bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microtubule stability along mammalian peripheral nerves
Authors: Donoso J. Alejandro 
Published: May 2005

AbstractMicrotubule (MT) number, axonal area, and MT density were examined in unmyelinated axons of rat cervical vagus nerve. Study of nerve regions proximal (1–5 mm) and distal (35–40 mm) to the nodosum ganglion in controls (incubation at 37°C for 1 h) showed that the number of MT per axon is significantly less in distal than in proximal nerve regions. Cooling (incubation at 0°C for 1 h) caused a significant reduction in the number of MT per axon in both nerve regions. The unmyelinated axons from both nerve regions showed a comparable reduction in MT number by cooling, indicating that axonal MT stability to cold was not significantly different between these two nerve regions. In these nerves no detectable changes were found in cross‐axonal area of unmyelinated axons between distal and proximal nerve regions. In another experimental series, in distal nerve regions (35–40 mm from the nodosum ganglion) the number of MT was not further reduced in nerves incubated at 0°C by increasing the incubation time. Similar results were obtained from colchicine treated nerves (incubation at 37°C, with 10 mM colchicine for 1 and 2 h). Distal nerve regions (35–40 mm from the nodosum ganglion) showed a similar reduction in the number of MT per axon when nerves were incubated at 0°C or with colchicine, suggesting that this drug, as well as cold, may be affecting a similar population of axonal MT, i.e., MT susceptible to anti‐MT agents. These results indicate that approximately one‐half of the axonal MT are stable to cold as well as to colchicine in rat unmyelinated axons.
Changes in intra‐axonal calcium distribution following nerve crush
Authors: Mata Marina , Staple Julie , Fink David J. 
Published: May 2005

AbstractWe used the oxalate‐pyroantimonate method to demonstrate the ultrastructural distribution of calcium within rat sciatic nerve 4 h after a crush injury. In normal nerve there are discrete gradients of axoplasmic calcium precipitate with the amount of precipitate decreasing in the axoplasm beneath the Schmidt Lantermann clefts and in the paranodal regions at the node of Ranvier. Near the crush site a marked increase in endoneurial and intra‐axonal calcium precipitate correlated with morphologic evidence of axonal degeneration. More distant from the crush site, both in the distal segment destined to degenerate and in the proximal segment destined to regenerate, the most prominent finding was a loss of the normal gradient of precipitate beneath the Schmidt Lantermann clefts. The calcium influx at the crush site corresponds to the known role of calcium in triggering degeneration. The alterations in the distal axon may be an early stage leading to degeneration. Alteration in calcium distribution in the proximal nerve stump may play a role in the regulation of the response to injury.
Discriminative behavior and pavlovian conditioning in the mollusc Pleurobranchaea
Authors: Mpitsos George J. , Cohan Christopher S. 
Published: May 2005

AbstractThe buccal motor system in the sea slug Pleurobranchaea californica is multifunctional; similar sets of neurons and muscles generate different behaviors through similar electrophysiological motor patterns. Such multifunctional systems compromise the traditional practice of identifying a motor pattern and then using that pattern to indicate the behavior in reduced preparations. We address this issue in a series of experiments leading to the comparison of differential Pavlovian conditioning in whole animals with the conditioned behavior of the same animals during electrophysiological recording. Because differential conditioning requires two conditioned stimuli (CSs), we show here that each of two CSs activated the conditioned response from animals after they received the stimulus (CS+) paired with an unconditioned stimulus (UCS). Conditioning sessions consisted of 5 training trials with a 2‐h intertrial interval. In one study, experimental animals received a 60‐s CS+, derived from beer (Sbr), paired with a 50‐s electrical shock UCS whose onset occurred 10 s after the CS+ onset; control animals received the Sbr and UCS explicitly unpaired. In a second study, animals received similar procedures as in the first but with a CS+ consisting of squid homogenate (Ssq). Tests with both CSs showed that animals did not discriminate between Sbr and Ssq before beginning conditioning, but did so afterward. Experimental animals exhibited robust food aversion (withdrawal and suppressed feeding) to the CS+, but retained strong appetitive responses to the CS they did not receive in training; response thresholds to the CS+ changed as much as 1000‐fold by comparison to the preconditioning values. Control animals exhibited similar though significantly smaller behavioral changes as the experimental animals. Both stimuli evoked associatively learned responses, but Sbr produced greater experimental‐control differences than Ssq did. Two accompanying papers show the results of using both CSs in differential conditioning, and describe the behavioral/electrophysiological comparisons.
Convergence in a distributed nervous system: Parallel processing and self‐organization
Authors: Mpitsos George J. , Cohan Christopher S. 
Published: May 2005

AbstractThe present findings show that the motor system of the carnivorous sea slug Pleurobranchea californica consists of parallel, distributed, and interconnected neuronal channels by which motor activity may emerge from the dynamics of the system rather than from “switchboard” circuitry. The findings are shown primarily through the properties of the buccal‐cerebral neurons (BCNs) that extensively converge and diverge monosynaptically and polysynaptically onto brain motoneurons, providing them with drive and patterned activity. The motoneurons, some of which are electrically coupled, feed back onto the BCNs. The BCNs are functionally heterogeneous both as a group and individually. Many are multifunctional in that they take part in the generation of different behaviors, and some also appear to change their timing with respect to the phase of the pattern generator in the different motor patterns. In the buccal ganglion, the BCNs affect the characteristics of the pattern generator and may be part of the pattern generator itself. By sending axons to buccal roots and to the brain, some BCNs may act as motoneurons and also integrate the activity of brain motoneurons. Because of the effects produced by the extensive interconnections among such functionally heterogeneous and nonlinerar elements, and because the “history” of activity in the system can bias subsequent activity, there is ambiguity in assessing the response properties of neurons by examining them individually or in pairs. Such an assessment requires, first, an understanding of the context of activity in which a neuron becomes coactive, and, second, because of inherent variability in the system, it is necessary to consider the temporal, nonlinear computations of the system as a whole. We discuss the findings with regard to the attractor theory that has been used to study complex mammalian systems but that does not rely on modeling of any neuronal activity. The Pleurobranchaea nervous system may provide the means for studying individual neurons within such analyses of global activity.
Adult‐specific neurons in the nervous system of the moth, Manduca sexta: Selective chemical ablation using hydroxyurea
Authors: Truman James W. , Booker Ronald 
Published: May 2005

AbstractThe segmental ganglia of adults of the moth, Manduca sexta, are constructed both from remodeled larval neurons and from adult‐specific cells. The latter are produced by identified stem cells (neuroblasts) during larval life and then differentiate to form functional neurons during metamorphosis. The mitotic activity of the larval neuroblasts could be irreversibly blocked by the DNA‐synthesis inhibitor hydroxyurea (HU). Treatment on day 1 of the third larval stage resulted in 80–90% of the neuroblasts being blocked before they produced any progeny while leaving the functional larval neurons unaffected. Treated larvae finished growth, underwent metamorphosis, and produced an adult CNS that contained the normal set of remodeled larval neurons but lacked most of the new adult‐specific cells. When HU treatment was delayed until the start of the fourth or fifth larval stage, the neuroblasts produced the early portions of their respective lineages before they were blocked. The immature neurons that were generated prior to treatment survived to contribute adult‐specific neurons to the moth CNS, but the remainder of each lineage was missing. This technique therefore enables one to produce adult nervous systems containing the basic set of remodeled larval cells plus defined sets of adult‐specific neurons.
Skin sensory innervation patterns in embryonic chick hindlimb following dorsal root ganglion reversals
Authors: Scott Sheryl A. 
Published: May 2005

AbstractDuring embryonic development skin sensory neurons in lumbosacral dorsal root ganglia (DRGs) establish their dermatomes and axonal projections in a precise, orderly fashion in the chick. To investigate mechanisms responsible for this specific outgrowth, the rostrocaudal order of DRGs T7‐LS3 was reversed by rotating the corresponding segments of neural crest, either alone or together with the underlying neural tube in St.15–16 embryos. The resulting skin sensory innervation patterns, mapped physiologically or an‐atomically at St.29–40, differed between the two experimental groups. Following neural tube rotations DRGs tended to establish innervation patterns that were consonant with their original position in the embryo. Axons from these rotated DRGs generally projected into the appropriate pathways and innervated the appopriate region of skin. Neural crest rotations left the ventral neural tube (including the motor neuron precursors) largely intact. In this case rotated DRGs tended to establish innervation patterns in accordance with their new position in the embryo, almost as if no rotation had been made. These results cannot be explained solely by the inherent specificity of sensory neurons. Instead, the results are largely consistent with the suggestion (Honig et al., 1986; Landmesser and Honig, 1986) that motor axons can direct the outgrowth of sensory axons and thereby influence the establishment of sensory innervation patterns. Other mechanisms that may also affect the development of sensory innervation patterns are discussed.
Diffusional and electrokinetic redistribution at the synapse: A physicochemical basis of synaptic competition
Authors: Poo Mu‐Ming , Young Steven H. 
Published: May 2005

AbstractCoinnervating nerve terminals may compete for “stabilizing factors” confined within the postsynaptic cell. The competition could be achieved through a diffusion‐mediated trapping the factor, facilitated by an activity‐dependent electrokinetic migration of the factor toward the synaptic site. We have examined the evidence for diffusional and electrokinetic motions of cell surface and cytoplasmic components, the profile and magnitude of the electric field produced by the synaptic current, and the plausibility that these motions underlie the process of synaptic competition.
Evidence for androgen receptors in sexually dimorphic perineal muscles of neonatal male rats. Absence of androgen accumulation by the perineal motoneurons
Authors: Fishman Renata B. , Chism Leila , Firestone Gary L. , Breedlove S. Marc 
Published: May 2005

AbstractDuring development, survival of the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB) and its target perineal muscles, the bulbocavernosus (BC) and the levator ani (LA) is androgen‐dependent. To define androgen's site of action in masculinizing SNB system structures, we examined whether or not androgen receptors are present in SNB motoneurons and/or BC/LA muscles of neonatal male rats. Using a receptor binding assay, we have identified androgen‐binding factors in the neonatal BC/LA (Bmax = 13.5 fmol/mg protein; Kd = 4.69 nM) for the first time. In contrast, androgen autoradiography provided no evidence that neonatal spinal motoneurons accumulate androgens. These results support the hypothesis that BC/LA muscles are a primary site of androgen action for masculinizing SNB system structures, and that androgen need not interact with SNB motoneurons directly to sexually differentiate them.
Hormonal control of neuron number in sexually dimorphic spinal nuclei of the rat: IV. Masculinization of the spinal nucleus of the bulbocavernosus with testosterone metabolites
Authors: Goldstein L. A. , Sengelaub D. R. 
Published: May 2005

AbstractThe spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic motor nucleus in the rat lumbar spinal cord. SNB motoneurons and their perineal target muscles are present in adult males but reduced or absent in females. This sexual dimorphism is due to the presence of androgen during development; females treated with testosterone (T) perinatally have a masculine SNB system. To assess whether masculinization of the SNB could involve the conversion of testosterone into its active metabolites, dihydrotestosterone (DHT) and estrogen, we examined the development of the SNB in females treated perinatally with estrogen alone or in combination with dihydrotestosterone.Counts of motoneurons in the developing SNB in all groups showed the typical prenatal increase followed by a differential postnatal decline; the incidence of degenerating cells reflected this decline. Motoneuron numbers and the frequency of degenerating cells in females treated with estrogen (E) alone did not differ from those of normal females, with both groups losing large numbers of motoneurons and having a high incidence of degenerating cells. In contrast, females treated with both estrogen and dihydrotestosterone did not show the female‐typical decline in motoneuron number and had a low, masculine incidence of degenerating cells. By postnatal day 10, females treated with estrogen and dihydrotestosterone had a fully masculine SNB motoneuron number, suggesting that dihydrotestosterone alone or in conjunction with estrogen may be involved in the development of the sexually dimorphic SNB system.
Hormonal regulation of adult sympathetic neurons: The effects of castration on neuropeptide Y, norepinephrine, and tyrosine hydroxylase activity
Authors: Hamill Robert W. , Schroeder Barbara 
Published: May 2005

AbstractPrevious studies utilizing the hypogastric ganglia (HG) have indicated that gonadal steroids exert organizational and activational effects on noradrenergic biochemistry. Bilateral castration of male rodents at birth prevents the normal maturation of tyrosine hydroxylase (T‐OH) activity in the HG; castration during adulthood results in a progressive decline in T‐OH activity. Testosterone replacement corrects both the ontogenetic and adult functional alterations in the neurotransmiter‐synthesizing enzyme. The present studies in adult male rats extend these previous observations and asked the question whether gonadal steroids regulate the neurotransmitters neuropeptide Y (NPY) and norepinephrine (NE) in the HG. Adult rodents were castrated and ganglia T‐OH, NPY, and NE were examined at various time points after surgery. All three indices of sympathetic neuron biochemistry declined following castration, but they exhibited different profiles. It appears that hormones may affect enzyme activity and neurotransmitter pools differently within neurons. Testosterone replacement therapy fully restored T‐OH activity, and NPY and NE levels in the HG. These studies extend the activational role of testosterone in regulating sympathetic neuron neurotransmitter and neuropeptide levels as well as neurotransmitter‐synthesizing enzymes.
Critical period for the androgenic block of neuromuscular synapse elimination
Authors: Jordan Cynthia L. , Letinsky Michael S. , Arnold Arthur P. 
Published: May 2005

AbstractJuvenile androgen treatment during developmental synapse elimination changes the pattern of innervation in the adult levator ani (LA), an androgen‐sensitive muscle (Jordan, Letinsky, and Arnold, 1989b). Most notably, such adult muscles contain an unusually high number of muscle fibers that are innervated by two or more axons indicating that these fibers are multiply innervated. Juvenile androgen treatment also increases the adult level of preterminal branching, the number of junctional sites per adult fiber, and the size of adult LA muscle fibers and motoneurons in the spinal nucleus of the bulbocavernosus (SNB). The present study was designed to determine when in development androgen treatment is most effective in maintaining multiple innervation in adulthood and whether there are different critical periods for the different effects of juvenile androgen treatment. Male rats were castrated on 7, 21, or 34 days after birth (roughly corresponding to the beginning, middle, and end of synapse elimination in the LA muscle) and treated daily with testosterone propionate for the next 2 weeks. All rats were sacrificed at 9 weeks and their spinal cords and LA muscles were stained and analyzed. Only during the first treatment period (7–20) did androgen treatment result in increased levels of multiple innervation at 9 weeks. During this period, androgen also increased the number of junctional sites per fiber and the size of SNB somata but did not influence the adult level of preterminal branching or the diameter of adult LA muscle fibers. Androgen treatment during the two later periods increased the level of preterminal branching and the size of LA muscle fibers without influencing the level of multiple innervation. These results suggest that androgen maintains multiple innervation independent of its effects on preterminal branching and muscle fiber size and that motoneuron soma size may be related importantly to the long‐term maintenance of multiple innervation. Androgen treatment during but not after synapse elimination results in elevated levels of multiple innervation in adulthood, suggesting that androgen maintains multiple innervation in adult LA muscle by preventing its normal elimination in development.
Immunocytochemical colocalization of progestin receptors and β‐endorphin or enkephalin in the hypothalamus of female guinea pigs
Authors: Olster Deborah H. , Blaustein Jeffrey D. 
Published: May 2005

AbstractDouble‐label immunocytochemistry was used to determine whether estradiol‐induced progestin receptors and either β‐endorphin or leucine‐enkephalin are colocalized in female guinea pig brain. Ovariectomized, adult guinea pigs were implanted with capsules containing estradiol‐17β to induce high levels of progestin receptors, and injected intracerebroventricularly with co chicine to improve visualization of the opiate peptides. Sections through the hypothalamus and preoptic area were processed for progestin receptor, followed by β‐endorphin or leucine‐enkephalin immunocytochemistry. As reported previously, high concentrations of progestin receptor‐immunoreactive (PR‐IR) cells were found in the preoptic area (medial and periventricular portions, medial preoptic nucleus) and hypothalamus (anterior hypothalamic and arcuate nuclei, ventrolateral area). Many β‐endorphin‐IR cells contained PR‐IR in the arcuate nucleus and its surroundings (33%) and in the dorsomedial area of the hypothalamus (64%). Scattered enkephalin‐IR cells were found in the septal nucleus, medial and lateral preoptic area, bed nucleus of the stria terminalis, and the arcuate nucleus. The ventromedial nucleus of the hypothalamus and dorsolateral magnocellular nucleus, respectively, contained moderate and heavy concentrations of enkephalin‐IR cells. Although some of these areas also contained PR‐IR, enkephalin‐IR was colocalized consistently with PR‐IR only in a small number of cells in the arcuate nucleus and ventromedial/ventrolateral area of the hypothalamus. These data, taken together with earlier observations that virtually all cells containing estradiol‐induced PR‐IR also contain estrogen receptor‐IR, provide neuroanatomical evidence that hypothalamic actions of progesterone and estradiol may be mediated by β‐endorphin and/or enkephalin.
Onset of the hormone‐sensitive perinatal period for sexual differentiation of the sexually dimorphic nucleus of the preoptic area in female rats
Authors: Rhees Reuben W. , Shryne James E. , Gorski Roger A. 
Published: May 2005

AbstractThe volume of the sexually dimorphic nucleus of the preoptic area (SDN‐POA) of the rat brain is severalfold larger in males than in females. The volume of the SDN‐POA can be influenced significantly by the hormonal milieu during the perinatal “critical period” of sexual differentiation of the brain. The purpose of the present study was to determine the onset of this period of sexual differentiation of the SDN‐POA. Pregnant rats received no treatment or were injected subcutaneously with oil on day 17, 18, or 20, or testosterone (T;5 mg) on days 16‐22 of gestation. On postnatal day 15, unilateral SDN‐POA volumes from female offspring prenatally exposed to testosterone on day 16 or 17 were not different from values of control (untreated or oil‐injected) offspring. Female offspring from mothers treated with testosterone on day 18, 19, or 20 of gestation showed a significant and similar increase in SDN‐POA volume over values from control animals. SDN‐POA volumes from female offspring exposed to testosterone on day 21 or 22, although larger than those of controls, were not different statistically. We conclude that with the specific paradigm used in this study SDN‐POA development is insensitive prior to day 18 of gestation, the day on which the onset of the hormone‐sensitive period occurs.