Lack of effect of the dopamine D1 antagonist, NNC 01-0687, on unstimulated and stimulated release of anterior pituitary hormones in males

Dopamine D1 receptor blockage potentiates AMPA-stimulated luteinising hormone release in the goldfish

Previous microarray analyses of the goldfish hypothalamus led us to hypothesise that dopamine could potentially inhibit the excitatory effects of glutamate on luteinising hormone (LH). Post-spawning female goldfish were pre-treated (-4.5 h) with either saline (C; control), SCH 23390 (S; D(1) -receptor antagonist) or sulpiride (L; D(2) -receptor antagonist), followed by an i.p. injection, at -0.5 h, of saline or the glutamate agonist AMPA (A, SA or LA). Blood, hypothalamus and telencephalon tissues were collected. Serum LH was not affected in the S, L, A, or LA groups relative to control as determined by radioimmunoassay. The SA group, however, showed a 289% (P<0.0005) increase in serum LH compared to either treatment alone or control. Real-time reverse transcriptase-polymerase chain reaction identified the mRNAs for ionotropic (Gria2a, Gria4) glutamate receptor subunits, activin βa, isotocin, and cGnRH-II as being significantly affected by some of the treatments. The same experiment conducted with sexually-regressed female fish showed a very different LH profile, indicating that this mechanism is seasonally-dependent. We also show that i.p. injection of 1 μg/g isotocin was able to increase LH levels by 167% in sexually regressed female fish relative to controls. Taken together, these results demonstrate that blockage of the D(1) receptor primes post-spawning goldfish for AMPA-stimulated LH release, and provides further insights into the central regulation of reproduction.

Cortisol hypersecretion in unipolar major depression with melancholic and psychotic features: dopaminergic, noradrenergic and thyroid correlates

Evidence supports that hyperactivity of the hypothalamic-pituitary-adrenal axis has a pivotal role in the psychobiology of severe depression. The present study aimed at assessing hypothalamic-pituitary dopaminergic, noradrenergic, and thyroid activity in unipolar depressed patients with melancholic and psychotic features and with concomitant hypercortisolemia. Hormonal responses to dexamethasone, apomorphine (a dopamine receptor agonist), clonidine (an alpha 2-adrenoreceptor agonist) and 0800 and 2300 h protirelin (TRH) were measured in 18 drug-free inpatients with a DSM-IV diagnosis of severe major depressive disorder with melancholic and psychotic features showing cortisol nonsuppression following dexamethasone and 23 matched hospitalized healthy controls. Compared with controls, patients showed (1) lower adrenocorticotropin and cortisol response to apomorphine (p<0.015 and <0.004, respectively), (2) lower growth hormone response to clonidine (p=0.001), and (3) lower responses to TRH: 2300 h maximum increment in serum thyrotropin (TSH) level (p=0.006) and the difference between 2300 and 0800 h maximum increment in serum TSH values (p=0.0001). Our findings, in a subgroup of unipolar depressed inpatients with psychotic and melancholic features, are compatible with the hypothesis that chronic elevation of cortisol may lead to dopaminergic, noradrenergic and thyroid dysfunction.

Selective alterations of the first NREM sleep cycle in humans by a dopamine D1 receptor antagonist (NNC-687)

This paper details the first study of the effects of dopamine D1 receptor antagonism on the regulation of human sleep EEG (electroencephalogram). The investigational drug NNC-687 (NNC 01-0687/CEE 03-310) was administered to 20 healthy young men in doses of 5, 10, and 15 mg in a double blinded, placebo controlled, crossover design. In rats, dopamine D1 receptor antagonism can produce large increases in the amounts of both rapid eye-movement (REM) and non-rapid eye-movement (NREM) sleep. In this study, drug effects were most prominent in the first NREM period. D1 antagonism markedly reduced the peak-amplitude of delta EEG waves but increased their instantaneous frequency as well as enhancing the total number, incidence, and burst-duration of sleep spindles. The length of the first NREM period was increased up to 47% over baseline. Despite these large increases in NREM sleep time, the amount of delta EEG power accumulated over the first NREM period was conserved at baseline levels. We note that the sleep-EEG profile of D1 antagonism is very similar to that of GABAA (gamma-aminobutyric acid) receptor modulators and suggest that D1 antagonism may alter the properties of the neuronal networks which generate delta and spindle, and K-complex EEG waveforms through the upstream modulation of GABAA receptor activity.