bluuebunny/crossref_metadata_2025 huggingface dataset:
The medullary dorsal horn: a target for the expression of opiate effects on the perceived intensity of noxious heat
Authors: Oliveras JL , Maixner W , Dubner R , Bushnell MC , Kenshalo DR , Duncan GH , Thomas DA , Bates R
Published: March 2018

We examined the effects of morphine microinjected into the medullary dorsal horn (MDH) on the ability of monkeys to detect temperature increases in the noxious heat range. Behavioral detection latency and the percentage of correct detections were used as measures of the perceived intensity of noxious heat stimuli. Three monkeys were trained to detect a change (T2) of 0.4, 0.6, or 1.0 degrees C from a previous noxious heat level of 46 degrees C (T1). Effects on attentional, motivational, and motoric aspects of the monkeys' behavior were assessed by having them detect innocuous cooling and visual stimuli in tasks of similar difficulty. Morphine (1, 3, and 10 micrograms) microinjected into the MDH produced a dose-dependent and stimulus- intensity-dependent increase in the latency to detection of the T2 stimuli. These effects were opiate receptor-mediated since they were antagonized by systemically administered naloxone (0.5 mg/kg, i.m.) given 40 min after the microinjection of morphine. There were no effects of morphine on the behavioral detection latencies to the innocuous cooling and visual stimuli, indicating that the effects of morphine were modality-specific and independent of changes in motivation, attention, or motoric ability. These data demonstrate a pharmacologically specific effect of opiates on the perceived intensity of noxious heat stimuli at the earliest central relay pathway transmitting noxious information.
Alterations in the ultrastructure of peripheral nodes of Ranvier associated with repetitive action potential propagation
Authors: Wurtz CC , Ellisman MH
Published: March 2018

We have studied the structure of the node of Ranvier following physiological activation and electrophysiological monitoring. Our results indicate that some structures within the nodal complex undergo microanatomic alterations concomitant with repetitive impulse propagation. The experiments were designed to determine the nature and extent of the morphologic changes and any associated changes in the compound action potential. Frog dorsal roots were examined by thin- section electron microscopy after having been either implanted, but not stimulated (“0 Hz control”), or orthodromically activated for 15 min at frequencies of 2, 5, 20, or 50 Hz. Roots were either fixed immediately and processed for electron microscopy or were allowed to recover for periods of 15, 30, or 45 min prior to fixation. A change in nodal structure was found that correlates with the different stimulation regimens. Specifically, there was an increase in the size and number of (extracellular) paranodal intramyelinic vacuoles after stimulation at 20 or 50 Hz when compared both to the implanted nonstimulated controls and to fibers stimulated at low frequency (2 or 5 Hz). This morphologic change occurs in the vicinity of the nodal complex without similar alterations in the morphology of the internodal regions or changes in the dimensions of the nodal gap. This form of microanatomic changes is reversible and is not seen if stimulation is halted and the fiber bundle allowed to recover in Ringer's prior to processing for morphologic evaluation. Changes in the compound action potential (CAP) parallel this structural alteration. The CAP is seen to slow and decrease in amplitude through the 15 min stimulation phase and then to regain its velocity and amplitude during the recovery. When TTX was applied to the preparation during stimulation the CAP was abolished and changes in the paranodal structure were not observed. Structure- function relationships indicated by these results are discussed in the context of several dynamic aspects of nodal physiology.
Characterization, distribution, and ontogenesis of adenosine binding sites in cat visual cortex
Authors: Shaw C , Hall SE , Cynader M
Published: March 2018

In vitro autoradiographic techniques were used to characterize binding sites for 3H-cyclohexyladenosine (CHA) and 3H-5′-N- ethylcarboxamidoadenosine (NECA) in cat and kitten visual cortex. 3H- CHA binding sites in adult cat have a Bmax of 1,363 fmol/mg protein and a Kd of 6.8 nM. Displacement experiments indicate that 3H-CHA binds to an adenosine receptor similar to the A1-adenosine receptor described by other investigators. 3H-NECA binding sites in adult cat have a Bmax of 518 fmol/mg protein and a Kd of 15.4 nM. Displacement experiments do not allow us to identify this binding site unambiguously. Bmax values increase during postnatal development for both binding sites, peaking in adulthood for 3H-CHA and at 30 d for 3H-NECA. Kd values show neither consistent nor significant differences during postnatal development for either binding site. 3H-CHA and 3H-NECA binding sites are concentrated in layers 1–3 and upper layer 5 in the visual cortex of adult cats. These laminar patterns, however, change during postnatal development, showing the densest binding in the deep cortical layers (5 and 6) in kittens younger than 30 d of age and a fairly homogeneous binding in older kittens before achieving the adult distribution.
The role of spinal cord cyclic AMP in the acoustic startle response in rats
Authors: Kehne JH , Astrachan DI , Astrachan E , Tallman JF , Davis M
Published: March 2018

Drugs thought to increase intracellular levels of cAMP were infused intrathecally into the subarachnoid space of the lumbar spinal cord, and the effects on the acoustic startle response in rats were measured. Intrathecal infusions of the cAMP analogs dibutyryl cAMP or 8-bromo cAMP (12.5–100 micrograms) produced marked, dose-dependent increases in startle amplitude compared to the infusion of artificial cerebrospinal fluid (CSF). Local infusions of dibutyryl cAMP at more rostral levels of the spinal cord or brain failed to mimic the excitatory effect seen following lumbar intrathecal infusion. No excitation of startle was seen following intrathecal infusion of cAMP itself, ATP, 5′-AMP, or dibutyryl cGMP. A weak excitation of startle was seen following intrathecal, but not intraventricular, infusion of the water-soluble adenylate cyclase activator forskolin 7-deacetyl-7–O-hemisuccinic acid (forskolin-DHA; 5.0–100 micrograms, in artificial CSF), whereas forskolin itself [0.01–200 micrograms, in dimethyl sulfoxide (DMSO)] was without consistent effect. Finally, intrathecal infusion of the selective phosphodiesterase inhibitor Rolipram (12.5–200 micrograms) produced a marked excitation of startle similar in magnitude to the effects produced by cAMP analogs. The excitatory effects of intrathecally infused dibutyryl cAMP, 8-bromo cAMP, forskolin-DHA, or Rolipram support a functional link between spinal cord cAMP and the acoustic startle reflex. Possible sites of cAMP action on startle are discussed.
Characterization of excitatory amino acid receptors expressed by embryonic chick motoneurons in vitro
Authors: O'Brien RJ , Fischbach GD
Published: March 2018

We have examined the effect of L-glutamate and other excitatory amino acids on embryonic chick motoneurons maintained in cell culture along with other types of spinal cord cells. When the motoneuron membrane is clamped at -50 mV, glutamate induces a dose-dependent inward current. Although the dose-response curve is hyperbolic with an ED50 of 78 microM, glutamate apparently activates 2 types of receptors on motoneurons. The first, G1, is activated by N-methyl-D-aspartate (NMDA) and aspartate and inhibited by 2-amino-5-phosphonovaleric acid (2-APV). The second, G2, is activated by kainate and quisqualate and is not inhibited by 2-APV. At -50 mV, 38% of the glutamate current is due to activation of G1 receptors and the remaining 62% to G2 activation. In contrast to motoneurons grown with other spinal cord cells, sorted motoneurons grown in isolation apparently exhibit only G2 receptor- mediated currents. Both G1 and G2 currents reverse polarity between -10 and -5 mV. However, they could be distinguished when the membrane was hyperpolarized. G2 currents increased but G1 currents decreased when the membrane potential was increased beyond -50 mV. Consistent with the mixed agonist action of glutamate, glutamate currents remained nearly constant on hyperpolarization. No evidence was obtained that the G2 class of receptors on motoneurons could be subdivided: Quisqualate and kainate apparently compete for the same sites; gamma-glutamylglycine blocked quisqualate as effectively as it blocked kainate currents when the different potencies of the 2 agonists were taken into account.(ABSTRACT TRUNCATED AT 250 WORDS)
Identification of a nicotinic acetylcholine receptor on neurons using an alpha-neurotoxin that blocks receptor function
Authors: Halvorsen SW , Berg DK
Published: March 2018

An alpha-neurotoxin, Bgt 3.1, that reversibly blocks the ACh response of chick ciliary ganglion neurons has been used to identify 2 classes of high-affinity binding sites on the cells in culture. The first class appears to be the alpha-bungarotoxin binding site on the neurons. The second class of Bgt 3.1 sites is distinct from the alpha-bungarotoxin binding sites and has the properties expected for the functional nicotinic ACh receptor on the cells. Equilibrium binding and kinetic studies indicate a Kd value of 5–6 nM for Bgt 3.1 at the second class of sites. The kinetics and affinity of binding are consistent with those inferred from previous physiological studies for Bgt 3.1 inhibition of receptor function. Bgt 3.1 binding to the sites is completely inhibited by each of the cholinergic ligands ACh, carbachol, nicotine, d-tubocurarine, and trimethaphan, but not by alpha- bungarotoxin. Highest site densities are found in cultures of ciliary and sympathetic ganglion neurons, cell types known to have ganglionic nicotinic ACh receptors. Low levels of sites may be present in cultures of spinal cord and dorsal root ganglion neurons; no binding is found in cultures of skeletal myotubes or cardiac cells when alpha-bungarotoxin is used to block Bgt 3.1 binding to alpha-bungarotoxin sites. These results demonstrate that Bgt 3.1 can be used as a specific probe for the nicotinic ACh receptor on chick autonomic neurons.
Contribution of sensory afferents and sympathetic efferents to joint injury in experimental arthritis
Authors: Levine JD , Dardick SJ , Roizen MF , Helms C , Basbaum AI
Published: March 2018

We used pharmacological and surgical methods to determine the contribution of several neural components to joint injury in rats with adjuvant-induced arthritis. Both neonatal administration of capsaicin, which eliminates small-diameter afferents, and peripheral sympathectomy, which depletes catecholamines, attenuated joint injury. In contrast, the arthritis was more severe in spontaneously hypertensive rats, which have increased sympathetic tone. To address the contribution of the central vs peripheral afferent terminal selectively, a group of rats underwent unilateral dorsal rhizotomy. These rats developed a more severe arthritis in the deafferented limb. The increase in arthritis severity produced by dorsal rhizotomy could be reduced by prior sympathectomy or, less effectively, by prior treatment with capsaicin. The latter observation suggests that large- diameter afferents that are cut during dorsal rhizotomy also influence inflammation. Finally, intracerebroventricular injection of morphine attenuated the severity of arthritis, possibly through activation of bulbospinal sympathoinhibitory circuits. Taken together, these data indicate that no one class of nerve fiber is wholly responsible for the neurogenic component of inflammation in experimental arthritis but that large- and small-diameter afferents, sympathetic efferents, and CNS circuits that modulate those fiber systems all influence the severity of joint injury in arthritic rats.
Induction of ornithine decarboxylase as a possible mediator of seizure- elicited changes in genomic expression in rat hippocampus
Authors: Baudry M , Lynch G , Gall C
Published: March 2018

Small electrolytic lesions placed in the hilus of the dentate gyrus have been shown to induce behavioral seizures, an elevation in the concentration of the opioid peptide enkephalin, and an increase in the transcription of the gene coding for the peptide precursor of enkephalin. Since polyamines and ornithine decarboxylase (ODC), the rate-limiting enzyme in their synthesis, have been shown to play critical roles in the growth and differentiation of several types of tissue, we tested for changes in ODC activity at various times following the initiation of seizures. ODC activity is significantly increased 3 hr after the lesions, reaches maximal (50-fold) levels about 12 hr later, and returns to control values after 48 hr. The increase occurs in both hippocampi following unilateral electrolytic lesions, is blocked by treatments that suppress limbic seizures, and does not occur after lesions that fail to elicit seizures; accordingly, we conclude that the increase in ODC activity results from epileptiform activity rather than some other consequence of the hilar lesion (e.g., deafferentation). The increase in ODC activity precedes the increase in the amount of mRNA coding for the enkephalin prohormone, which, in turn, precedes the increase in enkephalin levels. These results are consistent with the hypothesis that the early induction of ODC following the initiation of seizures leads to an alteration in genomic expression, which, in turn, changes neuropeptide levels. Adult brains thus appear to possess trophic responses of a type found in a variety of developing cell types and organs, and the possibility exists that these are involved in the control of seizure susceptibility.
Actin immunoreactivity localizes with segregated microtubules and membraneous organelles and in the subaxolemmal region in the beta,beta'- iminodipropionitrile axon
Authors: Papasozomenos SC , Payne MR
Published: March 2018

Using the peroxidase-antiperoxidase staining technique with monoclonal and polyclonal antibodies against actin, we found that, in beta,beta'- iminodipropionitrile (IDPN)-treated axons, actin immunoreactivity was codistributed with segregated microtubules and membranous organelles in the central region and excluded from the peripheral axoplasm occupied by neurofilaments. Actin immunoreactivity was also present in the subaxolemmal region. Fast axonal transport is localized in the central region of the IDPN axon (Papasozomenos et al., 1982a). As both microtubules and actin are present in the central region of IDPN axons, a possible role of actin in fast axonal transport warrants further investigation.
Microcircuitry of the dark-adapted cat retina: functional architecture of the rod-cone network
Authors: Smith RG , Freed MA , Sterling P
Published: March 2018

The structure of the rod-cone network in the area centralis of cat retina was studied by reconstruction from serial electron micrographs. About 48 rods converge on each cone via gap junctions between the rod spherules and the basal processes of the cone pedicle. One rod diverges to 2.4 cones through these gap junctions, and each cone connects to 8 other cones, also through gap junctions. A static cable model of this network showed that at mesopic intensities, when all rods converging on a cone pedicle are continuously active, the collective rod signal would be efficiently conveyed to the pedicle. At scotopic intensities sufficiently low for only one of the converging rods to receive a single photon within its integration time, the quantal rod signal would be poorly transmitted to the cone pedicle. This is because the tiny signal would be dissipated by the large network into which the individual rod diverges. Under this condition, the rod signal would also be poorly conveyed to the rod spherule. If, however, the rods are electrically disconnected from the network, the quantal signal would be efficiently conveyed to the rod spherule. This analysis suggests that the rod signal is conveyed at mesopic intensities by the cone bipolar pathway and, at scotopic intensities, by the rod bipolar pathway, in accordance with the results of Nelson (1977, 1982; Nelson and Kolb, 1985).
Guidance of neuronal growth cones in the grasshopper embryo. II. Recognition of a specific axonal pathway by the aCC neuron
Authors: du Lac S , Bastiani MJ , Goodman CS
Published: March 2018

In the previous paper, we experimentally analyzed the selective affinity of the pCC growth cone for the MP1/dMP2 fascicle in the grasshopper embryo. Here we describe a similar experimental analysis demonstrating the selective affinity of the aCC growth cone for the U fascicle. These results support the labeled-pathways hypothesis. The 2 sets of cell ablation experiments argue against the simple location of axons, the simple timing of axon outgrowth, and/or simple quantitative differences in the expression of a common surface label being the major determinant in pathway selection by neuronal growth cones. Rather, these 2 examples of growth-cone specificity, together with previous studies on the G growth cone, suggest that neuronal recognition molecules are differentially expressed on the surfaces of different embryonic axonal pathways and tracts and are used to guide growth cones through a series of choice points to their targets.
The relationship between the geniculocortical afferents and their cortical target cells during development of the cat's primary visual cortex
Authors: Shatz CJ , Luskin MB
Published: March 2018

To study the prenatal development of connections between the lateral geniculate nucleus (LGN) and the primary visual cortex in the cat, we have examined the relationship between the position of ingrowing afferents from the LGN and their target cells in cortical layers 4 and 6 at various times during the cat's 65 d gestation period and during the first 3 weeks of postnatal life. In 1 series of experiments, the method of transneuronal transport of intraocularly injected tritiated proline (3H-proline), followed by autoradiography, was used to label the developing geniculocortical pathway. In another series, the tritiated thymidine (3H-thymidine) method was employed to keep track of the cells destined for layers 4 and 6 by labeling them on their birthdates (layer 4: embryonic day (E) 37–43; layer 6: E31–36) (Luskin and Shatz, 1985b) and then charting their locations at subsequent times during development. The results of the 2 sets of experiments were compared at corresponding ages. By E39, many of the cells of cortical layer 6 have completed their migrations and are situated within the cortical plate immediately above the subplate. However, the transneuronal labeling pattern indicates that the geniculocotical afferents have not yet arrived within the vicinity of the future visual cortex, but rather are still en route and confined within the optic radiations of the telencephalon. By E42, a week after the first afferents can be detected in the radiations, substantial transneuronal label is found in the subplate immediately below future visual cortex. However, the overlying cortical plate is free of label. Over the next 2 weeks, geniculocortical axons continue to accumulate in the subplate zone, and, in addition, transneuronal label can be found in the marginal zone. By E55 a faint geniculocortical projection can be detected within the cortical plate, but only within its deeper half (future layers 5 and 6), and even then the major portion of the projection is still confined to the subplate. The absence of a projection to cortical layer 4 at these ages is remarkable in view of the results from our 3H-thymidine experiments, which indicate that by E57 the majority of cells destined to belong to layer 4 have already completed their migrations and assumed positions superficial to the cells of layers 5 and 6. By birth, a substantial geniculocortical projection to cortical layer 4 can be detected in the transneuronal autoradiographs.(ABSTRACT TRUNCATED AT 400 WORDS)
Functional consequences of neonatal infraorbital nerve section in rat trigeminal ganglion
Authors: Jacquin MF , Renehan WE , Klein BG , Mooney RD , Rhoades RW
Published: March 2018

tandard single-unit recording and stimulation techniques were used to assess the topographic organization, receptive field properties, and projections of cells (n = 297) in the ophthalmic-maxillary part of the trigeminal ganglion in 6 normal adult rats and 15 adults with unilateral infraorbital nerve section at birth (cells recorded ipsilateral to lesion: n = 641; cells recorded on the intact side: n = 223). Stimulating electrodes were placed on the central portion of the regenerate infraorbital nerve and in the trigeminal brain stem subnucleus caudalis in 6 nerve-damaged rats and at equivalent points in 5 normal animals. Data from the normal rats and the intact side of the nerve-damaged animals were identical and were considered together. Of these cells, 73.5% had infraorbital receptive fields. Of these, 77.2% were discharged by vibrissa stimulation (43.8% slow-adapt type I, 10.3% slow-adapt type II, 27.6% low-velocity sensitive rapid adapt, 16.8% high-velocity sensitive rapid adapt, and 1.5% noxious-biased), while the rest responded best to guard hair deflection (12.0%), gentle skin indentation (4.5%), or a strong pinch or deep pressure (6.3%). In stereotaxically matched penetrations in ganglia ipsilateral to the neonatal infraorbital nerve lesions, only 40.6% of the cells had infraorbital receptive fields. Of these, only 37.7% responded to vibrissa stimulation (29.8% slow-adapt type I, 1.2% slow-adapt type II, 2.2% low-velocity sensitive rapid adapt, 32.9% high-velocity sensitive rapid adapt, 33.9% noxious). Other infraorbital cells responded best to guard hair deflection (11.9%), gentle skin indentation (10.8%), or a strong pinch or deep pressure (39.6%). An additional 30 cells did not have a detectable receptive field and were identified only by infraorbital and brain-stem shocks. We also recorded cells with unusual infraorbital receptive fields: 9 units responded to more than 1 vibrissa, 4 were activated by both vibrissa and guard hair deflection, 10 had unusually large skin or deep receptive fields, 1 had a split receptive field, and 7 were discharged only by deep pressure to the region of the nerve section. Seven cells with infraorbital receptive fields were not driven by infraorbital shocks, and 2 were not activated by brain-stem shocks. In normal rats, all cells with infraorbital receptive fields were driven by both electrodes. The percentages of receptive field types for noninfraorbital cells were unchanged in ganglia ipsilateral to the damaged nerve.(ABSTRACT TRUNCATED AT 400 WORDS)
Biochemical and physical analyses of newly synthesized muscarinic acetylcholine receptors in cultured embryonic chicken cardiac cells
Authors: Hunter DD , Nathanson NM
Published: March 2018

Exposure of cultured embryonic chicken cardiac cells to the muscarinic agonist carbachol results in a 70–80% decrease in the number of muscarinic acetylcholine receptors (mAChR) expressed on the surface of the cells. Removal of the agonist results in a gradual increase in mAChR number because of the accumulation of newly synthesized receptors, reaching the control level in 14 hr. Measurements of increases in K+ permeability elicited by carbachol show that even after the complete recovery of receptor number, the sensitivity to agonist is reduced. The EC50 for carbachol is 13-fold higher in cells that have been exposed to carbachol and allowed to recover for 18 hr than in control cells, but is not significantly different from the EC50 for control cells 24 hr after agonist removal. The sensitivity of the mAChR- mediated inhibition of adenylate cyclase is also decreased at 18 hr, and recovers by 24 hr. These increases in sensitivity of mAChR-mediated responses are not blocked by administration of cycloheximide, and thus do not require de novo protein synthesis. The number of surface mAChR available for ligand binding can be reduced by 85–100% by treatment with the affinity-alkylating antagonist propylbenzilylcholine mustard. Newly synthesized mAChR that appear following affinity alkylation are also poorly coupled to mAChR-mediated increases in K+ permeability, indicating that decreased physiological sensitivity is not due to a nonspecific effect of long-term agonist exposure on general cellular function, but reflects, rather, an intrinsic property of newly synthesized mAChR. The decrease in sensitivity of the mAChR-mediated responses is due neither to a lack of expression of mAChR on the surface nor to reduced agonist affinity of the mAChR. Cells exhibiting decreased responsiveness contain GTP-binding proteins, which function normally in the inhibition of adenylate cyclase and appear to be identical to pertussis toxin substrates from control cells using gel electrophoresis; therefore, the decreased sensitivity does not appear to be the result of an alteration in coupling proteins. These cells also contain mAChR that do not differ from those in control cells either by molecular weight or isoelectric point. Thus, the diminished sensitivity observed in cells containing newly synthesized receptors is either caused by a small change in mAChR not detected by these electrophoretic techniques or by a change in an as-yet-undefined component of mAChR transduction system in the heart.
Long-range focal collateralization of axons arising from corticocortical cells in monkey sensory-motor cortex
Authors: DeFelipe J , Conley M , Jones EG
Published: March 2018

Small extracellular injections of HRP were placed into a stratum of corticocortical axons situated immediately deep to area 3b of the monkey somatic sensory cortex. This stratum had previously been demonstrated to contain corticocortical fibers linking the cytoarchitectonic fields of the somatic sensory cortex to one another and certain of them to the motor cortex. This method resulted in extremely successful filling of pyramidal cells, their axons, collateral axon branches, and terminations in areas 3b, 1, and 2 posterior to the injection and in areas 3a and 4 anterior to it. The major finding was that cells with somata situated in any one of these fields and with principal axons traversing the injection site have long collaterals, primarily in layers III and V, which can extend throughout their own cytoarchitectonic field and into one or more other fields. In these fields they give off focused, columnlike concentrations of terminal boutons, which can be separated from one another by 800 micron or more. The anterogradely labeled, primary corticocortical fibers, traced forwards into areas 3a and 4, have virtually identical focal terminations. These findings indicate that interareal connectivity in the sensory-motor cortex can be effected by the axon branches of single cells rather than by separate groups of cells, and this may form a basis for the convergence of place and modality information on single cells in the sensorimotor cortex, a convergence that is not seen in the thalamic input to this cortex.
Cross-linking of atrial natriuretic peptide to binding sites in rat olfactory bulb membranes
Authors: Wildey GM , Glembotski CC
Published: March 2018

Binding sites for 125I-atrial natriuretic peptide (ANP)2 in rat olfactory bulb membranes have been studied using pharmacological and biochemical methods. Various unlabeled ANP-related peptides were tested for the ability to inhibit the binding of the radioligand in membrane binding assays. ANP(92–126) and ANP(99–126) were the most potent inhibitors tested, both exhibiting an IC50 value of 0.40 nM. ANP(103– 126) and ANP(103–123) were 3 and 70 times less potent, respectively. ANP(111–126) was unable to inhibit the binding of the radioligand at a concentration of 1 microM. Several peptides unrelated to ANP were unable to inhibit the binding of the radioligand to rat olfactory bulb membranes. Membranes labeled with 125I-ANP were incubated with cross- linking agents and subjected to SDS-PAGE followed by autoradiography. A band possessing an apparent molecular mass of 116 kDa was identified. The labeling of this band was progressively decreased by increasing concentrations of unlabeled ANP(99–126) (IC50 = 0.6 nM) and by several other ANP-related peptides at nanomolar concentrations. For comparison purposes, ANP binding sites in rat aorta membranes were labeled with 125I-ANP and cross-linked using identical techniques. Three bands possessing molecular masses of 120, 72, and 62 kDa were identified. These results indicate that the ANP binding site in rat olfactory bulb membranes displays pharmacological and biochemical properties similar to peripheral ANP receptors.
Corticotropin-releasing factor receptors in the rat central nervous system: characterization and regional distribution
Authors: De Souza EB
Published: March 2018

A stable, iodine-125-labeled analog of rat/human corticotropin- releasing factor (CRF) was used to define the characteristics of CRF receptors in a crude mitochondrial/synaptosomal membrane preparation of rat olfactory bulb, and to study the distribution of CRF binding sites in discrete regions of the rat CNS. The binding of 125I-Tyro rat/human CRF (125I-rCRF) was time- and temperature-dependent, was sensitive to the pH, ionic strength, and cationic composition of the incubation buffer, and was linear over a broad range of membrane protein concentrations. 125I-rCRF binding to olfactory bulb membrane was saturable, reversible, and, on Scatchard analysis, revealed a high- affinity component with an apparent equilibrium dissociation constant (Kd) of 0.2 nM and a low-affinity binding site with Kd of approximately 20 nM. Data from pharmacological studies indicated that the ability of a variety of CRF fragments and analogs to inhibit 125I-rCRF to olfactory bulb membranes correlates well with their reported relative potencies in stimulating pituitary adrenocorticotropic hormone secretion in vitro. Consistent with a coupling of CRF receptors to adenylate cyclase, the binding of 125I-rCRF was decreased by guanine nucleotides and increased by magnesium ions. A heterogeneous distribution of 125I-rCRF binding sites was found in the rat CNS, with highest densities present in olfactory bulb, cerebellum, cerebral cortex and striatum, and progressively lower but significant levels of binding were detected in cervical spinal cord, hypothalamus, medulla, midbrain, thalamus, pons, and hippocampus. These data, using a rat CRF ligand homologous to the endogenous peptide, are consistent with those from previous studies demonstrating the presence of specific binding sites for ovine CRF in rat brain, and provide further support for the suggestion that endogenous CRF may function as a neurotransmitter in the CNS.
Newly synthesized catalytic and regulatory components of adenylate cyclase are expressed in neurites of cultured sympathetic neurons
Authors: Tolkovsky AM
Published: March 2018

Forskolin- and guanine nucleotide-stimulated adenylate cyclase activities were measured in microdissected sections of neurites from small explants and in dispersed cell cultures of sympathetic ganglion neurons to determine whether a competent system for regulated formation of cAMP, consisting of both catalytic units of adenylate cyclase and regulatory GTP binding proteins, is synthesized during neurite outgrowth and where it is distributed in the neuron. An increase in both guanine nucleotide- and forskolin-dependent activity of adenylate cyclase occurred concomitantly with neurite outgrowth and was directly proportional to neurite length. Separate analysis of adenylate cyclase activity in explant cell bodies or neurites showed that the increased activity was localized entirely in the neurites, while activity in the cell bodies remained virtually constant during growth. Concentric sections of neurites of approximately 500 microns width, which contained similar volumes of neurites as determined with the indicator BCECF (Rink et al., 1982), produced similar levels of cAMP, indicating an even distribution of adenylate cyclase in the neurites. Cell bodies, when stimulated by GTP gamma S, produced 236 +/- 46 attomol cAMP/min (30 degrees C)/cell body and an additional 52.6 +/- 20 attomol cAMP/min (30 degrees C)/neuron were produced with each day of neurite growth (approximately 400 microns). Assuming a turnover number of 2000 min-1, cell bodies and neurites were calculated to contain similar densities of catalytic unit molecules on their surface (9–28 molecules/micron 2). An abundant GTP binding protein, detected by ADP-ribosylation with pertussis toxin, was also widely distributed in the neuron.(ABSTRACT TRUNCATED AT 250 WORDS)
Picomolar affinity of 125I-SCH 23982 for D1 receptors in brain demonstrated with digital subtraction autoradiography
Authors: Altar CA , Marien MR
Published: March 2018

Iodinated SCH 23390, 125I-SCH 23982 (DuPont-NEN), was examined using quantitative autoradiography for its potency, selectivity, and anatomical and neuronal localization of binding to the dopamine D1 receptor in rat brain sections. 125I-SCH 23982 bound to D1 sites in the basal ganglia with very high affinity (Kd values of 55–125 pM), specificity (70–85% of binding was displaced by 5 microM cis- flupenthixol), and in a saturable manner (Bmax values of 65–176 fmol/mg protein). Specific 125I-SCH 23982 binding was displaced by the selective D1 antagonists SCH 23390 (IC50 = 90 pM) and cis-flupenthixol (IC50 = 200 pM) and the D1 agonist SKF 38393 (IC50 = 110 nM) but not by D2-selective ligands (I-sulpiride, LY 171555) or the S2 antagonist cinanserin. Compared with 3H-SCH 23390, the 5- to 10-fold greater affinity for the D1 site and 50-fold greater specific radioactivity of 125I-SCH 23982 makes it an excellent radioligand for labeling the D1 receptor. The concentrations of D1 sites were greatest in the medial substantia nigra and exceeded by over 50% the concentration of D1 sites in the lateral substantia nigra, caudoputamen, nucleus accumbens, olfactory tubercle, and entopeduncular nucleus. Lower concentrations of D1 sites were present in the internal capsule, dorsomedial frontal cortex, claustrum, and layer 6 of the neocortex. D1 sites were absent in the ventral tegmental area. Intrastriatal injections of the axon- sparing neurotoxin, quinolinic acid, depleted by 87% and by 46–58% the concentrations of displaceable D1 sites in the ipsilateral caudoputamen and medial and central pars reticulata of the substantia nigra, respectively. No D1 sites were lost in the lateral substantia nigra. Destruction of up to 94% of the mesostriatal dopaminergic projection with 6-hydroxydopamine did not reduce D1 binding nor, with one exception, increase striatal or nigral D1 receptor concentrations. 125I- SCH 23982 selectively labels D1 binding sites on striatonigral neurons with picomolar affinity, and these neurons contain the majority of D1 sites in rat brain.
Ultrastructural evidence related to presynaptic inhibition of primary muscle afferents in Clarke's column of the cat
Authors: Walmsley B , Wieniawa-Narkiewicz E , Nicol MJ
Published: March 2018

As part of an investigation on excitatory synaptic transmission in the mammalian CNS, we have examined ultrastructural details of the synaptic connection between primary afferent fibers and dorsal spinocerebellar tract (DSCT) neurons in Clarke's column of the cat spinal cord. Single primary muscle afferents (group Ia and Ib) and DSCT neurons were identified and stained intracellularly with HRP. The terminations of these afferent fibers were examined in serial sections under the EM. Five of 6 Ib boutons and 1 of 14 Ia boutons were contacted by small presynaptic boutons. An example was illustrated in which only 1 out of 7 boutons arising from the same Ia fiber and contacting the same postsynaptic DSCT neuron was contacted by a presynaptic bouton. It is likely that the presynaptic contacts are responsible for presynaptic inhibition of synaptic transmission between primary afferents and DSCT neurons. We have proposed that the observed differences in presynaptic contacts from bouton to bouton may be one of the causes of a nonuniformity in the probability of transmitter release between release sites at this connection.
An indoleamine system in photoreceptor cell terminals of the Long-Evans rat retina
Authors: Redburn DA , Churchill L
Published: March 2018

Uptake of 3H-serotonin is localized to the outer plexiform layer in Long-Evans rat retinas. Autoradiographic accumulation is seen only after in vitro incubation in the light, with retinas isolated from the underlying sclera. Potassium stimulates the release of 3H-serotonin. In this species, amacrine cells do not accumulate these compounds; thus the outer plexiform layer appears to be the only site of uptake and release of this indoleamine. The age-related loss of 3H-serotonin accumulation in the outer plexiform layer of retinal dystrophic rats coincides temporally with the spontaneous degeneration of photoreceptor cells that occurs in this species. Electron-microscopic autoradiography of 3H-serotonin accumulation further confirms that uptake is localized to rod and cone terminals in the outer plexiform layer. The specific accumulation of indoleamines into rod and cone terminals that is observed in the light but is absent in darkness suggests that indoles have an important physiological role in photoreceptors.
The toxic effects of ethylcholine mustard aziridinium ion on cholinergic cells in the chicken retina
Authors: Millar TJ , Ishimoto I , Boelen M , Epstein ML , Johnson CD , Morgan IG
Published: March 2018

The chicken retina has been used to examine the toxicity of a highly reactive chemical analog of choline, ethylcholine mustard aziridinium ion (ECMA). Following a single intravitreal injection, retinas were analyzed biochemically for CAT and AChE activities, and GABA, glycine, and dopamine levels. Retinas were also examined using histofluorescence for dopamine histochemistry, for AChE, and immunohistochemistry with antibodies to CAT, tyrosine hydroxylase, GABA, 5-HT, Leu-enkephalin, and somatostatin. A dose of 50 nmol ECMA caused a prolonged 70% depletion of CAT activity and a 40% depletion of AChE activity. The other biochemical parameters were unchanged. This result corresponds to the morphological finding that 2 populations of cholinergic cells were destroyed and that the AChE activity associated with their terminal arbors was lost. A third population of cholinergic cells, located towards the middle of the inner nuclear layer, was resistant to the toxic effects of ECMA. The other cell types, except for somatostatin- immunoreactive cells and photoreceptors, which showed transient effects, were unaffected. ECMA therefore appears to be a highly specific toxin for cholinergic cells in the retina.
Synaptic functions in rat sympathetic neurons in microcultures. IV. Nonadrenergic excitation of cardiac myocytes and the variety of multiple-transmitter states
Authors: Matsumoto SG , Sah D , Potter DD , Furshpan EJ
Published: March 2018

In the first 3 papers of this series (Furshpan et al., 1986a, b; Potter et al., 1986), a sensitive microculture procedure was used to show that sympathetic principal neurons, dissociated from newborn or adult superior cervical ganglia and grown singly on cardiac myocytes, display adrenergic, cholinergic, and purinergic functions, sometimes in isolation but more often in combination. In this paper we describe additional effects on cardiac myocytes evoked by these neurons; the effects were excitatory and insensitive to adrenergic blocking agents (and to agents that block the inhibitory effects of acetylcholine and purines). In some of these microcultures, evidence consistent with secretion of serotonin was obtained; the nonadrenergic excitatory effect was diminished or abolished by serotonin blockers or reserpine. Further evidence for serotonergic transmission is presented in the accompanying paper by Sah and Matsumoto (1987). In other cases, an as- yet-unidentified agent “X” also produced a nonadrenergic excitation. The X effect characteristically required a prolonged train of neuronal impulses, had a time course of 50–200 sec, and was insensitive to agents that affected the other transmitters, including serotonin. In addition, we discuss 2 remarkable features of the transmitter repertoire of the microcultured sympathetic neurons: expression of the several transmitters in a variety of combinations, including at-least- quadruple function, and expression of the transmitters within a particular combination in varying relative strengths. The result is a diversity of transmitter release greater than that previously reported for vertebrate or invertebrate neurons.
Multiple sensory neuronal correlates of site-specific sensitization in Aplysia
Authors: Walters ET
Published: March 2018

Noxious stimulation of a restricted site on the skin of Aplysia (training) causes site-specific sensitization of the tail-withdrawal reflex that is associated with several sensory correlates that are evident both 10 min and 2 hr after training. First, extracellularly recorded afferent activity evoked by test stimulation of the trained site increases, indicating peripheral sensory changes. Second, central sensory alterations are manifested by tail sensory neurons within the pleural VC cluster that innervate the trained site and are activated during training. These mechanosensory/nociceptive cells display a number of differences from unactivated tail sensory neurons innervating other sites: slow depolarization of the soma observed immediately after training, decrease in soma action potential threshold, and enhancement of monosynaptic EPSPs to identified motor neurons. Noxious stimulation of a more extensive region also produces site-specific sensitization of the tail-withdrawal reflex and site-specific enhancement of EPSP amplitude measured 1 d after training. This training produced a novel cellular correlate of behavioral enhancement in Aplysia--regenerative bursting responses (2–35 spikes) in response to brief depolarization of the sensory neuron soma. The changes in peripheral and central excitability appear similar to changes associated with mammalian models of primary hyperalgesia. Site-specific enhancement of nociceptive signaling also occurs during aversive associative conditioning in a noxious unconditioned stimulus (US) pathway. These site-specific changes involve activity-dependent extrinsic modulation (ADEM) of the VC sensory neurons, suggesting a close relationship to changes underlying associative conditioning in conditioned stimulus (CS) pathways in Aplysia.
Forskolin's effect on transient K current in nudibranch neurons is not reproduced by cAMP
Authors: Coombs J , Thompson S
Published: March 2018

Forskolin, a diterpene extracted from Coleus forskolii, stimulates the production of cAMP in a variety of cells and is potentially an important tool for studying the role of cAMP in the modulation of neuronal excitability. We studied the effects of forskolin on neurons of nudibranch molluscs and found that it caused characteristic, reversible changes in the amplitude and waveform of the transient K current, IA, and also activated an inward current similar to the cAMP- dependent inward current previously described in molluscan neurons. Forskolin altered the time course of IA activation and inactivation but did not affect the voltage dependence or the reversal potential of the current. IA normally inactivates exponentially, but in forskolin the time course of inactivation can be fit by the sum of 2 exponentials with an initial rate that is faster than the control and a final rate that is much slower. On depolarization in forskolin, IA begins to activate at the normal rate, but a slower component of activation is also seen. The changes in IA in the nudibranch cells were qualitatively different than the changes caused by forskolin in Aplysia bag cell neurons (Strong, 1984). Experiments were performed to determine whether these effects of forskolin require cAMP. Intracellular injection of cAMP, application of membrane-permeable analogs of cAMP, application of phosphodiesterase inhibitors, and intracellular injection of the active catalytic subunit of cAMP-dependent protein kinase did not affect the amplitude or waveform of IA. Also, the changes in IA that are caused by forskolin were not prevented or reversed by intracellular injection of an inhibitor of cAMP-dependent protein kinase. Cyclic AMP did, however, activate inward current at voltages near the resting potential. We conclude that the changes in IA and the activation of inward current represent separate affects of forskolin. The inward current appears to depend on an increase in intracellular cAMP, while the changes in IA do not. These experiments show that, in addition to activating adenylate cyclase, forskolin may have a separate direct affect on the transient K current.
Brain-stem perturbations during cortically evoked rhythmical jaw movements: effects of activation of brain-stem loci on jaw muscle cycle characteristics
Authors: Chandler SH , Tal M
Published: March 2018

The purpose of the present study was to further elucidate with the use of microstimulation techniques the influences of rostral pons and midbrain loci on the neuronal networks responsible for cortically induced rhythmical jaw movement (RJM) activity in the anesthetized guinea pig and to establish if these rostral brain-stem loci are capable of modulating the timing as well as the amplitude of rhythmical digastric (DIG) EMG activity. It was found that repetitive electrical stimulation of widespread areas of the rostral pons and mid-brain produced suppression of ongoing cortically induced rhythmical EMG activity. Prior to complete EMG suppression there was a reduction in amplitude of the DIG EMG and an increase in cycle duration. Repetitive stimulation of these suppressive loci also produced a reduction in the amplitude of the short-latency DIG EMG response produced by short pulse train stimulation of the masticatory cortex. This indicates that part of the suppression of cortically induced rhythmical EMG activity was due to a reduction in excitability of the polysynaptic short-latency pathway from cortex to DIG motoneurons. Short pulse train stimulation of these brain-stem suppressive loci during various phases of the rhythmical DIG cycle produced a phase-dependent increase in duration of the ongoing perturbed cycle. The cycles following the stimulus perturbation did not show any compensatory shortening in their durations suggesting that the stimulus produced a true resetting of the cycle. These data suggest that the brain-stem loci that produce suppression of RJMs evoked by repetitive cortical stimulation can affect the excitability of the central circuits responsible for cycle oscillation and timing as well as the excitability of the polysynaptic short-latency corticotrigeminal pathway to DIG motoneurons.