Peter Horvath

Parental Behavior and Reproductive Output in Male-Only Cared and Female-Only Cared Clutches in the Eurasian Penduline Tit (Remiz pendulinus)

ABSTRACT. Diverse patterns of parental care, including uniparental care by either the male or the female, provide excellent opportunities to investigate how variation in social traits is maintained in wild populations. Coexistence of different parental strategies within the same population is expected when they exhibit similar cost-benefit ratios. We investigated one of the most diverse avian breeding systems and compared parental behavior and reproductive output between nests that are uniparentally cared for by male or female Eurasian Penduline Tits (Remiz pendulinus). In this small passerine bird, full care (incubation and brood care) is provided by the male only (7–18% of nests) or the female only (48–65% of nests). Additionally, a third of all nests are deserted by both parents as a result of intense sexual conflict over care. We show that parental effort is similar between male and female parents, and they achieve similar offspring survival after controlling for clutch-size differences. Females care for larger clutches than males (5.7 ± 0.1 [SE] and 3.5 ± 0.2 eggs, respectively), and they produce more nestlings (3.6 ± 0.2 and 2.4 ± 0.3 nestlings, respectively), although this difference is not significant at fledging of the chicks (3.1 ± 0.2 and 2.4 ± 0.3 young, respectively). Therefore, sex difference in care does not explain the bias toward female-only care in Eurasian Penduline Tits. We propose that the differential benefits of desertion and/or the differential costs of care for males and females facilitate the existence of both uniparental care types in the population.

Impairment by lovastatin of neural relaxation of the rabbit sphincter of Oddi

We sought whether inhibition of cholesterol biosynthesis by lovastatin influenced the nitrergic relaxation response of the sphincter of Oddi. Rabbit sphincters of Oddi rings were tested for changes in isometric tension in response to field stimulation in the presence of 4 microM guanethidine and 1 microM atropine. Tissue samples were then analyzed for cAMP and cGMP content by radioimmunoassay for nitric oxide concentration by electron spin resonance and for vasoactive intestinal peptide and calcitonin gene-related peptide (CGRP) release by radioimmunoassay. Membrane G(salpha) protein was determined by Western blot analysis. Field stimulation relaxed the preparations with an increase in nitric oxide, cAMP and cGMP concentrations at increased calcitonin gene-related peptide and vasoactive intestinal polypeptide (VIP) release. Preparations from rabbits pre-treated with lovastatin (5 mg/kg/day intragastrically, over 5 days) contracted under the same conditions with an attenuated cGMP-increase at preserved increase in NO content and neuropeptide release. The relaxation was recaptured combining lovastatin with farnesol (1 mg/kg intravenously, twice a day for 5 days). The field stimulation-induced increase in cyclic nucleotides was also restored. Lovastatin decreased membrane G(salpha) protein content, which was re-normalized by farnesol. Farnesol treatment reinstates neurogenic relaxation of the sphincter of Oddi deteriorated by lovastatin possibly by normalizing G-protein coupling.

Impaired bronchomotor responses to field stimulation in guinea-pigs with cisplatin-induced neuropathy

Pre-treatment with cisplatin (3 mg/kg) i.p. once a day over 6 days induced sensory neuropathy as confirmed by femoral nerve conduction velocity test and significantly decreased contractions induced by electrical field stimulation (100 stimuli, 20 V, 0.1 ms, 20 Hz) in isolated main bronchial rings from guinea-pigs. The field stimulation-induced non-adrenergic, non-cholinergic (NANC) relaxations, however, were amplified in rings from animals with cisplatin neuropathy. The NANC relaxation response was completely blocked by 30 microM N(G)-nitro-L-arginine methyl ester in preparations from both control and cisplatin-treated animals. Superoxide dismutase (40 units/ml) was without effect on NANC relaxation in control rings, however, it substantially decreased NANC relaxation in preparations from animals with cisplatin neuropathy. These results show that cisplatin-induced sensory neuropathy is accompanied by attenuation of neural bronchoconstriction and an enhanced NANC relaxation. The latter is in part attained by an increased peripheral superoxide production.