摘要:

In the urodeles Proteus anguinus and Euproctus asper, thresholds of an overt avoidance response to weak electrical field stimuli (continuous sine-waves) were measured as a function of frequency. Thresholds down to 0.1 mV/cm (30 nA/cm2) were found in P. anguinus and 2 mV/cm (600 nA/cm2) in E. asper at ''best frequencies'' (B.F.) of 20–30 Hz, but sensitivity covered a total frequency range of below 0.1 Hz to 1–2 kHz, with up to 70 dB higher thresholds. Average thresholds of 1 mV/cm in P. anguinus and 40 mV/cm in E. asper were more than 30 dB apart and significantly different. Both species were sensitive to galvanic DC-pulses, clicks, and noise bursts with intensities of about the same order of magnitude. Specimens of the transparent catfish, Kryptopterus (Siluridae) reacted in the same frequency range as found for Proteus and Euproctus, and had still lower thresholds, down to 0.02 mV/cm (1.5 nA/cm2). The biological significance and possibly still ongoing evolution of the electrical sense in urodeles is interpreted in terms of comparative sensory physiology and more recent, still speculative, evolutionary diversification during and since the Pleistoc

ISSN:0006-8977    

DOI:10.1159/000112986

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The blind cave salamander''s (Proteus anguinus L.) sensitivity for electrical fields was determined by recordings from afferent fibers coming from ampullary electroreceptors. The animals were stimulated with single rectangular or continuous sinusoidal electrical signals passed through the cave water in the experimental tank. Best threshold sensitivities of the fibers for both kinds of signals were in the same range (0.1–0.5 mV/cm = 30–150 nA/cm2). The fibers showed phase-locked responses to rostrally cathodic phases of rectangular or sinusoidal stimuli and suppression to anodal phases. Units were tuned to ''best frequencies'' (B.F., sine waves) between 20 and 40 Hz. Any functional, i.e. phase-related, firing or suppression of firing occurs in a total frequency range of less than 0.1 to around 100 Hz. This frequency range of tuning in the primary fibers was the same as found in the behavior, and this therefore reflects the peripheral sensory properties. Electrical sensitivity might be of special value for these cave dwelling animals, as they may detect and recognize prey animals by means of the prey''s electrical field spreading into the surroundings, i.e. its electromyog

ISSN:0006-8977    

DOI:10.1159/000112987

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Immunocytochemistry was used to investigate the neuroanatomical distribution of the chicken-I form of gonadotropin-releasing hormone (cGnRH-I) in reproductively active, male, red-sided garter snakes (Thamnophis sirtalis parietalis). Cell bodies with cGnRH-I immunoreactivity (ir) were found in the terminal nerve ganglion, nucleus of the diagonal band of Broca, medial preoptic area, and the hypothalamus. Fibers containing cGnRH-Iir were distributed in the following brain areas. Within the olfactory bulb, fibers were found in the internal plexiform, mitral and glomerular cell layers, as well as in the terminal nerve; within the forebrain, fibers were observed in the diagonal band of Broca, rostral and lateral septum, lateral pallium, retrobulbar region pars dorsomedialis, nucleus accumbens, medial preoptic area, hippocampal commissure, amygdala, posterior dorsal ventricular ridge, hypothalamus, median eminence, and the thalamus; within the midbrain, fibers were found in the interpeduncular nucleus and the stratum album periventricular of the optic tectum. This study shows that the distribution of cell bodies for cGnRH-Iir in this reptile is consistent with the distribution of immunoreactivity for cGnRH-I in birds and mammalian GnRH in amphibians and mammals. Using antiserum specific to cGnRH-I, the endogenous form of GnRH, this is the first study to show that the terminal nerve in a reptile contains GnRH immunoreactivity.

ISSN:0006-8977    

DOI:10.1159/000112988

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Alpha-melanocyte-stimulating hormone (α-MSH) and adrenocorticotropin (ACTH) promote habituation of prey-catching behavior in toads. We tested the hypothesis that habituation is associated with alterations in the activity of α-MSH neurons in a toad, Bufo cognatus. We used immunocytochemistry and RIA to determine the organization and distribution of α-MSH neurons in the brain. In addition, we measured brain α-MSH and plasma concentrations in toads at different times before and during stimulus specific habituation of the turning response to a rotating prey dummy. Cell groups immunoreactive for α-MSH-/and ACTH were detected only in the infundibular hypothalamus. Projections from these cells innervated the olfactory nucleus, nucleus accumbens, septum, habenular nucleus, the preoptic area, the hypothalamus, the caudal thalamus, optic tectum and brain stem. The rank order of α-MSH concentrations in the brain of Bufo cognatus optic tectum (OT). The only difference observed in tissue α-MSH levels between habituated and non-habituated toads was an elevation in T/HT α-MSH levels in control toads after 20 min in the testing apparatus. In contrast, many differences were observed in both groups as a function of time spent in the test apparatus. Concentrations of α-MSH in the T/HT and PO increased while concentrations in the Tel decreased over time for both control and habituated toads. Plasma α-MSH titers rose over time in control toads but not in habituated toads. Our findings suggest that habituation per se is not associated with dramatic alterations in brain or plasma α-MSH levels. On the other hand, prolonged confinement causes pronounced alterations in the activity of brain and pituitary proopiomelano

ISSN:0006-8977    

DOI:10.1159/000112989

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

We describe the numbers, central positions, and axonal exit routes of the distal leg motor neurons of four decapod species: squat lobsters (Munida quadrispina), spiny sand crabs (Blepharipoda occidentalis), mole sand crabs (Emerita analoga), and signal crayfish (Pacifastacus leniusculus). As predicted by previous physiological and anatomical identification of axons at the periphery in crayfish and lobsters, cobalt backfills reveal about seventeen cell bodies, which are found in four areas in the ganglion. By comparing their positions and neurite morphologies with the previously identified neurons, functional identifications could be assigned to most of them. The common inhibitor and stretcher inhibitor are located posterior-medial. An anterior-lateral cluster of about twelve somata includes the opener≡stretcher excitor, one of two bender excitors (bender excitor α), four flexor excitors, and two excitors each to the extensor, reductor, and closer muscles. Three cell bodies are posterior-lateral. Of these, the opener inhibitor and the second bender excitor (bender excitor β) are on about the same dorsoventral plane. The third posterior-lateral cell, the accessory flexor excitor, is noticeably more dorsal than the other two posterior-lateral cell bodies. The reductor muscle is innervated by at least three neurons: the putative common inhibitor and fast and slow excitors. None of the leg motor neurons project into the contralateral hemiganglion. The most variable feature across species is the nerve through which motor axons exit the ganglion: axons leave the ganglia via different routes in each of the four species examined. These differences in the axons'' pathway, however, are insufficient to explain the differences in motor output and behaviour of these four spec

ISSN:0006-8977    

DOI:10.1159/000112990

出版商:S. Karger AG    

年代:1997

数据来源: Karger