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V D Ramirez

Publications and source records attributed to V D Ramirez.

At least 109 records · Page 6Linked to original sources
PubMed1983

Structural changes in nerve endings of rat median eminence superfused with media rich in potassium ions.

In vitro fragments of male rat mediobasal hypothalami were superfused with Krebs--Ringer solution in the presence or absence of CaCl2. Infusions containing up to 60 mM potassium chloride were applied, at the end of which tissues were fixed in osmium tetroxide and prepared for transmission electron microscopy. Control superfusions were run in parallel. Quantitative measurements performed on electron micrographs of the outermost palisade region showed significant (20-30%) increase in caliber of axon endings after intensive potassium ion stimulation. Ultrastructurally, widespread depletion of granular vesicles and microvesicles was found. Vesicle shift to the outer zone of the terminals, formation of membrane-bound tubules of the same diameter as microvesicles, and images of attachment and collapse of vesicles into the axolemma were found, particularly after 1 min stimulation. These findings were interpreted as consistent with exocytosis. Longer stimulations were followed by the appearance of large pleomorphic vacuoles that are probably the result of post-exocytotic membrane retrieval. Axon enlargement and vesicle depletion were absent in specimens superfused with calcium-free medium containing high potassium. The functional significance of these ultrastructural changes are interpreted as supporting the hypothesis that exocytosis of calcium-loaded microvesicles can contribute to extrude this ion from median eminence nerve endings during secretion.

Animals↗
PubMed1982

Ultrastructure of the rat median eminence after superfusion.

Isolated medio-basal hypothalami of adult rats were continuously superfused in a chamber with controllable inputs and outputs, for periods from 30 to 240 min. The median eminence was prepared for transmission electron microscopy under carefully controlled conditions by immersion fixation with osmium tetroxide. The ultrastructure of superfused median eminence was compared with that of directly fixed, non-superfused median eminence. Even after 4h of superfusion, the median eminence displays remarkably well preserved histological and cytological patterns; cytomembranes, cell organelles, intercellular relationships, and extracellular spaces were remarkably similar in superfused and non-superfused tissues. As a consequence of osmium tetroxide fixation, microtubules were not observable. The ultrastructural information obtained from unstimulated rat median eminence superfused in vitro provides a basis for future morphofunctional correlations in the study of neurosecretion.

Animals↗
PubMed1982

A functional dimorphism in the response of the hypothalamic-pituitary axis of prepubertal rats to steroid treatment.

In the present experiment we examined the circadian neural luteinizing hormone releasing hormone (LHRH) and serum luteinizing hormone (LH) response of prepubertal male and female rats under varying steroidal manipulations (Intact, Castrate, Castrate + estradiol 17 beta [E2] + oil and Castrate + E2 + progesterone[P]). Prepubertal males demonstrated greater and acyclic LHRH concentrations in both the medial basal hypothalamus (MBH) and preoptic-suprachiasmatic regions (POA-Sch) irrespective of steroid treatment. In steroid-treatment castrated male rats only the negative feedback action on serum LH levels were observed with maximal effect in animals injected with the combination E2 + P. In contrasts, prepuberal castrated females exhibited both inhibitory and stimulatory feedback actions on LH release following steroid treatment. Moreover, a distinctive, significant, progesterone-dependent increase in AM POA-Sch, but not MBH-LHRH concentrations was detected. These results demonstrate the existence of a functional sexual dimorphism in the positive feedback response of the POA-Sch-pituitary axis of prepubertal rats to progesterone treatment.

Animals↗
PubMed1982

Production and characterization of antisera to synthetic thyrotropin-releasing hormone (TRH).

To generate anti-thyrotropin-releasing hormone (TRH) antibodies TRH was rendered antigenic presumably by reaction of its histidine residue with bis-diazotized benzidine (BDB) coupled to bovine serum albumin (BSA). Six California white rabbits were each injected with 330 micrograms protein/ml of emulsified immunogen by the multisite intradermal immunization technique. Seven repeated injections were given at 30-day intervals using half of the original quantity of antigen. Antibodies binding 125I-TRH appeared in the serum of four of the six rabbits three months after the first injection. Five months later the sera of two rabbits bound 50% of the labeled TRH at 1:6000 final dilution. Using this antiserum a radioimmunoassay for TRH was developed in which as little as 10 pg/300 microliter unlabeled TRH can be detected. The linear range of detectable TRH was 10 to 10000 pg. No cross-reaction with various hypothalamic and pituitary hormones, neurotransmitters, neuropeptides, and BSA were detected in this immunoassay. Extracts from rat and frog hypothalami produced 125I-TRH-binding inhibition curves parallel to synthetic TRH. Samples from elutes of rat medio-basal hypothalami superfused in vitro were examined by using this antiserum. Serial dilution of superfusate showed a similar inhibitions curve. Stimulatory effect of K+ depolarization on TRH release from superfused hypothalami was inhibited in Ca2+-free ethylenediaminetetraacetic acid medium. Ouchterlony double diffusion test of the TRH antisera revealed that low levels of antibodies against albumin but not immunoglobulin G or ovalbumin were also produced. However, the immunoprecipitates could only be detected with undiluted serum. In conclusion, this antiserum generated one of the most sensitive TRH radioimmunoassay currently available in the literature. The anti-TRH serum produced by this method can be used to examine both content of TRH from several tissues as well as release from hypothalamic tissue in vitro and might be useful to trace brain TRH pathways by immunocytochemistry.

Animals↗
PubMed1982

Simultaneous measurement of luteinizing hormone-releasing hormone and luteinizing hormone release in unanesthetized, ovariectomized sheep.

The push-pull perfusion technique was used in combination with a sequential bleeding schedule to estimate simultaneously the release patterns of LHRH and LH in unanesthetized ovariectomized sheep and to determine the temporal relationship between the release of these two hormones. Ovariectomized (greater than 30 days) ewes received unilateral push-pull cannula (PPC) implants (od, 0.85 mm) into the median eminence. After at least 6 days of recovery, each ewe was fitted with an indwelling jugular catheter. For push-pull perfusion, a stylette was removed from the outer PPC, and an inner cannula assembly (od, 0.40 mm) was inserted. Artificial cerebrospinal fluid was pushed through the inner cannula and pulled up between the cannulae at 20 microliters/min. Continuous 10-min perfusate fractions were collected, acidified, and stored at -20 C for LHRH RIA. Blood samples were obtained every 10 min via the jugular catheter, each being drawn 5 min after the start of a perfusate collection interval. Plasma LH levels were determined by RIA. The duration of the sampling was 3-7 h. LHRH output was distinctly pulsatile, occurring at a frequency of approximately one pulse every 30-40 min (n = 5 sheep). LHRH pulse amplitude and frequency remained relatively constant throughout each perfusion. Plasma LH values also were pulsatile, and all LH peaks occurred either during the same interval or during the interval after a LHRH pulse. LH pulses always were accompanied or directly preceded by LHRH pulses, but LHRH pulses were not always followed by LH pulses. The amplitudes of LH pulses and corresponding LHRH pulses were highly correlated (r = 0.81; P less than 0.01). Histological examination revealed that detection of LHRH in perfusates depended upon the placement of the PPC tip into either the zona externa of the central median eminence or adjacent areas. These experiments demonstrate that 1) hypothalamic LHRH release in the Ovx ewe occurs in discrete pulses, with a mean interpulse interval of 38.7 +/- 1.5 min, 2) LH pulses invariably are preceded or accompanied by LHRH pulses, and 3) LH pulse amplitude is highly correlated with LHRH pulse amplitude.

Animals↗
PubMed1982

Prolactin stimulates dopamine release from male but not from female rat striatal tissue superfused in vitro.

Direct prolactin (PRL) effects on dopamine (DA) release from fragments of rat striatal tissues were studied by the in vitro superfusion technique. The DA collected in the superfusates was quantified by a radio-enzymatic assay. In the present experiments, intact and one-week gonadectomized adult male and female rats were used. The spontaneous release of DA from male and female rat striatal tissues was relatively stable after a 60 min equilibration period. The basal release rate of DA from striatal tissues from intact males infused only with medium over a 76 min period was 22.5 +/- 0.7 pg/mg/min (X +/- SE of 4 experiments). Infusion of highly purified PRL (NIAMDD-rPRL-I-5) at a concentration of 1 microgram/ml for 24 min significantly augmented DA release from striatal tissues from intact and castrated males (167 +/- 15% (n=6) and 203 +/- 32% (n=4), respectively) over pre-infusion basal levels. Infusion with heat-denatured PRL or other proteins had no effect on DA release from intact male striatal tissues. In parallel experiments, infusion of PRL at 0.1, 1 or 10 micrograms/ml concentrations for 24 min had no effect on the basal release of DA from striatal tissues from intact and ovariectomized females. These results demonstrate that an absolute sexual difference exists in the responsiveness of rat striatal tissues to PRL infused in vitro. Interestingly, this sexual difference was not modified by short-term castration.

Animals↗
PubMed1981

Male vole urine changes luteinizing hormone-releasing hormone and norepinephrine in female olfactory bulb.

Female prairie voles (Microtus ochrogaster) exposed to a single drop of male urine on the upper lip showed changes in concentrations of luteinizing hormone-releasing hormone (LHRH) and norepinephrine in olfactory bulb tissue; no such changes occurred in dopamine concentration. The changes were measured in the posterior but not the anterior olfactory bulb tissue of females within 1 hour after they were exposed to urine. These females also showed rapid increases in serum concentrations of luteinizing hormone. Females exposed to water on the upper lip showed none of these changes. These results suggest that in this species LHRH and norepinephrine in the olfactory bulb may mediate luteinizing hormone release in response to external (pheromonal) chemical cues.

Animals↗
PubMed1981

Sex differences in the amphetamine stimulated release of catecholamines from rat striatal tissue in vitro.

Sex and estrous cycle-related differences in the amphetamine (AMT)-stimulated release (pg/mg/min) of catecholamines (CA) from rat striatal and mediobasal hypothalamus (MBH) fragments were measured in an in vitro perifusion system. In striatal tissue from intact males, AMT stimulated the release of both norepinephrine (NE) and dopamine (DA). The AMT-stimulated release of DA from striatal tissue obtained from intact females varied with the stage of the estrous cycle. This increase in DA release was lower in striatal tissue from proestrous females than from females in estrus (P less than 0.05) or diestrus 1 (P less than 0.01). The NE release stimulated by AMT was greater than basal release only on estrus and diestrus. 2. Following castration (CAST) or CAST plus 500 micrograms testosterone propionate (TP), daily for 4 days, striatal tissue fragments from male rats continued to release CA in response to AMT stimulation. In contrast, ovariectomy (OVX) severely attenuated the AMT-stimulated release of both CA. Treatment of OVX females with 5 micrograms estradiol benzoate (EB), daily for 4 days, or 1.2 mg progesterone (P) slightly increased the AMT-stimulated release of DA but not NE. Treatment of OVX females with 5 micrograms EB, daily for 4 days, plus 1.2 mg P completely restored the AMT-stimulated release of both CA. Interestingly, MBH fragments from intact or gonadectomized rats, with or without hormonal treatment, demonstrated a consistent AMT-stimulated release of DA regardless of the sex of the animal. The AMT-stimulated NE release from these MBH fragments was less consistent, but there was no significant differences between the groups. These results demonstrate that the AMT-stimulated release of DA from striatal tissue in vitro is sex, hormonal, and tissue dependent.

Animals↗
PubMed1981

Presence and localization of immunoreactive luteinizing hormone-releasing hormone (LHRH) within the olfactory bulbs of adult male and female rats.

A sensitive and specific radioimmunoassay was employed to measure the immunoreactive luteinizing hormone releasing hormone (LHRH) concentration from localized areas within the olfactory bulbs of adult male and female rats. Although no significant sex differences or lateralization were obtained, LHRH concentration within the posterior half of the olfactory bulb was significantly greater than that obtained in the anterior half for both males and females. The presence of LHRH within the olfactory bulbs and localization to areas involved in the chemical stimulation of reproductive processes suggests the possibility that this olfactory bulb LHRH may be involved in mediating pheromonally stimulated endocrinological responses.

Animals↗
PubMed1980

Progesterone administration in vivo stimulates release of luteinizing hormone-releasing hormone in vitro.

The release of luteinizing hormone-releasing hormone (LHRH) from tissue from the mediobasal hypothalamic-anterior hypothalamic-preoptic area of prepuberal female rats was measured in a perfusion system. Measurements were also made of the concentrations of LHRH in these tissue fragments and of luteinizing hormone in serum obtained when the rats were killed. Four groups of immature rats were studied: intact, ovariectomized, ovariectomized and implanted with estradiol-containing capsules, and ovariectomized rats primed with estradiol and injected with progesterone. The release of LHRH from the tissue of ovariectomized animals was significantly less than that of intact females and was not modified when the ovariectomized rats received estradiol. However, there was a four- to fivefold increase in LHRH release from tissue of ovariectomized rats primed with estradiol when they were killed 6 hours after they received an injection of progesterone. The concentrations of LHRH in tissue and of luteinizing hormone in serum varied among groups and with the time of day that the animals were killed. The interactions among luteinizing hormone, gonadal steroids, and the photoperiod seem to set the appropriate conditions for neural processes triggering a complete and normal release of luteinizing hormone.

Animals↗
PubMed1980

Dynamics of endogenous catecholamine release from brain fragments of male and female rats.

A continuous flow perifusion system was used to measure the in vitro release rate, and percent release of endogenous norepinephrine (NE) and dopamine (DA) from rat brain fragments. Catecholamines (CA) were measured simultaneously in effluent fractions and in tissue fragments following perifusion using a modified radioenzymatic assay. Employing this perifusion system allows not only quantification of endogenous release, but also permits study of the dynamics of the release process. To validate the system, NE and DA release were measured in effluent from medial basal hypothalamus (MBH) and caudate nucleus (CN) fragments under various temperature and ionic conditions. K+-stimulated release (60 mM KCl), but not the basal release rate, is temperature and calcium dependent. Marked regional differences are seen in the parameters considered. DA release rate from the CN in male rats was 30 times greater than from the MBH. The percent of DA release was 2.5 times greater and there was a 3 times greater final tissue concentration of DA in the CN than in the MBH. Although the release rate of NE from CN fragments was higher than that of the MBH, it did not reach statistical difference. However, the percent of NE release from the CN was close to 4 times greater than the percent release from the MBH, and final tissue concentrations of NE were 87.9 pg/mg in the CN compared to 1,240 pg/mg in the MBH (postperifusion values). In a group of female rats, only the percent release of NE from the MBH was significantly different from that of similar tissue from male rats. However, the release rate and percent release of DA from the MBH of female rats were significantly lower than that of male rats. In appears that under this in vitro condition there are marked regional and sex differences in the metabolism of CA between the CN and the MBH fragments of male and female rats. Implications of these findings are briefly discussed.

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