Comments & suggestions  should be directed to jroese@lssu.edu Visit my website Injection Sites Intraperitoneal (IP) injections should be given in the lower right quadrant of the abdomen  to prevent puncturing the spleen which is located on the left side.  The mouse's head should be tipped downward while the mouse is held upside down to prevent puncturing the intestines.  A small (23 - 25 gauge) needle should be used, and a maximum volume of 2 - 3 ml in adult mice may be injected.  This is the most common method of administering drugs and anesthetics to mice. Subcutaneous (SC) injections may be administered ventrally or dorsally depending on the substance or cells to be injected.  When given dorsally the most common location is between the shoulder blades.  Care must be taken to avoid sticking the needle into your finger when holding the mouse as shown.  Alternatively, the mouse may be allowed to grasp the cage top while the handler pulls back gently on the tail and injects the loose skin over the shoulder blade area.  A small (23 - 25 gauge) needle should be used. Intravenous (IV) injections are most commonly delivered through the tail vein.  A tail vein is present at 90° on either side of the central tail artery.  It is helpful to warm the mouse or the tail to induce vessel dilation prior to attempting injection.  Use care to avoid inducing heat prostration in warmed mice.  Use a 26 - 30 gauge needle and introduce the needle bevel up.  This technique requires some practice to become efficient at hitting the vein, and good restraint of the mouse is essential.  Commercial restrainers are sold which facilitate tail vein injection. Intramuscular (IM) injections are not commonly used in mice, and are generally not recommended because of the small size of the animal and the correspondingly small muscle masses.  The quadriceps muscle can be used, but the volume should not exceed 0.2 ml per site. and a needle 25 gauge or smaller should be used to avoid muscle damage.  Irritating substances such as ketamine should not be administered IM as they may lead to self mutilation of the affected limb if muscle or nerve damage occurs.