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

Neurobehavioral Profiles of Six Genetically-based Rat Models of Schizophrenia- related Symptoms

Schizophrenia is a chronic and severe mental disorder with high heterogeneity in its symptoms clusters. The effectiveness of drug treatments for the disorder is far from satisfactory. It is widely accepted that research with valid animal models is essential if we aim at understanding its genetic/ neurobiological mechanisms and finding more effective treatments. The present article presents an overview of six genetically-based (selectively-bred) rat models/strains, which exhibit neurobehavioral schizophrenia-relevant features, i.e., the Apomorphine-susceptible (APO-SUS) rats, the Low-prepulse inhibition rats, the Brattleboro (BRAT) rats, the Spontaneously Hypertensive rats (SHR), the Wisket rats and the Roman High-Avoidance (RHA) rats. Strikingly, all the strains display impairments in prepulse inhibition of the startle response (PPI), which remarkably, in most cases are associated with novelty-induced hyperlocomotion, deficits of social behavior, impairment of latent inhibition and cognitive flexibility, or signs of impaired prefrontal cortex (PFC) function. However, only three of the strains share PPI deficits and dopaminergic (DAergic) psychostimulant-induced hyperlocomotion (together with prefrontal cortex dysfunction in two models, the APO-SUS and RHA), which points out that alterations of the mesolimbic DAergic circuit are a schizophrenia-linked trait that not all models reproduce, but it characterizes some strains that can be valid models of schizophrenia-relevant features and drug-addiction vulnerability (and thus, dual diagnosis). We conclude by putting the research based on these genetically-selected rat models in the context of the Research Domain Criteria (RDoC) framework, suggesting that RDoC-oriented research programs using selectively-bred strains might help to accelerate progress in the various aspects of the schizophrenia-related research agenda.

Further neurochemical and behavioural investigation of Brattleboro rats as a putative model of schizophrenia

Brattleboro (BRAT) rats are a mutant variant of the Long-Evans (LE) strain deficient in the neurohormone vasopressin. BRAT rats show behavioural alterations relevant to schizophrenia. In particular, BRAT rats show deficits in prepulse inhibition (PPI) and alterations in various measures of cognition. The aim of this study was to replicate the reported PPI deficits in BRAT rats and its reversal by antipsychotic drugs and to investigate other behavioural and neurochemical characteristics. Acoustic startle reactivity, PPI, spontaneous and amphetamine-induced locomotor activity (LMA) and ex-vivo steady state neurochemistry were measured in male homozygous BRAT rats and LE rats. The effects of antipsychotics on PPI deficits were also determined. Relative to LE, BRAT rats showed enhanced startle reactivity, hyperactivity to a novel environment, PPI deficits and decreased levels of dopamine and DOPAC (dihydroxyphenylacetic acid) in the frontal cortex. BRAT and LE rats showed similar levels of hyperactivity following amphetamine (0.26 mg/kg s.c.). PPI deficits were attenuated by acute clozapine (5-10 mg/kg s.c.), risperidone (0.1-1 mg/kg i.p.), haloperidol (0.1-0.5 mg/kg p.o.) and less robustly by olanzapine (0.3-3 mg/kg s.c.). Chronic administration of clozapine (5 mg/kg s.c., once daily) attenuated baseline hyperactivity and elevated PPI of both strains. Clozapine concentrations were higher in BRAT brains compared with LE rats. These data confirm the reported PPI deficit in BRAT rats and its reversal by antipsychotic drugs, suggesting BRAT rats may represent a potential model for identifying novel antipsychotic drugs.

Reversal of sensorimotor gating deficits in Brattleboro rats by acute administration of clozapine and a neurotensin agonist, but not haloperidol: a potential predictive model for novel antipsychotic effects

Prepulse inhibition (PPI) of acoustic startle is decreased in unmedicated schizophrenia patients and similar deficits can be induced in rats through pharmacological, environmental, or neuroanatomical manipulations. Recently, we reported that Brattleboro (BB) rats, a Long Evans (LE) strain with a single gene mutation, have inherent deficits in PPI homologous to those observed in schizophrenia patients. We also reported that PPI deficits in BB rats could be reversed by chronic but not acute administration of 0.5 mg/kg haloperidol. No other dose or drug was tested in that experiment. In this study, we tested the effects of acute subcutaneous administration of several doses of haloperidol as well as the second-generation antipsychotic, clozapine, and the putative novel antipsychotic, PD149163, a neurotensin mimetic that crosses the blood-brain barrier. Consistent with our previous report, BB rats exhibited PPI deficits compared to LE rats and none of the doses of haloperidol produced a significant effect on this PPI deficit. In contrast, 10 and 15 mg/kg of clozapine and all the doses of PD149163 tested reversed the PPI deficits in BB rats. In addition, haloperidol, but not clozapine or PD149163 produced significant catalepsy in BB rats, supporting the notion that PD149163 has a profile consistent with atypical antipsychotics and providing support for the predictive validity of the PPI results. These results further strengthen the notion that the BB rat is a useful predictive model of antipsychotic efficacy and suggest that this model may differentiate between antipsychotics belonging to different therapeutic categories, for example, first- and second-generation agents.

Null mutation of the arginine-vasopressin gene in rats slows attentional engagement and facilitates response accuracy in a lateralized reaction time task

The neurophysin vasopressin is thought to play an important role in emotional behavior and aspects of cognition in the rat, and the pathophysiology of this system has been implicated in two neurodevelopmental disorders, namely autism and schizophrenia. Genetic deficiency of vasopressin in rats, resulting from a null mutation of the vasopressin gene, causes alterations of brain development with resulting behavioral and neurochemical phenotypes in adulthood. We previously demonstrated that partial vasopressin deficiency (rats heterozygous for the null mutation) produces enhanced visuospatial attention and motor speeding. Here, the results of studies of homozygous Brattleboro rats that are fully vasopressin deficient are reported. We trained subjects to perform a lateralized reaction time task that measures visuospatial divided attention; in task conditions in which the duration of target stimuli was varied from trial to trial, homozygous Brattleboro rats showed a performance phenotype that consisted of more accurate responding for longer duration, and less accurate responding for briefer duration, target stimuli. No differences in response times were measured. Further experiments revealed that two separate processes produced this complex phenotype: a relatively slowed period of attentional engagement (resulting in compromised detection of fast onset-fast offset stimuli) that only partially masks a generally more accurate pattern of responding. These results, taken with earlier data, indicate that vasopressin plays a critical role in regulating visual attention and cognition, either directly, or via early alterations in neurodevelopment.

Genetic vasopressin deficiency facilitates performance of a lateralized reaction-time task: altered attention and motor processes

Brattleboro rats are a variety of the outbred Long-Evans strain that possess a single nucleotide deletion in the second exon of the arginine vasopressin gene, resulting in the synthesis of an altered protein that does not enter the normal secretory pathway. Rats heterozygous (di/+) for the deletion have a partial vasopressin deficiency and exhibit a variety of behavioral and neurochemical alterations compared with normal wild-type Long-Evans rats, which provide evidence for a CNS function for vasopressin. Here, we examined the acquisition and performance of a test of visuospatial attention by di/+ Brattleboro rats and their wild-type Long-Evans control counterparts. Surprisingly, di/+ rats exhibited superior performance of the task compared with wild-type controls; performance differences included greater accuracy of detection of visual target stimuli, faster overall reaction times, and fewer trial omissions. Di/+ rats also exhibited more approaches to the reinforcer receptacle at nonreinforcement times. These results indicate that alterations of vasopressin signaling result in a clear cognitive phenotype, including faster motor initiations and superior choice accuracy in a test of visual attention.

Vasopressin-deficient rats exhibit sensorimotor gating deficits that are reversed by subchronic haloperidol

BACKGROUND

Brattleboro (BB) rats are Long Evans rats with a single base pair genetic mutation that impairs their ability to synthesize vasopressin, a neurotransmitter and neurohormone. Brattleboro rats are known to have deficits in memory, emotional reactivity, motivation, attention, and social recognition, abnormalities associated with schizophrenia. Prepulse inhibition (PPI) of the acoustic startle reflex (ASR) is a measure of sensorimotor gating. Prepulse inhibition is deficient in unmedicated schizophrenia patients, and PPI deficits in schizophrenia may be related to the cognitive and behavioral abnormalities associated with this disorder. In this study we tested the hypothesis that BB rats exhibit PPI deficits analogous to those exhibited by schizophrenia patients.

METHODS

In one experiment, BB rats homozygous (BB-Ho) or heterozygous (BB-Hz) for the mutated vasopressin gene were compared with normal Long Evans (LE) rats from the same breeder source. In separate studies, BB-Ho and LE rats were treated with acute or subchronic (22 days) injections of haloperidol.

RESULTS

Both BB-Ho and BB-Hz rats had significantly higher ASR and significantly lower PPI compared with LE rats, with BB-Ho rats exhibiting the lowest PPI among all three genotypes. Furthermore, a single subcutaneous (SC) injection of haloperidol (0.5 mg/kg) did not reverse the PPI deficits in BB rats. In contrast, daily SC administration of haloperidol for 22 days reversed PPI deficits in BB rats.

CONCLUSIONS

These results suggest that PPI deficient BB rats may be an important genetic model of PPI deficits, which may help elucidate genetic, pharmacologic, and pathophysiologic mechanisms underlying PPI deficits and the effects of antipsychotic drugs on PPI.

Anatomical and functional demonstration of a multisynaptic suprachiasmatic nucleus adrenal (cortex) pathway

In view of mounting evidence that the suprachiasmatic nucleus (SCN) is directly involved in the setting of sensitivity of the adrenal cortex to ACTH, the present study investigated possible anatomical and functional connections between SCN and adrenal. Transneuronal virus tracing from the adrenal revealed first order labelling in neurons in the intermedio-lateral column of the spinal cord that were shown to receive an input from oxytocin fibres and subsequently second-order labelling in neurons of the autonomic division of the paraventricular nucleus. The latter neurons were shown to receive an input from vasopressin or vasoactive intestinal peptide (VIP) containing SCN efferents. The true character of this SCN input to second-order neurons was also demonstrated by the fact that third-order labelling was present within the SCN, vasopressin or VIP neurons. The functional presence of the SCN-adrenal connection was demonstrated by a light-induced fast decrease in plasma corticosterone that could not be attributed to a decrease in ACTH. Using intact and SCN-lesioned animals, the immediate decrease in plasma corticosterone was only observed in intact animals and only at the beginning of the dark period. This fast decrease of corticosterone was accompanied by constant basal levels of blood adrenaline and noradrenaline, and is proposed to be due to a direct inhibition of the neuronal output to the adrenal cortex by light-mediated activation of SCN neurons. As a consequence, it is proposed that the SCN utilizes neuronal pathways to spread its time of the day message, not only to the pineal, but also to other organs, including the adrenal, utilizing the autonomic nervous system.

Decreased hypothalamic serotonin levels in adult rats treated neonatally with clomipramine

Early postnatal treatment with the antidepressant drug clomipramine has repeatedly been shown to lead to behavioural and physiological changes in adult rats. To provide some neurochemical correlates to these studies we have measured a number of monoaminergic parameters in the brains of adult (one year old) rats that were treated twice daily with 15 mg/kg clomipramine from postnatal day 2-14. The most consistent finding was that the hypothalamic levels of serotonin (5-HT) were decreased and those of the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) were increased in rats irrespectively whether they went through a range of behavioural and physiological tests or not. The numbers of beta-adrenoceptors in the frontal cortex and of alpha 2-adrenoceptors in the amygdala/piriform cortex were not changed. The decrease in hypothalamic 5-HT concentrations appears to be up to now the most consistent neurochemical alteration in adult rats that were neonatally treated with antidepressant drugs. It is, however, not clear what the relation is with the functional changes in these rats, that are proposed by some authors as an animal model for depression.

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.

Interactions between vasopressin and food restriction on stress-induced analgesia

To investigate the role of the hormone vasopressin (VP) in mediating the response of an organism to food restriction stress-induced analgesia, tail flick latencies and scored qualitative behavioral responses were recorded in VP-containing (LE) rats and VP-deficient (DI) rats. These variables were measured under nonstressed (ad lib) and stressed (food restriction) conditions. In the ad lib condition, DI and LE rats had a similar tail flick latency and scored qualitative behavioral response to the stimulus eliciting the tail flick. During the food restriction condition, however, LE animals developed significant food restriction stress-induced analgesia, as measured by tail flick latency. On the other hand, DI animals did not develop significant analgesia. In addition, DI animals exhibited a significantly greater scored qualitative behavioral response to the stimulus eliciting the tail flick than LE animals. These results demonstrate that VP plays an important role in the regulation of food restriction stress-induced analgesia, as well as the scored qualitative behavioral response elicited by the tail flick stimulus.

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.

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.

Microdialysis administration of vasopressin into the septum improves social recognition in Brattleboro rats

The role of septal arginine vasopressin (AVP) in a social recognition test was investigated in both homozygous Brattleboro (HO-DI) and normal Long-Evans rats. To do this, the duration of investigation of conspecific juveniles by untreated adult males of both rat strains was measured before and after inter exposure intervals of 30 and 120 min. Additionally, a microdialysis administration technique was used to administer synthetic AVP (0.2 or 2.0 ng) or its V1 receptor antagonist d(CH2)5Tyr(Me)AVP (5.0 ng) into the mediolateral septum concomitantly with the behavioral test. Untreated HO-DI rats showed an impaired social recognition compared with untreated Long-Evans rats. A similarly impaired performance was observed after V1 receptor antagonist treatment of Long-Evans rats. Microdialysis administration of synthetic AVP, on the other hand, significantly improved social recognition in both rat strains. The data suggest that endogenous AVP in the septal brain area is critically involved in the acquisition, storage, and/or recall of olfactory cues in rats.

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.

Neonatal lesions of the ventral tegmental area affect monoaminergic responses to stress in the medial prefrontal cortex and other dopamine projection areas in adulthood

A mean decrease of dopamine (DA) to 20% and serotonin to 25-30% of control levels was found in the medial prefrontal cortex (mPFC) and amygdala/piriform cortex (A/PC) of adult rats with neonatal lesions of the ventral tegmental area (VTA). The metabolites were less decreased suggesting an increased activity of the remaining terminals. Moderate decreases to 30-75% were detected for DA and serotonin in the nucleus accumbens, olfactory tubercle and striatum. Footshock stress in control animals resulted in a strong increase (200% of control) in DA metabolites in mPFC and A/PC. The noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) in A/PC was strongly increased to 240%. When stress was given to the neonatally VTA-lesioned animals these neurochemical responses were reduced compared to the nonlesioned rats. In the case of DA in the mPFC this was clearly due to a loss of stress response in the severe lesion group where DA is depleted to less than 20% of control. The stress-induced small increases in DA metabolism in tubercle, accumbens and striatum and serotonin metabolism in the striatum (20-40%) were entirely lost, while the MHPG increase in the A/PC was blunted. The present results suggest that moderate and severe lesions of DA and serotonin alter or prevent the normal activation of these transmitter systems and even of the noradrenergic system to stress.

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.

Monoamine and amino acid content in brain regions of Brattleboro rats

Monoamine and amino acid content were measured in brain regions from 12 week old male, homozygous Brattleboro (DI, n = 12) and Long-Evans control (LE, n = 12) rats. Norepinephrine (NE) content was significantly elevated (16-25%) in the spinal cord, pons-medulla and anterior hypothalamus of DI rats when compared to LE controls. NE content of the neurointermediate lobe of pituitary in DI rats was almost twice that of LE controls. Serotonin content was also significantly elevated in the spinal cord, pons-medulla, anterior hypothalamus and forebrain of DI rats relative to the LE controls. Taurine content in DI rats was increased (31-42%) above that of LE rats in the anterior hypothalamus, striatum and forebrain. Glutamine content was also greater in DI rats than LE in the spinal cord, pons-medulla, anterior hypothalamus, striatum, hippocampus and forebrain. The changes in monoamine and amino acid content were discussed in relation to the cardiovascular and osmoregulatory deficits that are present in DI rats due to arginine vasopressin (AVP) deficiency. The possible role of AVP in modulating NE turnover was also discussed. The increase in brain TAU content in DI rats may be a physiological response to hypernatremia.