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  • 1
    ISSN: 1432-1106
    Keywords: Pudendal nerve ; Lordosis ; Cutaneous reflex ; Axial muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In 39 Urethane-anesthetized rats we have recorded the afferent volley in the dorsal roots and the electrical activity of the lateral longissimus muscle and its motor nerves during electrical stimulation of a cutaneous branch of the pudendal nerve. Male and female rats were used; the females were ovariectomized and either pretreated with estradiol or left without hormonal treatment. Conduction velocities in the pudendal nerve were 54 m/s for the largest Abeta fibers and averaged 10 m/s for A-delta fibers. Excitation of pudendal nerve afferents strongly potentiated the firing of axial motoneurons, at stimulus currents below threshold for A-delta fibers. Trains of three shocks to the pudendal nerve were considerably more effective than double or single shock trains. Repetition rates as low as 1/s had a long lasting excitatory effect on the lateral longissimus muscle and the magnitude of the responses increased gradually for several seconds with continued stimulation. Recordings from the axons of the epaxial motoneurons of female rats showed a strong activation of neuronal firing with an onset latency of 5.8 ms from the last shock of a three ms, three shock train; the onset in male rats, 8.4 ms, differed significantly. Peak spike activity occurred at mean latencies of 11, 22 and 102 ms in both sexes. A period of depressed firing was usually present from 34 to 50 ms. Males differed in having a larger peak in activity at 102 ms, but the overall profile of the responses was similar in males and females. No differences were seen in the overall response patterns of the estrogen-treated and untreated females. Responses of comparable magnitude were seen with ipsilateral or contralateral pudendal nerve stimulation; these were facilitated by bilateral stimulation. In electromyographic recordings, the onset of unit firings was seen at 6.4 ms latency in response to pudendal nerve stimulation. This unit activity was consistent with the firing pattern seen in the muscle nerves.
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  • 2
    ISSN: 1432-1106
    Keywords: Estradiol ; Autoradiography ; Hypothalamus ; Limbic system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary These experiments were done to compare quantitatively, on a cell-by-cell basis, estradiol retention by cells in the medial preoptic area, arcuate nucleus, ventrolateral subdivision of the ventromedial nucleus, and the caudal half of the medial nucleus of the amygdala. The steroid autoradiograms were prepared from 2 μ sections of brains from ovariectomized, adrenalectomized adult female rats that had been infused intravenously with [3H] estradiol (E2) in a regimen which kept circulating hormone concentration at or above proestrus levels for 3–4 h. Even in these brain regions, containing the most dense collections of E2-concentrating cells, a maximum of only 27–61% of the cells concentrated E2. Therefore, in these regions only a particular subset of the cells retain hormone; other cells in the region do not retain hormone. Frequency distribution histograms of the number of grains per cell versus the number of cells in each region showed a wide range in the amount of E2 retained per cell, and no modes among E2retaining cells. The data followed a distribution markedly different from that predicted by a simple Poisson distribution, confirming that E2-retention does not result from a random, passive process such as diffusion. The overall quantitative characteristics of the frequency distribution histograms were similar across the four brain areas. Therefore, we propose that the different E2-sensitive functions of these brain areas must depend on differences in the neural connectivity or differences in hormone regulated peptide content of the areas.
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  • 3
    ISSN: 1432-1106
    Keywords: Thyrotropin-releasing hormone ; Cy-clo(His-Pro) ; Ventromedial nucleus of hypothalamus ; Neuromodulation ; Desensitization ; Feeding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Electrical activity of neurons in rat hypothalamic ventromedial nucleus was recorded in tissue slices, to investigate central neural mechanisms underlying reduction of food intake caused by TRH and its metabolite, cyclo(His-Pro) [cHP]. Application of TRH had two actions: stimulation of neuronal activity, which was desensitized on closely repeated applications; and modulation of neuronal responses to neurotransmitters, even in the absence of the stimulatory action. The neuromodulatory but not the direct stimulatory action could also be achieved by cHP. The neuromodulatory action is more likely to be a neural mechanism underlying the inhibition of feeding, while other biological functions, unique to TRH, may depend on direct stimulation. In this way, TRH could achieve different biological results through different modes of action on hypothalamic neurons.
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  • 4
    ISSN: 1432-1106
    Keywords: LHRH messenger RNA ; Rat forebrain ; In situ hybridization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The purpose of the present study was to localize luteinizing hormone-releasing hormone (LHRH) mRNA within the male rat forebrain using an in situ hybridization approach. The expression of LHRH mRNA was compared in castrate and intact males to approach questions on the chronic influences of circulating testicular steroids on the gene expression of the peptide. Frozen 10 μm sections fixed in paraformaldehyde were obtained from the forebrain region of intact and 2 week post-castrate adult male rats. LHRH mRNA was autoradiographically detected using an oligomer (59mer) complementary to the mRNA coding for amino acids-5 to 15 of the human LHRH preprohormone. Individual brain sections were incubated in prehybridization buffer for 2 h to reduce nonspecific binding. Following this, 20 μl of hybridization buffer containing 65,000–120,000 cpm of the 59mer were applied to sections and hybridized at 37° C for 3 days. The sections were then rinsed over a 48 h period, dehydrated, dipped in Kodak NTB2 liquid emulsion and exposed for 22 days. Autoradiograms were developed and counterstained with fast green and cresyl violet. As reported in the female, LHRH message-containing cells were localized in ventral septal regions, the diagonal bands of Broca, preoptic area and anterior hypothalamus. On occasion, LHRH gene expressing cells were found to appear in loose clusters. Labeled cells were never found in control sections treated with hybridization buffer lacking the 59mer. The total number of LHRH mRNA-containing cells localized in intact rats did not differ significantly from the castrate group. The mean grain counts per cell (±SEM) for the intact (30.1±1.2) and castrate (24±1.1) groups were found to differ, as did the histogram distribution of these two populations. These results are in contrast to those expected on the basis of a negative feedback effect, and instead suggest that long term exposure to testicular steroids can actually increase the content of LHRH mRNA within individual neurons.
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  • 5
    ISSN: 1432-1106
    Keywords: Axial muscles ; Electromyography ; Reticular formation ; Lateral vestibular nucleus ; Descending systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of electrical stimulation of the lateral vestibular nucleus (LVN) and medullary reticular formation (RF) on electromyographic activity in axial muscles medial longissimus (ML) and lateral longissimus (LL) in the rat were studied. Long trains (150–500 ms) at 200–330 Hz and 20–100 μA were sufficient to activate ML and LL at latencies of 20–100 ms from the beginning of the train. Results of stimulation at 200–330 Hz to RF or LVN showed that muscle units were activated at a fixed latency from any effective pulse in the stimulus train. Using high frequency (1 kHz) trains of 3–6 pulses to LVN, EMG activity was detected at minimum latencies of 3.5–6 ms. When conduction times from the medulla to the spinal cord, and the spinal cord to the muscle are subtracted, this latency range is consistent with monosynaptic activation. In many cases, muscle units were recruited in order of size, with both RF and LVN stimulation. Combined stimulation of LVN and RF sites in n. gigantocellularis led to EMG activity in ML and LL at currents which were insufficient to evoke activity when presented singly. When stimulation of one site (300–400 ms train) was just sufficient to evoke a response, a shorter, overlapping train (100–150 ms) to the other site led to a higher rate of muscle activity that continued through the end of the long train, even after the short train had ended. In all cases, the effect of RF facilitating LVN was similar to the effect of LVN facilitating RF. The evidence for convergence between these two systems in the medulla and the spinal cord is discussed.
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  • 6
    ISSN: 1432-1106
    Keywords: Estrogen ; Synapse ; Ultrastructure ; Midbrain central gray ; Lordosis behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Axons of ventromedial hypothalamic (VMH) neurons have been previously shown to terminate in the midbrain central gray (MCG) (Chung et al. 1984, 1986). Since VMH synapses in this region may be involved in the mediation of estrogen-induced lordosis behavior, we examined the effect of estrogen on the morphology of synapses in the MCG. Ovariectomized adult female rats were given daily subcutaneous injections of estradiol benzoate (10 μg) or the vehicle control and after 20 days of injection, only the estrogen-treated rats showed the lordosis response. A quantitative analysis of MCG tissue from these animals demonstrates morphological changes in various synaptic parameters with estrogen treatment including: 1) an increase in the mean number of dense-cored vesicles and an increase in the number of terminals containing densecored vesicles, 2) an increase in the length of postsynaptic densities (PSDs), 3) an increase in the number of PSDs showing perforations, 4) an increase in the number of synapses, and 5) an increase in the number of synapses with positive synaptic curvature. No alterations in the number of subjunctional bodies were observed. The dense-cored vesicles may contain an estrogen-induced trophic factor which may function in maintaining the integrity of postsynaptic processes and cells in the MCG with which VMN endings contact (Chung et al. submitted) and/or which induces morphological changes in postsynaptic structures which facilitate the effects of estrogen on lordosis behavior.
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  • 7
    ISSN: 1432-1106
    Keywords: Receptor autoradiography ; Progesterone ; 3H muscimol binding ; Hamster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Quantitative receptor autoradiography was applied to evaluate the effects of one and three injections of 1 mg progesterone (P) on 3H muscimol binding levels in the different forebrain areas of the female hamster. The overall effect of P resulted in substantial increases in 3H muscimol binding in brain areas containing gonadal steroid receptors: medial preoptic area and ventromedial hypothalamic nucleus as well as in bed nucleus stria terminalis and subiculum. Similarly, the caudate putamen, a region where gonadal steroid receptors are not abundant, also showed substantial increases of 3H muscimol binding receptor levels. Moreover, female hamsters treated with P for 3 days presented altered 3H muscimol binding levels in the amygdala and thalamic nucleus that were, in some cases, not produced by one dose of P. P treatment also decreased GABAA binding in two areas of the thalamus. These results are consistent with the proposal that P may alter GABAergic inhibitory activity via changes in the levels of GABAA receptors in certain forebrain areas in the female hamster, changes which may be linked to the mediation of anxiolytic effects and to the inhibition of aggressive behavior. These data also suggest that P treatment increases the binding of high affinity GABA receptors in some forebrain sites and may be responsible for maintenance of the anxiolytic effects.
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  • 8
    ISSN: 1432-1106
    Keywords: Ventromedial hypothalamus ; VMH ; HRP gel implants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The afferent neural connections of the ventromedial nucleus of the rat hypothalamus (VMH) have been studied in detail using three horseradish peroxidase (HRP) application methods: HRP crystal implants, HRP-gel implants, and iontophoretic deposition of the enzyme. Examination of the cases in which the retrograde tracer was best confined to various subdivisions of the nucleus revealed that the septal area projects only to the ventrolateral VMH, and that the medial preoptic area, rostral lateral hypothalamus, and the ventral subiculum project mainly to the ventrolateral VMH. Thus, the subdivision of the VMH that contains the highest density of estradiol-concentrating neurons (Morrell et al. 1986) receives a larger set of inputs than the rostral and central parts of the nucleus. The central subdivision receives a more restricted set of projections than either the medial or the lateral regions. These studies suggest that there may be partial anatomical segregation of neural inputs to the various subdivisions of the VMH.
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  • 9
    ISSN: 1432-1106
    Keywords: Preoptic area ; Intrinsic neuron ; GABA ; Local neuron ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Neurons intrinsic to the preoptic area might participate in the control of neuroendocrine or behavioral events. To determine their existence and features, we deafferented the preoptic area of female rats, using completely circumscribing cuts with a Halasz knife. Despite obvious signs of degeneration of synapses originating from nerve cell bodies outside the preoptic island, some synapses survived complete deafferentation. We saw synaptic contacts not only on the neuronal cell body, but also on the dendritic shaft and spine. There were no peculiar morphological features, as might suggest unique physiologic functions of these intrinsic synapses. The prominence of intrinsic synapses in the preoptic area suggests that, in addition to hormone effects on preoptic neurons, and long ascending afferents, intrinsic synapses might play significant roles in neuroendocrine controls.
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  • 10
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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