Chronic light exposure alters serotonergic and orexinergic systems in the rat brain and reverses maternal separation-induced increase in orexin receptors in the prefrontal cortex

Maternal separation (MS) is a well-established rodent model of depression. Chronic constant light (CCL) treatment during adolescence has been shown to reverse the depression-like behaviour induced by MS. We aimed to further delineate the antidepressant effect of light by investigating the involvement of the dopaminergic, serotonergic and orexinergic systems. MS was used to induce changes in adult male Sprague-Dawley rats, some of whom were also treated with CCL for 3 weeks during adolescence. At P80, rats were decapitated and brain tissue collected for analysis of glutamate- and potassium-stimulated dopamine release in the nucleus accumbens (NAc) using an in vitro superfusion technique. Enzyme-linked immunosorbent assays were employed to measure 5-hydroxytryptamine (5-HT) levels in the hypothalamus and prefrontal cortex (PFC). Western blotting was used to measure orexin receptor 1 (OXR-1) and 2 (OXR-2) in the PFC. MS did not affect 5-HT levels in these rats. However, CCL increased hypothalamic 5-HT and reduced 5-HT levels in the PFC. CCL had opposite effects on OXR levels in the PFC of maternally separated and non-separated rats. MS increased OXR-1 and OXR-2 levels in the PFC, an effect that was normalized by CCL treatment. MS reduced glutamate-stimulated dopamine release in the NAc, an effect that was not reversed by CCL. The present results suggest that CCL treatment affects 5-HT and orexinergic systems in the MS model while not affecting the MS-induced decrease in dopamine release in the NAc. The reversal of changes in the orexinergic system may be of particular relevance to the antidepressant effect of CCL in depression.

Female rats are resistant to developing the depressive phenotype induced by maternal separation stress

Many stress-related psychiatric disorders are more common in women than in men. We aimed to determine how female rats respond to maternal separation (MS; removal of the dam from the litter for 3 h/day from postnatal day (P) 2-14)). A subset of MS females were also exposed to chronic constant light for 3 weeks during adolescence (P42-63) to investigate whether the antidepressant effect of light treatment, previously observed in male rats, could be seen in female rats. Ultrasonic vocalizations (22 kHz) were recorded and the forced swim test was conducted immediately after light exposure (P65-67) and 33 days later (P98-99) to determine depressive-like behaviour. Key proteins in the MAPK signal transduction pathway (MKP-1, phospho-ERK, total ERK) and a synaptosomal marker (synaptophysin) were measured in the ventral hippocampus. We found that MS decreased the duration of 22 kHz vocalizations at P65 which was reversed by subsequent light. Light exposure increased time spent in the inner zone of the open field and the number of 22 kHz calls in response to novelty at P98. MS decreased the time females spent immobile and increased time actively swimming in the forced swim test at P67 but not at P99. MKP-1 and synaptophysin levels remained unchanged while MS decreased phospho-ERK levels in the ventral hippocampus. In contrast to clinical findings, the results suggest that female rats may be resistant to MS-induced depression-like behaviour. The behavioural effects of MS and light treatment in female rats may involve the MAPK/ERK signal transduction pathway.

Behavioural and biochemical changes in maternally separated Sprague-Dawley rats exposed to restraint stress

Early life adversity has been associated with the development of various neuropsychiatric disorders in adulthood such as depression and anxiety. The aim of this study was to determine if stress during adulthood can exaggerate the depression-/anxiety-like behaviour observed in the widely accepted maternally separated (MS) Sprague-Dawley (SD) rat model of depression. A further aim was to determine whether the behavioural changes were accompanied by changes in hippocampal brain-derived neurotrophic factor (BDNF) and the protein profile of the prefrontal cortex (PFC). Depression-/anxiety-like behaviour was measured in the elevated plus maze, open field and forced swim test (FST) in the MS SD rats exposed to chronic restraint stress in adulthood. As expected, MS increased immobility of SD rats in the FST but restraint stress did not enhance this effect of MS on SD rats. A proteomic analysis of the PFC revealed a decrease in actin-related proteins in MS and non-separated rats subjected to restraint stress as well as a decrease in mitochondrial energy-related proteins in the stressed rat groups. Since MS during early development causes a disruption in the hypothalamic-pituitary-adrenal axis and long-term changes in the response to subsequent stress, it may have prevented restraint stress from exerting its effects on behaviour. Moreover, the decrease in proteins related to mitochondrial energy metabolism in MS rats with or without subsequent restraint stress may be related to stress per se and not depression-like behaviour, because rats subjected to restraint stress displayed similar decreases in energy-related proteins and spent less time immobile in the FST than control rats.

Methamphetamine reversed maternal separation-induced decrease in nerve growth factor in the ventral hippocampus

Stress has been suggested to predispose individuals to drug abuse. The early life stress of maternal separation (MS) is known to alter the response to drugs of abuse later in life. Exposure to either stress or methamphetamine has been shown to alter neurotrophic factors in the brain. Changes in neurotrophin levels may contribute to the underlying molecular mechanisms responsible for drug use- and stress-induced behaviours. The purpose of the present study was to investigate the individual effects of MS and methamphetamine administration during adolescence and the combined effects of both stressors on brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) levels in the dorsal and ventral hippocampus (HC) in adulthood. Methamphetamine administration (1 mg/kg, daily from postnatal day (PND) 33 to 36 and from PND 39 to 42), MS and the combination of the two stressors resulted in decreased BDNF levels in both the dorsal and ventral HC. MS decreased NGF levels in the ventral HC which was restored by methamphetamine administration in adolescence. In the dorsal HC, NGF remained unaltered by either stressor alone or in combination. We propose that the restoration of NGF levels in the ventral HC may reflect a possible compensatory mechanism in response to methamphetamine exposure in adolescence following the early life stress of MS.

Changes in behavior and ultrasonic vocalizations during antidepressant treatment in the maternally separated Wistar-Kyoto rat model of depression

Genetic predisposition and stress are major factors in depression. The objective of this study was to establish a robust animal model of depression by selecting the appropriate substrain of the Wistar-Kyoto (WKY) rat, and subjecting these rats to the stress of maternal separation during the early stages of development. The initial experiment identified WKY/NCrl as the appropriate substrain of WKY to use for the study. In the second part of the study, depression-like behavior and ultrasonic vocalizations (USVs) were recorded in WKY/NCrl and maternally separated WKY/NCrl rats during the course of reversal of depression-like behavior. Wistar rats served as the reference strain. In adulthood, non-separated WKY/NCrl, maternally separated WKY/NCrl and Wistar rats were injected intraperitoneally with either saline or desipramine (15 mg/kg/day) for 15 days and their behavior recorded. Desipramine decreased immobility and increased active swimming and struggling behavior of WKY/NCrl in the FST and also decreased their USVs in response to removal of cage mates. The USVs in this study appeared to signal an attempt to re-establish social contact with cage mates and provided a measure of social dependence. Maternally separated WKY/NCrl rats displayed more anxiety than normally reared WKY/NCrl rats and responded to the anxiolytic effects of desipramine. The present findings support the use of WKY/NCrl as an animal model of depression. Maternal separation increased the anxiety-like behavior of the WKY/NCrl, thus providing a robust model to study depression- and anxiety-related behavior.

Exercise partly reverses the effect of maternal separation on hippocampal proteins in 6-hydroxydopamine-lesioned rat brain

Animals subjected to maternal separation stress during the early stages of development display behavioural, endocrine and growth factor abnormalities that mirror the clinical findings in anxiety/depression. In addition, maternal separation has been shown to exacerbate the behavioural deficits induced by 6-hydroxydopamine (6-OHDA) in a rat model of Parkinson's disease. In contrast, voluntary exercise reduced the detrimental effects of 6-OHDA in the rat model. The beneficial effects of exercise appeared to be largely due to compensation in the non-lesioned hemisphere. The aim of the present study was to investigate whether voluntary exercise for 3 weeks could reverse the effects of maternal separation in rats challenged with the neurotoxin 6-OHDA infused into the medial forebrain bundle after 1 week of exercise, at postnatal day 60. The rats were killed 2 weeks later, at postnatal day 74. Their brains were dissected and the hippocampus rapidly removed for proteomic analysis by isobaric tagging (iTRAQ) and quantification of peptides by matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS). Maternal separation upregulated hippocampal proteins functionally involved in energy metabolism (nucleoside diphosphate kinase B, enolase and triosephosphate isomerase) and synaptic plasticity (α-synuclein, tenascin-R, Ba1-667, brevican and neurocan core protein) in the non-lesioned hemisphere. Exercise reversed many of these changes by downregulating the levels of hippocampal proteins functionally associated with energy metabolism (nucleoside diphosphate kinase B, enolase and triosephosphate isomerase) and synaptic plasticity (α-synuclein, tenascin-R, Ba1-667, brevican and neurocan core protein) in the non-lesioned hemisphere of rats subjected to maternal separation. Exercise and maternal separation therefore appeared to have opposing effects on the hippocampus in the non-lesioned hemisphere of the rat brain. Exercise seemed partly to reverse the effects of maternal separation stress on these proteins in the non-lesioned hemisphere. The partial reversal of maternal separation-induced proteins by exercise in the non-lesioned side sheds some insight into the mechanism by which exercise alters the molecular role players involved in determining the consequences of early life stress.

Effects of maternal separation and methamphetamine exposure on protein expression in the nucleus accumbens shell and core

Early life adversity has been suggested to predispose an individual to later drug abuse. The core and shell sub-regions of the nucleus accumbens are differentially affected by both stressors and methamphetamine. This study aimed to characterize and quantify methamphetamine-induced protein expression in the shell and core of the nucleus accumbens in animals exposed to maternal separation during early development. Isobaric tagging (iTRAQ) which enables simultaneous identification and quantification of peptides with tandem mass spectrometry (MS/MS) was used. We found that maternal separation altered more proteins involved in structure and redox regulation in the shell than in the core of the nucleus accumbens, and that maternal separation and methamphetamine had differential effects on signaling proteins in the shell and core. Compared to maternal separation or methamphetamine alone, the maternal separation/methamphetamine combination altered more proteins involved in energy metabolism, redox regulatory processes and neurotrophic proteins. Methamphetamine treatment of rats subjected to maternal separation caused a reduction of cytoskeletal proteins in the shell and altered cytoskeletal, signaling, energy metabolism and redox proteins in the core. Comparison of maternal separation/methamphetamine to methamphetamine alone resulted in decreased cytoskeletal proteins in both the shell and core and increased neurotrophic proteins in the core. This study confirms that both early life stress and methamphetamine differentially affect the shell and core of the nucleus accumbens and demonstrates that the combination of early life adversity and later methamphetamine use results in more proteins being affected in the nucleus accumbens than either treatment alone.

Early maternal separation leads to down-regulation of cytokine gene expression

Exposure to stressors may lead to subsequent alterations in the immune response. The precise mechanisms underlying such vulnerability are poorly understood, but may be hypothesized to include changes in cytokine systems. Maternal separation was used as a model of exposure to early life stressors. Subsequent cytokine gene expression was studied using a cytokine gene expression array. Maternal separation resulted in significant down-regulation of the expression of 6 cytokine genes; chemokine ligand 7, chemokine receptor 4, interleukin 10, interleukin-1beta, interleukin 5 receptor alpha and integrin alpha M. Specific cytokines may be involved in mediating the effects of early adversity on subsequent immunosuppression. Further work is needed to delineate fully the relationship between early adversity, immune alterations, and behavioural changes.

The effects of lobeline and naltrexone on methamphetamine-induced place preference and striatal dopamine and serotonin levels in adolescent rats with a history of maternal separation

Exposure to early life stress has been suggested to increase an individual's vulnerability to methamphetamine (MA) dependence. Although there is no cure for drug dependence, the opioid and vesicular monoamine transporter 2 (VMAT2) systems may be useful targets for treatment insofar as they play pivotal roles in the neurochemistry of addiction. Here we investigated the effects of naltrexone (opioid antagonist) and lobeline (VMAT2 inhibitor) on MA-induced place preference in adolescent rodents subjected to early life trauma (maternal separation, MS) and controls, as well as the effects on dopamine and serotonin levels in the striatum. We found: (1) maternal separation attenuated methamphetamine-induced place preference; (2) lobeline and naltrexone treatment had differential effects on serotonin and dopamine concentrations in the striatum, naltrexone increased serotonin levels in the maternally separated animals. The hypothesized effect of early adversity increasing MA-induced place preference may not be apparent in adolescence. However the data are consistent with the hypothesis that early life stress influences neurochemical pathways that predispose an individual to drug dependence.

Maternal separation alters nerve growth factor and corticosterone levels but not the DNA methylation status of the exon 1(7) glucocorticoid receptor promoter region

Separating rat pups from their mothers during the early stages of life is an animal model commonly used to study the development of psychiatric disorders such as anxiety and depression. The present study investigated how soon after the termination of the maternal separation period behavioural and neuroendocrine abnormalities relevant to above-mentioned illnesses would manifest. Sprague Dawley rat pups were subjected to maternal separation (3 h per day from postnatal day 2 through 14) and their behaviour and HPA axis activity determined 7 d later. We also measured nerve growth factor levels in their hippocampi and assessed the DNA methylation status of the promoter region of exon 1(7) of the glucocorticoid receptor in this brain region. As early as 7 d after the termination of the adverse event, a change in behaviour was observed that was associated with increased plasma corticosterone release and elevated nerve growth factor levels in the hippocampus. No alteration in the methylation status of the exon 1(7) glucocorticoid receptor promoter region was observed. Our data indicate that early life adversity may lead to the rapid development of abnormal behaviours and HPA axis dysregulation though no epigenetic changes to the exon 1(7) glucocorticoid receptor promoter region occurred. We further propose that the observed increased neurotrophin levels reflect compensatory mechanisms that attempt to combat the long-term deleterious effects of maternal separation.

Maternal separation exaggerates the toxic effects of 6-hydroxydopamine in rats: implications for neurodegenerative disorders

Many studies have shown that early life stress may lead to impaired brain development, and may be a risk factor for developing psychiatric pathologies such as depression. However, few studies have investigated the impact that early life stress might have on the onset and development of neurodegenerative disorders, such as Parkinson's disease, which is characterized in part by the degeneration of dopaminergic neurons in the nigrostriatal pathway. The present study subjected rat pups to a maternal separation paradigm that has been shown to model adverse early life events, and investigated the effects that it has on motor deficits induced by a unilateral, intrastriatal injection of 6-hydroxydopamine (12 microg/4 microl). The female rats were assessed for behavioral changes at 28 days post-lesion with a battery of tests that are sensitive to the degree of dopamine loss. The results showed that rats that had been subjected to maternal separation display significantly impaired performance in the vibrissae and single-limb akinesia test when compared to normally reared animals. In addition, there was a significant increase in the loss of tyrosine hydroxylase staining in maternally separated rats. Our results therefore suggest that adverse experiences sustained during early life contribute to making dopamine neurons more susceptible to subsequent insults occurring during more mature stages of life and may therefore play a role in the etiopathogenesis of Parkinson's disease.

Early pubertal female rats are more resistant than males to 6-hydroxydopamine neurotoxicity and behavioural deficits: a possible role for trophic factors

PURPOSE

The infusion of 6-hydroxydopamine (6-OHDA) into the nigrostriatal pathway in rats is commonly used to produce an animal model of Parkinson's disease (PD). However, most studies use male adult animals only. The present study focused on possible gender differences in vulnerability to 6-OHDA during the early pubertal period when the effects exerted by gonadal steroid hormones are unpronounced.

METHODS

Young Sprague-Dawley rats, 35 days of age, were given a low vs. a higher dose of 6-OHDA in the medial forebrain bundle (MFB). Control rats received equivalent saline infusions. At 14 days post-surgery the rats were evaluated for forelimb akinesia.

RESULTS

For the higher dose of 6-OHDA the female rats were less impaired than males in making adjustment steps in response to a weight shift and in a vibrissae-evoked forelimb placing test. Tyrosine hydroxylase (TH) immunoreactivity was significantly higher for the female rats.

CONCLUSION

Early gender differences in cell survival factors and/or other promoters of neuroplasticity may have contributed to the beneficial outcome in the females. For example, NGF was found to be higher in the female rats following administration of DA neurotoxin. It is unclear whether gonadal steroids are involved, and if so, whether female hormones are protective or whether male hormones are prodegenerative. Determining the mechanisms for the improved outcome in the young female rats may lead to potential treatment strategies in PD.

Increased AMPA receptor function in slices containing the prefrontal cortex of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) are used as a genetic model for attention-deficit hyperactivity disorder (ADHD), since they have behavioral characteristics that mimic the major symptoms of ADHD. We have previously shown that dopaminergic and noradrenergic systems are altered in the prefrontal cortex of SHR compared to normotensive Wistar-Kyoto (WKY) control rats. We also showed that neural circuits that use glutamate as a neurotransmitter increased norepinephrine release from rat prefrontal cortex slices and that glutamate caused significantly greater release of norepinephrine from prefrontal cortex slices of SHR than from those of WKY. The effect of glutamate did not appear to be mediated by NMDA receptors, since NMDA did not exert any effect on norepinephrine release and the NMDA receptor antagonist MK-801 did not reduce the effect of glutamate. In this investigation we show that the stimulatory effect of glutamate is greater in SHR than in WKY and that the effect can be antagonised by the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). The results suggest that glutamatergic neuron terminals in rat prefrontal cortex establish synaptic contacts with noradrenergic terminals to enhance norepinephrine release by activation of AMPA receptors and that this enhancement is amplified in SHR.

Increased glutamate-stimulated norepinephrine release from prefrontal cortex slices of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) have behavioral characteristics (hyperactivity, impulsiveness, poorly sustained attention) similar to the behavioral disturbances of children with attention-deficit hyperactivity disorder (ADHD). We have previously shown that dopaminergic and noradrenergic systems are disturbed in the prefrontal cortex of SHR compared to their normotensive Wistar-Kyoto (WKY) control rats. It was of interest to determine whether the underlying neural circuits that use glutamate as a neurotransmitter function normally in the prefrontal cortex of SHR. An in vitro superfusion technique was used to demonstrate that glutamate caused a concentration-dependent stimulation of [3H]norepinephrine release from rat prefrontal cortex slices. Glutamate (100 microM and 1 mM) caused significantly greater release of norepinephrine from prefrontal cortex slices of SHR than from control slices. The effect of glutamate was not mediated by NMDA receptors, since NMDA (10 and 100 microM) did not exert any effect on norepinephrine release and MK-801 (10 microM) did not antagonize the effect of 100 microM glutamate. These results demonstrate that glutamate stimulates norepinephrine release from rat prefrontal cortex slices and that this increase is enhanced in SHR. The results are consistent with the suggestion that the noradrenergic system is overactive in prefrontal cortex of SHR, the animal model for ADHD.

Methylphenidate affects striatal dopamine differently in an animal model for attention-deficit/hyperactivity disorder--the spontaneously hypertensive rat

The spontaneously hypertensive rat (SHR) is used as a model for attention-deficit/hyperactivity disorder (ADHD) because it has behavioural characteristics (hyperactivity, impulsiveness, poorly sustained attention) similar to those of ADHD. ADHD children have been shown to have reduced striatal activation in certain tasks. SHR have reduced striatal dopamine release in response to electrical stimulation. The present study set out to investigate possible long-term effects of methylphenidate treatment on dopaminergic function in striatal slices of SHR compared to their normotensive Wistar-Kyoto (WKY) control rats. Methylphenidate treatment (3 mg/kg daily for 14 days) did not normalize the decreased electrically-stimulated release of [(3)H]dopamine from SHR caudate-putamen slices nor did it affect postsynaptic D(2) receptor function. However, the second electrical stimulus caused a relatively greater release of [(3)H]dopamine from caudate-putamen slices of methylphenidate-treated SHR than from vehicle-treated SHR, suggesting that presynaptic mechanisms controlling dopamine release had been altered. Interestingly, [(3)H]dopamine release from WKY caudate-putamen slices in response to D(2) autoreceptor blockade by the antagonist, sulpiride, was selectively increased by methylphenidate treatment. This effect was not seen in SHR possibly because D(2) autoreceptor function had already been up-regulated. The results show that methylphenidate is unable to enhance D(2) autoreceptor function in SHR.

The nucleus accumbens motor-limbic interface of the spontaneously hypertensive rat as studied in vitro by the superfusion slice technique

The behavioral disturbances of attention-deficit hyperactivity disorder (ADHD) have been attributed to dysfunction of the mesolimbic dopaminergic (DA) projection from the ventral tegmental area of the midbrain. DA released from terminals in the nucleus accumbens (interface between limbic and motor areas of the brain) draws attention to unexpected, behaviorally significant events and provides the motivational drive for reward-related behavior. An in vitro superfusion technique was used to show that depolarization (25 mM K+)-induced release of DA from nucleus accumbens slices of spontaneously hypertensive rats (SHR, animal model for ADHD) was significantly lower than that of Wistar-Kyoto controls (WKY). Evidence also suggested that DA autoreceptor efficacy was increased at low endogenous agonist concentrations. D2 receptor blockade by the antagonist, sulpiride, caused a significantly greater increase in the electrically stimulated release of DA from nucleus accumbens slices of SHR compared to WKY. This suggested that presynaptic regulation of DA release had been altered in SHR to cause down-regulation of the DA system. This could have occurred at an early stage of development in an attempt to compensate for abnormally high DA concentrations. The reduction in DA transmission could have left the adult SHR with impaired DA reward/reinforcement mechanisms, resulting in the behavioral disturbances characteristic of ADHD.

Origins of the unusual hygroscopicity observed in LY297802 tartrate

Hygroscopicity is an important physical property of drug materials, which can significantly impact physicochemical stability and bulk processing and handling characteristics. Although moisture sorption behavior is routinely investigated for pharmaceutical compounds, the nature of water-solid interactions is generally not well-understood at the molecular level for nonstoichiometric or variable hydrates. The unusual hygroscopic behavior of the muscarinic agonist, LY297802 tartrate, has been investigated using moisture sorption analysis, solid-state NMR (SSNMR) spectroscopy, and X-ray crystallography. LY297802 tartrate shows a unique tendency to form nonstoichiometric hydrates of variable, but specific, composition, with water content varying continuously from 0 to 0.5 mol (hemihydrate). The propensity of this crystal form to rapidly equilibrate with the humidity in the environment may be rationalized in terms of a sequential migration of the weakly bound water of hydration in to and out of readily accessible hydrogen-bonding sites in the lattice.

Nanoporous Molecular Sandwiches: Pillared Two-Dimensional Hydrogen-Bonded Networks with Adjustable Porosity

Crystal engineering of molecular materials is commonly frustrated by the absence of reliable structural paradigms that are needed for systematic design of crystal lattices with predictable structure and desirable function. This problem can be attributed, at least partially, to the absence of robust supramolecular motifs that serve as synthons for the assembly of crystal lattices. A novel class of molecular crystals based on two-dimensional hydrogen (H)-bonded networks comprising guanidinium ions and the sulfonate groups of alkane- or arenedisulfonate ions is described. The disulfonate ions act as pillars that connect opposing H-bonded sheets and form nanoporous galleries with one-dimensional channels. The flexibility of the H-bonded network allows the galleries to adapt to changes in the steric requirements of guest molecules that occupy the channels. This robustness reduces crystal engineering to the last remaining dimension, enabling rational adjustment of the gallery heights by choice of the disulfonate pillar.

Kindled seizures do not affect adenosinergic inhibition of DA or ACh release in rat accumbens or PFC

Epileptic seizures are thought to terminate largely as a result of the extracellular accumulation of the purinergic neuromodulator, adenosine, released by discharging neurons. However, the postictal surge in extracellular adenosine and its widespread inhibitory effects are limited in time to only a few minutes and cannot directly account for increased resistance to seizures and the complex behavioural and motivational effects that may persist for hours or days after a seizure. The present study examined whether kindled seizures might alter the sensitivity or efficacy of inhibitory presynaptic adenosine receptors, and thereby induce more enduring changes in downstream transmitter systems. Rats were kindled in the amygdala of the dominant cerebral hemisphere, contralateral to the preferred direction of rotation, and their brains were removed either 2 h or 28 days after completion of kindling. Inhibition of electrically stimulated release of dopamine (DA) and acetylcholine (ACh) by the A1 adenosine-receptor agonist, R-phenylisopropyladenosine (R-PIA) was then measured in the prefrontal cortex (PFC) and nucleus accumbens. R-PIA (1.0 microM) inhibited [1H]DA release from PFC and nucleus accumbens tissue, and [14C]ACh release from nucleus accumbens tissue, but release was unaffected by prior kindling, regardless of the intervening interval. These results do not support suggestions that DA or ACh might mediate the effects of seizure-induced changes in purinergic inhibitory tone so as to cause long-term shifts in seizure threshold and postictal behavior.

Solid-state structure of a layered hydrogen-bonded salt: guanidinium 5-benzoyl-4-hydroxy-2-methoxybenzenesulfonate methanol solvate

Guanidinium 5-benzoyl-4-hydroxy-2-methoxybenzene-sulfonate methanol solvate [C(NH2)3 +.(C14H11O3)SO3 −.CH3OH] crystallizes into a layered structure containing a two-dimensional hydrogen-bonded network typical of guanidinium alkane- and arenesulfonates. All six guanidinium protons and six sulfonate oxygen lone-pair acceptors participate in hydrogen bonding to form nearly planar pseudohexagonal hydrogen-bonded sheets, which can be viewed as parallel connected hydrogen-bonded ribbons. The 5-benzoyl-4-hydroxy-2-methoxybenzene groups are oriented to the same side of each ribbon, but the orientation of these groups on adjacent ribbons alternates with respect to the hydrogen-bonded sheet. The planar sheets stack with interdigitation of the arene groups, resulting in a structure in which layers of 5-benzoyl-4-hydroxy-2-methoxybenzene groups are separated by ionic hydrogen-bonded sheets. Each methanol molecule forms a hydrogen bond to one of the sulfonate O atoms, resulting in this oxygen forming a total of three hydrogen bonds, and fills void volume between the interdigitated 5-benzoyl-4-hydroxy-2-methoxybenzene groups of neighboring sheets. The benzophenone hydroxyl proton forms an intramolecular hydrogen bond to the carbonyl oxygen.

Activation of the subthalamic nucleus and pedunculopontine tegmentum: does it affect dopamine levels in the substantia nigra, nucleus accumbens and striatum?

Parkinson's disease is a neurodegenerative disorder, of which the most prominent morphological feature is the progressive loss of dopaminergic nigrostriatal neurons. Increased glutamatergic transmission in the basal ganglia has been implicated in the pathophysiology of Parkinson's disease (PD). This study investigated whether death of substantia nigra (SN) dopaminergic neurons could be caused by the hyperactivity of afferent pathways resulting in the release of a toxic dose of excitatory amino acids in the SN. Twice-daily unilateral stimulation of the subthalamic nucleus (STN) for 21 days, using two different pulse frequencies and current strengths, significantly increased amphetamine-induced rotation, whereas sham stimulated rats showed significantly reduced rotation. Striatal and SN dopamine (DA) levels were unaffected when compared to naïve and sham stimulated rats. However, levels of the DA metabolite, homovanillic acid (HVA), were significantly higher in the ipsilateral anterior striata of rats that had been stimulated at high frequency (100 Hz) and low current (100 microA) as compared to sham treated animals. Stimulation of the pedunculopontine tegmentum (PPT), using a single kainic acid injection, did not affect DA concentration in the ipsilateral striatum and nucleus accumbens when compared to sham-treated rats. DA levels in the contralateral striatum and nucleus accumbens of lesioned rats were significantly higher than ipsilateral levels. DOPAC/DA ratios were lower in the contralateral striatum and nucleus accumbens, suggesting decreased DA turnover. Glutamic acid decarboxylase activity was significantly higher in the ipsilateral than the contralateral SN. The physical manifestations of PD require a large reduction in caudate and putamen DA levels and no such depletion was measured in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha 2-adrenoceptor mediated inhibition of [3H]dopamine release from nucleus accumbens slices and monoamine levels in a rat model for attention-deficit hyperactivity disorder

The spontaneously hypertensive rat (SHR) has been proposed as an animal model for attention-deficit hyperactivity disorder (ADHD). The behavioural problems have been suggested to be secondary to altered reinforcement mechanisms in which nucleus accumbens dopaminergic activity plays an important role. Interaction between the noradrenergic and dopaminergic system in the nucleus accumbens has been implicated in the locomotor hyperactivity and impaired discriminative performance of SHR. The present study therefore investigated whether there was any change in the alpha 2-adrenoceptor mediated inhibition of dopamine release from nucleus accumbens slices of SHR in comparison with their normotensive Wistar-Kyoto (WKY) controls. The electrically stimulated release of [3H]dopamine (DA) from nucleus accumbens slices was decreased to a similar extent by UK14,304, an alpha 2-adrenoceptor agonist, in SHR and WKY. Basal norepinephrine (NE) levels were increased in locus coeruleus (LC) and A2 noradrenergic nuclei, but not in the A1 nucleus of SHR, while basal serotonin (5-HT) levels were increased in all these pons-medulla nuclei. These results suggest that a primarily dysfunctional LC and A2 nucleus does not have a secondary effect on dopaminergic transmission in the nucleus accumbens via alpha 2-adrenoceptor mediated inhibition of DA release. Basal monoamine levels in several brain areas of SHR were significantly different from that of WKY. DA, and 5-HT turnover were decreased in SHR versus WKY suggesting hypofunctional dopaminergic and serotonergic systems in some brain areas of SHR.

Decreased hippocampal noradrenaline does not affect corticosterone release following electrical stimulation of CA1 pyramidal cells

Bipolar electrodes were implanted into the CA1 pyramidal cells of the dorsal hippocampus and the effect of electrical stimulation of these cells on corticosterone secretion was investigated in freely moving rats. Histology showed that the electrodes were positioned in close proximity to the CA1 pyramidal cells. Rats that were subjected to high intensity electrical stimulation (1, 10, and 100 microA) behaved differently when compared to their sham stimulated controls. They were more active and displayed wet dog shakes. Plasma corticosterone levels increased dose-dependently in rats subjected to different electrical stimulation intensities. Although prior treatment (24 hours) of rats with DSP4 (60 mg/kg, i.p.) significantly reduced hippocampal noradrenaline content by 46%, it did not bring about any behavioural changes. DSP4 treatment also had no effect on electrically stimulated corticosterone release. These data suggested that stimulation of CA1 pyramidal cells may lead to increased corticosterone release and that a decrease in hippocampal noradrenaline concentration was unable to alter this corticosterone response.

Lack of effect of bilateral locus coeruleus lesion and antidepressant treatment on gamma-aminobutyric acidB receptors in the rat frontal cortex

The aim of the present study was to investigate whether a disturbance of the central noradrenergic (NA) system could cause changes in gamma-aminobutyric acidB (GABAB) receptors in the rat frontal cortex. Manipulation of the NA projection to the frontal cortex was achieved by bilateral lesion of the locus coeruleus with 6-hydroxydopamine (6-OHDA) or chronic treatment with the NA reuptake blocker and antidepressant drug, desipramine. Precautions were taken to ensure that the GABAB receptor assay was performed optimally and was not confounded by the presence of endogenously generated GABA. The results show conclusively that manipulation of the NA projection did not result in any significant change in the number (Bmax) or affinity (Kd) of GABAB receptors in the frontal cortex. These results do not support the hypothesis that hypoactivity of the central NA system can lead to changes in cortical GABAB receptors and that antidepressant drugs act by increasing GABAB receptor binding in the frontal cortex.

The stimulatory effect of chronic lithium treatment on basal thyrotropin secretion in rats: in vivo antagonism by methylparaben

Chronic treatment of rats with lithium chloride was examined in order to determine its effects on hypothalamic monoamine and metabolite content, basal thyrotropin (TSH) secretion and thyroid function. The hypothalamic concentrations of noradrenaline (NA), dopamine (DA) and its metabolites, dihydroxyphenylacetic acid. (DOPAC) and homovanillic acid (HVA) in the lithium treated rats remained unaltered when compared to control levels. NA turnover and the NA metabolite, 3-methoxy-4-hydroxyphenylglycol (total MHPG), were significantly lower (p < 0.01), whereas both serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), were significantly higher (p < 0.01 and p < 0.02, respectively) in the lithium treated rat hypothalami than in controls. Chronic lithium treatment significantly elevated basal TSH levels (p < 0.05). This effect was antagonized by methyl p-hydroxybenzoate (methylparaben, p < 0.01), which did not itself affect basal TSH levels. Free serum T3 and T4 levels were not significantly affected by chronic lithium treatment, although T4 tended to be slightly lower than control levels. The monoamine changes observed in the hypothalamus of lithium treated rats did not appear to account for the elevated TSH levels observed in these rats since NA activity which is generally regarded as stimulatory was decreased and 5-HT which has an inhibitory effect on TSH secretion, was increased. The elevated TSH levels may have been due to a reduced negative feedback inhibition of TSH release by the mildly reduced circulating T4 levels caused by chronic lithium treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of interaction between alpha 2-adrenoceptors and dopamine D2-receptors in mediating their inhibitory effects on [3H]dopamine release from rat nucleus accumbens slices

The alpha 2-adrenoceptor agonist, UK14304, dose-dependently inhibited the electrically stimulated release of dopamine (DA) from rat nucleus accumbens slices. This effect was antagonized by idazoxan, confirming that it was an alpha 2-adrenoceptor mediated effect. There was no evidence of endogenous activation of noradrenergic receptors suggesting that the alpha 2-adrenoceptor agonist was not acting presynaptically to inhibit noradrenaline release. An in vitro superfusion technique was used to investigate whether there was any interaction between alpha 2-adrenoceptors and DA D2-receptors in mediating their inhibitory effects on [3H]DA release from rat nucleus accumbens slices. alpha 2-Adrenoceptors and DA D2-receptors interact with similar second messenger systems and it was considered that they may compete for a common pool of G-proteins. The inhibitory effects of the alpha 2-adrenoceptor agonist, UK14304, and the DA receptor agonists, quinpirole, apomorphine and pergolide were not independent. However, there was no evidence of any interaction between UK14304 and the DA D2-receptor antagonists, sulpiride or haloperidol, suggesting that the two receptors do not compete for a common pool of G-proteins in mediating their inhibitory effects on DA release.

Alpha 2- and beta-adrenergic stimulation of corticosterone secretion in rats

Bilateral injection of 6-hydroxydopamine into the medial forebrain bundle (MFB) significantly decreased monoamine concentrations in the hypothalamus. The noradrenaline and serotonin content of the paraventricular nucleus (PVN) was also significantly reduced. These drastic decreases in neurotransmitter concentration did not alter basal secretion of corticosterone. Isoproterenol, a beta-adrenoceptor agonist (1 mg/kg, i.p.), significantly stimulated corticosterone release in saline and MFB lesioned rats. This stimulation did not differ significantly between the two groups. Clonidine, an alpha 2-adrenoceptor agonist, injected either intraperitoneally or intracerebrally just dorsal to the PVN, caused a dose-dependent increase in corticosterone secretion. The stimulation of corticosterone release by clonidine (250 micrograms/kg, i.p.) was antagonised by the selective alpha 2-adrenoceptor antagonist, yohimbine (1 mg/kg, i.p.) and significantly reduced by the MFB lesion. These results suggest that corticosterone secretion is stimulated by activation of alpha 2-adrenoceptors which occur on noradrenergic nerve terminals in the PVN.

Effects of ?2- and ?-adrenoceptor agonists on growth hormone secretion following lesion of the noradrenergic system of the rat

The aim of the present investigation was to lesion the noradrenergic system and to measure the effect on growth hormone (GH) secretion following peripheral administration of alpha 2- and beta-adrenoceptor agonists. Direct injection of these agonists into the paraventricular nucleus of the hypothalamus (PVN) and its effect on GH secretion were also investigated. Systemic administration of N-2-chloroethyl-N-ethyl-2-bromobenzylamine (DSP4, 60 mg/kg, injected i.p. 10 days prior to experimentation) significantly decreased the noradrenaline (NA) content of the hippocampus, frontal cortex and hypothalamus but had no effect on the dopamine (DA) or serotonin (5-HT) content of these areas. Bilateral injection of 6-hydroxydopamine (6-OHDA, 10 micrograms/microliters, 14 days prior to experimentation) into the medial forebrain bundle (MFB) caused a greater reduction of NA and also decreased the DA and 5-HT content of the hypothalamus. Analysis of the PVN of the hypothalami of rats following 6-OHDA lesion of the MFB showed significantly decreased NA and 5-HT content. Neither DSP4 treatment nor 6-OHDA lesion of the MFB affected the clonidine (250 micrograms/kg, i.p.) induced stimulation of GH secretion. Injection of isoproterenol (1 mg/kg, i.p.) had varying effects on GH secretion. It stimulated GH release in control rats but not in DSP4 or MFB lesioned rats. Direct injection of clonidine (0.1 microgram/microliters) into the PVN significantly stimulated GH secretion, whereas injection of isoproterenol (2.5 micrograms/microliters) into the PVN did not affect GH levels when compared to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional effects of neurotensin on the electrically stimulated release of [3H]dopamine and [14C]acetylcholine in the rat nucleus accumbens

This study has shown that neurotensin (NT) increases the electrically stimulated release of [3H]DA to a similar extent in all but the extreme caudolateral area of the rat nucleus accumbens and appears to modulate DA release equally in the medial and lateral zones of this brain area. The simultaneous release of ACh was not significantly affected by NT.

Rat brain hypothalamic and hippocampal monoamine and hippocampal beta-adrenergic receptor changes during pregnancy

The concentration of noradrenaline (NA), dopamine (DA), serotonin (5-HT), and their metabolites was measured in hypothalamic and hippocampal brain tissue obtained from non-pregnant, 15- or 20-day pregnant and 4-day postpartum rats. At 20 days of pregnancy, hypothalamic NA and DA concentrations were significantly decreased and their turnover increased relative to postpartum and estrous values, respectively. Hippocampal 3-methoxy-4-hydroxy-phenylglycol (MHPG) levels were significantly decreased at 15 days of pregnancy and 4 days postpartum compared to estrous and 20-day pregnant levels and the MHPG/NA ratio was significantly reduced at 4 days postpartum relative to the estrous value. Hippocampal 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) levels were significantly decreased at 15 days of pregnancy while 5-HIAA levels and the 5-HIAA/5-HT ratio were significantly decreased at 20 days of pregnancy. Hippocampal beta-adrenergic receptor density was significantly lower at 4 days postpartum than at 15 days of pregnancy. A positive correlation was observed between plasma progesterone and hippocampal beta-adrenoceptor Kd values, suggesting a possible causal relationship between these two variables. The monoamine and beta-adrenoceptor changes which occur during pregnancy may be an important contributing factor in determining the mood changes which occur during pregnancy and postpartum.

Regional distribution of monoamines and dopamine D1- and D2-receptors in the striatum of the rat

Dopamine (DA) D1- and D2-receptor densities were determined in 18 discrete areas of the caudate-putamen-globus pallidus of male Wistar rats and compared to local DA concentrations. All three parameters were found to decrease caudally. The globus pallidus was distinguished by the low concentration of DA and its receptors and high noradrenaline (NA) content. While there were no mediolateral differences in DA or DA D1-receptors, a clear mediolateral gradient was observed for DA D2-receptors which extended over several sections of the brain. The ratio of DA D1- to D2-receptors was significantly higher in the dorsal than in the ventral areas of the mediolateral and caudal striatum. This is the first report of clear dorsoventral differences in parameters relating to DA activity in the striatum. These findings may be of particular significance in understanding the functional dichotomy between the dorsal and ventral striatum.

Effect of corticosterone on noradrenergic nuclei in the pons-medulla and [3H]NA release from terminals in hippocampal slices

The aim of the present study was to investigate possible membrane and genomic effects of corticosterone on the noradrenergic system of the rat brain. Corticosterone effects were studied in vivo by treating rats s.c. with 10 mg/kg corticosterone for 7 or 14 days. In the first two experiments corticosterone significantly decreased the noradrenaline (NA) and dopamine (DA) levels in the pons-medulla, an area which contains the A1-A7 noradrenergic cell groups, while the NA and DA levels in the dorsal hippocampus remained unchanged. In a third experiment where the locus coeruleus (LC) and the A1 and A2 nuclei (A1,A2) were analysed separately, NA levels were unchanged but total MHPG levels and the total MHPG/NA ratio were decreased in the A1,A2 area. Chronic corticosterone treatment (14 days) did not alter the alpha 2-adrenoceptor-mediated modulation of [3H]NA release from dorsal hippocampal slices. Neither the spontaneous outflow nor the electrically stimulated release of [3H]NA from dorsal hippocampal slices of untreated rats was affected by exposure of the slices to corticosterone (10(-7) M - 10(-4) M) in the superfusion buffer. Thus, chronic corticosterone treatment of rats altered the noradrenergic system of the pons-medulla, but did not change the alpha 2-adrenoceptor-mediated modulation of NA release in the dorsal hippocampus, a major terminal area of the LC neurons. Corticosterone also did not appear to have a direct membrane effect on the NA terminals in the dorsal hippocampus of the rat.

The effect of medial forebrain bundle lesion on thyrotropin secretion in the rat

The medial forebrain bundle (MFB) was partially lesioned with 6-hydroxydopamine (6-OHDA) in order to investigate the effect of deficient central noradrenergic regulation on thyrotropin (TSH) secretion in the rat. 6-OHDA injection into the MFB significantly reduced the noradrenaline (NA), dopamine (DA) and serotonin (5-HT) content of the whole hypothalamus. NA and 5-HT concentrations were also significantly decreased in the paraventricular nucleus (PVN). The MFB lesion did not affect the clonidine (250 micrograms/kg, i.p.) induced stimulation of TSH release or the isoproterenol (1 mg/kg i.p.) induced decrease in TSH levels. Thyrotropin releasing hormone (TRH, 5 micrograms/kg i.v.) caused a similar significant stimulation of TSH secretion in lesioned and non-lesioned rats. The present results do not support the hypothesis that the blunted TSH response to TRH observed in depressed patients results from a deficiency in noradrenergic neurotransmission.

Evidence that the stimulatory effect of neurotensin on dopamine release in rat nucleus accumbens slices is independent of dopamine D2-receptor activation

Neurotensin (NT, 10(-9) M and 10(-7) M) increased the electrically stimulated release of [3H]dopamine (DA) in rat nucleus accumbens slices. This effect was not altered by activation of DA D2-receptors with high or low concentrations of quinpirole (10(-6) M and 10(-8) M) or blockade of DA D2-receptors with near maximal concentrations of sulpiride (10(-6) M and 10(-5) M). The sulpiride-mediated increase in [3H]DA release and the release induced by NT were additive. These results suggest that NT functions independently of DA D2-receptor activation to modulate DA release in the nucleus accumbens. NT did not modulate the simultaneous release of [14C]acetylcholine.

Rat brain monoamine and Serotonin S2 receptor changes during pregnancy

The concentrations of noradrenaline (NA), dopamine (DA), serotonin (5-HT), and their metabolites were determined in 5 brain areas of non-pregnant, 15 and 20 day pregnant and 4 day post-partum rats. Striatal 5-HT content was significantly lower in 15 and 20 day pregnant rats than in estrous controls. A significant decrease in striatal and frontal cortex 5-hydroxyindole-3-acetic acid (5-HIAA) concentration was observed in 15 day pregnant rats. Significant increases in hypothalamic and hippocampal NA levels were observed at 4 days post-partum. Frontal cortex serotonin S2 receptor KD was reduced in 4 day post-partum rats. There was no significant change in S2 receptor Bmax during pregnancy. Levels of progesterone were negatively correlated with striatal DA, homovanillic acid (HVA), 5-HT, and 5-HIAA levels, hypothalamic DA, hippocampal 5-HT, and frontal cortex 5-HIAA values as well as striatal HVA to DA, and HVA to 3,4-dihydroxyphenylacetic acid (DOPAC) ratios and amygdaloid HVA to DOPAC ratios. The limbic neurotransmitter changes might possibly contribute to mood changes which occur during pregnancy and post-partum.

The effect of intrahippocampal injection of kainic acid on corticosterone release in rats

The aim of the present study was to investigate whether the hippocampus exerts a modulatory effect on the activity of the hypothalamic-pituitary-adrenal (HPA) axis. Kainic acid was stereotaxically injected into the CA1 pyramidal cell layer of the dorsal hippocampus, causing histological and behavioural changes typical of kainic acid toxicity. The CA3 pyramidal cells of the dorsal hippocampus were selectively lesioned. Rats treated with kainic acid were hyperactive, executed clockwise rotatory movements and displayed epileptic seizures. The acute excitatory effect of kainic acid on glutamatergic receptors in the hippocampus resulted in an elevation in plasma corticosterone levels, suggesting a stimulation of HPA axis activity. Direct or indirect stimulation of the CA1 pyramidal cells of the dorsal hippocampus appeared to have caused the increase in corticosterone secretion.

The effect of selective noradrenergic denervation on thyrotropin secretion in the rat

The effect of DSP4 [N-(2-chloroethyl)-N-ethyl-2 bromobenzylamine], a neurotoxin which selectively lesions noradrenergic projections from the locus coeruleus, on thyrotropin (TSH) secretion was investigated in the rat. DSP4 treatment (60 mg/kg injected i.p. 10 days prior to experimentation) significantly decreased the noradrenaline (NA) content of the hippocampus, frontal cortex and hypothalamus of the rat brain. DSP4 treatment did not affect the clonidine (250 micrograms/kg, i.p ) or TSH-releasing-hormone (TRH 5 micrograms/kg i.v.) induced stimulation or the isoproterenol induced inhibition of TSH secretion in the rat. These results suggest that the noradrenergic projection from the locus coeruleus to the hypothalamus does not play a significant role in the regulation of TSH secretion. Furthermore, the noradrenergic deficiency did not give rise to the development of the abnormal TSH response to TRH administration which is frequently observed in depression.

The effect of partial noradrenergic denervation on corticosterone secretion in the rat

DSP4(N-(-2-chloroethyl)-N-ethyl-2-bromobenzylamine) treatment significantly decreased the noradrenaline content in the hippocampus, frontal cortex and hypothalamus of the rat brain. DSP4 treatment did not affect plasma corticosterone levels. Clonidine, an alpha2-adrenoceptor agonist, had no effect on corticosterone secretion in either DSP4- or saline-treated rats. Isoproterenol, a beta-adrenoceptor agonist, significantly stimulated corticosterone secretion. This effect was inhibited by the prior administration of the beta-adrenoceptor antagonist propranalol. DSP4 treatment did not alter the isoproterenol-induced stimulation of corticosterone secretion. The administration of a high dose of dexamethasone (100 micrograms/kg, i.p.) significantly decreased the plasma corticosterone concentration of saline-treated controls, while an intermediate dose (25 micrograms/kg, i.p.) did not suppress corticosterone release significantly. DSP4-treatment did not influence dexamethasone-induced suppression of corticosterone secretion. These results show that significant decreases in noradrenaline content in the hippocampus, frontal cortex and hypothalamus appear to have no effect on the regulation of corticosterone secretion and that corticosterone secretion may be stimulated by catecholamines via beta-adrenoceptors.

Increased dopamine D2 receptor-mediated inhibition of [14C]acetylcholine release in the dorsomedial part of the nucleus accumbens

Dopamine (DA) D2 receptor-mediated inhibition of the K+-stimulated release of [14C]acetylcholine (ACh) from prelabeled rat dorsomedial nucleus accumbens slices was found to be 1.7 times greater than that observed in dorsorostral and ventromedial slices. This observation is consistent with the 1.9 fold higher DA D2 receptor density found in the dorsomedial area. In contrast, there were no differences in the DA D2 receptor-mediated effects on [3H]DA release in these areas. In addition, DA D2 receptor-mediated effects on [3H]DA and [14C]ACh release could not be demonstrated in the ventrorostral part of the nucleus accumbens consistent with the fact that DA D2 receptors were barely detectable in this area. The results suggest that cholinergic terminals in the dorsomedial part of the nucleus accumbens are under greater inhibitory DA control than in other areas of the nucleus accumbens.

Lack of effect of chronic desipramine treatment on dopaminergic activity in the nucleus accumbens of the rat

The binding of [3H]SCH 23390 to dopamine (DA) D1-receptors was measured in the nucleus accumbens of rats treated chronically with desipramine for 14 days. DA D1- and D2-receptor binding using [3H]SCH 23390 and [3H]spiperone, respectively as ligands, was determined in rats treated for 28 days. Neither Bmax nor Kd values were influenced by chronic desipramine treatment. In addition, chronic desipramine treatment (28 days) did not influence the dose dependent, quinpirole (10-1000 nM)-mediated inhibition of the electrically stimulated release of [3H]DA release and [14C]ACh from nucleus accumbens slices or the dose dependent increase in [3H]DA release and decrease in [14C]ACh release in the presence of 1 and 10 microM nomifensine. Therefore, our results suggest that the effect of chronic antidepressant treatment cannot be attributed to changes in either DA D1- or D2-receptor binding or DA D2-receptor function in the nucleus accumbens.

Effect of selective noradrenergic denervation on noradrenaline content and [3H]dopamine release in rat nucleus accumbens slices

DSP4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine) treatment (50 mg/kg i.p., 10 days previously) significantly decreased the noradrenaline (NA) content of the rostral part of the nucleus accumbens. The medial and caudal areas were not affected. The nucleus accumbens appears to receive noradrenergic innervation predominantly from subcoeruleus nuclei of the pons-medulla while the locus coeruleus neurons project to the rostral area. The isoproterenol-induced enhancement of the K+-evoked release of [3H]dopamine (DA) was not affected by DSP4 treatment. Noradrenergic denervation does not appear to have been sufficient to cause up-regulation of postsynaptic beta-adrenoceptors.

Noradrenergic function and hypothalamic-pituitary-adrenal axis activity in adolescents with major depressive disorder

Levels of plasma norepinephrine (NE), free 3-methoxy-4-hydroxyphenylglycol (MHPG), and cortisol in adolescents with major depressive disorder (10 girls, 1 boy; mean +/- SD age = 16.4 +/- 1.6 years, range = 14-19 years) did not differ significantly from those in a group of healthy adolescents (17 girls, 12 boys; mean +/- SD age = 15.9 +/- 1.5 years, range = 12-18 years). No correlations were observed between these variables and age within the adolescent groups. However, when the adolescent data were viewed in combination with data previously obtained for an adult population (De Villiers et al., 1987), significant positive correlations between the variables were observed within the patient group. A moderate positive correlation with age was also observed for patients' NE and free MHPG levels. No such correlations were observed for the combined control group. When groups were partitioned into three age categories, it became apparent that differences in the three variables between the patient and the control groups were restricted to elderly subjects (greater than 50 years). In adults (21-50 years old), only the patients' NE levels were significantly elevated. These findings suggest that duration of illness may be important in determining the full expression of the biochemical abnormality in major depression.

Regional distribution of monoamines in the nucleus accumbens of the rat

Monoamine concentrations were low in the rostral area of the nucleus accumbens. Their distributions were not identical. Differences were observed in the medial area. DA concentrations were high in both medial and caudal areas. Noradrenaline (NA) and serotonin (5-HT) concentrations were considerably lower than the dopamine (DA) concentration. The NA concentration was highest in the caudal area of the nucleus accumbens and the (5-HT) concentration was highest in the ventrocaudal area. There was a rostrocaudal decrease in the 3,4-dihydroxyphenylacetic acid (DOPAC)/DA and 5-hydroxyindole-3-acetic acid (5-HIAA)/5-HT ratios. Uptake of [3H]DA and [14C]choline was lowest in the rostral area. The K+-stimulated release of [14C]acetylcholine (ACh) was also lowest rostrally, but there was no rostrocaudal difference in the K+-stimulated release of [3H]DA. These results provide further evidence of the heterogeneity of the nucleus accumbens.

Effect of ethanol on [3H]dopamine release in rat nucleus accumbens and striatal slices

Ethanol (10-200 mM) transiently increased tritium overflow from superfused rat nucleus accumbens slices previously incubated with [3H]dopamine (DA) and [14C]choline. The effect was greater in striatal tissue and did not appear to be a non-specific membrane effect since [14C]acetylcholine (ACh) release was not affected. Lack of antagonism by picrotoxin suggested that gamma-aminobutyric acid (GABA) receptors were not involved. Calcium was not a requirement and the DA uptake blocker, nomifensine, was without effect. Ethanol appeared to be causing [3H]DA release into the cytoplasm. K+ -stimulated release of [3H]DA and [14C]ACh from nucleus accumbens and striatal slices was not affected. Clonidine-mediated inhibition of the K+-evoked release of [3H]DA remained unaltered. Ethanol attenuated the isoproterenol-induced enhancement of [3H]DA release. Ethanol therefore appeared to interact with components of the DA terminal causing a transient increase in the release of neurotransmitter without impairing K+-evoked release but apparently interfering with the isoproterenol-induced effect.

Characterization of the effects of serotonin on the release of [3H]dopamine from rat nucleus accumbens and striatal slices

The effect of serotonin agonists on the depolarization (K+)-induced, calcium-dependent, release of [3H]dopamine (DA) from rat nucleus accumbens and striatal slices was investigated. Serotonin enhanced basal 3H overflow and reduced K+-induced release of [3H]DA from nucleus accumbens slices. The effect of serotonin on basal 3H overflow was not altered by the serotonin antagonist, methysergide, or the serotonin re-uptake blocker, chlorimipramine, but was reversed by the DA re-uptake carrier inhibitors nomifensine and benztropine. With the effect on basal overflow blocked, serotonin did not modulate K+-induced release of [3H]DA in the nucleus accumbens or striatum. The serotonin agonists, quipazine (in the presence of nomifensine) and 5-methoxytryptamine, did not significantly affect K+-induced release of [3H]DA in the nucleus accumbens. This study does not support suggestions that serotonin receptors inhibit the depolarization-induced release of dopamine in the nucleus accumbens or striatum of the rat brain. The present results do not preclude the possibility that serotonin may affect the mesolimbic reward system at a site which is post-synaptic to dopaminergic terminals in the nucleus accumbens.

Biological markers in juvenile depression

3H-p-Aminoclonidine binding to platelets of children and adolescents with major depressive disorder was compared to that of a healthy control population. Significantly higher alpha 2-adrenoceptor Kd and Bmax values were observed in the patient population. 3H-Dihydroalprenolol binding to lymphocyte membranes of the same patient population showed significantly higher beta-adrenoceptor Bmax values than controls. Control females had significantly higher beta-adrenoceptor Kd values than control males, and the female patients had significantly lower beta-adrenoceptor Kd values than control females. 3H-Imipramine binding to platelets of these patients showed significantly higher imipramine Kd values in patients with a suicide attempt, whereas the imipramine Bmax values were significantly increased in patients with major depressive disorder with or without a suicide attempt. We propose that increased platelet alpha 2-adrenoceptor Kd and Bmax values, together with increased platelet imipramine Kd values, may serve as possible biological markers for children and adolescents with major depressive disorder and a tendency toward suicide. Elevated platelet imipramine and lymphocyte beta-adrenoceptor Bmax values may be biological markers for juvenile depression, and decreased beta-adrenoceptor Kd values may be a biological marker for depression in young females.

The modulatory effect of neurotensin on [3H]dopamine release from rat nucleus accumbens slices is enhanced after chronic desipramine treatment

In the presence of the reuptake blocker, nomifensine (1 microM), neurotensin caused a dose-dependent increase in the 25 mM K+-evoked release of [3H]dopamine ([3H]-DA) from rat nucleus accumbens slices. Chronic desipramine (DMI)-treatment (20 mg DMI/kg/day, orally for 28 days) caused a significant reduction in the K+-stimulated release of [3H]DA from rat nucleus accumbens slices. This could possibly have resulted from increased DA autoreceptor-mediated inhibition of DA release. Superfusion of the DMI-treated rat tissue with buffer-containing neurotensin (100 nM) resulted in an increase in the K+-evoked release of [3H]DA to a level which was higher than that observed with tissue obtained from untreated rats. A similar enhanced effect of neurotensin on DA release was observed when the DA agonist, apomorphine (APO), and ascorbate were included in the superfusion buffer. These findings are consistent with DMI treatment giving rise to impaired DA release possibly due to DA autoreceptor-mediated inhibition of DA release and cancellation of this effect by neurotensin.