Adenoviral vector-mediated gene transfer and neurotransplantation: possibilities and limitations in grafting of the fetal rat suprachiasmatic nucleus

Several studies have reported on the use of primary neural cells transduced by adenoviral vectors as donor cells in neurotransplantation. In the present investigation, we examined whether adenoviral vector-mediated gene transfer could be used to introduce and express a foreign gene in solid neural transplants of fetal suprachiasmatic nucleus (SCN) tissue. A recombinant adenoviral vector containing the reporter gene LacZ encoding for beta-galactosidase (Ad-LacZ) was used in order to establish the optimal procedure for ex vivo gene transfer. Expression of beta-galactosidase was dependent on the duration of the infection and on the vector concentration. Infection for a short period (< 4 h) with a high concentration of Ad-LacZ (3.4 x 10(9) pfu/ml), or for 18 h with a lower vector concentration (2 x 10(8) pfu/ml), resulted in expression of beta-galactosidase in a large number of neurons and glial cells up to 21 days in vitro. When infected fetal SCN tissue was implanted in the third ventricle of adult Wistar rats, expression was high after 8 days. After 21 days, the number of beta-galactosidase expressing cells had clearly declined, but expression remained present for at least 70 days. The method described in this paper might be applicable to introduce trophic factor genes in SCN grafts in order to support graft survival and to stimulate neurite outgrowth.

Synthesis and in vitro and in vivo characteristics of an iodinated analogue of the beta-adrenoceptor antagonist carazolol

A new (radio)iodinated, beta-adrenoceptor ligand, (S)-(-)-4-[3-[(1,1-dimethyl-3-iodo-(2E)-propenyl)-amino]-2- hydroxypropoxy]carbazole (CYBL8E, 1), was prepared. 1 is an iodinated analogue of the high-affinity beta-adrenoceptor antagonist carazolol (2). The asymmetric synthesis was achieved in four steps starting from 4-hydroxycarbazole. The iodine-123-labeled form was obtained by an iododestannylation reaction with [123I]NaI in the presence of H2O2. Using classical in vitro displacement experiments with membrane fractions of cardiac left ventricular muscle, 1 proved to have a high affinity for the receptor (Ki = 0.31 +/- 0.03). Biodistribution studies performed in New Zealand white rabbits demonstrated the specificity of the binding in vivo to the receptor. Uptake of [123I]1 was reduced significantly in both atrial muscle, left ventricular muscle, frontal cortex, cerebellum, and striatum, by the pretreatment of the animals with different beta-adrenoceptor antagonists. In conclusion, 1 is a potent nonselective beta-adrenoceptor antagonist, which binds specifically to the beta-adrenoceptor in vivo, and is therefore a promising radioligand for the imaging of beta-adrenoceptors using single photon emission computerized tomography.

Cardiac iodine-123 metaiodobenzylguanidine uptake in animals with diabetes mellitus and/or hypertension

The aim of the present study was to evaluate the use of the noradrenaline analogue iodine-123 metaiodobenzylguanidine ([123I]MIBG) for the assessment of cardiac sympathetic activity in the presence of diabetes mellitus and/or hypertension in animal models. One model used Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) rendered diabetic at 12 weeks of age by an intravenous injection of streptozotocin (STZ). The other model used lean and obese Zucker rats. In all groups basic haemodynamic values were established and animals received an intravenous injection of 50 microCi [123I]MIBG. Initial myocardial uptake and wash-out rates of [123I]MIBG were measured scintigraphically during 4 h. After sacrifice, plasma noradrenaline and left cardiac ventricular beta-adrenoceptor density was determined. The diabetic state, both in STZ-treated rats (direct induction) and in obese Zucker rats (genetic induction), appeared to induce a lower cardiac density of beta-adrenoceptors, indicative of increased sympathetic activity. Cardiac [123I]MIBG then showed increased wash-outs, thereby confirming enhanced noradrenergic activity. This parallism of results led to the conclusion that [123I]MIBG wash-out measurements could provide an excellent tool to assess cardiac sympathetic activity non-invasively. However, in hypertension (WKY vs SHR), both parameters failed to show parallelism: no changes in beta-adrenoceptor density were found, whereas [123I]MIBG wash-out rate was increased. Thus, either [123I]MIBG washout or beta-adrenoceptor density may not be a reliable parameter under all circumstances to detect changes in the release of noradrenaline. Changes in the initial uptake of [123I]MIBG were observed as well. This may be a good marker for the disappearance of cardiac innervation, but it seems not to be a good parameter for distinguishing between loss of sympathetic innervation and enhanced uptake of noradrenaline in pathological conditions.

In vitro and in vivo characterization of newly developed iodinated 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]piperazine derivatives in rats: limited value as dopamine transporter SPECT ligands

A series of 1-{2-[bis(4-fluorophenyl)methoxy]ethyl}piperazines (CYD1, 2, 3, 5) with a 4-substituent incorporating a 1-hydroxy-3-iodo-2-propenyl moiety, except CYD2 which lacks the hydroxy, was synthesized as potential in vivo imaging ligands for the dopamine transporter. For two of the piperazine derivatives (CYD3 and 5), possible stereoselectivity was considered as well (both E- and Z-form). Their in vitro potency for inhibition of [3H]dopamine uptake in rat striatal synaptosomes was 10-fold lower than that of GBR 12,909 used as a reference. The highest Ki values were 137 and 101 nM for CYD1E and CYD3E, respectively. Inhibition potency was higher for the E- than for the Z-isomers. In vivo distribution of radioactivity in rats injected with the 123I-labeled CYDs showed preferred striatal uptake for CYD1E and CYD3E as compared to the cerebellum and occipital cortex. Although the E-isomer of CYD3 showed the best in vitro and in vivo binding characteristics, its striatal uptake ratios (maximal value: 2.7 for striatum-to-cerebellum at 4 h p.i.) are too low to consider application in human Single Photon Emission Computed Tomography studies.

Developmental changes in NMDA-induced cell swelling and its transition to necrosis measured with 1H magnetic resonance imaging, impedance and histology

The vulnerability of the rat brain to intracerebrally injected N-methyl-D-aspartate (NMDA) drastically changes with age. We evaluated the developmental changes in the early and late responses to NMDA using 1H magnetic resonance imaging (MRI), cortical impedance and histology. NMDA, injected in the striatum of rats at postnatal days (P) 4, 7, 10, 14 and 21, induced a significant age-dependent reduction in the apparent diffusion coefficient (ADC) of tissue water in the striatum and the cerebral cortex monitored 1 h later using diffusion-weighted MRI. The reduction in ADC amounted 65% at P4 with lower values thereafter and was about 30% at P21. NMDA similarly induced a reduction in the cortical extracellular space (by 50% at P7 and 10% at P16) as measured with impedance recordings. The progressive decrease in the effect of NMDA with brain development was also indicated by a decrease in the volume of tissue in which the changes in ADC occurred (50 mm3 at P4 and 8 mm3 at P21). The diffusion of extracellular tracer molecules Mn2+ or [3H]-(R)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) injected in the striatum and monitored with T1-weighted MRI and autoradiography respectively showed a similar age dependence with the diffusion volume being twofold larger in P7 than in P21 brain. Thus restriction in diffusion during brain development may contribute to the decrease in NMDA-induced injury with age. The volume of tissue necrosis and gliosis, measured with T2-weighted MRI and histology 5 days after NMDA injection, was similar to that outlined by the ADC reduction detected soon after the insult at P4, P7 and P21. However, at P10 and P14 only 50% of the tissue showing a hyperintense signal in DW images displayed necrosis and gliosis 5 days later. This study shows that during development the early response to NMDA in terms of cytotoxic cell swelling (indicated both with impedance recordings and diffusion-weighted MRI) decreases with age. In addition, with maturation only part of the brain tissue acutely affected by NMDA does proceed into necrosis and gliosis, indicating an increased capacity of cells in the developing rat brain to survive NMDA-induced cell swelling.

Pharmacologic characterization in vitro and in vivo of iodine 123-labeled derivatives of the beta-adrenoceptor antagonist CGP12177, designed for the imaging of cardiac beta-receptors

BACKGROUND

Potential new radioligands for the noninvasive imaging of cardiac beta-adrenoceptors with single-photon emission computed tomography were investigated.

METHODS AND RESULTS

Two iodinated derivatives of CGP12177 para (S-CYBL2B) and ortho (CYBL2A) substituted CGP12177 and an iodinated form of nadolol (CYBL1) were synthesized. Their affinity was tested in vitro (left ventricular homogenates). The biodistribution of [123I]S-CYBL2B was evaluated in rabbits. Specific binding was assessed by pretreatment of the animals with 0.1 mumol propranolol. The inhibition constant values (in nanomolars, means +/- SEM; n = 3 to 5) were determined at 1.17 +/- 0.42, 28800 +/- 9260, 11.1 +/- 2.1, 53.0 +/- 19.9, and 1790 +/- 700 for CGP12177, CYBL2A, S-CYBL2B, nadolol, and CYBL1. Myocardial uptake of [123I]S-CYBL2B was not inhibited by pretreatment of the animals with propranolol, but uptake by lung tissue could be blocked by propranolol (0.63% +/- 0.09% vs 0.33% +/- 0.02% % injected dose/g x kg; p < 0.05). In isolated right atria, preincubation with S-CYBL2B induced a parallel rightward shift of the concentration-response curve with isoprenaline.

CONCLUSIONS

S-CYBL2B shows high affinity for cardiac beta-adrenoceptors, but binding proved nonspecific in vivo, whereas binding in lung tissue was specific. These results suggest that S-CYBL2B is probably not a suitable radioligand for receptor imaging.

The stereoisomers of 17alpha-[123I]iodovinyloestradiol and its 11beta-methoxy derivative evaluated for their oestrogen receptor binding in human MCF-7 cells and rat uterus, and their distribution in immature rats

We studied the potential of both stereoisomers of 17alpha-[123I]iodovinyloestradiol (E- and Z-[123I]IVE) and of 11beta-methoxy-17alpha-[123I]iodovinyloestradiol (E- and Z-[123I]MIVE) as suitable radioligands for the imaging of oestrogen receptor(ER)-positive human breast tumours. The 17alpha-[123I]iodovinyloestradiols were prepared stereospecifically by oxidative radio-iododestannylation of the corresponding 17alpha-tri-n-butylstannylvinyloestradiol precursors. Competitive binding studies were performed in order to determine the relative binding affinity (RBA) of the unlabelled 17alpha-iodovinyloestradiols for the ER in both human MCF-7 breast tumour cells and rat uterine tissue, compared with that of diethylstilboestrol (DES). Target tissue uptake, retention and uptake selectivity of their 123I-labelled analogues were studied in immature female rats. All four 17alpha-iodovinyloestradiols showed high affinity for the ER in human MCF-7 cells, as well as rat uterus. Their RBA for the ER showed the following order of decreasing potency: RBA of DES >Z-IVE >Z-MIVE >E-MIVE > or =E-IVE. Neither of these 17alpha-iodovinyloestradiols showed any significant binding to the sex hormone binding globulin in human plasma. The biodistribution studies showed ER-mediated uptake in the uterus, ovaries and pituitary, that of E- and Z-[123I]MIVE being higher than that of E- and Z-[123I]IVE. High target-to-non-target tissue uptake ratios, especially at longer periods after injection (up to 24h), were exhibited by both isomers of [123I]MIVE. The uterus-to-blood uptake ratio was higher for E-[123I]MIVE. However, the uterus-to-fat uptake ratio appeared to be higher for the Z-isomer of [123I]MIVE, especially at 24h after injection. Metabolic properties and temperature effects, which play a more important role in vivo, probably cause the discrepancies seen between in vitro and in vivo binding results. On the basis of their in vitro binding properties and in vivo distribution characteristics we conclude that E- and Z-[123I]MIVE could be suitable radioligands for the diagnostic imaging of ER in human breast cancer. Therefore, further studies with these radioligands in mature normal and tumour-bearing rats are warranted.

Increase in vasopressin binding sites in the human choroid plexus in Alzheimer's disease

Vasopressin binding sites were determined in the choroid plexus of five Alzheimer's disease patients and five non-demented controls using the 125I-labelled linear V1a-antagonist. The Alzheimer's disease patients showed a twofold increase in the density of vasopressin binding sites, whereas the increase in the affinity constant Kd did not reach significance.

Treatment with NMDA receptor antagonists does not affect developmental changes in NMDA receptor properties in vivo

Effects of acute and long-term treatment of neonatal rats with N-methyl-D-aspartate (NMDA) receptor antagonists on changes in NMDA receptor properties were examined. Animals received either on postnatal day 6 a single dose of the antagonists MK-801 (1 mg/kg), or D-CPPene (2 mg/kg) or during the period from postnatal day 5 to 14, two daily injections of MK-801 (0.25 mg/kg) or D-CPPene (0.75 mg/kg). Control littermates received saline injections. In both cases animals were sacrificed one day after the last injection. NMDA receptor properties were examined in membrane preparations derived from the cerebral cortex by studying the modulation of [3H]MK-801 binding by glutamate, Mg2+ and D-CPPene. The density of agonist- and antagonist-binding sites in the CA1 region of the hippocampus were determined by autoradiography, using [3H]CGP39653 or [3H]glutamate as ligands. A significant developmental increase in NMDA receptor binding sites was detected both in preparations of cerebral cortical membranes and in the CA1 area of the hippocampus. In addition, the Mg2+ sensitivity of [3H]MK-801 binding was significantly higher in membrane preparations from the cerebral cortex of postnatal day 15 compared to postnatal day 7 animals. Neither the single nor the subchronic treatment with NMDA receptor antagonists exerted a significant influence on the density of antagonist binding sites or on the modulation of [3H]MK-801 binding by glutamate, Mg2+ or D-CPPene. We conclude therefore that neonatal treatment with NMDA receptor antagonists in vivo does not involve significant alterations in the properties and the densities of NMDA receptors in the brain regions studies, i.e., during the period when expression of these receptors is subject to pronounced developmental regulation.

Agonist-induced down-regulation of NMDA receptors in cerebellar granule cells in culture

In contrast to the acute toxic effect of NMDA on mature cerebellar granule cells, chronic treatment with NMDA (140 microM from 1 to 9 days in vitro) did not compromise cell survival. Such treatment markedly suppressed NMDA receptor activity: at 8 days in vitro NMDA-induced 45Ca2+ influx was reduced by approximately 60% and acute exposure to NMDA (highest concentration tested, 1 mM) at 9 days in vitro did not cause detectable toxicity. The reduction in NMDA receptor activity was accompanied by a significant decrease (approximately 80% at 9 days in vitro) in the level of the NR1 and the NR2A NMDA receptor subunit protein, detected using the selective photoaffinity ligand [125I]CGP55802A. It seems, therefore, that the agonist-induced decrease in NMDA receptor activity is due to receptor down-regulation. In contrast to the marked influence of chronic NMDA exposure on the cellular content of the NMDA receptor subunit proteins, mRNA levels of the different subunits (NR1, NR2A, NR2B and NR2C) were not significantly affected. It seems, therefore, that agonist-induced down-regulation of the NMDA receptor involves critically mRNA translation and/or post-translational regulation.

Development and isoproterenol-induced regulation of adrenoceptor binding in cultured rat neocortical explants is seen only with the beta-1, not with the beta-2 subtype

The presence and time-course of beta-adrenoceptor density in cultured explants of neocortex obtained from 6-day-old rat pups were investigated using a [125I]ICYP binding assay. A delayed, but more pronounced, increase in the receptor expression was observed as compared to the situation previously described in vivo. These changes only occurred for the beta 1-subtype of the receptor, whereas the beta 2-subtype binding remained constant up to 3 weeks in vitro. The delay of beta 1-adrenoceptor expression may be due to the incomplete presence of the proper maturational input, and the late enhancement of receptor expression to upregulation related to the absence in vitro of noradrenergic input. Decreased beta-adrenoceptor levels could be induced by chronic treatment of the beta-agonist isoproterenol (1 microM) introduced either for 3 or 13 days. Again, changes in density were found only for the beta 1-adrenoceptor binding sites. There is no reduction of receptor density following return to control conditions for 10 days after a 3-day treatment with isoproterenol, demonstrating the ability of this model to attain its final receptor density notwithstanding the developmental insult.

Early postnatal appearance of enhanced noradrenaline content in the brain of vasopressin-deficient Brattleboro rat; normal adrenoceptor densities and aberrant influences of vasopressin treatment

The course of postnatal development of noradrenaline (NA) and its unconjugated free metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), as well as the influence on early chronic vasopressin treatment, were investigated in various brain regions of the hereditary vasopressin-deficient (homozygous di/di) Brattleboro rat. In addition, the densities of the adrenergic receptor subtypes were measured in adult brain. Brain NA levels of di/di pups appeared enhanced already at 7 days of age when compared with data of heterozygous (+/di) controls. This was also seen in areas not known to receive a vasopressinergic input, e.g. the frontal cortex. Levels of MHPG also differed between genotypes, but changes were slight and either a decrease or increase, depending on age and region tested. Saturation analyses of alpha 1-, alpha 2-, and beta-adrenoceptor binding on crude membrane preparations of some brain regions revealed no differences in adulthood. Chronic treatment with vasopressin between 6 and 13 days of age reduced the enhanced NA brain levels throughout the brain of the di/di Brattleboro pups. The known vasopressin-mediated enhancement of NA turnover in adult brain was also measurable in +/di pups of this neonatal period (MHPG/NA ratios), indicating the early maturation of the interaction of vasopressinergic and NAergic systems. However, the dose-response in the di/di Brattleboro rat was biphasic with a decrease at a low dose of vasopressin. Since changes were found throughout the brain, it was concluded that vasopressin deficiency had altered the maturation of NA neurons of the locus coeruleus which may be due to the absence of a presumed inhibitory control of vasopressin on synthesis and storage mechanisms at the perikaryal level.

Ethical guidelines for the use of human embryonic or fetal tissue for experimental and clinical neurotransplantation and research. Network of European CNS Transplantation and Restoration (NECTAR)

Recently a Network of European CNS Transplantation And Restoration (NECTAR) has been founded, aimed at a concerted effort to develop efficient, reliable, safe and ethically acceptable transplantation therapies for neurodegenerative diseases, in particular Parkinson's and Huntington's disease. Owing to the use of human fetal brain tissue in such studies, usually obtained from elective abortions, ethical concerns have been focused on the relationship between abortion and transplantation activities. There is no uniform code on the retrieval and use of human embryonal or fetal material for experimental and clinical research or application in Europe. NECTAR has therefore formulated self-restraining ethical guidelines for its European member groups. These guidelines consist of a series of restrictions intended to prevent the use of grafts from encouraging induced abortions and to maintain high standards of respect for life and human dignity. In order to support applications for human embryonal or fetal neurotransplantation studies of NECTAR member groups to local or national medico-ethical committees, and to stimulate the goal of obtaining European legislation on this issue, the guidelines are here presented. They are followed by extensive explanatory notes. Only in this public manner can the lines of thought behind these NECTAR guidelines be addressed critically by those working in the fields of biomedical ethics and legislation as well by politicians and the general public.

Activity-dependent plasticity of inhibitory and excitatory amino acid transmitter systems in cultured rat cerebral cortex

Chronic suppression of spontaneous bioelectric activity in cultures of dissociated fetal rat cerebral cortex increases neuronal cell death and results in electrophysiological changes which indicate an altered balance between excitatory and inhibitory neurotransmission in culture. To delineate whether alterations in neurotransmitter release could underlie this imbalance, we investigated the effects of chronic tetrodotoxin (TTX) treatment on the content and release of glutamate, aspartate and gamma-aminobutyric acid (GABA) in culture. Chronic TTX treatment decreased the content of all amino acids investigated. However, only GABA was decreased relative to the neuronal marker NSE (neuron-specific enolase), indicating a disproportionate loss of GABA production following chronic silencing. Depolarization-induced release of GABA, glutamate and aspartate increased about 10-fold between 7 and 21 days in control cultures. Chronic TTX treatment significantly increased the depolarization-induced release of glutamate and aspartate at 7 days in vitro relative to control levels. At all ages it caused a two-fold increase in the ratio of evoked excitatory amino acid release to that of GABA. These observations suggest that chronic silencing of developing neocortex cell cultures increases the ratio of excitatory to inhibitory synaptic activity either by differential cell death or by reduced synaptic efficiency, on which a decrease in GABA neurotransmission appears to play a major role. Since similar mechanisms may be involved in activity-dependent plasticity in vivo, these cultures provide a useful model to analyse this phenomenon at the cell biological and molecular level.

Growth conditions differentially modulate the vulnerability of developing cerebellar granule cells to excitatory amino acids

The survival of immature nerve cells in a cerebellar culture, predominantly excitatory granule cells, is known to be promoted by chronic exposure to high K+ (> 20 mM) or glutamate (Glu) receptor agonists. These treatments are believed to mimic the in vivo effect of the incoming glutamatergic afferents, the mossy fibres. Here we report that with maturation the cells become vulnerable to excitatory amino acids (EAAs) and that the characteristics of EAA sensitivity are dependent on the environmental influences being either "trophic" (25 mM K+ or 140 microM NMDA, K25 or K10 + NMDA) or "non-trophic" (10 mM K+, K10). Toxicity was assayed routinely at 9 days in vitro (DIV) after 24 h exposure to EAAs. Under all the tested conditions, the effect of Glu was mediated exclusively through NMDA receptors. However, the efficacy and potency of Glu were high in K25- and K10 + NMDA-grown cells compared with K10-grown cells. Growth conditions had the same influence on NMDA as on Glu-induced toxicity, but with the following special features: (1) in comparison with K25 cells, the potency of NMDA was significantly lower in K10 + NMDA cells. The K10 + NMDA cultures behaved as if they were completely insensitive to the NMDA which is present in their growth medium. (2) The K10-grown cells were not vulnerable to NMDA, unless the cell membrane was depolarised by shifting the cells into K25 medium. The efficacy of NMDA became then similar to that in K25 cultures, although the potency was about 7-fold less. Thus NMDA receptors can be activated by the depolarisation of K10 cells, implying the operation of Mg2+ blockade of the channel at normal resting membrane potential. Although non-NMDA receptors did not seem to be involved in Glu toxicity, cells were vulnerable to kainate, which killed significantly more cells than Glu (about 80% vs 70%). This was partly due to the resistance of GABAergic interneurons present in the cultures to Glu- or NMDA-induced toxicity. In contrast to the effects of Glu or NMDA, KA vulnerability was lower in cells grown in K25 or K40 than K10 medium (rank order K10 > K25 > K40). Under our experimental conditions, cultured cells were resistant to AMPA, quisqualate and the selective metabotropic Glu receptor agonist 1S,3R-ACPD. Collectively, the observations indicated that EAA sensitivity of cultured cerebellar interneurons is significantly and differentially influenced by environmental factors, believed to mimic in vivo trophic influences on these cells.

Effects of neonatal exposure to clonidine on basal and activated central noradrenaline metabolism and in vivo overflow

The occurrence of persistent effects of chronic neonatal exposure to the alpha 2-adrenoceptor agonist clonidine was investigated by determination of tissue concentrations of monoamines and metabolites and in vivo overflow of noradrenaline and its metabolites, in various rat brain regions during adulthood. Rat pups were treated with clonidine from postnatal day 10-20 and all measurements were carried out between postnatal day 40 and 58. Tissue concentrations of monoamines and metabolites of the early clonidine-treated rats did not differ significantly from the control group. A challenge with yohimbine did not reveal altered responses of monoaminergic systems, except for the failure of an increased serotonergic activity in the medulla pons. In vivo microdialysis measurements revealed an elevated basal extracellular noradrenaline level in amygdala, but not in frontal cortex and hippocampus. Pharmacological challenge in vivo with idazoxan did not reveal differences between clonidine- and saline-exposed rats. These results confirm previous findings that continuous activation of alpha 2-adrenoceptors during a particular period of rat brain development may result in long-lasting but small changes in monoaminergic activity. However, these alterations are not very consistent and may depend on the parameter chosen to reflect monoaminergic activity and are not revealed more clearly by activating (challenging) the noradrenaline system with alpha2-adrenoceptor antagonists.

Increased alpha 2-adrenoceptor mediated regulation of adult rat brain noradrenaline overflow after chronic neonatal exposure to propranolol; a microdialysis study

Direct and persistent effects of chronic neonatal administration of the beta-adrenoceptor antagonist propranolol on brain noradrenergic activity were investigated by measuring tissue concentrations of noradrenaline and its metabolites and in vivo overflow of noradrenaline during adulthood. Rat pups were chronically treated with propranolol from postnatal day 1 to day 10. Determination of monoamine metabolism after the last injection showed an increase in noradrenaline metabolism in frontal cortex, limbic system and hippocampus of propranolol-exposed rats, but 47 days after this last injection it was apparent that these effects were not long-lasting. Moreover, basal noradrenaline overflow in vivo in the hippocampus of 40-55 day-old propranolol-exposed rats did not differ from that in controls. However, the regulation of noradrenaline release seemed to have been altered, since a pharmacological challenge with the alpha 2-adrenoceptor antagonist idazoxan induced an enhanced increase in the in vivo noradrenaline overflow in propranolol-exposed rats compared to controls. It is suggested that the neonatal beta-blockade induced a supersensitivity of the presynaptic alpha 2-adrenoceptor. The precise mechanism underlying this effect has to be elucidated.

Regional differences in the in vivo regulation of the extracellular levels of noradrenaline and its metabolites in rat brain

Microdialysis was used to determine extracellular levels of both noradrenaline and its metabolites in several brain regions of rats under basal conditions and in response to drugs selective for the alpha 2-adrenoceptor to study regional differences in the regulation of noradrenaline overflow. Basal overflow of noradrenaline was about 1.3 fmol/min in frontoparietal cortex, amygdala and hippocampus and in the medial prefrontal cortex 2.4 fmol/min was measured, whereas the overflow of the noradrenaline metabolites 3,4-dihydroxyphenylglycol and 3-methoxy-4-hydroxyphenylglycol was 10-fold higher. After correction for recovery and membrane length no regional differences in the basal overflow of noradrenaline (NA) were found. There were, however, regional differences in the drug-induced effects: locally applied moxonidine decreased extracellular noradrenaline stronger in the frontoparietal cortex than in the medial prefrontal cortex. The increase in noradrenaline overflow caused by idazoxan (10(-4) M) was stronger in frontoparietal cortex than in amygdala and hippocampus. The metabolites were also generally decreased by moxonidine and increased by idazoxan, although less markedly. The present study shows that the regulation of noradrenaline overflow by the presynaptic alpha 2-autoreceptor was stronger in cortical regions than in amygdala and hippocampus. In those latter regions the uptake mechanism probably plays a relatively more important role in the regulation of noradrenaline overflow.

Mild sustained effects of neonatal vasopressin and oxytocin treatment on brain growth and behavior of the rat

The lasting effects of a 9-day neonatal exposure to vasopressin and oxytocin were examined in the rat to discover if peptide administration results in organizational effects. When tested in young adulthood, brain growth, not body growth, appeared to be impaired. Basal and challenge tests of urine production, carried out to see the development of the hormonal antidiuretic function of vasopressin, revealed no lasting changes, and therefore did not confirm earlier findings of an induced mild polyurea. Behavioral testing of learning by making use of a one-trail step-through paradigm with a 24-h retention trial--a test that is sensitive to vasopressin--did not show impairments. Open field tests, however, showed enhanced emotionality in the vasopressin-treated females, as well as an initially increased ambulation in the males, and increased grooming in both sexes, the latter also having been reported to be induced by vasopressin administration in the septal areas. Oxytocin treatment did not produce lasting changes. Our conclusion, therefore, is that peripherally circulating vasopressin can affect the organizational development of the rat brain. It remains to be established whether this is an effect obtained through changes in the general peripheral physiology or a reflection of plasticity phenomena at the level of central vasopressin neurotransmission.

Chronic oxytocin treatment during late gestation and lactation impairs development of rat offspring

The nonapeptide oxytocin (OT) plays an important role in timing and course of parturition, and in milk ejection during lactation. Exogenously enhanced OT levels were reported to impair body development of rat offspring at birth and during postnatal stages. In the present study, this effect was further investigated by giving pregnant rats of postcoital day 17 a SC implant that delivers small amounts of OT for 2 months (approximately threefold enhancement of OT levels), and by introducing a crossfostering protocol for the offspring. A slightly reduced body weight of 5 to 7% was again observed in pups born to OT-implanted dams. When reared postnatally by OT-treated mothers, pups lost weight gain (-7 to -10%). During the weaning period, however, body size caught up with that of control animals. When nursed by an untreated mother, this recovery took place before that period. Growth of control offspring was also hampered when placed with OT-treated mothers, but these pups failed to recover from low body weights which lasted up to at least 70 days of age (-7%). Daily urine production of the pups born of and reared by the OT-treated mothers was reduced at 1 month of age, but this effect was only transient and had disappeared at 70 days of age. Notwithstanding, the recovery of body growth, brain sizes, and cerebellar DNA, i.e., cell content was reduced in the pups born and reared by OT-treated mothers, indicative of a lasting effect on brain development.(ABSTRACT TRUNCATED AT 250 WORDS)

Preeclampsia is not associated with altered platelet vasopressin binding and cytosolic Ca++ concentration

OBJECTIVES

Preeclampsia is an important cause of fetal and maternal morbidity and mortality. Recently it was described that platelet cytosolic Ca++ levels could be used to screen for preeclampsia. The current study investigated platelet arginine vasopressin receptor characteristics, platelet cytosolic Ca++ levels, plasma- and platelet-bound arginine vasopressin in white pregnant women.

STUDY DESIGN

In a cross-sectional study nine third-trimester nulliparous pregnant women with gestational hypertension (seven with proteinuria, two with excessive weight gain without proteinuria) were compared with nine healthy nulliparous pregnant women matched for gestation length and age and 10 healthy age-matched nonpregnant women. Determined were (1) platelet arginine vasopressin receptor number and affinity, (2) platelet cytosolic Ca++ levels, both basal and on arginine vasopressin or thrombin stimulation, and (3) plasma- and platelet-bound arginine vasopressin levels.

RESULTS

None of the measured parameters differed significantly among the three groups studied. Mean arginine vasopressin receptor number and affinity ranged from 108 to 143 receptors per platelet and 0.35 to 0.40 nmol/L, respectively. A single population of binding sites was found (Hill number 0.96). Basal Ca++ levels ranged from 113.4 to 133.3 nmol/L, on arginine vasopressin stimulation from 199 to 250 nmol/L. Median arginine vasopressin levels in platelet-poor plasma were between 1.2 and 2.4 pg/ml, with circulating platelets being estimated to possess two to five molecules of arginine vasopressin per platelet. A significant correlation was found between platelet cytosolic Ca++ levels before and after arginine vasopressin stimulation (r = 0.69, p < 0.001) and a weak correlation between platelet receptor density and arginine vasopressin-stimulated platelet cytosolic Ca++ levels (r = 0.38, p < 0.05).

CONCLUSIONS

The studied parameters, platelet cytosolic Ca++ levels, whether basal or after stimulation with arginine vasopressin and vasopressin platelet receptor density and affinity, do not discriminate already hypertensive or preeclamptic white women from nondiseased subjects. A valuable test to screen for preeclampsia awaits further prospective studies.

In vivo microdialysis of noradrenaline overflow: effects of alpha-adrenoceptor agonists and antagonists measured by cumulative concentration-response curves

1. The purpose of the present study was to compare the effects of several alpha-adrenoceptor agonists and antagonists on cerebral cortical overflow of endogenous noradrenaline (NA) in freely moving rats. One or two days after the implantation of transcerebral dialysis tubes in the frontoparietal cortex, extracellular NA levels were monitored on-line with high performance liquid chromatography and electrochemical detection. The drugs were applied locally via the dialysis membrane, and effects on NA overflow were determined in cumulative concentration-response curves. 2. The average basal cortical NA overflow of all experiments was 0.25 pg min-1. The alpha 2-adrenoceptor agonists caused a concentration-dependent decrease in NA levels. UK-14,304 was the most potent and B-HT 933 the least potent agonist. The maximal decrease in NA overflow was to 10-15% of control levels after UK-14,304 or moxonidine, to 30% after clonidine and to 50% after B-HT 933 administration. Continuous activation of the presynaptic alpha 2-adrenoceptor with 10(-6) M UK-14,304 caused a decrease in NA levels to 40-50% of basal levels. This decrease was reached within 1 h and remained stable for the entire 3 h measurement period. The alpha 1-adrenoceptor agonists, phenylephrine and methoxamine, induced an increase in NA levels to 225% and 300%, respectively, at a concentration of 10(-3) M. 3. Local application of alpha 2-adrenoceptor antagonists caused an increase in NA levels, with idazoxan being more potent than piperoxan. Yohimbine did not cause any significant change. 4. All drugs used in these in vivo experiments had in vitro recoveries across the dialysis membrane between 10 and 20%. 5. We conclude that microdialysis with local drug application is suitable for the comparison of the pharmacological effects of drugs with affinity for alpha-adrenoceptors on cortical NA overflow in vivo,provided that the passage across the membrane is equal for the different drugs.

Increased loss of brain DNA in the neonatal vasopressin-deficient Brattleboro rat, but not in normal rat treated with vasopressin antagonist

In order to establish whether vasopressin (VP) influences brain cell survival, [3H]thymidine was injected in 10-day-old vasopressin-deficient Brattleboro rat pups, as well as in Wistar pups treated, neonatally, with the VP antagonist dP[Tyr(Me)2]VP followed by subsequent measurement of [3H]DNA in olfactory bulbs and cerebellum days and weeks thereafter. Results show, first of all, that the incorporation of [3H]thymidine into DNA was enhanced in the homozygous (HOM) Brattleboro, when compared with the heterozygous (HET; non-vasopressin-deficient) controls. The difference is due to the greater and prolonged tissue availability of [3H]thymidine, possibly pointing to an altered thymidine uptake and/or metabolism. Between postnatal days 25 and 39 no differences were seen in [3H]DNA content of the brain parts of the HET and Wistar control rats. For the HOM rats, however, a loss of [3H]DNA was seen (up to 8%), indicating that increased postnatal brain cell death might occur in the mutant. The antagonist treatment in Wistar rat up to 21 days of age failed to show a similar effect. It is proposed that general growth impairments, rather than VP receptor-mediated effects, lead to the brain cell loss.

Developmental changes in rat brain monoamine metabolism and beta-adrenoceptor subtypes after chronic prenatal exposure to propranolol

The aim of this study was to investigate whether a chronic prenatal beta-blockade can alter the maturation of the noradrenergic system in the rat brain. Pregnant female and adult male rats were treated for 10 days with the beta-antagonist propranolol dissolved in the drinking water (40-50 mg/kg/day). Direct and long-term effects on beta-adrenoceptors and monoamine metabolism in various rat brain regions were determined. After the prenatal treatment the propranolol level in the foetal brain was 0.9 micrograms/g, while in the adult brain 2.0 micrograms/g was present. The foetal beta 1-receptors were significantly up-regulated by propranolol (200%), whereas the beta 2-receptor number remained unaltered. On postnatal days 4 and 21 the number of both beta-subtypes was the same as that of controls. Noradrenaline, its metabolite 3-methoxy-4-hydroxyphenylglycol and their ratio were unaltered directly after the prenatal treatment. In the PN 21 offspring, however, the metabolite level had increased in the frontal cortex (+ 17%) and hippocampus (+ 32%), and the ratio in the hippocampus (37%) and medulla pons (+ 34%). Prenatal treatment also induced a significant increase of the 5-hydroxyindoleacetic acid.5-hydroxytryptamine ratio (+ 15%) in the medulla pons at GD 21. No direct or lasting effects were found on dopamine metabolism. Propranolol treatment of adult rats gave no direct changes in monoamine metabolism. We concluded that chronic prenatal propranolol exposure (a) reversibly up-regulates foetal beta 1-adrenoceptors, and (b) increases the NA activity in the brain in later life.