Cephalocaudal grooming refers to a specific type of grooming process that the mouse exerts on its whole body (which systematically begins at the head and progresses along the torso until finishing at the tail) and does not encompass all bouts of self-grooming.
Cephalocaudal grooming is related to self-grooming and entails a specific sequence of behaviors in which the paws, face, and body are groomed systematically. Research shows that this pattern is a serial, instinctive behavior.
Cephalocaudal grooming is a grooming sequence with a clear starting point and end, starting at the head and progressing all the way down the body until the mouse reaches its tail. In fact ‘cephalo-’ is from the Ancient Greek word κεφαλή meaning ‘head’ and ‘-caudal’ is from the Latin word caudum meaning ‘tail’.
During the sequence, the paws are licked first, and then the head is groomed carefully using the paws, followed by the body, and then the anogenital region, and finally the tail.
Notably, the cephalocaudal groom can be traced to specific areas of the rodent brain, including the cortex, striatum, and brainstem.
Cephalocaudal Groom: A Specific Behavioral Sequence
Cephalocaudal grooming is systematic cleaning that the mouse performs on its entire body in a specific order:
- Initiated by the licking of the paws.
- Then, the nose is washed through a series of bilateral elliptical paw strokes (using both paws simultaneously) which are performed near the nose.
- Next, the face is groomed through unilateral strokes (using one paw). The mouse specifically cleans the area that begins at the mystacial vibrissae (whiskers) and ends below the eye.
- The head is further groomed using bilateral strokes which are performed backwards and upwards.
- Then, body licking ensues, cleaning its torso and belly.
- Finally, the cephalocaudal grooming sequence concludes by the grooming of the anogenital region and the tail.
This progression is frequently referred to as the “cephalocaudal progression” and more technically as the “syntactic groom chain.”
This behavior may be interlaced with bouts of ‘non-chain grooming’ which are behaviors that do not neatly fit into the syntactic groom chain, such as sudden bouts of scratching.
Function of Cephalocaudal Grooming
The cephalocaudal groom is a specific chain of behaviors that serve as a maintenance behavior wherein the mouse cleans itself. This behavior has the following functions:
- To maintain hygiene and cleanliness. This behavior enables the mouse to systematically and efficiently clean itself and maintain hygiene. Thus, the mouse is able to stay healthy and survive longer.
- To reduce stress. It reduces stress by self-soothing and possibly reducing circulating stress-hormones. Thus, the mouse stays healthy by controlling and keeping its stress levels low by means of grooming.
Therefore, this type of grooming serves the purpose of self-care and preservation, increasing the chance of survival by reducing stress and maintaining hygiene.
Application of Cephalocaudal Grooming
The behavior is likely to be observed under the following circumstances:
- While self-grooming. Since cephalocaudal grooming is a specific sequence of grooming that occurs when a mouse cleans itself, it can be observable during bouts of self-grooming.
- In response to stress. It is triggered by high levels of circulating corticotropin-releasing hormone (CRH) in response to stress. In fact, researchers may subject a mouse to environmental stressors or chronic stress models, in order to study cephalocaudal grooming and compare its manifestation with non-stressed controls.
Research Techniques for Studying the Behavior
- Behavioral studies. The behavior can be observed during behavioral studies while a mouse is grooming itself. Behavioral studies characterize and quantify cephalocaudal grooming patterns across a variety of situations in order to determine how cephalocaudal grooming as a behavior is affected by variables such as genetics or drugs.
- Pharmaceutical studies. Pharmaceutical studies will examine how cephalocaudal grooming is affected by drugs. Oftentimes, this type of study will have elements of a behavioral study, especially when the research goal is to note the effect of dose on behavioral outcome.
Behavioral Tests for Assessing Cephalocaudal Grooming
Cephalocaudal grooming may be analyzed in many ways. One example of data analysis includes calculating the amount of incorrect transitions as a percentage of the total number of transitions. These assessments reveal how healthy and intact the mouse’s grooming abilities are.
Such data is acquired through behavioral testing using the following techniques:
- Grooming Analysis. Grooming analysis measures and quantifies the type of cephalocaudal sequencing that occurs. Each of the behaviors which makes up the sequence is assigned a number and, based on occurrence, recorded and analyzed.
- Video Analysis. Video analysis is commonly used to quantify the behaviors which constitute cephalocaudal grooming and capture the mouse’s grooming microstructure.
Pharmaceutical Effects on Cephalocaudal Grooming
Diazepam Enhances the Behavior
Diazepam, a γ-aminobutyric acid (GABA)-ergic anxiolytic compound, when administered to mice can affect the cephalocaudal sequence by decreasing the number of interrupted bouts and the overall percentage of incorrect transitions that a mouse performs when compared to a saline group.
Pentylenetetrazole Affects Cephalocaudal Grooming
Pentylenetetrazole, a γ-aminobutyric acid GABAergic anxiogenic compound, is associated with ‘high arousal’ grooming patterns in mice. When given this drug, the mouse will become very energetic, have high interruptions in the grooming sequence, and frequently display incorrect transitions.
Fluoxetine Decreases the Behavior
Fluoxetine, commercially known as Prozac, is a selective serotonin reuptake inhibitor which can also affect the cephalocaudal grooming profile observed in mice. Fluoxetine decreases the total number of cephalocaudal grooming bouts, transitions, and patterns.
Amitriptyline Decreases Grooming
Amitriptyline, a drug used to treat numerous psychiatric conditions (including anxiety disorders and major depressive disorder), has been demonstrated to be able to reduce cephalocaudal grooming bouts, the average number of patterns displayed within a bout, as well as the transitions across cephalocaudal grooming stages in mice.
Mouse Strains Exhibiting Cephalocaudal Grooming
129S1 Mice Demonstrate Low Grooming Activity
The 129S1/SvImJ mouse strain is widely used in behavioral research, but has an impaired grooming microstructure, meaning that these mice have frequently interrupted bouts (pausing abruptly amidst grooming) and incorrect transitions (i.e. not following the cephalocaudal sequence).
BALB/c and NMRI Mice Display Normal Cephalocaudal Grooming Patterns
Two other strains that are commonly used in behavioral research are the BALB/c and NMRI mouse strains. In contrast to the 129S1/SvImJ mouse strain, the BALB/c and NMRI mice show unimpaired, normal grooming patterns. The BALB/c strain is more active and likely to groom than the NMRI strain.
Abnormalities Altering Cephalocaudal Grooming
Lack of Vitamin D Receptor
The sequential pattern that constitutes cephalocaudal grooming (paw licking, nose/face washing, body washing, and tail/genital washing) is disrupted in mice that lack the vitamin D receptor gene.
Chronic stress is a variable that is known to cause an abnormal manifestation of cephalocaudal grooming. Prolonged periods of stress will alter a mouse’s grooming sequence and create disorganized patterning in their grooming response.
Disease Models with Cephalocaudal Grooming
Mouse Hoxb8 Mutants Modeling Trichotillomania
When cephalocaudal grooming is on endless repeat, mice are essentially exhibiting excessive grooming and inevitably remove their hair and fur. Such is the case with mouse Hoxb8 mutants which show excessive grooming patterns. Interestingly, when these mice are given a bone marrow transplant from wild-type mice, their pathological phenotype is rescued.
BTBR T+tf/J Mouse Model of Autism
The BTBR T+tf/J mouse model of autism displays a high frequency of cephalocaudal grooming in which the grooming pattern is repeated quickly. This model is further characterized by an increased frequency of interrupted bouts, meaning that the mouse can suddenly pause in between grooming stages before continuing to the next area of grooming.
- Cephalocaudal grooming is essentially self-grooming and entails a specific sequence of behaviors in which the paws, face, and body are groomed systematically.
- This sequence is also referred to as the “syntactic groom chain.”
- It may be interlaced with bouts of ‘non-chain grooming’ which are behaviors that do not neatly fit into the syntactic groom chain.
- Cephalocaudal grooming is important for maintaining the mouse’s health.
- Environmental stressors trigger the behavior.
- Diazepam enhances cephalocaudal grooming performance while other drugs (such as pentylenetetrazole, fluoxetine, and amitriptyline) may decrease it.
- This behavior is commonly measured using video recording and analysis.
- 129S1/SvImJ mice display frequently interrupted bouts and incorrect transitions in their cephalocaudal groom while BALB/c and NMRI mice do not.
- The BTBR T+tf/J mice modeling autism and mouse Hoxb8 mutants that model trichotillomania demonstrate high levels of repetitive cephalocaudal grooming.
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