Table of Contents
- Behavioral Sequence
- Function of Drinking Behavior
- Application of Drinking Behavior
- Research Techniques
- Behavioral Tests
- Pharmaceutical Studies on Drinking Behavior in Mice
- Drinking Across Mouse Strains
- Abnormalities in Drinking Behaviors in Mice
- Can Drinking Influence Assessment?
Drinking involves using the mouth and tongue for the ingestion of fluids.
Drinking is a maintenance behavior, crucial for keeping a mouse hydrated and its internal physiology at equilibrium.
In a laboratory setting, mice drink either from a dish or by licking the fluid from a waterspout by pressing the metallic ball with their tongue.
For experimental purposes, drinking is a very important behavior because it is the means by which many models get induced. By placing drugs or supplements in the mouse’s drinking water, the mouse ingests a certain substance which eventually leads to the induction of the desired model.
Drinking does not occur in isolation and has other behaviors which are involved in its behavioral sequence. In order to be able to drink water, a mouse must be able to search for it and have a neural representation of the water source’s location, then it must physically get to that location, position itself correctly, and make the correct movements with its mouth in order to intake and ingest the water or liquid.
The following auxiliary behaviors collectively serve to enable the mouse to hydrate itself:
- Searching: Searching may also be involved with drinking, especially in a naturalistic setting, because a mouse must search for a water source if it is thirsty and one is not immediately available.
- Upright posture: If drinking from a nozzle, a mouse must be able to maintain its balance in an upright position.
- Lick: In order to drink water or liquid substance, a mouse must be able to lick and use its tongue to ingest liquids from the nozzle or bowl.
Function of Drinking Behavior
Drinking has very important physiological functions, including:
- To maintain homeostasis: By drinking water, a mouse is able to keep its intracellular and extracellular gradients balanced.
- To keep activity levels optimal: Somewhat related to the previous point, when a mouse is hydrated, it can stay active and healthy; factors which ultimately contribute to its survival and longevity.
Application of the Behavior
Since drinking is a vital behavior for keeping the organism healthy and functioning optimally, it is likely to be seen throughout an observation period and particularly:
- After exercise or eating: Activities such as eating or exercise are likely to trigger a mouse’s thirst.
- During the dark phase: Since mice are most active during the dark phase, more drinking activity will occur than when compared to the light phase.
- Behavioral studies: Behavioral studies are commonly used to study drinking behavior. These studies are easy to run because all that is required is observing the mouse and recording the behavior.
- Pharmaceutical studies: Since drinking is a behavior related to the appetite, drugs which aim to affect appetite levels in humans will be tested in mice and behaviors such as drinking will be observed and measured at baseline and post-intervention.
- Optogenetics: Optogenetics is used to target and manipulate specific genes in mice, to excite or inhibit them. This technique enables scientists to explore how brain structure is involved in a mouse’s drinking behavior. For example, by using optogenetics, one study established that optogenetic stimulation of the median preoptic nucleus and lamina terminalis’ glutamatergic neurons led to increased water consumption. But, by stimulating the GABAergic neurons in the same region, water consumption in mice is significantly decreased.
- Video analysis: Using video recording equipment, a mouse’s activity levels can be recorded and quantified. Drinking behavior, in a laboratory setting, is measured whenever a mouse consumes the liquid from the designated source.
- Sodium Nitrate Induced Metabolic Hypoxia: Mice are taught a water source location. Then, they are water-deprived for 24 hours and their memory is impaired through subcutaneous injections of sodium nitrate (NaNo2) at 75 mg/kg. Retention testing is performed one day later, in order to evaluate how well the mouse searches for water based on what it was previously taught. This test relies on memory and the mouse’s primal need to drink.
- Sucrose Preference Test: This test relies on drinking behaviors, in order to be properly administered. It tests levels of depression in mice based on the fact that control mice prefer sweetened water while depressed mice are more likely to drink from regular water due to their anhedonic state.
- Vogel’s Test: In Vogel’s Test, a mouse is water-deprived, thus increasing its need and motivation to satiate its thirst. Then, it is placed in an apparatus which contains a drinking source. Every time that the mouse tries to drink water it receives a mild shock, thus receiving a form of punishment. Therefore, in this test, the mouse is presented with a conflict situation: it wants to drink and alleviate its thirst, but every time it tries to do that is receives punishment in the form of a foot shock. Vogel’s Test is usually used to analyze drugs and whether they have the ability to change drinking behavior in water-deprived mice by assessing how often mice will lick the water sprout or drinking source.
Measuring Drinking Behavior in Mice Accurately
There are two things to look out for when measuring drinking behavior in mice:
- Biting behavior: Always be certain that the mouse is actually drinking and not biting the nozzle. Sometimes it may look like a mouse is drinking when, in fact, it is biting the nozzle.
- Obstructed view: Sometimes, during video analysis, the view of the water nozzle may be obstructed, so it will be impossible to see what the mouse’s mouth is doing. If this is the case, simply look at the top of the water bottle, if the mouse is truly drinking from the nozzle, water bubbles will appear.
Pharmaceutical Studies on Drinking Behavior in Mice
Naloxone Decreases Mice’s Water Intake
Naloxone, an opiate antagonist which acts on the endogenous opioid (endorphin) systems is able to modify ingestive behavior in mice. When administered with 10 mg/kg of naloxone, water intake will be lower by as much as 50% in mice deprived of water for 12 hours when compared to controls.
Drinking Across Mouse Strains
Drinking is constant across all mouse strains since it is a behavior that is necessary for staying alive and well. When studying drinking behaviors and water intake, it is important to adjust for a mouse’s body weight, since higher body weight can explain higher instances of drinking. Below are mouse strains and their average drinking and water intake levels, derived from a study, adjusted for body weight:
- BALB/cByJ mice: 6 mL/30g of body weight (BW)
- CBA/L mice: about 6.5 mL/30g of BW
- 129P3/J mice: about 6.5 mL/30g of BW
- C57BL/6J mice: about 8 mL/30g of BW
- SWR/J mice: about 11 mL/30g of BW
- CAST/Ei mice: about 11.5 mL/30g of BW
Based on these findings, BALB/cByJ, CBA/L, and 129P3/J mice drink less water than C57BL/6J, SWR/J, and CAST/Ei mice. Furthermore, C57BL/6J mice drink less than SWR/J and CAST/Ei mice.
Abnormalities in Drinking Behaviors in Mice
Obese Mice Drink More
Obese mice drink more water than their lean, non-obese control counterparts. One study showed that obese mice drink about 9.4 mL +/- 1.0 mL of water compared to the controls’ 4.4 +/- 0.3 mL of water. Also, drinking patterns vary between obese and control mice such that obese mice will initiate drinking behavior more frequently than control mice (26.0 bouts and 17.6 bouts, respectively). Also, this difference of initiating bouts occurs only in the dark phase and there are no significant differences during the light phase. Of note, the amount of water that was consumed during the drinking bouts was not statistically different between the obese and control mice.
Mice with Angiotensin Knocked Out
Knock-out mice which do not have the angiotensin II type 1 receptor (AT1a) have higher drinking activity and general activity in both the light-dark cycle and in the constant dark cycle. The AT1a receptors are located in the suprachiasmatic nucleus in mice, a region of the brain known for maintaining circadian rhythmicity and regulating maintenance behaviors such as drinking. The increased amplitude of activity and drinking behavior in the angiotensin KO mice indicates that the circadian system still remains intact, regardless of the fact that this receptor is knocked out.
Dopamine-Deficient Mice Are Adipsic
By targeting and disrupting the tyrosine hydroxylase (TH) gene in mice, mice will become dopamine (DA) deficient. DA -/- mice, even when there are food and water placed in front of them, will completely stop drinking (and eating). When a mouse does not drink, it is referred to as being ‘adipsic,’ which is a Greek-derived word that means ‘not thirsty’ or ‘no thirst.’ When treating these mice with L-DOPA, an amino acid which can cross the blood-brain barrier and contribute to dopamine synthesis, their consumption of water and food increases dramatically.
Can Drinking Influence Assessment?
Since drinking is crucial for homeostasis and maintaining cellular balance and health, lack of drinking is bound to affect a mouse’s performance. However, mice can withstand not drinking water for 8 days before dying.
In the first 24 hours of acute water deprivation, noticeable physiological changes will occur, including decreases in body weight and increases in plasma corticosterone, sodium, and osmolality. Such findings show how drinking can significantly impact a mouse’s physiology which could, in turn, affect (and confound) results and test conclusions.
- Drinking involves using the mouth and tongue for the ingestion of fluids. It is a maintenance behavior that is very important for sustaining health and life.
- In a laboratory setting, mice drink either from a dish or by licking the fluid from a waterspout by pressing the metallic ball with their tongue.
- Drinking is likely to be observed during the dark phase and after exercise or eating.
- Commonly used techniques to study drinking behavior in mice include behavioral studies, pharmaceutical studies, and optogenetics.
- Behavioral tests are mainly conducted using observation and video analysis methods. The Sucrose Preference Test is an example of a test that relies on a mouse’s drinking behavior, in order to be administered.
- When measuring drinking behavior in mice, ensure that the mouse is truly drinking and not simply biting the apparatus’ nozzle.
- Naloxone is an opiate antagonist which decreases drinking behaviors in mice.
- When adjusted for body weight, the amount of drinking and water intake that mice perform varies significantly across strains.
- Research has shown that dopamine-deficient mice are adipsic, mice with the angiotensin receptor knock-out will drink more, and obese mice are likely to drink more.
- Drinking can influence behavioral assessment. Just 12 hours of water deprivation leads to a noticeable change in mice’s physiology, which could confound experiments acquiring such measurements.
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