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Biomedical subjects

M Segal

Publications and source records attributed to M Segal.

At least 289 records · Page 16Linked to original sources
PubMed1980

Metabolic changes induced in rat hippocampal slices by norepinephrine.

The oxidative metabolic activity of restricted regions of hippocampal slices was assessed by a continuous measurement of the fluorescence of intramitochondrial nicotinamide-adenine dinucleotide (NADH). A large increase in NADH fluorescence was triggered by substituting the oxygen supply to the slice by nitrogen gas. A large and transient increase in NADH fluorescence was also produced by superfusion of the the slice with a high (50 mM) potassium-containing medium. Addition of norepinephrine (NE) to the superfusion medium caused a propranolol-inhibited increase in NADH fluorescence. Furthermore, ouabain, which inhibits the Na-K pump, blocked the effects of NE. An analog of cyclic adenosine monophosphate (cAMP), 8-bromo cAMP, mimicked the effect of NE. Finally, effects of NE could still be produced in a kainic acid-treated hippocampus, where most neurons were previously destroyed by the drug. It is suggested that NE activates a Na-K-ATPase, that this effect might be mediated by cAMP, and that these interrelations may underly the physiological action of NE in the brain.

Animals↗
PubMed1980

Different cholinergic synapses converging onto neurons in Aplysia produce the same synaptic action.

We have investigated neurons that receive inputs from more than one cholinergic interneuron, to see whether one cholinergic input can depolarize and the other hyperpolarize by virtue of activating different ACh receptors. We have examined synapses made in the abdominal ganglion of Aplysia californica by 3 cholinergic interneurons. Two of those interneurons have previously been shown to be cholinergic. Using both biochemical and pharmacological tests we have shown a third interneuron to be cholinergic. For 7 postsynaptic cells, we compared 6 new connections that we have identified from cholinergic interneurons, and 12 previously known connections. In each case we found that different cholinergic inputs onto any given cell produced the same synaptic action. This finding held even for L7, a cell known to have two types of ACh receptors. These data are consistent with the hypothesis that a postsynaptic cell does not segregate different types of ACh receptors. If generally true, this lack of segregation may help explain why a nervous system uses more than one neurotransmitter as well as why certain interneurons are needed in neural networks.

Acetylcholine↗
PubMed1980

Brain aminergic axons exhibit marked variability in conduction velocity.

Impulses in rat locus coeruleus neurons exhibit pronounced conduction latency decreases, followed by even larger latency increases (of over 20 msec in some cases) during a single train of antidromic activation. The magnitude of latency fluctuation varies as a function of basal antidromic latency, frequency of stimulation, and number of stimuli in a train. These and additional data indicate that this variability in latency is a consequence of altered impulse conduction velocity along the axons, perhaps reflecting reduced ion concentration gradients resulting from impulse propagation. These latency changes may allow thin unmyelinated axons to influence target cells most effectively with short bursts of activity, and suggest that myelination and large axon diameter provide for high fidelity as well as for high velocity of impulse flow in nervous tissue.

Animals↗
PubMed1980

Pain sensitivity and opioid activity in genetically and experimentally hypertensive rats.

Pain sensitivity was studied in renal and DOCA-salt hypertensive rats, and in two strains of rats derived from the same parental strain for their sensitivity (H) or immunity (N) to hypertension induced by DOCA-salt treatment. Experimentally hypertensive rats, and H and N rats were less sensitive to painful stimuli than their appropriate controls, as assessed in the hot-plate and paw pinch tests. Naloxone reversed this hypoalgesia in both experimentally and genetically hypertensive rats while it did not affect blood pressure in any rat-type tested. Opioid activity was measured with the radioreceptor assay in several brain regions and pituitary gland of both experimentally and genetically hypertensive rats. Experimentally hypertensive rats had a 45% higher level of opioid activity in the spinal cord compared to control. Rats of the H and N strains both exhibited higher levels of opioid activity in the spinal cord, hypothalamus and pituitary. It is suggested that control systems for blood pressure and pain sensitivity are closely associated in the rat.

Animals↗
PubMed1980

Histamine produces a Ca2+-sensitive depolarization of hippocampal pyramidal cells in vitro.

Electrophysiological activity was recorded intracellularly from pyramidal neurons in rat hippocampal slices. Topical application of histamine produced a slow depolarization that was not associated with conductance changes. The depolarization was accompanied by an increase in the rate of action potential discharges. These effects were markedly reduced in slices maintained in a low Ca2+, high Mg2+ medium, indicating that histamine may act presynaptically on hippocampal pyramidal neurons.

Animals↗
PubMed1980

The action of serotonin in the rat hippocampal slice preparation.

1. Intracellular activity was recorded from neurones in the CA1 pyramidal layer of slices of rat hippocampus maintained in vitro. 2. Application of 5-HT in a droplet or via ionophoresis produced a 3-5 mV hyperpolarization associated with a 30% decrease in input resistance. 3. The response to 5-HT was minimal with a drop concentration of 1 microM and maximal with 100 microM. The responses appeared to be blocked by methysergide applied in the superfusion medium. 4. The responses to 5-HT were minimal when the drug was applied in the apical dendritic region and maximal when it was applied near the soma. 5. 5-HT produced no substantial changes in e.p.s.p.s evoked by stimulation of the Schaffer collateral-commissural system or in i.p.s.p.s which were occasionally encountered following stimuli to the stratum radiatum. 6. The responses to 5-HT are true post-synaptic responses and are not indirect effects since they are present in a Ca2+-deficient Mg2+-enriched medium which blocks synaptic transmission. 7. The responses to 5-HT were not dependent on extracellular Cl- concentration. 8. These experiments indicate that 5-HT produces its effects in the rat hippocampus by activating K+ channels.

Animals↗
PubMed1979

Functional reinnervation of rat hippocampus by locus coeruleus implants.

Transplants of the embryonic locus coeruleus (LC) region were implanted into the circuity of the hippocampal formation in adult rats in which the normal adrenergic afferents to the hippocampus had been removed. The growth of new adrenergic axons from the implant in the denervated hippocampus was followed for 1-14 months after surgery by means of fluorescence histochemistry, and the function of the implant-hippocampal connections was tested electrophysiologically after 2-3 months survival. In the successful cases the entire hippocampal formation was reinnervated from the LC implant within 3-6 months after operation, and the newly formed innervation still persisted unchanged by 14 months. The reinnervation was equally effective irrespective of the route by which the axons entered the hippocampus, i.e. along the lesioned fornix-fimbria or along a retrosplenial route. The pattern formed by the ingrowing LC axons mimicked to a large extent that of the normal LC afferents. Little growth was seen into denervated terminal fields of the commissural, septal or entorhinal afferents, pointing to a preference of the ingrowing LC fibers for the areas normally innervated by adrenergic afferents. In the electrophysiological experiments, stimulation of the LC implants caused (in 20 out of 29 cells monitored) an inhibition of the spontaneous activity of neurons in the host hippocampus. This inhibition had a relatively long latency and a long duration, similar to that observed after stimulation of the innate LC in the intact rat. As in the normal rat, the inhibitory responses were blocked by systemic or local application of the beta-adrenergic receptor blockers propranolol or sotalol. It is concluded that the adult rat brain is capable of carrying out all steps involved in correct functional reinnervation of a denervated region. Moreover, the implant-hippocampal preparation should be a highly suitable model system for functional studies of a central noradrenergic connection.

Adrenergic Fibers↗
PubMed1979

A pharmacologic study of analgesia produced by stimulation of the nucleus locus coeruleus.

Pharmacologic studies of analgesia produced by stimulation of the nucleus locus coeruleus (LC) were conducted using the rat hot-plate test. A correlation between self-stimulation and analgesia produced by stimulation of LC was found. Analgesia produced by LC stimulation was attenuated by naloxone, a morphine antagonist, cyproheptidine, a serotonin antagonist, and WB-4101, an alpha-adrenergic antagonist. The analgesia was absent in 6-OHDA-treated rats. Catecholamine synthesis inhibition by a combination of reserpine and AMT or more specific inhibition of noradrenaline synthesis by DDC elevated latency to paw lick and yet did not affect stimulation-produced analgesia. It is suggested that morphinergic, serotonergic, and alpha-adrenergic mechanisms mediate LC stimulation produced analgesia.

Adrenergic alpha-Antagonists↗
PubMed1979

Sex differences in behavioral and thermal responses to pargyline and tryptophan.

The effects of parenterally injected pargyline and tryptophan on rectal temperature and behavior have been studied in male and female rats. Pargyline alone (50 mg/kg) produced hypothermia in both sexes. Pargyline (50 mg/kg) followed by low doses (20--50 mg/kg) of tryptophan caused a behavioral syndrome consisting of tremor, hindlimb abduction, forepaw treading, and straub tail. In females, but not in males, hypothermia was potentiated. The same dose of pargyline followed by higher doses (60--150 mg/kg) of tryptophan produced a short hypothermia followed by a dose-dependent behavioral syndrome, hyperthermia, and mortality. On all of these measures, females responded following shorter latencies and lower doses of tryptophan. Both hypothermia and hyperthermia were observed in treated animals following pretreatment with a peripheral decarboxylase inhibitor. The results suggest a complex role for serotonin in thermoregulation. The sex differences observed suggest higher activity of serotonin in female rat brains following the drug treatment, which may be accounted for by a higher utilization rate of tryptophan.

Animals↗
PubMed1979

Alveolar hydatid disease in Minnesota. First human case acquired in the contiguous United States.

A 56-year-old woman from southwestern Minnesota underwent an extended left hepatic lobectomy to remove a large multinodular mass with a necrotic central cavity. The clinical, serological, and pathological findings led to the diagnosis of alveolar hydatid disease, and specific identification of Echinococcus multilocularis was achieved by growing mature larvas in voles inoculated intraperitoneally with tissue from the hepatic lesions. The patient probably acquired her infection some years previously from pet cats or dogs that had become infected by ingesting infected rodents. In North America E multilocularis is enzootic in the northern tundra zone of Alaska and Canada. Since 1964 the cestode has been recognized with increasing frequency in several north-central states, including Minnesota. The parasite may extend its range farther south, since suitable animal hosts occur throughout the United States.

Echinococcosis, Hepatic↗
PubMed1979

Serotonergic innervation of the locus coeruleus from the dorsal raphe and its action on responses to noxious stimuli.

The connexions between the dorsal raphe nucleus and the nucleus locus coeruleus were studied in urethane anaesthetized rats. 1. Cells in the locus coeruleus gave an excitatory response to a noxious stimulus, e.g. leg pinch. 2. This excitatory response was blocked by either a parenteral or an ionophoretic injection of morphine and recovered after an injection of naloxone. 3. Electrical stimulation in the region of the dorsal raphe blocked excitatory locus coeruleus responses to noxious stimuli. 4. While naloxone did not antagonize the effects of the dorsal raphe stimulation towards locus coeruleus activity, these effects were absent in rats pretreated with a serotonin synthesis inhibitor, PCPA or with 5,7-DHT which destroys serotonin-containing terminals, and were reduced by the serotonin antagonist methysergide. 5. A serotonin-containing inhibitory pathway between the dorsal raphe and the locus coeruleus is proposed to account for these results.

Action Potentials↗