Mesoaccumbens dopamine-opiate interactions in the control over behaviour by a conditioned reinforcer

These experiments examined the role of dopamine-opiate interactions in the ventral tegmental area (VTA) and nucleus accumbens in the mediation of reinforcement-related behaviour. It has been shown previously that opiates induce a dopamine-dependent increase in locomotor activity in rats when infused into the VTA, and a dopamine-independent hyperactivity when infused into the nucleus accumbens. The present study investigated the generality and significance of these two findings, by examining dopamine-opiate interactions in the control over behaviour exerted by a conditioned reinforcer (CR), an arbitrary stimulus which gains control by association with primary reinforcement. Rats were trained to associate a light/noise stimulus with sucrose reinforcement, and the efficacy of the CR in controlling behaviour was assessed by measuring its ability to support a new lever pressing response. Responding on one lever (CR lever) produced the CR, responding on the other lever had no programmed consequences. In experiment 1, intra-accumbens infusions ofd-amphetamine (10 µg), the D₁ dopamine receptor agonist SKF-38393 (0.1 µg), the D₂ dopamine receptor agonist LY-171555 (quinpirole; 0.1 µg) or the opiate receptor agonist [d-Ala²]-methionine enkephalinamide (DALA; 1 µg) selectively increased responding on the CR lever. Infusion with DALA intra-VTA had no effect. However, pretreatment with DALA intra-VTA (10 × 1 µg/day) subsequently reduced the selectivity of the response to infusions intra-accumbens withd-amphetamine or SKF-38393, and blocked the response to LY-171555 or DALA. Pretreatment also shifted to the right the dose-response function for DALA intra-accumbens. In experiment 2, intra-accumbens infusions ofd-amphetamine, SKF-38393, LY-171555 or DALA again increased responding on the CR lever only. Pretreatment with intra-accumbensd-amphetamine (5 × 1 µg/day) reduced the selectivity of the response subsequently tod-amphetamine, and blocked the response to SKF-38393, LY-171555 or DALA. In experiment 3, intra-accumbens infusions of the -opiate receptor agonist [d-Ala²,N-Me-Phe⁴,Gly⁵-ol]-enkephalin (0.003–0.1 µg), or the -opiate receptor agonist [d-Pen^2, 5]-enkephalin (0.03–1 µg) enhanced selectively responding on the CR lever. Thus, the dopamine-dependent locomotor-stimulant properties of intra-VTA infusions of opiates are associated with impaired conditioned reinforcer efficacy. Finally, repeated stimulation of the mesoaccumbens dopamine pathway may compromise the dopamine-independence of the opiate system within the nucleus accumbens.     

Unusual dynamics of killing of cultured lewis lung cells by the DNA-intercalating antitumour agentN-[2-(dimethylamino)ethyl]acridine-4-carboxamide

Summary The cytotoxicity ofN-[2-(dimethylamino)ethyl]acridine-4-carboxamide (AC; NSC 601 316), a new experimental DNA-intercalating antitumour drug, against a cultured Lewis lung adenocarcinoma cell line was compared with that of the DNA-intercalating antitumour drug amsacrine. In contrast to amsacrine, AC demonstrated self-inhibition of cytotoxicity following short (3–9 h) incubation periods and exponential killing (with a shoulder) after long (24–72 h) periods of incubation. The difference between these drugs was best demonstrated using a constant concentration x time (CxT) exposure (AC, 12 mol h l^–1; amsacrine, 3 mol h l^–1). In contrast to amsacrine, AC was minimally effective over exposure periods of 1 h and maximally effective over intermediate periods (4–6 h). The results suggest the possibility of designing AC administration protocols that maximise the drug's cytotoxicity towards solid tumours, which, because of diffusion barriers, are subjected to longer drug exposures than are well-vascularised tumours.Supported by the Auckland Division of the Cancer Society of New Zealand and by the Health Research Council of New Zealand     

A phase I study of SR-4554 via intravenous administration for noninvasive investigation of tumor hypoxia by magnetic resonance spectroscopy in patients with malignancy.

PURPOSE: To perform a Phase I study of SR-4554, a fluorinated 2-nitroimidazole noninvasive probe of tumor hypoxia detected by (19)F magnetic resonance spectroscopy (MRS). EXPERIMENTAL DESIGN: SR-4554 administration, on days 1 and 8, was followed by plasma sampling for pharmacokinetic studies and by three MRS studies performed over 24 h on days 8 and 9. Unlocalized MR spectra were acquired from tumor (10- or 16-cm dual resonant 1H/19F surface coil; 1.5 T Siemens Vision MR system; 2048 transients acquired over 34 min; 1.28-ms adiabatic pulse; repetition time, 1 s). Plasma drug concentrations were measured with a validated high-performance liquid chromatography method. Noncompartmental pharmacokinetic analysis was performed. RESULTS: Eight patients underwent pharmacokinetic studies, receiving doses of SR-4554 of 400-1600 mg/m(2). Peak plasma concentrations increased linearly with the SR-4554 dose (r(2) = 0.80; P = 0.0002). The plasma elimination half-life was relatively short (mean +/- SD, 3.28 +/- 0.59 h), and plasma clearance was quite rapid (mean +/- SD, 12.8 +/- 3.3 liters/h). Urinary recovery was generally high. SR-4554 was well tolerated. A single patient experienced dose-limiting toxicity (nausea and vomiting) at 1600 mg/m(2). The maximum tolerated dose was 1400 mg/m(2). SR-4554 was detected spectroscopically in tumors immediately after infusion at doses of 400-1600 mg/m(2). At the highest dose (1600 mg/m(2)), SR-4554 was detectable in tumor at 8 h, but not at 27 h. CONCLUSIONS: SR-4554 has plasma pharmacokinetic and toxicity profiles suitable for use as a hypoxia probe. It can be detected in tumors by unlocalized MRS. Additional clinical studies are warranted.     

Treatment of localized prostate cancer using a combination of high dose rate Iridium‐192 brachytherapy and external beam irradiation: Initial Australian experience

Combination high dose rate brachytherapy (HDRB) and external beam radiation therapy is technically and clinically feasible as definitive treatment for localized prostate cancer. We report the first large Australian experience using this technique of radiation dose escalation in 82 patients with intermediate‐ and high‐risk disease. With a median follow up of 3 years (156 weeks), complications were low and overall prostate‐specific antigen progression‐free survival was 91% using the American Society for Therapeutic Radiology and Oncology consensus definition. The delivery of hypofractionated radiation through the HDRB component shortens overall treatment time and is both biologically and logistically advantageous. As a radiation boost strategy, HDRB is easy to learn and could be introduced into most facilities with brachytherapy capability.     

Screening for complement deficiency in bacterial meningitis

Seventy-seven children with bacterial meningitis were screened for complement deficiency. Both the classical and the alternate pathways were normal in 75 patients. Transiently reduced total haemolytic activity of the classical pathway was documented in a boy with meningococcal meningitis. Total haemolytic activity of both the classical and the alternate pathways were reduced in another patient with pneumococcal meningitis: individual complement components determination indicated predominant activation of the alternate pathway.     

Dietary fibre and the occurrence of gut symptoms in cystic fibrosis

Accepted 26 October 1996
OBJECTIVE—To evaluate the effect of currently recommended energy rich cystic fibrosis diets on fibre intake and to investigate the relationship between fibre intake and the occurrence of gut symptoms.
METHOD—Prospective completion of non-weighed five day food diaries by 28 children with cystic fibrosis and comparison of mean daily fibre intake with age matched controls who did not have cystic fibrosis. Prospective completion of similar diaries to a total of 68 children with cystic fibrosis and comparison of fibre and lipase intake with the occurrence of gut symptoms.
RESULTS—Mean daily fibre intake in children with cystic fibrosis was 7.00 g compared with 14.65 g in controls (p<0.001). Mean daily fibre intake in eight patients troubled with moderate or severe abdominal pain was 0.144 g/kg. This was significantly lower (p<0.01) than mean values for 22 patients with occasional but mild symptoms (0.249 g/kg) and 38 with no gut symptoms (0.312 g/kg). There was a trend towards higher pancreatic enzyme doses (lipase/kg/day) in children with abdominal pain.
CONCLUSIONS—Currently recommended cystic fibrosis diets have a low fibre content. A low residue diet might be an important factor in the pathogenesis of gastrointestinal symptoms.