Sucrose Splash Test
Overview
The sucrose splash test (SST) is a rapid behavioral assay that measures self-directed grooming motivation as a proxy for hedonic and motivational state. A 10% sucrose solution is sprayed directly onto the dorsal fur of a mouse or rat in its home cage, and the animal's grooming response is recorded over a 5-minute observation period. Healthy rodents exhibit prompt and vigorous grooming of the sticky solution from their coat, driven by both the hedonic properties of sucrose (taste reward via orosensory pathways) and the innate motivation to maintain coat condition. The neural substrates involve ventral striatal reward processing, lateral hypothalamic motivational circuits, and cortical executive function governing the initiation of goal-directed behavior.
The primary dependent variables are grooming latency (time from sucrose application to first grooming bout) and total grooming duration. Increased grooming latency and reduced grooming time reflect motivational deficits analogous to psychomotor retardation and apathy observed in clinical depression. The SST dissociates from general locomotor impairment because the animal remains in its familiar home cage and the behavioral output (grooming) does not require spatial navigation or learning. Grooming frequency, mean bout duration, and grooming bout structure (sequential chain complexity from face-wash to body-lick to flank-lick) provide additional granularity.
ConductMaze automates SST scoring using overhead video tracking with posture-recognition algorithms that distinguish grooming from resting, rearing, and locomotion. The software identifies grooming onset with frame-level precision, classifies grooming subtypes by body region, and compiles a complete grooming ethogram. Automated scoring eliminates observer bias, enables high-throughput screening of multiple animals in parallel, and provides grooming chain analysis that reveals motivational microstructure changes missed by manual observation.
Trial Flow
Home Cage Baseline
Animal in home cage with bedding; 2-minute baseline recording to measure spontaneous grooming.
Sucrose Application
Two sprays of 10% sucrose solution applied to dorsal fur midline using calibrated spray bottle.
Timer Start
Five-minute observation period begins immediately after sucrose application.
Grooming Detection
Posture algorithm classifies each frame as grooming or non-grooming; first grooming onset timestamped.
Bout Analysis
Grooming parsed into discrete bouts by body region (face, dorsal, ventral, flank).
Duration Summation
Total grooming time, latency, and bout statistics compiled.
Session End
Recording ends at 5 minutes; data exported with baseline-corrected metrics.
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Test Duration | duration | 5 min | Duration of the observation period after sucrose application |
| Sucrose Concentration | float | 10.0 | Sucrose solution concentration as weight/volume percentage |
| Number of Sprays | integer | 2 | Number of spray applications to dorsal fur (each delivers approximately 0.5 mL) |
| Spray Volume | float | 0.5 | Volume per spray application in milliliters |
| Baseline Period | duration | 2 min | Pre-spray recording period to quantify spontaneous grooming |
| Testing Environment | enum | Home Cage | Environment for testing (Home Cage or Clean Cage) |
| Grooming Bout Threshold | seconds | 1.0 | Minimum inter-bout interval to separate discrete grooming episodes |
| Camera Frame Rate | integer | 30 | Video capture frame rate in frames per second for posture analysis |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Grooming Latency | seconds | Time from sucrose application to first grooming bout — primary measure of motivational initiation |
| Total Grooming Duration | seconds | Cumulative grooming time during the 5-minute test period |
| Grooming Frequency | count | Number of discrete grooming bouts during the test period |
| Mean Bout Duration | seconds | Average duration of individual grooming episodes |
| Grooming Percent | % | Percentage of test time spent grooming |
| Baseline Grooming | seconds | Spontaneous grooming during the pre-spray baseline period |
| Net Grooming | seconds | Test grooming minus baseline grooming rate — isolates sucrose-induced grooming motivation |
Sample Data
| Animal | Group | Latency_s | Total_Groom_s | Bouts | Mean_Bout_s | Groom_pct | Baseline_Groom_s |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Motivational deficit screening — detecting apathy-like phenotypes in chronic stress models without locomotor confounds
- 2Rapid antidepressant assessment — evaluating acute drug effects on grooming initiation in a 5-minute assay
- 3Self-care behavior modeling — translational proxy for psychomotor retardation and self-neglect in clinical depression
- 4Complement to SPT — confirming anhedonia findings with an independent hedonic measure that does not require learning
- 5High-throughput phenotyping — screening large cohorts with minimal equipment and short test duration
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