Amphibians

Top of page

Anatomy 

Salamanders

Amphibians have smooth non-scaly skin with two types of glands. Mucus glands help lubricate the skin. Granular glands secrete toxic substances as protection, especially in Bufo. Vibrations are sensed by clusters of sense cells in the lateral line, helping with posture and balance.{3569}

Frogs

Anurans (Order Anura, meaning "tailless") have limbs specialized for hopping or walking rather than swimming. The radius/ulna and femur/tibia are fused.{3569} The tadpoles are generally vegetarian, but the adults are predators. They do not drink water, and therefore must occasionally enter the water to absorb it transdermally. Their lungs are underdeveloped, with most respiration taking place transdermally. They have no ribs, breathing by using their suprahyoid muscles. Well-developed vascular and respiratory systems are thus not needed by anurans.{3562}

There are two families of anurans, Pipidae and Ranidae. Xenopus laevis, a representative pipid frog, lives only in Africa. It is characterized by a tongue (oops, see above) that is attached to the floor of its mouth, long digits on its front feet, three claws on three digits of its hind feet, and a diet of both live prey and dead stuff at the bottom of its pool.{3562}

In contrast, members of the family Ranidae such as Rana pipiens (the meadow or leopard frog) and Rana catesbeiana (the American bullfrog) have a wider distribution in the world with many species, and look more typically "frog-like". Their tongues are attached at a point in the lower jaw, enabling them to dart it out to catch prey. Their pupils are horizontal (rather than round as in Xenopus), and they have free fingers but webbed toes.{3562}

Amphibians have renal portal systems, which drain blood from the caudal parts of the body directly through the kidneys. Many frogs have lymph sacs, paired structures located subcutaneously on the back, which drain lymph into the veins.

Top of page

Physiology

Reproduction

Salamanders

Salamanders (Family Ambystomatidae) are found only in North America. The tiger salamander (Ambystoma tigrinum) and speckled salamander (A. maculatum) have both been studied extensively. They exhibit a phenomenon called neoteny, meaning that their larvae reach sexual maturity without metamorphosis. The occurrence of neoteny depends upon the species and climate, and results in very rapid development.{3562}{4178}

Most amphibian larvae breathe through gills and have two-chambered hearts. Adults breathe through lungs and have three-chambered hearts.{4178}

Top of page

Husbandry

Amphibians

Great care must be taken when amphibians arrive to manage their transition. Environmental temperature should be changed by not more than 1°C per hour. The shipment water should be transferred with the animals into their new container, and diluted gradually with new water.  Embryos can be kept in De Boers solution or reconstituted pond water, which should be changed every third day.{3569}

Housing systems can be of the once-through continuous flow type, or a recirculating system with filtered and treated water. Chlorine is toxic to larvae and aquatic forms.{3569} Amphibian cages should be covered to prevent dessication. Substrates for terrestrial forms includes sphagnum moss, hardwood mulch or paper. A place to hide should also be provided. Cages should be cleaned weekly with hot water, dilute chlorine or quaternary ammonium compounds; phenolics are toxic and should never be used. Salamanders prefer cool temperatures and low airflow.{4178}

Adults are carnivores and may require live prey such as crickets, mealworms, and fruit flies.{4178}

Frogs

	Xenopus will accept commercial pelleted diet because they locate food by olfaction rather than visually.{4178}
	Temperature in the water 20-22°C

Mycobacteriosis, especially from aquatic amphibians{4178}

	Lucké's renal adenocarcinoma (herpes virus) in Rana pipiens is temperature-sensitive. Lesions occur at cool temperatures, during hibernation. Transmission is vertical. Advanced stages have bloat, lethargy and death due to tumor size. Not usually a problem in captive-reared frogs.
	Redleg: Stress-related bacterial disease (usually Aeromonas hydrophila); subcutaneous hemorrhage, bloat, ascites, anorexia, splenic congestion and hepatic necrosis; treat by eliminating predisposing factors (crowding, diet, poor water, temperature, injuries)
	Mycobacterium xenopi causes cutaneous and internal granulomas; zoonotic
	Chlamydia psittaci causes disease similar to redleg, so check for typical intracytoplasmic inclusions in spleen and liver; treat with doxycycline; usually not zoonotic
	Pseudocapillaroides xenopi lives in skin of clawed frogs causing hemorrhage and slough; identify in scrapings.

Saprolegniasis is usually secondary to other skin lesions; appear as cottony tufts overlying ulcers; treat with chlorhexidine, betadine or benzalkonium chloride

MS222 (tricaine methanesulfonate) anesthetizes amphibians in about 20 minutes, after which they can be maintained by dripping the solution on the skin; recover by rinsing in clean water{4178}

	Tadpoles: 200-500 mg/liter
	Adults 0.5-2.0 grams/liter
	Toads 1-3 gm/liter

Isoflurane can be used in a chamber or mask{4178}

Top

Analgesia

An ACLAM Foundation-sponsored study evaluated drugs from a wide variety of classes as potential analgesics in the frog (Rana pipiens). Agents were administered subcutaneously into the dorsal lymph sac. An acetic acid test was used to measure analgesia; this involves painting the skin of the thigh with log-increasing doses of acetic acid until a "wiping" response is seen. Animals showing increased analgesia were tested for behavioral effects to document that sedation was not the cause of decreased response. Significant analgesia was obtained when the following were administered: chlorpromazine (30nmol/g), chlordiazepoxide (300nmol/g), buprenorphine (30nmol/g), diphenhydramine (200nmol/g), and haloperidol (30nmol/g). Less robust analgesia was induced by indomethacin (300nmol/g), ketorolac (100nmol/g), chlordiazepoxide (100nmol/g, a lower dose than above), butorphanol (100nmol/g), indomethacin (1000nmol/g, higher than above), pentobarbital (30nmol/g), butorphanol (30nmol/g, lower than above), and pentobarbital (10nmol/g, lower than above). There was high mortality when higher doses of most analgesics were used.{4507}

Dopamine may be involved in nociception in amphibians, as evidenced by the effects of chlorpromazine and haloperidol. The former drug has mixed antagonist activity at dopamine, cholinergic and adrenergic receptors, while haloperidol is more specific for dopamine receptors. Both drugs are classed as antipsychotics, and produced moderate analgesia in the frogs.{4507}

Agents enhancing GABA activity are effective analgesics in mammals and apparently also in the frog. Chlordiazepoxide and pentobarbital act by enhancing the efficacy of the inhibitory GABA neurotransmitter at its receptor.{4507}

Diphenhydramine is a histamine H1 antagonist, but at high doses it blocks muscarinic cholinergic receptors. Although fairly weak, it did produce noticeable analgesia in this study.{4507}

The NSAIDs indomethacin and ketorolac produced mild analgesia in the frog. In rats, these drugs do not produce analgesia when measured by tail-flick or hot plate testing. The frog may be an alternative model for NSAID testing.{4507}

There is likely a common way of processing nociceptive impulses in mammals and amphibians. Amphibian nervous tissues contain endogenous opioids, substance P, serotonin, calcitonin-gene related peptide and other substances known to modulate nociceptive processing. Careful clinical use of these analgesics may be warranted in amphibians. Other work has shown that opioids such as morphine, meperidine and fentanyl and also potent and safe.{4507}

Top