Postnatal exposure to the beta-adrenoceptor agonist clenbuterol has regionally selective direct and long-term effects on rat brain beta-adrenoceptors and monoamine metabolism

The effects of chronic postnatal beta 2-adrenoceptor activation on the maturation of the rat brain noradrenergic system have been studied. For that purpose, rat pups have been treated twice daily during the first 10 days of life with the beta 2-agonist clenbuterol-HCl (2.5 mg/kg s.c.), and the effects on the beta-adrenoceptor number and monoamine metabolism have been determined directly after the treatment and in adulthood. On postnatal day 10, 90 min after the last clenbuterol injection 4.5 micrograms/g of the drug was present in the brain. At the end of the treatment the beta-receptor binding had decreased in the cerebellum (35%), but not in the frontal cortex or mesolimbic system. Clenbuterol significantly increased the steady-state brain levels of noradrenaline (NA) in the striatum 90 min after the last injection, whereas the levels in the frontal cortex, meso-limbic system, medulla pons and cerebellum were unaffected. The NA metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), had significantly increased in the frontal cortex and striatum. The serotonergic (5-HT) and dopaminergic (DA) system were not altered. In general, no long-lasting effects on beta-adrenoceptor number and affinity or monoamine metabolism were measurable, except for the frontal cortex which showed a sustained increase of MHPG, a decrease of 5-HT and an increase of 5-HIAA/5-HT on PN 60. In conclusion, chronic postnatal activation of beta 2-adrenoceptors by clenbuterol treatment selectively causes changes in the setting of the neurochemical parameters investigated in the frontal cortex.

Functional development of fetal suprachiasmatic nucleus grafts in suprachiasmatic nucleus-lesioned rats

Recovery of circadian drinking rhythms in suprachiasmatic nucleus (SCN)-lesioned rats after fetal SCN grafting was related to the immunocytochemical appearance and fiber outgrowth of vasopressin (VP)-, vasoactive intestinal polypeptide (VIP)-, and somatostatin (SOM)-containing neurons in the implants. At 4 weeks postgrafting, the first recovered animal was found. After longer survival times, 38% of the animals showed recovery. Immunocytochemical evaluation indicated that full maturation of the SCN grafts was not reached until 4 weeks postgrafting. Grafted VP and VIP cells were always located together, whereas SOM cells were clustered nearby but separate. Neuropeptide Y fibers were observed with an increasing fiber density between 2 and 5 weeks posttransplantation and were clustered particularly at the level of the SOM cells. In all rhythm-recovered animals transplants of VP and VIP fibers had grown laterally into the hypothalamus. A few nonrecovered animals also showed ingrowth of such fibers, though more caudally to the lesioned SCN. Many of the nonrecovered rats showed similar stainings but without these efferent outgrowth to the host. We conclude that neither a humoral factor nor the presence of VP and VIP efferents in the host brain alone are enough for the restoration of circadian drinking rhythms.

NMDA receptor levels in chronically depolarized long-term neonatal rat neocortical explants

The levels of the N-methyl-D-aspartate subclass of glutamate receptor were determined in organotypic neocortical explants chronically exposed to a growth medium containing 25 mM potassium (K25). Explants exposed to 25 mM potassium for 2-3 weeks evinced significantly less binding of the non-competitive N-methyl-D-aspartate receptor-associated channel antagonist 125I-MK801 than did age-matched controls. Surprisingly, cultures that were returned to control growth medium for a further 2 or 7 days showed even less binding of the ligand. The Kd values of binding were not affected and were similar to those of fresh postnatal cortex. The maximum number of binding sites did not vary between postnatal day 6 and 14 days in vitro control cultures, but were significantly less than those measured at postnatal day 20 (comparable age: 14 days in vitro). Several conclusions can be drawn from these findings: (i) the density of the N-methyl-D-aspartate subclass glutamate receptor does not attain in vivo levels under the present culturing conditions, but remains at those levels associated with the stage of development at which the tissue was brought into culture, (ii) chronic depolarization results in a drastic reduction in N-methyl-D-aspartate receptor density, which is not compensated for after the return to normal growth conditions, (iii) depolarization selectively inhibits cellular maturation of the neocortex (but not survival, as shown previously), including neurotransmitter receptor production and/or insertion into membranes or assembly.

Treatment with excitatory amino acids or high K+ and NMDA receptors in cerebellar granule cells

N-methyl-D-aspartate (NMDA) receptor activity was examined, in terms of 45Ca2+ influx, during the development of cerebellar granule cells grown under 'non-trophic' [10 mM potassium (K10)] or 'trophic' conditions [25 mM potassium (K25), NMDA and kainate (KA)]. NMDA receptor activity increased sharply between 2 and 4 days in vitro (DIV) irrespective of growth conditions which upon further cultivation exerted a powerful influence, the NMDA response increasing progressively in K25 and NMDA grown cells, while remaining at a constant level in KA treated cells. In contrast, in K10 grown cells the NMDA response declined by 7 DIV to about 20% of the estimates in K25 at 9 DIV. Trophic conditions are, therefore, essential for the proper functional expression of NMDA receptors.

Gelatin embedding to preserve lesion-damaged hypothalami and intracerebroventricular grafts for vibratome slicing and immunocytochemistry

Vibratome sectioning of paraformaldehyde-fixed brains containing a lesion and/or intracerebroventricular grafts and staining of these sections often lead to damage around the site of the lesion and loss of the implants. Various embedding procedures were compared in order to find a method to overcome this problem. The best results were obtained when fixed brain tissue was first embedded under reduced pressure in 10% gelatin at 50 degrees C, and then fixed again, in 4% paraformaldehyde. The method did not affect the immunocytochemical staining for vasopressin, vasoactive intestinal polypeptide, somatostatin, gonadotropin releasing hormone and neuropeptide Y.

Chronic neonatal NMDA receptor blockade with MK-801 alters monoamine metabolism in the adult rat

Administration of non-competitive N-methyl-D-aspartate (NMDA) antagonists in rodents leads to a characteristic motor syndrome which has been related to changes in monoamine metabolism in a variety of brain regions. We examined the question whether chronic MK-801 treatment in neonatal rats from postnatal day 8 through 19, which has been shown previously to alter NMDA receptor function, would also affect monoamine metabolism in striatum and frontal cortex of adult rats. Monoamines and their metabolites were determined 5 months after the treatment using high-performance liquid chromatography with electrochemical detection. Dihydroxyphenylacetic acid (DOPAC) concentration was elevated (greater than 40%) in both regions tested, while 5-hydroxyindoleacetic acid (5-HIAA) concentration was significantly elevated only in the cortex (19%), and 3-methoxy-4-hydroxyphenylglycol (MHPG) only in the striatum (47%). These results demonstrate that the long-lasting effects of chronic neonatal MK-801 treatment are not restricted to glutamate transmission, but include monoamine transmission as well.

Changes in adrenoceptors and monoamine metabolism in neonatal and adult rat brain after postnatal exposure to the antihypertensive labetalol

1. The purpose of the present study was to investigate the acute (single injection), direct (chronic treatment) and the long-lasting effects after exposure to the alpha 1/beta-adrenoceptor antagonist labetalol during rat brain development on adrenoceptors and monoamine metabolism. 2. In 10-day-old rat pups, subcutaneously administered labetalol (10 mg kg-1) passed the blood-brain barrier, reaching a level of 2.1 micrograms g-1 tissue in the brain 90 min after injection. 3. Chronic labetalol treatment (10 mg kg-1, s.c., twice daily) during the first 10 days of life significantly increased alpha 1-adrenoceptor binding in the hypothalamus (+39%), but not in the occipital cortex. 4. This chronic postnatal labetalol treatment did not result in long-lasting changes in alpha 1- and beta-receptors measured on day 60. 5. A single labetalol injection (10 mg kg-1, s.c.) on postnatal day 10 significantly increased noradrenaline (NA) metabolism in all brain regions tested (+25 to 105%), but had no effects on 5-hydroxytryptamine (5-HT) or dopamine metabolism. 6. Chronic labetalol treatment between postnatal (PN) days 1 and 10 also increased NA metabolism on PN 10 (3-methoxy-4-hydroxyphenylglycol (MHPG)/NA, +20 to 100%), suggesting that tolerance to the acute effect of labetalol did not occur. A slight increase in 5-HT metabolism (20%) was induced by the chronic labetalol treatment in the hippocampus and meso-limbic system. 7. In general, long-lasting effects on NA metabolism could not be detected on day 60 more than one month after the treatment. However, 5-HT metabolism was significantly increased in all four brain regions measured (+20 to 70%). 8. We conclude that chronic labetalol exposure during early postnatal rat brain development does not cause long-lasting changes in beta-receptor number or NA metabolism, but appears to be critical for the rate of 5-HT metabolism in later life.

Early postnatal clonidine treatment results in altered regional catecholamine utilisation in adult rat brain

Clonidine is a clinically used antihypertensive which has been suggested to produce physiological changes in children after exposure in utero. The aim of our study was to test the hypothesis that chronic exposure of the developing brain to an alpha 2-adrenergic agonist like clonidine would influence the adult neurochemical setting of central monoamine neurotransmitter systems. Male rat pups were treated from postnatal day 8 to 21 twice daily with saline or with 0.1 mg/kg clonidine. After the last injection on day 21, brain regional catecholamine utilisation was determined using synthesis inhibition with alpha-methyl-p-tyrosine in a subgroup of the pups. The expected decrease in noradrenaline utilisation after clonidine was observed, although statistical significance was not reached in a number of brain regions. Dopamine utilisation was not affected. The other pups were left to reach young adulthood and catecholamine utilisation was measured on day 90. Noradrenaline utilisation on day 90 was significantly decreased in two regions: the medulla-pons and the mesolimbic (dopamine projection) areas. Dopamine utilisation was decreased in the hypothalamus and increased in the amygdala and the cerebellum. These adult neurochemical alterations corroborate previous findings of adult behavioural, physiological and central biochemical alterations in rats exposed to clonidine in early postnatal life.

Pre- and postnatal developmental changes of adrenoceptor subtypes in rat brain

beta-Adrenergic receptor subtypes, beta 1 and beta 2, were studied during pre- and postnatal development in the rat brain. [125I]Iodocyanopindolol (6-300 pmol/L) binding assays in the presence of 5-hydroxytryptamine (0.6-6 mumol/L) were used to measure exclusively beta-adrenergic receptors. In forebrain tissue, saturable and stereoselective binding was detected on gestational day 13. The amount of beta-adrenergic binding increased until postnatal day 23, when adult values were reached. The dissociation constants of [125I]iodocyanopindolol binding remained the same throughout development, as did the affinity of several beta-adrenergic and non-beta-adrenergic compounds. The proportion of the beta 2-adrenergic receptors was determined using the beta 1-selective antagonist ICI-89406 (7-150 nmol/L) and was found to change from 65% in prenatal forebrain tissue to 28% in adulthood. In cerebellum/medulla pons tissue, however, the proportion of beta 2-receptor binding (80%) remained unchanged during the whole developmental period.

Testicular oxytocin: effects of intratesticular oxytocin in the rat

The long-term effects of oxytocin administration on the testis were studied using intratesticular implants. Adult male rats had an Accurel device containing 20 micrograms oxytocin (releasing approximately 200 ng/day) implanted into the parenchyma of each testis; control animals received empty devices. The animals were killed at weekly intervals for 4 weeks. Some animals were perfused and the testes processed for light and electron microscopy. Blood was collected from the remaining animals for the measurement of testosterone, dihydrotestosterone, LH, FSH and oxytocin; epididymal sperm counts were measured and the testes were extracted and radioimmunoassayed for testosterone, dihydrotestosterone and oxytocin. Long-term administration of oxytocin resulted in a significant reduction in testicular and plasma testosterone levels throughout the 4-week period examined and, after 14 days of treatment, lipid droplets were seen in the Leydig cells of treated but not control animals. Concentrations of dihydrotestosterone in the plasma and testes of the oxytocin-treated animals, however, were significantly elevated after 7 and 14 days and at no time fell below control values. Plasma FSH levels were also lower in the oxytocin-treated animals. Intratesticular oxytocin treatment did not affect LH or oxytocin concentrations in the plasma, epididymal sperm counts or the number of Leydig cells in the testis. Empty Accurel devices had no effect on testicular morphology. This study provides the first evidence that oxytocin in vivo can modify steroidogenesis in the testis.

Chronic propranolol treatment in developing rats: acute and lasting effects on monoamines and beta-adrenergic receptors in the rat brain

During early postnatal development rat pups were treated twice daily with the beta-adrenergic antagonist propranolol (15 mg/kg) in order to study the acute and long-lasting effects of early blockade of noradrenergic beta-mediated neurotransmission. Treatments from postnatal days 1-10 or days 11-20 did not induce alterations in the number of beta-adrenergic receptors as measured three days after the last injection, nor could lasting effects be shown at 60 days of age. The day 1-10 treatment, however, had a significant effect on the regional brain levels of noradrenaline (NA) and its metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), measured 90 min after the last injection. The metabolite had increased by 40% in all brain regions examined. On day 60, the MHPG concentrations were still increased when compared to postnatally saline-treated animals. Propranolol treatment from day 11-20 only marginally increased MHPG on day 20 and induced no lasting differences. These results suggest that propranolol treatment during the first ten days of life produces a long-lasting increase in NA metabolism, possibly reflecting an increased neuronal NA turnover.

In vitro and in vivo D2-dopamine receptor binding with [123I]S(-) iodobenzamide ([123I]IBZM) in rat and human brain

As a promising dopamine D2-receptor imaging agent for single photon emission computerized tomography (SPECT), [123I](S)-(-)-2-hydroxy-3-iodo-6-methoxy-N [(1-ethyl-2-pyrrolidinyl)methyl]benzamide ([123I]IBZM) has recently been synthesized in a modified way along with its precursor, S(-)BZM, and the stereoisomer R(+)BZM. The present study applied this new product to investigate in vitro and in vivo D2-receptor binding in rat brain and in postmortem human brain. In vitro saturation binding curves with [123I]IBZM for rat crude striatal membrane preparations yielded an affinity constant (Kd) of 0.28 nM confirming data in the literature. Displacement curves revealed an order of increasing potency as follows: R(+)BZM less than S(-)sulpiride = less than S(-)BZM less than S(-)IBZM. A similar order was obtained when [3H]spiperone was used as ligand. For human putamen and caudate nucleus membranes slightly higher Kd values (0.49 nM) were obtained. Rank order of displacing potency for the various drugs was similar to that found in the rat preparations. In vivo uptake of [123I]IBZM in rat brain following injection of 50 microCi (12-16 pmol) in the tail vein revealed an increase in the striatum-to-cerebellum ratio from 1.5 at 5 min to 6.9 at 2 h. The olfactory tubercle-to-cerebellum ratio was also raised from 1.6 to 3.3. Other brain regions tested failed to show statistically significant enhancements. Coinjection of 40 nmol S(-)IBZM, 4 mumol S(-)BZM or 200 nmol haloperidol displaced [123I]IBMZ when tested at 90 min. The use of 4 mumol R(+)BZM resulted in minor displacement only, demonstrating that stereospecificity of the displacement was present in vivo and in vitro. Displacements were also observed in substantia nigra and pons-medulla oblongata, but not in hippocampus or frontal and occipital cortex. The data provide the required background needed in order to initiate in vivo binding studies for D2-receptors in basal ganglia of human patients using [123I]IBZM in SPECT analyses.

Developmental changes in B-50 (GAP-43) in primary cultures of cerebral cortex: content and phosphorylation of B-50

The content and phosphorylation of the neuronal growth-associated protein B-50 (GAP-43) were studied in cultured neocortex as a function of normal development and development in the presence of tetrodotoxin (TTX), a blocker of bioelectric activity (BEA). The observations were correlated with previous morphological findings on neurite outgrowth and B-50 immunolocalization in the same cultures. In control cultures, the concentration of B-50 reached a maximum at 7 days in vitro (DIV) and decreased thereafter, whereas the concentration of neuron specific enolase (NSE), which was used as a neuronal reference marker, rose till 28 DIV and leveled off towards 42 DIV. The degree of basal phosphorylation of B-50 (relative to that of total protein) decreased after the first week in vitro. Stimulation of B-50 phosphorylation by phorbol ester also decreased with age in vitro, indicating that changes in B-50 phosphorylation were mainly due to changes in protein kinase C (PKC) activity. The chronic presence of TTX led to a reduced content of B-50 and NSE after 14 DIV. The basal phosphorylation of B-50 was neither affected by acute nor chronic TTX treatment. However, upon stimulation of PKC with phorbol esters, some alterations of B-50 phosphorylation were revealed in cultures grown in TTX. These biochemical observations are in line with the absence of effects of TTX on neurite outgrowth during the first 2 weeks in culture, and later effects of TTX on neuronal survival. The developmental changes in B-50 concentration and phosphorylation largely correlate with previous morphological observations on axonal outgrowth and growth cone shape in the same cultures. We suggest that B-50 phosphorylation plays an important role in transducing extracellular signals into directed neurite outgrowth.

Microdialysis studies on cortical noradrenaline release: basic characteristics, significance of extracellular calcium and massive post-mortem increase

Extracellular noradrenaline was measured on-line in the cerebral cortex of the freely moving rat by microdialysis coupled to high performance liquid chromatography and electrochemical detection. High potassium concentrations in the perfusion fluid led to a strong increase, whereas tetrodotoxin led to almost undetectable levels of noradrenaline. This shows that noradrenaline in the dialysate was directly derived from active neuronal release. Noradrenaline levels were sensitive to calcium concentrations in the perfusion fluid: from 10% in calcium-free medium to 200% for 10 mM calcium. An overdose of anesthetic caused a 60-fold increase of noradrenaline post-mortem.

Widespread alterations in central noradrenaline, dopamine, and serotonin systems in the Brattleboro rat not related to the local absence of vasopressin

A comprehensive study of monoamine transmitter and metabolite concentrations measured by HPLC was undertaken in female (vasopressin-deficient) Brattleboro rats as compared to Long Evans rats. Noradrenaline was significantly increased in 8 out of 13 dissected brain regions, whereas concentrations of the metabolite 3-methoxy-4-hydroxyphenylglycol were not altered. The increases were not restricted to areas which are normally innervated by vasopressin-containing neurons. Serotonin was increased in 6 and dopamine in 4 regions and this was accompanied in some areas by increases in the metabolites 5-hydroxyindolacetic acid and dihydroxyphenylacetic acid. Only in the striatum, cerebellum, and the medulla-pons no changes could be detected in any of the compounds of interest. These results show that the long term absence of vasopressin in Brattleboro rats appears to be associated with increases in monoamine transmitter contents and decreased metabolite/transmitter ratios. The regional distribution of these changes does not bear any relationship to the regional distribution of vasopressin cell bodies or nerve endings.

Spontaneous DNA breaks in the rat brain during development and aging

The level of spontaneous DNA breaks in nuclei isolated from the cerebral cortex of rat embryos at 12, 15 and 19 days of gestation, and from cerebral cortex and cerebellum of 24-day-, 6-month- and 36-month-old rats was measured by alkaline elution. A constant low level of DNA breaks was found in brain DNA during development from an embryo at day 12 of gestation to a 24-day-old rat. During aging the level of DNA breaks remained at the same low level, as shown by comparing nuclei from the cerebral cortex and cerebellum of 6- and 36-month-old animals. By contrast, an almost 2-fold increase in the level of DNA breaks was observed in rat liver nuclei between 6 and 36 months of age, confirming our earlier findings on isolated liver cells. Although there were no changes in the level of DNA breaks in rat brain during development or during aging, breaks accumulated rapidly post mortem. The rate of this process was not age-dependent. Our data suggest that the level of spontaneous DNA breaks in the brain is not likely to be of fundamental importance in the complex cellular alterations associated with brain development and aging.

Lasting effects of early noradrenergic receptor occupation on brain noradrenaline turnover and on beta-receptors

Neuroactive substances reaching the developing brain can affect the formation of the functionality of nervous circuitry. To explain this so-called functional neuroteratology it has been proposed that neurotransmission has persistently been altered. Pharmacological interference with the developing central noradrenergic system in the rat by means of drugs like clonidine, yohimbine and propranolol, indeed revealed lasting changes in the turnover of noradrenaline in several brain areas, but no changes were found in beta-receptor density. It is assumed that either alpha-receptor density is affected or that signal transduction is altered, since electrophysiologically a persistent supersensitivity was found for the noradrenaline-evoked depression of glutamate-evoked firing in e.g. CA1 pyramidal cells of the hippocampus. Elucidation of the underlying neurochemical mechanisms of such lasting effects of perinatal exposure to noradrenergic drugs aims at establishing the role of noradrenaline in development, but also to provide physicians with the possibility to better assess the advantages and disadvantages of drugs to be prescribed during reproduction and, hence, to make the best choice of treatment.

Testosterone treatment restores reduced vasopressin-binding sites in the kidney of the ageing rat

Young, middle-aged and aged rats received s.c. testosterone implants for 50-52 days in order to investigate whether supplementation of testosterone in aged rats could normalize the reported reduction of kidney arginine vasopressin (AVP)-binding sites and increase the plasma concentration of AVP. Receptor number, which was measured by means of a membrane-binding assay with [3H]AVP as ligand, was below the detection level in the untreated aged rat. Following testosterone treatment, no effects were seen in the youngest groups, but in the aged group AVP receptors became clearly detectable, albeit with a lower affinity. A remarkable observation was the increase in affinity for renal AVP binding in the middle-aged compared with the young rat. Plasma levels of AVP in control aged rats tended to be higher. Such a tendency was completely absent in the testosterone-treated aged rats. Possible mechanisms underlying the restoration of reduced AVP-binding sites in the kidney of the aged rat by testosterone treatment are discussed.

Regulation of vasopressin receptors and phosphoinositide hydrolysis in the septum of heterozygous and homozygous Brattleboro rats

Accurel polypropylene mini-devices, loaded with arginine vasopressin (AVP) and implanted in the lateral cerebral ventricle were used to centrally treat heterozygous (HE) and homozygous (HO) Brattleboro (BB) rats. After 1 week of treatment, the concentration of AVP receptors in the HO-BB rat septum decreased from 19.4 +/- 2.6 to 12.4 +/- 1.1 fmol/mg protein, but remained unchanged in the HE-BB rat (10.7 +/- 0.8 and 7.0 +/- 1.1 fmol/mg protein). In the HO-BB rat the [3H]-AVP equilibrium dissociation constant (KD) of the septal AVP receptor decreased following AVP treatment (from 4.17 +/- 0.7 to 1.97 +/- 0.3 nM) compared to that of control animals. This decrease in receptor number following AVP treatment was accompanied by a decrease in the postreceptor response to AVP as measured by the AVP-stimulation of [3H]-inositol-1-phosphate (IP1) accumulation (22.0 +/- 6.1%) when compared to untreated animals (54.3 +/- 8.3%). This apparent AVP-induced down-regulation was not due to occupancy of the binding sites by AVP since preincubation of the tissue at 37 degrees C for 60 min (which was able to cause near-complete dissociation of the hormone-receptor complex) did not result in an increased number of binding sites upon reexposure to [3H]-AVP. This study thus provides evidence for the homologous down-regulation and desensitization in terms of [3H]-IP1 accumulation (phosphoinositide hydrolysis) of AVP receptors in the septum of the BB rat.

Ontogeny of vasopressin and oxytocin binding sites in the brain of Wistar and Brattleboro rats as demonstrated by lightmicroscopical autoradiography

Vasopressin (VP) and oxytocin (OT) binding sites were localized and quantified in the developing brain of the Wistar, heterozygous (Het) and homozygous (Hom) VP-deficient Brattleboro rat using an autoradiographical technique. VP binding sites could be demonstrated from prenatal day 20 onwards in the septum and in the lateral reticular nucleus. Between this and postnatal day 15, VP binding sites appeared in all other brain areas known to contain VP binding sites in adulthood. In the caudate putamen the regional distribution of VP binding changed during development, while in some areas, for instance, the dorsal hippocampus and post cingulate cortex, the concentration of binding sites increased early but decreased with age. Comparison of VP binding between Het and Hom rats showed significant differences in the lateral reticular nucleus during development. Moreover, at postnatal day 15 there was more VP binding in the anterior commissural and suprachiasmatic nucleus and less in the central amygdala, dorsal hippocampus and post cingulate cortex of the Hom rat. This study shows, for the first time, OT binding sites in the developing rat brain. There is a considerable overlap with VP binding in the brain, sometimes with the same developmental pattern, e.g. in the anterior olfactory nucleus and caudate putamen and sometimes with a later appearance, e.g. in the central amygdala and thalamic nuclei. However most areas with VP binding sites did not show OT binding. In some areas only OT binding sites were present, for instance in the islands of Calleja and ventromedial hypothalamus. Similar to some areas with VP binding, OT binding decreased between postnatal day 5 and 15 in the dorsal hippocampus and even completely disappeared in the parietal cortex. The existence of VP binding sites in the Hom rat, together with the only occasional relationship between the previously described ontogeny of VP and OT innervation of the brain and the presently described developmental course of binding sites, indicates that the early expression of binding sites is not initiated by endogenous ligand. However, the setting of the number of VP binding sites has probably been affected by the VP deficiency of the Hom Brattleboro rat.

Decrease of rapid-eye-movement sleep in the light by intraventricular application of a VIP-antagonist in the rat

Vasoactive intestinal polypeptide (VIP) has been shown to increase the amount of time spent in rapid-eye-movement (REM) sleep both in cats and in rats. In the present study we examined the effect of a newly available competitive VIP-antagonist ([4Cl-D-Phe6-Leu17]-VIP) on sleep-wake patterns in male rats during both the light and the dark phase of 24 h. Continuous intracerebroventricular application of this VIP-antagonist reduced by 44% the amount of time spent in REM sleep during the light period. It is concluded that VIP may play a role in the generation and maintenance of REM sleep.

Neonatal treatment with vasopressin antagonist dP[Tyr(Me)2]AVP, but not with vasopressin antagonist d(CH2)5[Tyr(Me)2]AVP, inhibits body and brain development and induces polyuria in the rat

Two vasopressin antagonists, d(CH2)5[Tyr(Me)2]AVP and dP[Tyr(Me)2]AVP, were given to Wistar rats from postnatal day 1 to 21 in order to investigate the influence on development and later diuresis. The latter antagonist significantly reduced body growth from day 3 postnatally onwards. At postnatal day 35 body, total brain, cerebellar and kidney weights were significantly reduced compared with controls. Diuresis, measured at one month of age, was four- to five-fold higher than the control group. Combined treatment with vasopressin failed to abolish the weight disturbances or polyuria. However, animals treated with the vasopressin antagonist d(CH2)5[Tyr(Me)2]AVP did not show developmental or diuretic deficits. Allometric analysis of brain/body relationship of the young animals indicated a disturbance of brain development by dP[Tyr(Me)2]AVP. Although the body and brain growth retardation induced by dP[Tyr(Me)2]AVP supports the hypothesis of a role for vasopressin in brain ontogeny, it can also be the result of a nonAVP-related toxic effect, since it could not be prevented by concomitant treatment with vasopressin.

Osmoregulation in rats with long-term enhanced cerebrospinal fluid levels of vasopressin or vasoactive intestinal polypeptide

The cerebrospinal fluid level of arginine vasopressin (AVP) or vasoactive intestinal polypeptide (VIP) was enhanced chronically by implantation of a device for controlled drug delivery in the lateral ventricle of the rat. Urine production, water consumption, urine osmolality as well as urinary AVP excretion were then measured for a period of 26 days. During this period the rats were studied under normal hydration and under conditions of osmotic stress induced by water deprivation (2 days) and the drinking of 2% (w/v) NaCl (6 days), in order to see whether the capacity of central systems to react adequately to osmotic stimuli was affected by high central peptide levels. Immediately after the central AVP treatment was started, a temporary increase was found in urinary AVP levels which was not accompanied by a change in any of the other parameters but which decreased again to control levels within 10 days. After this burst of AVP excretion, AVP-treated rats showed a tendency during periods of normal hydration for a lower urine osmolality, combined with a higher water intake and urine production without changes in urinary AVP excretion. Since there was no clear-cut correlation between urinary AVP excretion and body water turnover, this could still indicate a slowly acquired and slight inhibition of pituitary AVP release by long-term centrally administered AVP. However, the capacity of these rats to respond to osmotic stimuli was not different from the controls. In the VIP-treated rats a slight but significant reduction in urine production was found in all three periods of normal hydration.(ABSTRACT TRUNCATED AT 250 WORDS)