34 research outputs found
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Octavolateral projections and organization in the medulla of a teleost fish, the sleeper goby (Dormitator latifrons)
No full textThis study is the first to employ simultaneous labeling with different colored fluorescent dyes and confocal microscopy to investigate the central projections of the octavolateral nerves in any fish. Three-dimensional reconstructions of the hindbrain octavolateral nuclei were made and overlap of octavolateral projections was assessed in a teleost, the sleeper goby (Dormitator latifrons). The octavolateral nerves, which innervate the otolithic organs, semicircular canals, and lateral lines, project to seven hindbrain nuclei in diverse, complex patterns. The medulla is generally organized with auditory regions dorsal to vestibular regions. The intermediate subdivision of the descending octaval nucleus (DON) receives interdigitating projections from the otolithic organs, and the dorsomedial DON likely integrates multiple auditory inputs. Afferents from the three otolithic organs (the utricle, saccule, and lagena) project to the intermediate DON in approximately equal proportion, supporting physiological evidence that suggests auditory roles for all three otolithic organs in the sleeper goby. The anterior octaval nucleus receives partially segregated inputs from the octavolateral organs. The dorsal division of the magnocellular octaval nucleus (MgON) receives highly overlapping otolithic organ and semicircular canal input, and we propose that this region is a major octaval integration center. Regions in the ventral medulla (the tangential octaval nucleus, ventral DON, and ventral MgON) receive mainly utricular and semicircular canal inputs, suggesting vestibular roles. Each semicircular canal nerve projects to distinct regions of the hindbrain, with little overlap in most octaval nuclei. Efferent neurons receive bilateral input and project unilaterally to the octavolateral organs
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Auditory physiology and anatomy of octavolateral efferent neurons in a teleost fish
No full textVertebrate hair cell systems receive innervation from efferent neurons in the brain. Here we report the responses of octavolateral efferent neurons that innervate the inner ear and lateral lines in a teleost fish, Dormitator latifrons, to directional linear accelerations, and compare them with the afferent responses from the saccule, the main auditory organ in the inner ear of this species. Efferent neurons responded to acoustic stimuli, but had significantly different response properties than saccular afferents. The efferents produced uniform, omnidirectional responses with no phase-locking. Evoked spike rates increased monotonically with stimulus intensity. Efferents were more broadly tuned and responsive to lower frequencies than saccular afferents, and efferent modulation of the otolithic organs and lateral lines is likely more pronounced at lower frequencies. The efferents had wide dynamic ranges, shallow rate-level function slopes, and low maximum discharge rates. These findings support the role of the efferent innervation of the otolithic organs as part of a general arousal system that modulates overall sensitivity of the peripheral octavolateral organs. In addition, efferent feedback may help unmask biologically relevant directional stimuli, such as those emitted by a predator, prey, or conspecific, by reducing sensitivity of the auditory system to omnidirectional ambient noise
Ex Vivo Brain Imaging in <i>Drosophila</i>
No full textAnalysis of neuronal circuit function in Drosophila can be facilitated with an ex vivo imaging preparation. In this approach, the brain is isolated but intact, preserving neuronal connectivity and function. The preparation has several advantages, including stability, accessibility for pharmacological manipulations, and the ability to image over several hours. The full range of genetic approaches available in Drosophila can be readily combined with pharmacological manipulations in this preparation, and numerous genetically encoded reporters are available to image cellular events, ranging from Ca2+ signaling to neurotransmitter release
Imaging Olfactory Learning-Induced Plasticity in Vivo in the <i>Drosophila </i>Brain
No full textIn vivo imaging of brain activity in Drosophila allows the dissection of numerous types of biologically important neuronal events. A common paradigm involves imaging neuronal Ca2+ transients, often in response to sensory stimuli. These Ca2+ transients correlate with neuronal spiking activity, which generates voltage-sensitive Ca2+ influx. In addition, there is a range of genetically encoded reporters of membrane voltage and of other signaling molecules, such as second-messenger signaling cascade enzymes and neurotransmitters, enabling optical access to a range of cellular processes. Moreover, sophisticated gene expression systems enable access to virtually any single neuron or neuronal group in the fly brain. The in vivo imaging approach enables the study of these processes and how they change during salient sensory-driven events such as olfactory associative learning, when an animal (fly) is presented an odor (a conditioned stimulus) paired with an unconditioned stimulus (an aversive or appetitive stimulus) and forms an associative memory of this pairing. Optical access to neuronal events in the brain allows one to image learning-induced plasticity following the formation of associative memory, dissecting the mechanisms of memory formation, maintenance, and recall.</div
Neurons and Behavior: Ex Uno, Plures
No full textLi et al. demonstrate that a single interneuron can regulate analog- and digital-like behaviors guided by two different postsynaptic neurons. Releasing a single neurotransmitter onto downstream neurons that express receptors with distinct biophysical properties enables a small set of neurons to direct a range of functional responses
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Modulation of auditory signal-to-noise ratios by efferent stimulation
No full textOne of the primary challenges that sensory systems face is extracting relevant information from background noise. In the auditory system, the ear receives efferent feedback, which may help it extract signals from noise. Here we directly test the hypothesis that efferent activity increases the signal-to-noise ratio (SNR) of the ear, using the relatively simple teleost ear. Tone-evoked saccular potentials were recorded before and after efferent stimulation, and the SNR of the responses was calculated. In quiet conditions, efferent stimulation suppressed saccular responses to a tone, reducing the SNR. However, when masking noise was added, efferent stimulation increased the SNR of the saccular responses within a range of stimulus combinations. These data demonstrate that auditory efferent feedback can increase SNR in conditions where a signal is masked by noise, thereby enhancing the encoding of signals in noise. Efferent feedback thus performs a fundamental signal processing function, helping the animal to hear sounds in difficult listening conditions
Functional Imaging of Learning-Induced Plasticity in the Central Nervous System with Genetically Encoded Reporters in <i>Drosophila</i>
No full textLearning and memory allow animals to adjust their behavior based on the predictive value of their past experiences. Memories often exist in complex representations, spread across numerous cells and synapses in the brain. Studying relatively simple forms of memory provides insights into the fundamental processes that underlie multiple forms of memory. Associative learning occurs when an animal learns the relationship between two previously unrelated sensory stimuli, such as when a hungry animal learns that a particular odor is followed by a tasty reward. Drosophila is a particularly powerful model to study how this type of memory works. The fundamental principles are widely shared among animals, and there is a wide range of genetic tools available to study circuit function in flies. In addition, the olfactory structures that mediate associative learning in flies, such as the mushroom body and its associated neurons, are anatomically organized, relatively well-characterized, and readily accessible to imaging. Here, we review the olfactory anatomy and physiology of the olfactory system, describe how plasticity in the olfactory pathway mediates learning and memory, and explain the general principles underlying calcium imaging approaches
Dynamics of Learning-Related cAMP Signaling and Stimulus Integration in the Drosophila Olfactory Pathway
No full textSummaryFunctional imaging with genetically encoded calcium and cAMP reporters was used to examine the signal integration underlying learning in Drosophila. Dopamine and octopamine modulated intracellular cAMP in spatially distinct patterns in mushroom body neurons. Pairing of neuronal depolarization with subsequent dopamine application revealed a synergistic increase in cAMP in the mushroom body lobes, which was dependent on the rutabaga adenylyl cyclase. This synergy was restricted to the axons of mushroom body neurons, and occurred only following forward pairing with time intervals similar to those required for behavioral conditioning. In contrast, forward pairing of neuronal depolarization and octopamine produced a subadditive effect on cAMP. Finally, elevating intracellular cAMP facilitated calcium transients in mushroom body neurons, suggesting that cAMP elevation is sufficient to induce presynaptic plasticity. These data suggest that rutabaga functions as a coincidence detector in an intact neuronal circuit, with dopamine and octopamine bidirectionally influencing the generation of cAMP
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Biogenic amine synthesis and uptake in rodent taste buds
No full textAlthough adenosine triphosphate (ATP) is known to be an afferent transmitter in the peripheral taste system, serotonin (5-HT) and norepinephrine (NE) have also been proposed as candidate neurotransmitters and have been detected immunocytochemically in mammalian taste cells. To understand the significance of biogenic amines in taste, we evaluated the ability of taste cells to synthesize, transport, and package 5-HT and NE. We show by reverse transcriptase-polymerase chain reaction and immunofluorescence microscopy that the enzymes for 5-HT synthesis, tryptophan hydroxylase (TPH) and aromatic amino acid decarboxylase (AADC) are expressed in taste cells. In contrast, enzymes necessary for NE synthesis, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) are absent. Both TH and DBH are expressed in nerve fibers that penetrate taste buds. Taste buds also robustly express plasma membrane transporters for 5-HT and NE. Within the taste bud NET, a specific NE transporter, is expressed in some presynaptic (type III) and some glial-like (type I) cells but not in receptor (type II) cells. By using enzyme immunoassay, we show uptake of NE, probably through NET in taste epithelium. Proteins involved in inactivating and packaging NE, including catechol-O-methyltransferase (COMT), monoamine oxidase-A (MAO-A), vesicular monoamine transporter (VMAT1,2) and chromogranin A (ChrgA), are also expressed in taste buds. Within the taste bud, ChrgA is found only in presynaptic cells and may account for dense-cored vesicles previously seen in some taste cells. In summary, we postulate that aminergic presynaptic taste cells synthesize only 5-HT, whereas NE (perhaps secreted by sympathetic fibers) may be concentrated and repackaged for secretion
