Hormonal control of swimbladder sonic muscle dimorphism in the Lusitanian toadfish Halobatrachus didactylus.
(9/75)
The swimbladder and associated sonic muscle of the Lusitanian toadfish Halobatrachus didactylus increase in size throughout life and are, respectively, 25% and 30% larger in type I (nest-holder) males than females, which may generate sexual differences in sound production. Sexual dimorphism in swimbladder is also evident in the morphological features of sonic muscle fibers. During the breeding season, type I males have smaller myofibril contracting zones surrounded by larger sarcoplasm areas compared with females, possibly an adaptation to speed and fatigue resistance for the production of long mating calls. Type II (floater) males show characteristics that are intermediate, but statistically not significantly different, between type I males and females. Six weeks after castration and androgen (testosterone and 11-ketotestosterone) replacement in type I and type II males there were no alterations either in swimbladder mass or fiber morphology. However, 17beta-estradiol induced a significant decrease in swimbladder mass and sarcoplasm area/myofibril area ratio. Six months after castration there was a clear reduction in the seasonal swimbladder hypertrophy in males and induction of sonic fiber morphological characteristics that resemble those occurring in females (low sarcoplasm area/myofibril area ratio). These results suggest that testicular factors are required to initiate sonic muscle hypertrophy and type I sonic fiber phenotype in H. didactylus, but a specific involvement of androgens has not been completely clarified. (+info)
The venomous toadfish Thalassophryne nattereri (niquim or miquim): report of 43 injuries provoked in fishermen of Salinopolis (Para State) and Aracaju (Sergipe State), Brazil.
(10/75)
Fishes of family Batrachoididae are responsible for great number of injuries in fishermen in North and Northeast regions of Brazil. The genus Thalassophryne presents various venomous species of fishes found in the Brazilian coast, T. nattereri being the most common of them. The venom is ejected through two hollow spines on the dorsal fin and two on pre-opercular regions, which present a venomous gland in the base and can be erected or depressed by the fish. The manifestations of the envenoming were intense local pain, edema and erythema in 43 patients observed in Salinopolis (Para State) and Aracaju (Sergipe State). There were no systemic manifestations, but necrosis was detected in eight and bacterial infection in ten injured fishermen. The circumstances of the contacts and therapeutic aspects are discussed. Envenoming by the genus Thalassophryne is important and frequent and should be considered of moderate severity grade, since there are not the excruciating pain or the massive local necrosis provoked by scorpionfishes (Scorpaena) or stingrays injuries nor the systemic manifestations that are the most important marker of severe envenoming. (+info)
Effect of the anesthetic tricaine (MS-222) on nerve activity in the anterior lateral line of the oyster toadfish, Opsanus tau.
(11/75)
Inductive neural telemetry was used to record from microwire electrodes chronically implanted into the anterior lateral line nerve of the toadfish, Opsanus tau. Spontaneous neural activity and the response of lateral line fibers to water current were continually monitored from 17 primary afferent fibers before, during, and after the administration of the anesthetic tricaine (MS-222). Significant decrease in spontaneous and evoked activity and increase in interspike interval was noted when anesthetic concentrations were >/=0.010%. Neural activity returned to control levels within approximately 90 min of anesthetic withdrawal. Decreasing the pH of the solution without the anesthetic caused transient heightened sensitivity, indicating that tricaine and not the concurrent drop in pH was responsible for the decrease in sensitivity during anesthesia. During a secondary challenge with the anesthetic 24 h after the first, fibers initially showed faster recovery however overall recovery kinetics were similar. Although high tricaine concentration was correlated with decreased neural sensitivity, the concentrations normally used to maintain anesthesia in the toadfish did not have significant effect on the evoked firing rate. Thus given sufficient time to recover from the induction of surgical anesthesia, it may be possible to maintain the animal under light anesthesia while minimizing the physiological effects of tricaine. (+info)
Dogmas and controversies in the handling of nitrogenous wastes: 5-HT2-like receptors are involved in triggering pulsatile urea excretion in the gulf toadfish, Opsanus beta.
(12/75)
When injected arterially, serotonin (5-hydroxytryptamine; 5-HT) has been shown to elicit naturally sized urea pulse events in the gulf toadfish, Opsanus beta. The goal of the present study was to determine which 5-HT receptor(s) was involved in mediating this serotonergic stimulation of the pulsatile excretion mechanism. Toadfish were surgically implanted with caudal arterial catheters and intraperitoneal catheters and injected with either 8-OH-DPAT (1 micro mol kg(-1)), a selective 5-HT(1A) receptor agonist, alpha-methyl-5-HT (1 micro mol kg(-1)), a 5-HT(2) receptor agonist, or ketanserin, a 5-HT(2) receptor antagonist (0.01, 0.1, 1 and 10 micro mol kg(-1)) plus alpha-methyl-5-HT. 8-OH-DPAT injection did not mediate an increase in urea excretion, ruling out the involvement of 5-HT(1A) receptors in pulsatile excretion. However, within 5 min, alpha-methyl-5-HT injection caused an increase in the excretion of urea in >95% (N=27) of the fish injected, with an average pulse size of 652+/-102 micro mol N kg(-1) (N=26). With alpha-methyl-5-HT injection there was no corresponding increase in ammonia or [(3)H]PEG 4000 permeability. Urea pulses elicited by alpha-methyl-5-HT were inhibited in a dose-dependent fashion by the 5-HT(2) receptor antagonist ketanserin, which at low doses caused a significant inhibition of pulse size and at higher doses significantly inhibited the occurrence of pulsatile excretion altogether. However, neither 8-OH-DPAT nor alpha-methyl 5-HT injection had an effect on plasma cortisol or plasma urea concentrations. These findings suggest the involvement of a 5-HT(2)-like receptor in the regulation of pulsatile urea excretion. (+info)
Dogmas and controversies in the handling of nitrogenous wastes: ureotely and ammonia tolerance in early life stages of the gulf toadfish, Opsanus beta.
(13/75)
The marine gulf toadfish (Opsanus beta) is an unusual teleost fish as it is able to switch between ammoniotelism and ureotelism in response to a variety of laboratory conditions. The present study integrates field work conducted in Biscayne and Florida Bays, USA with laboratory studies to examine ureotelism during the early life history stages of O. beta. Adult toadfish voluntarily nested in artificial shelters placed amongst seagrass beds and were found to be predominantly ureotelic under natural conditions as the internal shelter water had mean urea and ammonia concentrations (N=51) of 14.2+/-1.6 micro mol N l(-1) and 8.9+/-0.9 micro mol N l(-1), respectively. Toadfish successfully spawned in shelters, providing eggs, larvae and juvenile toadfish for laboratory study. In the lab, juvenile toadfish were also ureotelic and urea was excreted in pulsatile events that accounted for 62.0+/-5.9% of total urea-N excreted. Excretion rates of urea-N and ammonia-N were 1.018+/-0.084 micro mol N h(-1) g(-1) and 0.235+/-0.095 micro mol N h(-1) g(-1), respectively. Field-collected eggs, larvae and juveniles expressed significant levels of the ornithine-urea cycle enzymes carbamoyl-phosphate synthetase III, ornithine transcarbamylase and arginase and the accessory enzyme glutamine synthetase, all of which increased in activity as toadfish developed through early life stages. In juveniles, the ammonia 96-h LC(50) value was 875 micro mol N l(-1) and there was a 3-fold increase in ornithine transcarbamylase activity in the 1000 micro mol N l(-1) NH(4)Cl treatment. The results are discussed in the context of the causal factor(s) for ureotelism in toadfish. Furthermore, the results of this study suggest it is unlikely that the adaptive significance of ureotelism in toadfish is a means to prevent fouling nests with ammonia and in turn poisoning offspring; however, additional study is warranted. (+info)
Rapid, hierarchical modulation of vocal patterning by steroid hormones.
(14/75)
Vocal control systems have been identified in all major groups of jawed vertebrates. Although steroid hormones are instrumental in the long-term development and maintenance of neural structures underlying vocalization, it is unknown whether steroids rapidly modulate the neural activity of vocal motor systems. The midshipman fish generates advertisement and agonistic calls that mainly differ in duration. A descending midbrain pathway activates a hindbrain-spinal vocal circuit that directly establishes the discharge frequency and duration of the rhythmic vocal motor volley. This vocal motor output, which can be monitored from occipital nerve roots, directly determines the rate and duration of contraction of a pair of sonic muscles and, in turn, the fundamental frequency and duration of vocalizations. Here, we demonstrate that the duration of the vocal motor volley, or fictive vocalization, is rapidly responsive to steroid hormones, including androgens, estrogens, and glucocorticoids. These responses are consistent, in part, with a nongenomic mechanism and are steroid specific at the receptor level, suggesting the possibility of multiple membrane-bound receptor populations. We also show, using intact and semi-intact preparations, that steroids hierarchically modulate fictive vocalizations; whereas the hindbrain-spinal region is both necessary and sufficient for rapid (within 5 min) effects on duration, descending midbrain input is necessary for maintenance (up to 120 min) of these effects. The conserved nature of vertebrate vocal motor systems suggests that the neuroendocrine principles outlined in this study may be a fundamental feature of all vocal vertebrates. (+info)
Steroid-dependent auditory plasticity leads to adaptive coupling of sender and receiver.
(15/75)
For seasonally breeding vertebrates, reproductive cycling is often coupled with changes in vocalizations that function in courtship and territoriality. Less is known about changes in auditory sensitivity to those vocalizations. Here, we show that nonreproductive female midshipman fish treated with either testosterone or 17beta-estradiol exhibit an increase in the degree of temporal encoding of the frequency content of male vocalizations by the inner ear that mimics the reproductive female's auditory phenotype. This sensory plasticity provides an adaptable mechanism that enhances coupling between sender and receiver in vocal communication. (+info)
Hair-cell versus afferent adaptation in the semicircular canals.
(16/75)
The time course and extent of adaptation in semicircular canal hair cells was compared to adaptation in primary afferent neurons for physiological stimuli in vivo to study the origins of the neural code transmitted to the brain. The oyster toadfish, Opsanus tau, was used as the experimental model. Afferent firing-rate adaptation followed a double-exponential time course in response to step cupula displacements. The dominant adaptation time constant varied considerably among afferent fibers and spanned six orders of magnitude for the population ( approximately 1 ms to >1,000 s). For sinusoidal stimuli (0.1-20 Hz), the rapidly adapting afferents exhibited a 90 degrees phase lead and frequency-dependent gain, whereas slowly adapting afferents exhibited a flat gain and no phase lead. Hair-cell voltage and current modulations were similar to the slowly adapting afferents and exhibited a relatively flat gain with very little phase lead over the physiological bandwidth and dynamic range tested. Semicircular canal microphonics also showed responses consistent with the slowly adapting subset of afferents and with hair cells. The relatively broad diversity of afferent adaptation time constants and frequency-dependent discharge modulations relative to hair-cell voltage implicate a subsequent site of adaptation that plays a major role in further shaping the temporal characteristics of semicircular canal afferent neural signals. (+info)