bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual effect of glycine on NMDA-induced neurotoxicity in rat cortical cultures
Authors: McNamara D , Dingledine R
Published: March 2018

To examine the roles of glycine in neurotoxicity caused by NMDA, primary rat cortical cultures were exposed to 100–300 microM NMDA plus glycine (0–3000 microM) or other glycine analogs in a simple saline solution, and toxicity was assessed by the amount of lactate dehydrogenase (LDH) released from the cultures. NMDA-induced neurotoxicity was abolished by 100 microM D-2-amino-5-phosphonovaleric acid (D-APV), phencyclidine (IC50, 4.1 microM), and Mg (IC50, 7.5 mM), or by reducing [Ca]0 to 0.1 mM. NMDA-induced neurotoxicity could also be abolished by 7-chlorokynurenic acid (IC50, 8.6 microM), suggesting the presence of residual glycine in the culture medium (confirmed by high-performance liquid chromatography measurement). Moreover, in the presence of 30 microM 7-chlorokynurenic acid, glycine, D-serine, D- alanine, beta-fluoro-D-alanine, and 1-aminocyclopropanecarboxylic acid could restore the neurotoxic action of NMDA, and their relative potencies and relative efficacies were the same as measured in electrophysiological assays in Xenopus oocytes or cultured neurons. The addition of greater than 100 microM glycine doubled the excitotoxic effect of NMDA. The potency of glycine was low (EC50, 27 microM), and this effect was not due to a direct action on the NMDA receptor. The above-mentioned agonists were unable to substitute for glycine, even at high concentrations (1 mM). On the other hand, beta-alanine, taurine, and GABA (1 mM) did potentiate NMDA neurotoxicity, and strychnine (IC50, 550 nM) could greatly reduce neurotoxicity in the presence of 1 mM glycine plus 300 microM NMDA.(ABSTRACT TRUNCATED AT 250 WORDS)
Naturally occurring fluctuation in dendritic spine density on adult hippocampal pyramidal neurons
Authors: Woolley CS , Gould E , Frankfurt M , McEwen BS
Published: March 2018

We have used Golgi-impregnated tissue to demonstrate that apical dendritic spine density in CA1 hippocampal pyramidal cells undergoes a cyclic fluctuation as estradiol and progesterone levels vary across the estrous cycle in the adult female rat. We observed a 30% decrease in apical dendritic spine density over the 24-hr period between the late proestrus and the late estrus phases of the cycle. Spine density then appears to cycle back to proestrus values over a period of several days. In contrast, no significant changes in dendritic spine density across the estrous cycle occur in CA3 pyramidal cells or dentate gyrus granule cells. These results demonstrate rapid and ongoing dendritic plasticity in a specific population of hippocampal neurons in experimentally unmanipulated animals.
Vault immunofluorescence in the brain: new insights regarding the origin of microglia
Authors: Chugani DC , Kedersha NL , Rome LH
Published: March 2018

The developmental appearance of ameboid and ramified microglia in the rat brain has been examined by immunofluorescent localization of vaults, recently described ribonucleoprotein particles (Kedersha and Rome, 1986a). Vaults are distinct, multiarched structures of unknown function expressed by higher and lower eukaryotic species. Although vaults have been detected in all mammalian cells examined to date, they are highly enriched in macrophages. In the brain, vault antisera is highly specific for both ameboid and ramified microglia. The developmental profile of vault immunoreactivity in rat brain slices suggests that microglia enter the brain at 2 locations, with different time scales for each. The first migration, which begins before embryonic day 15 and subsides between postnatal days 7 and 14, was identified by vault immunoreactivity and Bandeiraea simplicifolia B4- isolectin (a microglia marker) staining. The cells appear to enter from blood vessels and display a ramified morphology as soon as they are detected in the brain. The second microglial migration occurs in the first postnatal week, when ameboid microglia appear in the corpus callosum and other large fiber tracts. Ameboid microglia appear to differentiate into ramified microglia between postnatal days 4 and 14. Vault immunoreactivity, as a very early microglial marker, provides new insight regarding the much-debated origin of the ramified microglia. It is quite clear that ameboid cells are not the sole source of ramified microglia because ramified cells can be detected before the influx of ameboid microglia. Colocalization studies with monocyte/macrophage markers ED1 and OX42 demonstrate that both ramified and ameboid microglia originate from monocyte lineage.
Somatotopic organization of single primary afferent axon projections to cat spinal cord dorsal horn
Authors: Brown PB , Gladfelter WE , Culberson JC , Covalt-Dunning D , Sonty RV , Pubols LM , Millecchia RJ
Published: March 2018

Horseradish peroxidase injection of identified low threshold cutaneous mechanoreceptor (LTCM) primary afferent axons was used to assess the somatotopic organization of hindlimb projections to laminae III and IV of cat dorsal horn. Multiple injections in the same animals were used to assess bilateral symmetry and precision. Thirty-one axons were injected, with more than 1 axon injected in each of 8 animals (25 axons). Somatotopic relations between their receptive field (RF) centers and the centers of their dorsal horn projections were similar to the somatotopic relations between dorsal horn cell RF centers and cell locations. Very few reversals of mediolateral somatotopic gradients (proximodistal RF location as a function of mediolateral projection center) were observed. Two afferents with nearly identical RFs in 1 animal had nearly identical projections. These observations held for many different combinations of receptor types. A simple mathematical model was used to demonstrate that assembly of dorsal horn cell RFs via passive sampling of the presynaptic neuropil by dorsal horn cell dendrites cannot account for the sizes of dorsal horn cell LTCM RFs. Hypothesized mechanisms for assembly of dorsal horn cell RFs must take into account the functional selectivity of connections required to produce RFs smaller than those predicted by the passive assembly model.
Temporal interactions in the cat visual system. I. Orientation- selective suppression in the visual cortex
Authors: Nelson SB
Published: March 2018

The perception of a visual contour depends on the spatial and temporal context in which it is viewed. Interactions between visual contours are believed to underlie a wide range of perceptual phenomena, including geometric illusions and aftereffects, contrast adaptation, and visual masking. The physiological mechanisms that might underlie such interactions were studied in the visual cortex of the cat by recording responses of single neurons to pairs of brief stationary stimuli that were separated in time. The results revealed a long-lasting, orientation-selective suppression, termed “paired-pulse suppression,” which was strongest at the cell's preferred orientation, but which was more broadly tuned for orientation than the excitatory response of the cell. Although the strength and duration of the suppression varied widely, some degree of response reduction was present in most cells studied. The function of this suppression may be to regulate the gain with which visual inputs are transmitted to cortical neurons, thus preventing response saturation and positive feedback.
Temporal interactions in the cat visual system. II. Suppressive and facilitatory effects in the lateral geniculate nucleus
Authors: Nelson SB
Published: March 2018

Extracellular responses were recorded from single neurons in the lateral geniculate nucleus (LGN) of the cat during presentation of pairs of brief visual stimuli identical to those that produce orientation-selective paired-pulsed suppression in the visual cortex. LGN neurons also show paired-pulse suppression, but the suppression is not orientation selective, and it occurs only for short interstimulus intervals (ISIs; usually less than 200 msec). At longer ISIs, most LGN neurons show a period of facilitation. Thus, the paired-pulse suppression in the LGN cannot account for that seen in the visual cortex. Paired-pulse suppression in the LGN was found to be enhanced by stimulation of the receptive field surround. LGN neurons also showed a second type of suppression, termed “offset suppression,” which consisted of a more long-lasting suppression of spontaneous activity following the offset of an excitatory visual stimulus. The suppression of spontaneous activity was accompanied by a reduction of the antidromic excitability, assessed by stimulating LGN axons within the cortex or optic radiation. Unlike paired-pulsed suppression, offset suppression was not enhanced by increased stimulation of the receptive field surround. Paired-pulse suppression and offset suppression are most likely due to different mechanisms because they have different time courses and depend differently on the spatial properties of the stimuli. Functionally, paired-pulse suppression may be related to the reduced visual sensitivity that accompanies eye movements, while offset suppression may serve to enhance temporal contrast.
Immunofluorescent localization of three Na,K-ATPase isozymes in the rat central nervous system: both neurons and glia can express more than one Na,K-ATPase
Authors: McGrail KM , Phillips JM , Sweadner KJ
Published: March 2018

In the CNS, there are multiple isozymes of the sodium and potassium ion- stimulated adenosine triphosphatase (Na,K-ATPase) that have differences in affinity for Na+, ATP, and cardiac glycosides. Three forms of the catalytic subunit (designated alpha 1, alpha 2, and alpha 3) are known to be derived from different genes, but little is known of the cellular distributions of the proteins or their physiological roles. Isozyme- specific monoclonal antibodies permitted the immunofluorescent localization of the 3 Na,K-ATPases in the rat CNS, and markedly different patterns of staining were seen. All 3 isozymes were detected, singly or in combination, in 1 or more neuronal structures, while both alpha 1 and alpha 2 were detected in glia. Many different neuroanatomic structures or cell types stained for more than 1 isozyme. Even when a structure or region stained for more than 1 isozyme, the pattern of staining was frequently dissimilar, suggesting complex differences in gene expression and cellular localization.
Acidic and basic fibroblast growth factors in the nervous system: distribution and differential alteration of levels after injury of central versus peripheral nerve
Authors: Eckenstein FP , Shipley GD , Nishi R
Published: March 2018

Acidic and basic fibroblast growth factors (aFGF and bFGF) are known to stimulate mitogenesis in a variety of non-neuronal cell types. Recent work has also established that FGFs can act as neurotrophic factors that promote the survival and regeneration in vitro of a variety of neurons. The present study investigates the distribution of aFGF and bFGF in vivo by using a mitogenic bioassay on AKR-2B cells coupled with Western-blot analysis to estimate the levels of aFGF and bFGF in different areas of the rat nervous system. Acidic FGF and bFGF from extracts of nervous tissue were found to differ considerably in their relative dependencies upon heparin to potentiate their mitogenic activities: the effect of aFGF was strongly dependent upon heparin, whereas the effect of bFGF was only slightly potentiated by heparin. Heparin was also found to stimulate differentially the mitogenic activity of extracts prepared from different areas of the nervous system, indicating that spinal cord, cortex, pituitary, and optic nerve contained different ratios of aFGF to bFGF, whereas sciatic nerve contained extremely high levels of only aFGF. These results were confirmed in Western-blot experiments, using antibodies specific for either aFGF or bFGF. Transection of nerves had opposing effects in sciatic and optic nerves: aFGF rapidly declined in the sciatic nerve distal to the cut, whereas bFGF increased slightly in the distal portion of the cut optic nerve. This differential effect of injury on FGF levels in central versus peripheral nerves may reflect the differential regenerative potential of these two types of nerves.
Factors that determine the magnitude and time course of human H- reflexes in locomotion
Authors: Edamura M , Yang JF , Stein RB
Published: March 2018

The soleus H-reflex amplitude is deeply modulated during locomotion in humans (Capaday and Stein, 1986). Moreover, at a constant stimulus intensity, the slope of the relationship between the amplitude of the soleus H-reflex and the background electromyogram (EMG) changes with different locomotor tasks (Capaday and Stein, 1987a). Two further aspects are studied here. First, we recorded the reflex during overlapping speeds of walking (2.0–7.5 km/hr) and running (5–9 km/hr) to determine whether the speed, the motor output, or the form of locomotion was most important in setting the slope of this relationship between H-reflex and background EMG. Second, we determined the time course of change in the H-reflex amplitude and the possible site of action for the reflex depression during the transition from standing to walking. The primary determinant of the slope was found to be the form of locomotion. The differences between running and walking could not be explained entirely by either movement speed or motor output. For walking, the slope varied inversely with the speed and the motor output of locomotion. This compensation in slope as a function of motor output may prevent saturation of the motoneuron pool. The appropriate reflex amplitudes for a particular locomotor pattern are activated rapidly and completely within a reaction time, and simultaneously with the activation of muscle activity for the initiation of walking. Mechanisms for the rapid change seen during the initiation of locomotion most likely act presynaptically on the muscle spindle afferents. The time course and magnitude of this change are correlated with the activity of the tibialis anterior muscle.
Increased AMPA-sensitive quisqualate receptor binding and reduced NMDA receptor binding in epileptic human hippocampus
Authors: Hosford DA , Crain BJ , Cao Z , Bonhaus DW , Friedman AH , Okazaki MM , Nadler JV , McNamara JO
Published: March 2018

Based on results from the kindling model of epilepsy, we hypothesized that enhanced binding of radioligands to the NMDA receptor and decreased binding to the alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionate (AMPA)-sensitive quisqualate (ASQ) receptor would be found within epileptic hippocampi of humans with complex partial epilepsy (CPE). To test these hypotheses, we used tissue that was surgically removed from patients with intractable CPE, and control tissue that was obtained at autopsy. We used autoradiographic techniques to measure ASQ receptor binding (with 3H-AMPA as the radioligand) and binding to 2 sites on the NMDA receptor/channel complex: the agonist recognition site (with 3H-glutamate) and the phencyclidine (PCP) binding site that resides within the NMDA channel [with 3H-N-(1-[thienyl]cyclohexyl) piperidine (TCP) in the presence of saturating concentrations of NMDA and glycine]. Measurements of receptor binding were corrected for pathologic alterations in neuronal density. Contrary to our expectations, ASQ receptor binding was significantly increased (100%; p less than 0.02) in the dentate gyrus stratum moleculare in patients with CPE (n = 8), and it was unchanged in other hippocampal regions. In nearby sections from the same specimens, binding was significantly decreased to the agonist recognition site of the NMDA receptor in the stratum oriens of area CA3 (46%; p less than 0.05) and was also decreased to the PCP site in the stratum radiatum and stratum oriens of CA3 (44% and 74%, respectively; p less than 0.05). The increase in ASQ receptor binding may contribute to hyperexcitability in these epileptic patients.(ABSTRACT TRUNCATED AT 250 WORDS)
Elimination of the transient ipsilateral retinotectal projection is not solely achieved by cell death in the developing chick
Authors: Williams CV , McLoon SC
Published: March 2018

During development of the projection from the retina to the brain in the chick, a transient ipsilateral retinotectal projection forms and disappears. This disappearance is coincident with a wave of ganglion cell death in the retina. The contribution of cell death to the disappearance of this projection, as opposed to another mechanism such as axon retraction, was examined. Retinal ganglion cells with a projection to the ipsilateral tectum were retrogradely labeled by injection of long-lasting fluorescent dyes into the tectum prior to the onset of ganglion cell death. Large injections of fast blue labeled approximately 1800 ganglion cells in the ipsilateral retina before the period of cell death began. If the injected embryos were allowed to survive past the peak period of ganglion cell death, the average number of labeled ganglion cells in the ipsilateral retina was reduced by somewhat more than half. It is possible that the remaining labeled ganglion cells projected only to nontectal visual nuclei and were labeled by fast blue that had diffused out of the tectum. This was tested by repeating the study using very localized injections of 1,1′- dioctodecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate or fluorescent microspheres into the tectum. These small injections confirmed that cells with transient projections to the ipsilateral tectum survived past the elimination of this projection. Thus, ipsilaterally projecting ganglion cells have, at most, a slightly greater propensity for death than the average ganglion cell, and elimination of the transient ipsilateral retinotectal projection in chick can be explained only, in part, by the mechanism of cell death.(ABSTRACT TRUNCATED AT 250 WORDS)
Residual motion perception in a "motion-blind" patient, assessed with limited-lifetime random dot stimuli
Authors: Baker CL , Hess RF , Zihl J
Published: March 2018

A neurological patient (L.M.) suffering a specific loss of visual motion perception (Zihl et al., 1983) due to extrastriate cortical damage was studied using random dot “limited-lifetime” stimuli with a direction discrimination task. With a stimulus like that of Newsome and Pare (1988), the patient exhibited a severe deficit for motion perception, only being able to perform well for very high values of coherence. Different versions of the stimulus were employed to separate out the effects of limited lifetime versus the effects of additive noise as coherence was lowered. When all “signal” dots had a fixed, specified value of lifetime, and varying percentages of “noise” dots were added, the patient showed a profound deficit. In contrast, a stimulus consisting of no noise dots at all, and signal dots having fixed values of lifetime, revealed relatively good performance for surprisingly brief dot lifetimes. Thus, it is the presence of noisy, incoherent dot motion, rather than brief lifetimes, that causes such poor performance on the stimulus of Newsome and Pare (1988). Most surprising was the finding that the presence of even very small percentages of stationary noise dots was sufficient to disrupt totally direction discrimination of moving signal dots. The findings reported here suggest that one major role of extrastriate cortical processing might be the interpretation of stimuli that suffer from an impaired signal-to-noise ratio; the most commonly encountered form of “noise” would presumably be contamination by irrelevant directional spatio- temporal frequency components.
Characterization and localization of cannabinoid receptors in rat brain: a quantitative in vitro autoradiographic study
Authors: Herkenham M , Lynn AB , Johnson MR , Melvin LS , de Costa BR , Rice KC
Published: March 2018

A potent, synthetic cannabinoid was radiolabeled and used to characterize and precisely localize cannabinoid receptors in slide- mounted sections of rat brain and pituitary. Assay conditions for 3H- CP55,940 binding in Tris-HCl buffer with 5% BSA were optimized, association and dissociation rate constants determined, and the equilibrium dissociation constant (Kd) calculated (21 nM by liquid scintillation counting, 5.2 nM by quantitative autoradiography). The results of competition studies, using several synthetic cannabinoids, add to prior data showing enantioselectivity of binding and correlation of in vitro potencies with potencies in biological assays of cannabinoid actions. Inhibition of binding by guanine nucleotides was selective and profound: Nonhydrolyzable analogs of GTP and GDP inhibited binding by greater than 90%, and GMP and the nonhydrolyzable ATP analog showed no inhibition. Autoradiography showed great heterogeneity of binding in patterns of labeling that closely conform to cytoarchitectural and functional domains. Very dense 3H-CP55,940 binding is localized to the basal ganglia (lateral caudate-putamen, globus pallidus, entopeduncular nucleus, substantia nigra pars reticulata), cerebellar molecular layer, innermost layers of the olfactory bulb, and portions of the hippocampal formation (CA3 and dentate gyrus molecular layer). Moderately dense binding is found throughout the remaining forebrain. Sparse binding characterizes the brain stem and spinal cord. Densitometry confirmed the quantitative heterogeneity of cannabinoid receptors (10 nM 3H-CP55,940 binding ranged in density from 6.3 pmol/mg protein in the substantia nigra pars reticulata to 0.15 pmol/mg protein in the anterior lobe of the pituitary). The results suggest that the presently characterized cannabinoid receptor mediates physiological and behavioral effects of natural and synthetic cannabinoids, because it is strongly coupled to guanine nucleotide regulatory proteins and is discretely localized to cortical, basal ganglia, and cerebellar structures involved with cognition and movement.
Long-lasting potentiation and epileptiform activity produced by GABAB receptor activation in the dentate gyrus of rat hippocampal slice
Authors: Burgard EC , Sarvey JM
Published: March 2018

Bath application of the GABAB receptor agonist baclofen produced a concentration-dependent long-lasting potentiation (LLP) of the evoked population spike in the dentate gyrus of rat hippocampal slices. A high concentration of baclofen (5 microM) also produced a loss of inhibition that was manifested as the appearance of epileptiform, multiple evoked population spikes and a decrease in paired-pulse inhibition. Both baclofen-induced potentiation and epileptiform activity could be blocked or significantly reduced in slices from pertussis toxin-treated animals (1 microgram, intradentate) or in slices pretreated with the NMDA receptor antagonist D-(-)-2-amino-5-phosphonovaleric acid (10 microM). At a concentration that had no significant effect on individual evoked responses (0.1 microM) but still produced a loss in paired-pulse inhibition, baclofen facilitated the induction of beta- adrenergic receptor-mediated LLP. LLP was induced in the dentate gyrus by bath application of 1 microM, but not 0.1 microM, isoproterenol. Coapplication of baclofen and isoproterenol, both at a concentration (0.1 microM) that individually had no effect on the population spike, produced a synergistic LLP of the population spike. We propose that baclofen produces a selective disinhibitory effect in the granule cell layer of the dentate gyrus by inhibiting the activity of GABAergic interneurons. At a low concentration, the subtle loss of inhibition can facilitate the induction of isoproterenol-induced LLP. At a high concentration, baclofen can produce an LLP that is probably induced by a loss of inhibition.
Synaptic actions of identified peptidergic neuron R15 in Aplysia. I. Activation of respiratory pumping
Authors: Alevizos A , Weiss KR , Koester J
Published: March 2018

The purpose of the study described in this and the following two companion papers was to determine the synaptic actions of neuron R15, an endogenously bursting neurosecretory cell in Aplysia, as a step toward determining its physiological function. The results described in this paper demonstrate that activity in R15 increases the frequency of bursting in the R25/L25 network that triggers respiratory pumping. This excitatory modulatory effect appears to be mediated by R15 alpha 1 peptide. R15 activates both strong and weak modes of respiratory pumping. In contrast, the two R20 cells, which are thought to use the neuropeptides SCPA and SCPB as transmitters, elicit only strong episodes of respiratory pumping. The synaptic actions of R15 also differ from those of the R20 cells in being longer lasting and in exhibiting profound desensitization. Chronic recording of R15 activity in vivo indicates that it does not burst spontaneously in the intact animal, so the synaptic actions of R15 are not chronically desensitized. The neuroendocrine bag cells, which initiate egg laying, had been shown by others to excite R15 and the R25/L25 network that triggers respiratory pumping. Our data indicate that the excitatory effects of the bag cells on the R25/L25 cells are mediated in part by R15.
Synaptic actions of identified peptidergic neuron R15 in Aplysia. III. Activation of the large hermaphroditic duct
Authors: Alevizos A , Weiss KR , Koester J
Published: March 2018

The purpose of the study described in this and the preceding two companion papers was to determine the synaptic actions of neuron R15, an endogenously bursting neurosecretory cell in Aplysia, as a step toward determining its physiological function. The results described in this paper demonstrate that activity in R15 activates anterograde peristaltic movements in the segment of the large hermaphroditic duct through which eggs move during egg-laying behavior. This action is mimicked by R15 alpha 1 peptide, a putative transmitter of R15. The neuroendocrine bag cells, which initiate egg laying when they fire in a population burst, have been shown by others to excite R15. Our data suggest that R15 mediates excitatory effects of the bag cells on the large hermaphroditic duct. Taken with the results of the two companion papers, these data support the hypothesis that R15 integrates various aspects of egg-laying behavior. The desensitization of R15's postsynaptic actions may complement the long-lasting refractoriness of the bag cells described by others, with both effects contributing to the episodic nature of egg laying.
Chronic stress-induced acceleration of electrophysiologic and morphometric biomarkers of hippocampal aging
Authors: Kerr DS , Campbell LW , Applegate MD , Brodish A , Landfield PW
Published: March 2018

There is increasing evidence that experimental interventions that alter adrenal corticosteroid plasma concentrations can modulate aging changes in the rodent hippocampus. However, there still is very little evidence that elevation of endogenous corticosteroid levels within physiological ranges, such as occurs during chronic stress, can accelerate hippocampal aging-like changes. In addition, almost all prior intervention studies of corticosteroid effects on brain biomarkers of aging have utilized morphologic measures of aging, and it is not yet clear whether electrophysiologic biomarkers of hippocampal aging can also be accelerated by conditions that elevate corticosteroids. In the present studies, specific pathogen-free rats of three ages (4, 12, and 18 months at the start) were trained for 6 months (4 hr/d, 5 d/week) in a two-way shuttle escape task, using low intensity foot shock. This task induces “anxiety” stress, because animals receive little actual shock, but chronic training in the task has been shown to elevate plasma corticosteroids and to downregulate hippocampal corticosteroid receptors. At the end of 6 months, animals were allowed to recover for 3 weeks and were then assessed in acute, anesthetized preparations on a battery of hippocampal neurophysiological markers known to separate young from aged animals (frequency potentiation, synaptic excitability thresholds, EPSP amplitude). The brains were then fixed and sectioned for quantification of neuronal density in field CA1 (a highly consistent anatomic marker of hippocampal aging). The pattern of stress effects differed considerably across age groups. The two younger stress groups exhibited increased evidence of aging-like neurophysiologic change, but exhibited no indications of accelerated neuronal loss.(ABSTRACT TRUNCATED AT 250 WORDS)
Dopamine content and metabolism in mesencephalic and diencephalic cell cultures: sex differences and effects of sex steroids
Authors: Beyer C , Pilgrim C , Reisert I
Published: March 2018

Sexual differentiation of dopaminergic neurons was studied in gender- specific cultures. Dissociated cell cultures were prepared from di- or mesencephalon of gestational day 14 rat embryos and raised in the absence or presence of 17 beta-estradiol or testosterone for up to 13 days in vitro (DIV). Developmental profiles of levels of dopamine (DA) and metabolites as well as capacity for vesicular storage of the transmitter were determined by HPLC. Tyrosine hydroxylase- immunoreactive (TH-IR) neurons were counted. Higher levels of DA were measured in female than in male cultures of both brain regions. In mesencephalic cultures, the differences in DA levels were fully accounted for by sex differences in numbers of TH-IR cells, whereas no sex differences in cell numbers were found in diencephalic cultures. Dihydroxyphenylacetic acid (DOPAC) levels and vesicular storage capacity matured faster in mesencephalic than in diencephalic cultures, but no sex differences were observed. Homovanillic acid (HVA) could not be detected except in 13-DIV mesencephalic cultures. Hormonal treatment did not erase sexual differentiation of dopaminergic neurons. Irrespective of the gender, however, both steroids decreased DA and DOPAC contents in diencephalic cultures but not in mesencephalic cultures. It is proposed that sexual differentiation of dopaminergic systems proceeds in a region-specific fashion and that neurogenesis and development of various parameters of dopaminergic activity may be differentially affected. Sexual differentiation of dopaminergic neurons may be initiated independently of the action of gonadal steroid hormones and may subsequently be modified by differences in hormonal environment.
Distribution of dihydropyridine and omega-conotoxin-sensitive calcium currents in acutely isolated rat and frog sensory neuron somata: diameter-dependent L channel expression in frog
Authors: Scroggs RS , Fox AP
Published: March 2018

Calcium channel subtypes in adult rat and frog sensory neuron somata, acutely isolated from dorsal root ganglia (DRG neurons), were studied using Bay K 8644, nimodipine, and omega-conotoxin GVIA (omega-CgTx) as specific probes. The DRG neurons varied in diameter 15-60 microns (rat) and 20-80 microns (frog). Bay K 8644 produced a large increase in calcium currents of small-diameter rat DRG neurons and shifted channel activation and the peak of the I-V curve in the hyperpolarizing direction. At a physiological holding potential (HP) of -60 mV, nimodipine blocked 50% of the peak calcium current in small-diameter frog and rat DRG neurons, indicating a large L channel component. At HP -80 mV, nimodipine blocked a lower percentage of peak current in small- diameter rat and frog DRG neurons than expected (based on experiments at HP -60 mV) probably due to nimodipine's voltage dependence. At HP - 60 mV, omega-CgTx blocked 25% and 50% of peak current in small-diameter rat and frog DRG neurons, respectively. Omega-CgTx blocked a larger percentage of current at HP -80 mV than at -60 mV, probably because of the repriming of N channels. Observation of nimodipine- and Bay K 8644- sensitive calcium current in small-diameter rat and frog DRG neurons after omega-CgTx treatment, suggests that omega-CgTx is not a potent L channel blocker. The combination of omega-CgTx and nimodipine blocked all current in small-diameter frog DRG neurons but left a small portion of current unblocked in small-diameter rat DRG neurons at HP -60 mV, suggesting the possibility of omega-CgTx- and nimodipine-insensitive calcium channels in rat DRG neurons. Calcium current in most large- diameter frog DRG neurons was insensitive to nimodipine, but was completely blocked by omega-CgTx. This indicates significant variation in the expression of calcium channel subtypes in small- and large- diameter frog DRG neurons, which may subserve different sensory modalities.
Specific monosynaptic sensory-motor connections form in the absence of patterned neural activity and motoneuronal cell death
Authors: Mendelson B , Frank E
Published: March 2018

The importance of neural activity and motoneuronal cell death in the formation of specific synaptic connections between muscle afferents and motoneurons was studied in chick embryos. Patterned neural activity was blocked by applying d-tubocurarine (dtc) chronically to embryos during the period when sensory-motor connections are formed [stages (St) 28– 42]. Dtc blocks neurogenic muscle contractions, thereby abolishing any temporal correlation between neural activity in motoneurons and stretch- sensitive afferents. The normal pattern of motoneuronal bursting is also blocked (Landmesser and Szente, 1986), as is motoneuronal cell death (Pittman and Oppenheim, 1979). Dtc applications were started more than 1 d before muscle sensory afferent collaterals make anatomical contact with motoneuronal dendrites and continued until St 38–42, when the pattern of synaptic connectivity was examined by recording synaptic potentials intracellularly from identified lumbosacral motoneurons upon stimulation of identified populations of muscle afferents. In both normal and dtc-treated animals, large monosynaptic excitatory potentials were evoked in homonymous motoneurons (those that supply the same muscle as the sensory afferents) and were often observed in motoneurons that supplied synergistic muscles. Monosynaptic potentials were uncommon in motoneurons supplying antagonistic muscles. The overt patterns of sensory-motor connections in normal and dtc-treated embryos were essentially identical. However, the amplitudes of the composite EPSPs recorded in dtc-treated animals were consistently about twice as large as normal. These observations suggest that neither normal patterns of neuronal activity nor motoneuronal cell death play a large role in determining the specificity of connections between the sensory and motor neurons involved in the stretch reflex.
Imaging of synaptically evoked intrinsic optical signals in hippocampal slices
Authors: MacVicar BA , Hochman D
Published: March 2018

Imaging analysis techniques were used to examine changes in the intrinsic optical properties in hippocampal brain slices that occurred during synaptic activity evoked by Schaffer collateral stimulation in CA1. Repetitive synaptic activity was associated with an increase in light transmission in the synaptic region in stratum radiatum. The effect was seen at wavelengths of light between 450 and 800 nm but was of greater amplitude at longer wavelengths. Blocking synaptic transmission with either Ca(2+)-free EGTA perfusate or kynurenic acid (an excitatory amino acid antagonist) blocked the optical signal, indicating that it resulted from postsynaptic activation of the cells and was not due to presynaptic fiber volleys or transmitter release alone. Because the optical changes were blocked by reducing extracellular Cl- (by replacement with gluconate) or by furosemide (an anion transport inhibitor), increased Cl- transport (conceivably Na-K- 2Cl cotransport) may generate these signals possibly by causing cellular swelling and thereby less light scattering. These optical changes were not blocked, however, by bicarbonate-free solution, indicating that bicarbonate transport may not be involved. Changes in the intrinsic optical signal could be related to glial swelling due to K+ released during neuronal activity because high-K(+)-induced swelling of cultured astrocytes is blocked by furosemide and low-Cl- solution. Intrinsic optical signals of neuronal tissue should be considered when voltage- or ion-sensitive dyes are used.
Wocko, a neurological mutant generated in a transgenic mouse pedigree
Authors: Crenshaw EB , Ryan A , Dillon SR , Kalla K , Rosenfeld MG
Published: March 2018

Naturally occurring mutations involving the nervous system have provided virtually all of our current understanding of the genetic regulation of neural development (Caviness and Rakic, 1978). The difficulty of isolating the corresponding genes, however, has precluded a molecular analysis of these mutants. Insertional mutagenesis, induced by microinjection of DNA into fertilized ova to produce transgenic animals, provides a molecular tag that marks the site of the mutational event. In this article, we describe a transgenic neurological mutation, designated wocko (Wo), which disrupts the development of the inner ear. These mutant mice display a dominant behavioral phenotype that consists of circling, hyperactivity, and head tossing, reminiscent of the shaker/waltzer class of mutants, and they display a recessive homozygous sublethal phenotype. Anatomical analyses showed that both structural and neural components of the vestibular system were disrupted, while analyses of mutant fetuses showed that these morphological abnormalities were due to aberrant development. Although low levels of transgene expression were detected using a sensitive PCR assay, several nonmutant pedigrees that contain the same construct also expressed the transgene in the inner ear, suggesting that low levels of transgene expression alone were not responsible for the wocko phenotype. Because the integrated transgene provides a marker to clone the wocko mutation, the analysis of this mutant will give unique insight into the molecular genetics of inner ear development and into a broad class of neurological mutations that affect the inner ear.
Septal arginine vasopressin (AVP) receptor regulation in rats depleted of septal AVP following long-term castration
Authors: Poulin P , Pittman QJ
Published: March 2018

Arginine vasopressin (AVP) causes severe motor disturbances, including barrel rotations and myotonic/myoclonic convulsions, following repeated injections into either a lateral cerebral ventricle or the ventral septal area (VSA) of the rat brain. Because the AVP content of the rat septal area has been shown to be virtually eliminated following long- term castration, and because removal of a receptor ligand typically results in receptor upregulation and behavioral supersensitivity to the ligand, we tested the hypothesis that long-term castrated rats may be supersensitive to the motor actions caused by centrally injected AVP and may have upregulated septal AVP receptors. In these experiments, adult male Wistar rats were used 5 months after castration or, as controls, after sham castration. The effectiveness of long-term castration in eliminating AVP content of the VSA was indicated by the observation that a priming hypertonic saline stimulus (known to induce the central release of AVP and sensitize the rat brain) sensitized the brains of sham control rats but not of the castrated rats to the motor actions of a subsequent intracerbroventricular injection of AVP. The motor actions of centrally injected AVP, as well as septal AVP receptor characteristics (number and affinity), and AVP-stimulated phosphoinositide (PI) hydrolysis were then investigated in long-term castrated and sham control rats. Motor disturbances induced by either a first or a second injection of AVP were not greater in long-term castrated rats than in sham controls.
Transient and persistent expression of NT-3/HDNF mRNA in the rat brain during postnatal development
Authors: Friedman WJ , Ernfors P , Persson H
Published: March 2018

Neurotrophin-3 (NT-3) is closely related to two known neurotrophic agents, NGF and brain-derived neurotrophic factor (BDNF), and acts upon overlapping, yet distinct, populations of peripheral ganglia. NT-3 mRNA expression in the adult rat brain is largely confined to the hippocampus. In this study, we have used in situ hybridization to examine expression of this novel neurotrophic factor during postnatal development. The striking observation was made that NT-3 mRNA was transiently expressed at high levels in the cingulate cortex during the first 2 weeks of age. In the hippocampus, the adult pattern of expression, in the CA2, medial CA1, and granule layer of the dentate gyrus, was detected at all ages examined. However, there were two major differences in NT-3 mRNA expression in the developing hippocampus: Labeled cells were detected in the hilar region of the dentate gyrus at postnatal day 1 (P1) and 1 week that were absent by 2 weeks of age. Further, the caudal hippocampus, which has a lower intensity of labeling than the rostral region in the adult, was devoid of NT-3- expressing cells in the P1 and 1-week-old rat brain. These data indicate a substantial plasticity in NT-3 mRNA expression and suggest that the spectrum of neurons supported by NT-3 during development is partially different from that in the mature rat brain.
The effects of serotonin depletion and raphe grafts on hippocampal electrophysiology and behavior
Authors: Richter-Levin G , Segal M
Published: March 2018

The involvement of the serotonergic system in spatial learning and a possible correlation between serotonergic modulation of hippocampal electrical activity and spatial learning were studied in rats. Control, partial septal-lesioned (SL), 5,7-dihydroxytryptamine (5,7-DHT)- injected (DHT), double-lesioned (5,7-DHT and SL; DL), and DL rats that were transplanted with embryonic raphe grafts into the hippocampus (RG) were tested in a spatial task in a water maze and in an active avoidance shuttle-box task. The responses of the dentate gyrus (DG) to perforant-path (PP) stimulation were examined in the same rats, under the following conditions: (1) priming stimulation of the PP (testing feedback inhibition), (2) priming stimulation of the commissural pathway (testing feedforward inhibition), (3) during repeated stimulation of the PP at 7 Hz (frequency potentiation), and (4) following tetanic stimulation [long-term potentiation (LTP)]. DL, but not DHT or SL, treatment severely impaired the performance of rats in both reference- and working-memory tasks in the water maze. This effect was not seen in the shuttle box. The ability of the DG to exhibit LTP, which was reduced in the DHT and SL rats, was apparently similar to controls in the DL group, DL, but not DHT or SL alone, resulted in a reduction of inhibition in the DG. Both the behavioral deficits and the reduction in hippocampal inhibition were ameliorated by intrahippocampal raphe grafts. These results indicate that the serotonergic innervation of the hippocampus plays a role in spatial learning when the septohippocampal neurotransmission systems are disrupted. Furthermore, these results suggest that restoration of modulation of hippocampal inhibition, by raphe grafts, underlies the behavioral recovery observed in these rats.
Modulation of calcium-activated potassium channels from rat brain by protein kinase A and phosphatase 2A
Authors: Reinhart PH , Chung S , Martin BL , Brautigan DL , Levitan IB
Published: March 2018

By incorporating plasma membrane vesicles into planar lipid bilayers, we previously characterized a family of four types of Ca(2+)-activated K+ channels from rat brain (Reinhart et al., 1989). Two of these are “large-conductance” or “maxi”-K+ channels, which differ in their gating kinetics and toxin sensitivity and are henceforth referred to as “type 1” and “type 2” channels. Here we show that the gating of these two channel types can be modulated by phosphorylation and dephosphorylation. The effects of cAMP-dependent protein kinase catalytic subunit (PK-A) on type 1 maxi-K+ channels are complex in that, while half of these channels are upregulated by the kinase, about one out of seven channels is downregulated. Thus, there may be several distinct channels within the type 1 category. Type 2 maxi-K+ channels are consistently downregulated by PK-A. The effects of PK-A on both channel types are reversed by the catalytic subunit of protein phosphatase 2A (PP-2A), but not by protein phosphatase 1 (PP-1). Furthermore, some of the type 1 maxi-K+ channels can be modulated by PP- 2A, even without any prior PK-A treatment, indicating they are in a phosphorylated state when they are incorporated into the bilayer. The results demonstrate that (1) type 1 and type 2 maxi-K+ channels are substrates for PK-A; (2) phosphorylation can shift the open probability of channels in either direction, by a mechanism involving multiple phosphorylation sites; (3) phosphorylation alters the Ca2+/voltage sensitivity of these channels; and (4) dephosphorylation of type 1 and type 2 channels is catalyzed by specific phosphatases.
Differential intracellular calcium responses to glutamate in type 1 and type 2 cultured brain astrocytes
Authors: Jensen AM , Chiu SY
Published: March 2018

Fluorescence image analysis using the calcium indicator fluo-3 was used to examine changes in [Ca2+]i induced by glutamate in mixed glia populations cultured from neonatal rat brains. [Ca2+]i responses were correlated with glia type by performing immunohistochemistry using markers specific for type 1 and type 2 astrocytes on the same cells used in the imaging experiments. Glutamate (30–500 microM) induced two markedly different [Ca2+]i responses in the two astrocyte types: the response in type 1 astrocytes consisted of an initial fast transient followed by varying degrees of oscillations, whereas the predominant response in type 2 astrocytes was a slow rise in [Ca2+]i to a more or less sustained and nonoscillatory level. In some type 2 astrocytes, an initial spikelike transient similar to that in type 1 astrocytes was observed; the overall size of the spike, however, was smaller than in type 1 astrocytes. Two agonists for the ionotropic glutamate receptor, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) and kainate, elicited a 6-cyano-7-dinitroquinoxaline-2,3-dione (CNQX)- sensitive, external Ca(2+)-dependent, sustained [Ca2+]i rise in type 2 but not type 1 astrocytes. The initial spike in type 2 astrocytes was less dependent on external Ca2+ and not blocked by CNQX. [Na+]i as measured by the Na(+)-fluorescence dye SBFI, was elevated by kainate in both astrocyte types, though the increase was larger in type 2 astrocytes. This increase was reduced by CNQX, suggesting this [Ca2+]i increase was mediated, at least in part, by ionotropic glutamate receptors. The results are discussed in terms of the relative distribution of two classes of glutamate receptors on these two astrocyte types: one, the ionotropic class, is linked directly to an ion channel, and the other, the metabotropic class, induces internal mobilization of Ca2+ via inositol phospholipid hydrolysis.