Investigation of Mechanical Properties of Twin Wire Arc Repair of Cast Iron Components.

Twin wire arc is a commonly used thermal spray technology for application of steel coatings to cast iron components. Hardness and adhesion strength are critical properties of such coatings, and significant research is available reporting these properties. However, the lamellar structure of the coatings and residual stresses induced during the coating process leads to significantly different behavior in bending applications than in purely tensile applications which are evaluated by the standard adhesion test. In addition, microstructural features that are controlled by certain process parameters during deposition of the coating can have a significant effect on these properties. This work relates the hardness, adhesion strength, and wear resistance to the coating microstructure and assesses the related bending strength and failure mode. Comparisons between bend tests and pull-off adhesion tests show significant differences to consider when designing a twin wire arc coating.

A parallel-arm phase I trial of the humanised anti-IGF-1R antibody dalotuzumab in combination with the AKT inhibitor MK-2206, the mTOR inhibitor ridaforolimus, or the NOTCH inhibitor MK-0752, in patients with advanced solid tumours.

BACKGROUND: Two strategies to interrogate the insulin growth factor 1 receptor (IGF-1R) pathway were investigated: vertical inhibition with dalotuzumab and MK-2206 or ridaforolimus to potentiate PI3K pathway targeting and horizontal cross-talk inhibition with dalotuzumab and MK-0752 to exert effects against cellular proliferation, angiogenesis, and stem cell propagation. METHODS: A phase I, multi-cohort dose escalation study was conducted in patients with advanced solid tumours. Patients received dalotuzumab (10 mg kg(-1)) and escalating doses of MK-2206 (90-200 mg) or escalating doses of dalotuzumab (7.5-10 mg kg(-1)) and MK-0752 (1800 mg) weekly. Upon maximum tolerated dose determination, patients with low-RAS signature, high-IGF1 expression ovarian cancer were randomised to dalotuzumab/MK-2206 versus dalotuzumab/ridaforolimus, whereas patients with high IGF1/low IGF2 expression colorectal cancer received dalotuzumab/MK-0752. RESULTS: A total of 47 patients were enrolled: 29 in part A (18 in the dalotuzumab/MK-2206 arm and 11 in the dalotuzumab/MK-0752 arm) and 18 in part B (6 in each arm). Dose-limiting toxicities (DLTs) for dalotuzumab/MK-2206 included grade 4 neutropenia and grade 3 serum sickness-like reaction, maculopapular rash, and gastrointestinal inflammation. For dalotuzumab/MK-0752, DLTs included grade 3 dehydration, rash, and diarrhoea. Seven patients remained on study for >4 cycles. CONCLUSIONS: Dalotuzumab/MK-2206 and dalotuzumab/MK-0752 combinations were tolerable. Further developments of prospectively validated predictive biomarkers to aid in patient selection for anti-IGF-1R therapies are needed.

Phase II trial of vorinostat in advanced melanoma.

INTRODUCTION: Vorinostat is a small molecule inhibitor of class I and II histone deacetylases with preclinical activity in melanoma. METHODS: We evaluated 32 patients with advanced primary cutaneous or ocular melanoma in a multi-institutional setting (PMH Phase II Consortium) with continuous daily oral vorinostat 400 mg. The primary endpoint was response rate by RECIST, with time to progression as a secondary endpoint. The study was designed to distinguish a response rate of 20 % from a RR of 5 % and to distinguish a 2 month median progression-free survival (PFS), from one of 3.1 months. The study proceeded to stage 2 following 2 of 16 responses.. We also assessed VEGF, FGF levels, P52 polymorphisms and chromatin-associated proteins as potential biomarkers. RESULTS: Therapy was associated with significant side effects, including fatigue, nausea, lymphopenia, and hyperglycemia. Eleven patients experienced at least one grade 3 or higher adverse event. There were two confirmed PRs in patients with cutaneous melanoma. Sixteen patients had stable disease and 14 patients had progressive disease for best response. In addition, two patients with cutaneous melanoma scored as stable disease had early unconfirmed partial responses with subsequent progression. Patients with stable disease or partial response (n = 18) had a median progression free survival of 5 months. (range 2-12 months). CONCLUSIONS: Vorinostat demonstrated some early responses and a high proportion of patients with stable disease, but did not meet its primary endpoint of response. Different schedules of this agent with BRAF mutation status and markers of histone acetylation could be explored in melanoma.

Phase I study of axitinib combined with paclitaxel, docetaxel or capecitabine in patients with advanced solid tumours.

BACKGROUND: Axitinib, a potent and selective second-generation inhibitor of vascular endothelial growth factor receptors, enhanced the efficacy of chemotherapy in human xenograft tumour models. This phase I study investigated the safety, tolerability, pharmacokinetics and antitumour activity of axitinib combined with chemotherapy. METHODS: A total of 42 patients with advanced solid tumours received a continuous axitinib starting dose of 5 mg twice daily (b.i.d.) plus paclitaxel (90 mg m(-2) weekly), docetaxel (100 mg m(-2) every 3 weeks) or capecitabine (1000 or 1250 mg m(-2) b.i.d., days 1-14). RESULTS: Common treatment-related adverse events across all cohorts were nausea (45.2%), hypertension (45.2%), fatigue (42.9%), diarrhoea (38.1%), decreased appetite (33.3%) and hand-foot syndrome (31.0%). There was one complete response, nine partial responses and seven patients with stable disease. Ten patients (23.8%) remained on therapy for >8 months. Paclitaxel and capecitabine pharmacokinetics were similar in the absence or presence of axitinib, but docetaxel exposure was increased in the presence of axitinib. Axitinib pharmacokinetics were similar in the absence or presence of co-administered agents. CONCLUSIONS: Axitinib combined with paclitaxel or capecitabine was well tolerated; no additive increase in toxicities was observed. Antitumour activity was observed for each treatment regimen and across multiple tumour types.

Phase I trial of axitinib combined with platinum doublets in patients with advanced non-small cell lung cancer and other solid tumours.

BACKGROUND: This phase I dose-finding trial evaluated safety, efficacy and pharmacokinetics of axitinib, a potent and selective second-generation inhibitor of vascular endothelial growth factor receptors, combined with platinum doublets in patients with advanced non-small cell lung cancer (NSCLC) and other solid tumours. METHODS: In all, 49 patients received axitinib 5 mg twice daily (b.i.d.) with paclitaxel/carboplatin or gemcitabine/cisplatin in 3-week cycles. Following determination of the maximum tolerated dose, a squamous cell NSCLC expansion cohort was enroled and received axitinib 5 mg b.i.d. with paclitaxel/carboplatin. RESULTS: Two patients experienced dose-limiting toxicities: febrile neutropenia (n=1) in the paclitaxel/carboplatin cohort and fatigue (n=1) in the gemcitabine/cisplatin cohort. Common nonhaematologic treatment-related adverse events were hypertension (36.7%), diarrhoea (34.7%) and fatigue (28.6%). No grade ≥3 haemoptysis occurred among 12 patients with squamous cell NSCLC. The objective response rate was 37.0% for patients receiving axitinib/paclitaxel/carboplatin (n=27) and 23.8% for patients receiving axitinib/gemcitabine/cisplatin (n=21). Pharmacokinetics of axitinib and chemotherapeutic agents were similar when administered alone or in combination. CONCLUSION: Axitinib 5 mg b.i.d. may be combined with standard paclitaxel/carboplatin or gemcitabine/cisplatin regimens without evidence of overt drug-drug interactions. Both combinations demonstrated clinical efficacy and were well tolerated.

A phase II study single agent of aflibercept (VEGF Trap) in patients with recurrent or metastatic gynecologic carcinosarcomas and uterine leiomyosarcoma. A trial of the Princess Margaret Hospital, Chicago and California Cancer Phase II Consortia.

OBJECTIVE: The aim of this multi-institutional non randomized phase II trial was to determine the efficacy and safety of single agent aflibercept (VEGF Trap), a recombinant fusion protein that blocks multiple vascular endothelial growth factor isoforms, in women with gynecologic soft tissue sarcoma. METHODS: Patients were enrolled in two cohorts each with Simon two stage designs: uterine leiomyosarcoma and carcinosarcoma of endometrial, ovarian or fallopian tube origin. Eligibility criteria included ≤2 prior lines of chemotherapy for metastatic disease and ECOG performance status of ≤2. Aflibercept 4mg/kg was administered intravenously on day 1 of a 14 day cycle. Primary endpoints were objective response and disease stabilization (Progression Free Survival (PFS) at 6 months). RESULTS: 41 patients with uterine leiomyosarcoma and 22 patients with carcinosarcoma (19 uterine, 3 ovarian) were enrolled on study. In the leiomyosarcoma cohort, eleven (27%) patients had stable disease (SD), 4 with SD lasting at least 24 weeks. The 6 month PFS was 17%, with median time to progression (TTP) of 1.8 (95% CI:1.6-2.1) months. In the carcinosarcoma cohort, two (9%) patients had SD, one lasting >24 weeks, median TTP was 1.6 months (95%CI: 1.1-1.7) No partial responses were observed in patients from either cohort. Grade 3 or more aflibercept related toxicity was uncommon and included hypertension, fatigue, headache and abdominal pain. CONCLUSIONS: Single agent aflibercept has modest activity in patients with uterine leiomyosarcoma and minimal activity in women with carcinosarcoma.

Electrophysiological comparison of 5-Hydroxytryptamine1A receptor antagonists on dorsal raphe cell firing.

Single-unit recording studies were undertaken in chloral hydrate-anesthetized rats to compare the effects on dorsal raphe cell firing of several putative 5-hydroxytryptamine (HT)1A receptor antagonists, including WAY 100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide), p-MPPI (4-(2-methoxyphenyl)1-[2'-[N-(2"-pyridinyl)-p-iodobenzamido]ethyl] pip erazine), and two newly described 5-HT1A receptor antagonists, NDL-249 [(R)-3-(N-propylamino)-8-fluoro-3, 4-dihydro-2H-1-benzopyran-5-carboxamide] and NAD-299 [(R)-3-N, N-dicyclobutylamino-8-fluoro-3, 4-dihydro-2H-1-benzopyran-5-carboxamide]. Consistent with a 5-HT1A receptor antagonist profile, pretreatment with an approximately equimolar (0.02-0.03 micromol/kg) i.v. dose of each compound caused a significant rightward shift in the dose-response curve for 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin]. Antagonist potency was clearly highest for NAD-299 and WAY 100635, which caused shifts roughly 3 times greater than those for either p-MPPI or NDL-249 (ED50 for 8-OH-DPAT, 1.3 +/- 0.3 microg/kg; after NAD-299, 18.2 +/- 1.0 microg/kg; after WAY 100635, 16.9 +/- 2.9 microg/kg; after NDL-249, 6.0 +/- 1.2 microg/kg; after p-MPPI, 4.7 +/- 1.1 microg/kg). In separate studies, each of the antagonists was administered alone in increasing cumulative doses to evaluate whether they possessed intrinsic agonist activity in this system. At doses below 0.01 micromol/kg, none of the drugs altered firing by more than +/-20% basal rates. At higher doses (>0.1 micromol/kg), WAY 100635, NDL-249, and NAD-299 caused a dose-dependent suppression of dorsal raphe cell firing (ED50 = 0.6 +/- 0.2, 0.7 +/- 0.3, and 0. 9 +/- 0.4 micromol/kg, respectively). However, the ED50 values for inhibition by these drugs were roughly 30 times higher than the doses that antagonized effects of 8-OH-DPAT. Moreover, the inhibition by all three antagonists (but not 8-OH-DPAT) was readily reversed by d-amphetamine (3.2 mg/kg i.v.), a releaser of norepinephrine, suggesting that these effects were likely due to alpha adrenergic receptor blockade rather than to 5-HT1A receptor agonism. Thus, it was concluded that WAY 100635, NAD-299, NDL-249, and p-MPPI all fulfill criteria as 5-HT1A receptor antagonists lacking intrinsic efficacy in the dorsal raphe system. The newly described compound NAD-299 exhibits antagonist potency comparable to that of WAY 100635 in this electrophysiological assay.

Expression of a dopamine D2 receptor-activated K+ channel on identified striatopallidal and striatonigral neurons.

One view of the efferent circuitry of the basal ganglia holds that dopamine D1 and D2 receptors are segregated to striatonigral and striatopallidal neurons, respectively. The present studies investigated whether functional D2-like receptors are, in fact, restricted to striatopallidal neurons. Single, freshly dissociated cells from rat striatum were identified as either striatonigral or striatopallidal projection neurons by fluorescence retrograde labeling. By using cell-attached patch-clamp recordings, neurons of each efferent group were evaluated for the presence of a D2-like receptor-activated 85-pS K+ channel as a measure of receptor function. We now report the presence of this D2 receptor-mediated response on both striatal efferent populations, but we observed an approximately 2-fold higher likelihood of encountering the channel on pallidal- versus nigral-projecting neurons. The channel's conductance properties appeared identical in both groups of neurons, but there was a significantly greater open probability for channels detected on striatopallidal neurons. These results indicate that functional D2 receptors are not segregated to striatopallidal neurons, but may be expressed in a higher proportion of, or at a higher density and/or efficiency of coupling on, pallidal- versus nigral-projecting striatal efferents.

Elongation behavior of calcaneofibular and cervical ligaments during inversion loads applied in an open kinetic chain.

The cervical ligament plays a significant role in lateral stability of the subtalar joint but has received little attention compared with other ankle and subtalar joint ligaments. The purpose of this research was twofold. First, the elongation behavior of the cervical ligament was assessed with the calcaneofibular ligament intact and cut during two different types of inversion loads (manual and mechanical). Second, inversion range of motion was determined concomitantly with inversion loading and the difference in inversion range of motion between the calcaneofibular ligament intact to cut state was compared. The mean elongation of the cervical ligament with the calcaneofibular intact was 0.58 mm (+/- 0.33 mm) and 0.46 mm (+/- 0.23 mm) for manual and mechanical methods, respectively, and 0.88 mm (+/- 0.37 mm) and 0.78 mm (+/- 0.37 mm), respectively, for the same methods in the absence of the calcaneofibular ligament. This difference was statistically significant (P < 0.05 manually and P < 0.02 mechanically). An average increase in the inversion range of motion was noted with both methods [7.5 degrees manually (+/- 2.75 degrees) and 7.7 degrees mechanically (+/- 2.95 degrees)] after lesioning of the calcaneofibular ligament. This difference was statistically significant (P < 0.001) for both manual and mechanical range of motion testing. The results of this study indicate that there is a significant increase in elongation of the cervical ligament in the absence of the calcaneofibular ligament during manual and mechanically applied inversion loads in a open kinetic chain. Clinical and theoretical implications of this data are discussed.

Functional roles of dopamine D2 and D3 autoreceptors on nigrostriatal neurons analyzed by antisense knockdown in vivo.

Two different 19-mer antisense oligodeoxynucleotides complementary to the initial coding regions of dopamine D2 or D3 receptor mRNA were infused unilaterally into the substantia nigra of rats for 3-6 d to suppress synthesis of D2 and/or D3 receptors on substantia nigra dopaminergic neurons, thereby producing specific reductions of D2 and/or D3 receptors. Autoradiographic receptor binding revealed that D2 and D3 antisense oligodeoxynucleotides specifically and significantly reduced D2 or D3 binding in the ipsilateral substantia nigra, respectively, without affecting dopamine receptor binding in the neostriatum. Either D2 or D3 antisense oligodeoxynucleotides greatly attenuated the ability of apomorphine to inhibit dopaminergic neurons in vivo, an effect that was potentiated by simultaneous administration of D2 and D3 antisenses. Despite these effects, neither the rate nor the pattern of spontaneous activity of antisense-treated nigrostriatal neurons differed from those in the control groups. The proportion of antidromic responses consisting of full spikes from antisense-treated rats was significantly greater, and the mean antidromic threshold was significantly lower than in controls, indicating that autoreceptor knockdown increased both somatodendritic and terminal excitability. These data demonstrate that selective reduction of specific dopamine receptor subtypes by antisense infusion can be effected in vivo, and that nigrostriatal neurons express both D2 and D3 autoreceptors at their somatodendritic and axon terminal regions. Although the somatodendritic and terminal autoreceptors modulate dendritic and terminal excitability, respectively, the interaction of endogenously released dopamine with somatodendritic autoreceptors does not appear to exert a significant effect on spontaneous activity in anesthetized rats.

Dopamine D2, receptor-mediated modulation of the GABAergic inhibition of substantia nigra pars reticulata neurons.

Neurons of the substantia nigra pars reticulata can be readily and fully inhibited by endogenously released or iontophoretically applied GABA. We have previously shown that co-application of dopamine or the D2-like agonist quinpirole causes a current-dependent attenuation of the inhibitory response of these neurons to GABA. To determine if the modulation of GABA responsiveness was mediated by activation of D2 receptors, effects of iontophoretic quinpirole were examined after various treatments which block or inactivate D2 receptors, or uncouple D2 receptors from their G-proteins. Results showed that the GABA-attenuating effect of quinpirole could be attributed to stimulation of D2 receptors, and not a non-specific effect of the drug, since (1) co-iontophoresis of the D2 antagonist YM 09151-2 antagonized the GABA-modulatory effect of quinpirole, (2) prior intranigral injection of the receptor inactivator N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ; 50 nmol/0.5 ml one day before recording) prevented the response to quinpirole, and (3) prior intranigral injection of the Gi-Go-protein inactivator pertussis toxin (1 mg/ml 0.9% NaCl 24 h before recording) completely abolished the ability of quinpirole to lessen the inhibitory response to GABA. The location of the involved D2 receptors was examined using selective lesioning approaches. Kainic acid lesions of the striatonigral pathway did not prevent the ability of quinpirole to attenuate responses of pars reticulata neurons to GABA. Similarly, in previous studies [59], 6-hydroxydopamine lesions of the adjacent pars compacta dopamine neurons were found not to abolish the GABA-attenuating effect of dopamine. Thus, it appears that the receptors mediating the response are not localized to either striatonigral terminals nor to the adjacent dopamine neurons, leaving open the possibility that the response is mediated by D2 receptors located on pars reticulata neurons. Collectively these results suggest that dendritically released dopamine may act via nigral D2 receptors, perhaps located on pars reticulata neurons themselves, to regulate basal ganglia output from the substantia nigra.

GABAA receptor-mediated inhibition of rat substantia nigra dopaminergic neurons by pars reticulata projection neurons.

Evidence from electrophysiological studies has suggested an inhibitory interaction between GABAergic neurons in substantia nigra pars reticulata and dopaminergic neurons in pars compacta. However, that this inhibitory interaction is due to a projection from pars reticulata to pars compacta has never been demonstrated directly, nor has the GABAergic neuron that mediates the interaction been identified either electrophysiologically or anatomically. To more closely examine interactions between substantia nigra pars reticulata GABA neurons and dopaminergic neurons, single unit extracellular recordings were obtained from antidromically identified nigrostriatal neurons and their response to antidromic activation of nigral GABAergic projection neurons observed. Stimulation of superior colliculus or thalamus produced a short latency inhibition of dopaminergic neurons. This inhibition was blocked by local application of bicuculline but not 2-hydroxysaclofen. Bicuculline caused most dopaminergic neurons to fire in a bursty mode, whereas saclofen caused most dopaminergic neurons to fire in a pacemaker-like mode. The thalamic-evoked inhibition was not affected by kainate lesions of the globus pallidus, but these lesions produced effects on firing pattern identical to those produced by saclofen. These data demonstrate a short latency inhibition of nigral dopaminergic neurons mediated by GABAA receptors that arises from the axon collaterals of pars reticulata projection neurons. We propose a model in which the firing pattern of nigral dopaminergic neurons in vivo is modulated differentially by disinhibition of GABAA inputs arising from pars reticulata projection neuron axon collaterals and disinhibition of pallidonigral GABAergic inputs mediated by GABAB receptors.

D1 agonist-induced excitation of substantia nigra pars reticulata neurons: mediation by D1 receptors on striatonigral terminals via a pertussis toxin-sensitive coupling pathway.

Iontophoresis of dopamine or the D1 agonist SKF 38393 has been shown to elicit current-dependent increases in the firing of rat substantia nigra pars reticulata neurons, suggesting a discrete physiological role for the D1 dopamine receptor population in the substantia nigra. The effects of SKF 38393 differed from those of dopamine, however, in that the D1 agonist also augmented inhibitory responses to applied GABA, whereas dopamine and D2-like agonists were previously found to attenuate responses to GABA. The present studies involved various manipulations of the nigral D1 receptors in order to examine the pharmacological specificity, receptor localization, and second messenger coupling underlying the D1 agonist response. The excitatory and GABA-potentiating effects of SKF 38393 were found to be attributable to D1 receptor stimulation, rather than a nonspecific action, since (1) the effect was mimicked by iontophoresis of A-68930, a D1 agonist of a different structural class than SKF 38393, and (2) the response to SKF 38393 was prevented by intranigral injection of the receptor inactivator N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ; 50 nmol/0.5 microliter) 1 d before, or the D1 antagonist SCH 23390 (1 microgram/microliter) 1 hr before electrophysiological testing. Additional studies revealed that the involved D1 receptors were located presynaptically on striatonigral terminals. For instance, in rats given ipsilateral striatal kainic acid lesions 1 week earlier, application of SKF 38393 failed to elicit the usual increases in cell firing, but loss of the response was observed only among the group of pars reticulata neurons that were shown to be unresponsive to striatal stimulation (i.e., those whose striatonigral inputs had been terminated by the lesion). Finally, to examine the second messenger coupling characteristics of the involved D1 receptors, several membrane-permeable analogs of cAMP were tested iontophoretically in place of SKF 38393. Surprisingly, none of these compounds gave a pattern of response typical of the D1 agonist, raising questions about the involvement of cAMP. Even more suggestive of an unconventional D1 coupling pathway, the excitatory and GABA-potentiating effects of applied SKF 38393 were completely abolished by prior intranigral injection of the G(i)/G(o) protein inactivator, pertussis toxin. Collectively, these results suggest that stimulation of D1 receptors on striatonigral terminals causes an excitation of substantia nigra pars reticulata neurons with an exaggerated responsiveness to GABA, and the effects appear to be mediated by a pertussis toxin-sensitive (i.e., a non-G-like) G-protein and possibly a second messenger other than cAMP.

Behavioural, biochemical and electrophysiological studies on the motor depressant and stimulant effects of bromocriptine.

Bromocriptine (BRC) produced a biphasic behavioural effect in mice; an early depressant phase which lasted for about 1 h and a later stimulant phase which lasted from about 1 to 5 h. The stimulation was blocked with SCH23390. Both phases of activity were accompanied by marked striatal DA autoreceptor effects as indicated by reductions in dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels and by a reduction in the accumulation of DOPA (after inhibition of nigrostriatal DA nerve firing and DOPA decarboxylase). However, while the autoreceptor effects were still evident during the behavioural stimulant phase, there was a gradual rise in DOPAC and HVA from 1 to 4 h after injection, indicating a gradually increasing DA turnover. We were unable, using a variety of behavioural and biochemical paradigms, to demonstrate any change in DA autoreceptor sensitivity after one dose of BRC. In electrophysiological studies, however, it was found that prior exposure of rats to one dose of BRC rendered them subsensitive to the rate-inhibiting effects of a second dose of BRC, as measured in anaesthetized animals using extracellular single cell recordings of identified DA neurons in the substantia nigra pars compacta. It is concluded firstly, that the stimulant phase of BRC in mice occurs despite continued occupation of the DA autoreceptors by BRC because adequate endogenous DA is available to provide the required D1 receptor stimulation and secondly, that the terminal autoreceptors in the striatum (as assessed in mice using biochemical techniques) may be regulated differently to the somatodendritic autoreceptors (as assessed electrophysiologically in rats).

Efficacy and potency comparisons among aporphine enantiomers: effects on dopamine neurons in substantia nigra of rat.

Extracellular single unit recording studies were carried out on male rats to determine the responses of dopamine neurons of the substantia nigra to intravenous administration of the enantiomers of the aporphine congeners, apomorphine (APO), N-n-propylnorapomorphine (NPA) and 11-hydroxy-N-n-propylnorapomorphine (11-OH-NPa). The R-(-)-configuration was found to be the most critical determinant of the efficacy and potency of the agonists. All R-(-)-aporphines were full agonists, able to inhibit completely firing of dopamine cells. The order of potencies, defined by the ID50s, was: (-)NPA, 2.0 +/- 0.4 nmol/kg greater than (-)11-OH-NPa, 4.7 +/- 0.7 nmol/kg greater than (-)APO, 18.0 +/- 4.0 nmol/kg. Thus, potency was increased about 9-fold by replacing the 6N methyl of APO with an n-propyl (NPA). Conversely, the 10-hydroxy was not essential for agonist activity (11-OH-NPa) but could increase potency. In the S-(+)-series responses varied. (+)N-n-Propylnorapomorphine exhibited agonist properties and could fully inhibit dopamine cells, but its potency was low (ID50 1550 nmol/kg); (+)APO produced only slight but significant decreases in firing at large (8434 nmol/kg) doses and (+)11-OH-NPa was devoid of efficacy in that it caused no significant changes in firing. Despite their loss of efficacy and potency, the (+)-enantiomers apparently did retain affinity for DA receptors, since they could act as antagonists if given before (-)APO or NPA. These findings suggest that stereochemical conformation and key structural elements of the aporphines are interactive in determining agonist efficacy and potency within this physiological test system.