bluuebunny/crossref_metadata_2025 huggingface dataset:
Omega-conotoxin GVIA binding to a high-affinity receptor in brain: characterization, calcium sensitivity, and solubilization
Authors: Wagner JA , Snowman AM , Biswas A , Olivera BM , Snyder SH
Published: March 2018

We describe unique, high-affinity binding sites for omega[125I]conotoxin GVIA in membranes from rat brain and rabbit sympathetic ganglia which appear to be primarily associated with N-type voltage-dependent calcium channels. The dissociation constant (KD) for the toxin in rat brain membranes is 60 pM. Physiologic extracellular concentrations of calcium inhibit toxin binding noncompetitively (IC50 = 0.2 mM). The regional distribution of the binding sites in rat brain differs markedly from that of dihydropyridine calcium antagonist receptors associated with L-type calcium channels. In detergent- solubilized brain membranes, toxin binding retains the same affinity, specificity, and ionic sensitivity as in particulate preparations.
Expression of calcium/calmodulin-dependent protein kinase in relation to dopamine islands and synaptic maturation in the cat striatum
Authors: Newman-Gage H , Graybiel AM
Published: March 2018

During pre- and postnatal development the dopamine-containing nigrostriatal afferents of the striatum are arranged as a conspicuous series of patches (the “dopamine islands”). The development of this dopamine island system, which metamorphoses in early postnatal life to the striosomal architecture of the adult, has recently received considerable attention, but the factors initiating and influencing maturation of this architecture are largely unknown. In an attempt to clarify the relationships between the onset of clustering of dopamine- containing afferents, the grouping of neurons within future striosomes and the maturation of synapses in the striatum, we compared the initial prenatal appearance and subsequent development of immunohistochemical markers for the dopamine-containing innervation [tyrosine hydroxylase (TH)-like immunoreactivity], for synaptic vesicles (SV48-like immunoreactivity), and for a phosphorylation-related enzyme Ca2+/calmodulin-dependent protein kinase type II (CaM kinase II-like immunoreactivity) that is expressed in virtually all striatal neurons by adulthood. Here we present evidence that during striatal ontogeny, both neurons and neuropil expressing CaM kinase II-like immunoreactivity and SV48-positive terminals form discrete patches that are in register with dopamine islands. It is CaM kinase II-positive elements, however, rather than the TH-positive island fibers (or SV48- positive synapses), that initially form overt clusters. Dopamine- containing fibers begin to innervate the striatal anlage just prior to embryonic day (E) 32. Their distribution follows the general lateral to medial developmental gradient characteristic of the striatum but is not yet distinctly islandic. At this time, CaM kinase II-like immunoreactivity was very weak or not present at all and SV48-like immunoreactivity was undetectable. By E36, CaM kinase II-positive neurons are visible in discrete patches of immunopositive neuropil, but only faint inhomogeneities are detectable in the distribution of TH- positive fibers and scarcely any SV48-like immunoreactivity can be seen. By E45, all 3 markers are focused in typical islandic patterns, and they remain so into the early postnatal period. These observations suggest a developmental sequence in which dopamine-containing fibers invade the striatal anlage prior to forming distinct islandic foci and prior to the maturational events signaled by the production of CaM kinase II within the neurons and neuropil of future striosomes.(ABSTRACT TRUNCATED AT 400 WORDS)
Mu and delta opiate receptors coupled negatively to adenylate cyclase on embryonic neurons from the mouse striatum in primary cultures
Authors: Chneiweiss H , Glowinski J , Premont J
Published: March 2018

Primary cultures of pure populations of neuronal or glial cells from the striatum, the cerebral cortex, and the mesencephalon of the mouse embryo were used to look for the presence of opiate receptors coupled to adenylate cyclase. Leu-enkephalin inhibited cAMP production in membranes of embryonic striatal neurons but not in those of other cell types examined. Mu and delta opiate receptors seemed to be coupled negatively to adenylate cyclase in embryonic striatal neurons. It was found that DTLET (a selective delta agonist), as well as DAGO (a selective mu agonist), inhibited cAMP production on these cells. DTLET but not, however, DAGO produced a similar effect on homogenates from the adult rat striatum and on membranes from the neuroblastoma x glioma hybrid cell line NG 108–15, two preparations known to possess only delta receptors negatively coupled to adenylate cyclase. The selective kappa agonist U 50.488 was ineffective on all types of membrane preparations used. The inhibitory effects of both DTLET and DAGO on basal adenylate cyclase activity in striatal neurons were reversed by naloxone with a similar efficacy. Two other selective mu agonists, trimu 5 and morphiceptin, inhibited cAMP production in membranes of striatal neurons as well. The nonadditivity of the inhibitory effects of DTLET and DAGO on basal or forskolin-induced activation of adenylate cyclase suggested that mu and delta receptors were colocalized on a similar subpopulation of striatal cells in primary culture. These cells possess dopaminergic receptors of the D1 subtype as well since the amplitude of the inhibitory effects of DTLET and DAGO on cAMP production was increased in the presence of dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)
Desensitization of acetylcholine receptors in rat myotubes is enhanced by agents that elevate intracellular cAMP
Authors: Middleton P , Rubin LL , Schuetze SM
Published: March 2018

Incubating skeletal muscle fibers with forskolin, an activator of adenylate cyclase, increases the rate at which nicotinic acetylcholine receptors (AChRs) desensitize when exposed to ACh. Several reports indicate that this is due to the phosphorylation of AChRs by cAMP- dependent protein kinase, but other studies suggest that forskolin interacts with AChRs directly and that second-messenger systems are not required. To help clarify this issue, we studied the effects of forskolin and several other drugs on AChR function in embryonic rat myotubes. AChR function was studied by recording ACh-induced membrane depolarizations and ACh-induced single-channel currents. Our results indicate that forskolin at low concentrations enhances AChR desensitization through the action of a second messenger, most likely cAMP. An analog of forskolin that is much less effective in activating adenylate cyclase (1,9-dideoxyforskolin) is also much less potent in enhancing desensitization. Forskolin at low concentrations does not alter single-channel conductance or mean channel open time. However, when used at concentrations above 20 microM, forskolin may also exert direct drug effects on AChRs.
Fast axonal transport of modulatory neuropeptides from central ganglia to components of the feeding system in Aplysia
Authors: Lloyd PE
Published: March 2018

The transport of neuropeptides from central ganglia to components of the feeding system was studied in Aplysia. Peptide transport was determined by incubating buccal or cerebral ganglia with 35S-methionine and measuring the appearance of labeled peptides by high-pressure liquid chromatography (HPLC) of extracts of target tissues. Selected nerves were left intact and passed through a Vaseline diffusion barrier separating the ganglia and their targets. Five major labeled peptides were observed to be transported from the buccal ganglia to feeding muscles. They were buccalin, FMRFamide, myomodulin, and 2 small cardioactive peptides. Each of these peptides has been shown to modulate the responses of these muscles to their motor neurons. The peptides were transported by fast axonal transport, as judged by the distance transported and the sensitivity to colchicine. When normalized to correct for differences in total incorporation, the patterns of peptide transport were reproducible between animals. The nature and amount of the peptides transported were different for different muscles. The nature of peptide transport also varied for different nerve groups. These results support the proposition that these 5 peptides act as modulatory transmitters at feeding muscles. No transport of neuropeptides from the cerebral ganglia to feeding muscles was observed, although myomodulin was specifically transported to the buccal ganglia. This suggests that this peptide may play an important role in the previously observed regulation of buccal ganglia activity by neurons in the cerebral ganglia.
Laminar organization and contrast sensitivity of direction-selective cells in the striate cortex of the Old World monkey
Authors: Hawken MJ , Parker AJ , Lund JS
Published: March 2018

The directional preference of neurons sampled from all layers of the striate cortex was determined using the responses to drifting grating stimuli of optimal spatial and temporal frequency. In addition, contrast sensitivity as a function of spatial frequency was measured and from the resulting spatial contrast sensitivity function the peak contrast sensitivity and optimal spatial frequency were obtained. The distribution of directionally selective cells showed a distinct laminar pattern. Upper layer 4 (4a, 4b, and 4c alpha) and layer 6 were the only cortical layers with neurons that showed a pronounced preference for the direction of stimulus motion. The directionally selective cells in these layers are among those with the highest contrast sensitivities but had optimal spatial frequencies that were confined to the low and middle range of the optimal spatial frequency distribution. These findings suggest that the directionally selective cells may fall into at least 2 distinct populations, which may be the first stages in the visual pathway that correspond to those channels, inferred from psychophysical experiments, that underlie the detection of movement.
Dendritic amputation redistributes sprouting evoked by axotomy in lamprey central neurons
Authors: Hall GF , Cohen MJ
Published: March 2018

In the previous paper (Hall and Cohen, 1988), we showed that axotomy of anterior bulbar cells (ABCs) in the hindbrain of the larval lamprey results in the sprouting of axonlike neurites from either the end of the proximal axon stump, the dendritic tips, or both, depending on the site of axotomy. Here we show that, unlike axotomy, dendritic amputation (dendrotomy) does not by itself induce sprouting from ABCs. However, dendrotomy does induce sprouting from dendrites in the immediate vicinity of the dendritic lesion in cells that have been previously axotomized. We found that dendrotomy acts primarily to rearrange the distribution of sprouts induced by axotomy rather than serving as an additional stimulus to neurite outgrowth. We propose that (1) dendritic sprouting in ABCs occurs because the dendritic tips become attractive sites for sprout initiation when they are either directly injured (as with dendrotomy) or are situated relatively close to the site of injury (as with axotomy close to the soma), and (2) the axon stump, dendritic stumps, and uninjured dendritic tips of the cell compete to initiate a limited total amount of sprouting induced by axotomy. The probability that a given locus will support sprouting is determined both by its proximity to the nearest lesion site and by whether there are other attractive potential sprouting sites in the cell.
Biological activities of nerve growth factor bound to nitrocellulose paper by Western blotting
Authors: Pettmann B , Manthorpe M , Powell JA , Varon S
Published: March 2018

We have previously developed a cell-blot technique to visualize directly in tissue extracts molecules that display the biological activity of ciliary neuronotrophic factors (CNTFs). This technique involves SDS-PAGE of the tissue extract, Western blotting on nitrocellulose paper, neuronal cell culture on the paper, and, using a vital dye, visualization of the neurons that selectively survive on the trophic factor band. In this report, we show that (1) NGF, either purified or in a crude extract from submaxillary glands, can also be successfully recognized using a slightly modified cell-blot technique; (2) a variety of ganglionic neurons can respond to distinct nitrocellulose-anchored trophic factors; (3) while CNTF and NGF can both support the survival of their common target cells, only NGF also promotes neuritic extension; and (4) both the dimeric and the monomeric forms of immobilized beta-NGF are active.
Voltage-clamp analysis of sodium channels in wild-type and mutant Drosophila neurons
Authors: O'Dowd DK , Aldrich RW
Published: March 2018

In this study we describe a preparation in which we examined directly, using tight-seal whole-cell recording, sodium currents from embryonic Drosophila neurons maintained in culture. Sodium currents were expressed in approximately 65% of the neurons prepared from wild-type Drosophila embryos when examined at room temperature, 24 hr after plating. While current density was low, other features of the sodium current in wild-type neurons, including the voltage sensitivity, steady- state inactivation, macroscopic time course, and TTX sensitivity were similar to those found in other excitable cells. Physiological and biochemical evidence has led to the suggestion that mutations in the nap, seizure, and tip-E loci of Drosophila may affect voltage-dependent sodium channels. There was no significant difference in the percentage of neurons expressing sodium currents in cultures prepared from embryos with mutations at the nap, sei or tip-E loci compared with wild-type cultures. Sodium currents recorded from napts appeared similar in all of the properties examined to those in wild-type cells. However, neuronal sodium current density was 40–60% lower in cultures prepared from both tip-E and seits1 embryos. The voltage dependence and gating properties of these sodium channels, as well as the TTX sensitivity, appear similar to wild type. These results indicate that both the tip-E and sei loci are important in regulation of sodium current density in embryonic neurons.
Activation of locus coeruleus from nucleus paragigantocellularis: a new excitatory amino acid pathway in brain
Authors: Ennis M , Aston-Jones G
Published: March 2018

Recent anatomic and physiologic experiments revealed that a major afferent to the nucleus locus coeruleus (LC) is the nucleus paragigantocellularis (PGi) in the rostral ventrolateral medulla (Aston- Jones et al., 1986). In the present studies, responses of LC neurons to electrical activation of PGi were characterized in anesthetized rats. Low-intensity stimulation of PGi synaptically activated 73% of LC neurons at short latencies (mean onset, 11.3 msec), while a smaller population (16%) of LC neurons exhibited purely inhibitory responses. The excitatory transmission from PGi to LC was pharmacologically analyzed, revealing it to be resistant to cholinergic receptor antagonism, but completely abolished by the excitatory amino acid (EAA) antagonists kynurenic acid and gamma-D-glutamylglycine. The specific N- methyl-D-aspartate antagonist 2--amino-7-phosphonoheptanoic acid (AP7) and the preferential quisqualate receptor antagonist glutamate diethyl ester (GDEE) did not block LC responses to PGi stimulation, leading us to the tentative conclusion that EAAs may operate primarily at a kainate-type receptor on LC neurons to effect excitation from PGi. In addition to their blockade of PGi-evoked activity, kynurenic acid and DGG exerted a similar, simultaneous blockade of the characteristic excitation of LC neurons evoked by electrical stimulation of the hindpaw. These and other results indicate that the proposed EAA pathway from PGi may serve as a final link in a variety of sensory inputs to LC.
Response-dedicated trigger neurons as control points for behavioral actions: selective inhibition of lateral giant command neurons during feeding in crayfish
Authors: Krasne FB , Lee SC
Published: March 2018

Feeding behavior suppresses lateral giant neuron-mediated escape behavior in crayfish. The suppression appears to result from reduced transmission to the lateral giants from primary afferents and/or sensory interneurons, while the operation of sensory and motor networks themselves is unaffected. It is suggested that control occurs at the level of the lateral giants because these neurons are pivotal in, and dedicated solely to, producing the type of escape that needs to be controlled. It is hypothesized that response-dedicated sets of neurons that play a similar role will probably be found wherever it is necessary to control particular responses selectively.
Evidence for the presence of serotonergic nerves and receptors in the iris-ciliary body complex of the rabbit
Authors: Tobin AB , Unger W , Osborne NN
Published: March 2018

The rabbit iris-ciliary body contains 78 +/- 6 ng/gm serotonin (5-HT) while the amine content in the aqueous humor is less than 0.01 ng/100 microliter. The low levels of endogenous 5-HT in the iris-ciliary body could not be directly detected by immunocytochemistry. However, pretreatment in vivo and in vitro with L-tryptophan and pargyline resulted in the localization of a sparse population of 5-HT fibers. These fibers could not be studied by exposing the tissue to exogenous 5- HT since the amine was taken up by noradrenergic fibers as well. This was confirmed in studies involving superior cervical ganglionectomy. It is concluded that 5-HT is taken up by both serotonergic and adrenergic fibers of the iris-ciliary body. In the presence of lithium, 5-HT stimulated an increase in the 3H-inositol phosphate accumulation in a dose-dependent manner in tissue where the phosphoinositide pool was labeled with 3H-inositol. A variety of agonists and antagonists were used to show that the 5-HT response is mediated, at least partly, by 5- HT2 receptors. The 5-HT-mediated effect on inositol phosphates is unaffected by superior cervical ganglionectomy. The effect of noradrenaline, which also stimulates inositol phosphate accumulation (but via alpha 1-adrenergic receptors in the iris-ciliary body), was elevated following superior cervical ganglionectomy.
Modulation of excitatory synaptic transmission by glycine and zinc in cultures of mouse hippocampal neurons
Authors: Forsythe ID , Westbrook GL , Mayer ML
Published: March 2018

The monosynaptic EPSP between cultured hippocampal neurons is mediated by activation of 2 classes of excitatory amino acid receptors. Kainate or quisqualate receptors generate a fast conventional EPSP, while NMDA receptors mediate a slow, voltage-sensitive EPSP. Recently, 2 substances have been shown to modulate the activity of the NMDA receptor-channel complex: glycine increases the probability of channel opening, while zinc acts as a noncompetitive antagonist. Since these substances are present in the CNS and thus may function as neuromodulators, we have examined their role in excitatory synaptic transmission in hippocampal cultures using the whole-cell-patch- recording technique. The slow, NMDA-receptor-mediated EPSP was strikingly dependent on the presence of a conditioning substance that gradually accumulated in the extracellular fluid during a 30 min incubation in physiological saline. Washout of the conditioned medium eliminated the slow EPSP, and perfusion with physiological saline containing 1 microM glycine restored the slow EPSP to control levels. Furthermore, conditioned medium collected from astroglial-only cultures also potentiated the response to NMDA. Zinc (20–50 microM) overcame the potentiation of the response by glycine and resulted in a reversible block of the slow EPSP, providing the first evidence for a direct action of zinc on excitatory synaptic transmission. Our results show that the expression of the slow EPSP may be subject to regulation by several endogenous substances: positive modulation by glycine (or a glycine-like substance), which can be released from astroglial cells, and negative modulation by physiological levels of zinc.(ABSTRACT TRUNCATED AT 250 WORDS)
Presynaptic actions of carbachol and adenosine on corticostriatal synaptic transmission studied in vitro
Authors: Malenka RC , Kocsis JD
Published: March 2018

The purpose of this study was to identify, in the in vitro rat neostriatal slice preparation, an electrophysiological response corresponding to the activation of striatal neurons by cortical afferents, and to study the actions of a variety of putative neurotransmitters on modulating synaptic transmission at this synapse. Local stimulation of the neostriatal slice evokes a field potential composed of 2 prominent negativities. Experiments using calcium antagonists and tetrodotoxin indicate that the first negativity (N1) reflects the direct activation of intrinsic neurons and axons, while the second negativity (N2) is synaptically mediated. The afferent fibers eliciting the second negativity have not previously been identified because of the mixing of afferents within the striatum. However, similar field potential responses are elicited by stimulation of the corpus callosum, in which the only striatal afferents are crossed corticostriatal fibers. Kynurenate, gamma-D-glutamylglycine, and piperidine dicarboxylate all reversibly reduced or abolished N2, suggesting that the transmitter generating the response is an excitatory amino acid. Together, these results strongly suggest that N2 reflects activation of striatal neurons by corticostriatal afferents. Three putative striatal neurotransmitters, dopamine, acetylcholine and adenosine, were studied with respect to their ability to modulate the corticostriatal response. Dopamine had minimal effects on the waveform of the field potential. In contrast, carbachol or adenosine consistently reversibly reduced or eliminated N2. Atropine blocked carbachol's actions, while theophylline blocked adenosine's actions, indicating that the compounds were acting on muscarinic and adenosine receptors, respectively. To test whether these were primarily pre- or postsynaptic actions, we recorded the response to ionophoretically applied glutamate while simultaneously recording the synaptically evoked field potential from the same location.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of lesions of temporal-parietal junction on perceptual and attentional processing in humans
Authors: Robertson LC , Lamb MR , Knight RT
Published: March 2018

When stimuli with larger forms (global) containing smaller forms (local) are presented to subjects with large lesions in the right hemisphere, they are more likely to miss the global form than the local form, whereas subjects with large lesions in the left are more likely to miss the local than the global form. The present study tested whether the global/local impairment in subjects with posterior lesions was due to deficits in controlled attentional processes, passive perceptual processes, or both. Attentional control was examined by measuring reaction time changes when the probability of a target appearing at either the global or local level was varied. Patients with unilateral right or left lesions centered in temporal-parietal regions and age-matched controls served as subjects. Because neurophysiological and neuropsychological evidence have implicated temporal regions in visual discrimination and inferior parietal regions in the allocation of attention to locations in the visual field, patients with left hemisphere lesions were further subdivided into those with lesions centered in the superior temporal gyrus (LSTG) or rostral inferior parietal lobule (LIPL). Patients with right hemisphere injury could not be analogously subdivided. The results revealed that the LSTG group was able to control the allocation of attention to global and local levels normally, while the LIPL group was not. In contrast, the LSTG group showed a strong baseline reaction time advantage toward global targets, while normals and the LIPL group showed no advantage toward one level or the other. Finally, the perceptual component was affected differentially by lesions in the right hemisphere and LSTG, with lesions in the left favoring global targets and lesions in the right favoring local targets. These findings indicate that the hemispheric global/local asymmetry is due to a perceptual mechanism with a critical anatomical locus centered in the STG.
Glycine potentiates strychnine-induced convulsions: role of NMDA receptors
Authors: Larson AA , Beitz AJ
Published: March 2018

Strychnine poisoning leads to seizures that have traditionally been attributed to competitive antagonism of glycine receptors in the spinal cord. Although glycine is thought to act as an inhibitory neurotransmitter, a strychnine-insensitive glycine (Gly2) receptor has been recently described in cultured mouse neurons that is thought to be allosterically linked to the excitatory amino acid NMDA receptor. The present study demonstrates that intrathecally administered glycine, in contrast to other putative inhibitory transmitters, potentiates rather than inhibits strychnine-induced convulsions in mice. The seizure- potentiating effects of glycine are blocked by aminophosphonovaleric acid, an NMDA antagonist. In addition, in animals pretreated with a subconvulsive dose of strychnine to block strychnine-sensitive glycine receptors (Gly1), glycine enhances, rather than inhibits, NMDA-induced convulsions. Together, these results indicate that the seizure- potentiating effects of glycine involve activation of NMDA receptors. This study provides the first evidence that glycine is capable of modulating the activity of NMDA receptors in the spinal cords of adult animals. In light of the elevated concentrations of glycine found in epileptogenic brain foci, these data also suggest that glycine may be a positive modulator in the production of epileptic seizures.
The voltage-dependent, slow inward current induced by the neuropeptide FMRFamide in Aplysia neuron R14
Authors: Ichinose M , McAdoo DJ
Published: March 2018

The effects of the peptide FMRFamide (Phe-Met-Arg-Phe-NH2) on the soma of neuron R14 in the abdominal ganglion of Aplysia californica and A. brasiliana were characterized. Pressure-ejected FMRFamide caused 3 types of responses, (1) a fast outward current (duration, less than 30 sec), (2) a fast inward current (duration, less than 20 sec), and (3) a slow inward current (peak at 0.5–1 min; duration, 2–3 min). The slow inward current, the chief object of this study, arises from a voltage- dependent conductance increase. The FMRFamide-elicited slow inward current is largest between -40 mV and -20 mV, the region of a negative slope resistance in the normal current-voltage relationship for R14. The slow FMRFamide-induced inward current is largely carried by Na+. This current is independent of external [K+] but depends inversely on external [Ca2+] and [Cl-]. The concentrations of the latter ions may influence the voltage dependence of the response. The slow inward current has many properties in common with inward currents induced in other molluscan neurons by applications of neuropeptides or intracellular injections of cyclic nucleotides.
Systemic approaches to modifying quinolinic acid striatal lesions in rats
Authors: Beal MF , Kowall NW , Swartz KJ , Ferrante RJ , Martin JB
Published: March 2018

Quinolinic acid (QA) is an endogenous excitotoxin present in mammalian brain that reproduces many of the histologic and neurochemical features of Huntington's disease (HD). In the present study we have examined the ability of a variety of systemically administered compounds to modify striatal QA neurotoxicity. Lesions were assessed by measurements of the intrinsic striatal neurotransmitters substance P, somatostatin, neuropeptide Y, and GABA. Histologic examination was performed with Nissl stains. The antioxidants ascorbic acid, beta-carotene, and alpha- tocopherol administered s.c. for 3 d prior to striatal QA lesions had no significant effect. Other drugs were administered i.p. 1/2 hr prior to QA striatal lesions. The following were ineffective in blocking QA excitotoxicity: allopurinol, 50 and 100 mg/kg; ketamine, 75 mg/kg; nimodipine, 2.4, and 10 mg/kg; baclofen, 10 mg/kg; 2-amino-5- phosphonovalerate, 50 mg/kg; and 2-amino-7-phosphonoheptanoate, 50 mg/kg. Oral taurine administration for 4 weeks resulted in significantly increased levels of brain taurine but had no significant effect in blocking QA neurotoxicity. Systemic administration of the noncompetitive N-methyl-D-aspartate (NMDA) antagonist MK-801 resulted in a dose-responsive protection against QA toxicity, with complete block at a dose of 4 mg/kg. If the pathogenesis of HD involves QA or another excitotoxin acting at the NMDA receptor, it is possible that MK- 801 could retard the degenerative process.
A local circuit interaction in the flight system of the locust
Authors: Robertson RM , Reye DN
Published: March 2018

Most of the interneurons that have been identified in the locust flight system to date are spiking, intersegmental interneurons and the described interactions between them are spike-mediated postsynaptic potentials. We wished to discover whether the same interneurons also communicate via subthreshold interactions to form local circuits independent of their spike-mediated connections. Using a deafferented flight preparation of the locust and glass microelectrodes, we recorded simultaneously from the neuropil segments of different interneurons within a single thoracic ganglion. Interneuron 301 had an indirect connection with the contralateral 301 and an indirect connection feeding back to itself. The feedback circuit could be activated with subthreshold stimuli. Spikes in a 301 affected self and contralateral partner, whereas subthreshold stimuli affected only self. Thus, this paper demonstrates the existence of 2 pathways from a single interneuron that can be functionally separate depending on whether activity in the interneuron is subthreshold or suprathreshold for spiking. The results show that dendritic regions of spiking intersegmental interneurons in the locust can participate in local circuits whose operation could have a considerable role to play in neural integration.
Differential biosynthesis and posttranslational processing of vasopressin and oxytocin in rat brain during embryonic and postnatal development
Authors: Altstein M , Gainer H
Published: March 2018

The biosynthesis and posttranslational processing of arginine vasopressin (AVP) and oxytocin (OT) peptides in the developing rat brain and pituitary were studied using antibodies and complementary separation methods that permitted a quantitative radioimmunoassay (RIA) analysis of precursor, intermediate, and completely processed forms of the peptides. Precursor forms of the peptides were first detected in rat brain as early as embryonic day (E) 15 for AVP and E17 for OT. Proteolytic cleavage products of the precursors were detected 1 d later for both peptides. AVP was present in a fully processed (amidated) from immediately (E16) and throughout fetal development. OT was cleaved from its precursor starting on E18 but remained in an intermediate (C- terminal extended) form until E21, when amidated OT was first detected in the pituitary. Hence, Pro-AVP processing in the fetus was immediate and complete, whereas Pro-OT processing in the fetus was much slower and incomplete, resulting in the generation of partially processed, nonamidated stable forms of the peptide (OT-Gly10, OT-Gly10-Lys11, and OT-Gly10-Lys11-Arg12). The presence of OT-Gly10-Lys11-Arg12 as a major, stable intermediate form, indicated that the in vivo pattern of endoproteolytic cleavage occurred principally at the C-terminus of the pair of basic amino acids at the tripeptide spacer sequence (Gly-Lys- Arg) in the precursor. Although both precursors were first expressed nearly simultaneously in the brain, the steady-state levels of the precursors were very different throughout fetal life. From E16-E21, the quantities of AVP precursors and peptides were 5- to 10-fold greater than those of OT, suggesting a much higher level of precursor biosynthesis in the AVP neurons. In addition to these differences in the regulation of biosynthesis and processing, AVP peptides were axonally transported to the pituitary 3 d earlier than OT peptides, and in far greater (20-fold) abundance. The early presence and abundance of amidated AVP in the brain and pituitary suggests a trophic function for this peptide during development.
Embryonic divergence of oligodendrocyte and astrocyte lineages in developing rat cerebrum
Authors: LeVine SM , Goldman JE
Published: March 2018

Oligodendrocyte and astrocyte lineages were traced in rat forebrain sections using single- and double-label immunoperoxidase and indirect immunofluorescent techniques. Antibodies were directed against antigenic markers, the expressions of which overlapped in time: GD3 ganglioside in immature neuroectodermal cells; vimentin in radial glia; glial fibrillary acidic protein (GFAP) in astrocytes; and carbonic anhydrase (CA) and galactocerebroside (GC) in oligodendrocytes. A histochemical stain for iron was also used as a marker of oligodendrocytes. Small cells of the subventricular zone (SVZ) were stained with anti-GD3 but not with the other antibodies. By 16 d of gestation (E16), the SVZ generated large, round cells and thick, process-bearing cells that were GD3+/CA+/iron+. These cells then appeared in the cingulum and, with time, increased in numbers and extended thick processes as they filled the subcortical white matter. These cells eventually lost their reactivity to anti-GD3 but became GC+/CA+ with processes extending to myelin sheaths. At E15 radial glia were stained with the anti-vimentin antibody but were negative for GFAP. At birth, only the vimentin+ radial glia midline between the 2 ventricles were GFAP+, but with time more vimentin+ cells became GFAP+. By 7 d of postnatal age all the vimentin+ cells were GFAP+ and had converged predominately on the cingulum. With time these cells condensed and took on characteristic shapes of astrocytes. The embryonic separation of the oligodendrocyte and the astrocyte lineage is supported by four pieces of evidence: (1) GD3+ cells were double labeled with anti-CA, and then went on to become GC+; (2) vimentin+ and GFAP+ cells were not also GD3+; (3) ultrastructural localization of anti-GD3 was confined to cells with characteristics consistent with developing oligodendrocytes; and (4) the shapes of GD3+, CA+, GC+, or iron+ cells did not resemble those of the vimentin+ or GFAP+ cells.
Early development of two types of nicotinic acetylcholine receptors
Authors: Leonard RJ , Nakajima S , Nakajima Y , Carlson CG
Published: March 2018

Functional changes of acetylcholine receptor (AChR) channels in embryonic Xenopus myotomal muscle cells were examined during their development in culture. Single-channel currents evoked by 50 or 500 nM ACh were measured using the patch-clamp technique. In Xenopus myocytes the first emergence of AChRs takes place at about stage 20 (Nieuwkoop and Faber). Myotomes were dissociated at very early stages and plated in culture. Single-channel currents through AChRs were recorded at times ranging from a few hours (stage 21) to several days (stage 47) after the first emergence of AChRs. Two classes of AChR channel were recorded: One class had a low conductance with a long burst duration (low-conductance channel), and the other had a high conductance with a short burst duration (high-conductance channel). Both of these classes were active from the earliest time recorded (stages 21–24). One effect of development was a shift in the relative activity of the low- and high-conductance channels. Initially (stages 21–24), the low conductance channels predominated, accounting for over 95% of the observed events. After 3 d in culture, however, high- and low- conductance events occurred with roughly equal frequency. The other effect of development was a 4-fold decrease in the mean burst length of the low-conductance channel. The decrease in burst length took place rapidly, with about 60% of the change occurring within 24 hr in culture. The burst length of the high-conductance channel remained virtually constant during development, as did the unitary conductance of both channels and the voltage dependence of their mean burst lengths. The developmental change in the proportion of low- and high- conductance channels is likely due to the increased insertion of new high-conductance channels. However, the molecular mechanism of the shortening of burst length of the low-conductance channel is unknown.
Androgen regulates synaptic input to motoneurons of the adult rat spinal cord
Authors: Matsumoto A , Micevych PE , Arnold AP
Published: March 2018

Adult male rats (Sprague-Dawley) were castrated and implanted subcutaneously with Silastic capsules containing testosterone or nothing. Sham-castrated males served as controls. Four weeks following castration, cholera toxin-horseradish peroxidase (CT-HRP) was injected bilaterally into the bulbocavernosus muscles and animals were sacrificed 2 d later. The spinal cords containing the spinal nucleus of the bulbocavernosus (SNB) were dissected, processed with a modified tetramethylbenzidine (TMB) method for visualization of retrogradely transported CT-HRP, and examined at the ultrastructural level. Neuronal structures apposing the membranes of 150 TMB-labeled SNB neurons were analyzed by measuring the percentage of somatic and proximal dendritic membranes covered by synaptic contacts, synaptoid contacts, and neuron- neuron contacts. Most of the neuronal structures in the control and experimental SNB motoneurons consisted of synaptic contacts. The mean percentage of somatic and proximal dendritic membranes covered by synapses 4 weeks after castration was reduced to approximately 30% of those in control animals. However, treatment with testosterone for 4 weeks after castration prevented this decline. Castration and testosterone treatment also influenced the size and number of synaptic contacts per unit length of somatic and proximal dendritic membranes, and the incidence of neuron-neuron contacts and double synapses onto SNB motoneurons. These results indicate that androgen is critical for maintaining the organization of synaptic inputs to these spinal motoneurons in adult male rats.
Identification of motoneurons and interneurons in the spinal network for escapes initiated by the mauthner cell in goldfish
Authors: Fetcho JR , Faber DS
Published: March 2018

We used intracellular recording and staining techniques to study the spinal circuitry of the escape behavior (C-start) initiated by the Mauthner axon (M-axon) in goldfish. Simultaneous intracellular recordings from one or both M-axons and a spinal neuron, followed by HRP labeling of the spinal cell, show that each M-axon makes monosynaptic, chemical excitatory synapses onto 2 populations of ipsilateral spinal neurons. The first consists of the large primary motoneurons that, based on earlier work (Fetcho, 1986), innervate exclusively the faster, white muscle fiber types in the myomeres. The second group of cells is formed by previously undescribed descending interneurons with ipsilateral axonal branches that have contacts with primary and secondary motoneurons spread over 2 or more body segments. Indirect evidence suggests that these descending interneurons are excitatory, and they may explain the polysynaptic activation of motoneurons observed in earlier studies of the spinal circuitry (Diamond, 1971). Both classes of neurons excited by the ipsilateral M- axon are disynaptically inhibited by the contralateral one. The morphology and physiology indicate that this inhibition is mediated by interneurons that are electrotonically coupled to one M-axon and have processes that cross the cord to inhibit contralateral neurons in the region where these postsynaptic cells receive excitatory input from the other M-axon. We have identified interneurons with the physiological and morphological features of these predicted crossed inhibitory interneurons. These cells are electrotonically coupled to the ipsilateral M-axon and receive a chloride-dependent disynaptic inhibitory input from the contralateral M-axon. Their very simple somata give rise to a process that crosses the spinal cord between the 2 M-axons. Once on the opposite side of the cord, the crossing process sends myelinated branches that run rostrally and caudally, roughly parallel to the contralateral M-axon. Processes that arise from these longitudinal branches terminate in a striking association with collaterals of the M-axon; nearly every M-axon collateral along the longitudinal course of an interneuron is met by a branch or branches of the interneuron whose terminals are apposed to neurons postsynaptic to the collateral.(ABSTRACT TRUNCATED AT 400 WORDS)
Dendritic growth and remodeling of cat retinal ganglion cells during fetal and postnatal development
Authors: Ramoa AS , Campbell G , Shatz CJ
Published: March 2018

We have studied the development of retinal ganglion cell morphology in the cat's visual system from early fetal to postnatal times. In particular, we have examined the contribution of growth and remodeling to the establishment of mature retinal ganglion cell form. Ganglion cells were identified by retrograde labeling with rhodamine latex microspheres deposited in the superior colliculus and lateral geniculate nucleus between embryonic day 34 (E34; birth = E65) and adulthood. To reveal the fine morphological details of retrogradely labeled ganglion cells, 48 hr later Lucifer yellow was injected intracellularly in living retinae that had been dissected and maintained in vitro. Our results show that at E35–37 the majority of ganglion cells are very simple in morphology, with a few dendritic processes that are generally aligned in a radial direction towards or away from the optic disc. During the ensuing 2 week period, there is a progressive growth and elaboration of dendrites. By E50, some ganglion cells resembling the adult alpha, beta, and gamma classes can be identified based on comparisons of the appearance and dimensions of their dendritic trees and somata with neighboring filled cells. However, ganglion cell dendrites and axons at this age express several transient morphological features. The axons of ganglion cells give rise to delicate processes originating from the intraretinal portion of the axon, including side branches, present in about half of the cells, and occasionally bifurcations that give rise to axon collaterals. These transient axonal features are present throughout development, including the neonatal period; no axon collaterals were observed after postnatal day 15, while axonal side branches persisted even at P31 but were gone by adulthood. Ganglion cell dendrites exhibit excessive branches and exuberant somatic and dendritic spines. Quantitative analysis of these processes shows that after E45 dendritic trees increase dramatically in complexity, reaching the peak number of spines and branch points by the first week of postnatal life. The number of dendritic processes then falls abruptly to reach near-adult levels by the end of the first postnatal month. Even though dendritic morphology closely resembles that seen in the adult at this age, ganglion cell bodies and dendrites must continue to grow to reach their adult size.(ABSTRACT TRUNCATED AT 400 WORDS)
Electron microscopic localization of type I protein kinase C in rat Purkinje cells
Authors: Kose A , Saito N , Ito H , Kikkawa U , Nishizuka Y , Tanaka C
Published: March 2018

A monoclonal antibody against protein kinase C (PKC) was used for immunocytochemical studies of the type I PKC encoded by gamma-cDNA sequence (gamma-subspecies) in rat Purkinje cells. Dense gamma- subspecies-like immunoreactivity was found on the cell membrane and in the cytoplasm except within cell organelles of the perikaryon, dendrites, axon, and axon terminals. The nucleus was also stained but less heavily, and the nucleoli remained unstained. Synaptic vesicles in the axon terminals were densely stained. The results suggest that gamma- subspecies might be functionally involved in modulation of nuclear function and of pre- and postsynaptic functions including transmitter release in the rat Purkinje cells.
Anatomic and functional development of the suprachiasmatic nuclei in the gray short-tailed opossum
Authors: Rivkees SA , Fox CA , Jacobson CD , Reppert SM
Published: March 2018

The anatomic and functional development of the suprachiasmatic nuclei (SCN) was studied in the gray short-tailed opossum, Monodelphis domestica. To provide a background for developmental studies, daily patterns of wheel-running behavior and SCN metabolic activity were studied in adult animals. Adult opossums manifested robust circadian rhythms in locomotor activity that were entrained by the daily light- dark cycle. The temporal course of SCN metabolic activity, studied by the 14C-labeled deoxyglucose autoradiographic technique, showed that the adult SCN were metabolically active throughout subjective day and relatively inactive during subjective night. SCN neurogenesis, determined using 3H-thymidine autoradiography, was active at postnatal day 3, the earliest age studied, and continued until postnatal day 7. It was not until postnatal day 16 that the SCN appeared as distinct nuclei by light microscopy. Study of the ontogeny of the daily rhythm in SCN metabolic activity showed that the nuclei were metabolically active during both day and night at postnatal day 16. On day 20, a clear day-night rhythm in SCN metabolic activity was first observed; the rhythm was even more pronounced on day 27. These results indicate that the gray short-tailed opossum has a functioning circadian timing system and that the anatomic and functional development of the SCN in this species occurs during the postnatal period.
Distribution of glycine receptors on the membrane of a central neuron: an immunoelectron microscopy study
Authors: Seitanidou T , Triller A , Korn H
Published: March 2018

The distribution of glycine receptors on the plasmalemma of the teleost Mauthner cell was examined with light and electron microscopy using monoclonal antibodies raised against the glycine receptors of the rat. These immunoglobulins recognize a peptide of 93 kDa associated with the intracellular side of the receptor complex. With indirect immunofluorescence, labeling appeared as small clusters over the whole surface of the neuron. This distribution indicates that, unlike other neurons, the Mauthner cell can express glycine receptors at the dendritic and at the somatic level as well. Vestibular or reticular neurons lying in the proximity of the Mauthner cell were also stained. At the ultrastructural level, the immunoenzymatic reaction product, localized in front of the presynaptic active zones, slightly overextends the limits of the synaptic complex. This observation may account for vesicular exocytosis at the border of the presynaptic grid. More generally, inside and outside the axon-cap, stained postsynaptic membranes were apposed to terminals identified as unmyelinated club endings and some small vesicle boutons, respectively. Each of them could establish classical flat synapses or spinelike contacts, the latter being described here for the first time. Patches of membrane remained unstained, however, particularly along the lateral and ventral dendrites of the cell; they corresponded to the contact sites of excitatory afferents. In order to enhance the penetration of immunoreactive substances, a particular fixation procedure was used; its effect on the shape of the synaptic vesicles is described. Our results support the notion that glycine is responsible for both somatic and remote dendritic Cl- -dependent inhibition of the Mauthner cell. The first one is produced by the so-called PHP exhibiting neurons, which correspond to cells of recurrent collateral network and vestibulovestibular pathway. In contrast, cells giving rise to the more distal inhibitory synapses on both dendrites are not yet characterized.