Dean E. Dluzen

Bimodal Effect of Progesterone on in vitro Dopamine Function of the Rat Corpus striatum

In the present experiment we examined the temporal effects of progesterone (P) upon in vitro dopamine (DA) release from superfused corpus striatum (CS) and medial basal hypothalami (MBH) tissue fragments. In ovariectomized-estrogen-primed adult female rats, P was systemically administered at 0.5, 2, 4, 12 or 24 h prior to sacrifice for CS and at 4 or 24 h for MBH superfusions. Control groups receiving either steroid alone and/or the oil vehicle were included. Progesterone at the 2- to 12-hour periods stimulated spontaneous and amphetamine-evoked DA release and increased post-superfusion tissue concentrations of DA from the CS when compared to controls. At 24 h P apparently produced an active inhibition, with all parameters of DA activity (spontaneous and AMPH-induced DA release), significantly decreased compared to controls. In contrast, P failed to alter the spontaneous or marginal amphetamine response of the MBH but did significantly reduce post-superfusion DA concentration at 24 h. We hypothesize that the dual effect of P upon brain dopaminergic systems (facilitation followed by inhibition), in the CS but not in the MBH represents changes in DA synthesis and release which are coupled in the CS but not in the MBH.

In vivo activity of the LHRH pulse generator as determined with push-pull perfusion of the anterior pituitary gland of unrestrained intact and castrate male rats.

In the present article we report that in vivo LHRH output as measured at the anterior pituitary following castration significantly increased, due to larger and more frequent LHRH signals arriving to this gland. This contrasts with the decreased amplitude and overall mean LHRH release of castrate males bearing a push-pull cannula within the hypothalamus. These divergent results have generated a new thesis regarding the role of gonadal steroids upon the LHRH pulse generator. This thesis submits that following castration there is an increased frequency and decreased amplitude of the LHRH signal from discrete loci within the medial basal hypothalamus, but an increased synchrony of LHRH release throughout the entire hypothalamus, resulting in an increased frequency and amplitude of LHRH arriving at the anterior pituitary.

Intermittent infusion of progesterone potentiates whereas continuous infusion reduces amphetamine-stimulated dopamine release from ovariectomized estrogen-primed rat striatal fragments superfused in vitro

In the present experiment we examined the effect of a direct in vitro infusion of progesterone upon spontaneous and amphetamine-stimulated in vitro dopamine (DA) release and post-superfusion DA tissue concentration of corpus striatum tissue fragments from ovariectomized and estrogen-treated female rats. An intermittent infusion of progesterone at a dose of 2 ng/ml produced a significant increase in amphetamine-stimulated DA release and post-superfusion DA tissue concentration compared to similar superfusions infused with medium alone or cholesterol (2 ng/ml). Higher (50 ng/ml) or lower (0.2 ng/ml) doses of progesterone were ineffective and a continuous infusion of progesterone at an identical total concentration to that of the intermittent 2 ng/ml dose inhibited both amphetamine-stimulated DA release and post-superfusion DA tissue concentration. With the exception of 5 alpha DHP (dihydroxyprogesterone) intermittent infusions of various metabolites, a synthetic progestin (R5020) at 2 ng/ml and estradiol at both 0.2 ng/ml and 2 ng/ml failed to modify significantly the amphetamine-stimulated DA response. However, pregnanolone, 5 alpha DHP, R5020 at 2 ng/ml and estradiol at 0.2 ng/ml increased post-superfusion DA tissue concentration to levels comparable to that of progesterone. These results demonstrate that in vitro progesterone can directly alter the amphetamine-stimulated DA release from dopaminergic terminals of corpus striatal tissue fragments. This effect appears quite specific for progesterone as well as for a specific dose and mode of infusion of this gonadal steroid. Moreover, progesterone can exert opposite effects upon the amphetamine-evoked DA release from the corpus striatum as a function of its mode of infusion suggesting a means by which one hormone can differentially alter central nervous system function.

Progesterone effects upon dopamine release from the corpus striatum of female rats. II. Evidence for a membrane site of action and the role of albumin.

In the present experiment we used immobilized progesterone linked to bovine serum albumin (P4-3-BSA) as a probe to examine whether the effects of a direct in vitro infusion of progesterone upon dopamine (DA) release from corpus striatal (CS) tissue fragments from ovariectomized estrogen-treated rats may be attributable to a surface membrane site of action. In Expt. I, a direct in vitro pulsatile infusion of P4-3-BSA resulted in two discrete episodes of stimulated DA release which were not observed in superfusions receiving a continuous infusion of P4-3-BSA or compared to data of control superfusions. In contrast to that of a pulsatile administration, a continuous infusion of P4-3-BSA completely abolished the amphetamine-stimulated response from these tissue preparations with significantly lower DA release rates compared to the pulsatile P4-3-BSA (P less than 0.02) and control (P less than 0.04) conditions. In Expt. II, the addition of tetrodotoxin (TTX, 1 microM) to the superfusion medium abolished the discriminatory response between pulsatile and continuous administration of immobilized progesterone. These results indicate that the action of progesterone on DA release from the CS is mediated primarily through a surface membrane site of an interneuron(s) which can discriminately respond to a specific infusion mode of this steroid.

Suppression of reproductive maturation in male-stimulated virgin female microtus by a female urinary chemosignal

Urine from female Microtus ochrogaster possesses a chemosignal that suppresses reproductive maturation in other females. Uterine enlargement in virgin females stimulated by a male was suppressed by subsequent association with another female or by application of female urine on the nose. Females so suppressed are not able to achieve estrus. Urine from virgin sibling and non-sibling females and from pregnant females possesses the suppressing effect.

Ovarian hormones regulating sexual and social behaviors in female prairie voles, Microtus ochrogaster

In the induced ovulator, Microtus ochrogaster (the prairie vole), daily injections of estradiol benzoate (EB 0.5 μg or 5.0 μg) facilitated high levels of sexual receptivity in ovariectomized females withing 48 hr of the onset of treatment. A lower level of EB (0.05 μg) with or without progesterone (0.5 mg) for five days did not induce lordosis. Four hr after sexually receptive EB-primed females received progesterone (0.5 mg) they either continued to show lordosis (EB 5.0 μg group) or showed an inhibition of lordosis (EB 0.5 μg group). Within 24 hr lordosis was markedly reduced in both groups. Progesterone-associated inhibitions were no longer apparent 48 hr after progesterone was discontinued. This general pattern of response to ovarian hormones is consistent with data described for other induced ovulators.

Localized and discrete changes in neuropeptide (LHRH and TRH) and neurotransmitter (NE and DA) concentrations within the olfactory bulbs of male mice as a function of social interaction

Individually housed male mice were exposed to either an intact male or an ovariectomized female mouse for 1 min and decapitated at 5, 15, or 60 min to examine the hypothesis whether discrete changes in olfactory bulb neuropeptide (LHRH and TRH) and neurotransmitter (NE and DA) concentrations would occur following onset of exposure. A nonexposed control group (decapitated at time 0) was also included. Bilateral olfactory bulbs were dissected into anterior dorsal (ADOB) and posterior dorsal (PDOB) olfactory bulb fragments and prepared for radioimmunoassays (LHRH and TRH) or radioenzymatic assays (NE and DA). Concentrations of LHRH and NE, but not of TRH and DA, from the PDOB were significantly greater than those of ADOB fragments. Exposure to a male resulted in a significant increase of PDOB LHRH at 5 min following exposure and a significant increase in LHRH at 15 min following female exposure. Norepinephrine within the ADOB and PDOB and DA within the PDOB demonstrated a statistically significant increase at 60 min following exposure to an ovariectomized female. In marked contrast, no statistically significant changes were obtained following male exposure. These results not only demonstrate a preferential localization of neuroregulators within the olfactory bulb of male mice but discrete changes in the concentration of these neuroregulators in response to male or female exposure, suggesting the possibility that some processing and coding of chemical cue information during social encounters already occurs at the level of the olfactory bulb.

In vitro progesterone modulation of amphetamine-stimulated dopamine release from the corpus striatum of ovariectomized estrogen-treated female rats: response characteristics

We have previously reported that a pulsatile infusion of progesterone directly into superfusion chambers containing corpus striatal tissue fragments of ovariectomized estrogen-treated female rats augmented amphetamine-stimulated dopamine release in vitro. In an attempt to understand some of the means by which progesterone modulates dopamine release under these in vitro conditions, we examined two characteristics of this effect of progesterone. First, to determine the threshold dose of progesterone and whether it was necessary for progesterone to be administered in a pulsatile mode, in Expt. I we examined the effect of a single, brief infusion of progesterone at doses of 2, 4 and 40 ng/ml. Second, to evaluate the temporal relationship between progesterone infusion and its capacity to augment amphetamine-stimulated dopamine release, in Expt. II we varied the interval between progesterone infusion and amphetamine challenge, with amphetamine infused at 10, 30, 50 or 90 min post-progesterone. The results of Expt. I indicate that a single 10-min infusion of progesterone at 2 ng/ml was adequate to produce an accentuated response to amphetamine infusion. Although further increases were obtained following the 4 and 40 ng/ml doses, these values failed to differ significantly from the levels obtained with the 2 ng/ml dose. From Expt. II, we observed that this effect of progesterone was relatively rapid with statistically significant increases in amphetamine-stimulated dopamine release occurring at 30 min post-progesterone and similar responses being maintained at 50 and 90 min post-progesterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Orchidectomy on Nigro‐Striatal Dopaminergic Function: Behavioral and Physiological Evidence

In the present experiments, we examined the effect of castration upon two indices of nigro‐striatal dopaminergic function in the male rat. In Experiment I, differences in spontaneous locomotor behavioral activity between intact and castrated male rats were examined. The total distance traveled, horizontal activity and mean revolutions of castrated male rats were significantly greater than that of intact males. No significant differences between intact and castrated males were obtained for vertical activity. In Experiment II, the spontaneous in vitro dopamine release from the corpus striatum of intact and castrated rats as sampled during the light‐phase (1500 h) and dark‐phase (2400 h) of the photoperiod was examined. At both time periods, the spontaneous in vitro dopamine release of castrated males was significantly greater than that of intact males. Both intact and castrated males showed statistically significant increases in dopamine release at the 2400 h compared to the 1500 h time period. To examine if testicular hormones were responsible for these castration induced changes in dopamine release, in Experiment III we treated castrated male rats with testosterone propionate. Administration of testosterone propionate (0.1 mg/day × 5 days) significantly reduced in vitro dopamine release compared to untreated or castrated male rats receiving vehicle treatment. These results demonstrate that testicular hormones, most likely testosterone, have a markedly suppressive effect upon the nigro‐striatal dopaminergic system as evidenced from changes in spontaneous behavioral activity and in vitro dopamine release.

In vitro Dopamine Release from the Rat Striatum: Diurnal Rhythm and Its Modification by the Estrous Cycle

In the present experiment we examined spontaneous endogenous in vitro dopamine release from the corpus striatum of female rats during the morning (09.00-09.30 h) and afternoon (15.00-15.30 h) photoperiod on each day of the estrous cycle. In the morning, the spontaneous dopamine release rates of D-1, D-2 and proestrous female rats were characterized by initial low values which gradually increased (approximately 3-fold) over the 2.5-hour in vitro perifusion. In the afternoon, spontaneous release rates of D-1, D-2 and estrous females gradually declined (approximately 2.5-fold) over the perifusion period. This rhythmic diurnal fluctuation was disrupted in the afternoon of proestrus and morning of estrus when release rate profiles remained stable over the entire perifusion period. These results suggest that changes in spontaneous in vitro dopamine release of corpus striata derived from rats in different phases of the estrous cycle may reflect novel in vivo interactions of both photoperiodic and hormonal cues.