bluuebunny/crossref_metadata_2025 huggingface dataset:
Estrogen and progestin receptors appear in transplanted fetal hypothalamus-preoptic area independently of the steroid environment
Authors: Paden CM , Gerlach JL , McEwen BS
Published: March 2018

Sexual maturation and differentiation of the rat brain are believed to result from the interaction of gonadal steroids with specific neural receptors during late fetal and early postnatal life. A variety of evidence indicates that the first appearance of estrogen receptors in the hypothalamus-preoptic area (HPOA) during the perinatal period is a crucial evident underlying these processes. However, it is unknown to what extent the ontogeny of estrogen receptors is itself influenced by gonadal steroids present in the fetal environment. In order to address this question, estrogen receptors were assayed in HPOA 8 weeks after transplantation of the tissue from embryonic day 15 to 18 fetuses to either the choroidal pia overlying the superior colliculus or to the anterior chamber of the eye of adult female hosts. Host animals were either intact or ovariectomized and adrenalectomized, with or without estrogen replacement. The saturable binding of estradiol to cytosol of HPOA transplants exhibited the steroid specificity and high affinity characteristic of authentic estrogen receptors. No differences in the level of cytosol estrogen receptors in transplanted HPOA grown in the presence or absence of gonadal steroids were found. Receptor concentrations were also similar in HPOA taken from male or female fetuses. Autoradiography with [3H]estradiol revealed clusters of estrophilic cells in the transplants similar to those of the adult host hypothalamus, again regardless of whether the transplant developed in the presence of gonadal steroids. Estrogen receptors from both groups were also found to be biochemically functional as indicated by the ability of acute estrogen treatment to induce progestin receptors in the transplants.(ABSTRACT TRUNCATED AT 250 WORDS)
Ouabain-evoked norepinephrine release from intact rat sympathetic neurons: evidence for carrier-mediated release
Authors: Sweadner KJ
Published: March 2018

Inhibition of the Na,K-ATPase is known to cause transmitter release from many neurons. The mechanism of [3H]norepinephrine release was examined in primary cultures of sympathetic neurons. Ouabain caused [3H]norepinephrine release at concentrations that produced 80 to 90% inhibition of Na,K-ATPase activity. The effect of ouabain was compared with the effects of high K+ and the Ca2+ ionophore A23187. [3H]Norepinephrine release elicited by depolarization with high extracellular K+ was dependent on extracellular Ca2+, was unaffected by tetrodotoxin, was potentiated by reducing extracellular Na+, and was potentiated by the norepinephrine uptake inhibitor desipramine. These are the results expected if high K+ causes release by exocytosis, and if blockade of the Na+-dependent norepinephrine uptake system increases the net measurable release of the transmitter. The Ca2+ ionophore A23187 caused [3H]norepinephrine release that was not dependent on extracellular Ca2+ but which was like the release elicited by high K+ in other respects. Release elicited by ouabain was independent of extracellular Ca2+, was delayed for several hours by tetrodotoxin, was inhibited by reducing the concentration of extracellular Na+, and was inhibited by desipramine. These results suggest that the measured increase in transmitter release is secondary to a rise in the concentration of intracellular Na+. The data are consistent with the hypothesis that at high levels of pump inhibition, ouabain elicits nonvesicular [3H]norepinephrine release through reversal of the Na+- dependent plasma membrane carrier.
The neuropeptide FMRF-amide decreases both the Ca2+ conductance and a cyclic 3',5'-adenosine monophosphate-dependent K+ conductance in identified molluscan neurons
Authors: Colombaioni L , Paupardin-Tritsch D , Vidal PP , Gerschenfeld HM
Published: March 2018

The molluscan neuropeptide FMRF-amide (10 to 50 microM) decreases the duration of the Ca2+-dependent action potential recorded in the cell body of identified neurons of the snail Helix aspersa (cells D3 and E2). In these neurons, FMRF-amide evokes a decrease of the Ca2+ current resulting from a decrease in Ca2+ conductance. In another single neuron, cell E11, FMRF-amide, besides evoking a decrease of the Ca2+ conductance, induces a decrease of the S-current (Klein, M., J. S. Camardo, and E. R. Kandel (1982) Proc. Natl. Acad Sci. U. S. A. 79: 5713–5717), a K+ current controlled by cyclic AMP. However, in this E11 cell, FMRF-amide also evokes a decrease of the amplitude of the Ca2+ spike plateau. As discussed in the preceding paper (Paupardin-Tritsch, D., L. Colombaioni, P. Deterre, and H. M. Gerschenfeld (1985) J. Neurosci. 5: 2522–2532), it is suggested that these FRMF-amide-induced modulations of ionic conductances involved in the Ca2+-dependent spike recorded in these neuronal somata may intervene in processes of presynaptic inhibition and facilitation.
Voltage clamp analysis of tetrodotoxin-sensitive and -insensitive sodium channels in rat muscle cells developing in vitro
Authors: Gonoi T , Sherman SJ , Catterall WA
Published: March 2018

Sodium currents in cultured rat muscle cells converted to myoballs by treatment with colchicine were recorded using a giga-ohm seal voltage clamp procedure in the whole cell configuration. The mean peak Na+ conductance of the myoballs was 90 pS/microns2 of surface membrane. Half-maximal activation of Na+ currents was observed for test pulses to -31 mV and half-maximal inactivation was observed for prepulses to -74 mV. Titration of the inhibition of Na+ currents by tetrodotoxin (TTX) yielded a biphasic inhibition curve consistent with the presence of two classes of Na+ channels differing in affinity for TTX. The TTX- sensitive channels carried 28% of the Na+ current and had an apparent KD for TTX of 13 nM at 20 degrees C. The TTX-insensitive Na+ channels had an apparent KD for TTX of 3.2 microns. Inhibition of TTX- insensitive Na+ channels by TTX was enhanced by repetitive stimulation of the myoballs at 2 Hz, whereas the inhibition of TTX-sensitive Na+ channels by TTX was not frequency dependent. We conclude that rat muscle cells developing in vitro synthesize physiologically functional, TTX-sensitive Na+ channels in the absence of innervation. These channels, which are characteristic of adult skeletal muscle, function in parallel with TTX-insensitive Na+ channels that are present in embryonic muscle.
Giant Aplysia neuron R2 reliably forms strong chemical connections in vitro
Authors: Schacher S , Rayport SG , Ambron RT
Published: March 2018

The giant cholinergic neuron R2 of Aplysia was cultured in combination with identified neurons L11 and R15 and members of a group of left upper quadrant (LUQ) cells L2 to L6 from the abdominal ganglion. All of these neurons receive cholinergic input from other cells in vivo, but not from R2. In vitro, R2 reliably formed unidirectional chemical connections with these cells. Single action potentials in R2 produced a dual fast and slow inhibitory response in LUQ cells (L2 to L6), a dual fast inhibitory-slow excitatory response in L11, and a slow inhibitory response in R15. The connections formed on LUQ cells were characteristic of their cholinergic input, but the R2-L11 and the R2-R15 connections also had noncholinergic properties. Thus, unlike L10 which forms connections only with its normal targets in vitro, R2 forms strong chemical connections with other neurons which are not found in vivo. The properties of the R2 connections also suggest that it may release another neurotransmitter besides acetylcholine.
Ultrastructural localization of slow retrograde axonal transport: an autoradiographic study
Authors: Mata M , Staple J , Fink DJ
Published: March 2018

We used [3H]-N-succinimidylpropionate ([3H]-N-SP) to covalently label endogenous intra-axonal proteins within the nerve in order to study their bidirectional transport. At the time of injection virtually all of the labeled proteins are found at the injection site. At later times specific patterns of labeled proteins are found within the nerve both proximal to and distal from the injection site, as a result of retrograde and anterograde axonal transport, respectively. We undertook the current study to determine the ultrastructural distribution of the [3H]-N-SP-labeled transported proteins in the nerve. One microliter of [3H]-N-SP was injected subepineurially in sciatic nerve, and 5 days later the nerves were processed either for light and electron microscopic autoradiography or for gel electrophoresis and fluorography. At the injection site the labeled proteins are predominantly myelin proteins. Distally, a pattern similar to that described for slow anterograde transport is seen. Proximal to the injection site a constellation dominated by the 68-kilodalton protein is seen. Light microscopic autoradiography shows diffuse labeling both in axons and in myelin at the injection site, with predominant axonal labeling distant from the injection site. Electron microscopic autoradiography of segments distal to the injection site show silver grains which are distributed within the axoplasm without apparent relationship to organelles. In contrast, segments proximal to the injection site show silver grains which seem closely related to membrane-bound organelles, predominantly mitochondria. These results suggest that slow retrograde transport has a unique subcellular distribution that is distinct from that of slow anterograde transport.
Dual ultrastructural localization of two neurotransmitter-related antigens: colloidal gold-labeled neurophysin-immunoreactive supraoptic neurons receive peroxidase-labeled glutamate decarboxylase- or gold- labeled GABA-immunoreactive synapses
Authors: van den Pol AN
Published: March 2018

To study the morphological substrate for interaction between two chemically distinct neuronal types, two double ultrastructural immunolabeling strategies were employed. In the first, two different electron-dense markers were used to examine simultaneously two different neurotransmitter-related antigens in the hypothalamic supraoptic nucleus in the same thin section. Results obtained with the first method were confirmed with a second approach based on postembedding immunostaining of alternate serial thin sections with different antisera. Antiserum against glutamate decarboxylase, the enzyme responsible for the synthesis of the inhibitory amino acid transmitter gamma-aminobutyric acid (GABA), or antisera against GABA, was used to localize immunoreactive axons in the hypothalamic supraoptic nucleus. With light microscopy, glutamate decarboxylase- and GABA-immunoreactive axon terminals immunostained with peroxidase were found arborizing throughout all areas of the nucleus; terminal boutons were found adjacent to unlabeled somata within the nucleus. Cells containing immunoreactive oxytocin, vasopressin, and neurophysin were localized with peroxidase. Glutamate decarboxylase-immunoreactive axons stained with peroxidase prior to embedding in plastic were demonstrated to contact neurons which contained vesicles immunostained with neurophysin antiserum by a post-embedding immunocytochemical procedure which used immunoglobulins or protein A adsorbed to colloidal gold as a second ultrastructural marker. Quantitative evaluation of post- embedding staining with colloidal gold using a neurophysin primary antiserum indicated a specific antigen localization in neurosecretory vesicles. A critical factor in this double-labeling paradigm was that immunological reagents used in the second series did not cross-react with those used in the first series, regardless of the species of origin of antisera. To provide further verification of GABAergic synapses on neurophysin-containing neurons, alternate serial ultrathin sections were stained with colloidal gold using antisera against either neurophysin or GABA; boutons immunoreactive for GABA made synaptic contact with supraoptic neurons containing neurophysin immunoreactivity. Converging results obtained with these two procedures indicate that GABAergic axons synapse directly on neurons containing oxytocin or vasopressin in the rat hypothalamic supraoptic nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)
The distribution, relationships to other organelles, and calcium- sequestering ability of smooth endoplasmic reticulum in frog olfactory axons
Authors: Burton PR , Laveri LA
Published: March 2018

Ultrastructural studies of single and serial sections of bullfrog olfactory axons showed that smooth endoplasmic reticulum (SER) tubules, which usually appear as single profiles in cross-sections of axons, are continuous over considerable distances, but that discontinuities do exist. Computer-assisted three-dimensional reconstruction of portions of axons indicated that the SER tubules show considerable variation in the volume of the cisternal space along the tubule, which often follows a tortuous path. Some branching and anastomosing appears to occur, and electron-dense material was present in the cisternal space of some tubules. SER tubules are often bridged to neurofilaments and less often to microtubules. The usual two to three microtubules in the axoplasm form a domain which is characterized by a clear area, or zone of exclusion, around the microtubules. Ultrastructural cytochemistry was used to demonstrate that SER tubules actively sequester Ca. The electron-dense product (calcium oxalate) was uniformly and specifically associated with the SER of axons at both proximal (closest to the perikarya in the olfactory epithelium) and distal (closest to the olfactory lobe of the brain) ends of the olfactory nerve. It is concluded that the primary function of SER tubules in these axons is to serve in the regulation of Ca in the axoplasm, probably to facilitate fast axoplasmic transport, and that a secondary function may be the translocation of material in the cisternal space. The observations are discussed as they may relate to the “microstream” hypothesis of axoplasmic transport, and it is argued that fast transport occurs through the zone of exclusion associated with the microtubule domain(s) of axons.
Stereoselective L-[3H]quinuclidinyl benzilate-binding sites in nervous tissue of Aplysia californica: evidence for muscarinic receptors
Authors: Murray TF , Mpitsos GJ , Siebenaller JF , Barker DL
Published: March 2018

The muscarinic antagonist L-[3H]quinuclidinyl benzilate (L-[3H]QNB) binds with a high affinity (Kd = 0.77 nM) to a single population of specific sites (Bmax = 47 fmol/mg of protein) in nervous tissue of the gastropod mollusc, Aplysia. The specific L-[3H]QNB binding is displaced stereoselectively by the enantiomers of benzetimide, dexetimide, and levetimide. The pharmacologically active enantiomer, dexetimide, is more potent than levetimide as an inhibitor of L-[3H]QNB binding. Moreover, the muscarinic cholinergic ligands, scopolamine, atropine, oxotremorine, and pilocarpine are effective inhibitors of the specific L-[3H]QNB binding, whereas nicotinic receptor antagonists, decamethonium and d-tubocurarine, are considerably less effective. These pharmacological characteristics of the L-[3H]QNB-binding site provide evidence for classical muscarinic receptors in Aplysia nervous tissue. The physiological relevance of the dexetimide-displaceable L-[3H]QNB-binding site was supported by the demonstration of the sensitivity of the specific binding to thermal denaturation. Specific binding of L-[3H]QNB was also detected in nervous tissue of another marine gastropod, Pleurobranchaea californica. The characteristics of the Aplysia L-[3H]QNB-binding site are in accordance with studies of numerous vertebrate and invertebrate tissues indicating that the muscarinic cholinergic receptor site has been highly conserved through evolution.
Intrinsic connections of macaque striate cortex: afferent and efferent connections of lamina 4C
Authors: Fitzpatrick D , Lund JS , Blasdel GG
Published: March 2018

We have studied the intrinsic organization of macaque striate cortex by tracing the pattern of horseradish peroxidase (HRP)-labeled axons and cell bodies produced by microinjections of HRP into single cortical laminae. Both anterograde and retrograde transport results were used to examine: (1) the pattern of projections from lamina 4C to the superficial layers; (2) the projection from lamina 4C to deeper cortical layers; and (3) the projections to lamina 4C from other cortical laminae. Laminae 4C alpha and 4C beta differ in their pattern of projections to the superficial layers of striate cortex. Axons from neurons in lamina 4C beta ascend through lamina 4B without giving off collaterals and terminate in lamina 4A and in the base of lamina 3. By contrast, axons from neurons in lamina 4C alpha terminate in lamina 4B and less densely in the 4A/3B region. The projection from lamina 4C beta to lamina 4A is particularly dense and is distributed in a patchy fashion immediately above each injection site. The projection from lamina 4C beta to lamina 3B appears less dense and more widespread; we estimate that individual 4C beta axons may spread laterally for more than 400 micron. Furthermore, the pattern of HRP-labeled cell bodies in lamina 4C beta following injections into laminae 4A and 3B provides evidence for a subdivision within 4C beta. These injections always produce a large number of labeled neurons in the upper part of lamina 4C beta, whereas the lower portion contains few labeled neurons that are located immediately under the center of the injection site. Both lamina 4C alpha and lamina 4C beta also contribute less dense projections to the deeper layers of cortex. Lamina 4C beta projects mainly to lamina 6, whereas lamina 4C alpha contributes axon terminals to both lamina 5A and lamina 6. Neurons in lamina 6 provide the bulk of the intracortical projections to lamina 4C. The axons of these neurons are fine in caliber and have a delicate side-spine morphology that is quite distinct from lateral geniculate axon arbors. Neurons in lamina 5A also project onto lamina 4C, but the projections of these neurons appear concentrated in lamina 4C alpha. These results confirm or refine many conclusions about intrinsic connections of striate cortex drawn from Golgi material and suggest new patterns of connections not suspected from previous work.
Functional substance P receptors on a rat pancreatic acinar cell line
Authors: Womack MD , Hanley MR , Jessell TM
Published: March 2018

A pancreatic acinar cell line, AR4–2J, that expresses a high density of substance P (SP)-binding sites has been identified. SP-binding sites on intact AR4–2J cells were detected with 125I-Bolton-Hunter SP (125I- BHSP). 125I-BHSP binding to AR4–2J cells has an apparent Kd of 40 pm with slow rates of association and dissociation. The number of high affinity binding sites was about 10(4)/cell. Binding of 125I-BHSP was inhibited by SP and by structurally related peptides. Physalaemin was a more potent inhibitor of binding than SP, whereas kassinin, eledoisin, and neurokinin A (substance K, neuromedin alpha, or neurokinin L) were much less potent. SP-free acid and SP (7–11) were 3 to 4 orders of magnitude less potent than SP itself. The membrane, intracellular, and secretory events elicited by exposure of AR4–2J cells to SP have also been examined. Intracellular recording from AR4–2J cells revealed resting membrane potentials of -40 to -65 mV. Pressure application of SP (100 pM to 100 nM) evoked depolarizations of 20 to 40 mV which were maintained for prolonged periods. The intracellular free calcium concentration in AR4–2J cells, measured with (2-[2-amino-5- methylphenoxy)-methyl)-6-methoxy-8-aminoquinolone tetra-acetoxy methyl ester), was between 100 and 500 nM. Addition of SP (100 pM to 10 nM) or physalaemin (1 nM) induced a transient rise in intracellular free calcium. AR4–2J cells synthesize amylase, and exposure of cells to SP resulted in a dose-dependent increase in amylase secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
Reserpine changes the dynamic state of enkephalin stores in rat striatum and adrenal medulla by different mechanisms
Authors: Mocchetti I , Guidotti A , Schwartz JP , Costa E
Published: March 2018

The administration of reserpine increases enkephalin content in rat striatum and adrenal medulla. In order to investigate the mechanisms operative in this increase, we have studied in vivo the dynamic state of enkephalin stores by determining the content of proenkephalin mRNA, enkephalin precursors, and enkephalins in rats receiving reserpine. We measured proenkephalin mRNA by using a cDNA probe for human proenkephalin mRNA which hybridizes to the same species of mRNA either in the brain or in adrenal medulla. (Met5)-Enkephalin-Arg6-Phe7, as well as the high and low molecular weight forms of the enkephalins separated by Sephadex G-75 column chromatography, were measured by radioimmunoassay. Reserpine (2 mg/kg, i.p., repeated daily for two consecutive days) led 3 to 5 days later to an increase in the striatal content of proenkephalin mRNA as well as high and low molecular weight peptides containing enkephalin. The same treatment produced, in adrenal medulla, a shift from higher molecular weight to lower molecular weight enkephalin-containing peptides, an increase of enkephalin peptides, and a decrease of proenkephalin mRNA content. The results in striatum suggest that reserpine increases enkephalin synthesis by removing a tonic dopaminergic inhibition: those in adrenal medulla indicate that reserpine causes an accumulation of enkephalins by blocking the release and/or increasing the processing which may trigger a feedback- regulatory mechanism leading to a decrease in proenkephalin mRNA content.
The occurrence of long openings in the purified cholinergic receptor channel increases with acetylcholine concentration
Authors: Labarca P , Montal MS , Lindstrom JM , Montal M
Published: March 2018

To establish the relationship between cholinergic ligand occupancy and channel open states, we recorded single-channel currents activated by different acetylcholine (ACh) concentrations from Torpedo californica ACh receptors reconstituted in lipid bilayers. Inspection of single- channel records shows that the frequency of occurrence of long openings increases with ACh concentration. Analysis of the probability distribution of open dwell times indicates that the ACh receptor channel has two distinct channel open states, short- and long-lived. The frequency of occurrence of the long openings over the short increased with ACh concentration, whereas the corresponding time constants were virtually unaltered. The extent of agonist occupancy at the ACh-binding sites in the purified cholinergic receptor appears, therefore, to correlate with an increased probability of the long-lived open state. These results are consistent with the notion that the two open-channel states arise from different extents of ligand occupancy at the receptor molecule.
Neurotoxin-sensitive sodium channels in neurons developing in vivo and in vitro
Authors: Couraud F , Martin-Moutot N , Koulakoff A , Berwald-Netter Y
Published: March 2018

Fetal mouse brain cells were investigated by 22Na+ flux assays with the aim to determine the ontogenetic time course of appearance of functional voltage-sensitive sodium channels. Their pharmacological properties were assessed by measurement of the response to known neurotoxins, acting at site 1, 2, or 3 of the Na+ channel. Brain cell suspensions, prepared at 11–19 d of prenatal development in vivo, and fetal brain neurons in culture were explored. In vivo neurotoxin- sensitive Na+ influx becomes detectable at 12 d of gestation, in concordance with the time of appearance of saturable binding sites for alpha-scorpion toxin (alpha-ScTx) and saxitoxin. Progression in fetal age or in time in vitro is accompanied by an increase in the initial rate and in the amplitude of Na+ uptake stimulated by batrachotoxin or veratridine. The general pharmacological properties of developing Na+ channels are very similar to the known properties of voltage-dependent Na+ channels in adult nerve: Batrachotoxin acts as a full channel agonist and veratridine as a partial agonist. Their respective apparent affinities are increased in presence of alpha-ScTx, in agreement with the known positive cooperativity of toxins acting at sites 2 and 3 of the Na+ channel. alpha-ScTx alone induces a small increase in Na+ permeability; its effect is greatly amplified in the presence of batrachotoxin or veratridine. The apparent affinity of alpha-ScTx is reduced by cell depolarization. Tetrodotoxin and saxitoxin block the increase in Na+ permeability induced by batrachotoxin, veratridine, and alpha-ScTx.(ABSTRACT TRUNCATED AT 250 WORDS)
Neurons of the olfactory epithelium in adult rats contain vimentin
Authors: Schwob JE , Farber NB , Gottlieb DI
Published: March 2018

In the developing nervous system, the intermediate filament protein vimentin is found in the proliferating neuroepithelium and neural crest. As development proceeds, postmitotic neurons cease vimentin expression and neurofilament proteins begin to accumulate. We have shown that olfactory receptor neurons deviate from the general pattern of neuronal intermediate filament expression, in that they continue to express vimentin or a highly vimentin-like protein rather than neurofilament proteins in the adult rat. With light-microscopic immunohistochemistry, three independently derived antibodies to vimentin label all portions of the primary olfactory projection, including the sensory neuron cell bodies in the olfactory epithelium, the fascicles of the olfactory nerve, and their axonal arbors in the glomeruli of the olfactory bulb. In contrast, anti-neurofilament antisera stain only rare scattered receptor cells and a small number of axons in the olfactory nerve. Electron-microscopic immunohistochemistry shows dense staining of olfactory axons with anti-vimentin. The vimentin-like immunoreactive material in the olfactory nerve layer was characterized by SDS-PAGE and by immunoblotting. On immunoblots of homogenates of the olfactory nerve, the anti-vimentin monoclonal antibody SBV-21 (Blose et al., 1984) stains only a single protein of Mr = 55 kDa. This band comigrates with vimentin in crude cytoskeletal material from the neonatal rat brain prepared according to the method of Dahl et al. (1981). SBV-21 does not stain neurofilament triplet proteins or glial fibrillary acidic protein, which are also present in these blots. These results demonstrate that the vast majority of olfactory receptor neurons and their axons contain vimentin or a protein of similar immunological character and electrophoretic mobility, while identifiable expression of neurofilament proteins is confined to a very small subpopulation. Hence, the switch in intermediate filament proteins that normally accompanies neuronal maturation is arrested in most olfactory neurons, and a “juvenile” biochemical marker is retained. This population of neurons is also unique among mammalian neurons in several other respects, including that olfactory neurons die during normal adult life or following injury and then are replaced from a proliferating pool of stem cells.
Electrophysiological evidence for the existence of both D-1 and D-2 dopamine receptors in the rat nucleus accumbens
Authors: White FJ , Wang RY
Published: March 2018

Extracellular single-unit recording and microiontophoretic techniques were used to characterize the pharmacological properties of dopamine (DA) receptors within the rat nucleus accumbens (NAc), a forebrain structure that receives a dense innervation from mesolimbic DA- containing neurons (A10 DA neurons) located in the ventral tegmental area (VTA). Of the NAc neurons tested, 75% were inhibited by microiontophoretic administration of the selective D-2 receptor agonist, LY-141865, whereas 38% were inhibited by microiontophoretic administration of the selective D-1 receptor agonist, SKF-38393. Of the 30 NAc neurons that were tested with both of these agonists, nine were inhibited by both agonists, 11 were inhibited only by LY-141865, five were inhibited only by SKF-38393, and five were not affected by either of these compounds. The inhibitory effects of LY-141865 were blocked and reversed by either intravenous or iontophoretic administration of the selective D-2 antagonist (-)-sulpiride, which, however, failed to alter the inhibitory effects of SKF-38393. In contrast, the purportedly selective D-1 antagonist, SCH-23390, selectively blocked and reversed the inhibitory effects of SKF-38393, suggesting that the two agonists were producing their inhibitory effects via distinct DA receptors. Additional experiments indicated that intravenous administration of LY- 141865 caused a biphasic increase/decrease in the activity of NAc neurons. The initial rate increase was apparently due to disinhibition since it was also shown that D-2 DA receptors located on A10 DA neurons exhibited a 3–10-fold greater sensitivity to LY-141865 and DA as compared to the NAc D-2 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
The relationship of brain-tissue loss volume and lesion location to cognitive deficit
Authors: Grafman J , Salazar A , Weingartner H , Vance S , Amin D
Published: March 2018

We examined the relationship of preinjury intelligence, a lesion- severity variable (brain-tissue loss volume), and lesion location to the persistence of cognitive deficits in Vietnam veterans with penetrating brain wounds. Using stepwise multiple linear regression procedures, we found that preinjury intelligence predicted a significant amount of the variance on postinjury cognitive testing, being a better predictor for tests requiring a number of complementary cognitive processes (e.g., intelligence tests) than for tests measuring a specific cognitive process (e.g., face recognition). Brain-tissue volume loss was found to play a larger role when a global cognitive measure was used, but a smaller role when a specific cognitive process was measured. Finally, lesion location was shown to be a significant predictor of performance only for specific cognitive processes. Nevertheless, preinjury intelligence/education appears to play an even larger role in postinjury performance than either brain-tissue loss volume or a particular structural loss.
Induction of glutamate binding sites in hippocampal membranes by transient exposure to high concentrations of glutamate or glutamate analogs
Authors: Kessler M , Baudry M , Cummins JT , Way S , Lynch G
Published: March 2018

The number of Na+-independent, Cl--dependent glutamate binding sites in rat hippocampal membranes is increased two- to fourfold after pre- exposing isolated membranes or hippocampal slices to high concentrations (0.1–10 mM) of L-glutamate or of glutamate analogs with high affinity for this binding site, such as quisqualate, homocysteate, or aminoadipate. N-Methylaspartate and kainate are ineffective. A similar binding increase is induced by transient exposure to the dipeptide tyrosylglutamate. The newly induced binding sites appear to be identical with pre-existing Cl--dependent binding sites by several criteria: They have a similar pharmacological profile, they are sensitive to low concentrations of Na+, and the number of sites can be further increased by transient exposure to micromolar calcium concentrations. Moreover, binding of [3H]APB, a ligand selective for the Cl--dependent glutamate binding sites, is also increased after glutamate preincubation. The induction of binding sites by high glutamate concentrations, described herein, is calcium-independent, not inhibited by leupeptin and, therefore, different from the previously described activation of binding sites by a calcium-sensitive protease. The high concentration of ligand needed to induce increased binding suggests the presence in hippocampal membranes of a binding site with low, millimolar affinity that is functionally related to the known high- affinity binding sites. Several interpretations of the observed effects and their implications for the possible relationship between the binding site and the synaptic receptor are discussed.
Glial domains and nerve fiber patterns in the fish retinotectal pathway
Authors: Maggs A , Scholes J
Published: March 2018

Optic nerve fibers run parallel from the retina as far as the optic tract in fish, then suddenly criss-cross into a new pattern matching the tectal map. This change coincides with a unique demarcation between two astroglial territories in the retinotectal pathway, located where the optic chiasm occurs in other vertebrates, which we defined using antibodies directed against intermediate filaments (IF). We found that astroglia in optic nerve territory express an Mr 56,000 IF polypeptide, band 3, which we identify as the fish equivalent of vimentin in mammals. These astrocytic cells lack glial fibrillary acidic protein (GFAP; cf. Dahl and Bignami, 1973). Conversely, glia in brain territory, that is, in the optic tract and elsewhere in the CNS, lack the fish vimentin, but express GFAP. By electron microscopy, we obtained evidence that new retinal axons extend swiftly through the growing optic nerve, where they are tightly shepherded into a narrow track by newly differentiating glial cells, positive for the fish vimentin. In the GFAP-positive glial territory of the optic tract, by contrast, growing axons are slowed down and probably branch. We suggest that this allows them to fasciculate accurately with older fibers and thereby propagate a tectotopic pattern established by pioneer axons in the embryo.
Investigation of the failure of parenterally administered haloperidol to antagonize dopamine released from micropipettes in the caudate
Authors: Johnson SW , Hoffer BJ , Freedman R
Published: March 2018

An anomaly in the experimental data underlying the theory that neuroleptics act by blockade of dopaminergic neurotransmission is the repeatedly demonstrated failure in several laboratories of parenterally administered neuroleptics to antagonize electrophysiologic actions of locally applied dopamine (DA) in striatum. This failure is enigmatic since many investigators have successfully demonstrated antagonism when both dopamine and neuroleptic are applied directly to striatal neurons by microiontophoresis. We used multibarrel micropipettes to pressure- eject DA agonists onto rat caudate neurons while observing the ability of parenterally administered haloperidol to block the inhibitory actions of dopaminergic agonists on neuronal activity. Experiments performed at times of maximal behavioural effect of haloperidol did not demonstrate agonist-antagonist interaction. This result has been obtained by four other teams of investigators. A variety of pharmacologic manipulations were employed to help solve this enigma. Acute treatment with reserpine and alpha-methyl-paratyrosine, performed to minimize any possible interference by endogenous DA, did not permit blockade of dopamine by haloperidol. To see if this failure of antagonism could be generalized to other DA agonists, apomorphine, amphetamine, and phencyclidine (PCP) were also investigated. Although the direct dopaminergic agonist apomorphine was not antagonized by haloperidol, the indirect DA agonist PCP was successfully antagonized. Amphetamine, which has both direct and indirect actions when applied locally, was not antagonized. Antagonism of direct agonists was demonstrated in rats with unilateral 6-hydroxydopamine-induced lesions of the nigrostriatal pathway. In these preparations, parenterally administered haloperidol reversed the receptor-mediated supersensitivity to the inhibitory effects of locally applied DA and apomorphine.(ABSTRACT TRUNCATED AT 250 WORDS)
Serotonin decreases the duration of action potentials recorded from tetraethylammonium-treated bullfrog dorsal root ganglion cells
Authors: Holz GG , Shefner SA , Anderson EG
Published: March 2018

Neurotransmitter effects on calcium currents activated by sensory neuron action potentials have been previously studied in embryonic or neonatal dorsal root ganglion (DRG) cells in culture. In the present study we examined the effects of serotonin (5-HT) on the shape of action potentials recorded from fully differentiated primary afferent neurons in isolated DRG of adult bullfrogs. Intracellular recordings were obtained from cell bodies of type A and C neurons. Concentrations of 5-HT that had no effect on membrane potential or input resistance had little or no effect on action potential shape. Treatment with 5–20 mM tetraethylammonium ion (TEA) led to the appearance of a plateau phase on the falling limb of the spike. This plateau phase appears to result from calcium influx, as it was dramatically reduced in amplitude and duration by solutions containing low concentrations of calcium or the calcium channel blocker, manganese. In preparations treated with 7.5 mM TEA, low concentrations of 5-HT (10 nM-1 microM) produced a dose- dependent narrowing of the calcium-dependent plateau phase of the mixed sodium/calcium spike. A decrease in spike afterhyperpolarization was also noted. The decrease in spike duration was recorded from 74% of type A neurons and 57% of type C neurons, and was not secondary to a change in resting potential or input resistance. The 5-HT receptor antagonists methysergide and metergoline did not block the response to 5-HT. Instead, they exhibited weak agonist-like actions. Serotonin also reduced the rate of rise and peak amplitude of calcium spikes recorded in the presence of tetrodotoxin and TEA.(ABSTRACT TRUNCATED AT 250 WORDS)
Serotonin enhances the excitatory acetylcholine response in the RB cell cluster of Aplysia californica
Authors: Simmons LK , Koester J
Published: March 2018

The RB cells, an identified cluster of serotonergic neurons in the abdominal ganglion of Aplysia californica, are excited by ACh. We have found that serotonin (5-HT) enhances the ACh responses recorded from the RB cells. The locus and specificity of the serotonergic interaction with the ACh response were analyzed using the conventional two- electrode voltage-clamp technique. We compared the current responses evoked in RB cells by constant-current iontophoretic pulses of ACh in control solutions and in solutions containing various concentrations of 5-HT. Serotonin consistently enhances the ACh evoked response in a dose- dependent manner while simultaneously directly activating the RB cells by turning on a small steady-state inward current. The dose-response characteristics for the 5-HT-mediated steady-state current differ, however, from those of the 5-HT-induced ACh response facilitation. The ACh response enhancement appears to be an effect of 5-HT upon RB cell ACh receptors since the enhancement is present under conditions that eliminate presynaptic input, and 5-HT is still capable of enhancing the iontophoretically evoked response when the AChE-resistant agonist carbachol is substituted for ACh. We tested other neurons in the Aplysia CNS exhibiting ACh evoked responses qualitatively similar to the RB cell ACh responses; 5-HT does not enhance the iontophoretically evoked ACh responses of these cells. Also, although the RB cells are responsive to dopamine and histamine, these putative neurotransmitters do not enhance the ACh response.
Migration of neuroblasts along preexisting axonal tracts during prenatal cerebellar development
Authors: Hynes RO , Patel R , Miller RH
Published: March 2018

During prenatal development of the cerebellum in rats, a secondary stem cell layer, the external granular, or germinal, layer (EGL) develops at the pial surface of the cerebellar anlage. The EGL cells arise in a region at the caudolateral margin of the fourth ventricle, and the cells migrate over the surface of the developing cerebellum. A key question is how this migration is guided. We have investigated the possible role of the extracellular matrix protein, fibronectin, and find none present in the EGL during the migration. Instead, we find that the EGL neuroblasts migrate in close contact with axons that are present prior to the onset of migration. It appears that these axons serve as the substrate for EGL neuroblast migration and that axonal guidance of cell migration may be a third general mechanism to be added to the previously studied guidance by glial processes and extracellular matrix.
Cholinergic modulation of an acetylcholine receptor-like antigen on the surface of chick ciliary ganglion neurons in cell culture
Authors: Smith MA , Margiotta JF , Franco A , Lindstrom JM , Berg DK
Published: March 2018

Chick ciliary ganglion neurons have a membrane component that shares an antigenic determinant with the “main immunogenic region” of the alpha subunits in nicotinic ACh receptors from skeletal muscle and electric organ. Ultrastructural studies on antibody binding in the ganglion have shown that the cross-reacting antigen on the neuron surface is located predominantly in synaptic membrane. Biochemical studies have shown that the cross-reacting component has a number of other properties expected for the ganglionic nicotonic ACh receptor and that it is distinct from the alpha-bungarotoxin binding component in the tissue. Here we show that ciliary ganglion neurons grown in dissociated cell culture express a similar component that cross-reacts with monoclonal antibodies to ACh receptors, and that the number of antibody-binding sites on the neurons can be modulated by exposure to cholinergic agonists and a protein neurotoxin that reversibly inhibits ACh receptors on the neurons. In most, though not all, cases, levels of ACh sensitivity associated with the neurons are specifically comodulated in parallel with the changes in number of antibody binding sites. The results suggest that at least a portion of the cross-reacting sites on the surface of ciliary ganglion neurons is likely to represent nicotinic ACh receptors. The fact that in some instances levels of ACh sensitivity can be altered without changing the number of cross-reacting sites, however, leaves open the possibility that not all of the sites are associated with receptors or that the neurons can alter the proportion of receptors that is functional.
Synaptic functions in rat sympathetic neurons in microcultures. III. A Purinergic effect on cardiac myocytes
Authors: Furshpan EJ , Potter DD , Matsumoto SG
Published: March 2018

In the first two of this series of papers, a sensitive microculture procedure was used to show that rat sympathetic neurons grown singly on small islands of heart cells release norepinephrine (NE) and/or acetylcholine (ACh). We report here the release of a third transmitter in response to stimulation of these neurons. This agent was recognized by its effect on the cocultured cardiac myocytes: an inhibition of beating or a hyperpolarization that, in contrast to cholinergic inhibition, was unaffected by atropine (up to 5 microM). Evidence described here indicates that this agent was primarily adenosine (or a closely related compound): the atropine-resistant myocyte inhibition was antagonized by adenosine-receptor blockers [8-phenyltheophylline, theophylline, 7-(2-chloroethyl) theophylline] and was attenuated by an enzyme (adenosine deaminase) that hydrolyzes adenosine to pharmacologically inactive inosine. Many of the neurons, whether initially dissociated from ganglia of newborn or adult rats, evoked this purinergic response, almost always in combination with adrenergic and cholinergic responses. In a few cases it was the only detectable response. The relative strength of the adrenergic, cholinergic, and purinergic responses varied widely from neuron to neuron, suggesting that the adrenergic and purinergic or the cholinergic and purinergic agents were not stored at constant stoichiometric ratios.
Axonal transport of monoclonal antibodies
Authors: Ritchie TC , Fabian RH , Choate JV , Coulter JD
Published: March 2018

Three monoclonal antibodies against rat brain synaptosomes, produced by conventional hybridoma techniques, were screened for their ability to undergo uptake and axonal transport in vivo. Injections of ascitic fluid or of purified immunoglobulin G (IgG) were made into the vitreal chamber of the eye in anesthetized rats to test for anterograde transport in retinal afferents to the contralateral superior colliculus. Retrograde transport by facial nucleus motoneurons was evaluated after injections of antibody into the mystatial vibrissal skin and musculature. Transported immunoglobulins were localized in tissue sections using a modification of the peroxidase-antiperoxidase technique. One monoclonal antibody, S-2C10, was found to undergo anterograde transport in retinal ganglion cells and retrograde axonal transport in facial motoneurons. Transported immunoglobulins were detectable even after injections of dilute antibody solution (0.01– 0.05% IgG), and the uptake-transport process for this antibody appeared saturable. Two other antibodies tested, S-4E9 and S-1G10, exhibited the ability to undergo retrograde transport, but only after injections at relatively high antibody concentrations (greater than or equal to 1.0% IgG). Neither of these antibodies was shown to undergo anterograde transport. Following retrograde transport in motoneurons, the S-2C10 antibody was localized in neuronal perikarya, proximal dendrites, and the adjacent neuropil of the facial motor nucleus. In contrast, the S- 4E9 and S-1G10 antibodies were localized in punctate granules within neuronal cell somata following transport. The findings suggest that the uptake-transport process for the S-2C10 antibody is mediated by adsorptive endocytosis following binding of the antibody to a plasma membrane component (or components) present in somadendritic and nerve terminal membranes.(ABSTRACT TRUNCATED AT 250 WORDS)
Immunohistochemical demonstration of GABAergic neurons in the enteric nervous system
Authors: Jessen KR , Hills JM , Saffrey MJ
Published: March 2018

Application of a highly specific antiserum against GABA to whole-mount preparations of the guinea pig and rat myenteric plexus resulted in discrete and unambiguous immunolabeling of a subpopulation of myenteric neuronal cell bodies and fibers. The anti-GABA antiserum, which was raised against GABA conjugated by glutaraldehyde to BSA, was applied to glutaraldehyde-fixed whole mounts and subsequently visualized using the peroxidase-antiperoxidase method. In the guinea pig ileum and colon, immunoreactive varicose nerve fibers and scattered nerve cell bodies were found within the myenteric plexus. Immunostained fibers were also seen in the tertiary plexus and in the circular muscle, running parallel to the muscle bundles. GABA immunoreactivity in these intramuscular nerves was most pronounced in the colon. In the rat, immunoreactive fibers were prominent throughout the myenteric plexus. They formed dense networks within the myenteric ganglia, which also contained immunopositive nerve cell bodies, and ran between them in the interconnecting nerves. Some immunoreactive nerve fibers were seen in the circular muscle. Control experiments using non-immune sera or adsorbed anti-GABA antiserum showed no staining. These results add a definitive support to our previous suggestion that GABA serves as an autonomic neurotransmitter in vertebrates. In addition to the present immunohistochemical evidence, this hypothesis is supported by biochemical, autoradiographic, transmitter release, electrophysiological, and pharmacological studies on the enteric nervous system of several species. It is now important to determine the functional role of GABAergic neurons within the complex neuronal circuitry that controls gut functions.