Black Side Plait Frog Smell, And Jacobson's Organ Of Histological Observation

The olfactory organ and vomeronasal organ are the most important chemistry sense organs in anura. They play important roles in feeding, reproduction, predator avoidance and so on. The tadpole at G20-G30stage and young frog in Pelophylax nigromaculatus were investigated using histological method and NADPH-d histochemical staining to reveal the development of the olfactory system and vomeronasal system or the adaptive evolution of smell in amphibians. The main results and conlusions as follows:1. At the G20stage, the olfactory organ is already visible. The appearance of the vomeronasal organ is a little later than the olfactory organ. Anlage of the vomeronsal organ is evident at the G25Ⅱ stage(The G25stage continues about27days under laboratory conditions. Because the stage is very long, so we divide it into G25Ⅰ, G25Ⅱ and G25Ⅲ). At the G25Ⅰ stage, the inner gill breathing begins and the vomeronsal organ is not visible; At the G25Ⅱ stage, the organ is only a medicine ball, and the vomeronsal glands not exist; At the G25Ⅲ stage, the vomeronsal organ appears empty cavity and a small strip of vomeronasal glands can be observed. At hindlimb development stage, the vomeronsal organ becomes gradually developed and may be related to the terrestrial life stage. As with most anurans, the vomeronasal glands appear later than the vomeronasal organ.2. The lateral appendix is an ephemeral structure during the embryo period and located in lateral portion of the olfactory organ. In P. nigromaculatus, the lateral appendix is found at G22stage and disappears at G25Ⅲ. It is typical larval organ related to aquatic life and may enhance chemosensory sampling. The lateral appendix in the anurans might be homologous with the vomeronasal organ in the urodeles, because they are located in the same position:in the ventrolateral of the olfactory organ.3. At G24stage, the choana and cornua trabeculae appear. The appearance of the choana is prepared for the inner gill breathing and has double fuctions for smelling and breathing. The cornua trabeculae are one of the most important cartilages during the embryo period. Besides, the cornua trabeculae support the olfactory cavity in order to facilitate air movement.4. After the G26stage, the vomeronsal organ is almost completed. After the metamorphosis, from dorsal to the ventral, the nasal cativy of frog is divided into three chambers communicating with each other:the cavum principale, the cavum medium and the cavum inferius. The cavum principale is lined with olfactory epithelium; the cavum medium is covered with non-sensory epithelium and connects with the Harderian glands by the nasolacrimal duct; the cavum inferius is covered with non-sensory epithelium too. In the medial, the cavum inferius contains the vomeronasal organ. The vomeronasal organ is lined with vomeronsal epithelium. Attached to the septum nasi, there are amount of vomeronsal glands.5. In the caudal portion of nasal cavity in juvenile frog, the eminentia olfactoria is found as a small bump in the floor of the cavum principale. The eminentia olfactoria can increase the contact surface with the air in order to facilitate air movement. Therefore, the origin of eminentia olfactoria in olfactory cavity may be an adaption to the terrestrial environment. Bowman’s glands, which produce mucus, are present in the olfactory epithelium of P. nigromaculatus at the onset of metamorphosis. It can detect molecules in the air and may be related to the onset of the terrestrial life stage. The cavum medium and nasolacrimal duct appear at the metamorphic stage, too. In most frogs, the cavum medium is water-filled and does not to detect water-borne or air-borne odorants. The cavum medium connects with the Harderian glands by the basal portion of the nasolacrimal duct. The nasolacrimal duct carries mucus from the Harderian gland to the nasal cavity. Then, the fluids activate the vomeronasal organ so as to sense the stimuli. In brief, the eminentia olfactoria, Bowman’s glands, the cavum medium and the nasolacrimal duct emerged at the onset of metamorphosis could be an adaption to the terrestrial environment.6. The olfactory epithelium structure is composed of the sustentacular cell layer, receptor cell layer and basal cell layer. Three layers are hard to distinguish with HE staining. However, in tissues stained with Silver staining, the olfactory epithelium of P. nigromaculatus are distinct. The sustentacular cell in olfactory epithelium is dyed deep black, the receptor cell the spotted color, and the basal cell the brownish black.7. The distribution of NO in olfactory epithelium can be labelled with NADPH-d histochemistry. There is strongly reactive through their entire sustentacular cell layer in olfactory epithelium. However, the vomeronasal epithelium expresses enzymatic activity at low levels, increasing from basal surface to free surface. The nitric oxide synthase(NOS) positive neurons mainly distribute in sustentacular cell layer. P. nigromaculatus and Pipa americana have the same pattern staining. It is effect to research the vomeronasal system with NADPH-d histochemistry. The fuction of the vomeronasal system may be relevant with NOS.8. The vomeronasal system is composed of the vomeronasal epithelium in the vomeronsal organ and a set of centers in the forebrain. The centers consist of the accessory olfactory bulb, the medial amygdala and the lateral hypothalamus. Recent studies in amphibians have shown that the accessory olfactory bulb projects only to the medial amygdala. The vomeronasal projections of the neurons in the vomeronasal epithelium reach the accessory olfactory bulb and vomeronsal connections exist through the medial amygdala to the hypothalamus, as they do in tetrapods.