John H. Gordon

Effects of estrogen on dopamine turnover, glutamic acid decarboxylase activity and lordosis behavior in septal lesioned female rats ☆

Abstract Estradiol benzoate (EB) treatment (2.0 μg/day × 3) of septal lesioned adult female rats produces a marked increase in lordosis behavior over similarly treated sham operated animals. In these animals endogenous dopamine (DA) and norepinephrine (NE) levels were measured and turnover rates were estimated following tyrosine hydroxylase inhibition with α-methyltyrosine, in both EB and oil (0.05 ml × 3 days) treated groups. No consistent pattern of change in the level or rate of turnover of NE was noted for any of the treatment groups. No differences in either the level or turnover of DA were seen in the oil treated septal lesioned group, relative both to EB and oil treated sham operated groups. However, in the amygdala, corpus striatum and nucleus accumbens septi of the septal lesioned animals primed with EB there was both a reduction in endogenous levels (20–50%) and a decrease in synthesis rates (30–70%) of DA relative to both EB and oil treated sham operated groups and the oil treated septal lesioned group. The EB treated septal lesioned animals showed a significant negative correlation between DA levels in the corpus striatum and the level of lordosis behavior ( r = −.850), supporting the concept of a possible inhibitory role for DA on female sexual receptivity. Glutamic acid decarboxylase (GAD; the rate limiting enzyme in the synthesis of γ-aminobutyric acid (GABA)) activity was measured in the substantia nigra and ventral tegmental region from the same animals. GAD activity was reduced in both areas in the EB primed sham operated animals, while the EB and oil treated septal lesioned groups remained comparable to the oil treated sham operated animals. Because of the proposed existence of a GABA mediated inhibitory neuronal feedback on DA cell bodies in the midbrain, the reduction in DA turnover in the EB primed septal lesioned female rat and thus the increase in behavioral receptivity could be due in part to the failure of the septal lesioned animal to show a compensatory decrease in GAD activity.

Time Course and Localization of the Effects of Estrogen on Glutamic Acid Decarboxylase Activity

Abstract: Two approaches were used in an attempt to characterize the effect of estrogen on glutamic acid decarboxylase (GAD) [EC 4.1.1.15] activity in ovariectomized rats. In the first experiment, estradiol‐17β (E2) was unilaterally implanted in one of five different brain areas. After 3 days of estrogen exposure, the animals were sacrificed, and GAD activity in the substantia nigra (SN) and ventral tegmental region (VTR) was measured. Estrogen implanted into the preoptic area and the ventromedial nucleus was ineffective, as were implants of cholesterol, regardless of implant site. However, GAD activity was decreased in the SN when E2 was implanted into the caudate nucleus or amygdala and in the VTR when implanted into the nucleus accumbens septi. Furthermore, this decrease in GAD activity occurred only in the implanted side. In the second experiment, the time course of changes in GAD activity was measured in ovariectomized rats given a single systemic injection of either 8μg estradiol benzoate (EB) or oil. Rats were sacrificed at 0, 12, 29, or 53 h postinjection. It was found that GAD activity in the SN was maximally suppressed 29 h after EB, whereas decreased GAD activity in the VTR was apparent 12 h after EB but had returned to normal by 29 h. Oil injections had no significant effect on GAD activity. These results suggest that there may be two separate and distinct γ‐aminobutyric acid pathways, which are differentially responsive to estrogen.

Examination of some factors that control the effects of septal lesions on lordosis behavior.

Various experimental parameters related to the effects of septal lesions on the lordosis behavior of rats have been examined. First, the failure of septal lesions to facilitate lordosis behavior in male rats appears to be related to the degree of exposure to androgens neonatally. The normal facilitation in lordosis behavior associated with septal destruction in adult female rats does not occur if these female rats are treated with 1.0 mg of testosterone propionate (TP) on Day 1 of life. Yet female rats given 270 mug of TP on Day 3 of life respond the same as do normal females to septal lesions. Second, these sexually dimorphic effects of septal lesions can be modified in adult rats by chronic treatment with gonadal hormones following septal destruction. Whereas previous studies indicated that chronic estrogen injections permit a facilitation in lordosis behavior to occur in septal lesioned male rats, the present results showed that chronic injections of TP following a septal lesion attenuates the facilitation in lordosis behavior typically observed in adult female rats following a septal lesion. Third, examination of the time course for the facilitation in lordosis behavior following a septal lesion revealed a four to six day delay before the appearance of heightened female sexual behavior. Fourth, in support of the possibility that modifications in lordosis behavior by septal lesions may be mediated by a depletion or imbalance in brain amines, amphetamine was found to reduce the high levels of lordosis behavior of septal lesioned female rats to control levels. Finally, further evidence of a potential role for brain amines in the effects of septal lesions was provided by the observation of significantly lower content and turnover of dopamine in the amygdala of septal lesioned female rats, relative to sham operated controls.

Δ9-Tetrahydrocannabinol enhancement of Lordosis Behavior in estrogen treated female rats

levo-alpha-Acetylmethadol was orally administered via a sucrose solution to rats in their drinking water for 24 days. A control group received only sucrose. Bodyweight and fluid consumption were monitored daily. The behavioral effects during chronic drug administration and during eight days of withdrawal were studied using behavior controlled by a fixed-interval schedule of food reinforcement. Body weights of treated animals remained stable during drug administration but decreased by approximately 25% during withdrawal. There were no significant differences in volume of fluid consumed by the two groups. Response rate and number of reinforcements were decreased during drug administration. During withdrawal, response rates were greater than pre-drug control rates.Abstract Estrogen and progesterone (PROG) are both considered essential hormones for the display of sexual receptivity in the female rat. Δ 9 -tetrahydrocannabinol (THC), one of the active components of marijuana, was tested in ovariectomized rats for possible estrogenic and anti-estrogenic activity using the display of lordosis behavior, one of the components of sexual receptivity, as an endpoint. Test animals were treated with THC (1.25, 2.50 or 10.00 mg/kg/day) or estradiol benzoate (EB) + THC (2.0 μg/kg/day and 10.0 mg/kg/day, respectively) followed by 500 μg PROG and tested for lordosis behavior on Day 5. The animals treated with THC alone failed to show any lordosis behavior, similar to oil and vehicle controls, while the behavioral effects of EB were not antagonized by the 10.0 mg/kg dose of THC. Thus, the estrogenic effects of THC, using the lordosis system as an end point, are at best minimal, if present at all. The effects of acute THC in EB primed rats (2.0 μg/kg/day × 3) were also tested in this study. At relatively low doses (0.5 and 1.5 mg/kg) of THC, a significant increase in the lordosis quotient (LQ; number of lordosis responses/number of mounts × 100) was noted. At a higher dose (3.0 mg/kg) of THC, a significant reduction in the LQ was noted, indicating a dose-dependent effect of THC. Following adrenalectomy, the dose-response curve for THC was shifted to the left, as a lower dose (0.15 mg/kg) of THC was now capable of enhancing the LQ, while the 0.5 and 1.5 mg doses were no longer effective (similar to the 3.0 mg/kg dose in non-adrenalectomized animals). The biphasic action of PROG on LQ was also utilized to rule out adrenal involvement in the enhanced behavior seen in the EB primed and THC treated animals. When a behaviorally effective dose of PROG was administered, 18 hr prior to PROG followed by a behavioral test, it antagonized the behavioral effects of the second dose of PROG, while a behaviorally effective dose of THC, given 18 hr prior to PROG followed by a behavior test, was ineffective in antagonizing the behavioral effects of PROG, indicating that minimal, if any, PROG is released from the adrenal following a behaviorally effective dose of THC. Thus, it appears that THC is capable of enhancing sexual receptivity of female rats by a direct action on the central nervous system.

Influence of γ-aminobutyric acid on lordosis behavior and dopamine activity in estrogen primed spayed female rats

In the first experiment the role of gamma-aminobutyric acid (GABA) in the display of lordosis behavior was examined in septal-lesioned and sham-operated ovariectomized rats. Following estradiol benzoate (EB) priming, septal-lesioned rats were tested for lordosis behavior before and after bilateral infusion of picrotoxin or saline directly into the substantia nigra (SN). Sham animals were given the same behavioral tests but received intranigral infusion of either hydrazinopropionic acid (HPA) or saline. Picrotoxin, which blocks GABA receptors, was effective in suppressing the high levels of lordosis behavior seen in the EB-primed septal-lesioned female rat 30 min after infusion, but not at 120 min. Conversely, HPA, which elevates endogenous GABA levels, was effective in facilitating lordosis behavior in sham-operated rats treated with EB only. The lordosis quotient was moderately increased 30 min after HPA infusion, reached high levels at 120 min, and returned to low levels by 360 min post-infusion, demonstating the reversibility of the drug effect. Saline infusions in lesioned and sham-operated controls were without effect. In the second experiment sepal-lesioned and sham-operated rats were primed with EB and infused with the drugs as in the first experiment, but were sacrificed at the time the macimal behavioral effect had been observed in the first experiment. Tyrosine hydroxylase (TH) activity and dopamine (DA) and homovanillic acid (HVA) levels were measured. No effect on TH activity was found. However, sham-operated rats receiving HPA infusions had lower DA and HVA levels compared to those of saline-injected controls, and septal-lesioned rats receiving picrotoxin infusions had higher DA and HVA levels than those of lesioned saline-injected controls. Septal-lesioned saline-infused rats also showed decreased DA and HVA levels relative to sham-operated saline-infused animals. These results support the concept of a GABA inhibitory neuronal feedback system which modulates DA turnover and perhaps plays a critical role in the neural control of lordosis behavior.

Effects of septal lesions and chronic estrogen treatment on dopamine, GABA and lordosis behavior in male rats

Septal lesions (SL) in female rats result in an increased sensitivity to the behavioral effects of acute estradiol benzoate (ACUTE-EB; 2 microgram/day X 3) treatment as measured by the lordosis quotient (LQ: number of lordotic responses X 100/number of mounts). Male rats, intact or castrated, do not show this enhanced behavioral response to ACUTE-EB unless they are treated with EB (2 microgram/day) for 2--4 weeks immediately following the production of SL. The present study was undertaken to examine possible neurochemical alterations which could account for the enhanced behavioral sensitivity to ACUTE-EB seen in the SL male rat treated chronically with EB during the postlesion period (SL-EB). Three groups, normal males, SL-EB and SL males chronically treated with oil (SL-oil), were subdivided and treated with ACUTE-EB or oil and decapitated. The brains were removed, frozen and stored at -50 degrees C prior to dissection and assay. Tyrosine hydroxylase (TH) activity was assayed in the dopamine (DA) rich areas of the forebrain (striatum, STR, nucleus accumbens septi, ACB; and olfactory tubercle). The TH activity was significantly suppressed in both the STR and ACB of the SL-EB males treated with ACUTE-EB. The glutamic acid decarboxylase (GAD) activity in both the substantia nigra and ventral tegmentum was significantly increased in the SL-EB males given ACUTE-EB relative to that of all other groups. In summary, SL-EB males given ACUTE-EB show (1) an enhanced LQ, (2) decreased TH activity in the region of DA terminals, and (3) increased GAD activity in the region of DA cell bodies. The increase in GAD activity is suggested to be a result of an altered neuronal feedback because of plastic changes that occur during chronic EB treatment following production of SL. This probable increase in inhibitory tone in the region of the DA cell bodies may explain the observation that the SL-EB male exhibits decreased DA turnover following ACUTE-EB treatment. Moreover, since DA may be inhibitory to the display of lordosis behavior, the SL-EB males may show an enhanced LQ, at least partially, because of this reduction in DA activity.

Effects of olfactory bulbectomy and estrogen on tyrosine hydroxylase and glutamic acid decarboxylase in the nigrostriatal and mesolimbic dopamine systems of adult female rats

Abstract Following olfactory bulbectomy (BULBX), ovariectomized female rats show enhanced behavioral sensitivity to estradiol benzoate (EB) as measured by an index of sexual receptivity, lordosis responding. We have proposed previously that alterations in EB sensitivity which also are produced by septal destruction reflect disruptions of gamma-aminobutyric acid (GABA) inhibitory feedback on dopamine (DA) cell bodies in the midbrain, which may be inhibitory to the expression of lordosis. Since the olfactory system as well as the septum receives mesolimbic DA projections, in the present study we examined the effects of EB given to bulbectomized and sham-operated rats on tyrosine hydroxylase (TH) activity in the olfactory tubercle (OT), nucleus accumbens septi and corpus striatum. Glutamic acid decarboxylase (GAD) activity was measured in the ventral tegmental region (VTR) and the substantia nigra (SN). Rats received 2 μg EB/day for 3 days and were tested on Day 4 in a 20 mount behavioral test. Ten bulbectomized rats demonstrating enhanced behavioral sensitivity to EB and all sham-operated rats (N = 10) were selected for further study. Five rats in each group received 0.05 ml oil/day X 3 (BULBX-oil, SHAM-oil), and five received 2 μg EB/day X 3 (BULBX-EB, SHAM-EB). Rats were sacrificed on Day 4. Subsequent assays revealed a bulbectomy-dependent decrease in TH activity in the striatum, and a lesion plus EB-dependent decrease in TH activity in the OT. GAD activity was slightly but significantly suppressed in the VTR in the SHAM-EB group relative to that in the SHAM-oil group. Rats of the BULBX-EB group failed to exhibit decreased GAD activity. Thus, bulbectomy may result in enhanced behavioral sensitivity to EB due to disruptions in GABA-DA interactions, which are similar to those observed following septal destruction and which result in diminished behaviorally inhibitory DA tone.

Long-lasting dopamine receptor up-regulation in amphetamine-treated rats following amphetamine neurotoxicity

Amphetamine (A) (9.2 mg/kg, IP), in combination with iprindole (I) (10.0 mg/kg, IP), caused long-lasting dopamine (DA) depletions in striatum (-49%, 4 weeks) but not in nucleus accumbens following one A/I injection. Striatal DA had recovered by 4 months. DA receptors (DAr) were up-regulated: 1) behavioral responses to a DA receptor agonist (apomorphine) were significantly elevated. These included apomorphine-induced locomotor activity (+103% and +160%, on weeks 3 and 10) and apomorphine-induced stereotypy (day 10). 2) Bmax for [3H]spiroperidol binding to striatal D2 DAr (12 weeks) increased (+53%, week 12). Injection of the DAr neuromodulator cyclo(leucyl-glycyl) (8 mg/kg/day x 4 days, SC) reversed the Bmax increase. Thus toxicity (DA depletion) following high-dose amphetamine appears to induce compensatory changes in DAr. This DAr upregulation may explain the lack of abnormal movements despite enduring DA depletion. Additionally, the A/I paradigm as an animal model of long-lasting DAr up-regulation, could be used to screen neuromodulatory agents, like CLG, that might treat disorders (e.g., tardive dyskinesia and schizophrenia) thought to involve up-regulated DAr.

Delta-9-Tetrahydrocannabinol Inhibition of Suckling-Induced Prolactin Release in the Lactating Rat

To study effects of delta-9-tetrahydrocannabinol (THC) on the regulation of prolactin (PRL) release, a chronic cannula was placed in the right atrium of postpartum lactating rats. Two or more days later their pups were removed for 6--8 hours. A blood sample was drawn from the mother just prior to reintroducing the pups, for determination of basal levels of plasma PRL. A second sample was drawn following 30 min of continuous suckling. THC (1.25 or 4.0 mg/Kg) or vehicle was then injected intravenously and blood samples obtained 30, 60, 120 min later. Relative to vehicle-injected controls, both doses of THC significantly reduced plasma PRL levels and disrupted all components of maternal behavior. These findings indicate that THC inhibits suckling-induced PRL release in the postpartum rat.

Further characterization of fat diet-induced changes in responsiveness to estrogen and glucose

Possible reasons for hyperresponsiveness to the anorexic influence of estrogen of rats fed a high-fat (F) diet were explored. It was found that (1) hyperresponsiveness appeared unrelated to body weight, (2) other estrogenic effects (upon vaginal epithelia and upon mating behavior) were normal in F-fed rats, (3) hyperresponsiveness to estrogen was not a result of alterations in brain dopamine or norepinephrine, (4) F-fed rats were also hyperresponsive to postabsorptive satiating effects of intragastric glucose loads. Thus, an altered glucose metabolism of F-fed rats may be related to an increased responsiveness to the anorexic effects of estrogen.