Materials / Reagents Required :

            10 % Neutral Buffered Formalin (NBF), Davidson’s fluid (1 litre), Modified Davidson’s fluid (1 litre), Normal saline (10 litre), 70 % Ethanol (1 litre), different sizes of scissors, forceps, scalpel, spatula, bone cutter, cardboard paper, etc.

Safety Precautions :

            Protective equipments including laboratory coats, gloves, apron, etc., should be worn during euthanasia, necropsy as well as during the preparation of the solutions.

Anatomy:

• The kidneys of the mature rat are bean-shaped and are located retroperitoneally, ventrolateral to the vertebral column. The right kidney is located cranially to the left, and is within the protective province of the rib cage.
• It has a basicunipapillary architecture, the simplest type of mammalian kidney. The lower urinary tract extends from the kidney pelvis bilaterally through the ureters, into the urinary bladder, and ultimately out the urethra.
• The urinary bladder, a highly-distendable organ, is located in the posterior abdominal cavity. The most anterior portion of the bladder in rodents is referred to as the dome, and the more posterior portion, formed by a triangle-like area where the ureters enter and the urethra exits the bladder, is referred to as the trigone.
• The urethra of the female is short, slightly flattened dorsoventrally, and extends from the urinary bladder to the clitoral fossa just anterior to the vaginal orifice. The urethra of the male is considerably longer, extending from the bladder through the pelvic girdle (membranous urethra), and continuing through the penis as the penile urethra, opening at the tip of the penis.
• The rat has the most prominent outer stripe (of outer medulla) visible subgrossly, constituting one-third of the medulla by volume. Each testis is enclosed in a scrotal sac that lies outside the abdominal cavity.
• The testicular parenchyma is composed of seminiferous tubules separated by interstitial tissue and enclosed in a capsule. The testis is supplied by the internal spermatic artery, a highly coiled tortuous vessel. The spermatic artery gives off the superior and inferior epididymal branches, which supply the cauda and corpus epididymis, and continuous as the testicular artery to supply the testis.
• This vessel divides into radiate arteries, which in turn give rise to intertubular arterioles. The venous return from the testis enters the pamphiniform plexus, a system of venous channels that closely surrounded the incoming spermatic artery, acting as a countercurrent heat-exchange system.
• The rete testis is situated in a subcapsular position at the cranial pole of the testis. The efferent ducts (ductal efferentes) arise from the extratesticular rete and extend through the epididymal fat to empty into the initial segment of the epididymis.
• The initial segment of the caput epididymis is richly vascularised, and its reddish colour is grossly visible. There is no sharp anatomical or histological demarcation between the end of the caput and the beginning of the corpus. The corpus is the narrow portion of the epididymis between the caput and the cauda.
• The cauda forms a grossly distinct structure due to dilatation with stored sperm. The vas deferens (ductus deferens) is a thick walled convoluted tube that is continuous with the tail of the epididymis and extends to the prostatic urethra. The final part of this tube is dilated to form the ampulla, which joins the duct of the seminal vesicle to become the ejaculatory duct.
• The prostate that forms multiple lobes around the urethra is a compound tubuloalveolar gland that secretes a colourless serous fluid into the urethra through a number of ducts. In the rat, a discrete pair of ventral lobes and a smaller group of dorsal and lateral lobes are situated at the neck of the bladder.
• A pair of anterior lobes, otherwise known as the coagulating glands, is situated closely adjacent to the seminal vesicle. The seminal vesicles are paired elongated hollow organs filled with a yellowish-white viscous fluid. They are situated distal to the ampulla of the vas deferens and empty via the ejaculatory duct into the urethra.
• The paired ovaries, suspended from the dorsal abdominal wall by the mesovarium, are globose in the rat. The ovaries of rodents are enclosed within the ovarian bursa, which obscures gross examination. In rodents, the ovaries are located in the caudal portion of the lumbar region posterior to the kidneys.
• In rodents, several follicles and corpora lutea may develop during each cycle. These structures often protrude from the ovarian surface, thus giving rise to the grape-like appearance of the ovary. The rat has a duplex uterus with two separate uterine bodies joined externally at their cervical ends but with two independent cervical openings.
• The uterus is enlarged and hyperemic during proestrus and early estrus, reduced in size at metestrus, and small and pale during diestrus. The vagina consists of an inner layer, the mucosa, a middle layer, the muscularis, and an outer layer, the adventitia.

Collection of urogenital system of rat :

Procedure :

• After induction of anaesthesia/euthanasia, exsanguination shall be accomplished by severing the femoral arteries, abdominal aorta or by incising the skin at the neck region. Normal saline shall be kept ready during the necropsy to keep the lungs moist.
• The fur of the animal shall be moistened with alcohol to prevent the fur from getting adhered into the tissue samples. Skin of the abdomen (in the shape of V) shall be removed first. The reflected flap of the skin of abdomen is cut to expose the sternum.
• Both the kidneys shall be removed by cutting through the attachments taking care not to damage the kidneys. The testes and epididymis shall be exposed by applying gentle pressure over the scrotal sac, separated and dissected out carefully.
• The seminal vesicles with coagulating gland, prostate gland and urinary bladder shall be dissected out, placed over a cardboard paper and fixed. If the urinary bladder is not distended, it shall be infused with 10 % NBF.
• The female reproductive system including the ovaries, uterus and vagina shall be dissected out carefully and fixed. The ovaries alone shall be kept in tissue cassettes as they may be easily lost and then, are fixed.