Sulfated CCK-8 Induces Anxiety-Like Behavior in Zebrafish

2026-04-15

Sulfated CCK-8 and Anxiety-Like Behavior in Zebrafish: Mechanistic Insights

Study Background and Research Question

Cholecystokinin (CCK) is a pleiotropic neuropeptide extensively studied in mammals for its roles in digestive regulation, neuroprotection, and behavioral modulation. Of particular interest is the sulfated C-terminal octapeptide variant, CCK-8s, which acts through G protein–coupled receptors (CCK1R/CCKAR and CCK2R/CCKBR) and is implicated in the regulation of feeding, nociception, and anxiety-like behavior. While mammalian studies have established the anxiogenic and anorexigenic actions of CCK-8s, there is a knowledge gap regarding its distribution and behavioral roles in non-mammalian vertebrates such as zebrafish (Danio rerio) (paper). The reference study addresses a central research question: How do two zebrafish-specific molecular forms of sulfated CCK-8 modulate anxiety-like behavior, and what are their neural localizations and receptor-mediated mechanisms?

Key Innovation from the Reference Study

The key innovation lies in the direct demonstration that both zebrafish CCKA-8s and CCKB-8s, when administered intracerebroventricularly (ICV), induce robust anxiety-like responses. This is the first in vivo evidence detailing the behavioral effects of these endogenous CCK-8s forms in zebrafish, coupled with a mapped distribution of CCK-like immunoreactivity within specific brain nuclei. Notably, the study bridges the evolutionary conservation of CCK signaling from mammals to teleosts, advancing zebrafish as a functional model for neuropeptidergic behavioral regulation (paper).

Methods and Experimental Design Insights

The investigators first mapped CCK-like immunoreactivity throughout the zebrafish brain, observing pronounced localization in the ventral habenular nucleus, interpeduncular nucleus, and superior raphe. Subsequently, synthetic zebrafish CCKA-8s and CCKB-8s peptides were administered ICV at doses of 1, 5, and 10 pmol/g body weight. Behavioral assays exploited the zebrafish’s innate preference for lower tank zones as a readout for anxiety-like states; decreased time spent in the upper tank area is a validated index of heightened anxiety (paper). To control for specificity, the CCK receptor antagonist proglumide was co-administered in separate trials. FG-7142, a benzodiazepine receptor inverse agonist, was used as a positive control for anxiogenic effect.

Protocol Parameters

anxiety-like behavior induction in zebrafish | 10 pmol/g body weight (ICV) | in vivo behavioral assay | Highest dose significantly reduced exploration of upper tank, mirroring established anxiogenic controls | paper
CCK receptor antagonism (control) | 200 pmol/g body weight (ICV, proglumide) | in vivo behavioral rescue | Fully reversed CCK-8s-induced anxiogenic effect, demonstrating receptor-specific action | paper
CCK-8 ammonium experimental range | 1–10 pmol/g body weight (ICV) | zebrafish/neurobehavioral models | Dose-response relationship aligns with prior CCK-8 literature in vertebrates | product_spec
ICV administration technique | direct brain injection | teleost/neuropeptide studies | Established method for precise central delivery in small aquatic models | paper
in vitro concentration (for neuronal/immune assays) | 0.01–1 μmol/L | cell-based CCK-8 studies | Suggested range for downstream signaling and apoptosis modulation | product_spec

Core Findings and Why They Matter

Both zebrafish-specific CCKA-8s and CCKB-8s peptides, when administered at 10 pmol/g body weight, significantly decreased the time spent in the upper tank region, indicating a pronounced anxiogenic effect. This behavioral phenotype closely paralleled that induced by FG-7142. Importantly, the anxiogenic effect was abrogated by co-administration of the CCK receptor antagonist proglumide, confirming that the behavioral change was mediated via endogenous CCK signaling pathways rather than off-target effects (paper). The study’s localization of CCK-like immunoreactivity in critical brain regions aligns with known mammalian sites of anxiety modulation, suggesting evolutionary conservation of function. These findings provide a robust framework for using zebrafish as a translational model to study neuropeptide-mediated modulation of anxiety-like behaviors, with potential applications for dissecting the roles of CCK1R and CCK2R receptor agonists in both neural and immune contexts.

Comparison with Existing Internal Articles

Recent internal reviews have elaborated on the mechanistic landscape of cholecystokinin octapeptide ammonium (CCK-8 ammonium) in neurobiological and immunological workflows. For example, the article “Cholecystokinin Octapeptide Ammonium: Mechanistic Insight...” (internal) details how CCK-8 ammonium activates CCK1R and CCK2R, modulating pathways such as β-arrestin 2, p38 MAPK, and Akt, which are implicated in both inhibition of apoptosis in neuronal cells and modulation of immune responses. While these reviews provide a cellular and molecular context, the reference study delivers unique behavioral and in vivo neuroanatomical evidence, directly linking CCK-8s administration to observable anxiety-like phenotypes in a whole-organism model. Additionally, “Cholecystokinin Octapeptide Ammonium: From Zebrafish Anxi...” (internal) highlights the utility of CCK-8 ammonium in zebrafish behavioral assays, reinforcing the translational relevance of the reference findings. These internal resources collectively underscore that the precise, sulfated structure of CCK-8 ammonium is critical for receptor activation and downstream effects, echoing the reference study’s demonstration of the inactivity of non-sulfated analogs.

Limitations and Transferability

Despite the strengths of the experimental approach, several limitations warrant consideration. First, while intracerebroventricular administration enables targeted delivery, it may not fully recapitulate endogenous neuropeptide release dynamics. The study also focuses on acute behavioral outcomes and does not address longer-term neuroadaptive processes. Dose ranges were limited to 1–10 pmol/g body weight, and effects at lower, more physiological concentrations remain to be explored (paper). Transferability to mammalian systems is supported by the conserved localization and function of CCK-8s and its receptors, yet direct extrapolation to human anxiety disorders must be made with caution. Furthermore, while the zebrafish model is powerful for behavioral and neuroanatomical mapping, differences in blood–brain barrier properties and neuropeptide processing could influence pharmacodynamics in other species.

Research Support Resources

For researchers aiming to replicate or extend these findings, Cholecystokinin octapeptide ammonium (SKU C8717) is available as a research-grade, sulfated CCK-8 ammonium salt, supporting workflows in both behavioral and molecular assays. This reagent is suitable for studies targeting G protein–coupled CCK receptors in neuronal, immune, and endocrine models (source: product_spec). For additional protocol guidance and troubleshooting, internal reviews such as "Cholecystokinin Octapeptide Ammonium: Advanced Applications" (internal) provide actionable insights for optimizing experimental designs involving CCK-8 ammonium.