Publication: Marmoset superior colliculus: neuronal expression of somatostatin but not vasoactive intestinal peptide or neuropeptide Y (2025)
Authors: N Atapour et al
Department of Physiology and Neuroscience Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, Australia
Funding: This research was funded by a grant from the National Health and Medical Research Council.
Key Definitions
Somatostatin (SST): A neuropeptide that helps regulate communication between neurons by suppressing certain signals in the brain.
Vasoactive Intestinal Peptide (VIP): A neuropeptide involved in communication between neurons and the regulation of processes such as blood flow, circadian rhythms, and neural signalling.
Neuropeptide Y (NPY): A neuropeptide involved in regulating appetite, stress responses, energy balance, and communication between neurons.
Neuropeptides: Small chemical messengers used by brain cells (neurons) to communicate with one another. They help regulate how neural circuits function and influence processes such as vision, movement, stress, and behaviour.
Superior Colliculus: A region of the brain involved in processing visual information and coordinating eye and head movements in response to what we see.
Transcriptomic Research: Research that examines which genes are active within cells or tissues. This can help predict whether certain proteins or chemical messengers are likely to be present.
Immunohistochemistry: A laboratory technique that uses specialised stains to detect specific proteins within tissue samples.
Sodium Pentobarbitone: A drug commonly used to euthanise animals in research and veterinary settings. In high doses, it causes rapid loss of consciousness followed by death.
Phylogeny: The evolutionary history and genealogical relationship among species or groups of organisms
The Study
The study aimed to increase understanding of neuronal diversity of the Superior Colliculus in primates to better understand its function and phylogeny.
This study examined whether three specific neuropeptides were present in the superior colliculus, a region of the brain involved in visual processing, in seven healthy adult marmoset monkeys.
To obtain the brain tissue, all seven marmosets were euthanised using a lethal overdose of sodium pentobarbitone. Their brains were then removed, preserved, and sliced into microscopic sections for analysis.
The study found that one neuropeptide (somatostatin) was present, while the other two (VIP and NPY) were absent. However, previous transcriptomic studies and gene atlases had already indicated that VIP and NPY were likely absent in this region of the adult marmoset brain, meaning the findings largely confirmed what was already suspected.
Ethical Considerations
This study raises concerns about whether the harms inflicted on the animals were justified by the benefits generated.
Seven marmosets were killed to investigate an anatomical question, despite existing genetic research already suggesting that two of the three target neuropeptides were absent in this region of the brain. The findings largely confirmed previous observations rather than producing a significant new scientific discovery. The authors do not make clear if the marmoset were used in research previously or solely used for this study.
The strongest human-benefit argument is that the superior colliculus is involved in vision, attention, sensory integration, and eye/head movements, and the authors state primate data are scarce. However, the human benefits are indirect, speculative, and long-term, with the scientific value being incremental contribution to primate neuroanatomy.
Importantly, the research was not aimed at developing a treatment, improving patient outcomes, or addressing a specific unmet medical need. Instead, the stated purpose was to fill a gap in the scientific literature and contribute to our understanding of neuronal diversity and brain evolution in primates.
While expanding scientific knowledge can have value, it is difficult to identify any tangible benefit arising from this study. The findings do not offer a pathway towards new treatments, do not advance human clinical research, and are unlikely to improve outcomes for people living with disease.
There is also no apparent benefit to marmoset populations themselves. The research does not contribute to the prevention or treatment of disease in marmosets, nor does it improve their welfare or conservation.
Alternatives
A complete like-for-like non-animal replacement for mapping peptide-positive cells in adult marmoset superior colliculus is limited, but the study could likely have existing datasets, or human post-mortem tissue. If the justification is understanding human vision, attention, or brain circuitry, then human post-mortem superior colliculus tissue would be more directly relevant than marmoset tissue, although AFSA recognise there are limitations in acquiring human post-mortem tissue within optimal timeframes. .
Conclusion
From a cost-benefit perspective, the ethical justification for this study appears weak. Seven healthy primates were killed to confirm findings that were already largely supported by existing genetic evidence, generating knowledge that is primarily descriptive in nature and offers little foreseeable benefit to either humans or marmosets.
Seven healthy marmosets lost their lives in this study for findings that offered little foreseeable benefit to either humans or marmosets. As human-relevant research methods continue to advance, experiments like these become increasingly difficult to justify.
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