Preoperative brain µ-opioid receptor availability predicts weight development following bariatric surgery in women.

Bariatric surgery is the most effective method for weight loss in morbid obesity. There is significant individual variability in the weight loss outcomes, yet factors leading to postoperative weight loss or weight regain remain elusive. Alterations in the µ-opioid receptor (MOR) and dopamine D2 receptor (D2R) systems are associated with obesity and appetite control, and the magnitude of initial brain receptor system perturbation may predict long-term surgical weight loss outcomes. We tested this hypothesis by studying 19 morbidly obese women (mean BMI 40) scheduled to undergo bariatric surgery. We measured their preoperative MOR and D2R availabilities using positron emission tomography with [11C]carfentanil and [11C]raclopride, respectively, and then assessed their weight development association with regional MOR and D2R availabilities at 24-month follow-up. MOR availability in the amygdala consistently predicted weight development throughout the follow-up period, but no associations were found for D2R. This is the first study to our knowledge to demonstrate that neuroreceptor markers prior to bariatric surgery are associated with postoperative weight development. Postoperative weight regain may derive from dysfunction in the opioid system, and weight loss outcomes after bariatric surgery may be partially predicted based on preoperative brain receptor availability, opening up new potential for treatment possibilities.

Detection of G Protein-Coupled Receptor Complexes in Postmortem Human Brain by Proximity Ligation Assay.

Combining immunological and molecular biological methods, the antibody-based proximity ligation assay (PLA) has been used for more than a decade to detect and quantify protein-protein interactions, protein modification, and protein expression in situ, including in brain tissue. However, the transfer of this technology to human brain samples requires a number of precautions due to the nature of the specimens and their specific processing. Here, we used the PLA brightfield detection technique to assess the expression of dopamine D2 receptor and adenosine A2A receptor and their proximity in human postmortem brains, and we developed a systematic random sampling method to help quantify the PLA signals. © 2019 by John Wiley & Sons, Inc. Basic Protocol 1: Sample preparation and sectioning for PLA_BF Basic Protocol 2: PLA_BF staining of brain tissue Basic Protocol 3: Image acquisition and result analysis Support Protocol: Luxol fast blue/cresyl violet staining.

Cigarette Use and Striatal Dopamine D2/3 Receptors: Possible Role in the Link between Smoking and Nicotine Dependence.

BACKGROUND: Cigarette smoking induces dopamine release in the striatum, and smoking- or nicotine-induced ventral striatal dopamine release is correlated with nicotine dependence. Smokers also exhibit lower dopamine D2/3 receptor availability in the dorsal striatum than nonsmokers. Negative correlations of striatal dopamine D2/3 receptor availability with smoking exposure and nicotine dependence, therefore, might be expected but have not been tested. METHODS: Twenty smokers had positron emission tomography scans with [18F]fallypride to measure dopamine D2/3 receptor availability in ventral and dorsal regions of the striatum and provided self-report measures of recent and lifetime smoking and of nicotine dependence. RESULTS: As reported before, lifetime smoking was correlated with nicotine dependence. New findings were that ventral striatal dopamine D2/3 receptor availability was negatively correlated with recent and lifetime smoking and also with nicotine dependence. CONCLUSION: The results suggest an effect of smoking on ventral striatal D2/3 dopamine receptors that may contribute to nicotine dependence.

Pancreatic Endocrine Effects of Dopamine Receptors in Human Islet Cells.

OBJECTIVE: To date, there are no reports on the cellular localization of dopamine receptors in the human pancreas. In our study, we determined the localization and expression of 5 dopamine receptors (D(1), D(2), D(3), D(4), and D(5)) in normal human pancreas tissue. METHODS: Human nonpathological pancreas tissues were fixed with 4% paraformaldehyde, paraffin-embedded, and processed for immunohistochemical analysis to detect dopamine receptors in the human pancreas tissue by using double immunofluorescent labeling and confocal microscopy. RESULTS: We found that the D(1) receptor is present in ß cells; the D(2) receptor is expressed by α, δ, and pancreatic polypeptide cells; the D(4) receptor is expressed by ß and polypeptide cells; whereas the D(5) receptor is expressed only by δ cells. CONCLUSIONS: Our results identify the dopamine receptors (D(1)-D(5)) in normal pancreas tissue and provide a morphological basis for studying the pancreatic endocrine effects of dopamine and suggest a new target for the clinical treatment of diabetes.

Dopamine D2 receptor blocker thioridazine induces cell death in human uterine cervical carcinoma cell line SiHa.

AIM: The aim of this study was to explore the correlation of dopamine D2 receptor (DRD2) and the development of uterine cervical cancer, and the effect of thioridazine (an antagonist of DRD2) on the SiHa cell line. MATERIAL AND METHODS: The expression of DRD2 in tissues was detected with immunohistochemistry. SiHa cells were exposed to different concentrations of thioridazine for 24 h, and then cell viability was determined. After 20-µM thioridazine treatment for 24 h, the protein level of DRD2 in SiHa cells was analyzed by Western blots, apoptosis was detected with the phosphatidylserine externalization and comet assay, and necrosis was detected by measuring high-mobility group box 1 protein (HMGB1). RESULTS: The expression of DRD2 gradually increased from normal to cancer tissues (P < 0.01). In vitro, DRD2 blocker thioridazine treatment resulted in death of SiHa cells with the expression of DRD2 significantly regulated down (P < 0.05), and thioridazine significantly induced SiHa apoptosis (P = 0.016) and necrosis (P < 0.01). CONCLUSION: Higher DRD2 expression is closely associated with cervical cancer progression. After blocking DRD2, SiHa cell growth is significantly suppressed, indicating that DRD2 may function as a novel tumor marker and a potential therapeutic target for cervical cancer.

Detection of antigen interactions ex vivo by proximity ligation assay: endogenous dopamine D2-adenosine A2A receptor complexes in the striatum.

The existence of G protein-coupled receptor (GPCR) dimers and/or oligomers has been demonstrated in heterologous systems using a variety of biochemical and biophysical assays. While these interactions are the subject of intense research because of their potential role in modulating signaling and altering pharmacology, evidence for the existence of receptor interactions in vivo is still elusive because of a lack of appropriate methods to detect them. Here, we adapted and optimized a proximity ligation assay (PLA) for the detection in brain slices of molecular proximity of two antigens located on either the same or two different GPCRs. Using this approach, we were able to confirm the existence of dopamine D2 and adenosine A2A receptor complexes in the striatum of mice ex vivo.

Somatostatin and dopamine receptor interaction in prostate and lung cancer cell lines.

Somatostatin analogues inhibit in vitro cell proliferation via specific membrane receptors (SSTRs). Recent studies on transfected cell lines have shown a ligand-induced formation of receptor dimers. The aim of this study is 1) to evaluate the role of specific ligands in modulating receptor interactions in the androgen-dependent prostate cancer cell line, LNCaP, and in the non-small cell lung cancer line, Calu-6, by co-immunoprecipitation and immunoblot; and 2) to correlate the antiproliferative effect of these compounds with their ability in modulating receptor interactions. In LNCaP, we have demonstrated the constitutive presence of sstr1/sstr2, sstr2/sstr5, sstr5/dopamine (DA) type 2 receptor (D2R), and sstr2/D2R dimers. BIM-23704 (sstr1- and sstr2-preferential compound) increased the co-immunoprecipitation of sstr1/sstr2 and significantly inhibited proliferation (-30.98%). BIM-23244 (sstr2-sstr5 selective agonist) significantly increased the co-immunoprecipitation of sstr2/sstr5, and induced a -41.36% inhibition of proliferation. BIM-23A760, a new somatostatin/DA chimeric agonist with a high affinity for sstr2 and D2R and a moderate affinity for sstr5, significantly increased the sstr5/D2R and sstr2/D2R complexes and was the most powerful in inhibiting proliferation (-42.30%). The chimeric compound was also the most efficient in modulating receptor interaction in Calu-6, increasing the co-immunoprecipitation of D2R/sstr5 and inhibiting cell proliferation (-30.54%). However, behind BIM-23A760, BIM-53097 (D2R-preferential compound) also significantly inhibited Calu-6 proliferation (-17.71%), suggesting a key role for D2R in receptor cross talk and in controlling cell growth. Indeed, activation of monomeric receptors did not affect receptor co-immunoprecipitation, whereas cell proliferation was significantly inhibited when the receptors were synergistically activated. In conclusion, our data show a dynamic ligand-induced somatostatin and DA receptor interaction, which may be crucial for the antiproliferative effects of the new analogues.

Dopamine receptor alterations in female rats with diet-induced decreased brain docosahexaenoic acid (DHA): interactions with reproductive status.

Decreased tissue levels of n-3 (omega-3) fatty acids, particularly docosahexaenoic acid (DHA), are implicated in the etiologies of non-puerperal and postpartum depression. This study examined the effects of a diet-induced loss of brain DHA content and concurrent reproductive status on dopaminergic parameters in adult female Long-Evans rats. An alpha-linolenic acid-deficient diet and breeding protocols were used to produce virgin and parous female rats with cortical phospholipid DHA levels 20-22% lower than those fed a control diet containing adequate alpha-linolenic acid. Decreased brain DHA produced a significant main effect of decreased density of ventral striatal D(2)-like receptors. Virgin females with decreased DHA also exhibited higher density of D(1)-like receptors in the caudate nucleus than virgin females with normal DHA. These receptor alterations are similar to those found in several rodent models of depression, and are consistent with the proposed hypodopaminergic basis for anhedonia and motivational deficits in depression.

Direct effects of prolactin and dopamine on the gonadotroph response to GnRH.

The intrapituitary mechanisms underlying the inhibitory actions of hyperprolactinaemia on the reproductive axis remain unclear. Previous work on primary pituitary cultures revealed combined suppressive effects of prolactin (PRL) and dopamine on the gonadotrophin response to GnRH. However, whether these effects occur directly at the level of the gonadotroph and are accompanied by changes in gene expression is still unresolved. Here, alphaT(3)-1 and LbetaT2 cells were used to investigate the effects of PRL and dopamine on gonadotrophin synthesis and release in gonadotroph monocultures under basal and GnRH-stimulated conditions. PRL receptor and dopamine receptor mRNA expressions were first determined by RT-PCR in both cell lines. Then, PRL and the dopamine agonist bromocriptine (Br), alone or in combination, were shown to block the maximal alpha-subunit and LHbeta-subunit mRNA responses to a dose-range of GnRH. The LH secretory response was differentially affected by treatments. GnRH dose-dependently stimulated LH release, with a 4-5 fold increase at 10(-8) M GnRH. Unexpectedly, PRL or Br stimulated basal LH release, with PRL, but not Br, enhancing the LH secretory response to GnRH. This effect was, however, completely blocked by Br. These results reveal direct effects of PRL and dopamine at the level of the gonadotroph cell, and interactions between these two hormones in the regulation of gonadotrophin secretion. Moreover, uncoupling between LH synthesis and release in both the basal and the GnRH-stimulated responses to PRL and dopamine was clearly apparent.

Correlation of in vitro and in vivo somatotropic adenoma responsiveness to somatostatin analogs and dopamine agonists with immunohistochemical evaluation of somatostatin and dopamine receptors and electron microscopy.

OBJECTIVE AND PATIENTS: Twenty-four pituitary adenomas from acromegalic patients (13 females, 11 males; age range 19-65 yr) were characterized for somatostatin receptor subtype 2A (sst(2A)), dopamine D(2) receptor (D(2)R), GH, and prolactin (PRL) expression by immunohistochemistry, and results correlated with the in vitro and in vivo hormone responses to octreotide and quinagolide. In nine cases, GH and PRL content was further studied by immunoelectron microscopy. RESULTS: Immunoreactivity was semiquantitatively scored as 2 (>50% stained cells), 1 (10-50% stained cells), and 0 (<10% stained cells). Sst(2A) was scored as 2 in 13 cases, 1 in 10, and 0 in one; D(2)R was scored as 2 in 13 cases, 1 in nine, and 0 in 2; GH was 2 in 15 cases and 1 in nine; PRL was 2 in six cases, 1 in 13, and 0 in 5. Sst(2A) was positively correlated with in vitro (P = 0.003) and in vivo (P = 0.006) percent GH suppression by octreotide and with the chronic suppression of IGF-I by somatostatin analogs (P =0.008). D(2)R was positively correlated with in vitro percent GH (P =0.000) and PRL (P =0.005) suppression by quinagolide. Electron microscopy revealed two pure somatotroph adenomas, five somatomammotrophs with a variable coexpression of GH and PRL in the same cells, and two tumors consisting of mixed cell types, which were less sensitive to quinagolide and octreotide. CONCLUSION: Sst(2A) and D(2)R are frequently coexpressed in adenomas from acromegalic patients, and immunohistochemistry may be helpful in characterizing receptor expression in pituitary adenomas to select patients responsive to different treatments.

Striatal D2 receptor availability after shunting in idiopathic normal pressure hydrocephalus.

UNLABELLED: Gait disturbance in idiopathic normal pressure hydrocephalus (iNPH) is reminiscent of parkinsonism. Our recent PET study showed reduction in postsynaptic D(2) receptor binding concomitant with a normality of presynaptic dopamine transporter binding. Here, we investigated the plasticity of D(2) receptor in treating iNPH patients with ventriculoperitoneal (VP) shunting using PET with (11)C-raclopride and discuss the contribution of D(2) receptor to the pathophysiology of iNPH. METHODS: Eight iNPH patients participated in this study. After evaluation of their neuropsychologic abilities, all patients underwent 3-dimensional MRI and quantitative PET measurements twice before and 1 mo after VP shunting. MRI-based morphometric analyses were performed to examine postoperative variations of the ventricles. Estimation of binding potential (BP) for (11)C-raclopride was based on Logan plot analysis. Region-of-interest analysis was used to examine changes in (11)C-raclopride BP in the striatum. A 2-tailed paired t test was used for evaluating changes in PET and MRI parameters between conditions, and correlation analysis was used to investigate clinicopathophysiologic relevance (clinical vs. in vivo findings). RESULTS: Clinical evaluation revealed significant recovery in a 5-m back-and-forth navigation test and an affect test and a mild increase in Mini-Mental State Examination scores after VP shunting. Significant postoperative increases in (11)C-raclopride BP were found in the nucleus accumbens and dorsal putamen, and the increases were significantly associated with emotional (Spearman rank r = 0.66, P < 0.05) and navigational improvement (r = 0.72, P < 0.05), respectively. The (11)C-raclopride BP increase in the striaum as a whole correlated significantly with improvement in general cognitive ability. There was a mild ventricular shrinkage after surgery, albeit there was no correlation of its size with clinical and PET parameters. CONCLUSION: Striatal upregulation of D(2) receptor after VP shunting is associated with amelioration of hypokinetic gait disturbance and anhedonic mentation in iNPH patients, indicating that the effect of VP shunting may reside in noninhibition of functionally suppressed D(2) receptor in the striatum. D(2) receptor responsiveness may indicate a mechanism for iNPH pathophysiology.

Multitracer positron emission tomographic imaging of exogenous gene expression mediated by a universal herpes simplex virus 1 amplicon vector.

To develop efficient and safe gene therapy approaches, the herpes simplex virus type 1 thymidine kinase gene (HSV-1-tk) has been shown to function as a marker gene for the direct noninvasive in vivo localization of thymidine kinase (TK) expression by positron emission tomography (PET) using radiolabeled nucleoside analogues as specific TK substrates. Moreover, the gene encoding dopamine type 2 receptor (d2r) could be used as a PET marker gene using specific radiolabeled receptor binding compounds. Here we describe the quantitative colocalization of d2r and HSV-1-tk gene expression mediated from a universal HSV-1 amplicon vector in a subcutaneous human Gli36dEGFR glioma model by PET. The HSV-1 amplicon vector was constructed using a bicistronic gene cassette to contain (1) the d2r80A mutant, which is able to bind its ligand racloprid but unable to activate downstream signal transduction pathways, and (2) the tk39 mutant with enhanced enzymatic activity toward guanosine analogues fused to the green fluorescent protein gene (tk39gfp) serving as a marker gene in cell culture. After infection of human Gli36dEGFR glioma cells with the HSV-d2r80AIREStk39gfp (HSV-DITG) amplicon vector in cell culture, D2 receptor expression and its targeting to the cell surface were determined by Western blotting and immunolabeling. Vector application in vivo served for quantitative colocalization of d2r80A- and tk39gfp-derived PET signals employing the specific D2 receptor binding compound [(11)C]racloprid and the specific TK39 substrate 9-(4-[(18)F]fluoro-3-hydroxymethylbutyl)guanine. Our results demonstrate that for the range of gene expression studied in vivo, both enzymatic and receptor binding assays give comparable quantitative information on the level of vector-mediated gene expression in vivo. The d2r80A in combination with a specific binding compound passing the intact blood-brain barrier might be an alternative marker gene for the noninvasive assessment of vector-mediated gene expression in the brain using PET.

Strain-specific steroidal control of pituitary function.

We have previously shown that 7B2 null mice on the 129/SvEvTac (129) genetic background die at 5 weeks of age with hypercorticosteronemia due to a Cushing's-like disease unless they are rescued by adrenalectomy; however, 7B2 nulls on the C57BL/6NTac (B6) background remain healthy, with normal steroid levels. Since background exerts such a profound influence on the phenotype of this mutation, we have evaluated whether these two different mouse strains respond differently to high circulating steroids by chronically treating wild-type 129 and B6 mice with the synthetic steroid dexamethasone (Dex). Dex treatment decreased the dopamine content of the neurointermediate lobes (NIL) of 129 mice, leading to NIL enlargement and increased total D(2)R mRNA in the 129, but not the B6, NIL. Despite the decrease in this inhibitory transmitter, Dex-treated 129 mice exhibited reduced circulating alpha-melanocyte-stimulating hormone (alpha-MSH) along with reduced POMC-derived peptides compared with controls, possibly due to reduced POMC content in the NIL. In contrast, Dex-treated B6 mice showed lowered cellular ACTH, unchanged alpha-MSH and beta-endorphin, and increased circulating alpha-MSH, most likely due to increased cleavage of NIL ACTH by increased PC2. Dex-treated 129 mice exhibited hyperinsulinemia and lowered blood glucose, whereas Dex-treated B6 mice showed slightly increased glucose levels despite their considerably increased insulin levels. Taken together, our results suggest that the endocrinological response of 129 mice to chronic Dex treatment is very different from that of B6 mice. These strain-dependent differences in steroid sensitivity must be taken into account when comparing different lines of transgenic or knockout mice.

[Distribution and function of dopamine D1, D2 receptor].

Positron emission tomography (PET) techniques have made it possible to measure changes in target molecular in living human brain. PET can be used to investigate various brain functions such as receptors, transporters, enzymes and various biochemical pathways; therefore, it could be a powerful tool for molecular imaging of functional neurotransmission. Since dopamine is an important molecule for pathophysiology of Parkinson's disease and schizophrenia, we reviewed in vivo imaging studies focusing on dopaminergic transmission. Dopamine D2 receptor occupancy by antipsychotics and it's time-course have been measured using PET. This approach can provide in vivo pharmacological evidences of antipsychotics and establish the rational therapeutic strategy. PET is a powerful tool not only in the field of brain research but also drug discovery. On the other hand Dopamine D1 receptor is highly expressed in the prefrontal cortex, has been implicated in the control of working memory, seeking, craving, reward. We propose that dysfunction of Dopamine D1 receptor signalling in the prefrontal cortex may contribute to the negative symptoms and cognitive deficits seen in schizophrenia and we suggest that Dopamine D1 receptor binding and cerebral blood flow changes in ventral striatum play the important role of cigarette craving.

Dopamine agonist therapy of clinically non-functioning pituitary macroadenomas. Is there a role for 123I-epidepride dopamine D2 receptor imaging?

OBJECTIVE: Clinically non-functioning pituitary adenomas (NFPAs) can express functional dopamine D2 receptors. Therapy with dopamine (DA) agonists may result in a NFPA size reduction. However, DA agonist-sensitive and -resistant NFPAs are clinically indistinguishable. We have studied the correlation between in vivo imaging of D2 receptors using (123)I-epidepride and the radiological response of NFPA to DA in 18 patients. METHODS: Patients were treated with either cabergoline (1-2 mg/week) or quinagolide (150-300 mug/day) for a mean period of 89.7 months (range, 34-187 months). RESULTS: Pituitary uptake of (123)I-epidepride varied from slight uptake classified as grade 0 to very high classified as grade 3. Grade 0 uptake was found in four patients; grade 1 in three; grade 2 in ten, and grade 3 in one. NFPA stabilization or shrinkage with DA agonist therapy showed no significant difference between grade 0, 1, and 2 tumors (mean tumor stabilization or shrinkage: 31, 30, and 36% respectively). However, when we considered a decrease in tumor size ranging from 0 to 20% as tumor stabilization and >20% decrease in tumor size as true shrinkage, one out of four NFPAs with grade 1 uptake, two out of three with grade 1 uptake, and eight out of ten with grade 2 uptake showed tumor shrinkage. CONCLUSION: In conclusion, there is limited clinical usefulness of dopamine D2 receptor imaging for predicting the clinical efficacy of DA agonist in selected patients with NFPAs. DA agonist therapy in NFPAs can result in tumor stabilization and shrinkage.

Low-dose dopamine agonist administration blocks vascular endothelial growth factor (VEGF)-mediated vascular hyperpermeability without altering VEGF receptor 2-dependent luteal angiogenesis in a rat ovarian hyperstimulation model.

No specific treatment is available for ovarian hyperstimulation syndrome (OHSS), the most important complication in infertile women treated with gonadotropins. OHSS is caused by increased vascular permeability (VP) through ovarian hypersecretion of vascular endothelial growth factor (VEGF)-activating VEGF receptor 2 (VEGFR-2). We previously demonstrated in an OHSS rodent model that increased VP was prevented by inactivating VEGFR-2 with a receptor antagonist (SU5416). However, due to its toxicity (thromboembolism) and disruption of VEGFR-2-dependent angiogenic processes critical for pregnancy, this kind of compound cannot be used clinically to prevent OHSS. Dopamine receptor 2 (Dp-r2) agonists, used in the treatment of human hyperprolactinemia including pregnancy, inhibit VEGFR-2-dependent VP and angiogenesis when administered at high doses in animal cancer models. To test whether VEGFR-2-dependent VP and angiogenesis could be segregated in a dose-dependent fashion with the Dp-r2 agonist cabergoline, a well-established OHSS rat model supplemented with prolactin was used. A 100 microg/kg low-dose Dp-r2 agonist cabergoline reversed VEGFR-2-dependent VP without affecting luteal angiogenesis through partial inhibition of ovarian VEGFR-2 phosphorylation levels. No luteolytic effects (serum progesterone levels and luteal apoptosis unaffected) were observed. Cabergoline administration also did not affect VEGF/VEGFR-2 ovarian mRNA levels. Results in the animal model and the safe clinical profile of Dp-r2 agonists encouraged us to administer cabergoline to oocyte donors at high risk for developing the syndrome. Prophylactic administration of cabergoline (5-10 microg/kg x d) decreased the occurrence of OHSS from 65% (controls) to 25% (treatment). Therefore, a specific, safe treatment for OHSS is now available.

Regulation of dense core vesicle release from PC12 cells by interaction between the D2 dopamine receptor and calcium-dependent activator protein for secretion (CAPS).

We identified CAPS1 (calcium-dependent activator protein for secretion) as a D2 dopamine receptor interacting protein (DRIP) in a yeast two-hybrid screen of a human brain library using the second intracellular domain of the human D2 receptor (D2IC2). CAPS1 is an evolutionarily conserved calcium binding protein essential for late-stage exocytosis of neurotransmitters from synaptic terminals. CAPS1 interaction was confirmed for both the long and short isoforms of the D2 receptor, but not with any other dopamine receptor subtype. Interaction between CAPS1 and the D2 receptor was validated using both pulldown and coimmunoprecipitation assays. Deletion mapping localized the D2 receptor binding site to a segment located within the C-terminal region of CAPS1 as well CAPS2. In PC12 cells, CAPS1 and D2 receptors were found to colocalize within both cytosolic and plasma membrane compartments. Overexpression of a truncated D2 receptor fragment caused a significant decrease in K(+)-evoked dopamine release from PC12 cells, whereas no effect on norepinephrine or BDNF release was observed. These results suggest that D2 dopamine receptors may modulate vesicle release from neuroendocrine cells via direct interaction with components of the exocytotic machinery.

Pharmacologic resistance in prolactinoma patients.

Pharmacologic resistance to dopamine agonists is defined here as failure to normalize PRL levels and failure to decrease macroprolactinoma size by >or=50%. Failure to normalize PRL levels is found in about one-quarter of patients treated with bromocriptine and 10-15% of those treated with pergolide or cabergoline. Failure to achieve at least a 50% reduction in tumor size occurs in about one-third of those treated with bromocriptine and 10-15% of those treated with pergolide or cabergoline. The cause of dopamine resistance is primarily a decrease in D(2) receptors but the receptors have normal affinity for dopamine. Treatment approaches for patients resistant to dopamine agonists include changing to another dopamine agonist and increasing the dose of the drug as long as there is continued response to the dose increases and no adverse effects with higher doses. Transsphenoidal surgery is also an option. Clomiphene, gonadotropins, and GnRH can be used if fertility is desired. For those not desiring fertility, estrogen replacement may be used unless there is a macroadenoma, in which case control of tumor growth is also an issue and dopamine agonists are generally necessary. In many patients modest or even no reduction in tumor size may be acceptable as long as there is not tumor growth. Hormone replacement (estrogen or testosterone) may cause a decrease in efficacy of the dopamine agonist so that it must be carried out cautiously. Reduction of endogenous estrogen, use of selective estrogen receptor modulators, and aromatase inhibitors are potential experimental approaches.

Sex differences and repeated intravenous nicotine: behavioral sensitization and dopamine receptors.

The present study examined the sex-dependent expression of behavioral sensitization as well as changes of dopamine (DA) transporters and D1, D2, and D3 receptors following repeated intravenous nicotine administration. Male and female Sprague-Dawley rats were implanted with indwelling jugular catheters, equipped with subcutaneous intravenous injection ports. Rats were habituated to activity chambers for 3 days and were subsequently administered 15-s bolus injections of intravenous nicotine (50 microg/kg/ml) 1/day for 21 days. Animals were placed in activity chambers for 60 min immediately after the 1st and 21st nicotine injection. Observational time sampling was also performed. Brains were subsequently removed and frozen for autoradiographic DA transporter/DA receptor analysis on the afternoon females were in proestrus. With one exception, no robust sex differences were observed for locomotor activity or any rearing measures either during baseline or after initial nicotine injection. Females exhibited markedly more behavioral sensitization of locomotor activity, rearing, duration of rearing, and incidence of observed rearing. There were no sex differences in the number of D1 or D2 receptors. Females exhibited an increased number of DA transporters and decreased D3 receptors in the NAcc, relative to males. Multiple regression analyses suggest that D3 receptors and DA transporters in various striatal and NAcc subregions differentially predicted nicotine-induced behaviors for males and females. Collectively, these findings demonstrate that repeated intravenous nicotine produces sex differences in the expression of behavioral sensitization, and suggest that nicotine-induced changes of DA transporters and D3 receptors are partly responsible for increased behavioral sensitization in female rats.