bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel use of cobalt(III) meso‐tetraphenylporphyrin as a chiral shift reagent
Authors: Abraham Raymond J. , Plant James , Bedford Geoffrey R. , Wright Brian
Published: May 2005

The NMR spectra of the diastereomeric complexes formed by the coordination of nitrogenous enantiomeric bases with cobalt(III) meso‐tetraphenylporphyrin (CoTPP) allow the immediate differentiation of these complexes. The spectra are interpreted on the basis of symmetry (RR and SS) and pseudo‐chirality (RS and SR) considerations. The effects are observed in both the proton and carbon spectra and the complexes are stable in both CDCl3 and DMSO‐d4 solution. This technique, in principle, allows the ready determination of the optical purity of multifunctional ligands.
Regeneration of the antennules in the Australian freshwater crayfish, Cherax destructor
Authors: Sandeman D. C. , Luff Susan E.
Published: May 2005

Removal of one eye from the Australian freshwater crayfish, Cherax destructor, results in the growth of a heteromorph appendage which re‐ sembles the outer flagellum of the antennule. The heteromorph is con‐ sistently uniramous.

Transplanting part of the animal's own antennule into the eye stalk after removal of the ipsilateral eye results in a significant number of biramous appendages being developed in the eye socket. Biramous appendages when they possess fully differentiated hairs, can be identified as being the external and internal flagella of the antennule. Triramous appendages were never observed.

The specificity of the antennular sensilla was tested in relation to the cleaning behavior released by stimulating them electrically. Sensilla on the external flagellum of the antennule produce depression of the antennule and cleaning using the maxillipeds. This behavior is also produced when the heteromorph appendage is stimulated although in this case it is misdirected. Stimulation of the hairs in the eye socket releases cleaning of the eye socket with the 2nd and 3rd walking legs. Eye socket cleaning is not released by stimulation of the heteromorph indicating that the antennular sensilla retain their specificity in relation to the cleaning behavior released.

Removal of the antennule results in the ipsilateral olfactory lobe becoming smaller than the contralateral lobe. No change was observed in the accessory lobes.
Cyclic AMP and amine effects on phosphorylation of specific protein in abdominal ganglion of Aplysia californica; localization and kinetic analysis
Authors: Levitan Irwin B. , Madsen Carol J. , Barondes Samuel H.
Published: May 2005

Incubation of abdominal ganglia, obtained from Aplysia californica weighing 120‐‐260 g, with octopamine or serotonin led to marked increases in cAMP (cyclic adenosine 3′,5′‐monophosphate) levels after 10 min of incubation; these increases were blocked by phentolamine and methysergide, respectively. Incubation for 21 hr with octopamine also produced an elevation in cAMP levels but prolonged incubation with serotonin did not. Both these amines increased incorporation of 32P or 33P into a specific protein with apparent molecular weight of 118,000, upon incubation with the ganglion for 21 hr. The selective effect on this phosphoprotein was previously shown to be blocked by phentolamine (for octopamine effect) or methysergide (for serotonin effect) and could be mimicked by addition of dibutyryl cAMP to the medium.

Incubation for more than 15 hr was required to generate a stable phosphoprotein pattern in which 5 phosphoprotein peaks could be reliably identified on polyacrylamide gels. With shorter incubations there was marked variability between ganglia with respect to the proteins which incorporated radioactive phosphate. The dibutyryl cAMP effect on phosphorylation of specific protein could not be demonstrated with incubations shorter than 15 hr.

The specific effect on the phosphoprotein with molecular weight 118,000 was not observed in a number of large identified cells removed from the ganglion after 21 hr of incubation with radioactive phosphate and dibutyryl cAMP. The effect was also not observed in connective nerves and the bag cell clusters, but was consistently present in that portion of the ganglion remaining after these dissections. Upon subcellular fractionation the phenomenon was not observed in a crude nuclear fraction but was consistently present in a crude mitochondrial fraction. All these results are consistent with the possibility that the change in phosphoprotein metabolism produced by dibutryl cAMP may be localized in the neuropil, which contains all the synaptic contacts in this ganglion.
Neurobiology of Stomotoca. I. Action systems
Authors: Mackie G. O. , Singla C. L.
Published: May 2005

The layout of nerves, muscles, and conducting epithelia is described for the simple hydrozoan medusa Stomotoca. Comparisons are drawn with Sarsia and other recently studied forms. The major action systems are those responsible for swimming, crumpling (protective involution), tentacle posture, pointing (unilateral reciprocal flexions of the manubrium and margin), and visceral movements (barely mentioned). Crumpling is a simple summating response in this species. Crumpling and pointing are considered to use the same effectors but different conduction pathways.

New histological results include the demonstration of a nerve plexus running through the endodermal canal system and a nerve plexus in the ectoderm encircling the peduncle. Special attention is given to the distribution of synapses and gap junctions, as possible trasmission pathways in behavioral responses. Some details are included on organization within the marginal nerve rings.
Stop‐flow: A new technique for measuring axonal transport, and its application to the transport of dopamine‐β‐hydroxylase
Authors: Brimijoin Stephen
Published: May 2005

An apparatus was devised which utilizes local cooling to reversibly interrupt the axonal transport of dopamine‐β‐hydroxylase (DBH) in rabbit sciatic nerves in vitro. Lowering the temperature of a short region of nerve to between 1 and 3°C, while keeping the remainder at 37°C, caused DBH activity to accumulate in and proximal to the cooled region. This accumulation was evident after 0.5 hr of cooling and increased in a nearly linear fashion with time for about 3 hr. The cooling‐induced interruption in transport was rapidly reversed when nerves were rewarmed to 37°C. Upon rewarming after local cooling for 1.5 hr, a peak of accumulated DBH activity migrated toward the distal end of the nerve at a velocity of 300 ± 17 mm/day. This velocity was maintained for as long as the peak could be followed and was four times greater than the average velocity estimated from the rate of accumulation of DBH activity above a ligature at the distal end of these same nerves. It is concluded that ligation experiments grossly underestimate the true velocity of axonal transport of DBH and that the present technique offers great advantages in permitting direct study of the migration of separate axonal compartments of transported materials.
The tail flattening reflex in Lumbricus: Reconstitution after tail amputation and modifications in segmental nerve roots
Authors: Gras Heribert
Published: May 2005

On stimulation of the head, the caudal 20–30 segments of intact earthworms exhibit a marked dorso‐ventral flattening reflex which is an element of the escape response. When the tail is removed this reflex is reconstituted gradually in segments anterior to the amputation level without regeneration of new tail segments. It takes longer to reestablish the flattening if larger parts of the body are cut off, but after 60 days p.o. all animals regained the full response independent of the number of segments amputated.

Extirpation of three consecutive ganglia from the ventral nerve cord also suffices to develop flattening anterior to the operated segments, but the reaction is less pronounced and appears later than after tail amputation. Moreover, it vanishes at the same time the normal tail flattening is observed again, presumably after regeneration across the gap in the cord.

In different regions of the body, area and perimeter distributions of transversely sectioned axons in the three pairs of segmental nerves (SN I–III) of the cord were measured. Characteristic changes along the length of the animal were found for SN I and SN III. In tail segments the axonal size distributions are more variable than in “typical” segments. The flattening reflex is mediated by axons in SN III (Pallas and Drewes, 1981). In body segments having reconstituted behavioral characteristics of the lost tail segments, the area of the largest axons and the general size distribution in SN III approximate those found in normal tail segments.
Conduction block in a branching axon innervating two muscles under physiological conditions
Authors: Baranes‐Shahrabany O. , Grossman Y. , Parnas I.
Published: May 2005

The escape reflex of the lobster consists of a series of tail flips resulting from alternating activity of the abdominal flexor and extensor muscles. Electromyographic (EMG) activity was recorded from the medial (DEAM) and the lateral (DEAL1) deep abdominal extensor muscles during free swimming. During the escape response, the muscles were active either synchronously or separately, at frequencies of 100–120 Hz. This activity pattern could be generated either by central programming, or by a peripheral mechanism such as frequency‐dependent differential conduction block into one of the two branches of the common excitor axon (C.Ex) innervating these muscles.

In order to explore the latter possibility in a living animal, we left the DEAM and DEAL1 muscles innervated only by the C.Ex from the tested segment. This was accomplished by manually cutting all other axons in the nerve under visual control. During escape responses in six successfully dissected animals, we found 27 sudden failures of the DEAM responses and only three in DEAL1. The failures were usually preceded by an increase in the delay of the response. These findings strongly suggest that conduction block occurs in the M branch innervating the DEAM under physiological conditions.
Octopamine and chlordimeform enhance sensory responsiveness and production of the flight motor pattern in developing and adult moths
Authors: Kinnamon Sue C. , Klaassen Leland W. , Kammer Ann E. , Claassen Dale
Published: May 2005

Octopamine and an agonist, chlordimeform, increase the responsiveness of adult and pharate adult Manduca sexta to gentle mechanical stimulation of the wing. Higher doses of chlordimeform elicit almost continuous production of the flight motor pattern in both adults and pharate adults, and the effect persists for more than 24 h. The dose of chlordimeform necessary for this effect increases with age. Mechanical stimulation of the wing of pharate adults elicits several cycles of flight motor pattern, but with repeated stimulation the animal habituates. Habituation is slower in chlordimeform‐treated animals than in controls. Injection of octopamine (1–8 × 10−8 mol) or chlordimeform (3 × 10−9 mol) into the mesothoracic ganglion elicits the flight motor pattern. The excitatory actions of both compounds can be blocked by cyproheptidine. Chlordimeform (5 × 10−8 mol) in acetone applied to the wing does not cause a noticeably greater increase in the electrical activity of sensory neurons than does acetone applied alone; this result suggests that chlordimeform does not act on these peripheral sites or on axonal membranes in general. We suggest that chlordimeform and octapamine act on the thoracic ganglia to alter the level of excitation on reffectiveness of synaptic transmission among central neurons, including those involved in producing the flight motor pattern.
Comparison of differential pavlovian conditioning in whole animals and physiological preparations of Pleurobranchaea: Implications of motor pattern variability
Authors: Mpitsos George J. , Cohan Christopher S.
Published: May 2005

The present study compares differential Pavlovian conditioning in whole animals with the behavior of the same animals during electrophysiological recording. Untrained specimens of the sea slug Pleurobranchaea did not discriminate between two appetitive stimuli, one derived from an extract of beer (Sbr) and the other from a homogenate of squid muscle (Ssq). When animals received Sbr as the CS+ and Ssq as the CS− in a single day of five‐trial, differential Pavlovian conditioning they learned to avoid selectively the Sbr but continued to exhibit appetitive responses to Ssq. Quantitative measures show that there was over a 1000‐fold increase in the thresholds of the proboscis extension and bite‐strike responses, many animals ceased all feeding behavior, and exhibited withdrawal responses to Sbr. We examined the behavior of the same trained animals immediately before preparing them for physiological recording and during the recording session. There was a close one‐to‐one relationship between these behavioral observations, showing that the qualitative and quantitative features of whole‐animal Pavlovian conditioning persist into the physiological preparations. Unexpectedly, motor patterns from untrained preparations showed considerable variability both within the same preparation at different times and between preparations; conditioning appeared to increase such variability. Thus, it was not possible to state unequivocally the behavior of the animal by examining the electromyogram recording alone. Many of the trained preparations not only exhibited suppressed feeding behavior and withdrawal responses to Sbr, but, as a consequence of the multifunctional nature of the Pleurobranchaea buccal‐oral system, also regurgitated previously ingested Ssq or squid meat when they were stimulated with Sbr. We discuss the findings with respect to self‐organizing mechanisms that may establish motor patterns in multifunctional systems, and suggest that such mechanisms may lead to the generation of behaviors that are not specifically encoded by the conditioned cellular changes.
Auditory and hormonal stimulation interact to produce neural growth in adult canaries
Authors: Bottjer Sarah W. , Schoonmaker Judith N. , Arnold Arthur P.
Published: May 2005

Gonadal hormones can produce striking behavioral and neural plasticity in adult organisms. For example, systemic administration of testosterone to adult female canaries induces the development of male‐typical song behavior and results in a striking increase in the size of brain nuclei that are known to be involved with song control. The mechanism whereby androgens produce such neural plasticity is not known, although it has seemed likely that growth‐promoting effects of androgens are due to a direct induction of protein synthesis in cells containing hormone receptors (following activation of specific genes by the hormone‐receptor complex). In this experiment we have examined the trophic effect of testosterone in the song‐control nucleus HVc (caudal nucleus of the ventral hyperstriatum), which has been shown to contain androgen‐concentrating cells as well as neurons that are especially responsive to conspecific song. We report here that testosterone administration increases the volume of HVc in hearing adult female canaries only; testosterone‐induced growth of HVc is greatly attenuated in birds that are deprived of auditory stimulation via deafening. Thus, testosterone treatment alone is not a sufficient stimulus for neural growth in HVc. This result suggests that testosterone does not stimulate growth solely via a direct action on hormone receptors in HVc, but rather that testosterone and sensory stimulation can act synergistically to produce structural plasticity in the adult brain.
Autoradiographic identification of ecdysteroid‐binding cells in the nervous system of the moth Manduca sexta
Authors: Fahrbach S. E. , Truman J. W.
Published: May 2005

The steroid hormone 20‐hydroxyecdysone regulates many aspects of nervous system development in the moth Manduca sexta, including stage‐specific neuronal morphology and stage‐specific neuronal death. We have used steroid hormone autoradiography to study the distribution of cells that cocentrate ecdysteroids in the ventral nervous system of this insect. The ligand was [3H]‐ponasterone A, a bioactive phytoecdysone. Tissue was examined from three stages of development: the end of larval life (first day of wandering), the end of metamorphosis (pharate adult), and 4‐day‐old adults. In the abdominal ganglia of wandering larvae and pharate adults, a subset of neurons including both motoneurons and interneurons exhibited a nuclear concentration of radiolabeled hormone. The pattern of binding was reproducible but stage‐specific, with a greater proportion of neurons showing binding in the larvae than in pharate adults. No labeled neurons were found in abdominal ganglia from mature (4‐day‐old) adults. In the case of the pharate adult ganglia, the ecdysteroid receptor content of specific, identified motoneurons was determined. These results are discussed in light of the responses of these neurons to physiological changes in levels of circulating ecdysteroids.
Regeneration of an identifiable motoneuron in the crayfish. II. Patterns of reconnection and synaptic strength established in the presence of an extra nerve
Authors: Hunt William P. , Vélez Samuel J.
Published: May 2005

The regeneration of neuromuscular connections to the superficial flexor muscle system in the crayfish has been studied under a variety of experimental manipulations. These have provided insight into the factors that can influence the regeneration program of neurons. In this work the regeneration of the largest excitor motoneuron was studied under two different conditions: (1) when the original neuron and a transplanted neuron were growing simultaneously into a denervated target, and (2) when a transplanted neuron was growing into a target that had its original nerve supply intact. In condition 1 both the transplanted and the original neuron formed normal patterns of connectivity and synaptic strength in comparable periods of time. In condition 2 the rate of growth of the transplanted neuron is significantly reduced and does not extend into the lateral fibers of the muscle. It is concluded that the regeneration program of this neuron is not affected by the presence of other neurons growing at the same time into a denervated muscle. Since regeneration is seriously affected if growth occurs into a fully innervated target area, it is suggested that lack of growth stimuli from the target or competitive interactions between established and growing synaptic terminals could influence the regeneration program of this neuron.
Competitive interactions between retinal ganglion cells during prenatal development
Authors: Shatz Carla J.
Published: May 2005

In the mammalian visual system, retinal ganglion cell axons terminate within the LGN in a series of alternating eye‐specific layers. These layers are not present initially during development. In the cat they emerge secondarily following a prenatal period in which originally intermixed inputs from the two eyes gradually segregate from each other to give rise to the characteristic set of layers by birth. Many lines of evidence suggest that activity‐dependent competitive interactions between ganglion cell axons from the two eyes for LGN neurons play an important role in the final patterning of retinogeniculate connections. Studies of the branching patterns of individual ganglion cell axons suggest that during the period when inputs from the two eyes are intermixed, axons from one eye send side branches into territory later occupied exclusively by axons from the other eye. Ultrastructural studies indicate that these branches in fact are sites of synaptic contacts, which are later eliminated since the side branches disappear as axons form their mature terminal arbors in appropriate territory. In vitro microelectrode recordings from LGN neurons indicate that they can receive convergent synaptic excitation from electrical stimulation of the optic nerves before but not after the eye‐specific layers form, suggesting that at least some of the synaptic contacts seen at the ultrastructural level are functonal. Finally, experiments in which tetrodotoxin was infused intracranially during the two week period during which the eye‐specific layers normally form demonstrate that it is possible to prevent, or at least delay, the formation of the layers. Accordingly, individual axons fail to develop their restricted terminal arbor branching pattern and instead branch widely throughout the LGN. These results indicate that all of the machinery necessary for synaptic function and competition is present during fetal life. Moreover, it is highly likely that neuronal activity is required for the formation of the eye‐specific layers. If so, then activity would have to be present in the form of spontaneously generated action potentials, since vision is not possible at these early ages. Thus, the functioning of the retinogeniculate system many weeks before it is put to the use for which it is ultimately designed may contribute to the final patterning of connections present in the adult.
Down‐regulation of progestin receptors in guinea pig brain: New findings using an immunocytochemical technique
Authors: Blaustein Jaffery D. , Turcotte Joanne C.
Published: May 2005

Progesterone injection in estradiol‐primed, ovariectomized guinea pigs results in down‐regulation of hypothalamic progestin receptors determined by in vitro binding assays. In order to determine if progesterone also decreases immunostaining of progestin receptors and if progestin receptors are down‐regulated preferentially in particular neuroanatomical areas, ovariectomized guinea pigs were injected with doses of estradiol benzoate (10 μg at 42 h before progesterone injection) and progesterone (500 μg at 4, 12, or 24 h before perfusion) that reliably induce the expression of lordosis and subsequent behavioral refractoriness to progesterone. Progestin receptor‐immunoreactive cells were counted in sections from discrete parts of the preoptic area and hypothalamus. As expected, estradiol dramatically increased cell nuclear, and, to a lesser extent, cytoplasmic, immunostaining in defined regions of the preoptic area and hypothalamus. By 12 h after progesterone injection, the number of progestin receptor‐immunoreactive cells had decreased in some areas, but not others. The rostral and caudal aspects of the ventrolateral hypothalamus were particularly responsive showing a substantial decrease in progestin receptor‐immunoreactivity by 12 h after injection. No decreases in the progestin receptor‐immunoreactive cell number were observed in any of the preoptic regions examined, although obvious decreases in immunostaining intensity were seen. The results of these immunocytochemical experiments extend earlier findings from in vitro progestin binding experiments and demonstrate that as with progestin binding, progestin receptor‐immunoreactivity decreases when progesterone is injected in a behavioral desensitization procedure. Furthermore, they point to the ventrolateral hypothalamus as one site in which the down‐regulation of progestin receptors may be particularly responsive to progesterone.
Sex differences in hormonal responses of vasopressin pathways in the rat brain
Authors: De Vries Geert J. , Al‐Shamma Hussien Ali
Published: May 2005

Vasopressin (AVP) immunoreactivity in cells and projections of the bed nucleus of the stria terminalis (BST) and medial amygdaloid nucleus (MA) depends on gonadal steroids. In addition, the AVP projections from the BST show denser fiber staining in males than in females. To study whether these differences depend on different hormone levels in adulthood, male and female rats were gonadectomized and similarly treated with testosterone for 4 weeks prior to sacrifice. Immunocytochemistry showed that males had significantly more AVP‐immunoreactive (AVP‐IR) cells in the BST and significantly denser AVP‐IR projections from this nucleus to the lateral septum, lateral habenular nucleus, and periaqueductal central gray than did females. The number of AVP‐IR cells in the MA nucleus was not statistically different, but denser AVP‐IR fiber networks were found in the MA and ventral hippocampus, which receives its input from the MA. No differences were found in the anteroventral portion of the periventricular nucleus and the dorsomedial nucleus of the hypothalamus that receive their AVP innervation from the suprachiasmatic nucleus. These results indicate that the sex difference in the steroid‐sensitive AVP pathways depends on other factors besides circulating hormone levels in adulthood.
Immunohistochemical localization of cholecystokinin in the medial preoptic area and anterior hypothalamus of the Brazilian gray short‐tailed opossum: A sex difference
Authors: Fox Charles A. , Adam Diane E. , Watson Robert , Hoffman Gloria E. , Jacobson Carol D.
Published: May 2005

We have studied the anatomical localization of cholecystokinin‐like immunoreactivity (CCK IR) in somata and fibers in the medial preoptic area (MPA) and anterior hypothalamus (AH) of the Brazilian gray shorttailed opossum, (Monodelphis domestica). With the aid of an avidin‐biotin, nickel‐enhanced, immunohistochemical technique, CCK IR neuronal elements were found within the MPA and AH. A large number of CCK IR cell bodies were located in the MPA of colchicine‐treated opossums. The MPA also contained a CCK IR fiber plexus. Quantitative image analysis revealed that the periventricular preoptic area of noncolchicine‐treated male opossums had a significantly higher percent of blocked light measurements than that of the noncolchicine‐treated females, indicating a higher density of CCK IR neuronal elements in the males. Neuronal fibers and somata containing CCK IR were also found within the periventricular hypothalamic nucleus (Pe), and the suprachiasmatic nucleus (SCh). These results show that CCK IR neuronal elements are found within the MPA and AH of the Brazilian short‐tailed opossum. Furthermore, there is a sexually dimorphic distribution of CCK IR elements within the MPA of this small marsupial.
Are separable aromatase systems involved in hormonal regulation of the male brain?
Authors: Hutchison J. B. , Schumacher M. , Steimer Th. , Gahr M.
Published: May 2005

In vitro study of testosterone (T) metabolism shows that formation of estradiol‐17β (E2) is regionally specific within the preoptic area (POA) of the male ring dove. The POA is known to be involved in the formation of E2 required for specific components of male sexual behavior. Two sub‐areas of high aromatase activity, anterior (aPOA) and posterior preoptic (pPOA) areas, have been identified. Aromatase activity is higher in aPOA than in pPOA. The aromatase activity within the aPOA is also more sensitive to the inductive effects of low circulating T, derived from subcutaneous silastic implants, than the enzyme activity in pPOA. Kinetic analysis of preoptic fractions indicates that a similar high‐affinity enzyme occurs in both areas (apparent Km < 14nM), but the Vmax of aPOA enzyme activity is higher than pPOA. Cells containing estrogen receptors (ER) are localized in areas of high aromatase activity. There is overlap between immunostained cells in the aPOA and in samples containing inducible aromatase activity measured in vitro. Within the aPOA there is a higher density of ER cells in the nucleus preopticus medialis. The pPOA area also contains ER, notably in the nucleus interstitialis, but at a lower density. We conclude that the hormonal regulation of the male preoptic‐anterior hypothalamic region, which is a target for the behavioral action of T, involves at least two inducible aromatase systems with associated estrogen receptor cells.
Human chorionic gonadotropin‐induced shifts in the electrosensory system of the weakly electric fish, Sternopygus
Authors: Zakon Harold H. , Yan Hong‐Young , Thomas Peter
Published: May 2005

Sternopygus macrurus of both sexes were injected with human chorionic gonadotropin (hCG) or saline. Electric organ discharge (EOD) frequency rose after hCG injections in females and gradually declined to baseline levels over the next few weeks. EOD changes in males were more complex and variable; most males showed an initial minor rise in EOD frequency followed by a larger decrease, or simply a decrease. hCG treatment also resulted in a rise in electroreceptor best frequency and shortened electric organ pulse duration in females, and had the opposite effect on these parameters in males. The saline‐injected controls showed no changes in any of these parameters. Levels of testosterone (T) and 11‐ketotestosterone, but not estrogen (E), were elevated in males preceding the fall in EOD frequency, whereas neither T nor E changed significantly in females before EOD frequency increases. Saline injections caused a drop in T in the male control group and had no effect in the female control group. We presume that the effect of hCG on the electrosensory system of males is mediated via androgens. Whether the effects of hCG on females are mediated by slight increases in circulating levels of gonadal steroids, the release of hormones other than T or E, or are due to direct effects on the nervous system is not known.
Seasonal differences in the physiology and morphology of crayfish motor terminals
Authors: Lnenicka Gregory A. , Zhao Yangu
Published: May 2005

The physiology and morphology of identified crayfish motor terminals were compared at different seasons. We examined initial excitatory postsynaptic potential (EPSP) amplitudes, synaptic fatigue, and the frequency of synaptic varicosities along the motor terminals of an identified phasic motoneuron in animals collected over a period of 5 years. The physiology and morphology of identified crayfish motor terminals are different for animals collected in summer and winter. In winter animals, phasic axon motor terminals in the claw closer muscle produce large EPSPs initially, but show dramatic synaptic fatigue during repetitive stimulation. In summer animals, these terminals produce smaller initial EPSPs, but are more fatigue resistant. Due to their greater fatigue resistance, synaptic terminals have a greater overall capacity for transmitter release in summer animals than do those of winter animals. Morphologically, terminals in summer animals have more synaptic varicosities, this result supports earlier studies that have shown that fatigue‐resistant motor terminals have more synaptic varicosities. Experiments in which the electrical activity of the motoneuron was experimentally altered suggest that these differences in motor terminals may be due to seasonal differences in activity.
Axotomy accelerates slow component b of axonal transport
Authors: Jacob Jane M. , McQuarrie Irvine G.
Published: May 2005

Because the integrity of an axon depends on the supply of proteins synthesized in the cell body, we examined the effect of axotomy on the transport of structural proteins in rat motor axons, and the effect of altered transport on the rate of outgrowth after a subsequent testing axotomy. To examine the axonal transport of structural proteins, we labeled newly synthesized proteins with 35 S‐methiomine 7 days after a “conditioning” lesion of the sciatic nerve, and removed the nerve 7–21 days later for SDS‐PAGE. Tubulin, actin, calmodulin, and the 68‐kD light neurofilament protein (NF‐L) were identified by fluorography and removed for liquid scintillation counting. The fastest moving structural proteins were carried by slow component b (SCb) of axonal transport, which advanced 20% faster in conditioned axons: 4.2 versus 3.5 mm/day (p < 0.01). NF‐L was not accelerated, indicating that the motor for subcomponent a (SCa) of slow axonal transport was unaffected by axotomy. To measure outgrowth distances, the testing lesion was made 7 days after the conditioning lesion, and growth cones were located by the fast transport method 3 or 9 days later. The regression analysis of outgrowth distance on time showed that sprouts elongated 25% faster in conditioned axons: 4.0 versus 3.2 mm/day (p < 0.001). These accelerated sprouts were formed too far from the spinal cord to contain SCb proteins that were synthesized after axotomy. Because the rate of outgrowth correlates closely with the rate of SCb in outgrowing sprouts (McQuarrie and Jacob, J. Comp. Neurol. 305:139–147, 1991), we conclude that SCb is accelerated throughout the length of the axon by 7 days after axotomy.
Release of pedal peptide from Aplysia neurons in primary culture
Authors: Hall Jon D. , Lloyd Philip E.
Published: May 2005

Pedal peptide (Pep) is a modulatory neuropeptide that is predominantly synthesized in a group of neurons on the dorsal surfaces of the pedal ganglia of Aplysia. Following the determination that Pep is the major peptide selectively present in these neurons in situ, primary cell culture of single Pep‐neurons was used to study the release of this neuropeptide. Individual Pep‐neurons were grown in culture where they extended many branched neurites with large varicosities. Immunocytology revealed that these newly grown varicosities were intensely Pep immunoreactive. Cultured Pep‐neurons, grown in a medium containing radiolabeled methionine, synthesized labeled Pep and transported it into their regenerated neurites. Finally, these neurons released radiolabeled Pep in a calcium‐ and stimulation‐dependent fashion. These results, taken together with previous findings, strongly support the proposition that Pep is a transmitter in Aplysia.
Localization of ventral giant interneuron connections to the ventral median branch of thoracic interneurons in the cockroach
Authors: Casagrand Janet L. , Ritzmann Roy E.
Published: May 2005

A detailed morphological study was performed to localize the probable sites of connections between two identified populations of interneurons (ventral giant interneurons and type‐A thoracic interneurons) in the cockroach. Type‐A thoracic interneurons (TIAs) appear to play an important role in orienting the cockroach during windmediated escape. However, their large number, approximately 100 neurons, precludes analyzing each cell's role electrophysiologically. The TIAs are characterized by a prominent branch located on one or both sides of the ventral median (VM) region of the thoracic ganglion in which their soma resides. The presence of this ventral median branch can be used to predict connectivity with left or right ventral giant interneurons (vGIs) (Ritzmann and Pollack, 1988) and is correlated with the TIA's directional response to wind (Westin, Ritzmann, and Goddard, 1988), suggesting that this is the locus of synaptic connection. Two approaches were employed to address this hypothesis. Morphological overlap of differentially labelled cells (ethidium bromide, Lucifer Yellow) was examined at the light microscopic level to locate areas of possible synaptic contact. Experiments were also performed in which one‐half of the vGI input to the TIAs was surgically removed early in postembryonic development. Although no changes in the overall branching pattern were observed, the VM branches on the operated side were significantly shorter than were those on the unoperated side. Thoracic interneurons that do not receive inputs from vGIs were unaffected by this surgery. The data reported here thereby confirm previous observations by localizing the vGI inputs specifically to the VM branch, and provide a morphological cue for predicting connectivity and function.
Gonadal steroids affect LHRH preoptic cell number in a sex/role changing fish
Authors: Grober Matthew S. , Jackson Ivor M. D. , Bass Andrew H.
Published: May 2005

In diandric sex‐reversing fishes, sexually active males and females (primary phase) regularly transform into an alternative reproductive morph, terminal‐phase males, that are morphologically and behaviorally distinct. The transformation from primary to terminal phase is associated with a twofold increase in the number of luteinizing hormone‐releasing hormone (LHRH) immunopositive cells in the forebrain preoptic area, a region involved in both the initial development and daily control of reproductive physiology and behavior. We now show that implants of 11‐ketotestosterone induce increases in LHRH cell number in both primary phase sexes to the level observed in field‐collected terminal phase males. Conversely, gonadal steroids had no effect on the number of LHRH preoptic cells in terminal phase males, suggesting that this is indeed a terminal stage in the development of this species. These results demonstrate that transition to the terminal phase by both sexes involves a parallel and convergent change in LHRH cell number, which utilizes an evolutionarily conserved mechanism of sexual differentiation: the inductive effects of gonadal steroid hormones.
Early estrogen treatment alone causes female zebra finches to produce learned, male‐like vocalizations
Authors: Simpson H. Blair , Vicario David S.
Published: May 2005

The male zebra finch produces learned song and long calls while the female does not. This difference in behavior is believed to result from the action of sex steroids on brain areas responsible for vocal production and learning. In this study, the female zebra finch was used to explore further the specific role sex steroids play in vocal masculinization. We show that estradiol (E2) treatment at birth was sufficient to masculinize the vocal behavior of female zebra finches. Thirteen of 18 females treated with E2 as nestlings produced song‐like vocalizations. Fifteen of 18 produced long calls with male‐typical features. The degree of masculinization varied between individuals. Of the 15 early E2 females that produced at least one type of male‐like vocalization, 7 showed evidence of vocal learning from their tutors. The ability of E2 to cause masculinization of vocal behavior was age dependent: treatment from birth was most effective, treatment at 20 days of age was partially effective, and treatment in adulthood was ineffective. The effect of subsequent testosterone exposure in adulthood differed depending on the quality of the vocalization produced after E2 treatment alone. These results suggest that E2 may play a more important role than previously thought in the development of sex differences in vocal behavior. Further‐more, this study demonstrates that exogenous E2 treatment alone can induce vocal learning.
Early estrogen treatment of female zebra finches masculinizes the brain pathway for learned vocalizations
Authors: Simpson H. Blair , Vicario David S.
Published: May 2005

Telencephalic nucleus HVC and its two efferent targets, RA and X, play essential roles in the production of complex, learned vocalizations in the male zebra finch. Normal females do not produce these learned vocalizations; HVC, RA, and X are small in volume, and HVC and RA are not synaptically connected. We have shown that estrogen treatment during development causes females to learn and produce male‐like vocalization. This article describes the neural masculinization of these E2 females, replicating and extending the work of others. Female zebra finches were treated with 17β‐estradiol (E2) at hatching, at 14–22 days of age, or as adults. In adulthood, the volumes of nucleus RA and area X were measured and the efferent projections of nucleus HVC examined using the anterograde tracer PHA‐L. Early, sustained E2 treatment caused the greatest increase in the volume of RA and X, the innervation of RA and X by HVC axons, and the masculinization of auditory responses of cells in RA. Treatments that lasted for a shorter period or started later in development resulted in different patterns of partial brain masculinization. E2 treatment in adulthood had no effect on the volume of RA or X or their innervation by HVC. Bilateral lesions of the tracheosyringeal nerves or of HVC had the same effects on the male‐typical vocalizations produced by E2 females as they do on the vocalizations produced by males. These results demonstrate that the neural masculinization of telencephalic nuclei induced by E2 treatment sets up a functional circuit in females similar to one in males that enables the learning and production of complex vocalizations.
Development and specificity of inhibitory terminal arborizations in the central nervous system
Authors: Sanes Dan H. , Siverls Veronica
Published: May 2005

This study examined the morphological development of single inhibitory arborizations in the gerbil central auditory brain stem. Using a brain slice preparation, neurons of the medial nucleus of the trapezoid body (MNTB) were filled with horseradish peroxidase (HRP), and their complete arborizations were analyzed along the tonotopic axis of the lateral superior olive (LSO). The projections in neonatal animals displayed well‐defined arbors that were ordered appropriately within the LSO. It was evident from the axonal pathways that the MNTB afferents could correct for projection errors after reaching the postsynaptic population. As development progressed, a number of arbors established diffuse or inappropriate projections within the LSO. These immature arborizations were no longer apparent by 18–25 days postnatal. The anatomical specificity of arbors at 12–13 and 18–25 days was quantified by measuring the distance that terminal boutons spread across the frequency axis. There was a significant reduction of this distance in older animals. In addition, there was a significant reduction in the mean number of boutons per arbor between 12–13 days and 18–25 days. The maximum nucleus cross‐sectional area continued to increase through 15–16 days, indicating that the refined arbors occupied an even smaller fraction of the postsynaptic structure. Taken together, these observations suggest that central inhibitory arbors form exuberant contacts that must be eliminated during development.
Intracellular recordings from nonspiking interneurons in a semiintact, tethered walking insect
Authors: Schmitz Josef , Büschges Ansgar , Kittmann Rolf
Published: May 2005

Nonspiking interneurons were investigated in a tethered, walking insect, Carausius morosus, that was able to freely perform walking movements. Experiments were carried out with animals walking on a lightweight, double‐wheel treadmill. Although the animal was opened dorsally, the walking system was left intact. Intracellular recordings were obtained from the dorsal posterior neuropil of the mesothoracic ganglion. Nonspiking inter‐neurons, in which modulations of the membrane potential were correlated with the walking rhythm, were described physiologically and stained with Lucifer Yellow. Interneurons are demonstrated in which membrane potential oscillations mirror the leg position or show correlation with the motoneuronal activity of the protractor and retractor coxae muscles during walking. Other interneurons showed distinct hyperpolarizations at certain important trigger points in the step cycle, for example, at the extreme posterior position. Through electrical stimulation of single, nonspiking interneurons during walking, the motoneuronal activity in two antagonistic muscles—protractor and retractor coxae—could be reversed and even the movement of the ipsilateral leg could be influenced. The nonspiking interneurons described appear to be important premotor elements involved in walking. They receive, integrate, and process information from different leg proprioceptors and drive groups of leg motoneurons during walking.
Fiber‐type proportions in mammalian soleus muscle during postnatal development
Authors: Wigston Donald J. , English Arthur Wm.
Published: May 2005

We analyzed the fiber‐type composition of the soleus muscle in rats and mice to determine whether the adult proportion of fiber types is fixed soon after birth or whether it changes during postnatal maturation. We examined muscles from animals varying in age from 1 week to 1 year using monoclonal antibodies that distinguish between fast and slow isoforms of myosin heavy chains. In cross sections of unfixed muscle containing profiles of all myofibers in the muscle, we counted the fibers that stained with antibodies to fast myosin, and in adjacent sections, those that stained positive with an antibody to slow myosin. We also counted the total number of fibers in each section. Rat soleus contained about 2500 myofibers, and mouse about 1000 at all ages studied, suggesting that myogenesis ceases in soleus by 1 week after birth or sooner. In mouse soleus, the relative proportions of fibers staining positive with fast and slow myosin antibodies were similar at all ages studied, about 60%–70% being fast and 30%–40% slow. In rat soleus, however, the proportions of fast antibody‐positive and slow antibody‐positive fibers changed dramatically during postnatal maturation. At 1 week after birth, about 50% of rat soleus fibers stained with fast myosin antibodies, whereas between 1 and 2 months this value fell to about 10%. In mouse, about 10% of fibers at 1 week, but none at 1 year, reacted with both fast and slow antibodies, whereas in rat, fewer than 3% bound both antibodies to a significant degree at 1 week. It is puzzling why, in rat soleus, the majority of apparently fast fibers present at 1 week is converted to a slow phenotype, whereas in mouse soleus the predominant change appears to be the suppression of fast myosin expression in a subset of fibers that expresses both myosin types at 1 week. It is possible that this may be related to differences in size and the amount of body growth between these two species.
Differential expression of neuropeptide gene mRNA within the LUQ cells of Aplysia californica
Authors: Landry Claire , Crine Philippe , Desgroseillers Luc
Published: May 2005

Two neuropeptide precursor cDNAs (LUQ‐1 and L5‐67) have been recently isolated from the Left Upper Quadrant (LUQ) neurons of the abdominal ganglion of Aplysia californica (Shyamala, Fisher, and Scheller, 1986; Wickham and DesGroseillers, 1991). Using in situ hybridization techniques as well as dot blot and polymerase chain reaction (PCR) assays, we have studied the expression of these genes in the central nervous system (CNS) of Aplysia californica. The LUQ‐1 gene was found to be expressed in neuron L5 in the abdominal ganglion, whereas the expression of the L5‐67 gene was observed in the other four LUQ cells (L2‐4 and L6). When in situ hybridization was performed on paraffin sections of the abdominal ganglion, clusters of smaller cells located in the left hemiganglion, were also found to express either the LUQ‐1 on the L5‐67 gene, never both. In many sections, the mRNAs coding for the two neuropeptides were found not only in cell bodies but also in the axon of individual LUQ neurons and even as far as the pericardial nerve. The presence of neuropeptide mRNA in axons, pericardial nerve, and kidney has been confirmed by polymerase chain reaction. A specific, although diffuse hybridization in the left upper quadrant also suggests that mRNA is present in the neuritic field. Taken together these results indicate that neuron L5 is the only giant neuron expressing the LUQ‐1 gene and might therefore have a physiological function different from the other four LUQ cells. Neuropeptide mRNAs were also found in the axon and/or the neuritic field of giant neurons and could play important roles related to cell signalling in axons and nerve termini.