bluuebunny/crossref_metadata_2025 huggingface dataset:
Superinnervation enhances the dendritic branching pattern of the Mauthner cell in the developing axolotl
Authors: Goodman LA , Model PG
Published: March 2018

Mauthner cells (M-cells) occur as a pair of large, uniquely identifiable neurons at ear level in the hindbrain of premetamorphic amphibians. Each receives synapses from the ipsilateral vestibular nerve (nVIII); these morphologically distinctive terminals, or club endings, are confined to the proximoventral surface and branches of the M-cell lateral dendrite. We have superinnervated this portion of the M- cell to examine the extent to which forming afferent contacts regulate the growth and branching of the lateral dendrite. Superinnervation was brought about in the developing axolotl (Ambystoma mexicanum) by unilaterally implanting an extra vestibular primordium rostral to the in situ one. The contralateral side served as control. When the larvae reached 21 mm in length, the ectopic nerve was labeled with HRP. Subsequent microscopic examination revealed that the grafts developed into anatomically normal ears. The HRP-labeled ectopic axons entered the medulla at the level of nV and confined to the nVIII tract, coursed caudad toward the ipsilateral M-cell. Electron microscopic analysis demonstrated labeled club endings on the appropriate region of the M- cell lateral dendrite. The number of club endings on experimental M- cells was significantly greater than that on the contralateral controls, and the extra terminals appeared to be distributed randomly among unlabeled ones. Comparison of reconstructed experimental and control M-cells revealed that superinnervation produced a localized enhancement of dendritic branching in the region receiving the extra nVIII synapses. In the donor embryos (those from which the vestibular primordium was removed), M-cells were unilaterally deprived of nVIII afferents. Comparison of reconstructed experimental and control M-cells in 21 mm donor larvae demonstrated that deprivation produced a localized decrease of dendritic surface in the region that normally receives nVIII synapses. Together, these data show that ingrowing axons stimulate dendritic growth and thus regulate the development of a normal dendritic branching pattern on target neurons.
High-affinity uptake of noradrenaline in quail dorsal root ganglion cells that express tyrosine hydroxylase immunoreactivity in vitro
Authors: Xue ZG , Smith J
Published: March 2018

During embryonic life, avian sensory ganglia contain cells with the potential to express, under appropriate experimental conditions, a number of properties characteristic of autonomic sympathetic neurons. Thus, cells capable of synthesizing noradrenaline (NA) from tyrosine differentiate when dorsal root ganglia (DRG) from 10–15 d embryonic quail are grown in culture (Xue et al., 1985a, b). In the present study, we show that cultures of DRG from 10 d embryos can take up 3H-NA by a high-affinity (Km = 1.0 microM), temperature-dependent process that can be inhibited by desmethylimipramine. By means of combined immunocytochemistry and autoradiography, it was demonstrated that the majority (70–80%) of the tyrosine hydroxylase (TH)-immunoreactive cells that developed in the cultures possessed a transport system for NA. Catecholamine (CA) uptake also occurred in a small, but relatively constant, number of TH-negative cells, but was absent from substance P- containing neurons. In contrast to TH, which appears only after 3–4 d in vitro, cells capable of taking up NA with high affinity were found in DRG cultures after only a few hours, and a small number (less than 0.5% of the total cell population) was detected in freshly removed, uncultured ganglia. Such cells did not react with antibodies directed against substance P or neurofilament proteins. We conclude that autonomic precursors are identifiable in a subset of non-neuronal DRG cells, prior to full expression of a noradrenergic phenotype, by their possession of a high-affinity uptake system for CA.
Three-dimensional pattern of enkephalin-like immunoreactivity in the caudate nucleus of the cat
Authors: Groves PM , Martone M , Young SJ , Armstrong DM
Published: March 2018

Recent anatomical investigations of the mammalian neostriatum have uncovered discrete neurochemical zones characterized by low levels of AChE and high levels of enkephalin-like immunoreactivity (ELI) compared with the surrounding neostriatal tissue. These regions, termed striosomes, which appear as patches in individual sections, have been associated with specific afferent and efferent pathways that differ from those of the surrounding neostriatal tissue. In the present study, the 3-dimensional distribution of these enkephalin-rich compartments in the caudate nucleus of the adult cat was investigated using computer- assisted 3-dimensional reconstruction techniques. Series consisting of coronal, sagittal, and horizontal tissue sections were obtained. In individual sections, discrete patches of intense enkephalin-like immunoreactivity appeared against a lighter-staining background. Three- dimensional reconstructions revealed that these patches overlapped across sections to form a highly inter-connected structure within the head and body of the caudate nucleus. Several structural features were evident in these reconstructions that appeared to be similar across animals. One consistent pattern was the formation of enkephalin-labeled finger-like structures radiating from the ventricular edge diagonally across the width of the nucleus. Smaller crossbridges were seen connecting the fingers, which often resulted in the formation of claws or rings of enkephalin-like immunoreactivity. These elements appear to align across planes to form a lattice-like structure outlining continuous regions of matrix. This structure may provide a basis for the orderly interaction between the patch and matrix compartments.
Quinolinic acid metabolism in the rat brain. Immunohistochemical identification of 3-hydroxyanthranilic acid oxygenase and quinolinic acid phosphoribosyltransferase in the hippocampal region
Authors: Kohler C , Eriksson LG , Flood PR , Hardie JA , Okuno E , Schwarcz R
Published: March 2018

Quinolinic acid (QUIN) is a potent endogenous excitotoxin, which has been shown to be present in the brain (Wolfensberger et al., 1983). In order to study the cellular localization of QUIN metabolism in the hippocampus, specific antibodies raised against purified rat liver 3- hydroxyanthranilic acid oxygenase (3HAO) and quinolinic acid phosphoribosyltransferase (QPRT), the enzymes directly responsible for QUIN synthesis and catabolism, respectively, were used for immunohistochemical studies in the adult male rat. Cells containing 3HAO immunoreactivity (3HAO-i) were present in all subfields of the hippocampal region, including the area dentata, Ammon's horn, the subicular complex, and the entorhinal area. The highest density of 3HAO- i cells was found in the molecular layer of Ammon's horn and in the hilus of area dentata, while the granular cell layer of area dentata and stratum pyramidale of Ammon's horn contained the lowest number of 3HAO-stained cells. A majority of hippocampal 3HAO-i cells were also stained with monoclonal antibodies against glial fibrillary acidic protein (GFAP) or S-100 protein, suggesting that 3HAO-i is present primarily in astrocytes. At the ultrastructural level, 3HAO-i was found to be distributed uniformly throughout the cytoplasm, with intense immunostaining present in the internal and the external layers of the mitochondria. QPRT-i was detected in 3 morphologically distinct cell types present in all parts of the hippocampus. The total number of QPRT- i cells was lower than that of the 3HAO-i cells. QPRT-i cells were relatively numerous in the molecular and radial layers of Ammon's horn, while they occurred only sporadically in stratum pyramidale of Ammon's horn and in the granular cell layer of area dentata. Many QPRT-i cells stained with antibodies against GFAP and S-100, but the proportion of cells in which QPRT was colocalized with these glial marker proteins was lower than that for 3-HAO-i cells. At the ultrastructural level, 2 types of QPRT-i glial cells were detected. The smaller cell type had a diffuse cytoplasmic staining, while the larger cell type, which also contained glial filaments, showed diffuse cytoplasmic staining and intense staining of lysosomal structures. The observation that 3HAO and QPRT only partially coexist in hippocampal glial cells suggests that while synthesis and catabolism of QUIN may occur in the same glial cells, catabolism of QUIN can also take place in cells lacking the synthetic enzyme.
Heterogeneity of GABAergic cells in cat visual cortex
Authors: Demeulemeester H , Vandesande F , Orban GA , Brandon C , Vanderhaeghen JJ
Published: March 2018

Antibodies against neuropeptides and against a vitamin D-dependent calcium-binding protein (CaBP) label small cells with nonpyramidal-like morphology in the cat visual cortex (areas 17, 18, and 19). Since GABAergic cells are interneurons, a double-staining procedure was used to test for the coexistence of cholecystokinin (CCK), somatostatin (SRIF), neuropeptide Y (NPY), corticotropin-releasing factor (CRF), vasoactive intestinal polypeptide (VIP), and CaBP with glutamic acid decarboxylase (GAD). Our results show that CRF and VIP do not coexist with GAD, while the 3 other peptides and CaBP do. Hence GAD-positive cells can be subdivided into 4 broad groups: (1) cells that are only GAD-positive, (2) cells that are GAD- and CaBP-positive, (3) GAD- positive neurons also containing CCK, and (4) GAD-positive cells that also contain SRIF. A small subset of class 2 also contains SRIF and most cells of class 4 also contain NPY. The 4 classes of GAD-positive cells differ in laminar position: class 1 predominates in layers IV and V, classes 2 and 3 in the upper laminae (II and III), and class 4 in the deepest layer (VI).
Preferential reinnervation of motor nerves by regenerating motor axons
Authors: Brushart TM
Published: March 2018

Regeneration of axons into inappropriate distal nerve branches may adversely affect functional recovery after peripheral nerve suture. The degree to which motor axons reinnervate sensory nerves, and vice versa, has not been determined. In these experiments, HRP is used to quantify the sensory and motor neurons that reinnervate sensory and motor branches of the rat femoral nerve after proximal severance and repair. Motoneurons preferentially reinnervate the motor branch in juveniles and adults, even if the repair is intentionally misaligned or a gap is imposed between proximal and distal stumps. A specific interaction thus occurs between regenerating motor axons and the Schwann cell tubes that lead to the motor branch. This interaction is independent of mechanical axon alignment.
The formation of chemical synapses between cell-cultured neuronal somata
Authors: Haydon PG
Published: March 2018

The study of the development and plasticity of chemical synaptic connections is frequently restricted by the lack of access to the synaptic terminals. This can, in part, be overcome by plating neurons into cell culture where all regions of a neuron are made experimentally accessible. However, the small size of synaptic terminals still makes direct experimental manipulation difficult. In this study we have found in the absence of neurite extension, directly contacting cell somata (diameter 50–100 mumol) will form chemical synapses. Identified neurons B5 and B19 of Helisoma were plated into culture under conditions that promote adhesion between cell pairs. Under these conditions, neurite outgrowth was absent, but action potentials in B5 evoked inhibitory postsynaptic potentials in B19 that were reversed in sign by the injection of chloride ions and were blocked by tubocurare (10(-5) M), reduced extracellular Ca2+, and Cd2+ ions. Such synapses exhibited classical properties of chemical synapses, including the spontaneous release of neurotransmitter. Since somatic synapses represent an appropriate model of synaptic transmission, this system was utilized to study the role of mutual neuronal contact in the development of transmitter release capabilities. Future pre- and postsynaptic somata were cultured separately for 3 d, the period required for the development of synaptic transmission under conditions of maintained contact. Then, neurons were made to contact and intracellular recordings taken within 0 to 4 hours. Postsynaptic potentials were detected as early as 10 sec following contact. Thus, qualitatively the development of transmitter release capabilities does not require maintained contact.
Nodose placode contributes autonomic neurons to the heart in the absence of cardiac neural crest
Authors: Kirby ML
Published: March 2018

The objective of this research was to determine the origin of the cholinergic neurons that populate the heart following ablation of the neural crest area, which normally gives rise to the cardiac ganglia. Using ablation of various areas of surface ectoderm--including neural crest migrating to the heart, nodose placode, and neural crest plus nodose placode--it was determined that regeneration of the neural component of cardiac neural crest did not occur in the absence of the nodose placodes. When cells from the nodose placode were followed in quail to chick chimeras of nodose placode with ablated cardiac neural crest, quail nodose placode-derived neurons were found in the cardiac ganglia. These results explain the “regeneration” of cholinergic cardiac ganglia in embryos lacking cardiac neural crest.
Synaptic vesicle redistribution during hippocampal frequency potentiation and depression in young and aged rats
Authors: Applegate MD , Landfield PW
Published: March 2018

Technical complexities associated with studies of defined synapses in the mammalian CNS have made it difficult to determine whether CNS synaptic vesicles respond to repetitive monosynaptic activation in the same ways as do PNS vesicles. Moreover, even in the PNS, the specific ultrastructural correlates of short-term synaptic potentiation are not well characterized. In the present studies, therefore, the Schaffer collateral-commissural fiber projection to field CA1 of the hippocampus was used as a model brain system in which to assess quantitative relations between dynamic vesicle patterns and frequency potentiation and depression. Anesthetized rats were perfused with aldehyde fixative during stimulation trains and concomitant microelectrode recording in order to study temporal correlations between physiology and synaptic structure. In addition, young and aged animals were compared to determine whether there are ultrastructural correlates of a previously described age-related impairment of hippocampal frequency potentiation. After 1 min of 10 Hz synaptic stimulation (stim), frequency potentiation of the population spike was correlated with increases in local vesicles (LV; within 150 nm of the active zone) and in vesicles directly apposed (AV) to the active zone membrane of CA 1 synapses. In addition, the ratio LVD: DVD of local-to-distant vesicle (DV; beyond 150 nm) densities was increased under all stimulation conditions. After 10 min of 10 Hz stim, or 1 min of 40 Hz stim, some vesicle depletion (approximately 25%) was present, as was some spike depression or decline from peak potentiation. However, LV depletion was not well correlated with degree of spike depression. Mean dendritic spine area was also increased in association with potentiation (at 1 min of 10 Hz stim) in young rats. Membrane infoldings similar to the cisternae described in other systems were seen with repetitive stimulation, providing evidence of vesicle recycling in these CNS terminals. In comparison to young control animals, terminals in non-stimulated aged group control rats exhibited a higher LVD:DVD ratio and a reduced DVD. In addition, the stimulation-induced increase in AV at 1 min of 10 Hz stim was not present in aged rat synapses. However, no age-related differences in vesicle-density measures were found at any stimulation point.
Neuronal organization of fetal striatal grafts in kainate- and sham- lesioned rat caudate nucleus: light- and electron-microscopic observations
Authors: DiFiglia M , Schiff L , Deckel AW
Published: March 2018

Behavioral and biochemical studies have suggested that fetal striatal grafts in the adult rat neostriatum can reverse deficits induced by excitotoxic lesions of the host caudate tissue. In this study, fetal day 17–18 striatal grafts were examined at 2, 5–6, 12, and 44–48 weeks following their implantation into saline- or kainic acid-treated host caudate nucleus in order to compare the neuronal organization of the grafts and the host caudate nucleus and to determine whether the differentiation of graft tissue was influenced by the period of implantation or prior lesion of the host caudate nucleus with kainic acid. Compared to host neostriatum, the grafts at the light-microscopic level lacked bundles of myelinated axons and had neurons that were tightly packed in clusters and rich in Nissl substance. Neurons in the grafts were mostly of medium size, had significantly larger cross- sectional areas, and more frequently exhibited indented nuclei than host caudate neurons. At the electron-microscopic level, grafts 2 weeks following implantation contained many features seen in the normally developing neostriatum, such as growth cones, immature synapses, and degenerating profiles. Grafts appeared mature by 5–6 weeks and contained at least 6 types of neurons and 8 types of axon terminals, which formed synapses with cell bodies, dendrites, spines, and axon initial segments. Both symmetric and asymmetric synapses were found within the grafts. The density of synapses was significantly lower in all the transplants than in host tissue, with the exception of the 5–6 week grafts, where values were statistically comparable to host caudate. A significantly higher proportion of axodendritic synapses was present in the graft neuropil than in the caudate nucleus. The lengths of the synaptic junctions in the grafts were the same as those in the neostriatum. There was little qualitative or quantitative difference in synaptic organization between transplants in kainic acid and sham- lesioned host, with grafts in both host treatment conditions exhibiting the same synaptic density and proportion of axodendritic/axospinous synapses. The development of a high differentiated ultrastructure within striatal grafts is consistent with recent anatomical evidence showing interconnections between striatal grafts and host-lesioned caudate nucleus. Although graft neuropil shows striking similarities in neuronal organization to the caudate nucleus, it also exhibits some distinct differences that may have implications for understanding the functional properties of fetal striatal grafts in animal models of Huntington's disease.
Serotonin acting via cyclic AMP enhances both the hyperpolarizing and depolarizing phases of bursting pacemaker activity in the Aplysia neuron R15
Authors: Levitan ES , Levitan IB
Published: March 2018

Bath application of 5-HT, at concentrations below 10 microM, enhances the amplitude of the interburst hyperpolarization in the Aplysia bursting pacemaker neuron R15. It is known that 5-HT acts via cyclic AMP to produce this effect by increasing the inwardly rectifying potassium current (IR). Here, we report that further elevating the concentration of 5-HT produces an enhancement of the depolarizing phase of the burst cycle that can eventually lead to tonic spiking activity. Voltage-clamp studies reveal that high concentrations of 5-HT continue to increase IR and, in addition enhance a voltage-gated inward current active near the action potential threshold. Pharmacological treatments and ion substitution experiments demonstrate that the inward current increased by high concentrations of 5-HT is a subthreshold calcium current (ICa). The 5-HT-induced increase in ICa is mimicked by bath application of the adenylate cyclase activator forskolin or injection of 8-bromo-cyclic AMP and is potentiated by the phosphodiesterase inhibitor isobutylmethylxanthine. It is concluded that 5-HT, acting via the second messenger cyclic AMP, can increase both potassium and calcium currents in neuron R15. It is also shown that the 5-HT-induced increase in these 2 opposing voltage-gated currents not only produces complex changes in bursting activity, but also dramatically alters R15's response to inhibitory and excitatory stimuli.
A cyclic GMP analog decreases the currents underlying bursting activity in the Aplysia neuron R15
Authors: Levitan ES , Levitan IB
Published: March 2018

Bath application of 8-parachlorophenylthio-cyclic GMP (8-pcpt-cGMP) has been shown to increase the number of action potentials per burst in the Aplysia neuron R15. Here we report that 8-pcpt-cGMP can eventually inhibit R15's bursting activity and cause the cell to exhibit slow tonic spiking activity. This action is preceded by decreases in spike frequency and in the amplitude of the interburst hyperpolarization. The ionic mechanism underlying these various changes in burst pattern was investigated using voltage clamp. 8-pcpt-cGMP reduces steady-state inward current, and this effect is blocked by manganese but is unaffected by internal EGTA or elevation of extracellular potassium. Dopamine, which decreases the subthreshold calcium current in R15, diminishes the change in current induced by 8-pcpt-cGMP. 8-pcpt-cGMP also reduces the spike-evoked calcium-dependent inward and outward currents known to underlie burst generation. These data lead us to conclude that 8-pcpt-cGMP acts directly to reduce the steady-state subthreshold calcium current (ICa). This decrease in ICa may also indirectly reduce the calcium-dependent currents. It is suggested that 8-pcpt-cGMP produces its effects on bursting by decreasing both the inward and outward currents required for generating bursting behavior, and thus effectively dampens bursting until the cell is in a beating state. It is also shown that 8-pcpt-cGMP dramatically alters R15's responses to depolarizing and hyperpolarizing stimuli. Thus, this cyclic GMP analog alters not only the cell's intrinsic activity, but also its response to external inputs.
The central projections of the stretch receptor neurons of crayfish: structure, variation, and postembryonic growth
Authors: Bastiani MJ , Mulloney B
Published: March 2018

Each stretch receptor neuron (SR) of the crayfish abdomen projects from its peripherally located soma an axon that enters the CNS through the second nerve (N2) of its segmental ganglion. Co2+ backfills of N2 revealed that this axon bifurcates, sending one branch to the brain and the other to the terminal abdominal ganglion. Each axon makes many short lateral branches as it traverses each of the other segmental ganglia, and has 2 major arborizations--one in the tritocerebrum of the brain and the other in the terminal abdominal ganglion, G6. These projections to G6 are described in detail. Individual SR axons from different segments were impaled in G6 with a Lucifer yellow-filled microelectrode, identified physiologically, and then filled to discover their structures. In a sample of more than 50 SR neurons, no systematic structural differences between the projections of phasic SR neurons and tonic SR neurons were observed. Three kinds of structural variability occurred in these projections to G6: unusual primary axon shape, long primary axon, and large terminal varicosities. Comparisons of SR neurons that originated in different segments revealed a segmental gradient in the probability of each structural variant. SR neurons from more anterior segments were more likely to show these structural variations. Comparisons of these variations in crayfish of different sizes showed that unusual primary axon shape and long primary axons were more probable in large crayfish than in small ones. Therefore, these variations are probably the products of postembryonic growth of the nervous system.
Synaptic transmission mediated by single club endings on the goldfish Mauthner cell. I. Characteristics of electrotonic and chemical postsynaptic potentials
Authors: Lin JW , Faber DS
Published: March 2018

Simultaneous pre- and postsynaptic intracellular recordings, combined with HRP injections, were used to study the properties of junctional transmission between club endings of saccular nerve afferents and the Mauthner (M-) cell in goldfish. All endings were electrotonically coupled to the M-cell, but impulses in less than 20% of the afferents produced chemically mediated excitatory postsynaptic potentials as well. There were no differences between the coupling potentials of those endings that mediated chemical transmission and those that did not, and presynaptic injections of HRP confirmed that in both cases the studied fibers terminated on the M-cell as single club endings. Since electron microscopic studies (Nakajima, 1974; Kohno and Noguchi, 1986; Tuttle et al., 1986) have consistently revealed structural correlates of chemical synapses in all the endings, we propose that the chemical synapses in the majority of the club endings are functionally silent. The electrotonic coupling at these junctions was characterized on the basis of coupling coefficients and DC transfer resistances. Coupling coefficients for anti- and orthodromic action potentials averaged 0.076 and 0.011, respectively. The transfer resistances measured with injections of constant-current pulses were the same in both directions (approximately 18.6 k omega), indicating the junctions do not rectify. Two separate calculations of the gap junctional resistance indicated that it is in the range of 6.7–35.8 M omega, with a mean value of 15.5 M omega. This calculated junctional resistance corresponds to 670 open gap junction channels, assuming a single-channel conductance of 100 pS. As that estimate is about 2 orders of magnitude smaller than the number of the presumed morphological correlates of the channels, i.e., intramembranous particles observed with the technique of freeze- fracture (Kohno and Noguchi, 1986; Tuttle et al., 1986), we conclude that only a small fraction of the morphologically observed channels are open at any time. The characteristics of the chemically mediated EPSPs were as follows: amplitude, 0.139 +/- 0.075 mV (mean +/- SD; n = 16); latency from onset of the coupling potential, 636 +/- 26 mu sec (n = 24); 10–90% rise time, 244 +/- 33 mu sec (n = 14); and decay time constant, 1.32 +/- 0.51 msec (n = 6). The decay phase was fit by a single exponential, and its time constant presumably is the same as that of the underlying conductance change since the M-cell's membrane time constant is significantly faster, 0.3–0.4 msec.
Prostaglandins inhibit endogenous pain control mechanisms by blocking transmission at spinal noradrenergic synapses
Authors: Taiwo YO , Levine JD
Published: March 2018

Spinal intrathecal injections of the nonsteroidal antiinflammatory analgesics (NSAIAs) indomethacin and acetylsalicylic acid, which inhibit prostaglandin synthesis, cause dose-dependent hypoalgesia in the rat. Intrathecal injections of prostaglandin-E2 (PGE2) produce dose- dependent hyperalgesia. To determine whether this action of prostaglandins on the central nervous system is mediated through pain- generating or analgesia pathways, we studied the effect of intrathecal PGE2 on endogenous opioid-induced analgesia. Intrathecal PGE2 antagonized the analgesia produced by both brain stimulation and intracerebroventricular morphine. In contrast, the NSAIAs synergized with brain stimulation and morphine-induced analgesia. The alpha- adrenergic antagonist phentolamine and the catecholaminergic selective neurotoxin 6-hydroxydopamine, used to block tonic catecholamine activity in endogenous opioid-mediated analgesia systems, prevented the hyperalgesia induced by intrathecal PGE2. Phentolamine did not, however, block the hyperalgesia caused by intradermal PGE2. These findings suggest that prostaglandins can block endogenous opioid- mediated analgesia systems by inhibiting the bulbospinal noradrenergic component of this analgesia pathway.
The projection from the superficial to the deep layers of the superior colliculus: an intracellular horseradish peroxidase injection study in the hamster
Authors: Mooney RD , Nikoletseas MM , Hess PR , Allen Z , Lewin AC , Rhoades RW
Published: March 2018

Intracellular recording and horseradish peroxidase (HRP) injection techniques were employed to examine the projections of superficial layer [stratum griseum superficiale (SGS) and stratum opticum (SO)] superior collicular (SC) neurons in the hamster that sent axon collaterals into the deep laminae (those ventral to the SO) of this structure. Sixty-nine neurons were studied, selected from a sample of over 185 HRP-filled superficial layer cells on the basis of having heavily stained axons. Of the 69 cells included in the study, 43.4% (n = 30) sent at least one axon collateral to the deep laminae. Not all cell types in the superficial layers contributed equally to this interlaminar projection: 78.6% (n = 11) of the recovered wide-field vertical cells, 55.0% (n = 11) of the narrow-field vertical cells, 16.7% (n = 2) of the stellate cells, 40.0% (n = 2) of the marginal cells, 18.2% (n = 2) of the horizontal cells, and 28.6% (n = 2) of neurons we could not classify on the basis of their somadendritic morphology projected to the deep layers. Within a given cell class, there were no significant morphological or physiological differences between the neurons that possessed deep axon collaterals and those that did not. The deep axon collaterals of most of the interlaminar projection neurons were restricted to the stratum griseum intermediate (SGI). In this layer, the largest segment of the axon arbor was located lateral to a projection line that was orthogonal to the SC surface and that passed through the soma of the cell in question. These results, along with those of a previous study (Mooney et al., 1984), which demonstrated that the dendrites of deep layer cells may extend through the SO and into the SGS, indicate that there is an extensive anatomical substrate by which sensory information may be communicated from superficial to deep layer SC neurons.
Stratum lacunosum-moleculare interneurons of hippocampal CA1 region. I. Intracellular response characteristics, synaptic responses, and morphology
Authors: Lacaille JC , Schwartzkroin PA
Published: March 2018

Stable intracellular recordings were obtained from nonpyramidal cells (interneurons) in stratum lacunosum-moleculare (L-M) of the CA1 region of guinea pig hippocampal slices. The intracellular response characteristics of these interneurons were distinctly different from responses of pyramidal cells and of other interneurons (basket cells and oriens-alveus interneurons). L-M interneurons had a high resting membrane potential (-58 mV), a high input resistance (64 M omega), and a large amplitude (60 mV), relatively long duration (2 msec) action potential. A large afterhyperpolarization (11 mV, 34 msec) followed a single action potential. Most L-M interneurons did not display any spontaneous firing. Lucifer yellow (LY)-filled L-M interneurons showed nonpyramidal morphology. Cells were generally fusiform or multipolar, with aspinous, beaded dendritic processes ramifying in stratum lacunosum-moleculare, radiatum, and (sometimes) oriens. The varicose axon originated from a primary dendrite, projected along stratum lacunosum-moleculare, branched profusely in stratum radiatum, and coursed toward and into stratum pyramidale and occasionally into oriens. Processes of cells with somata in the L-M region of CA1 were not restricted to the CA1 region. The dendritic and axonal processes of some L-M interneurons were seen ascending in stratum lacunosum- moleculare, crossing the hippocampal fissure, and coursing in stratum moleculare of the dentate gyrus. Excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) were evoked in L-M interneurons from stimulation of major hippocampal afferents. EPSPs were most effectively elicited by stimulation of fiber pathways in transverse slices, whereas IPSPs were predominantly evoked when major pathways were stimulated in longitudinal slices. We have identified a population of interneurons with intracellular response characteristics and morphology distinctly different from previously described pyramidal and nonpyramidal neurons of CA1 region. The possible role of these interneurons in hippocampal circuitry is discussed.
The establishment of polarity by hippocampal neurons in culture
Authors: Dotti CG , Sullivan CA , Banker GA
Published: March 2018

By the end of the first week in culture, hippocampal neurons have established a single axon and several dendrites. These 2 classes of processes differ in their morphology, in their molecular composition, and in their synaptic polarity (Bartlett and Banker, 1984a, b; Caceres et al., 1984). We examined the events during the first week in culture that lead to the establishment of this characteristic form. Hippocampal cells were obtained from 18 d fetal rats, plated onto polylysine- treated coverslips, and maintained in a serum-free medium. The development of individual cells was followed by sequential photography at daily intervals until both axons and dendrites had been established; identification of the processes was confirmed by immunostaining for MAP2, a dendritic marker. Time-lapse video recording was used to follow the early stages of process formation. Hippocampal neurons acquired their characteristic form by a stereotyped sequence of developmental events. The cells first established several, apparently identical, short processes. After several hours, one of the short processes began to grow very rapidly; it became the axon. The remaining processes began to elongate a few days later and grew at a much slower rate. They became the cell's dendrites. Neurons that arose following mitosis in culture underwent this same sequence of developmental events. In a few instances, 2 processes from a cell exhibited the rapid growth typical of axons, but only one maintained this growth; the other retracted and became a dendrite. Axons branched primarily by the formation of collaterals, not by bifurcation of growth cones. As judged by light microscopy, processes are not specified as axons or dendrites when they arise. The first manifestation of neuronal polarity is the acquisition of axonal characteristics by one of the initial processes; subsequently the remaining processes become dendrites.
Postnatal dendritic maturation of alpha and beta ganglion cells in cat retina
Authors: Dann JF , Buhl EH , Peichl L
Published: March 2018

Of the 3 anatomically defined classes of ganglion cell in adult cat retina, the alpha and beta cells are the most well documented, thus providing a basis of comparison for developing ganglion cells. Alpha and beta ganglion cells in cat retinae at various ages from birth (P0) to adult were intracellularly injected with Lucifer yellow. At all ages, both cell types strongly resembled their adult counterparts. However, transient developmental characteristics established their immaturity. These features included spiny protuberances and “rings” along the dendritic surface that were no longer detectable after 3 weeks of age. In a small proportion of both inner and outer stratifying alpha ganglion cells, there was aberrant dendritic arborization. However, by P5 there was no remaining evidence of this deviant stratification pattern and all alpha and beta cells displayed the adult pattern of unistratification (present among the majority of these cells from birth). For both alpha and beta cells, the area of greatest development was the retinal periphery. In this region alpha cell dendritic trees continued to grow until 3 weeks postnatally, when they approached the adult dendritic field size; around this time, the major period of beta cell dendritic expansion began. From birth to adulthood, the distance between alpha cell dendritic branching points increased, while the number of nodes and tips decreased with age. The temporal disparity between alpha and beta cell dendritic expansion suggests that postnatal dendritic development involves an active process of growth, rather than merely passive stretching.
Functional anatomy of macaque striate cortex. II. Retinotopic organization
Authors: Tootell RB , Switkes E , Silverman MS , Hamilton SL
Published: March 2018

Macaque monkeys were shown retinotopically-specific visual stimuli during 14C-2-deoxy-d-glucose (DG) infusion in a study of the retinotopic organization of primary visual cortex (V1). In the central half of V1, the cortical magnification was found to be greater along the vertical than along the horizontal meridian, and overall magnification factors appeared to be scaled proportionate to brain size across different species. The cortical magnification factor (CMF) was found to reach a maximum of about 15 mm/deg at the representation of the fovea, at a point of acute curvature in the V1-V2 border. We find neither a duplication nor an overrepresentation of the vertical meridian. The magnification factor did not appear to be doubled in a direction perpendicular to the ocular dominance strips; it may not be increased at all. The DG borders in parvorecipient layer 4Cb were found to be as sharp as 140 micron (half-amplitude, half width), corresponding to a visual angle of less than 2′ of arc at the eccentricity measured. In other layers (including magnorecipient layer 4Ca), the retinotopic borders are broader. The retinotopic spread of activity is greater when produced by a low-spatial-frequency grating than when produced by a high-spatial-frequency grating. Orientation- specific stimuli produced a pattern of activation that spread further than 1 mm across cortex in some layers. Some DG evidence suggests that the spread of functional activity is greater near the foveal representation than near 5 degrees eccentricity.
V1-type vasopressin receptors in rat brain septum: binding characteristics and effects on inositol phospholipid metabolism
Authors: Shewey LM , Dorsa DM
Published: March 2018

Specific binding sites for 3H-arginine8-vasopressin (AVP) have been characterized in rat septal membranes. Scatchard analyses revealed a single class of high-affinity binding sites having an equilibrium dissociation constant of 1.7 +/- 0.3 nM and total binding capacity of 22.6 +/- 4.2 fmol/mg protein. Binding displacement studies with peptide analogs of AVP indicate that this binding site is similar to the V1 (pressor)-type receptor for AVP. When added to rat brain septal slices that had been prelabeled with 3H-myo-inositol, vasopressin stimulated the accumulation of 3H-inositol-1-phosphate (IP1) in the presence of 7 mM lithium. This effect was dose dependent with maximal stimulation (65% over basal) occurring at a concentration of 0.5 microM AVP. Higher concentrations, however, tended to inhibit phosphoinositide hydrolysis. The vasopressin-stimulated accumulation of 3H-IP1 was completely inhibited by the vasopressin V1 antagonist, d(CH2)5[Tyr(Me)2]AVP, in a concentration-dependent manner. Oxytocin, at concentrations of 10(-8) and 10(-5) M, only slightly increased 3H-IP1 accumulation (17–20% over basal). In contrast, the V2 agonist deamino-D-arginine vasopressin (dDAVP), failed to produce significant stimulation of 3H-IP1 accumulation, even at high concentrations. The effects of these analogs on phosphoinositide hydrolysis is consistent with their potencies in displacing 3H-AVP from septal binding sites. These results indicate that vasopressin stimulates hydrolysis of inositol phospholipids in rat brain septum through an interaction with V1-type vasopressin receptors.
Postnatal development of a brain-specific subspecies of protein kinase C in rat
Authors: Hashimoto T , Ase K , Sawamura S , Kikkawa U , Saito N , Tanaka C , Nishizuka Y
Published: March 2018

Protein kinase C in the developing rat brain was investigated by a biochemical assay and by light-microscopic immunocytochemistry. The protein kinase was resolved on hydroxyapatite column chromatography into 3 fractions, designated types I, II, and III. Type I, with structure encoded by a gamma-sequence, was not detected early postnatally, maintained a low level of activity during the first week, which increased gradually, and reached its maximum around postnatal day 28. This type of enzyme was expressed specifically in nervous tissues, and was not found in any other tissues thus far tested. Type II enzyme activity, a mixture of the 2 subspecies encoded by the beta I- and beta II-sequences, was found at birth, increased rapidly, and reached a plateau level between postnatal days 14 and 28. This type was the predominant subspecies of protein kinase C in the brain. Type III, its structure encoded by the alpha-sequence, was also detected at birth, and reached its maximum level on postnatal day 7. Immunocytochemical studies with a monoclonal antibody, which recognized preferentially the type I enzyme, visualized the developmental pattern of type I subspecies in the Purkinje cell, a typical cell having a large quantity of type I protein kinase C.
Cardiovascular function is altered by picomole injections of glutamate into rat medulla
Authors: Nelson DO , Cohen HL , Feldman JL , McCrimmon DR
Published: March 2018

Local neural circuitry in the nucleus tractus solitarius (NTS) involved in cardiovascular control was studied by injecting nanoliter volumes of excitatory amino acids into the structure. Experiments were performed on urethane-anesthetized, artificially ventilated rats. Multibarrel micropipettes were used for pressure ejection of drugs or a dye for marking ejection sites. Ejected volumes, ranging from 200 pl to 25 nl, were directly monitored for every injection. Injections of as little as 200 fmol of L-glutamate in 200 pl into the medial and lateral NTS region rostral to the obex elicited marked, site-specific decreases in arterial pressure and heart rate. The majority of these responses were eliminated by blockade of parasympathetic and sympathetic neural outflow. At sites caudal to obex, in the commissural region of the NTS, L-glutamate injections produced marked elevations in heart rate and arterial pressure which were sympathetically mediated. Responses to L- glutamate were attenuated by concurrent injection of glutamic acid diethyl ester and DL-2-amino-4-phosphonobutyrate, or lidocaine. These results indicate a heterogeneity in the spatial organization of brain- stem circuitry underlying cardiovascular control that has not been previously described.
The organization of chromatic and spatial interactions in the primate striate cortex
Authors: Ts'o DY , Gilbert CD
Published: March 2018

The cytochrome oxidase-rich patches or blobs of the monkey striate cortex have been shown to contain cells that have unoriented receptive fields, many of which are color selective. We studied the functional organization of color opponency in the blob regions of the parafoveal representation of the visual cortex. We also examined the patterns of connectivity among blob and nonblob cells by multiple electrode penetrations and cross-correlation analysis. Some of the color- selective cells in the blobs exhibited receptive fields that were similar to those found in the parvocellular layers of the lateral geniculate nucleus (LGN): one type exhibited center-surround spatial and chromatic opponency corresponding to the Type I cell found in the LGN; another had center-only chromatic opponency, corresponding to the Type II cell of the LGN. A blob color-selective cell with no LGN counterpart had center color opponency with a nonchromatically opponent surround antagonism. We termed this cell the “modified Type II” cell. Contrary to previous reports, few true double color-opponent cells were found. Some blob cells previously characterized as double opponent probably belong to our modified Type II category and, unlike true double opponent cells, do not respond well to isoluminant color boundaries. Occasional color-selective oriented cells were either intermixed or in close proximity to blob cells. Neighboring electrode penetrations within the same blob yielded cells of the same color opponency, either red versus green or blue versus yellow, suggesting that individual blobs are dedicated to processing one color opponency. Blobs dedicated to red/green color opponency were 3 times more numerous than blue/yellow blobs. Furthermore, the cells in layer 4C lying beneath blobs of a given color opponency had identical color opponency to the overlying cells in blobs. Cross-correlation analysis of pairs of nonblob, oriented cells in the superficial layers showed interactions between cells with matched orientation and eye preference, at varying horizontal separations. Such interactions are consistent with anatomically demonstrated clustered horizontal connections. Positive cross-correlograms were found between blob cells in the same and in adjacent blobs when the cells' receptive field type, color opponency, and ocular dominance matched. Correlograms also indicated monosynaptic connections from Type II to modified Type II cells of the same color opponency, suggesting that Type II cells may contribute to the construction of the modified Type II fields in the cortex.(ABSTRACT TRUNCATED AT 400 WORDS)
Axotomy-induced alterations in the synthesis and transport of neurofilaments and microtubules in dorsal root ganglion cells
Authors: Oblinger MM , Lasek RJ
Published: March 2018

Changes in the synthesis and axonal transport of neurofilament (NF) proteins and tubulin were examined after various selective axotomies of adult rat DRG cells. For axonal transport studies, DRGs were labeled by microinjection of 35S-methionine 14 d after axonal injuries, and nerves were retrieved 7 or 14 d after labeling. Slowly transported proteins were examined by quantitative PAGE/fluorography. After distal peripheral nerve crush (50–55 mm from the DRG), the cytoskeleton that entered undamaged regions of peripheral branch DRG axons by slow axonal transport differed from normal, while the cytoskeleton that entered dorsal root axons did not. Specifically, smaller-than-normal ratios of labeled NF protein/tubulin were transported in peripheral DRG axons after distal peripheral nerve crush. This change was almost entirely due to a selective decrease in the output of labeled NF proteins rather than to an increase in the amount of tubulin transported with NF proteins. Since the efficiency of axonal regeneration is known to be lower after cut injury than after nerve crush, we compared the effect of cut versus crush axotomy of peripheral DRG axons on cytoskeletal protein output. A more substantial reduction in the labeled NF/tubulin transport resulted in peripheral DRG axons if the distal sciatic nerve was cut rather than crushed but, even under these axotomy conditions, the labeled NF/tubulin ratios in dorsal root axons were not reduced. Peripheral cut axotomy did result in a lag in the advance of the labeling peak of the NF/microtubule protein wave in dorsal root axons, suggesting either that these proteins were delayed in exiting the cell body or that a slowing of the rate of their transport occurred. Pulse- labeling DRGs in vitro using 35S-methionine, and analysis of labeled proteins by 2-dimensional PAGE-fluorography demonstrated that the incorporation of radioactivity into NF proteins was significantly reduced, while the labeling of tubulins was unchanged 14 d after distal peripheral axotomy. In contrast to the results of peripheral axotomy, dorsal root crushes made close to the DRG (2–3 mm) or considerably distal (at the CNS entry zone 28–30 mm from the DRG) did not produce detectable changes in the amount of labeled NF or tubulin transport in central or peripheral branch axons. These findings indicate that the down-regulation of NF production/output that is exhibited at 14 d after peripheral branch axotomy is not present after central branch injury.(ABSTRACT TRUNCATED AT 400 WORDS)