Toad

About: Toad is a research topic. Over the lifetime, 1624 publications have been published within this topic receiving 28732 citations.

Seasonal changes in the activity of cytochrome P450(C17) from the testis of Bufo arenarum.

Abstract: In Bufo arenarum, the biosynthesis of testosterone and 5α-dihydrotestosterone takes place through a complete 5-ene pathway, 5-androsten-3β,17β-diol being the immediate precursor of testosterone. Besides androgens, testes are able to synthesise 5α-pregnan-3,20-dione and several 3α and 20α reduced derivatives. During the breeding season, steroid biosynthesis turns from androgen to C21-steroid production. As a consequence, the cytochrome P450 17-hydroxylase, C17,20-lyase (CypP450c17) could be a key enzyme in that metabolic shift. The present study demonstrates that in testes of B. arenarum, CypP450c17 co-localises with glucose-6-phosphatase in the microsomal fraction. CypP450c17 possesses more affinity for pregnenolone than for progesterone in both non-reproductive (Km=43.76±4.63 nM and 2,170±630 nM, respectively) and reproductive (Km=37.46±4.19 nM and 3,060±190 nM, respectively) seasons. These results could explain the predominance of the 5-ene pathway for testosterone biosynthesis. Toad CypP450c17 activity is higher in the non-reproductive period than the reproductive period, suggesting that this enzyme is an important factor in toad steroidogenic changes. Animals in reproductive conditions showed a significant reduction in circulating androgens. This is in agreement with the decrease in Vmax of cytochrome P450 17-hydroxylase activity, enhancing the physiological relevance of these in vitro results.

The effect of sex hormones on lipid content and mast cell number in the harderian gland of the female toad, Bufo viridis.

Abstract: The Harderian gland of the toad Bufo viridis is a dimorphic gland owing to the presence of lipid droplets in the female glandular cells present only during summer months. Ovariectomy causes the disappearance of sudanophilia and estrogen-treatment completely prevents this change, while testosterone-injection has little effect. Estradiol-treatment also provokes a proliferation of the interstitial connective tissue concomitantly with the mast cell number increase. Our results suggest that estradiol acts, stimulating both mast cell and connective tissue proliferation, and plays a role in determining the expression of the female type of the toad Harderian gland.

Chohlinergic transmission in the recurrent facilitatory pathway of the spinal motoneuron of the toad

Abstract: 1. The VR-EPSP of the spinal motoneuron of the toad was investigated by intracellular recording. Concerning the size, time course, and effect of membrane potential displacements, no essential difference was found between the VR-EPSP in the toad and that in the frog. A remarkable facilitatory effect of the DR-EPSP on the VR-EPSP was observed.2. The effects of various pharmacological agents on the VR-EPSP were tested by topical application using a double- or triple-barrel microelectrode, or by application to the perfusion fluid through the vascular system.3. The VR-EPSP was increased in size and the decaying phase was prolonged by topical application of physostigmine. Acetylcholine was effective in increasing the size of the VR-EPSP when applied topically or through the vascular system.4. A transient depolarization, which may be called acetylcholine potential, was recorded intracellulary when acetylcholine was applied extracellularly by a brief outward current from the microelectrode filled with acetylcholine.5. Curare was found to have no effect on the VR-EPSP, while nicotine and atropine were effective in depressing the VR-EPSP.6. Cholinergic trasmission at the synapse between motor axon collaterals and motoneurons in the toad was demonstrated. It was, furthermore, pointed out that the present investigation did not exclude the possibility of electrical interaction between motoneurons.

Expression of cystic fibrosis transmembrane conductance regulator in the skin of the toad, Bufo bufo and possible role for Cl- transport across the heterocellular epithelium.

Abstract: Evidence is discussed that apical CFTR Cl − channels of mitochondria-rich (MR) cells of Bufo bufo skin conduct β-adrenergic receptor-activated Cl − currents. Ussing chamber studies revealed the following selectivity sequence of the receptor activated conductance, Cl − >Br − >NO 3 − >I − . With ion selective microelectrode-techniques, it was shown that receptor-coupled Cl − channels are not located in principal cells. A small conductance (7–10 pS) CFTR-like Cl − channel is located in the apical plasma membrane of MR cells. Short life times of sealed patches prevented detailed study of its selectivity to other halide ions and its molecular regulation. With monoclonal h CFTR-antibodies, selective expression in MR cells of the targeted antigens could be demonstrated. A transcript of CFTR was amplified in the skin, and a bb CFTR cDNA clone was generated from toad skin mRNA that exhibits 89% amino acid identity with the human homologue. The frequency of obtaining channels in patch clamp studies was too low for accounting quantitatively for the macroscopic conductance. Since MR cells were isolated by trypsin, and a putative extracellular loop of the deduced bb CFTR protein contains a target peptide bond for trypsin, enzyme treatment may have destroyed apical CFTR molecules.