Biomedical subjects

M A Dichter

Publications and source records attributed to M A Dichter.

At least 73 records · Page 4Linked to original sources

PubMed1985

Cholecystokinin-octapeptide enhances synaptic activity in neurons cultured from rat cerebral cortex.

Cholecystokinin-octapeptide (CCK-8) was applied by local microperfusion techniques to neurons cultured from fetal rat cerebral cortex while membrane properties and synaptic activity were monitored with intracellular recording techniques. There were no consistent effects of CCK-8 on resting membrane potential, membrane input resistance, or excitability of the recorded neuron. Nevertheless, the application of CCK-8 was associated both with an increase in the frequency of ongoing synaptic activity and with an initiation of new synaptic activity not seen during control periods of recording prior to peptide application. CCK-8 was more potent evoking increased synaptic activity than its non-sulfated CCK-8 analogue. The existence of areas in proximity to the recorded neuron which were particularly sensitive to the effect of CCK-8 was noted. These results suggest that CCK-8 has a predominantly excitatory effect on cerebral cortical neurons. While a mechanism cannot be determined from the present data, a presynaptic site of action is suggested.

Animals↗

PubMed1985

The picrotoxinin binding site and its relationship to the GABA receptor complex.

The binding characteristics of [3H] alpha-dihydropicrotoxinin to the picrotoxinin binding site were investigated in membrane preparations of adult rat forebrain and living cultures of rat cerebral cortex. The binding of [3H]alpha-dihydropicrotoxinin to rat forebrain was decreased by lysing, treating with Triton X-100, and heating. Coincubation with gamma-aminobutyric acid (GABA), benzodiazepines, or alterations in the Na+ or Cl- composition of the media had no effect on the binding to the rat brain preparation. However, in the living neurons in tissue culture both GABA and diazepam significantly decreased the binding of [3H]alpha-dihydropicrotoxinin. The dose-response relationships for GABA antagonism of [3H]alpha-dihydropicrotoxinin binding and for picrotoxinin antagonism of the GABA enhancement of [3H]flunitrazepam binding in cultured cortical neurons were also investigated. The Hill coefficients for these actions were reciprocal, suggesting that they result from complementary interactions between the binding sites for GABA and picrotoxinin. These data support the association of the picrotoxinin binding site with the postsynaptic GABA receptor complex.

Acetates↗

PubMed1984

Expression of the Thy-1 antigen in long-term cultures of embryonic mouse spinal cord.

Immunofluorescent studies of the Thy-1 antigen in cultures of mouse spinal cord demonstrated positivity on the surfaces of a fraction of neurons and glia. Positivity was evident by one week and increased slowly over the lifespan of the cultures, often several months. Thy-1 positivity was most apparent in regions of clustering of neurons and glia. Neuroglial clusters were identified by morphologic appearance; the identity of astrocytes was confirmed by immunofluorescent staining of glial fibrillary acidic protein.

Animals↗

PubMed1984

Neuron generation in dissociated cell cultures from fetal rat cerebral cortex.

Examination of dissociated cell cultures of rat fetal cortex revealed that mature cultures contained more neurons (identified by phase contrast morphology and tetanus toxin staining) than the number of cells initially adhering to the coverslips. Labeling with [3H]thymidine confirmed that neuronal precursors were undergoing mitosis throughout at least the first 10 days in vitro.

Animals↗

PubMed1984

Localization of cholecystokinin-octapeptide-like-immunoreactivity in neurons cultured from rat cerebral cortex.

Cholecystokinin-octapeptide-like-immunoreactivity (CCK-8-LI) is demonstrable by the indirect immunofluorescent technique in cerebral cortical neurons cultured from fetal rats. Prominent and widespread staining is seen in widely ramifying cellular processes throughout the cultures. Staining in neuronal cell bodies is enhanced by treatment of the cultures with colchicine prior to fixation and can be seen to extend from the perikaryal region into dendrites and axonal processes. While several morphological types of neurons contain CCK-8-LI, there is a relative preponderance of small and moderate-sized bipolar and, to a lesser extent, multipolar neurons. These findings are in concordance with the findings of several investigators in studies of brain sections. The further finding of frequent groupings of CCK-8 neurons is noted and discussed.

Animals↗

PubMed1984

Physiology and pharmacology of olfactory bulb neurons in dissociated cell culture.

Cells from olfactory bulbs of embryonic rats were grown in dissociated cell culture for up to 5 weeks. Both neurons and non-neuronal cells grew in these cultures, with a variety of neuronal populations appearing. A population of 20-25% of the neurons were GABAergic by the criterion of [3H]GABA uptake. Electrophysiologic measurements were made of the baseline activity of the cultured neurons. Cells showed a mean resting potential of 60.1 +/- 1.2 mV and a mean input resistance of 87.6 +/- 9.5 M omega. All cells were sensitive to microperfusion of GABA with half-maximal effect occurring at about 20 microM. Glutamate was universally excitatory but with variations in degree. Carnosine (beta-Ala-L-His), tested over the concentration range of 10 nM to 100 microM, had no effect on input resistance, resting potential, action potential shape, on-going synaptic activity or the responsiveness to either GABA or glutamate. These results are further evidence against a role for carnosine as the excitatory transmitter of the primary olfactory afferents.

Action Potentials↗

PubMed1984

Coexistence of acetylcholinesterase and somatostatin-immunoreactivity in neurons cultured from rat cerebrum.

Cultures derived from rat cerebral hemispheres were sequentially stained for acetylcholinesterase activity and for either somatostatin-like immunoreactivity or cholecystokinin-like immunoreactivity. Somatostatin-like immunoreactivity was found to coexist with acetylcholinesterase activity in individual neurons of several morphological subtypes, but cholecystokinin-like immunoreactivity and acetycholinesterase activity were never seen in the same neurons. These findings suggest a specific anatomical association, perhaps even an overlap, of the cholinergic and somatostatinergic systems in the mammalian cerebrum, and indicate that the combined deficiencies of somatostatin and cholinergic markers in Alzheimer's dementia and senile dementia of the Alzheimer type may be of pathophysiological importance.

Acetylcholinesterase↗

PubMed1984

Infection of neuronal cell cultures with reovirus mimics in vitro patterns of neurotropism.

Primary neuronal cell cultures of rat fetal cerebral cortex serve as in vitro models for the study of a variety of neuronal membrane receptors. Such studies have focused primarily on receptors for neurotransmitters and drugs. In the present series of experiments, we have employed this model to study the in vitro pattern of infection with reovirus types 1 and 3, two well-characterized neurotropic viruses that show specificity for neurons (type 3) or ependymal cells (type 1) in vivo and whose specificity has been linked with surface receptors on somatic cells. We have found that in primary neural cell culture, reovirus type 3 maintained its specificity by infecting neurons whereas reovirus type 1 did not infect neurons. Both serotypes infected astrocytes in the cultures, type 1 to a greater extent than type 3. In addition, reovirus type 3 bound to the surface of neurons whereas type 1 did not. Using recombinant viral clones, the in vitro tropism and the neuronal binding were shown to be properties of the viral hemagglutinin, a small outer capsid viral protein, as is the case with the neurotropism in vivo. It is postulated that the neurotropism of reovirus type 3 is related to the interaction of the viral hemagglutinin with an as yet undefined structure on the neuronal surface.

Animals↗

PubMed1984

Effects of ethosuximide and tetramethylsuccinimide on cultured cortical neurons.

In cultured cortical neurons, ethosuximide (ESM) had unexpected actions for an antiepileptic drug; it slightly diminished the effects of inhibitory neurotransmitters, GABA, and glycine. ESM had no direct membrane effects, did not change action potential characteristics or alter spontaneous activity, and did not reverse the effects of convulsants that are GABA antagonists. The structurally related convulsant tetramethylsuccinimide (TMSM) reduced the amplitude of GABA-mediated inhibitory postsynaptic potentials and antagonized responses to applied GABA, effects not reversed by ESM. The convulsant effects of TMSM include a blockade of postsynaptic GABA actions, but the antiepileptic effects of ESM are not due to an enhancement of GABA-mediated inhibition.

Animals↗

PubMed1983

Action potential mechanism of mammalian cortical neurons in cell culture.

Rat cortical neurons in 4- to 7-week-old dissociated cell cultures have action potentials (APs) which are tetrodotoxin-sensitive and appear to be generated by conventional sodium mechanisms. Approximately 10% of neurons can also generate APs when sodium channels are blocked. These latter APs are smaller, slower and sensitive to cobalt. When voltage sensitive potassium channels are blocked by TEA or when Ba is substituted for calcium, all the neurons are capable of generating large, overshooting, slow and prolonged, calcium-dependent APs. The amplitudes of these APs are proportional to the log of the divalent cation concentration and the APs are blocked by either cobalt or verapamil. We conclude that under physiological conditions, calcium currents are not likely to play a major role in the AP morphology in 'mature' neurons, but are more likely to be involved with other aspects of cell excitability and neurotransmitter function. APs in younger neurons (3-4 weeks in vitro) have a large calcium component even under physiological conditions.

Animals↗

PubMed1983

Anticonvulsant sensitivity of absence seizures in the tottering mutant mouse.

Homozygous tottering mice (tg, autosomal recessive) exhibit frequent spontaneous "absence" seizures accompanied by bilaterally synchronous spike-and-wave or polyspike electrocorticographic discharges. In adult tottering mice, the antiepileptic effects of a single dose of ethosuximide, diazepam, phenobarbital, or phenytoin were assessed using continuous electrocorticographic recording to monitor seizure incidence. The dose chosen for each drug was selected to correspond to an effective antiepileptic dose in standard murine models. Ethosuximide, 150 mg/kg, diazepam, 1.4 mg/kg, and phenobarbital, 25 mg/kg were effective against absence seizures. In contrast, phenytoin at 5, 10, 30, or 60 mg/kg produced no significant reduction in the incidence of absence seizures. These results suggest that absence seizures in the tottering mutant may represent a relatively specific pharmacological model for the identification of drugs effective for clinical absence epilepsy, and emphasize the potential value of this new model for the study of fundamental mechanisms of absence of epilepsy and the actions of antiepileptic drugs.

Animals↗

PubMed1983

Etazolate (SQ20009): electrophysiology and effects on [3H]flunitrazepam binding in cultured cortical neurons.

The actions of etazolate (SQ20009) on cultured cortical neurons have been examined in electrophysiological experiments and in receptor binding studies. Etazolate (0.3 to 100 microM) prolongs the duration of spontaneously occurring IPSPs. Higher concentrations of etazolate produce an increase in membrane chloride conductance, an effect which is picrotoxinin and bicuculline sensitive. Etazolate potentiates the response to exogenously applied GABA and acts synergistically with diazepam to enhance GABA-mediated conductance. Etazolate does not increase glycine-mediated conductance changes. Etazolate increases [3H]flunitrazepam binding and stimulates the GABA enhancement of [3H]flunitrazepam binding. In addition, GABA stimulates the etazolate enhancement of [3H]flunitrazepam binding. The etazolate-mediated increases in binding are Cl- dependent and picrotoxinin and bicuculline sensitive. The dose response relationships for etazolate-mediated effects are similar in physiological experiments and in binding studies. These data suggest that etazolate interacts with the postsynaptic GABA receptor complex at a site distinct from either the GABA recognition site or the benzodiazepine binding site to enhance GABA-mediated inhibition and to increase benzodiazepine binding.

Animals↗

PubMed1983

Effects of somatostatin on mammalian cortical neurons in culture: physiological actions and unusual dose response characteristics.

Somatostatin was applied to rat cortical neurons grown in dispersed cell culture while electrophysiological effects were monitored with intracellular recordings. The effects of somatostatin were predominantly excitatory, but they varied and were dose dependent. Somatostatin at concentrations between 100 pM and 1 microM depolarized 30 of 87 neurons, often with a concomitant increase in spontaneous action potentials and a small increase in membrane input resistance. Somatostatin also increased the frequency of synaptic activity coming into the recorded neuron in 45 of 78 recordings, an effect which was seen even in the absence of direct effects. In six of nine neurons, somatostatin decreased the amplitude of large ongoing inhibitory synaptic potentials, concomitant with an increase in membrane input resistance. Somatostatin occasionally caused inhibition of neuronal activity, an effect predominantly associated with the application of higher concentrations. The unpredictability of the response of an individual neuron to somatostatin is partially explained by three phenomena: a marked tachyphylaxis, an inverted U-shaped dose response curve for membrane depolarization, and qualitatively different responses depending on the concentration of somatostatin. These findings show that somatostatin is predominantly an excitatory agent when applied to cortical neurons, but it may cause several different changes in membrane properties. The dose response data suggest a considerable complexity of the actions of somatostatin at a cellular level.

Action Potentials↗

PubMed1983

Cell receptors for the mammalian reovirus. I. Syngeneic monoclonal anti-idiotypic antibody identifies a cell surface receptor for reovirus.

We have prepared and characterized a syngeneic monoclonal anti-idiotype directed against the idiotype (Id3) of the anti-reovirus type 3 hemagglutinin B cell hybridoma 9BG5. We have shown this monoclonal antibody to be anti-idiotypic in a series of inhibition studies with purified sigma 1 (hemagglutinin) protein and with absorption studies on the idiotypic R1.1 cell line. That the idiotype Id 3 defined by the monoclonal anti-idiotype is distinct from H-2 was demonstrated by its presence on an idiotype-expressing H-2 negative cell line (R1.E). Binding of the anti-idiotype is relatively tunicamycin resistant and pronase/trypsin sensitive, which suggests that the recognition site of the anti-idiotypic receptor is poorly glycosylated. The presence of idiotype-like receptors on reovirus type 3 susceptible neurons may have important implications for the presence of related gene families between neural and lymphoid tissue. The implications of recognition by neuronal cells of an anti-idiotypic monoclonal antibody directed against the reovirus 3 attachment receptor for the pathogenesis of viral-induced auto-immunity are discussed.

Animals↗

PubMed1983

Morphological classification of rat cortical neurons in cell culture.

Neurons in "mature" (4- to 6-week-old) dissociated cell cultures of 15-day gestational age rat fetal cortex were injected with Lucifer Yellow in order to compare their detailed morphological features with those of cortical neurons in situ, and in order to determine which features of cellular morphology were dependent on local environmental conditions. Neurons were characterized by their cell form (pyramidal, multipolar, fusiform, etc.), dendritic branching pattern, spine density, and axonal projections. The neurons in culture appeared to display all the morphological features seen in cortical neurons in situ. These characteristics appeared to be independent of whether an individual neuron grew in a dense or sparse region of the culture. In addition, examination of neurons during early differentiation indicated that many of their morphological features developed as soon as the neurons could be recognized and before extensive synapse formation occurred.

Animals↗

PubMed1982

Identification of a hemagglutinin-specific idiotype associated with reovirus recognition shared by lymphoid and neural cells.

A xenogeneic antiserum raised to antireovirus immunoglobulin was used to define an idiotypic determinant present on antibodies to reovirus type 3 hemagglutinin. The same idiotype was identified on nonimmune lymphoid cells and on neuronal cells that specifically bind the hemagglutinin of type 3 reovirus. This idiotypic determinant, called Id3, is shared by (a) a monoclonal antibody to the neutralization site of hemagglutinin from type 3 reovirus; (b) BALB/c serum antibodies to the hemagglutinin of reovirus type 3; (c) R1.1, a murine thymoma cell line that binds reovirus type 3; (d) primary cultures of murine neuronal cells. The presence of an idiotype shared by antihemagglutinin antibodies and by structures on nonlymphoid cells suggests a general relationship between disparate receptors that recognize a common determinant. Furthermore, this suggests a novel approach for the study of viral receptor interactions and for analysis of mechanisms of autoimmune responses.

Animals↗

PubMed1981

Benzodiazepine binding and interactions with the GABA receptor complex in living cultures of rat cerebral cortex.

Benzodiazepines bind to living cultures of dissociated rat cerebral cortex. This binding is saturable, and kinetic analyses indicate that the binding is to a single class on sites with kinetic constants very close to those obtained using neuronal membrane preparations. The efficacy of a number of benzodiazepines, xanthine derivatives and other drugs in competition experiments is similar to that seen in neuronal membrane preparations, and suggests that the benzodiazepine binding site studied in these investigations is the same as that found in neuronal membrane preparations and believed to be the pharmacologically active benzodiazepine binding site. GABA agonists increase the binding of benzodiazepines, and this increase has the same order of efficacy as their ability to hyperpolarize the neurons when applied at known concentrations with muscimol greater than GABA greater than THIP. At high concentrations THIP potentials benzodiazepine binding to the same level as GABA. Diazepam increases the ability of both GABA and THIP to hyperpolarize the neurons as well as the amplitude of spontaneous IPSPS which, in this system, are GABA-mediated. The competitive GABA antagonist bicuculline methiodide slightly decreased benzodiazepine binding and also antagonized the increase due to GABA. The non-competitive GABA antagonist picrotoxinin had no effect on benzodiazepine binding but did antagonize the GABA-induced increase in benzodiazepine binding. Replacement of Cl- in the incubation medium by acetate, which does not permeate the GABA-mediated Cl-- ionophore, increases benzodiazepine binding, and GABA no longer increases the binding. Picrotoxinin decreases the increase in benzodiazepine binding is Cl--free media, and this decrease is blocked by GABA. These results are discussed in terms of interactions at the GABA receptor complex consisting of a GABA recognition site, a benzodiazepine recognition site, a picrotoxinin recognition site, and a Cl- ionophore.

Animals↗

PubMed1981

Somatostatin and cortical neurons in cell culture.

Rat cortical neurons in culture have morphological, physiological and biochemical properties similar to their counterparts in situ. Neuropeptides are synthesized by these cultures and can in situ. Neuropeptides are synthesized by these cultures and can be localized to individual neurons. One such peptide, somatostatin, is produced in relatively large amounts, exists in a discrete neuronal population, and is released in the culture medium. Somatostatin has no detectable effect on membrane potential, resistance, or action potential of cells to which it is applied but does not appear to increase incoming spontaneous postsynaptic potentials in some neurons. Somatostatin potentiates the direct membrane effects of glutamate and aspartate. Somatostatin may play a role as a neuromodulator in mammalian cerebral cortex by potentiating the effects of excitatory neurotransmitter agents.

Action Potentials↗