Corticotropin-releasing factor release from the mediobasal hypothalamus of the rat as measured by microdialysis

Oxytocin levels in saliva correlate better than plasma levels with concentrations in the cerebrospinal fluid of patients in neurocritical care

In the converging fields of neuroendocrinology and behavioural neuroscience, the interaction between peripheral secretion and central release of oxytocin in humans has not yet been comprehensively assessed. As the human brain is not directly accessible and as the collection of human cerebrospinal fluid (CSF) usually requires invasive procedures, easier accessible compartments such as blood or saliva attract increasing attention. In this study, we prospectively determined oxytocin concentrations in the three compartments plasma, CSF and saliva of fifty critically ill patients with neurological and neurosurgical diseases. All samples per patient were collected concomitantly. Oxytocin was measured by a highly sensitive and specific radioimmunoassay. Strength of correlation was assessed by the Spearman rank correlation coefficient. Correlation analyses revealed modest to strong correlations for oxytocin between the saliva and CSF compartments while predominantly weak correlations were found between the CSF and plasma as well as between the plasma and saliva compartments. In conclusion, we demonstrated modest to strong correlations between the saliva and CSF compartment suggesting that saliva oxytocin may help to assess CSF oxytocin levels. In contrast, plasma oxytocin failed to correspond well with CSF oxytocin levels as predominantly weak correlations were found between the CSF and plasma as well as between the plasma and saliva compartments which are unlikely to have a biological relevance. Further research is needed to clarify to what extent saliva oxytocin may serve as a biomarker reflecting brain oxytocin activity. This article is protected by copyright. All rights reserved.

Effects of chronic noise on mRNA and protein expression of CRF family molecules and its relationship with p-tau in the rat prefrontal cortex

Chronic noise exposure has been associated with Alzheimer's disease (AD)-like pathological changes, such as tau hyperphosphorylation and β-amyloid peptide accumulation in the prefrontal cortex (PFC). Corticotropin-releasing factor (CRF) is the central driving force in the stress response and a regulator of tau phosphorylation via binding to CRF receptors (CRFR). Little is known about the CRF system in relation to noise-induced AD-like changes in the PFC. The aim of this study was to explore the effects of chronic noise exposure on the CRF system in the PFC of rats and its relationship to tau phosphorylation. Male Wistar rats were randomly divided into control and noise exposure groups. The CRF system was evaluated following chronic noise exposure (95dB sound pressure level white noise, 4h/day×30days). Chronic noise significantly accelerated the progressive overproduction of corticosterone and upregulated CRF and CRFR1 mRNA and protein, both of which persisted 7-14days after noise exposure. In contrast, CRFR2 was elevated 3-7days following the last stimulus. Double-labeling immunofluorescence co-localized p-tau with CRF in PFC neurons. The results suggest that chronic noise exposure elevates the expression of the CRF system, which may contribute to AD-like changes.

Mass spectrometric detection of neuropeptides using affinity-enhanced microdialysis with antibody-coated magnetic nanoparticles

Microdialysis (MD) is a useful sampling tool for many applications due to its ability to permit sampling from an animal concurrent with normal activity. MD is of particular importance in the field of neuroscience, in which it is used to sample neurotransmitters (NTs) while the animal is behaving in order to correlate dynamic changes in NTs with behavior. One important class of signaling molecules, the neuropeptides (NPs), however, presented significant challenges when studied with MD, due to the low relative recovery (RR) of NPs by this technique. Affinity-enhanced microdialysis (AE-MD) has previously been used to improve recovery of NPs and similar molecules. For AE-MD, an affinity agent (AA), such as an antibody-coated particle or free antibody, is added to the liquid perfusing the MD probe. This AA provides an additional mass transport driving force for analyte to pass through the dialysis membrane and thus increases the RR. In this work, a variety of AAs have been investigated for AE-MD of NPs in vitro and in vivo, including particles with C18 surface functionality and antibody-coated particles. Antibody-coated magnetic nanoparticles (AbMnP) provided the best RR enhancement in vitro, with statistically significant (p < 0.05) enhancements for 4 out of 6 NP standards tested, and RR increases up to 41-fold. These particles were then used for in vivo MD in the Jonah crab, Cancer borealis, during a feeding study, with mass spectrometric (MS) detection. 31 NPs were detected in a 30 min collection sample, compared to 17 when no AA was used. The use of AbMnP also increased the temporal resolution from 4 to 18 h in previous studies to just 30 min in this study. The levels of NPs detected were also sufficient for reliable quantitation with the MS system in use, permitting quantitative analysis of the concentration changes for 7 identified NPs on a 30 min time course during feeding.

Stress and glucocorticoids regulated corticotropin releasing factor in rat prefrontal cortex

Corticotropin releasing factor (CRF) is considered as the central driving force in the stress response and plays a key role in the pathogenesis of depression. CRF neurons have been identified to locate in most regions of the prefrontal cortex (PFC), a brain region that is highly associated with the control of emotion and cognition. However, little is known on the regulation of CRF in this region. In this study, we aimed to identify the regulatory effect of acute restraint stress and glucocorticoid on PFC CRF and characterize the possible function of CRF in the PFC. We found that acute restraint stress increased and glucocorticoid decreased PFC CRF mRNA expression. The expression of glucocorticoid receptor (GR) was found to colocalize with CRF neurons in the PFC. In addition, recruitment of GR by the CRF promoter was observed in vivo. Specific attention was paid to the effect of CRF on CRF receptor 1 (CRFR1) expression in primary PFC cultures. The results showed that CRF increased CRFR1 expression through the MEK-ERK1/2 pathway. In summary, this study may contribute to the better understanding of CRF functions in the PFC.

Immediate and prolonged effects of alcohol exposure on the activity of the hypothalamic-pituitary-adrenal axis in adult and adolescent rats

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis. Part of this influence is likely exerted directly at the level of the corticotropin-releasing factor (CRF) gene, but intermediates may also play a role. Here we review the effect of alcohol on this axis, provide new data on the effects of binge drinking during adolescence, and argue for a role of catecholaminergic circuits. Indeed, acute injection of this drug activates brain stem adrenergic and noradrenergic circuits, and their lesion, or blockade of α1 adrenergic receptors significantly blunts alcohol-induced ACTH release. As alcohol can influence the HPA axis even once discontinued, and alcohol consumption in young people is associated with increased adult drug abuse (a phenomenon possibly mediated by the HPA axis), we determined whether alcohol consumption during adolescence modified this axis. The number of CRF-immunoreactive (ir) cells/section was significantly decreased in the central nucleus of the amygdala of adolescent self-administering binge-drinking animals, compared to controls. When another group of adolescent binge-drinking rats was administered alcohol in adulthood, the number of colocalized c-fos-ir and PNMT-ir cells/brain stem section in the C3 area was significantly decreased, compared to controls. As the HPA axis response to alcohol is blunted in adult rats exposed to alcohol vapors during adolescence, a phenomenon which was not observed in our model of self-administration, it is possible that the blood alcohol levels achieved in various models play a role in the long-term consequences of exposure to alcohol early in life. Collectively, these results suggest an important role of brain catecholamines in modulating the short- and long-term consequences of alcohol administration.

Antibody-enhanced microdialysis collection of CCL2 from rat brain

Chemokine(C-C motif) Ligand 2 (CCL2 or MCP-1) is a signaling protein that is released under various conditions. In this study we demonstrate the first microdialysis collection of CCL2 from rat brain tissue using antibody-enhanced microdialysis. A monoclonal antibody to CCL2 was included in the dialysis perfusion fluid as an affinity agent to enhance the recovery of CCL2 both in vitro and in vivo. In vitro it was found that the use of antibody affinity agent increases the relative recovery of CCL2 from 9.6±3.4% to 37.5±10.2% and 64.8±11.7% (n=10) at flow rates of 2μL/min and 1μL/min, respectively. Following the in vitro observation, CCL2 was collected from rat brain with microdialysis sampling using both control and antibody-included perfusion fluids. The in vivo data showed that relative recovery was increased at all but the first time point. This shows that the use of free antibody in the perfusion fluid increases the relative recovery of CCL2 and this enhanced microdialysis method may be applicable to other cytokines.

Transient forebrain over-expression of CRF induces plasma corticosterone and mild behavioural changes in adult conditional CRF transgenic mice

BACKGROUND

Converging findings support a role for extra-hypothalamic CRF in the mediation of the stress response. The influence of CRF in the amygdala is well established, while less is known of its role in other areas of the forebrain where CRF and CRF(1) receptors are also expressed. In the present study CRF was genetically induced to allow forebrain-restricted expression in a temporally-defined manner at any time during the mouse lifespan. This mouse model may offer the possibility to establish a model of the pathogenesis of recurrent episodes of depression.

METHODS

Mice were engineered to carry both the rtTA transcription factor driven by the CamKII alpha promoter and the doxycycline-regulated operator (tetO) upstream of the CRF coding sequence. Molecular, biochemical and behavioural characterisation of this mouse is described.

RESULTS

Following a three-week period of transcriptional induction, double transgenic mice showed approximately 2-fold increased expression of CRF mRNA in the hippocampus and cortex, but not hypothalamus. These changes were associated with 2-fold increase in morning corticosterone levels, although responses to the dexamethasone suppression test or acute stress were unaffected. In contrast, induced mice displayed modestly altered behaviour in the Light and Dark test and Forced Swim test.

CONCLUSIONS

Transient induction of CRF expression in mouse forebrain was associated with endocrine and mild anxiety-like behavioural changes consistent with enhanced central CRF neurotransmission. This mouse allows the implementation of regimens with longer or repeated periods of induction which may model the initial stages of the pathology underlying recurrent depressive disorders.

An in vitro comparison of microdialysis relative recovery of Met- and Leu-enkephalin using cyclodextrins and antibodies as affinity agents

Cyclodextrins and antibodies have been used as affinity agents to improve relative recovery during microdialysis sampling. Two neuropeptides, methionine-enkephalin (ME) and leucine-enkephalin (LE), were chosen to compare the use of cyclodextrins and antibodies as possible affinity agents for improving their relative recovery across polycarbonate and polyethersulfone membranes during in vitro sampling. Cyclodextrins (CD) including beta-CD, 2-hydroxypropyl-beta-cyclodextrin (2HPbeta-CD), and gamma-CD gave improvements of relative recovery for both peptides of less than 2-fold as compared to controls. Comparisons of relative recovery between tyrosine-glycine-glycine, tyrosine, and phenylalanine using different cyclodextrins in the perfusion fluid were also obtained. Inclusion of an antibody against met-enkephalin in the microdialysis perfusion fluid resulted in relative recovery increases of up to 2.5-fold. These results show that using antibodies as affinity agents during microdialysis sampling may be more effective agents to improve the relative recovery of these opioid neuropeptides.

The role of corticotropin-releasing factor-like peptides in cannabis, nicotine, and alcohol dependence

The corticotropin-releasing factor (CRF)-like peptides, which include the mammalian peptides CRF, urocortin 1, urocortin 2, and urocortin 3, play an important role in orchestrating behavioral and physiological responses that may increase an organism's chance of survival when confronted with internal or external stressors. There is, however, evidence that a chronic overactivity of brain CRF systems under basal conditions may play a role in the etiology and maintenance of psychiatric disorders such as depression and anxiety disorders. In addition, there is evidence of a role for CRF-like peptides in acute and protracted drug abstinence syndromes and relapse to drug-taking behavior. This review focuses on the role of CRF-like peptides in the negative affective state associated with acute and protracted withdrawal from three widely abused drugs, cannabis, nicotine, and alcohol. In addition, we discuss the high comorbidity between stress-associated psychiatric disorders and drug dependence. A better understanding of the brain stress systems that may underlie psychiatric disorders, acute and protracted drug withdrawal, and relapse to drug-taking behavior may help in the development of new and improved pharmacotherapies for these widespread psychiatric disorders.

A bio-behavioral model of addiction treatment: applying dual representation theory to craving management and relapse prevention

A bio-behavioral approach to drug addiction treatment is outlined. The presented treatment model uses dual representation theory as a guiding framework for understanding the bio-behavioral processes activated during the application of expressive therapeutic methods. Specifically, the treatment model explains how visual processing techniques can supplement traditional relapse prevention therapy protocols, to help clients better manage cravings and control triggers in hard-to-treat populations such as chronic substance-dependent persons.

Stress induces CRF release in the paraventricular nucleus, and both CRF and GABA release in the amygdala

In the hypothalamus, corticotropin-releasing factor (CRF) initiates the hypothalamic-pituitary-adrenal (HPA) axis response to stress, resulting in the release of glucocorticoids, including cortisol. Extrahypothalamic CRF, particularly in the limbic system, also appears to play a role in the stress response. To further define brain CRF response to stress, immunosensor-based microdialysis probes were used to measure the extracellular levels of CRF in the paraventricular nucleus of the hypothalamus (PVN) and in the amygdala of sheep during a predator (dog) exposure stress. In addition, gamma amino butyric acid (GABA) was measured in the amygdala and cortisol was measured in venous blood. Exposure to the predator stress increased CRF in the PVN and both CRF and GABA in the amygdala. These were followed in time by a rise in venous cortisol. Application of a CRF antagonist to the amygdala, immediately prior to stress, had a small effect on the subsequent observed stress responses. This treatment, however, significantly reduced the responses to a repeat stress administered 2 days later, compared to nontreated animals. Application of a GABA antagonist to the amygdala prior to stress had no effect on the subsequent observed stress response but increased the response to the stress repeated 2 days later. Perfusion with 4-aminopyridine, a neuronal depolarising agent, into the PVN induced a release of CRF accompanied shortly thereafter by a small increase in CRF in the amygdala, and 5-10 min later by an increase in venous cortisol. Perfusion into the amygdala increased the levels of both CRF and GABA but had no effect on either PVN CRF or venous cortisol. These data support roles for both the PVN and amygdala in stress responsiveness. It suggests further that actions at the amygdala can strongly influence subsequent responsiveness to a further stress, mediated in part by both CRF and GABA actions.

Differential release of corticotropin-releasing hormone (CRH) in the amygdala during different types of stressors

The purpose of this study was to determine if differences exist between the effects of acute treadmill running and restraint stress on corticotropin-releasing hormone (CRH) release within the amygdala of rats. Extracellular CRH immunoreactivity (CRH-IR) was measured in microdialysate collected from the central nucleus of the amygdala (CeA) during exposure to an inactivated treadmill (TC), during 1 h treadmill running to exhaustion (RUN), and 1 h restraint (RES). Extracellular CRH-IR increased from control levels during the first 20-min period for TC, RUN, and RES, with the largest increase during RES. During the second 20-min period, only RES maintained levels higher than control values. CRH release was higher than control during the third 20-min period of RES and RUN. A second experiment consisted of four groups of either cage controls (CC), TC, RUN, or RES. Immediately following the 60-min treatment, brains were removed and trunk blood collected for analysis of tissue CRH-IR and plasma corticosterone. While amygdala tissue CRH-IR was not different in the CC, TC and RUN rats, these groups had significantly lower levels than the RES animals. Hypothalamic tissue CRH-IR was not different between the CC and TC rats, but the levels were significantly higher in the RES and RUN rats than in the two control groups. Plasma corticosterone levels were elevated only in RES and RUN rats. Results from tissue analysis indicate that increased tissue CRH-IR in the amygdala and hypothalamus can be elicited by RES, while only the hypothalamus shows an increase following RUN. Further, extracellular CRH release in the CeA is increased throughout the period of RES, when rats are placed on the treadmill, and when the animals are approaching physical exhaustion. No increase is observed during the running period between placement on the treadmill and intense exertion. Overall, the data suggest that amygdala CRH release is regulated differently during treadmill running and restraint.

Glucocorticoid feedback increases the sensitivity of the limbic system to stress

In the hypothalamus, corticotropin-releasing hormone (CRH) has a well-described role initiating the hypothalamic-pituitary-adrenal (HPA) axis response to stress. Cortisol, released from the adrenal gland, exerts negative feedback on this axis. The role of extrahypothalamic CRH in stress responses is less well known. The purpose of this study was to measure the response of CRH in the amygdala to acute and repeated stress and to examine if cortisol had any effect on this response. Immunosensor-based microdialysis probes were used to measure CRH and cortisol in the amygdala and cortisol systemically in sheep exposed to a predator stress (a dog). Upon presentation of a dog, CRH increased in the amygdala of the sheep and then fell off. Cortisol levels rose both systemically and in the amygdala, and as they peaked, a second CRH response was observed. Repeated stress changed this response, with the magnitude of the first CRH peak decreasing while the second peak increased. Repeated stress also produced an exaggeration in both of the CRH peaks to presentation of a subsequent novel stress (a forelimb electric shock). Animals that had an escape route from the repeated dog stress did not show this exaggeration when faced subsequently with the novel stress. Administration of mifepristone, a glucocorticoid receptor antagonist, prior to the delivery of the repeat stress prevented subsequent changes in the CRH response. The data suggest that the amygdala shows a CRH response to presentation of a stressor acutely and repeatedly and that repeated stress can alter subsequent amygdala responsiveness to the same or a different stressor. This alteration appears dependent on circulatory glucocorticoids.

An inhibitory effect of cytokine-induced neutrophil chemoattractant on corticotropin-releasing factor-induced increase in locomotor activity

To investigate whether cytokine-induced neutrophil chemoattractant (CINC) has an influence on corticotropin-releasing factor (CRF) in the central nervous system, the effects of intracerebroventricular (i.c.v.) injection of CINC on CRF-induced behavior were examined. Intracerebroventricular CRF injection produced an increase in locomotor activity, which was significantly reduced by i.c.v. injection of CINC. The intravenous injection of CINC did not alter CRF-induced locomotor hyperactivity. These results suggested that CINC has a functional antagonistic action on the response to CRF and may attenuate stress responses.

Compulsive drug-seeking behavior and relapse. Neuroadaptation, stress, and conditioning factors

The development of addiction and vulnerability to relapse following withdrawal is proposed to be the result of neuroadaptive processes within the central nervous system that oppose the acute reinforcing actions of drugs of abuse. These changes lead to impairment in the mechanisms that mediate positive reinforcement and the emergence of affective changes such as anxiety, dysphoria, and depression during withdrawal. Considerable evidence exists implicating perturbations in DA and 5-HT transmission in the nucleus accumbens--neurochemical systems that are activated by cocaine and ethanol self-administration and deficient during withdrawal--as potential substrates for these affective changes. In addition, growing evidence suggests that enhanced CRF release in the central nucleus of the amygdala represents a mechanism underlying the anxiogenic and stress-like consequences of withdrawal that are common to all drugs of abuse. A growing body of evidence also implicates dysregulation of the non-neuroendocrine CRF stress system within the central nucleus of the amygdala as a common factor in the anxiogenic and aversive consequences of withdrawal from drugs of abuse. Moreover, a possible link may exist between long-lasting abnormalities in CRF function in the CeA and vulnerability to relapse during protracted abstinence. Another presumably critical element contributing to the chronic relapsing nature of drug addiction is the learned responses to drug-related stimuli. The long-lasting efficacy of drug- and alcohol-associated contextual stimuli in eliciting drug-seeking behavior in animal models of relapse resembles the endurance of conditioned cue reactivity and cue-induced cocaine craving in humans and confirms a significant role of learning factors in the long-lasting addictive potential of cocaine. With cocaine, D1-dependent neural mechanisms within the medial prefrontal cortex and basolateral amygdala may be important substrates for the motivating effects of drug-related environmental stimuli. With ethanol, available data suggest a role for opioid receptors in the mediation of conditioned drug-seeking behavior. Finally, conditioning factors (i.e., exposure to drug-associated stimuli) and stress can interact to augment vulnerability to relapse. This finding emphasizes that it will be important to consider the simultaneous effects of multiple environmental triggers for relapse in the development of treatment and medication strategies.

Footshock-induced changes in brain catecholamines and indoleamines are not mediated by CRF or ACTH

Stressful treatments have long been associated with increased activity of brain catecholaminergic and serotonergic neurons. An intracerebroventricular (icv) injection of the corticotropin-releasing factor (CRF) also activates brain catecholaminergic neurons. Because brain CRF-containing neurons appear to be activated during stress, it is possible that CRF mediates the catecholaminergic activation. This hypothesis has been tested by assessing the responses in brain catecholamines and indoleamines to footshock in mice pretreated icv with a CRF receptor antagonist, and in mice lacking the gene for CRF (CRFko mice). Consistent with earlier results, icv administration of CRF increased catabolites of dopamine and norepinephrine, but failed to alter tryptophan concentrations or serotonin catabolism. A brief period of footshock increased plasma corticosterone and the concentrations of tryptophan and the catabolites of dopamine, norepinephrine and serotonin in several brain regions. Mice injected icv with 25 microg alpha-helical CRF(9-41) prior to footshock had neurochemical responses that were indistinguishable from controls injected with vehicle, while the increase in plasma corticosterone was slightly attenuated in some experiments. CRFko mice exhibited neurochemical responses to footshock that were indistinguishable from wild-type mice. However, whereas wild-type mice showed the expected increase in plasma corticosterone, there was no such increase in CRFko mice. Similarly, hypophysectomized mice also showed normal neurochemical responses to footshock, but no increase in plasma corticosterone. Hypophysectomy itself elevated brain tryptophan and catecholamine and serotonin metabolism. Treatment with ACTH icv or peripherally failed to induce any changes in cerebral catecholamines and indoleamines. These results suggest that CRF and its receptors, and ACTH and other pituitary hormones, are not involved in the catecholamine and serotonin responses to a brief period of footshock.

Behavioral responses to stress are intact in CRF-deficient mice

Corticotropin-releasing factor (CRF) has been implicated in endocrine and behavioral responses associated with stress. We have now studied the behavior of mice lacking the CRF gene (CRFko), comparing them to wild-type (WT) mice. Behaviors were observed in untreated mice, as well as following restraint or intraperitoneal administration of mouse interleukin-1beta (mIL-1beta). In the multicompartment chamber (MCC), the behaviors of CRFko and WT mice were very similar, and prior restraint and IL-1beta induced similar decreases in stimulus-contact times in both genotypes. In the elevated plus maze (EPM), restraint decreased the number of open arm entries but the behavior of both genotypes was very similar. In the open field (OF), the changes in locomotor activity in response to restraint were similar in both genotypes, although CRFko mice displayed slightly increased locomotor activity compared to WT mice. In both the MCC and the EPM, grooming behavior was increased by restraint, and was higher in the CRFko than in the WT mice. Compared to WT mice, CRFko mice had lower basal plasma concentrations of corticosterone which did not increase significantly following footshock. Thus, CRFko mice showed a clear dichotomy; the stress-related activation of the hypothalamo-pituitary-adrenal (HPA) axis was absent, whereas the stress-related behavioral responses thought to be mediated by brain CRF were unaffected. These results suggest that when mice develop in the absence of CRF, another factor (or factors) assumes the behavioral functions normally ascribed to brain CRF, but not activation of the HPA axis. Alternatively, the natural modulator of behavior may not be CRF, but some other molecule that can act on receptors sensitive to CRF. Thus, redundant CNS mechanisms appear to be involved in stress-related behaviors.

In vivo CRF release in rat amygdala is increased during cocaine withdrawal in self-administering rats

Previous studies have suggested a role for corticotropin-releasing factor (CRF) in the central nucleus of the amygdala (CeA) in the aversive and anxiogenic effects of withdrawal from opiates and ethanol. To test whether this role of CRF extends to cocaine withdrawal as well, the release of CRF in rat amygdala was monitored by intracranial microdialysis during a 12-hour session of intravenous cocaine self-administration and subsequent 12-hour cocaine withdrawal period. Cocaine self-administration tended to lower dialysate CRF concentrations to approximately 75% of CRF levels in controls. In contrast, subsequent cocaine withdrawal produced a profound increase in CRF release, which reached peak levels of approximately 400% of baseline between 11 and 12 hours post-cocaine. These results provide evidence that cocaine withdrawal activates CRF neurons in the amygdala, a site that has been implicated in emotional and anxiogenic effects of stress and drug withdrawal syndromes.

Release of vasopressin within the brain contributes to neuroendocrine and behavioral regulation

In addition to its peripheral secretion from the neurohypophysis, the neuropeptide vasopressin (VP) is released within the mammalian brain from probably all parts of the neuronal membrane. In particular the development of brain microdialysis in vivo together with blood microdialysis or blood sampling provides the advantage of being able to reliably compare the dynamic release patterns into different compartments of the organism. The central VP release within hypothalamic (e.g., supraoptic, paraventricular and suprachiasmatic nuclei) and limbic (e.g., septum, amygdala) rat brain areas is stimulated by a variety of substances and stressors, including interleukin-1 beta, social defeat and forced swimming. Furthermore, it is characterized by positive and negative feedback mechanisms and the capacity of the VP system for co-ordinated or independent release, the latter being observed, for example, during social defeat. This emotional stressor, in contrast to exposure to a novel cage, increased VP release within the supraoptic nucleus, but not into plasma. This failure to release VP peripherally could be observed also during forced swimming, despite a dramatic rise in plasma osmolality and a markedly stimulated central release. In another series of experiments we studied the effects of centrally-released VP on cognitive and emotional aspects of behavior using reverse microdialysis for antagonist administration during the behavioral tests and antisense targeting to downregulate either VP or its local V1 receptor subtype. In this way, centrally (in particular septally) released VP could be shown to be causally involved in short-term memory and anxiety-related behavior. Furthermore, VP release within the hypothalamic paraventricular nucleus is likely to provide a negative tonus on the activity of the hypothalamic-pituitary-adrenocortical axis. This neuroendocrine effect together with cognitive, emotional and immunological effects of centrally released VP is thought to be essential to ensure adequate behavior of the animal during challenging situations and to contribute to the development of efficient coping strategies.

N-methyl-D-aspartate (NMDA)-mediated corticotropin-releasing factor (CRF) release in cultured rat amygdala neurons

Corticotropin-releasing factor (CRF) plays an important role in the activation of centrally mediated responses to stress. The amygdala, a limbic structure involved in the stress response, has a significant number of CRF cell bodies and CRF receptors. Activation of glutamatergic projections to the amygdala has been implicated in the stress response. Few studies have evaluated neurotransmitter-stimulated CRF release in the amygdala. We measured the effects of glutamate (0.1-1000 microM) and N-methyl-D-aspartate (NMDA, 0.1-1000 microM) on CRF release from the amygdala using primary neuronal cultures from embryonic rat brains (E18-19). Experiments were performed after the cultures grew for 17-20 days. CRF was measured using radioimmunoassay. The excitatory amino acid neurotransmitters, glutamate and NMDA, stimulated CRF release in a concentration-dependent manner. The apparent EC50 values for glutamate and NMDA were 17.5 microM and 12 microM, respectively. Consistent with a NMDA receptor-driven event, glutamate-stimulated CRF release was blocked by the NMDA antagonist, 2-amino-5-phosphonovaleric acid (AP-5, 1-100 microM) and antagonized by the addition of 1.2 mM MgCl2 to the incubation medium. These results implicate an inhibition of CRF release in the amygdala as a possible mechanism for the reported anxiolytic effects of NMDA antagonists.

Simultaneous glutamate and perfusion fMRI responses to regional brain stimulation

Functional magnetic resonance imaging (fMRI) rests on the assumption that regional brain activity is closely coupled to regional cerebral blood flow (rCBF) in vivo. To test the degree of coupling, cortical brain activity was locally stimulated in rats by reversed microdialysis infusion of picrotoxinin, alphagamma-aminobutyric acid-A antagonist. Before and during the first 30 minutes of infusion, simultaneous fMRI (rCBF) and neurochemical (interstitial glutamate concentration) measures of brain activity were highly correlated (r = 0.83). After 30 minutes of picrotoxinin-induced stimulation, glutamate levels decreased but rCBF remained elevated, suggesting that additional factors modulate the relationship between neuronal neurotransmitters and hemodynamics at these later stages.

Induction of corticotropin-releasing hormone gene expression by glucocorticoids: implication for understanding the states of fear and anxiety and allostatic load

Evidence supports the idea of two distinct corticotropin-releasing hormone (CRH) systems in the brain: one which is constrained by glucocorticoids and the other which is not. It is this latter system that includes two primary sites (central nucleus of the amygdala and the lateral bed nucleus of the stria terminalis) in which the regulation of CRH gene expression can be disassociated from that of the paraventricular nucleus of the hypothalamus. It is this other system that we think is linked to fear and anxiety and to clinical syndromes (excessively shy fearful children, melancholic depression, post-traumatic stress disorder and self-administration of psychotropic drugs). The excess glucocorticoids and CRH, and the state of anticipatory anxiety, contribute to allostatic load, a new term that refers to the wear and tear on the body and brain arising from attempts to adapt to adversity.

Inherent glucocorticoid response potential of isolated hypothalamic neuroendocrine neurons

Within the broader framework of facilitating investigations into the inherent responses of restricted neuronal phenotypes devoid of their in vivo afferents, serum- and steroid-free cultures enriched in corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), and beta-endorphin (beta-END) peptidergic neurons were prepared from the hypothalamic paraventricular (PVN: CRH and AVP) and/or arcuate (ARC: beta-END) nuclei of juvenile male rats. The functional viability of these ARC/PVN cultures was verified by their ability to synthesize and secrete CRH, AVP, and beta-END under basal and depolarizing (veratridine) conditions in vitro. Peptide secretion was shown to be Ca2+ and Na+ dependent in that it was blocked in the presence of verapamil and tetrodotoxin, respectively. Exposure of ARC/PVN cocultures to the glucocorticoid dexamethasone (DEX) resulted in a dose-dependent increase of CRH secretion and an inhibition of AVP and beta-END; the CRH responses deviated strikingly from predictions based on in vivo experiments. Steroid withdrawal or treatment with the glucocorticoid receptor antagonist RU38486 reversed these trends. Opposite effects of DEX on CRH secretion were observed in cultures consisting of PVN cells only. Supported by studies using an opioid receptor agonist (morphine) and antagonist (naloxone), these observations demonstrate that ARC-derived (beta-END) neurons modulate the responses of PVN neurons to DEX.

Antisense oligonucleotides in neuroendocrinology: enthusiasm and frustration

Antisense oligodeoxynucleotides (ODN) offer the potential advantage to manipulate neuropeptide or neuropeptide receptor expression within the brain transiently and site-specifically, thus providing a tool for neuroendocrinological research into the physiological function of a particular neuropeptide system. In this study, various approaches are introduced which reveal that antisense ODN may exert acute, short-term effects on neuronal responsiveness to afferent stimuli, as well as long-term effects on neuropeptide/receptor protein availability in a given system depending on the duration of treatment. Short-term effects were seen in that oxytocin (OXT) and vasopressin (AVP) antisense ODN affected electrophysiological and secretory parameters of oxytocinergic and vasopressinergic neurons, respectively, as well as their ability to express the Fos protein in response to afferent stimulation a few hours after a single infusion into the hypothalamic supraoptic nucleus. In this study, two methodological approaches to study long-term effects of the antisense ODN are exemplified, in which antisense ODN directed against the mRNA coding for the neuropeptide itself or its receptor were used. The repeated infusion of corticotropin releasing hormone (CRH) antisense ODN into the paraventricular nucleus resulted in reduced immunoreactive CRH, but not AVP, in the external zone of the median eminence. Furthermore, in order to evaluate the receptor-mediated effects of CRH and AVP released locally within the paraventricular nucleus on adrenocorticotropin (ACTH) release from the pituitary, CRH receptor (and also AVP receptor) antisense ODN were repeatedly infused into the hypothalamic nuclei; this treatment resulted in an elevation of stimulated, but not basal, ACTH release into the blood. However, in addition to these obvious antisense effects, results are discussed which demonstrate sequence-unspecific effects of phosphorothioated ODN, suggesting that some of their mechanisms of action are not yet understood.

Activation of corticotropin-releasing factor in the limbic system during cannabinoid withdrawal

Corticotropin-releasing factor (CRF) has been implicated in the mediation of the stress-like and negative affective consequences of withdrawal from drugs of abuse, such as alcohol, cocaine, and opiates. This study sought to determine whether brain CRF systems also have a role in cannabinoid dependence. Rats were treated daily for 2 weeks with the potent synthetic cannabinoid HU-210. Withdrawal, induced by the cannabinoid antagonist SR 141716A, was accompanied by a marked elevation in extracellular CRF concentration and a distinct pattern of Fos activation in the central nucleus of the amygdala. Maximal increases in CRF corresponded to the time when behavioral signs resulting from cannabinoid withdrawal were at a maximum. These data suggest that long-term cannabinoid administration alters CRF function in the limbic system of the brain, in a manner similar to that observed with other drugs of abuse, and also induces neuroadaptive processes that may result in future vulnerability to drug dependence.

Somatostatin release as measured by in vivo microdialysis: circadian variation and effect of prolonged food deprivation

In vivo microdialysis was used to determine SRIF release from the hypothalamus in unanesthetized male rats over a period of 24 h and in rats deprived of food for 72 h, in relation to changes in plasma GH levels. Before the experiment, a microdialysis probe was inserted into the anterior pituitary gland of the rats with an indwelling right atrial cannula. Dialysates and blood samples were collected serially, after normal feeding or 72-h deprivation of food. Normal rats implanted with the microdialysis probe showed an episodical pattern of GH secretion at intervals of 3 h. SRIF was secreted in a pulsatile fashion in the dark period in a similar manner to the light period. Mean SRIF pulse amplitude and mean SRIF level were significantly increased in the dark period. There was no significant correlation between the SRIF and GH pulses in the light period. SRIF levels in dialysates obtained from fed rats and food-deprived rats showed a pulsatile pattern. Food deprivation resulted in significant increases in mean SRIF level and mean SRIF pulse amplitude. These results suggest that the existence of circadian rhythm in SRIF release and the increase in SRIF release play an important role in suppressing GH secretion during prolonged food deprivation.

Release of vasopressin within the rat paraventricular nucleus in response to emotional stress: a novel mechanism of regulating adrenocorticotropic hormone secretion?

The effects of emotional stressors on the release of arginine vasopressin (AVP) and oxytocin (OXT) within the rat hypothalamus and the origin and physiological significance of AVP released within the hypothalamic paraventricular nucleus (PVN) were investigated. First, adult male Wistar rats with a microdialysis probe aimed at the PVN or the supraoptic nucleus were exposed to either a dominant male rat (social defeat) or a novel cage. Release of AVP within the PVN was significantly increased in response to social defeat but not to novelty. In contrast to an activation of the hypothalamic-pituitary-adrenal (HPA) system, neither stressor stimulated the hypothalamic-neurohypophysial system (unchanged plasma AVP and OXT and unchanged release within the supraoptic nucleus [AVP] and the PVN [OXT]). Next, we demonstrated by simultaneous microdialysis of the suprachiasmatic nucleus and the PVN that AVP measured in PVN dialysates during social defeat was probably of intranuclear origin. Finally, a mixture of a V1 AVP and the alpha-helical corticotropin-releasing hormone (CRH) receptor antagonists administered via inverse microdialysis into the PVN caused a significant increase in the plasma adrenocorticotropic hormone (ACTH) concentration compared with vehicle-treated controls both under basal conditions and during social defeat, indicating inhibitory effects of intra-PVN-released AVP and/or CRH on HPA system activity. The antagonists failed to affect anxiety-related behavior of the animals as assessed with the elevated plus-maze. Taken together, our results show for the first time that AVP is released within the PVN in response to an emotional stressor. We hypothesize that this intranuclear release provides a negative tonus on ACTH secretion.

Fetal alcohol syndrome: early olfactory learning as a model system to study neurobehavioral deficits

The goal of basic research examining the deficits underlying fetal alcohol syndrome is to develop an animal model which allows investigation and assessment of the neural and cognitive impairments resulting from prenatal alcohol exposure. The following review focuses on animal models and their relationship to human deficits following prenatal alcohol exposure. In addition, this review examines a unique, well-established model system which may permit an increased understanding of the role of alcohol on the developing brain and cognitive behavior. Specifically, large metabolic, neurochemical, neuropharmacological, morphological and neurophysiological changes in young rats have been reported as a consequence of early olfactory preference conditioning, a form of learning that normally occurs during both human and rat development. This olfactory odor preference training paradigm can be used to assess changes in learning as well as the neural substrates underlying this learning. Olfactory preference training has been used to examine: 1) learning, as demonstrated by a behavioral preference for an odor previously paired with stimulation which mimics maternal care; 2) metabolism, by measuring 2-deoxyglucose uptake and distribution in response to the trained odor; 3) neurotransmitter levels, by using in vivo microdialysis, to examine changes in neurotransmitter levels in the olfactory bulb in response to a trained odor. Using in vivo microdialysis enables measurement of both baseline responsiveness of alcohol-exposed pups as well as learned responses at several different developmental ages. The established neural features of this olfactory model include an increase in behavioral preference for a trained odor, increases in 2-DG uptake in specific foci within the olfactory bulb in response to the odor, and increases in dopamine in response to olfactory preference training stimuli, as well as conditioned increases in norepinephrine following olfactory preference training. Using these known behavioral, metabolic and neurochemical indices in control pups allows identification of some of the neurotransmitter systems involved in deficits and the neurobiological basis for impairments induced by prenatal alcohol exposure.

Measurement of extracellular fluid carboplatin kinetics in melanoma metastases with microdialysis

Clinical anti-tumour efficacy of anti-cancer drugs is a function of dose intensity, i.e. the concentration--time profile in tumour tissue. Hence, information on drug concentration profiles in tumours is of critical importance but appropriate methods for measurement are lacking. The aim of the present study was to obtain, by microdialysis sampling, concentration--time profiles in a solid tumour (melanoma) of a model anti-cancer drug, carboplatin, and thereby to assess the scope of microdialysis for tumour pharmacokinetic studies in man. Six patients with cutaneous melanoma metastases at the extremities or body trunk, scheduled to receive carboplatin (400 mg m-2 i.v.) were studied. Carboplatin concentrations were monitored in serum, intratumoral and subcutaneous tissue. Calibration of the microdialysis probes was carried out in vitro and in vivo with use of the retrodialysis method. Complete carboplatin concentration vs time profiles in tumour and subcutaneous tissue were obtained. Major pharmacokinetic parameters (maximum concentration, time to maximum concentration, area under the curve, elimination half-life) were calculated for tissues and tumour/serum concentration ratios for carboplatin were derived. Mean free concentrations of carboplatin in cutaneous melanoma metastases reached only about 50-60% of total serum levels; maximal intratumoral concentrations were 7.6 (+/-2.0; s.e.m.) microgram/ml, mean concentrations in subcutaneous tissue were similar to those in tumour. The present study demonstrates that microdialysis is a novel tool for measuring drug concentrations in solid tumours in humans in vivo and appears to be a valuable addition for pharmacokinetic/pharmacodynamic studies in oncology.

Cationic lipid-mediated delivery and expression of prepro-neuropeptide Y cDNA after intraventricular administration in rat: feasibility and limitations

The utility of in vivo lipofection for delivery and expression of a neuropeptide gene in the adult rat brain was explored. Prepro-neuropeptide Y (NPY) cDNA was cloned into the episomal eucaryotic expression vector pCEP4. This construct was complexed to lipofectamine or lipofectin. Complexed DNA was injected into the lateral ventricles of adult rats. Brains were removed for analysis following various time intervals. Polymerase chain reaction (PCR) reactions were designed for specific detection of endogenous and vector derived NPY sequence, respectively. PCR of DNA preparations from 5 major brain regions (frontal and parietal cortex, striatum, hypothalamus, brain stem) demonstrated presence of vector DNA up to 1 month (longest interval studied) in all brain regions. Reverse-transcription (RT-) PCR of DNase treated RNA-preparations from brain tissue demonstrated presence of both vector-derived and endogenous NPY mRNA in treated animals, while only endogenous mRNA was detected in controls. In situ hybridization histochemistry indicated scattered patches of vector uptake into tissue in the vicinity of the CSF compartment, but not into deeper located structures. Weight gain was not affected, indicating that the expression levels achieved may not be sufficient to play a functional role, and/or may need to be targeted to specific brain areas. These findings suggest a potential for cationic lipid mediated gene transfer in the brain as an experimental tool and as a possible future therapeutic principle, but also indicate the need for optimization of delivery strategies in order to achieve functionally relevant expression levels.

The role of CRF in behavioral aspects of stress

CRF in the central nervous system appears to hve activating properties on behavior and to coordinate behavioral responses to stressors. These behavioral effects of CRF appear to be independent of the pituitary-adrenal axis and can be reversed by CRF antagonists. CRF antagonist administration reverses not only decreases in behavior associated with stress, but also increases in behavior associated with stress, thus suggesting that the role of CRF is stress dependent and not intrinsic to a given behavioral response. Further, microinjection of alpha-helical CRF 9-41 and immunotargeting of CRF neurons in separate brain compartments reveal a link between the anatomical sites that contain CRF and the nature of the behavioral response to stressors that can be modified by suppression of endogenous CRF activity therein. These actions of CRF in coordinating coping responses to stress at several bodily levels are consistent with a role for CRF similar to the dual role of other hypothalamic releasing factors in integrating hormonal and neural mechanisms by acting both as secretagogues for anterior pituitary hormones and as extrapituitary peptide neurotransmitters. Moreover, dysfunction in such a fundamental homeostatic system may be the key to a variety of pathophysiological conditions including mental disorders.

Sensitization of cocaine-stimulated increase in extracellular levels of corticotropin-releasing factor from the rat amygdala after repeated administration as determined by intracranial microdialysis

Using intracranial microdialysis, the effect of repeated cocaine (30 mg/kg i.p.) versus saline administration for 10 consecutive days upon basal and stimulated release of corticotropin-releasing factor (CRF) was examined in the central amygdaloid nucleus (CeA) of anesthetized rats. No significant differences in basal CRF levels between daily cocaine and saline treated groups were found. However, after cocaine challenge (10 mg/kg i.p.) the increase in CRF overflow was significantly greater in cocaine- as opposed to saline-pretreated rats (266 +/- 55.4% versus 149 +/- 8.5% of basal levels). Local administration of 4-aminopyridine produced a significant increase in CRF efflux (195 +/- 58.5%) in daily cocaine-treated rats with only a weak response in the control group (127 +/- 30.9%). These data demonstrate that repeated administration of cocaine enhances cocaine-induced release of CRF in the rat CeA. The sensitization of CRF release may play a significant role in psychostimulant-induced sensitization phenomena.

Rapid induction of tumor necrosis factor alpha in the cerebrospinal fluid after intracerebroventricular injection of lipopolysaccharide revealed by a sensitive capture immuno-PCR assay

Tumor necrosis factor alpha (TNF-alpha) is an important mediator in many pathophysiologic processes, both in the central nervous system (CNS) and in the periphery. For this study, we have designed a very sensitive immuno-PCR detection system to investigate the time course of TNF-alpha induction in the rat cerebrospinal fluid after intracerebroventricular administration of bacterial lipopolysaccharide (LPS). Immuno-PCR combines antibody specificity with PCR signal amplification and provides a sensitivity in the picomolar range. The enhanced sensitivity of this assay allowed the detection of TNF-alpha in the cerebrospinal fluid as early as 15 min after intracerebroventricular administration of LPS. The present results suggest that the ventricular compartment of the CNS, although confined within the blood-brain barrier, is highly responsive to proinflammatory stimuli such as LPS administration. Insight into the molecular mechanisms underlying this compartmentalization could be key to the pathology and treatment of many CNS diseases, especially the meningitides.

The role of corticotropin-releasing factor in the anxiogenic effects of ethanol withdrawal

In summary, endogenous CRF has been demonstrated to play an important role in the endocrine but also autonomic and behavioral responses to a stressor and to mediate some of the signs and symptoms observed in human affective and anxiety disorders. These findings led to the hypothesis that the anxiety that characterizes drug withdrawal, such as ethanol withdrawal in humans, may be related in part to the action of CRF-producing neurons in the CNS. Indeed, rats made dependent on an ethanol liquid diet showed significant signs of enhanced stress responsiveness that was blocked by intracerebral administration of a CRF antagonist. At this time little is known about the specific site of action for endogenous CRF. However, recent studies using local administration of CRF antagonist and in vivo CRF microdialysis suggest that the central nucleus of the amygdala may be an important site for the increases in CRF activity associated with the anxiogenic effects of ethanol withdrawal. Although preliminary, these results propound that ethanol dependence may involve a prolonged dysregulation of the CRF system in the basal forebrain that may contribute to the increased motivational effect of ethanol withdrawal.

In vivo microdialysis of corticotropin releasing factor (CRF): calcium dependence of depolarization-induced neurosecretion of CRF

Corticotropin releasing factor (CRF) is a large neuropeptide which functions as a major neurotransmitter in physiological stress responses. We have developed a microdialysis method for detecting CRF release from the median eminence of anesthetized rats. Depolarizing concentrations of KCl increased release of CRF into the perfusion media; this effect was inhibited by 100 microM verapamil. Our characterization of the physiologic conditions of KCl-induced release of neuronal CRF using the microdialysis technique provides evidence that the CRF release system is Ca(2+)-dependent and maintains its integrity over many hours in anesthetized rats.

Corticotropin-releasing factor and neuropeptide Y: role in emotional integration

The amygdala complex integrates stressful stimuli and is critical in transducing their aversive value into autonomic, endocrine and behavioural responses. Stimulation within the amygdala complex produces signs of fear without a relevant external object, while lesions in this region abolish normal fear responses. In a manner characteristic of phylogenetically old limbic brain areas, the complex neurochemical anatomy of the amygdala involves a large number of phylogenetically old peptide mediators. The distribution and connectivity of these peptide systems have been extensively studied, but less is known about their functional role. Recent evidence suggests that two neuropeptides, corticotropin-releasing factor (CRF) and neuropeptide Y (NPY) exert a reciprocal regulation of responsiveness to stressful stimuli, possibly via an interaction of these two systems in the amygdala.

The role of limbic and hypothalamic corticotropin-releasing factor in behavioral responses to stress

CRF in the central nervous system appears to have activating properties on behavior and to coordinate behavioral responses to stress. These behavioral effects of CRF appear to be independent of the pituitary-adrenal axis and can be reversed by a CRF antagonist, alpha-helical CRF9-41. The CRF antagonist reverses not only decreases in behavior associated with stress, but also increases in behavior associated with stress, thus suggesting that the role of CRF is stress dependent and not intrinsic to a given behavioral response. Further, microinjection of alpha-helical CRF9-41 and immunotargeting of CRF neurons in separate brain compartments reveal a link between the anatomical sites that contain CRF and the nature of the behavioral response to stress that can be modified by suppression of endogenous CRF activity therein. Hence, consistent with the dual role of other hypothalamic-releasing factors in integrating hormonal and neural mechanisms by acting both as secretagogues for anterior pituitary hormones and as extrapituitary peptide neurotransmitters, CRF may coordinate coping responses to stress at several bodily levels (Fig. 6). Moreover, dysfunction in such a fundamental homeostatic system may be the key to a variety of pathophysiological conditions including mental disorders.