Tumor Enucleation of Renal Cell Carcinoma in a Solitary Kidney.

We describe the case of a 57 year old man with a solitary kidney after undergoing resection of a Wilm's tumor as a child and a recent left partial colectomy who presents with an incidentally found clinical T1b renal mass. The patient underwent tumor enucleation and had no change in his renal function twelve days after surgery as compared to his preoperative baseline, highlighting the additional nephron-sparing associated with tumor enucleation as compared to partial nephrectomy that includes a gross margin of normal parenchyma.

Plasma protein(s) yields met-enkephalin-related peptides in near-micromolar concentrations when treated with pepsin.

Treatment of animal and human plasmas with pepsin yielded large quantities of immunoreactive methionine5-enkephalin (i-met-ENK). The concentrations measured after pepsin treatment were 0.1-0.5 microM, about 1000 times the normal circulating level of i-met-ENK (0.03-0.3 nM). The reaction was shown to be time and pH dependent and to involve the action of pepsin on a protein(s) of about 65,000 mol wt. Pepsin-generated i-met-ENK from rat plasma gave three major peaks during reverse phase HPLC, one of which (approximately 25% of the total) coeluted with methionine5-enkephalin sulfoxide and also completed in a radioreceptor assay for opiate-related substances. In addition, this material produced met-ENK-like effects on vascular permeability in rat skin and inhibited electrically induced contractions of the isolated guinea pig ileum in a naloxone-sensitive manner. The plasma substrate(s) that yielded i-met-ENK was distinguished from adrenal proenkephalins, since partially purified plasma substrate(s) did not liberate i-met-ENK upon digestion with trypsin and carboxypeptidase B. Although it is possible that these peptides differ from met-ENK in amino acid sequence, the results presented here suggest that met-ENK-related substances might be formed physiologically by the action of a pepsin-related processing enzyme(s) on plasma substrate(s). Such a mechanism would be analogous to that used in the renin-angiotensin system.

Cerebral and ocular hemodynamic effects of sumatriptan in the nitroglycerin headache model.

BACKGROUND AND PURPOSE: Sumatriptan is a selective 5-hydroxytryptamine1d (5-HT1d)-receptor agonist, highly effective in the short-term treatment of migraine headaches. However, the mechanism underlying the action of sumatriptan is not yet completely understood. To further characterize the vascular effects of sumatriptan, we studied the effects on cerebral and ocular circulation in the well-established nitroglycerin headache model. METHODS: In a double-blind, placebo-controlled, randomized, two-way crossover study in 10 healthy male subjects, we administered either placebo plus nitroglycerin or sumatriptan plus nitroglycerin. Blood flow velocity in the middle cerebral artery and the ophthalmic artery, as well as ocular fundus pulsations and systemic hemodynamic parameters, were measured after sumatriptan and placebo and during the following infusion of nitroglycerin. RESULTS: After infusion of nitroglycerin, blood flow velocity in the middle cerebral decreased by -13.3% versus baseline after placebo pretreatment, but by only -2.2% after sumatriptan (treatment effect, +10.8%; p < 0.05). In contrast, sumatriptan had no effect in the ophthalmic artery. Ocular fundus pulsations, which estimate local pulsatile ocular blood flow, were slightly reduced after sumatriptan. Moreover, sumatriptan partially prevented the increase in fundus pulsations during nitroglycerin infusion (treatment effect, -5.4%; p < 0.05). CONCLUSIONS: Sumatriptan prevents the effect of nitroglycerin-induced vasodilation in the middle cerebral artery but not in the ophthalmic artery, which strongly supports the concept that sumatriptan directly vasoconstricts distended basal cerebral arteries. Measurement of ocular fundus pulsations indicates that sumatriptan also has a small vasoconstrictor action on resistance vessels.

In vivo drug-response measurements in target tissues by microdialysis.

To study the suitability of the microdialysis technique for the measurement of target tissue pharmacodynamics in humans, the model compounds theophylline, milrinone, and compound 48/80 were administered locally by means of reversed microdialysis to the interstitial space of skeletal muscle or skin in 24 healthy volunteers. Simultaneously, interstitial concentrations of cyclic adenosine monophosphate (cAMP; as an indicator of phosphodiesterase activity) were measured in skeletal muscle, and interstitial concentrations of histamine (as an indicator of mast cell release) were measured in skin. In muscle, reversed microdialysis with milrinone led to a dose-dependent increase in interstitial cAMP concentrations (n = 8), whereas no significant effect on cAMP was observed for theophylline versus placebo (1.63 +/- 0.53 nmol/L; n = 6), even at local concentrations exceeding those attained after therapeutic doses. In skin, reversed microdialysis with compound 48/80 increased interstitial histamine concentration dose dependently versus placebo (5.99 +/- 2.74 nmol/L; n = 10). From our experiments in human skeletal muscle and skin, we concluded that microdialysis was a suitable technique for the characterization of in vivo drug response at the relevant target site. Extension of these measurements to several other human tissues is readily feasible.

Amphetamine reverses or blocks the operation of the human noradrenaline transporter depending on its concentration: superfusion studies on transfected cells.

Whether amphetamine enhances noradrenergic activity by uptake blockade or a releasing action is still a matter of debate. In order to gain insight into the interaction of amphetamine with the noradrenaline transporter its cDNA was transfected into COS-7 cells (NAT-cells) or cotransfected with the cDNA of the vesicular monoamine transporter (NAT/VMAT-cells); cells were loaded with [3H]noradrenaline, superfused and the efflux analysed for total tritium and [3H]noradrenaline. In NAT-cells amphetamine stimulated [3H]noradrenaline efflux concentration-dependently when added to the superfusion buffer at 0.01, 0.1 and 1 microM. By contrast, 10 or 100 microM amphetamine stimulated efflux to a smaller extent or not at all; however, on switching back to amphetamine-free buffer a prompt increase of efflux was observed. Cocaine did not increase efflux per se and blocked the amphetamine-induced efflux. In NAT/VMAT-cells amphetamine stimulated efflux in a concentration-dependent manner. The effect showed saturation at 1 microM and was not suppressed at higher concentrations. Cocaine also elicited efflux from NAT/VMAT-cells concentration-dependently; the maximum was reached at approximately 1 microM and amounted to only about half of the amphetamine-induced efflux. It is concluded that amphetamine can induce noradrenaline transporter mediated release only at high nanomolar to low micromolar concentrations. At higher concentrations it blocks the noradrenaline transporter; in this case, the releasing action of amphetamine, like that of cocaine, is dependent on a vesicular pool of noradrenaline.

Synthesis of alkyl-substituted arecoline derivatives as gamma-aminobutyric acid uptake inhibitors.

A series of N-methyltetrahydropyridine-3-carboxylic acids and methyl esters have been synthesized and biologically evaluated. Arecoline (6) was lithiated with LDA in THF to give 7, which was treated with various alkyl halides to afford exclusively the alpha-substituted products 8a-g. Thermodynamic reaction of 7 with carbonyl compounds gave the corresponding 5-substituted arecoline derivatives 10a-q. When phenyldiazonium tetrafluoroborate was used as electrophile, 8h and 9 were obtained. The relative stereochemistry of 10j-o was established by 1H NMR spectroscopy. Compound 12 was obtained by condensation of the silylketene acetal 11 with N-acetylindoxyl. Dehydration of 10a-c yielded 14a-c, respectively. Deprotection of the esters 14a, 14c, and 15 followed by chromatography on an ion-exchange resin gave the amino acids 16a, 16c, and 16d. The alcohol 17 was obtained by LiAlH4 reduction of the corresponding ester 14c. The amino acid 16c displayed a marked inhibitory effect on the synaptosomal uptake of gamma-amino[3H]butyric acid ([3H]GABA). The type of inhibition was competitive with a Ki of 12.9 microM. Compound 16d also inhibited [3H]GABA uptake but was about 10 times weaker than 16c. None of the biologically tested compounds (8a-g, 9, 10a-q, 12, 14a-c, 16a-d, 17) showed any effect in binding studies using [3H]GABA as ligand.

In vitro superfusion method for the investigation of nerve-immune cell interaction in murine spleen.

Immune defence mechanisms can be modulated by brain function. To study such interactions, an in vitro method was developed to examine the release of cytokines and norepinephrine (NE) after electrical stimulation. Slices of mouse spleen were placed in chambers with a volume of 80 microliters and superfused with culture medium. To characterize electrically evoked NE release and cell viability a suitable stimulation protocol was developed using of [3H]NE. As parameter for immune function, modulation of interleukin-6 (IL-6) release by the spleen cells brought about by electrical stimulation was investigated. Splenic [3H]NE overflow was calcium-dependent, tetrodotoxin-sensitive and elicited by 54 mM potassium. Electrically evoked [3H]NE release at 22 h was about 80% of the release at 5.3 h. Electrical stimulation substantially reduced IL-6 secretion at 6 h (control: 143.4 +/- 14.3 vs. electrical: 71.3 +/- 7.9 pg/ml/10(6) leukocytes, P = 0.0001). This effect was inhibited in a concentration-dependent manner by the beta-adrenergic antagonist propranolol (P = 0.0298, EC50 approx. 10(-7) M). In conclusion, this new technique allows long-term investigation of cell function in slices of murine spleen. In addition, these are the first in vitro data indicating the presence of a functional neuroimmunological link in murine lymphoid tissue.

Kainic acid induced seizures: changes in somatostatin, substance P and neurotensin.

The neuropeptides somatostatin, neurotensin and substance P were investigated in rats during and after limbic seizures induced by systemic injection of kainic acid (10 mg/kg, i.p.). Three hours after injection of the toxin, pronounced decreases (40-50%) in somatostatin-like immunoreactivity in frontal cortex, striatum, dorsal hippocampus and amygdala/pyriform cortex were observed. Concomitantly, neurotensin-like and substance P-like immunoreactivities were also reduced in the frontal cortex and the hippocampus. These early decreases in peptide levels may result from increased release and subsequent inactivation of the peptides during acute seizures. At later time intervals, 3, 10 and 30 days after injection of kainic acid, the initially decreased peptide levels were partially normalized. However, the reduction in somatostatin-like immunoreactivity in amygdala/pyriform cortex and striatum persisted up to 30 days. Neurotensin-like immunoreactivity remained decreased in the frontal cortex. On the other hand, neurotensin- and substance P-like immunoreactivities were increased in the striatum and substantia nigra 10-30 days after injection of kainic acid. These late changes in peptide levels may suggest destruction of peptidergic neurons or adaptive changes induced by the convulsions. Pretreatment of rats with cysteamine (100 mg/kg, i.p.), an agent which decreases brain somatostatin levels, had no effect on the intensity of kainic acid induced convulsions, although a slightly earlier onset of seizures was observed. The changes in peptide levels, especially the marked decreases in somatostatin content after systemic injection of kainic acid, suggest considerable acute and chronic alterations in peptidergic systems caused by limbic convulsions.

Hypotensive effects of 8-hydroxy-2-(di-n-propylamino)tetralin and 5-methylurapidil following stereotaxic microinjection into the ventral medulla of the rat.

1. The effects of the 5-HT1a receptor agonists 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and 5-methylurapidil (5-MU) on blood pressure and heart rate were investigated in the anaesthetized normotensive rat after local injection into the ventral medulla (medial part of the area of the B1/B3 cell group). 2. Both 8-OH-DPAT and 5-MU, decreased arterial blood pressure and heart rate. Local injection of the alpha 1-adrenoceptor antagonist prazosin did not affect cardiovascular parameters. 3. Subcutaneous injection of the 5-HT1a receptor antagonists spiroxatrine or spiperone inhibited the cardiovascular response to 8-OH-DPAT and 5-MU. 4. Histological examination showed the injection sites which were associated with cardiovascular responses to the agonists to be contained within the medial part of the area of the B1/B3 cell group, corresponding to the region of the nucleus raphe magnus and pallidus. Injections of agonists into adjacent areas had no effect on blood pressure or heart rate. 5. The results support the hypothesis that activation of somatodendritic 5-HT1a autoreceptors located on 5-hydroxytryptaminergic neurones in the ventral medulla of the rat results in a decrease in blood pressure and heart rate. The region of the B1/B3 cell group is suggested as a possible site for the hypotensive action of 5-HT1a receptor agonists.

Central alpha 2-autoreceptors: agonist dissociation constants and recovery after irreversible inactivation.

1. Rats received an intraperitoneal injection of 1.6 mg kg-1 N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) to achieve an irreversible inactivation of presynaptic release-modulating alpha 2-autoreceptors. Cerebral cortex slices were prepared at different times after the injection (24, 48, 96, 192, 336, 774 h), incubated with [3H]-noradrenaline ([3H]-NA), superfused and stimulated electrically with 4 pulses at 100 Hz (= autoinhibition-free condition). Overflow of radioactivity was used to measure release. Furchgott analysis was used to estimate agonist dissociation constants (KA) and pool size of resynthesized receptors (q). 2. The KA values of the three alpha 2-autoreceptor agonists, bromoxidine (UK-14304), clonidine and noradrenaline (NA) were 187 nM, 72 nM, and 1202 nM, respectively. 3. The release-inhibiting effects of the agonists returned considerably faster than the receptor pool. The calculated half-lives for the recovery of the maximal release-inhibiting effects of bromoxidine, clonidine and NA were 30.7, 63.6 and 20.8 h, respectively, whereas the half-life for the recovery of the receptor pool was 445 h. 4. The data indicate a large receptor reserve at presynaptic alpha 2-autoreceptors for the agonists used and validate the use of EEDQ as a tool for the determination of agonist dissociation constants.

Induction by low Na+ or Cl- of cocaine sensitive carrier-mediated efflux of amines from cells transfected with the cloned human catecholamine transporters.

1. COS-7 cells transfected with the cDNA of the human dopamine transporter (DAT cells) or the human noradrenaline transporter (NAT cells) were loaded with [3H]-dopamine or [3H]-noradrenaline and superfused with buffers of different ionic composition. 2. In DAT cells lowering the Na+ concentration to 0, 5 or 10 mM caused an increase in 3H-efflux. Cocaine (10 microM) or mazindol (0.3 microM) blocked the efflux at low Na+, but not at 0 Na+. Lowering the Cl- concentration to 0, 5 or 10 mM resulted in an increased efflux, which was blocked by cocaine or mazindol. Desipramine (0.1 microM) was without effect in all the conditions tested. 3. In NAT cells, lowering the Na+ concentration to 0, 5 or 10 mM caused an increase in 3H-efflux, which was blocked by cocaine or mazindol. Desipramine produced a partial block, its action being stronger at 5 or 10 mM Na+ than at 0 mM Na+. Efflux induced by 0, 5 or 10 mM Cl- was completely blocked by all three uptake inhibitors. 4. In cross-loading experiments, 5 mM Na(+)- or 0 Cl(-)-induced efflux was much lower from [3H]-noradrenaline-loaded DAT, than NAT cells and was sensitive to mazindol, but not to desipramine. Efflux from [3H]-dopamine-loaded NAT cells elicited by 5 mM Na+ or 0 Cl- was blocked by mazindol, as well as by desipramine. 5. Thus cloned catecholamine transporters display carrier-mediated efflux of amines if challenged by lowering the extracellular Na+ or Cl-, whilst retaining their pharmacological profile. The transporters differ with regard to the ion dependence of the blockade of reverse transport by uptake inhibitors.

Parallel secretion of endogenous 5-hydroxytryptamine and histamine from mast cells stimulated by vasoactive peptides and compound 48/80.

The peptides, neurotensin, substance P, somatostatin, and bombesin, several analogues and fragments of neurotensin and compound 48/80, all caused the secretion of both endogenous 5-hydroxytryptamine (5-HT) and histamine. There was no differential effect of any of the secretagogues tested on the secretion of 5-HT and histamine. Amitriptyline prevented the secretion of histamine in response to stimulation by neurotensin, substance P, somatostatin or compound 48/80 but was without effect on the secretion of endogenous 5-HT.

Rapid, agonist-induced desensitization of alpha 2-autoreceptors modulating transmitter release.

1. The release of previously incorporated [3H]-noradrenaline was investigated in cultures of dissociated chick or rat sympathetic neurones and in cerebrocortical slices from neonatal or adult rats. Noradrenaline, in the presence of 10 mumol l-1 of the uptake inhibitor, cocaine, or the selective alpha 2-adrenoceptor agonist, 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK 4,304), was applied for different periods of time in order to detect a possible time-dependence of the alpha 2-adrenoceptor-mediated inhibition of electrically evoked tritium outflow. 2. In chick sympathetic neurones, stimulation-evoked overflow was reduced to 30%, 42%, or 56% of control when noradrenaline (1 mumol l-1) was present for 2, 8, or 16 min, respectively. Likewise, UK 14,304 (1 mumol l-1) present for these periods of time reduced 3H overflow to 35%, 51%, and 53% of control, respectively. Addition of 1 nmol l-1 to 10 mumol l-1 UK 14,304 for either 2 or 16 min did not produce significantly different IC50 values, but the inhibitory effects were smaller with 16 min as compared to 2 min exposure at concentrations > or = 10 nmol l-1. 3. In rat sympathetic neurones, noradrenaline (100 nmol l-1) reduced stimulation-evoked overflow to 33%, 56%, or 57% of control, when present for 2, 8, or 16 min, respectively. Addition of UK 14,304 (1 mumol l-1) for these periods of time caused inhibition to 11%, 41%, and 46% of control. Applying UK14,304 for either 2 or 16 min did not result in significantly different IC5o values, but the inhibition induced by 16 min as compared to 2 min exposure was smaller at concentrations > 10 nmol 1-1.4. In cerebrocortical slices from either neonatal or adult rats, exposure to 0.1 to 1.0 micromol 1-1 UK14,304 for 16 min never caused a smaller inhibition than a corresponding 3 min exposure, although various experimental conditions were investigated.5 The results demonstrate that alpha 2-adrenoceptors which regulate noradrenaline release from sympathetic neurones undergo agonist-induced desensitization within minutes. Such rapid desensitization of alpha 2-autoreceptors was not detected in brain slice preparations.

Immunohistochemical and chromatographic studies of peptides with tachykinin-like immunoreactivity in the central nervous system of the lamprey.

The distribution and chemical properties of compounds with tachykinin-like immunoreactivity (TK-LI) in the spinal cord and brain of lampreys (Lampetra fluviatilis and Ichthyomyzon unicuspis) were investigated by means of immunohistochemistry and various chromatographic methods combined with radioimmunoassay. The distribution of TK immunoreactive fibers in the lamprey spinal cord was investigated with 13 different TK antisera which gave positive staining in pilot experiments. The antisera were raised against substance P (SP) (n = 6), physalaemin (PHY) (n = 1), neurokinin A (NKA) (n = 2), kassinin (KAS) (n = 2) or eledoisin (ELE) (n = 2). Pre-incubation of these antisera with their corresponding TKs abolished or reduced the immunostaining. Four different patterns of distribution were found with the 13 antisera, and they did not seem to be related to the TKs against which the antisera were raised. The different patterns could be explained by assuming the presence of the three different TKs. Six different antisera, raised against SP (n = 2), KAS (n = 2) or ELE (n = 2), were used for radioimmunoassay. The TK-LI material eluted as several separate components in various chromatographic systems. The central nervous system (CNS) of the lamprey did not contain measurable amounts of SP, NKA, neurokinin B (NKB), KAS or ELE. The present data imply that the lamprey CNS contains at least three different TKs probably different from SP, PHY, NKA, NKB, KAS or ELE; these are possibly new, not earlier described TKs. The three hypothetical TKs differ in their distribution.

In vivo synthesis of substance P in the corpus striatum of the rat and its transport to the substantia nigra.

Incorporation of [35S]methionine into substance P in the striatum of the rat and the subsequent transport of the labelled peptide to the substantia nigra has been demonstrated in vivo. After a 4-h infusion of [35S]methionine into the corpus striatum and an additional interval of 4 h radiolabelled substance P was found in the striatum and the substantia nigra of the animals. The criteria for concluding that the labelled product was substance P were: (a) gel chromatography and subsequent ion exchange chromatography of an acetic acid extract of the infused striatum of the ipsilateral substantia nigra yielded a peak of radioactivity co-eluting with endogenous immunoreactive substance P or a sample of synthetic substance P; (b) the radioactive material from this peak also co-chromatographed with synthetic substance P on high-voltage paper electrophoresis or high-pressure liquid chromatography; and (c) bound specifically to the substance antibody. Intracisternal injection of colchicine (70 microgram, i.c.) completely suppressed the appearance of radiolabelled substance P immunoreactive material in the substantia nigra. The data indicate that synthesis of substance P occurs in nerve cell bodies located in the corpus striatum and that substance P is transported to the substantia nigra by a colchicine sensitive mechanism.

Inhibition of vasopressin-stimulated flank marking behavior by V1-receptor antagonists.

Flank marking, a form of olfactory communication displayed by hamsters, is dependent upon vasopressin-sensitive neurons in the anterior hypothalamus. In the present study two vasopressin type-1 (V1) receptor antagonists, d(CH2)5Tyr(Me)AVP and dPTyr(Me)AVP were tested for their ability to block flank marking stimulated by the microinjection of arginine vasopressin (AVP) into the anterior hypothalamus. Dose-response curves were established for AVP and flank marking in the presence or absence of different concentrations of each antagonist. DPTyr(Me)AVP was microinjected into the anterior hypothalamus 1 h before the microinjection of AVP while d(CH2)5Tyr(Me)AVP and AVP were prepared together and delivered as a single microinjection. This procedure was necessary because dPTyr(Me)AVP, but not d(CH2)5Tyr(Me)AVP, had agonist activity when initially injected into the anterior hypothalamus in concentrations ranging from 0.90-900 microM. The ED50 values (microM) for dPTyr(Me)AVP and AVP were 17.9 and 0.90, respectively. The initial agonist activity of dPTyr(Me)AVP was always followed by blocker activity. Both V1-receptor antagonists caused a dose-dependent decrease in AVP-stimulated flank marking. Maximal inhibition of AVP-stimulated flank marking was produced with approximately 1.0 mM of either antagonist. Both antagonists blocked AVP-stimulated flank marking behavior for over 12 h following their microinjection.

Substantial loss of substrate by diffusion during uptake in HEK-293 cells expressing neurotransmitter transporters.

Human embryonic kidney 293 (HEK-293) cells stably transfected with the human serotonin (5-HT) or dopamine transporter (hSERT, hDAT), or the rat GABA transporter GAT-1 were incubated with saturating concentrations of transporter substrates (hSERT: [(3)H]5-HT, [(3)H]N-methyl-phenyl-pyridinium (MPP+); hDAT: [(3)H]dopamine, [(3)H]MPP(+); rGAT: [(3)H]GABA). Uptake velocities decreased significantly over time for [(3)H]5-HT and [(3)H]dopamine (already visible at 1 min), but not for [(3)H]MPP(+) or [(3)H]GABA. In efflux experiments cells were preloaded and substrate diffusion into the medium was studied following the addition of appropriate uptake inhibitors. Fractional effluxes were (% min(-1)) 1.27, 0.72, 0.27 and 0.08 for [(3)H]5-HT, [(3)H]dopamine, [(3)H]MPP(+) and [(3)H]GABA, respectively. The results suggest that in uptake experiments the more lipophilic substrates [(3)H]5-HT and [(3)H]dopamine leave the cells by diffusion already after a short time (1 min) of accumulation.

Electrically induced release of endogenous noradrenaline and dopamine from brain slices: pseudo-one-pulse stimulation utilized to study presynaptic autoinhibition.

Slices of rat hypothalamus (noradrenaline experiments) or rabbit caudate nucleus (dopamine experiments) were prepared, superfused, and field-stimulated using series of monophasic rectangular pulses. Noradrenaline, dopamine and the main dopamine metabolite, dihydroxyphenylacetic acetic acid (DOPAC), were determined using HPLC with electrochemical detection. Electrical stimulation was performed using the following protocols: 1) 4 pulses delivered at 100 Hz; this type of stimulation is referred to as pseudo-one-pulse stimulation (POP); its short duration of only 32 ms does not allow the development of autoinhibition; 2) 2 bursts of 4 pulses at 100 Hz, delivered 1 s apart (2-POP-stimulation); 3) 8 pulses at 1 Hz (dopamine experiments only); 4) 36 pulses at 3 Hz. Noradrenaline experiments. The alpha 2-adrenoceptor antagonist yohimbine (1 mumol/l) did not enhance noradrenaline overflow following POP stimulation, but enhanced the overflow following 2-POP-stimulation by about 50% and that following 36-pulse-stimulation by almost 100%. Dopamine experiments. The D2-dopamine receptor antagonist sulpiride (3 mumol/l) facilitated the overflow of dopamine elicited with 2-POP-stimulation (66%), 8 pulses/1 Hz (92%), and 36 pulses/3 Hz (140%). It did not significantly facilitate the overflow of dopamine following POP-stimulation (19%). The overflow of DOPAC was not, or only slightly, increased by electrical stimulation, and its spontaneous outflow was more than three times higher than that of dopamine. Furthermore, the electrically induced overflow of dopamine did not exceed the outflow of DOPAC at any of the stimulation conditions employed. The results of the present study bear out important claims of the autoreceptor theory and confirm the data obtained in previous experiments using labelled transmitters.

B-HT 920, B-HT 933, and B-HT 958: presynaptic effects on electrically evoked 3H-noradrenaline release from slices of rat brain cortex and hypothalamus.

The effects of the three azepine compounds, B-HT 920 (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]azepine), B-HT 933 [2-amino-6-ethyl-5,6,7,8-tetrahydro-4H-oxazolo[4,5-d]azepine; azepexole] and B-HT 958 (2-amino-6-(p-chloro-benzyl)-4H-5,6,7,8-tetrahydrothiazolo[5,4-d]a zepine) on electrically evoked overflow of 3H-noradrenaline were studied. Slices from parietal cortex (Cx) or nucleus anterior hypothalami (nah) were incubated with 3H-noradrenaline, superfused at 23 degrees C or 37 degrees C in the presence of the noradrenaline uptake inhibitor desipramine (3 mumol/l) and field stimulated at frequencies of 0.3 or 3 Hz. At 37 degrees C/0.3 Hz, B-HT 920 and B-HT 933 concentration-dependently decreased the evoked overflow of tritium in both regions studied, whereas B-HT 958 had no effect. In a second set of experiments each drug was tested under three additional experimental conditions, i.e. 37 degrees C/3 Hz, 23 degrees C/0.3 Hz and 23 degrees C/3 Hz. Increasing the stimulation frequency to 3 Hz or lowering the superfusion temperature to 23 degrees C reduced the effects of B-HT 920 (1 mumol/l) and B-HT 933 (10 mumol/l) as compared to the effects at 37 degrees C/0.3 Hz. When tested at 23 degrees C/3 Hz, both drugs did not significantly affect the evoked overflow of tritium in the Cx or the nah. In contrast, B-HT 958 (10 mumol/l), caused a facilitation of evoked overflow in both regions when the higher stimulation frequency or the lower superfusion temperature was used. Its release-enhancing action was most pronounced at 23 degrees C/3 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Only activated but not non-activated presynaptic alpha 2-autoreceptors interfere with neighbouring presynaptic receptor mechanisms.

Experiments were carried out in rabbit cerebrocortical slices in order to find out whether the attenuation by presynaptic alpha 2-autoreceptors of effects mediated by presynaptic opioid kappa- and adenosine A1-receptors requires activation of the alpha 2-receptors. The slices were preincubated with 3H-noradrenaline and then superfused with medium containing desipramine 1 mumol/l. They were stimulated electrically either with single pulses or with trains of 32 pulses at 1 Hz. The overflow of tritium elicited by a single pulse amounted to 0.21% of the tritium content of the tissue. It was Ca2+-dependent and tetrodotoxin-sensitive and not changed by rauwolscine 1 mumol/l or yohimbine 0.3 mumol/l. Ethylketocyclazocine (EK; 0.1-10 nmol/l) and R-(-)-N6-phenylisopropyladenosine (PIA; 1-1,000 nmol/l) potently inhibited the overflow evoked by a single pulse, and their effects were not changed by yohimbine. - The overflow of tritium elicited by trains of 32 pulses at 1 Hz amounted to 0.92% of the tritium content of the tissue and was increased approximately fourfold by yohimbine 0.3 mumol/l. EK and PIA were less potent inhibitors than in the one pulse experiments. Yohimbine greatly enhanced the effects of EK and PIA. The enhancement was even more pronounced when the Ca2+ concentration in the medium was reduced in order to obtain a control tritium overflow similar to that evoked by 32 pulses in the absence of yohimbine. The results demonstrate that there is no alpha 2-adrenergic autoinhibition when noradrenaline release is elicited by a single pulse. Under these conditions, the non-activated presynaptic alpha 2-adrenoceptor does not interfere with presynaptic opioid kappa- and adenosine A1-receptor mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)