see Table 7.1). Another difference is that neuropeptides are more versatile in their range of biological activities. For example, some peptide hormones are synthesized in endocrine glands, in fat cells and in the GI tract, but are also produced in the brain, where they act as neurotransmitters or neuromodulators. Another significant distinguishing characteristic of neuropeptides is their mode of synthesis. Classical neurotransmitters such as amino acids or catecholamines are formed by two or three enzymatic steps, often in the nerve terminal. Neuropeptides, on the other hand, are synthesized from large prepropeptides in the neuronal cell body (e.g. see section 7.2.1; Figure 7.2). In terms of nomenclature, peptide hormones were traditionally and sensibly named after the first function they were known to serve. Thus, the pituitary hormones (ACTH, TSH, FSH, GH, etc.) were named for their actions at their target cells; for example, TSH stimulates the thyroid gland. Hypothalamic-releasing hormones (CRH, TRH, GnRH, GHRH, etc.) were named for their functions at pituitary target cells; and the hormones of the gastrointestinal (GI) tract (CCK, VIP, gastrin, etc.) were named based on their gastrointestinal functions.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.003 | 0.002 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.015 | 0.009 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".