Biomedical subjects

O A Ramírez

Publications and source records attributed to O A Ramírez.

12 recordsLinked to original sources

PubMed2005

Huperzia saururus, activity on synaptic transmission in the hippocampus.

Huperzia saururus (Lam.) Trevis. (Lycopodiaceae) known as cola de quirquincho is used in folk medicine to improve memory. The cholinergic neurons of the basal forebrain, including those in the medial septum, and in the vertical limbs of the diagonal band of Broca and the nucleus basalis of Meynert, provide a major source of cholinergic enervation of the cortex and hippocampus. These neurons have also been shown to play an important role in learning and memory processes. Thus, the effects of this traditional Argentinean species were studied in relation to its activity on synaptic transmission in the hippocampus. The alkaloid extract obtained first by decoction of the aerial parts and by subsequent alkaline extraction, was purified by using a Sephadex LH 20 packed column. Electrophysiological experiments were developed with the purified extract (E(2)) on rat hippocampus slices, thus eliciting long-term potentiation (LTP). Results show a marked increase in the hippocampal synaptic plasticity. The threshold value for generation of LTP was 22 +/- 1.01 Hz on average for E(2), while for controls it was 86 +/- 0.92 Hz. All of these factors could explain the use of Huperzia saururus as a memory improver as is reported in the ethnomedicine.

Animals↗

PubMed2001

Increased neuronal activity in locus coeruleus from adult rats undernourished at perinatal age: its reversal by desipramine.

The spontaneous activity of locus coeruleus (LC) noradrenergic neurons was assessed by single unit recording in adult recovered rats undernourished at perinatal age as compared with wellnourished animals. Locus coeruleus activity, measured by the firing rate of noradrenergic neurons and the number of spontaneously active cells/track was significantly higher in deprived rats than in controls. In addition, dose-response curves for the inhibitory LC activity of clonidine showed a shift to the right in deprived animals indicating a subsensitivity of alpha2-adrenergic autoreceptors. This fact suggests an alteration in the negative feedback mechanism mediated by somatodentritic alpha2 autoreceptors that modulate the activity of LC neurons, and may account for the behavioral alterations attributed to early undernutrition. Repeated desipramine (DMI) administration to deprived rats reduced LC activity to values comparable to controls, which were not affected after a similar treatment. These data extend to previous reports on long-lasting or permanent plastic changes in the CNS induced by early undernutrition, which may be reverted by pharmacological manipulations. In addition, these results support the hypothesis that alterations induced by early undernutrition are in the same direction as and resemble those described for patients with panic disorders. Furthermore, together with behavioral alterations and selective anxiolytic effect of DMI and other drugs with antipanic effects described in early malnourished rats, the present data support the proposal that perinatally deprived rats may be a useful model for screening drugs with potential antipanic activity.

Animals↗

PubMed1996

Equivalent performance in the water maze by rats with an inborn high or low learning capacity in a shuttle box paradigm.

The learning capacity of rats with an inborn high performance (HP) and low performance (LP) in an avoidance shuttle box paradigm, was evaluated in the Morris water maze. Escape latencies evaluated in HP and LP rats indicate that acquisition and retention of spatial information were not different from control animals. When a free swim trial was carried out, all groups showed a significant preference towards the target quadrant. Our results suggest that the altered hippocampal physiology described in HP and LP rats does not influence the performance of a spatial tasks such as the Morris water maze.

Animals↗

PubMed1993

Phosphatidylserine increases hippocampal synaptic efficacy.

In the present study, the effects of phosphatidylserine (BC-PS) on hippocampal synaptic transmission were evaluated. Extracellular potentials evoked by low-frequency stimulation (0.2 Hz) of the perforant path (PP) were recorded from the granule cell layer of the dentate gyrus in 400 microns hippocampal slices. Slices were perfused with either BC-PS alone (10 microM) or BC-PS in combination with DL-2-amino-5-phosphonovaleric acid (APV, 20 microM), or after previous perfusion with dizocilpine (MK-801, 10 microM). BC-PS significantly potentiated PP-evoked responses (mean percent increase +/- SEM, 108 +/- 18%), an effect that was blocked by perfusion of MK-801, but not APV. The increase in hippocampal synaptic efficacy produced by BC-PS is discussed in terms of N-methyl-D-aspartate receptors (NMDA) and the associated channels.

2-Amino-5-phosphonovalerate↗

PubMed1992

Effect of acute ethanol exposure during pregnancy on dentate gyrus synaptic plasticity in 45-day-old rats.

Pregnant Wistar rats were treated during the eighth day of gestation (GD8) with two IP injections, spaced by an interval of 4 h, of either ethanol (2.9 g/kg in saline solution) or saline. At 45 days of age, rats prenatally exposed to alcohol showed an improved hippocampal synaptic plasticity in granule cells layer of dentate gyrus. This was assessed measuring the threshold to generate long-term potentiation (LTP) on hippocampal slices. We propose that this result might account for the good performance in some learning tasks observed in animals prenatally exposed to alcohol during short periods.

Animals↗

PubMed1990

Long-term potentiation-induced synaptic changes in hippocampal dentate gyrus of rats with an inborn low or high learning capacity.

Structural changes induced by high frequency (HF) stimulation on granule cells of the hippocampal dentate gyrus of rats with inborn high (HP) and low (LP) learning capacity was examined in this study. Two types of axodendritic synapses were processed morphometrically; the axonal bouton on dendritic shafts and those making contact through dendritic spines. The occurrence of granule cell spine synapses on LP rats before tetanus is less than the one in control animals. However, after long-term potentiation (LTP) produced by HF stimulation the number of spine synapses decreased, as happened in the control rats. Moreover, the number of granule cells shaft synapses counted on LP rats, before tetanus is less than the one on control rats, and after LTP this number increased greatly. There was no change in the number of granule cell shaft synapses in HP rats before and after LTP. LP rats which did not show LTP in spite of HF stimulation did not show changes in the number of spine and shaft synapses. From these results we can conclude that: (1) the great hippocampal synaptic plasticity observed in HP rats compared to LP rats can be attributed, at least in part, to the increased number of spine and shaft synapses observed in HP rats; (2) the minor number of spine and shaft synapses in LP rats may account for the impossibility to obtain LTP after HF stimulation in these animals.

Animals↗

PubMed1989

Sexual receptivity after destruction of serotonergic terminals in hypothalamus or amygdala.

In order to localize the sites in the brain where serotonergic (5-HT) input may affect the performance of lordotic responses, the serotonin neurotoxin 5-7-dihydroxytryptamine was injected in the ventromedial hypothalamic nucleus (VMN) or in the medial amygdala (AM) in ovariectomized rats. Estrogen induced receptivity as measured by the lordotic quotient was significantly greater in animals injected in AM, but it was smaller in animals injected in the VMN, as compared to controls or animals injected with the vehicle. No differences were found when the same animals were injected with progesterone. It is proposed that serotonergic afferents exert facilitatory influences in the hypothalamus and inhibitory influences in the amygdala, as concerns estrogen-induced sexual receptivity. The integrity of 5-HT terminals in VMN and AM is not necessary for progesterone to exert its potentiating effects.

Amygdala↗

PubMed1988

Differential threshold for long-term potentiation in the hippocampus of rats with inborn high or low learning capacity.

Threshold of stimulation frequency in the perforant path to induce long-term potentiation (LTP) in dentate gyrus was determined in hippocampal slices obtained from two different lines of rats inbred for 30 generations according to their performance in an avoidance escape test in a shuttle box. High-performance (HP) rats were defined as those giving at least 70% conditioned responses (CRs) and low-performance (LP) rats as those giving less than 15% CRs. LTP was defined as a 30% or more increase in the amplitude of the evoked population spike (PS), lasting at least 20 min. Stimulation frequency threshold was determined by stimulating with a train of pulses of 0.5 ms duration during 1 s. The same slice was stimulated with trains of increasing frequency from 5 to 400 Hz, each train separated by an interval of at least 20 min. HP rats showed a lower threshold (13 +/- 4 Hz) than LP rats (92 +/- 42 Hz) for the induction of LTP; there were no differences in the magnitude of LTP. The greater learning ability of HP rats may be related to the plasticity of hippocampal synaptic transmission.

Action Potentials↗

PubMed1985

Involvement of a serotonergic control in the regulation of plasma levels of immunoreactive beta-endorphin.

Beta-endorphin immunoreactivity was measured in plasma and hypothalamus of rats treated with alpha-methyl-p-tyrosine (alpha -MT) (two doses of 200 mg/kg) or p-chloro-phenyl-alanine (PCPA) (two doses of 150 mg/kg). It was also measured in plasma after a single dose (5 mg/kg) of amphetamine or after electrical stimulation of median raphe nucleus (MRN). Plasma levels of immunoreactive beta-endorphin (ir B-E) were significantly decreased by PCPA and were elevated by electrical stimulation of MRN. Alpha -MT was ineffective to modify ir B-E plasma concentration as well as amphetamine. These findings suggest a role for 5-hydroxytryptamine (5-HT) in the regulation of plasma B-E content.

Animals↗

PubMed1983

Noradrenergic modulation of neuronal transmission in the offspring of amphetamine-treated rats.

The model of noradrenergic modulation of synaptic transmission between the entorhinal cortex and dentate gyrus was used to investigate the function of catecholaminergic neurones in the offspring of rats injected with dl-amphetamine during pregnancy (0.5 mg . kg-1 . day-1; s.c.). A conditioning train of pulses applied to the locus coeruleus produces an increase in the amplitude of the population spike evoked in the granule layer of the gyrus dentatus by perforant path stimulation. Results show that, in the offspring of amphetamine-treated rats, the potentiating effect of locus coeruleus stimulation was two to three times greater than in control animals (151 +/- 30 vs. 66 +/- 20%; p less than 0.05). This effect may be due to the changes in catecholamine metabolism and (or) catecholamine receptors observed in these animals and could help explain the behavioral alterations caused by amphetamine exposure in utero.

Amphetamine↗

PubMed1982

Effect of estrogen and progesterone priming on the uptake and release of serotonin and noradrenaline from the ventromedial hypothalamus.

Estradiol benzoate (EB) or EB plus progesterone (P) were administered to chronic ovariectomized rats in doses which are known to induce sexual receptivity. P was injected 48 hr after EB and the animals were decapitated 54 hr after E.B. The ventromedial hypothalamus (VMH) (excluding the arcuate-median eminence region) was dissected out and used to determine 3H-noradrenaline (3H-NA) and 3H-serotonin (3H-5-HT) uptake and release induced by high potassium concentration. Animals injected with oil were used as controls. VMH from EB (10 micrograms/kg) plus P (2 mg/kg) primed animals had higher release of 3H-NE than controls; uptake and release of 3H-5-HT was also augmented in these animals. EB (100 micrograms/kg) priming alone did not induce significant variations. The increase in 3H-NA release is interpreted as evidence of incremented activity in a 3H-NA system, facilitating sexual receptivity. The change in 3H-5-HT uptake and release is discussed in respect to the existence of an inhibitory serotonergic system modulating sexual behavior.

Animals↗

PubMed1980

A reliable and sensitive method for the simultaneous determination of dopamine, noradrenaline, 5-hydroxytryptamine and 5-hydroxy-indolacetic acid in small brain samples.

A sensitive and reliable fluorometric method for the simultaneous determination of dopamine, noradrenaline, 5-hydroxytryptamine and 5-hydroxy-indol acetic acid in small samples of brain tissues is described. The procedure is based on solvent extraction; catecholamines are oxidized by the Chang's method and 5-hydroxytryptamine and 5-hydroxy-indol acetic acid determined by reaction with o-phthalaldehyde, alpha-methyl-p-tyrosine causes a negligible interference with the procedure. Results of determination of these amines in different brain areas are reported.

Animals↗