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R Guevara-Guzmán

Publications and source records attributed to R Guevara-Guzmán.

9 recordsLinked to original sources
PubMed2004

Effect of photoperiod on the mechanical response of the pregnant rabbit uterus to oxytocin.

We present findings suggesting that photoperiod is important in determining the sensitivity of the late-pregnant rabbit uterus to oxytocin (OT). Longitudinal myometrial strips were taken from term-pregnant and estrous rabbits and mounted in an organ bath for isometric myographic recording at different times during a 16:8-h light-dark cycle (lights on 0600-2200; n = 5/group), and the strength of contractions was registered in response to the application of OT or KCl. Strength of contractions was dose dependent and was up to 200 times greater at doses three to four orders of magnitude lower in tissue taken from pregnant animals during the light phase (0700 and 1300) than during the dark phase (2400 and 0400). Strips from nonpregnant estrous females also showed greater sensitivity and contractile force when taken in the light (0700) than in the dark (0400), although the differences were not significant. Consistent with the influence of photoperiod on uterine sensitivity to OT, strips taken from two groups of pregnant females (n = 5/group) maintained on a light-dark cycle advanced 12 h showed significantly greater sensitivity and force in response to OT during the new subjective light than during the new subjective dark phase. The photoperiod-dependent contractile response to OT was specific and not simply the result of a change in general mechanical properties of the muscle, because administration of KCl resulted in dose-dependent contractions of similar magnitude in both the light and dark phase. These results are consistent with the fact that rabbits, like other nocturnal mammals, typically give birth during the day.

Animals↗
PubMed2001

Vaginocervical stimulation-induced release of classical neurotransmitters and nitric oxide in the nucleus of the solitary tract varies as a function of the oestrus cycle.

The effects of vaginocervical stimulation (VCS) on glutamate (GLU), aspartate (ASP), gamma-aminobutyric acid (GABA), noradrenaline (NA), arginine (ARG) and nitric oxide (NO) (citrulline) release in the nucleus of the solitary tract (nTS) were measured in anaesthetised female rats as a function of the oestrus cycle. During pro-oestrus/oestrus (P/E), but not during met-oestrus/di-oestrus (M/D), VCS significantly increased concentrations of NA, ASP, GLU, NO (citrulline) and GABA, but not ARG. Basal NA concentrations were also increased in P/E. These effects were prevented by bilateral section of either the vagus nerve or pelvic and hypogastric nerves. Vagotomy also significantly decreased basal NO concentrations in M/D and P/E while pelvic and hypogastric nerve section significantly increased GABA concentrations. Our results therefore confirm that the nTS is a relay structure for the visceral afferents sending information from the uterus into the central nervous system. The ability of VCS to trigger classical transmitter release and NO in the female is influenced by the stage of the oestrous cycle and is routed both via the vagus and pelvic/hypogastric nerves.

Animals↗
PubMed2000

Release of classical transmitters and nitric oxide in the rat olfactory bulb, evoked by vaginocervical stimulation and potassium, varies with the oestrus cycle.

In vivo microdialysis was used to investigate the effects of ovariectomy and the oestrus cycle on vaginocervical stimulation-evoked classical transmitter and nitric oxide release in the olfactory bulb of anaesthetized (urethane) and conscious rats. During pro-oestrus/oestrus, vaginocervical stimulation (1 or 10 min) significantly increased concentrations of glutamate, aspartate, GABA, noradrenaline, dopamine and nitric oxide (citrulline) but failed to do so in met-oestrus/di-oestrus or following ovariectomy. Potassium chloride-evoked GABA, noradrenaline and nitric oxide release in the olfactory bulb was also significantly enhanced during pro-oestrus/oestrus. The effects of vaginocervical stimulation on olfactory bulb transmitter release during pro-oestrus/oestrus were significantly reduced by pelvic or vagus nerve section. Basal concentrations of classical transmitters and nitric oxide in the olfactory bulb did not vary across the oestrus cycle although noradrenaline and dopamine levels were reduced following ovariectomy. These results confirm our previous electrophysiological data showing that the olfactory bulb mitral cells are only excited by vaginocervical stimulation during pro-oestrus/oestrus. They also suggest that sex hormones acting primarily at the level of the olfactory bulb dramatically enhance the ability of vaginocervical stimulation to evoke release of both classical transmitters and nitric oxide in this region. Such alterations in neurochemical release in the olfactory bulb may be important for mediating plasticity changes underlying olfactory recognition of mates or offspring.

Animals↗
PubMed1995

Neuronal regeneration and estrous cycle restoration after locus coeruleus-periventricular gray substance section.

The locus coeruleus (LC) was anatomically separated from the periventricular gray substance (PVG) by means of knife cuts in the adult female rat presenting regular estrous cycling. This resulted in a transient suppression of the estrous cycling that lasted 10-13 days after surgery. After this period, irregular or regular cycling activity was observed. The regular cycling was restored 30-45 days after the knife cuts. Golgi impregnation of some of the brains of these rats revealed regenerative elements in the knife-cut-insulted area. Thus, blood vessels, macrophagic-like elements, and glial-like elements were observed in close relation with the knife-cut pathway. Additionally, well-defined stained neurons typical of the LC and PVG were observed in close proximity to the knife-cut pathway. Dendritic and axon projections towards the insulted area were observed. Well defined axons were seen across the knife-cut pathway. These data support, first, that the LC-PVG communication is part of a circuitry for the modulation of gonadotropic activity, and second, that in the restoration of the estrous cyclicity after the knife cut, regenerative processes leading to a LC-PVG functional reconnection occurred after the knife cut.

Animals↗
PubMed1993

Olfactory bulb neurons respond to cervicovaginal distension.

Mitral cell layer neuronal activity in the olfactory bulb (OB) of the anesthetized rat is modulated by cervicovaginal distension. Data are reported on 22 cells that decreased and 6 that increased in response to the distension. These results provide support for the existence of a functional interaction between the reproductive tract and the olfactory system.

Animals↗
PubMed1992

Natriuresis after a water load in humans under different sodium body content.

The present study was aimed at observing the diuretic and natriuretic responses after a water load (2% body weight) in four groups of young consenting volunteers submitted previously, during three days, to a hypersodic (500 mEq Na/day), hyposodic (35 mEq Na/day), and normosodic (200 mEq Na/day) diet, or treated with furosemide (Lasix, 40 mg/day). During the treatment urine was collected each day. On the fourth day, in the morning, the bladder was emptied, the water load was ingested, and the urine collected during 10 periods of 20 min each. The urinary, sodium, and chloride flows were determined. The four groups displayed diuretic curves following a similar pattern. In contrast, the natriuretic curves of the four groups were completely different; totally flat with low values for the furosemide group and a large initial natriuretic curve for the hypersodic group with a gradual decrease but maintaining high values. The results indicate that the way the organism compensates for the excess of water by means of urinary water loss is independent of the body sodium content, whereas the way in which sodium loss is accomplished is determined by its body content and is independent of the way in which the water is lost.

Adult↗
PubMed1990

Vagus nerve afferent and efferent innervation of the rat uterus: an electrophysiological and HRP study.

To determine a possible brainstem connection with the uterus, a study with electrophysiological techniques and horseradish peroxidase (HRP) tracing was performed in the rat. Neurons of the nucleus of the tractus solitarius decreased in discharge frequency during cervicovaginal distension. HRP injections into the uterine walls resulted in the appearance of labelled cells in the nodose ganglion and in the dorsal motor nucleus of the vagus nerve. The results demonstrate a direct bidirectional vagal complex-uterus connection via the vagus nerve. Results are discussed in terms of a complex uterus control system in which the paraventricular nucleus might play an integrative role.

Animals↗
PubMedDate not supplied

Electrophysiological evidences of a bidirectional communication between the locus coeruleus and the suprachiasmatic nucleus.

To assess a possible relation between the suprachiasmatic nucleus (SCN) and the locus coeruleus (LC), a study with evoked potentials was performed in the rat. An evoked potential was recorded in the SCN area after electrical stimulation of the LC. Also, an evoked potential was recorded in the LC after electrical stimulation of the SCN area. The results indicate specificity of the projecting regions and of the activated regions, suggesting the existence of a possible bidirectional communication between the LC and the SCN. The pathways possibly involved are discussed.

Action Potentials↗