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Biomedical subjects

R Andrade

Publications and source records attributed to R Andrade.

At least 91 records · Page 5Linked to original sources
PubMed1984

Intrinsic regulation of locus coeruleus neurons: electrophysiological evidence indicating a predominant role for autoinhibition.

Locus coeruleus neurons were antidromically activated and the resulting post-stimulation inhibition was compared to the interspike interval and examined for its dependency on antidromic invasion and stimulus intensity. The post-stimulation inhibition seen in these cells following antidromic activation approximated the interspike interval, was critically dependent on the antidromic invasion of the cell under study and was only weakly dependent on stimulus intensity. These results suggest that the post-stimulation inhibition following antidromic activation in the locus coeruleus is mediated principally by autoinhibition and not by hypothesized local inhibitory interactions between locus coeruleus neurons.

Animals↗
PubMed1984

Standardization of various applications of methacrylate embedding and silver methenamine for light and electron microscopy immunocytochemistry.

The use of butyl-methyl-methacrylate embedding and the application of the silver methenamine (SM) method as a poststaining of the immunoperoxidase-DAB (IP) procedure led to the standardization of several useful methods for the visualization of tissue antigens at the light and electron microscope level. These procedures included: 1) Standardization of the actual methacrylate embedding; 2) The IP-SM method with and without periodic acid oxidation, which provided 100% intensification of the IP staining; 3) The IP-SM method made it possible to stain semithin sections (0.5 micron), and this in turn, permitted a) clear visualization under the light microscope of the intracellular distribution of antigens and, b) staining, in several adjacent sections, of roughly the same cytoplasmic region of the same cell with different primary antisera; 4) a double immunostaining whereby the first antigen in the sequence was revealed by the IP-SM method and the second by the IP procedure; 5) standardization of the IP and the IP-SM methods for post-embedding staining of ultrathin methacrylate sections. The combined application of methacrylate embedding and the IP-SM, and the use of an appropriate fixative, resulted in an ultrastructural immunocytochemical procedure characterized by a good immunoreactivity of the tissue sections, a strong and selective immunoreaction and a well preserved ultrastructure.

Acrylates↗
PubMed1984

Hypoglycemic hemiplegic syndrome.

Hypoglycemia must be considered in any patient with an acute change of mental status or in a patient who shows a focal neurological deficit. Treatment with high IV glucose concentrations can save the patient from grave irreversible neurological sequelae and death.

Female↗
PubMed1984

Locus coeruleus activity in vitro: intrinsic regulation by a calcium-dependent potassium conductance but not alpha 2-adrenoceptors.

Locus coeruleus neurons recorded intracellularly in rat brainstem slices exhibited spontaneous activity and a marked afterhyperpolarization following a burst of spikes. This afterhyperpolarization was associated with an increase in membrane conductance and resulted in a marked postactivation inhibition of spontaneous activity. Since the reversal potential of the afterhyperpolarization was found to be virtually identical when recorded with KCl or potassium acetate-filled electrodes and shifted in the hyperpolarizing and depolarizing direction with decreases and increases in extracellular potassium concentrations, respectively, the afterhyperpolarization seen following a burst of spikes in this cell group appears to be mediated by an increase in potassium conductance. The afterhyperpolarization and postactivation inhibition were markedly attenuated by reducing calcium influx by either omitting extracellular calcium in the bathing medium or blocking calcium channels with manganese or cadmium. Thus, the afterhyperpolarization and the resulting postactivation inhibition appear to be largely mediated by the activation of a calcium-dependent potassium conductance. Previous reports in vivo have suggested that activation of alpha 2-adrenoceptors by norepinephrine release from recurrent axons or dendrites may mediate self-inhibition in the locus coeruleus. In this study, we examined the effect of blocking alpha 2-adrenoceptors on the afterhyperpolarization and postactivation inhibition. Administration of the alpha 2-adrenoceptor antagonist piperoxane failed to produce any changes in either of these parameters, suggesting that at least in vitro the afterhyperpolarization and postactivation inhibition seen in locus coeruleus neurons do not result from the activation of alpha 2-adrenoceptors.

Action Potentials↗
PubMed1983

Intracellular studies on the role of calcium in regulating the activity and reactivity of locus coeruleus neurons in vivo.

EGTA, a specific calcium chelator, was injected intracellularly into presumed noradrenergic neurons of the rat locus coeruleus to evaluate the importance of calcium-dependent processes in regulating the activity and reactivity of these cells in vivo. The amplitude and duration of postactivation after hyperpolarizations induced by intracellular depolarizing pulses were markedly reduced in EGTA-treated cells; this change was associated with: (1) an increase in spontaneous firing rate; (2) a reduction in postactivation inhibition of firing; and (3) an increased reactivity to sensory stimulation. In control cells the reversal potential of the after hyperpolarization was at least 25 mV below 'resting' levels, indicating that an increase in potassium conductance was probably involved. Since EGTA virtually abolished the after hyperpolarization, the data are consistent with the concept that the after hyperpolarization is mediated by a calcium-activated potassium current. A calcium-dependent release of norepinephrine acting via alpha 2-adrenoceptors might also contribute to the after hyperpolarization. In conclusion, the influx of calcium into locus coeruleus neurons appears to serve a negative feedback function in the regulation of both spontaneous activity and reactivity to orthodromic stimulation.

Animals↗
PubMed1983

Morphine tolerance and dependence in the locus coeruleus: single cell studies in brain slices.

Extracellular single unit recordings in vitro from the locus coeruleus in rat brainstem slices revealed the presence of spontaneously active neurons. These cells fired between 0.1 and 3.0 spikes/s and were inhibited by nM concentrations of morphine and clonidine. Locus coeruleus neurons in slices from animals treated chronically, but not subacutely, with morphine exhibited a significant decrease in sensitivity to morphine. This tolerance appeared to be specific for opiates since no decrease in sensitivity was seen for the alpha 2-adrenoceptor agonist clonidine. However, in contrast to what has been reported in vivo, no signs of dependence (withdrawal activation) were evident in slices from morphine tolerant animals.

Animals↗
PubMed1982

Single cell activity in the noradrenergic A-5 region: responses to drugs and peripheral manipulations of blood pressure.

Single unit recordings were obtained from the region of the A-5 noradrenergic cell group in the ventrolateral tegmentum at the level of the exiting VIIth nerve. In this region a distinct cell population was identified which exhibited moderate spontaneous rates of activity, a regular firing pattern, wide action potentials, and a characteristic response to sensory stimulation consisting of a brief excitation followed by a more prolonged period of inhibition. Simultaneous visualization of recording sites and catecholamine cells by fluorescence histochemistry indicated a close association between the location of the recorded units and the A-5 noradrenergic cell group. Antidromic responses could be elicited by stimulation of the spinal cord and forebrain indicating that A-5 cells project both anteriorly and posteriorly. The spontaneous activity of A-5 cells was invariably suppressed by low doses of clonidine and L-amphetamine, while adjacent cells showed varying responses to these agents. The effects of clonidine and L-amphetamine could be reversed by low doses of the alpha2-adrenoceptor antagonist, piperoxane. When applied by microiontophoresis, clonidine and norepinephrine were effective in inhibiting A-5 neurons. The rank order of inhibitory potencies for agonists applied microiontophoretically to A-5 neurons was characteristic of an alpha2-receptor (i.e. clonidine greater than norepinephrine greater than phenylephrine). Thus, the physiological and pharmacological properties of the A-5 neurons closely matched those previously reported for noradrenergic neurons elsewhere. Sixty percent of A-5 neurons responded to peripherally induced changes in blood pressure with reciprocal changes in spontaneous firing rate. Increases in blood pressure led to decreases in spontaneous activity while decreases in pressure led to the opposite response. These observations are consistent with the proposed vasomotor role for the A-5 noradrenergic cell group.

Amphetamine↗