bluuebunny/crossref_metadata_2025 huggingface dataset:
Protease nexin-1 and thrombin modulate neuronal Ca2+ homeostasis and sensitivity to glucose deprivation-induced injury
Authors: Smith-Swintosky VL , Zimmer S , Fenton JW , Mattson MP
Published: April 2018

Protease nexin-I (PN-1) is a 44 kDa serine proteinase inhibitor that rapidly inhibits thrombin by forming SDS stable complexes with serine at the catalytic site of the protease. Levels of both PN-1 and thrombin are increased in the brain in response to insults such as ischemia, suggesting roles in neural injury and repair processes. We now report that PN-1-protected cultured rat hippocampal neurons against glucose deprivation- induced damage (GDID), and the protection was abolished by equimolar thrombin. PN-1 reduced resting intracellular free calcium levels ([Ca2+]i) and attenuated the elevation of [Ca2+]i normally associated with GDID. Thrombin reduced neuronal survival and caused a significant increase in [Ca2+]i. Submaximally toxic levels of thrombin exacerbated GDID. Calcium responses to thrombin were attenuated in neurons contacting PN-1 immunoreactive astrocytes. These findings suggest that PN-1 and thrombin play important roles in modulating neuronal calcium responses, and vulnerability, to metabolic/excitotoxic insults.
Semantic encoding and retrieval in the left inferior prefrontal cortex: a functional MRI study of task difficulty and process specificity
Authors: Demb JB , Desmond JE , Wagner AD , Vaidya CJ , Glover GH , Gabrieli JD
Published: April 2018

Prefrontal cortical function was examined during semantic encoding and repetition priming using functional magnetic resonance imaging (fMRI), a noninvasive technique for localizing regional changes in blood oxygenation, a correlate of neural activity. Words studied in a semantic (deep) encoding condition were better remembered than words studied in both easier and more difficult nonsemantic (shallow) encoding conditions, with difficulty indexed by response time. The left inferior prefrontal cortex (LIPC) (Brodmann's areas 45, 46, 47) showed increased activation during semantic encoding relative to nonsemantic encoding regardless of the relative difficulty of the nonsemantic encoding task. Therefore, LIPC activation appears to be related to semantic encoding and not task difficulty. Semantic encoding decisions are performed faster the second time words are presented. This represents semantic repetition priming, a facilitation in semantic processing for previously encoded words that is not dependent on intentional recollection. The same LIPC area activated during semantic encoding showed decreased activation during repeated semantic encoding relative to initial semantic encoding of the same words. This decrease in activation during repeated encoding was process specific; it occurred when words were semantically reprocessed but not when words were nonsemantically reprocessed. The results were apparent in both individual and averaged functional maps. These findings suggest that the LIPC is part of a semantic executive system that contributes to the on-line retrieval of semantic information.
NGF modulates sympathetic innervation of lymphoid tissues
Authors: Carlson SL , Albers KM , Beiting DJ , Parish M , Conner JM , Davis BM
Published: April 2018

Immune tissues are known to be innervated by the sympathetic nervous system, but little is known of what directs the innervation to specific tissue compartments. This report examines the sympathetic innervation of immune tissues in transgenic mice that overexpress nerve growth factor (NGF) in skin and other epithelial structures. NGF transgenic mice exhibited dramatic hyperinnervation in the splenic marginal zone, and the medulla and capsule of peripheral lymph nodes. In contrast, the transgenic mesenteric lymph nodes showed no hyperinnervation. This difference correlated with the location of these nodes; peripheral lymph nodes drain skin where the transgene was expressed while mesenteric lymph nodes drain non-transgene-expressing structures. In addition, the level of innervation correlated with the level of NGF peptide content as assayed by ELISA (3- and 13-fold increase in transgenic spleen and axillary lymph nodes, respectively; no increase in mesenteric nodes) and immunocytochemistry. RT-PCR showed that the NGF transgene was not being expressed in the immune tissues, suggesting that immune tissues can concentrate transgene-produced NGF. It was also demonstrated that the change in innervation had functional consequences. The mitogen response to concanavalin A (ConA) by spleen cells was decreased in the transgenics suggesting that elevated catecholamines or NGF can modulate the proliferative response of these cells. These mice demonstrate that NGF can modulate the sympathetic innervation and function of the immune system.
Non-TrkA-expressing small DRG neurons are lost in TrkA deficient mice
Authors: Silos-Santiago I , Molliver DC , Ozaki S , Smeyne RJ , Fagan AM , Barbacid M , Snider WD
Published: April 2018

Experiments over the past decade in which NGF/TrkA signaling has been abolished by antibodies or targeted gene mutations have shown that 70- 85% of dorsal root ganglion (DRG) neurons require NGF for survival during development. There is consensus that many of the NGF-dependent neurons are small-diameter, peptidergic neurons subserving nociception. These neurons express the signaling receptor for NGF, TrkA. There is a major discrepancy, however, between the percentage of DRG neurons which require NGF for survival (70–85%) and percentage of DRG neurons expressing TrkA receptors (40–50%). The identity of these non-TrkA expressing, NGF-dependent neurons has not been established. A candidate group is a population of small DRG neurons with unmyelinated axons which bind BSI isolectins from the plant, Bandeiraea simplicifolia. We show here that most of these BSI-binding DRG neurons do not express TrkA in adult mice. However, in mutant mice in which NGF/TrkA signaling has been abolished by inactivation of the trkA gene, BSI-staining in the DRG and dorsal horn is completely eliminated. BSI-binding DRG cells are thus the first identified neuronal population in which cells do not express TrkA in maturity, but require NGF/TrkA signaling for survival during embryonic development. These neurons must either depend on NGF via a novel, indirect mechanism or alternatively, downregulate TrkA expression during development.
The notochord and floor plate guide growth cones in the zebrafish spinal cord
Authors: Greenspoon S , Patel CK , Hashmi S , Bernhardt RR , Kuwada JY
Published: April 2018

Elimination of the floor plate, a row of distinctive cells at the ventral midline of the spinal cord, dramatically increased the frequency of errors made by specific growth cones in the zebrafish embryo. This demonstrated that the floor plate participated in guiding specific growth cones at the ventral midline of the spinal cord. However, since a significant proportion of these growth cones followed their normal pathway despite the absence of the floor plate, we hypothesized that a second source of cues must exist at or near the ventral midline. We tested whether the notochord, which is located just ventral to the spinal cord, was an additional source of pathfinding cues by eliminating it prior to axonogenesis. Laser ablation of the notochord in wildtype embryos increased errors by spinal growth cones. Likewise, spinal growth cones made errors in no tail mutants that are missing the notochord but not the floor plate. These results demonstrate that the notochord also participates in guiding growth cones at the ventral midline. Furthermore, removal of both the floor plate and notochord resulted in a higher error rate than removal of either one alone. These results suggest that the notochord and floor plate normally act in concert to guide spinal growth cones at the ventral midline.
Early ontogeny of the secondary proliferative population of the embryonic murine cerebral wall
Authors: Takahashi T , Nowakowski RS , Caviness VS
Published: April 2018

The present report is an analysis of the proliferative behavior of the secondary proliferative population (SPP) of the dorsomedial region of the embryonic mouse cerebral wall. It is based upon experiments undertaken on embryonic days 14–16 (E14-E16) and exploits methods in which proliferative cells are labeled in S phase with either or both bromodeoxyuridine and tritiated thymidine. The SPP, which arises from the PVE by E13, is principally the progenitor population to the neuroglial population of the mature neocortex and subjacent cerebral wall. By the end of E14 the SPP comes to be distributed diffusely from the outer margin of the ventricular zone throughout subventricular zone and intermediate zone. The length of the cell cycle of the SPP is constant at approximately 15 hr throughout this interval; thus, this population undergoes 1.6 cell cycles/24 hr or 3.2 cycles in the course of the 48 hr period, E14-E16. Over this 48 hr period, the SPP increases from 11% to 35% of the total proliferative population of the dorsomedial cerebral wall. The absolute size of the SPP increases nearly sixfold. With these values taken together it may be estimated that approximately 87% of postmitotic cells of the SPP reenter S phase after each cell division in this interval which means that only approximately 13% of the proliferative population exits the cycle. These findings illustrate the massive expansion of the SPP antecedent to the explosive diffusion of glial cells through the neocortex and subjacent cerebral wall as neuronal migration comes to completion and neocortical growth and differentiation accelerate.
Identification of mammalian noggin and its expression in the adult nervous system
Authors: Valenzuela DM , Economides AN , Rojas E , Lamb TM , Nunez L , Jones P , Lp NY , Espinosa R , Brannan CI , Gilbert DJ
Published: April 2018

The multiple roles of noggin during dorsal fate specification in Xenopus embryos, together with noggin's ability to directly induce neural tissue, inspired an effort to determine whether a similar molecule exists in mammals. Here we describe the identification of human and rat noggin and explore their expression patterns; we also localize the human NOGGIN gene to chromosome 17q22, and the mouse gene to a syntenic region of chromosome 11. Mammalian noggin is remarkably similar in its sequence to Xenopus noggin, and is similarly active in induction assays performed on Xenopus embryo tissues. In the adult mammal, noggin is most notably expressed in particular regions of the nervous system, such as the tufted cells of the olfactory bulb, the piriform cortex of the brain, and the Purkinje cells of the cerebellum, suggesting that one of the earliest acting neural inducers also has important roles in the adult nervous system.
ARIA is concentrated in nerve terminals at neuromuscular junctions and at other synapses
Authors: Sandrock AW , Goodearl AD , Yin QW , Chang D , Fischbach GD
Published: April 2018

Skeletal muscle ACh receptors (AChRs) accumulate at neuromuscular junctions (nmjs) at least partly because of the selective induction of AChR subunit genes in subsynaptic myotube nuclei by the motor nerve terminal. Additionally, mammalian AChRs undergo a postnatal change in subunit composition from embryonic (alpha 2 beta gamma delta) to adult (alpha 2 beta epsilon delta) forms, a switch that also depends on innervation. ARIA, a protein purified from chicken brains based on its ability to induce AChR synthesis in primary chick muscle cells, is a strong candidate for being the molecule responsible for these early developmental events. ARIA mRNA has been detected in embryonic motor neurons during synapse formation, and the gene continues to be expressed postnatally. In this report, we provide evidence that ARIA- like immunoreactivity is concentrated in rat motor nerve terminals from early postnatal ages, and that it can be detected in motor neurons in E18 embryos. ARIA is also detectable in axons within colchicine-treated sciatic nerves, suggesting that the protein in the nerve terminal has been transported from the cell body. ARIA mRNA is present in, but not restricted to, cholinergic neurons. Likewise, we report here that ARIA- like immunoreactivity is present in some noncholinergic central synapses. We also present evidence that isoforms of ARIA are differentially distributed among functionally distinct classes of neurons.
Activation of dopamine cell firing by repeated L-DOPA administration to dopamine-depleted rats: its potential role in mediating the therapeutic response to L-DOPA treatment
Authors: Harden DG , Grace AA
Published: April 2018

The administration of L-dihydroxyphenylalanine (L-DOPA) to patients with Parkinson's disease is known to produce acute effects that include the reduction of rigidity as well as delayed therapeutic actions involving the resumption of complex motor behavior. In order to examine the potential role of dopamine (DA) cell activity in mediating these responses, the effects of acute and repeated L-DOPA administration on the electrophysiological activity of the residual dopamine (DA) neurons were examined in rats that had received partial 6-hydroxydopamine (6- OHDA)-induced DA lesions. DA cell activity was assessed along three dimensions: (1) the relative proportion of DA neurons exhibiting spontaneous spike firing, (2) their basal firing rate, and (3) their firing pattern. Following 6-OHDA-induced DA depletion, rats were treated for 1 month with saline or L-DOPA. In addition, rats from each group received either an acute injection of L-DOPA or saline on the day of recording. In rats receiving repeated saline treatment, the DA neurons recorded following acute L-DOPA administration were firing at significantly slower basal firing rates and exhibited less burst firing when compared to saline-pretreated rats given acute saline. In contrast, DA cells recorded from rats that had received repeated L-DOPA administration for 4 weeks followed by an acute saline injection did not exhibit any significant differences from DA cells of intact control rats with respect to basal firing rate or firing pattern; however, there was a substantial increase in the proportion of DA neurons exhibiting spontaneous spike firing after correcting for 6-OHDA-induced cell loss. In addition, in rats receiving repeated L-DOPA treatment, the DA cells recorded following acute administration of L-DOPA showed significantly less of a reduction in firing rate when compared to the cells recorded following acute L-DOPA in the saline treatment group. These results show that: (1) acute L-DOPA administration appears to exert its actions by DA autoreceptor stimulation, whereas (2) repeated L-DOPA administration increases the proportion of spontaneously active DA neurons in partially lesioned rats. As a result, repeated L-DOPA administration would be expected to cause an increase in spike- dependent DA release as a consequence of the greater proportion of DA cells showing spontaneous activity. This may be the major factor underlying the delayed therapeutic benefits of L-DOPA therapy in the treatment of Parkinson's disease.
Differential expression of two vesicular monoamine transporters
Authors: Peter D , Liu Y , Sternini C , de Giorgio R , Brecha N , Edwards RH
Published: April 2018

Specific transport proteins package classical neurotransmitters into vesicles so that their release can be regulated by neural activity. Previous studies have suggested that a single activity mediates the vesicular transport of monoamines in the adrenal gland, brain, and other tissues such as mast cells and platelets. However, molecular cloning has recently identified two vesicular transporters for monoamines. Although the predicted proteins are closely related in sequence, they show a range of differences in their physiologic and pharmacologic properties. To clarify further the biological significance of the observed functional differences, we have generated anti-peptide antibodies to the C-termini of the two transporters and used them to determine the distribution and localization of the proteins in the rat. We have detected expression of vesicular monoamine transporter 1 (VMAT1) in adrenal chromaffin cells but not in neural cells. Interestingly, some adrenal chromaffin cells also express VMAT2 but the amount of VMAT2 relative to VMAT1 appears much lower than in the bovine adrenal gland. In contrast, sympathetic ganglion cells express only VMAT2, as do enteric neurons and enterochromaffin-like cells of the stomach. Thus, although adrenal chromaffin cells, sympathetic and enteric neurons derive from the neural crest, they express different vesicular amine transporters. In the CNS, dopamine, norepinephrine, epinephrine, 5-HT, and histamine cell groups all express VMAT2. These findings are consistent with the functional characteristics of VMAT1 and VMAT2 and help to explain several classic pharmacological observations. VMAT2-immunoreactivity is generally stronger in cell bodies, proximal dendrites and axonal processes, indicating the potential for monoamine storage at each of these sites. Surprisingly, dopaminergic interneurons in the olfactory bulb show no detectable immunoreactivity for either VMAT1 or VMAT2.
NGF regulates the PC12 cell cycle machinery through specific inhibition of the Cdk kinases and induction of cyclin D1
Authors: Yan GZ , Ziff EB
Published: April 2018

We have examined the effects of NGF on components of the PC12 cell cycle machinery. We show that NGF represses over 6–8 d the levels of specific cdk kinase proteins and the G2-M phase specific cyclin B1 and the S phase marker PCNA as well as the level of phosphorylation of the retinoblastoma (Rb) protein. All of these changes may provide a basis for a NGF block to cell cycling. Unexpectedly, the G1 phase-specific cyclin D1 was dramatically increased by inducers of differentiation (NGF and FGF), but not by inducers of proliferation (EGF and insulin). Although the levels of cyclin D1/cdk2 and cyclin D1/cdk4 complexes increased following NGF treatment, as did cyclin D1/Rb complexes, the associated kinase activities declined, indicating that NGF also induces an inhibitor of cdk kinase activity. In agreement, NGF induced the cdk inhibitory protein, p21, which was found in cyclin D1/cdk kinase complexes after NGF treatment. We show that vector over expression of cyclin D1 in PC12 is sufficient on its own to arrest the cells in G1 phase and inhibit expression of PCNA. These results indicate that NGF induction of cyclin D1 and inactivation of cdk kinases, the latter possibly by increase of p21, play a central role in the NGF block of PC12 cell cycling.
The persistence of behavioral sensitization to cocaine parallels enhanced inhibition of nucleus accumbens neurons
Authors: Henry DJ , White FJ
Published: April 2018

The mesoaccumbens dopamine system is intricately involved in the locomotor stimulation produced by cocaine and sensitization of this effect following repeated cocaine administration. The mechanisms responsible for the expression of sensitized locomotion appear to involve alterations in both presynaptic (increased dopamine release) and postsynaptic (increased responsiveness of dopamine D1 receptors) aspects of dopamine neurotransmission within the nucleus accumbens. The present experiments used behavioral and single-cell electrophysiological techniques to determine the persistence of sensitization and of enhanced postsynaptic responses to cocaine within the nucleus accumbens following various periods of withdrawal from repeated cocaine treatment (10 mg/kg i.p., twice daily, 14 d). Behavioral sensitization to the locomotor stimulant effects of cocaine was evident after 1 d, 1 week, and 1 month, but not 2 months of withdrawal. A similar time course was observed for the enhanced efficacy of cocaine-induced inhibition of nucleus accumbens neurons, whether cocaine was administered systemically or locally by microiontophoresis. Nucleus accumbens neurons also exhibited sensitized inhibitory responses to iontophoretically applied GABA after 1 d of withdrawal, but not later times. These findings suggest that cocaine sensitization is relatively persistent, but not necessarily permanent, and support the hypothesis that expression of behavioral sensitization to cocaine involves actions within the NAc, particularly those mediated by dopamine D1 receptors.
Distribution of an APP homolog, APLP2, in the mouse olfactory system: a potential role for APLP2 in axogenesis
Authors: Thinakaran G , Kitt CA , Roskams AJ , Slunt HH , Masliah E , von Koch C , Ginsberg SD , Ronnett GV , Reed RR , Price DL
Published: April 2018

Deposition of beta-amyloid (A beta) in senile plaques is a major pathological characteristic of Alzheimer's disease. A beta is generated by proteolytic processing of amyloid precursor proteins (APP). APP is a member of a family of related polypeptides that includes amyloid precursor-like proteins APLP1 and APLP2. To examine the distribution of APLP2 in the nervous system, we generated antibodies specific for APLP2 and used these reagents in immunocytochemical and biochemical studies of the rodent nervous system. In this report, we document that in cortex and hippocampus, APLP2 is enriched in postsynaptic compartments. In the olfactory system, however, APLP2 is abundant in olfactory sensory axons, and axon terminals in glomeruli. Confocal microscopy revealed that APLP2 is present in both pre- and postsynaptic compartments in the olfactory bulb. Notably, mRNA encoding chondroitin sulfate glycosaminoglycan (CS GAG)-modified forms of APLP2 are enriched in the olfactory epithelium, relative to alternatively-spliced mRNA, encoding CS GAG-free forms of APLP2. In addition, we demonstrate that CS-modified APLP2 forms accumulate in the olfactory bulb. CS proteoglycans are known to play an important role in regulating cell migration and neuronal outgrowth. Since sensory neurons in the olfactory epithelium are in a state of continual turnover, axons of newly generated cells must establish synaptic connections with neurons in the olfactory bulb in adult life. The presence of APLP2 in olfactory sensory axons and glomeruli is consistent with the view that this protein may play an important role in axonal pathfinding and/or synaptogenesis.
Persistent polyneuronal innervation in partially denervated rat muscle after reinnervation and recovery from prolonged nerve conduction block
Authors: Barry JA , Ribchester RR
Published: April 2018

The contribution of activity to the long-term stability of synaptic connections is a subject of ongoing debate. In the present study we examined the effects of recovery from chronic disuse on the pattern of reinnervation of partially denervated adult rat skeletal muscles, using tension measurements, intracellular recordings, and observations of vital staining with activity-dependent styryl dyes. Fourth deep lumbrical muscles were partially denervated by crushing the lateral plantar nerve (LPN) bilaterally. Denervated muscle fibers became innervated by sprouts from the sural nerve (SN); 17-23 d after LPN crush, conduction in the right sciatic nerve was blocked by connecting an osmotic minipump containing tetrodotoxin to a cuff placed around the nerve. Distal muscles remained continuously paralysed for 10-19 d. After 2 weeks of nerve block the tension produced by stimulating the regenerated LPN axons had reached about 70% of the total. Regenerating axons in contralateral muscles reinnervated only about 55% of the muscle fibers. The level of dual innervation by both regenerating and intact axons reached about 50% of the total muscle fibers after 2 weeks of paralysis, but only about 20% in contralateral controls. We then measured the rate and amount of decline in motor unit tension and polyneuronal innervation in reinnervated muscles during an eight week period of recovery from nerve block. Some LPN and SN connections regressed within 2-4 weeks, but about 35% of the muscle fibers still retained convergent inputs from LPN and SN motor axons 8 weeks after activity had resumed. This was about twice the level observed in contralateral reinnervated muscles. Vital staining with the styryl dyes FM1-43 and RH414 confirmed that many of the reinnervated motor end- plates were convergently supplied by both SN and LPN axons. Intracellular recordings showed that most of the dually innervated fibers in paralyzed muscles were supplied by suprathreshold inputs from both LPN and SN axons. The increased excitability of these muscle fibers was partly explained by their two-fold increased input resistance. Input resistance recovered to control levels within 4 weeks of resumption of activity, but dually innervated fibers in previously blocked muscles still gave mostly suprathreshold responses to stimulation of both the LPN and the SN. We conclude that chronic nerve conduction block generates or sustains a local environment which allows some convergent synaptic inputs on reinnervated muscle fibers to become consolidated and strengthened, independent of subsequent neuromuscular activity.
Cerebellar precursors transplanted to the neonatal dentate gyrus express features characteristic of hippocampal neurons
Authors: Vicario-Abejon C , Cunningham MG , McKay RD
Published: April 2018

During the development of the CNS, a salient issue is whether neuronal phenotype is defined by the lineage or by the environment of precursor cells. Transplants permit these two possibilities to be tested, as cell fate can be examined in a new location. Dissociated cerebellar cells from newborn rats treated with tritiated thymidine or from NSE-lacZ transgenic mice were grafted into the dentate gyrus of the developing hippocampus. Implanted cells integrated into the granule cell layer, which contains the cell bodies of host granule neurons. Immunohistochemistry showed that grafted cells in the granule cell layer, like the host hippocampal granule neurons, were calbindin positive and upregulated FOS in a seizure paradigm. Electron microscopic analysis also showed that cells grafted to the dentate gyrus share features with host dentate neurons. These assays indicate that transplanted cerebellar cells acquired morphological and antigenic features characteristic of hippocampal neurons. These results show that metencephalic precursors are capable of differentiating in response to signals in the telencephalon, suggesting that the environment controls the regional fate of neuronal precursor cells during neurogenesis.
Upregulation of bax protein levels in neurons following cerebral ischemia
Authors: Krajewski S , Mai JK , Krajewska M , Sikorska M , Mossakowski MJ , Reed JC
Published: April 2018

The patterns of expression of the bcl-2, bax, and bci-X genes were examined immunohistochemically in neurons of the adult rat brain before and after 10 min of global ischemia induced by transient cardiac arrest. High levels of the cell death promoting protein Bax and concomitant low levels of the apoptosis-blocking protein Bcl-2 were found in some populations of neurons that are particularly sensitive to cell death induced by transient global ischemia, such as the CA1 sector of the hippocampus and the Purkinje cells of the cerebellum. Moreover, within 0.5 to 3 hr after an ischemic episode, immunostaining for Bax was markedly increased within neurons with morphological features of degeneration in many regions of the brain. Use of a two-color staining method for simultaneous analysis of Bax protein and in situ detection of DNA-strand breaks revealed high levels of Bax immunoreactivity in many neurons undergoing apoptosis. Postischemic elevations in Bax protein levels in the hippocampus, cortex, and cerebellum were also demonstrated by immunoblotting. At early times after transient ischemia, regulation of Bcl-2 and Bcl-x protein levels varied among neuronal subpopulations, but from 3 hr on, those neurons with morphological evidence of degeneration uniformly contained reduced levels of Bci-2 and particularly Bci-X immunoreactivity. The findings suggest that differential expression of some members of the bcl-2 gene family may play an important role in determining the relative sensitivity of neuronal subpopulations to ischemia and that postischemic alterations in the expression of bax, bcl-2, and bcl-x may contribute to the delayed neuronal cell death that occurs during the repurfusion phase after a transient ischemic episode.
Role of calcium channel subtypes in calcium transients in hippocampal CA3 neurons
Authors: Elliott EM , Malouf AT , Catterall WA
Published: April 2018

Multiple subtypes of voltage-gated calcium channels are differentially localized in brain neurons suggesting that they serve distinct roles in neuronal excitation and signaling. In organotypic hippocampal slice cultures, class D (L-type) calcium channels are predominantly located in the cell bodies of CA3 neurons while class B (N-type) and class A (P or Q-type) are localized in dendrites and associated presynaptic terminals with relatively low somal expression. Using specific antagonists to inhibit calcium transients recorded in CA3 neuronal cell bodies, we found that L-type calcium channels have a predominant role in somal calcium transients elicited by trains of strong stimuli applied to either the soma or the distal apical dendrite while class A calcium channels make a smaller contribution. Presynaptic class B (N- type) and class A (P- and/or Q-type) calcium channels are critical for glutamate-mediated synaptic transmission onto the dendrites of CA3 neurons. Postsynaptic class A and B calcium channels detected on the dendritic shaft by immunocytochemistry were not found to contribute substantially to somal calcium transients during repetitive stimulation of distal dendrites, but sodium channels were required for calcium transients elicited by somatic or dendritic stimulation. Our results show that the different calcium channel subtypes serve distinct roles in cellular activation and transmission of signals in CA3 neurons, consistent with their differential subcellular localization.
Axotomy-induced axonal degeneration is mediated by calcium influx through ion-specific channels
Authors: George EB , Glass JD , Griffin JW
Published: April 2018

We examined the role of extracellular calcium entry, the possible involvement of axonal calcium channels, and the potential protective effect of calcium channel and calpain antagonists in axotomy-induced axonal degeneration using murine dorsal root ganglia in cell culture. We found that calcium entry is both necessary and sufficient to induce axonal degeneration after axotomy, and may be inhibited by cobalt, manganese, dihydropyridines, and bepridil. Tetrodotoxin and omega- conotoxin are ineffective in preventing axonal degeneration. The activation of calpains also appears to be necessary and sufficient for axonal degeneration to proceed, and can be blocked with membrane- permeant leupeptin analogs and the oxirane aloxistatin. Although other calcium-activated events may occur, it appears that inhibition of calpain is sufficient to preserve the axon at the light microscope level, and to prevent axonal cytoskeleton degradation as detected by immunofluorescent staining. Our results suggest that axonal degeneration after axotomy involves the following sequence of events: (1) a lag-period after axotomy prior to the onset of axonal degeneration, (2) entry of calcium into the axon through an intact axolemma via a calcium-specific ion transport mechanism, (3) activation of calcium-dependent effector molecules such as calpains, (4) degradation of the axonal cytoskeleton. The details of the second step require further elucidation, and are of particular interest because this step is a potential target for therapies directed towards peripheral neuropathies.
Phosducin and PP33 are in vivo targets of PKA and type 1 or 2A phosphatases, regulators of cell elongation in teleost rod inner-outer segments
Authors: Pagh-Roehl K , Lin D , Su L , Burnside B
Published: April 2018

Teleost rod photoreceptors elongate in the light and shorten in darkness. We are investigating the role of cAMP-dependent protein kinase (PKA), phosphatases and target phosphoproteins in the regulation of photoreceptor cell shape. Preparations of rod fragments, consisting of the motile inner segment with attached photosensory outer segment (RIS-ROS), undergo light-stimulated elongation in culture. The PKA- selective inhibitor, H89, enhanced RIS-ROS elongation in both light and darkness, suggesting that elongation is associated with dephosphorylation of PKA substrates. Okadaic acid and calyculin A, inhibitors of type 1 and 2A phosphatases, blocked light-dependent and light-independent elongation with relative potencies suggesting that elongation requires dephosphorylation by type 1 phosphatase in light and type 2A phosphatase in darkness. To identify targets of PKA and phosphatases, RIS-ROS were isolated from retinas prelabeled with 32P- orthophosphate, and then incubated in the presence of kinase inhibitors or phosphatase inhibitors. Two phosphoproteins, PP33 and PP35, were phosphorylated by PKA and dephosphorylated by type 1 or 2A phosphatases in light- and dark-cultured RIS-ROS. PP35 (but not PP33) was immunoprecipitated by an antibody to phosducin, a PKA-regulated modulator of phototransduction (Lee et al., 1992); PP35 was also phosphorylated in vitro by a Ca2+ calmodulin-activated kinase. PP33 further differed from PP35 in its phosphopeptide maps and phosphorylation by PKC. We conclude that RIS-ROS elongation is correlated with the dephosphorylation of PKA substrates by type 1 or 2A phosphatases. Candidate mediator proteins include PP35, a fish phosducin homolog, and PP33, a newly described photoreceptor phosphoprotein.
Cloning and characterization of chi-1: a developmentally regulated member of a novel class of the ionotropic glutamate receptor family
Authors: Ciabarra AM , Sullivan JM , Gahn LG , Pecht G , Heinemann S , Sevarino KA
Published: April 2018

Ionotropic glutamate receptors are composed of homomeric or heteromeric configurations of glutamate receptor subunits. We have cloned a member of a novel class of the rat ionotropic glutamate receptor family, termed chi-1. This subunit exhibits an average identity of 27% to NMDA subunits and 23% to non-NMDA subunits. Regional transcript levels of chi-1 are elevated just prior to and during the first postnatal week, with the highest levels present in the spinal cord, brainstem, hypothalamus, thalamus, CA1 field of the hippocampus, and amygdala. The spatial distribution of chi-1 expression is similar from postnatal day 1 (P1) to adulthood. However, transcript levels decline sharply between P7 and P14 and remain attenuated into adulthood. Functional expression studies in Xenopus oocytes injected with in vitro transcribed chi-1 RNA did not demonstrate agonist-activated currents. Pairwise expression of chi-1 with members of the AMPA, KA, or delta class of glutamate recepto subunits either failed to generate agonist-activated currents or failed to alter the underlying current generated by the coexpressed subunit. However, coexpression of chi-1 with subunits forming otherwise functional NMDA receptors resulted in an inhibition of current responses. Since chi-1 did not alter the currents generated by non-NMDA subunits, this suggests that chi-1 may specifically interact with NMDA receptor subunits. Further characterization will be required to establish the precise role of this glutamate receptor subunit in neuronal signaling.
Sympathetic neurons in neonatal rats require endogenous neurotrophin-3 for survival
Authors: Zhou XF , Rush R
Published: April 2018

Gene deletion of neurotrophin-3 (NT3) results in severe sensory and sympathetic deficits that are incompatible with postnatal life in mice. We have now addressed the question of whether NT3 plays a role in the postnatal animal. An antiserum specific for NT3 and capable of blocking the survival effect of the factor in vitro has been generated and given to neonatal rats. Antiserum administration during either or both of the first 2 postnatal weeks resulted in a 54-74% reduction in the size of the superior cervical ganglia, reflecting a loss of as many as 80% of all neurons, with a predominant effect on the neuropeptide Y containing subpopulation. The immunoreactivities of NPY, tyrosine hydroxylase, and p75 low affinity NGF receptor in nerve terminals within the mesenteric artery were also reduced, whereas that of the sensory neuron neuropeptide, calcitonin gene related peptide was less affected. These results demonstrate that the majority of sympathetic neurons of the neonatal rat are dependent on endogenous NT3 for their survival at a time when they are also dependent on another survival factor, NGF, thus apparently providing a clear example of a population of neurons requiring for their survival the simultaneous supply of more than one trophic factor.
Expression of EPSP/spike potentiation following low frequency and tetanic stimulation in the CA1 area of the rat hippocampus
Authors: Bernard C , Wheal HV
Published: April 2018

Low frequency stimulation (LFS, 1 Hz for 15 min) has been shown to produce an NMDA receptor dependent homosynaptic long-term depression (LTD) of synaptic potentials in the CA1 area of the rat hippocampus. Here we describe experiments aimed at characterizing EPSP/spike (E/S) coupling associated with this form of LTD. Our data show that following LFS neurons have a higher probability of synchronous discharge in response to a population EPSP of fixed slope (E/S potentiation). This E/S potentiation was not significantly enhanced by a tetanic stimulation. When the protocol was reversed, that is, starting with a tetanic stimulus, E/S potentiation was observed which was unaffected by a subsequent LFS. Saturating these synaptic responses to either a maximal or a minimal value produced similar effects on E/S coupling. E/S depression was never encountered. Finally, we found that the expression of E/S potentiation did not require the activation of NMDA receptors. These data suggest that at the level of a local neuronal network in the CA1 area, LFS is not a very powerful tool since the synaptic depression is associated with a potentiation of the population response of these neurons. Furthermore, the expression of E/S dissociation seems different from that of homosynaptic long-term potentiation and LTD.
Cannabinoids activate an inwardly rectifying potassium conductance and inhibit Q-type calcium currents in AtT20 cells transfected with rat brain cannabinoid receptor
Authors: Mackie K , Lai Y , Westenbroek R , Mitchell R
Published: April 2018

Rat brain cannabinoid receptor (CB-1) was stably transfected into the murine tumor line AtT-20 to study its coupling to inwardly rectifying potassium currents (Kir) and high voltage-activated calcium currents (ICa). In cells expressing CB-1 (“A-2” cells), cannabinoid agonist potently and stereospecifically activated Kir via a pertussis toxin- sensitive G protein. ICa in A-2 cells was sensitive to dihydropyridines and omega CTX MVIIC, less so to omega CgTX GVIA and insensitive to omega Aga IVa. In CB-1 expressing cells, cannabinoid agonist inhibited only the omega CTX MVIIC-sensitive component of ICa. Inhibition of Q- type ICa was voltage dependent and PTX sensitive, thus similar in character to the well-studied modulation of N-type ICa. An endogenous cannabinoid, anandamide, activated Kir and inhibited ICa as efficaciously as potent cannabinoid agonist. Immunocytochemical studies with antibodies specific for class A, B, C, D, and E voltage-dependent calcium channel alpha 1 subunits revealed that AtT-20 cells express each of these major classes of alpha 1 subunit.
Cholinergic modulation of activity-dependent synaptic plasticity in the piriform cortex and associative memory function in a network biophysical simulation
Authors: Hasselmo ME , Barkai E
Published: April 2018

The effect of activation of cholinergic receptors on long-term potentiation (LTP) in rat piriform cortex pyramidal cells was studied using extracellular and intracellular recordings in brain slice preparations. The functional role of this modulation was studied in a realistic network biophysical stimulation. Repetitive stimuli were applied in two paradigms: one in which the recorded cell was held at its resting potential and one in which synaptic activity was superimposed on a depolarizing pulse strong enough to evoke four action potentials. In the absence of cholinergic modulation, stimulation at 5 Hz induced LTP primarily in the second condition (13.7%, n = 6 out of 9, measured at 10 min after tetanus). When stimuli were applied in the presence of the muscarinic agonist carbachol (20 microM), LTP of greater amplitude was induced in both paradigms (resting: 41.5%, n = 11 out of 16, depolarized: 36%, n = 5 out of 7, measured at 10 min after tetanus). Increases in excitatory postsynaptic potential (EPSP) amplitudes in the presence of carbachol were gradual, starting at the time 5 Hz stimuli were applied and continuing until an action potential was evoked synaptically. In the presence of the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV), LTP could not be induced. The muscarinic antagonist atropine also prevented LTP induction in the presence of carbachol. Cholinergic modulation of synaptic plasticity was examined in a previously developed realistic biophysical network simulation. In simulations, use of a gradual rate of synaptic modification prevented excessive strengthening of synapses, which could cause interference between stored patterns. The effect of excess synaptic strengthening can be avoided by introducing activity dependent depression of synaptic strength. Coactivation of learning and depression rules results in a stable system where no interference occurs, at any rate of learning. Implementing the depression rule only during recall does not improve the network's performance. This implies that reduction in the strength of synaptic connections should occur in the presence of ACh, more than in normal conditions. We propose that two effects of ACh--enhancement of LTP and enhancement of LTD--should act together to increase the stability of the cortical network in the process of acquiring information.
A serine proteinase involved in contact mediated repulsion of retinal growth cones by DRG neurites
Authors: Baird JL , Raper JA
Published: April 2018

Cultured retinal ganglion cell growth cones avoid neurites extending from PNS explants. Here we characterize a growth cone collapsing activity in detergent extracts of newborn calf adrenal plasma membranes that has characteristics expected for an avoidance cue on peripheral neurites. This adrenal derived activity induces the rapid and reversible collapse of retinal growth cones grown on either of two distinct adhesion substrata, mouse laminin or the chick cell surface axonal glycoprotein G4/NgCAM. The collapsing activity is inhibited by several different types of serine proteinase inhibitors, including the irreversible inhibitor PPACK (D-phenylalanyl-prolyl-arginine chloromethyl ketone). The activity is not inhibited by the specific thrombin inhibitor, hirudin. We have named the adrenal derived collapsing activity erase. PPACK blocks the collapse of temporal retinal growth cones on contact with DRG neurites, but does not block the collapse of the same growth cones on contact with nasal retinal neurites. These results support the hypothesis that a serine proteinase on peripheral axons serves as an avoidance cue which induces contact mediated collapse of retinal growth cones.
Altered sexual partner preference in male ferrets given excitotoxic lesions of the preoptic area/anterior hypothalamus
Authors: Paredes RG , Baum MJ
Published: April 2018

Numerous experiments suggest that perinatal exposure of male vertebrates to testosterone (T), or its estrogenic metabolites, masculinizes aspects of coital function, including males' characteristic preference to seek out and mate with a female as opposed to another male conspecific. Other research has shown that this perinatal action of sex steroids also masculinizes aspects of neuronal morphology in the medial preoptic area/anterior hypothalamus (mPOA/AH). We asked whether neurons of the mPOA/AH contribute to males' preference to mate with a female. The ferret is an ideal species in which to ask this question. When tested in a T-maze after gonadectomy and treatment with estradiol benzoate (EB), female ferrets prefer to approach and receive neck grips from a stimulus male whereas males prefer to approach and neck grip an estrous female. In the minority of trials when EB-treated males approach a stimulus male, they occasionally receive a neck grip to which they display receptive postures as opposed to agonistic behaviors. In Experiment 1 castrated, EB-treated male ferrets which received bilateral infusions of the NMDA excitotoxin, quinolinic acid aimed at the dorsomedial POA/AH, preferred to approach a stimulus male significantly more often than groups of control males which either received a sham lesion, received a unilateral mPOA/AH lesion or in which bilateral infusions of quinolinic aci produced no histologically detectible excitotoxic damage to the mPOA/AH. Males with bilateral mPOA/AH lesions also displayed neck gripping on a significantly lower percentage of trials than control males when they approached the stimulus female. Ovariectomized, EB-treated female ferrets with bilateral mPOA/AH lesions, like control females, preferred to approach and receive neck grips from a stimulus male. The males used in Experiment 1 had never experienced circulating levels of T characteristic of the breeding season. Therefore, in Experiment 2 prepubertally gonadectomized males and females were treated chronically with a high dose of T propionate (TP) and tested several times with a receptive female prior to brain surgery. Males which received bilateral excitotoxic lesions of the mPOA/AH neck gripped and mounted stimulus females significantly less than control males. Again, when given EB followed by T-maze tests of partner preference, males with bilateral mPOA/AH lesions, like sham-operated female controls, preferred to approach the sexually active stimulus male significantly more often than control males, which preferred to approach the stimulus female. Our results suggest that neurons in the mPOA/AH play an important role in the integration of sensory cues which determine heterosexual partner preference in the male ferret, in addition to facilitating masculine coital performance.
Modeling direction selectivity of simple cells in striate visual cortex within the framework of the canonical microcircuit
Authors: Suarez H , Koch C , Douglas R
Published: April 2018

Nearly all models of direction selectivity (DS) in visual cortex are based on feedforward connection schemes, where geniculate input provides all excitatory synaptic input to both pyramidal and inhibitory neurons. Feedforward inhibition then suppresses feedforward excitation for nonoptimal stimuli. Anatomically, however, the majority of asymmetric, excitatory, synaptic contacts onto cortical cells is provided by other cortical neurons, as embodied in the Canonical Microcircuit of Douglas and Martin (1991). In this view, weak geniculate input is strongly amplified in the preferred direction by the action of intracortical excitatory connections, while in the null direction inhibition reduces geniculate-induced excitation. We investigate analytically and through biologically realistic computer simulations the functioning of a cortical network based on massive excitatory, cortico-cortical feedback. The behavior of this network is compared to physiological data as well as to the behavior of a purely feedforward model of DS based on nonlagged input. Our model explains a number of puzzling features of direction selective simple cells, including the small somatic input conductance changes that have been measured experimentally during stimulation in the null direction, and the persistence of DS while fully blocking inhibition in a single cell. Although the operation at the heart of our network is amplification, the network passes the linearity test of (Jagadeesh et al., 1993). We make specific predictions concerning the effect of selective blockade of cortical inhibition on the velocity-response curve.