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Biomedical subjects

A H Bass

Publications and source records attributed to A H Bass.

At least 37 records · Page 2Linked to original sources
PubMed1999

Steroid hormones and paternal care in the plainfin midshipman fish (Porichthys notatus).

The present study investigated the relationship between plasma steroid hormone levels and the expression ofpaternal behavior in the plainfin midshipman fish (Porichthys notatus), where males may simultaneously care for multiple clutches in different stages of development. Blood samples were collected from free-living parental males during that part of the breeding season when males may be found in various stages of parental care. Plasma 11-ketotestosterone levels were significantly higher in males with empty nests and nests containing only eggs than in males with nests containing embryos. All males with nests containing embryos had undetectable testosterone levels, whereas testosterone levels were detectable in many males with empty nests or nests containing only eggs. Estradiol levels were detectable in only a few males from nests with no eggs or nests containing only eggs. Cortisol levels were not correlated with stage of paternal care or with handling time. These results follow the frequently reported vertebrate pattern of declining androgen levels over the course of the breeding season or during the period of parental care. However, many male midshipman guarding nests containing only eggs had androgen levels similar to those of males whose nests contained no offspring. Thus the pattern of androgen levels exhibited by reproductively active parental male midshipman may reflect a compromise between investment in paternal care versus courtship and/or territoriality.

Animals↗
PubMed1999

Peripheral encoding of behaviorally relevant acoustic signals in a vocal fish: single tones.

The midshipman fish, Porichthys notatus, generates acoustic signals for intraspecific communication. Nesting males produce long-duration "hums" which attract gravid females and can be effectively mimicked by pure tones. In this study we examine the encoding of tonal signals by the midshipman peripheral auditory system. Single-unit recordings were made from afferents innervating the sacculus while presenting sounds via an underwater loudspeaker. Units were characterized by iso-intensity spike rate and vector strength of synchronization curves, as well as by peristimulus time histograms. Additionally, response-intensity curves and responses to long-duration (up to 10 s) stimuli were obtained. As has been seen in other teleosts, afferents had highly variable activity profiles. Excitatory frequencies ranged from 60 to over 300 Hz with most units responding best around 70 or 140 Hz. Thresholds at 90 Hz ranged from 95 to 145 dB re 1 microPa. Strong synchronization provided a robust temporal code of frequency, comparable to that described for goldfish. Spike rate showed varying degrees of adaptation but high rates were generally maintained even for 10-s stimuli. The midshipman peripheral auditory system is well suited to encoding conspecific communication signals, but nonetheless shares many response patterns with the auditory system of other teleosts.

Acoustic Stimulation↗
PubMed1999

Midbrain combinatorial code for temporal and spectral information in concurrent acoustic signals.

All vocal species, including humans, often encounter simultaneous (concurrent) vocal signals from conspecifics. To segregate concurrent signals, the auditory system must extract information regarding the individual signals from their summed waveforms. During the breeding season, nesting male midshipman fish (Porichthys notatus) congregate in localized regions of the intertidal zone and produce long-duration (>1 min), multi-harmonic signals ("hums") during courtship of females. The hums of neighboring males often overlap, resulting in acoustic beats with amplitude and phase modulations at the difference frequencies (dFs) between their fundamental frequencies (F0s) and harmonic components. Behavioral studies also show that midshipman can localize a single hum-like tone when presented with a choice between two concurrent tones that originate from separate speakers. A previous study of the neural mechanisms underlying the segregation of concurrent signals demonstrated that midbrain neurons temporally encode a beat's dF through spike synchronization; however, spectral information about at least one of the beat's components is also required for signal segregation. Here we examine the encoding of spectral differences in beat signals by midbrain neurons. The results show that, although the spike rate responses of many neurons are sensitive to the spectral composition of a beat, virtually all midbrain units can encode information about differences in the spectral composition of beat stimuli via their interspike intervals (ISIs) with an equal distribution of ISI spectral sensitivity across the behaviorally relevant dFs. Together, temporal encoding in the midbrain of dF information through spike synchronization and of spectral information through ISI could permit the segregation of concurrent vocal signals.

Acoustic Stimulation↗
PubMed1998

Preoptic AVT immunoreactive neurons of a teleost fish with alternative reproductive tactics.

Recent reports have implicated an important role for arginine vasotocin (AVT) in the socially mediated sexual differentiation of fishes. This study focuses on the plainfin midshipman (Porichthys notatus) which exhibits two male morphs, type I and type II, differing in a suite of behavioral, neurobiological, and endocrine traits. Immunocytochemical techniques were used to detect neurons containing AVT-like peptide in the forebrain of juveniles, adult females, and type I and type II males. AVT immunoreactive (ir) somata were localized to three regions: the terminal nerve ganglion, the preoptic area (POA), and the pineal stalk. The profile area, or size, of AVT-ir POA neurons differed across the four classes of midshipman and was strongly correlated to differences in body size among the groups. By contrast, the number of AVT-ir cells in the POA exhibited no difference across the classes of midshipman. The number of POA cells containing AVT is therefore likely to be set early in development and not to change with the growth of the animal. An analysis of AVT-ir cell number normalized by body mass revealed that the larger morphs, type I males and females, have fewer cells per gram body mass than type II males and juveniles. Therefore, type II males have a juvenile-like AVT POA phenotype with smaller cells and more numerous cells per unit body mass than type I males. Type II males also exhibit more variability in the number of AVT-ir cells found in the POA compared to type I males.

3-Hydroxysteroid Dehydrogenases↗
PubMed1998

Behavioral assessment of acoustic parameters relevant to signal recognition and preference in a vocal fish.

Acoustic signal recognition depends on the receiver's processing of the physical attributes of a sound. This study takes advantage of the simple communication sounds produced by plainfin midshipman fish to examine effects of signal variation on call recognition and preference. Nesting male midshipman generate both long duration (> 1 min) sinusoidal-like "hums" and short duration "grunts." The hums of neighboring males often overlap, creating beat waveforms. Presentation of humlike, single tone stimuli, but not grunts or noise, elicited robust attraction (phonotaxis) by gravid females. In two-choice tests, females differentiated and chose between acoustic signals that differed in duration, frequency, amplitude, and fine temporal content. Frequency preferences were temperature dependent, in accord with the known temperature dependence of hum fundamental frequency. Concurrent hums were simulated with two-tone beat stimuli, either presented from a single speaker or produced more naturally by interference between adjacent sources. Whereas certain single-source beats reduced stimulus attractiveness, beats which resolved into unmodulated tones at their sources did not affect preference. These results demonstrate that phonotactic assessment of stimulus relevance can be applied in a teleost fish, and that multiple signal parameters can affect receiver response in a vertebrate with relatively simple communication signals.

Acoustics↗
PubMed1998

Sonic/vocal motor pathways in catfishes: comparisons with other teleosts.

Among teleost fishes, representatives of several distantly related groups have sound-producing (sonic/vocal) muscles associated with the swimbladder or pectoral girdle/fin. Here, the diversity of vocal organs and central motor pathways in four families of catfish, order Siluriformes, is compared to that in families from two distantly related orders, the Scorpaeniformes and Batrachoidiformes. Several catfish families have two sonic mechanisms--a swimbladder vibration established by 'drumming muscles' that differ in origin and insertion between families, and a pectoral spine stridulatory apparatus. In ariids, mochokids and doradids, sonic swimbladder muscles originate at various cranial or postcranial elements and insert onto an 'elastic spring' that vibrates the swimbladder, while in pimelodids the muscles insert ventrally at the swimbladder. Sonic motoneurons are located along the midline, ventral to the fourth ventricle/central canal in doradids and mochokids but lateral to the medial longitudinal fasciculus in ariids; pimelodids have motoneurons in both locations. The axonal trajectory for the lateral motoneurons in pimelodids and ariids implies that they are a migrated, midline population of sonic motoneurons. Pectoral spine-associated motoneurons are located in the ventral motor column. Unlike catfishes, a diversity of sonic mechanisms in Scorpaeniformes is not associated with different positions for sonic motoneurons. Cottids (sculpin) lack a swimbladder but have sonic muscles that originate at the occipital cranium and insert at the pectoral girdle; sonic motoneurons are located within the ventral motor column. Some triglids have intrinsic swimbladder muscles, although ontogenetic data indicate a transient association with the pectoral girdle; sonic motoneurons are in the same location as in cottids. Among Batrachoidiformes, all known representatives have intrinsic swimbladder muscles that are never associated with the pectoral girdle and are innervated by midline sonic motoneurons. The results suggest two patterns of organization for sound-producing systems in teleost fishes: pectoral fin/girdle-associated muscles are innervated by sonic motoneurons positioned within the ventral motor column, adjacent to the ventral fasciculus; non-pectoral associated muscles are innervated by sonic motoneurons located on or close to the midline, adjacent to the medial longitudinal fasciculus.

Air Sacs↗
PubMed1997

Temporal coding of concurrent acoustic signals in auditory midbrain.

A fundamental problem faced by the auditory system of humans and other vertebrates is the segregation of concurrent vocal signals. To discriminate between individual vocalizations, the auditory system must extract information about each signal from the single temporal waveform that results from the summation of the simultaneous acoustic signals. Here, we present the first report of midbrain coding of simultaneous acoustic signals in a vocal species, the plainfin midshipman fish, that routinely encounters concurrent vocalizations. During the breeding season, nesting males congregate and produce long-duration, multiharmonic mate calls that overlap, producing beat waveforms. Neurophysiological responses to two simultaneous tones near the fundamental frequencies of natural calls reveal that midbrain units temporally code the difference frequency (dF). Many neurons are tuned to a specific dF; their selectivity overlaps the range of dFs for naturally occurring acoustic beats. Beats and amplitude-modulated (AM) signals are also coded differently by most units. Although some neurons exhibit differential tuning for beat dFs and the modulation frequencies (modFs) of AM signals, others exhibit similar temporal selectivity but differ in their degree of synchronization to dFs and modFs. The extraction of dF information, together with other auditory cues, could enable the detection and segregation of concurrent vocalizations, whereas differential responses to beats and AM signals could permit discrimination of beats from other AM-like signals produced by midshipman. A central code of beat dFs may be a general vertebrate mechanism used for coding concurrent acoustic signals, including human vowels.

Acoustic Stimulation↗
PubMed1997

Modification of gonadotropin releasing hormone (GnRH) mRNA expression in the retinal-recipient Thalamus.

Although the environmental cues that trigger reproductive behaviors are known for many species, the mechanisms through which these signals influence the neurochemistry of the brain to produce behavior have been elusive. In this study, we describe a retinally modulated system of gonadotropin releasing hormone (GnRH) producing neurons in the thalamus of the plainfin midshipman fish, Porichthys notatus. Previously, we cloned and sequenced the cDNA for prepro-GnRH in midshipman. Here, using in situ hybridization, we localized prepro-GnRH mRNA to the ventrolateral nucleus of the thalamus, three divisions of the preoptic area, the ganglion of the terminal nerve, and the olfactory bulb. Since the thalamus, terminal nerve ganglion, and preoptic area have been associated with visual functions, we investigated the retinal connections in midshipman. In particular, biocytin tract tracing delineated a reciprocal connection between the ventrolateral nucleus of the thalamus and the retina. Retinofugal projections are exclusively contralateral. Experimental manipulation of this retinalthalamic loop through complete optic nerve transection shows that GnRH mRNA expression in the contralateral ventrolateral nucleus may be influenced by the retina. We hypothesize that a reciprocal retinothalamic GnRH circuit is important in modulating the expression of seasonal reproductive behaviors.

Animals↗
PubMed1997

Phenotypic specification of hindbrain rhombomeres and the origins of rhythmic circuits in vertebrates.

This essay considers the ontogeny and phylogeny of the cranial neural circuitry producing rhythmic behaviors in vertebrates. These behaviors are characterized by predictable temporal patterns established by a neuronal network variously referred to as either a pacemaker, neural oscillator or central pattern generator. Comparative vertebrate studies have demonstrated that the embryonic hindbrain is divided into segmented compartments called rhombomeres, each of which gives rise to a distinct complement of cranial motoneurons and, as yet, unidentified populations of interneurons. We now propose that novel rhythmic circuits were innovations associated with the adoption of cardiac and respiratory pumps during the protochordate-vertebrate transition. We further suggest that the pattern-generating circuits of more recent innovations, such as the vocal, electromotor and extraocular systems, have originated from the same Hox gene-specified compartments of the embryonic hindbrain (rhombomeres 7-8) that gave rise to rhythmically active cardiac and respiratory circuits. Lastly, we propose that the capability for pattern generation by neurons originating from rhombomeres 7 and 8 is due to their electroresponsive properties producing pacemaker oscillations, as best typified by the inferior olive which also has origins from these same hindbrain compartments and has been suggested to establish rhythmic oscillations coupled to sensorimotor function throughout the neuraxis of vertebrates.

Animals↗
PubMed1996

Sonic/vocal-acousticolateralis pathways in teleost fishes: a transneuronal biocytin study in mochokid catfish.

Mochokid catfish have two sound producing (sonic) organs--a pectoral spine stridulatory apparatus and a swimbladder whose vibration is established by nearby "drumming" muscles. Dextran-biotin or biocytin application to sonic nerves or muscles identified topographically separated motoneuron pools. Pectoral spine-related motoneurons are located within the ventral motor column whereas swimbladder motoneurons lie just ventral to the central canal or fourth ventricle. Axons of both groups of motoneurons exit the brain and spinal cord via ventral roots of occipital (swimbladder and pectoral) and spinal (swimbladder only) nerves. Transneuronal biocytin transport identified an extensive premotor network only for the swimbladder motor nuclei. Premotoneuron somata are located ipsilaterally in 1) a dorsolateral region of the sonic motor nucleus (SMN); motoneurons were clustered in the ventromedial region of the SMN and 2) the ventromedial medulla at the rostral pole of the SMN. Biocytin-filled fibers and less frequently premotoneuron somata were also found in the contralateral SMN. Biocytin-labeled fibers were continuous farther rostrally with 1) a commissural bundle that terminated bilaterally in the medial reticular formation near the caudal pole of the descending octaval nucleus and 2) a lateral brainstem bundle that terminated ipsilaterally in regions of the medulla and cerebellum considered to subserve acoustic and lateral line functions. Together with other data in distantly related teleost fishes, the results support the hypotheses that 1) central pathways linking sound-generating (sonic or vocal) and acoustic regions of the brain are traits common to both teleosts fishes and tetrapods that actively generate sounds, and 2) sonic/vocal pathways in teleosts have a conserved pattern of organization suggestive of common developmental origins.

Animals↗
PubMed1996

Nonsequential developmental trajectories lead to dimorphic vocal circuitry for males with alternative reproductive tactics.

Midshipman fish, Porichthys notatus, have two male reproductive morphs: type 1 males generate long duration advertisement calls ("hums") to attract females to a nest; type II males sneak-spawn and, like females, do not produce mate calls but generate short duration agonistic calls. A vocal pacemaker circuit includes: motoneurons in the caudal brain stem and rostral spinal cord that innervate vocal/sonic muscles; pacemaker neurons that are located ventrolateral to motoneurons and establish their fundamental discharge frequency; and a ventral medullary nucleus that couples the motoneuron-pacemaker circuit bilaterally. Transneuronal biocytin transport identified morph-specific developmental trajectories for the vocal circuit. Among nonreproductive, juvenile type I males, motoneuron soma size and motor nucleus volume increase most during a stage prior to sexual maturation. An additional increase in motoneuron size and nucleus volume is coupled to the greatest increase in pacemaker soma size at a stage coincident with the onset of sexual maturity; ventral medullary neurons show similar growth increments during both stages. Type II males (and females) mature with no or little change in cell size or motor nucleus volume. The results indicate that alternative mating tactics are paralleled by alternative developmental trajectories for the neurons that determine tactic-specific behaviors, in this case vocalizations. Together with aging data based on otolith growth, the results support the hypothesis that alternative male morphs in midshipman fish adopt nonsequential, mutually exclusive life history tactics.

Aging↗
PubMed1995

Structure, localization, and molecular phylogeny of a GnRH cDNA from a paracanthopterygian fish, the plainfin midshipman (Porichthys notatus).

Multiple forms of gonadotropin releasing hormone (GnRH) are found within several species of teleost fishes. Within the infradivision Euteleostei, the superorder Paracanthopterygii represents one of the last major groups to be examined with respect to the GnRH mRNA sequence. The plainfin midshipman, Porichthys notatus, is a common member of this superorder which is intermediate between the ancestral euteleost taxa and the more derived Acanthopterygians (percomorphs). The goals of this study were to: (1) determine the cDNA sequence of prepro-GnRH in the plainfin midshipman, (2) address the anatomical localization of midshipman prepro-GnRH gene expression, and (3) perform a cladistic analysis using all currently known cDNA sequences of prepro-GnRH. We report 460 base pair of cDNA sequence containing the entire protein coding region, and 5'- and 3'-untranslated regions. The deduced amino acid sequence indicates that this cDNA encodes a GnRH decapeptide identical in sequence to that originally isolated in salmon (Trp7, leu8 - GnRH). Northern analysis demonstrated transcripts in brain, ovary, and testis (600-700 nucleotides). PCR showed that the ovarian prepro-GnRH was identical to that found in brain. In situ hybridization labeled neurons in the ganglion of the terminal nerve and the preoptic area, forebrain areas previously observed to contain GnRH-like immunoreactivity. Last, a phylogenetic analysis of 18 prepro-GnRH sequences grouped the Paracanthopterygii with the Acanthopterygii. However, this recent clade was distinct from two separate and more ancestral lineages, the Paracanthopterygii (salmonids) and Ostariophysi (represented by catfish).

Amino Acid Sequence↗
PubMed1995

GnRH-like immunoreactivity in the peripheral olfactory system and forebrain of Atlantic salmon (Salmo salar): a reassessment at multiple life history stages.

Neurons with gonadotropin releasing hormone-like immunoreactivity (GnRH-ir) were identified within the peripheral olfactory system of Atlantic salmon (Salmo salar) at multiple life history stages. Within the forebrain, GnRH-ir somata were found in the preoptic area and in the caudomedial olfactory bulb in a position comparable to the ganglion of the nervus terminalis of other teleosts. Somata positive for GnRH were also found throughout the rostro-caudal extent of the olfactory nerve, and clustered within the medial component of the olfactory nerve as it arises from the olfactory epithelium. Results from tract tracing experiments with horseradish peroxidase indicate that at least some cells in this cluster project to the retina, suggesting that they too are part of a terminal nerve ganglion as anatomically defined in other vertebrates. We suggest that the presence of a distinct cluster of terminal nerve ganglion cells in the immediate vicinity of the olfactory epithelium may point to a peripheral site of neuromodulatory control in the olfactory system in salmon and perhaps in other teleosts as well.

Animals↗
PubMed1994

GnRH cell size and number in a teleost fish with two male reproductive morphs: sexual maturation, final sexual status and body size allometry.

Gonadotropin releasing hormone-like immunoreactive (GnRH-ir) cells in both the ganglion of the terminal nerve (TN) and the preoptic area (POA) have been implicated in the development and maintenance of reproductive behavior and physiology in teleost fishes. One marine species, the plainfin midshipman, Porichthys notatus, exhibits two sexually mature male morphs (types I and II) which differ with respect to size at sexual maturation, gonad/body weight index, reproductive tactic and vocal motor traits. Type II males become reproductively active at a smaller body size than either females or type I males. Immunocytochemical techniques and quantitative analyses were used here to determine the size and number of GnRH-ir cells in the TN and POA amongst field collected juveniles, sexually mature females, and type I and II males. Mean GnRH-ir cell size and number in the TN did not vary across the entire range of specimens. However, mean GnRH-ir cell size and number in the POA were 50-100% greater in sexually mature adults compared to juveniles. Analyses of covariance indicated that increases in cell number, but not cell size, could be explained solely on the basis of changes in body size. However, regression analyses showed that body size had a significant influence on increasing cell number only in the juvenile-type I male transition and the juvenile-female transition, not in the juvenile-type II male transition. The latter suggests that type II males, unlike the other adult morphs, have 'escaped' from a body size constraint imposed on increasing GnRH-ir cell number in the POA. There were also significant differences among the adult morphs in the size of GnRH-ir POA cells that could not be explained on the basis of differences in body size but, rather, appear to reflect differences in the temporal onset of sexual maturation. Together, the data suggest that the timing of changes in POA phenotype may provide a proximate mechanism permitting the development of alternative male reproductive morphs.

Animals↗
PubMed1994

Vocal-acoustic pathways in a teleost fish.

Many teleost fish generate acoustic signals for vocal communication by the synchronized, high-frequency contraction of skeletal, sonic muscles. In midshipman, eight groups of brainstem neurons were distinguished after biocytin application to the sonic nerve that, we propose, represent the entire vocal motor circuit. Biocytin-filled terminals were ubiquitous within all areas containing labeled neurons and, together with ultrastructural evidence, suggested a serial, transneuronal transport at synaptic sites between at least three neuronal groups. The most intensely labeled neurons were positioned in the caudal brainstem and included a previously characterized pacemaker-motoneuron circuit and a newly recognized ventral medullary nucleus that itself gave rise to extensive commissural and lateral brainstem bundles linking the pacemaker circuitry to the rostral brainstem. Five additional groups formed a column rostrally within the medial brainstem adjacent to eighth nerve (octaval)-recipient nuclei largely presumed to be acoustic. This column extended dorsally up to the ventricular cell layer and as far anterior as midbrain isthmal levels. The best-defined group was in the octaval efferent nucleus that directly innervates the sacculus that is considered the auditory division of the inner ear. Saccular afferents and neurons throughout the medial column were also filled after biocytin application to the saccular nerve. This vocal-acoustic network overlaps low-threshold, electrical stimulation sites in the rostral brainstem that elicit vocalizations. The medial column must therefore be the origin of the descending pathway controlling activation of the vocal pacemaker circuitry and likely forms the basis for acoustically elicited vocalizations. We suggest this network, together with input from the pacemaker circuitry, is also the origin of a vocal-related, corollary discharge to acoustic nuclei. Direct links between vocal and acoustic brain regions are thus traits common to aquatic and terrestrial vertebrates.

Animals↗
PubMed1993

Early events in myofibrillogenesis and innervation of skeletal, sound-generating muscle in a teleost fish.

The plainfin midshipman, Porichthys notatus, generates acoustic communication signals through the rapid contraction of a pair of vocal (sonic) muscles attached to the walls of the swimbladder. Light and electron microscopic methods were used to study two aspects of sonic muscle ontogeny: 1) the development and transformation of myotubes into muscle fibers and 2) innervation, including the formation of sonic neuromuscular junctions and the myelination of sonic motor axons. Sonic motor axons are associated with sonic mesenchyme during its initial migration away from occipital somites. However, myofibrillogenesis, the formation of neuromuscular junctions, and axon myelination do not occur until sonic mesenchyme reaches its final destination (i.e., the swimbladder). A continuum of developing myotubes is present rather than two temporally distinct populations of primary and secondary myotubes as observed for skeletal muscles in mammalian and avian species. Potential reasons for the lack of primary and secondary myotubes are considered, including the functional homogeneity of the sonic motor system and the sonic muscle's unique architecture, namely its direct attachment to the wall of the swimbladder.

Animals↗
PubMed1993

Androgen effects on vocal muscle structure in a teleost fish with inter- and intra-sexual dimorphism.

The plainfin midshipman fish Porichthys notatus has both inter- and intra-sexual dimorphism in the sound-producing (vocal or sonic) muscles attached to the swimbladder wall. The "Type I" and "Type II" male morphs differ in that dramatic structural changes related to sexual maturity occur in the mass, the area of mitochondria-filled sarcoplasm, and the myofiber number of the sonic muscles of Type I males, but not in those of Type II males (nor of females). Androgen implantation for 9 weeks markedly increased the relative sonic muscle size in juvenile males, juvenile females, and Type II males, whereas estradiol or cholesterol treatment did not. The principal androgen effect on myofiber structure was an increase in the area of mitochondria-filled sarcoplasm. The ratio of sarcoplasm area to myofibril area (Sr/Mf) increased by 1.4- to 2-fold in myofibers of all androgen-treated groups, with the greatest structural change occurring in juvenile males. When androgen implants were removed from juvenile males, the muscle mass and Sr/Mf ratio reverted toward the unimplanted juvenile phenotype. Total fiber number in sonic muscle increased significantly in juvenile males following androgen implantation but did not detectably change in juvenile females or Type II males. These results suggest: 1) sonic muscle in Porichthys notatus is an androgen target tissue, 2) fiber structure and fiber number are androgen-sensitive features, and 3) there exist sex- and morph-specific patterns of sonic muscle responsiveness to androgen implants.

Androgens↗