Emerging evidence for a central epinephrine-innervated alpha 1-adrenergic system that regulates behavioral activation and is impaired in depression

Peripheral to brain and hippocampus crosstalk induced by exercise mediates cognitive and structural hippocampal adaptations

Endurance exercise leads to robust increases in memory and learning. Several exercise adaptations occur to mediate these improvements, including in both the hippocampus and in peripheral organs. Organ crosstalk has been becoming increasingly more present in exercise biology, and studies have shown that peripheral organs can communicate to the hippocampus and mediate hippocampal changes. Both learning and memory as well as other hippocampal functional-related changes such as neurogenesis, cell proliferation, dendrite morphology and synaptic plasticity are controlled by these exercise responsive peripheral proteins. These peripheral factors, also called exerkines, are produced by several organs including skeletal muscle, liver, adipose tissue, kidneys, adrenal glands and circulatory cells. Previous reviews have explored some of these exerkines including muscle-derived irisin and cathepsin B (CTSB), but a full picture of peripheral to hippocampus crosstalk with novel exerkines such as selenoprotein 1 (SEPP1) and platelet factor 4 (PF4), or old overlooked ones such as lactate and insulin-like growth factor 1 (IGF-1) is still missing. We provide 29 different studies of 14 different exerkines that crosstalk with the hippocampus. Thus, the purpose of this review is to explore peripheral exerkines that have shown to exert hippocampal function following exercise, demonstrating their particular effects and molecular mechanisms in which they could be inducing adaptations.

Lactobacillus rhamnosus Sex-Specifically Attenuates Depressive-like Behavior and Mitigates Metabolic Consequences in Obesity

Background

Patients with diabetes exhibit an increased prevalence for emotional disorders compared with healthy humans, partially due to a shared pathogenesis including hormone resistance and inflammation, which is also linked to intestinal dysbiosis. The preventive intake of probiotic lactobacilli has been shown to improve dysbiosis along with mood and metabolism. Yet, a potential role of Lactobacillus rhamnosus (Lacticaseibacillus rhamnosus 0030) (LR) in improving emotional behavior in established obesity and the underlying mechanisms are unknown.

Methods

Female and male C57BL/6N mice were fed a low-fat diet (10% kcal from fat) or high-fat diet (HFD) (45% kcal from fat) for 6 weeks, followed by daily oral gavage of vehicle or 1 × 108 colony-forming units of LR, and assessment of anxiety- and depressive-like behavior. Cecal microbiota composition was analyzed using 16S ribosomal RNA sequencing, plasma and cerebrospinal fluid were collected for metabolomic analysis, and gene expression of different brain areas was assessed using reverse transcriptase quantitative polymerase chain reaction.

Results

We observed that 12 weeks of HFD feeding induced hyperinsulinemia, which was attenuated by LR application only in female mice. On the contrary, HFD-fed male mice exhibited increased anxiety- and depressive-like behavior, where the latter was specifically attenuated by LR application, which was independent of metabolic changes. Furthermore, LR application restored the HFD-induced decrease of tyrosine hydroxylase, along with normalizing cholecystokinin gene expression in dopaminergic brain regions; both tyrosine hydroxylase and cholecystokinin are involved in signaling pathways impacting emotional disorders.

Conclusions

Our data show that LR attenuates depressive-like behavior after established obesity, with changes in the dopaminergic system in male mice, and mitigates hyperinsulinemia in obese female mice.

Neurotransmitter Gene Polymorphisms Are Associated with Symptom Clusters in Patients Undergoing Radiation Therapy

OBJECTIVES

Purpose was to evaluate for associations between the severity of three distinct symptom clusters (ie, sickness-behavior, mood-cognitive, treatment-related) and polymorphisms for 16 genes involved in catecholaminergic, GABAergic, and serotonergic neurotransmission.

DATA SOURCES

Patients with breast and prostate cancer (n = 157) completed study questionnaires at the completion of radiation therapy. Memorial Symptom Assessment Scale was used to assess the severity of 32 common symptoms. Three distinct symptom clusters were identified using exploratory factor analysis. Associations between the symptom cluster severity scores and neurotransmitter gene polymorphisms were evaluated using regression analyses.

CONCLUSION

Severity scores for the sickness-behavior symptom cluster were associated with polymorphisms for solute carrier family 6 (SLC6A) member 2 (SLC6A2), SLC6A3, SLC6A1, and 5-hydroxytryptamine receptor (HTR) 2A (HTR2A) genes. For the mood-cognitive symptom cluster, severity scores were associated with polymorphisms for adrenoreceptor alpha 1D, SLC6A2, SLC6A3, SLC6A1, HTR2A, and HTR3A. Severity scores for the treatment-related symptom cluster were associated with polymorphisms for SLC6A2, SLC6A3, catechol-o-methyltransferase, SLC6A1, HTR2A, SLC6A4, and tryptophan hydroxylase 2.

IMPLICATIONS FOR NURSING PRACTICE

Findings suggest that polymorphisms for several neurotransmitter genes are involved in the severity of sickness-behavior, mood-cognitive, and treatment-related symptom clusters in oncology patients at the completion of radiation therapy. Four genes with various associated polymorphisms were common across the three distinct symptom clusters (ie, SLC6A2, SLC6A3, SLC6A1, HTR2A) which suggest that these clusters have common underlying mechanisms.

Antidepressant-Like Activity of Solvent Fractions of the Root Bark of Carissa spinarum Linn. (Apocynaceae) in Rodents Involves Multiple Signaling Pathways

Background

The root bark of Carissa spinarum Linn. (Apocynaceae) is claimed to be used for the management of depression in Ethiopian folkloric medicine, and the crude extract has been reported to possess antidepressant-like activity in rodents.

Objective

This study aimed to evaluate the antidepressant-like effect of different fractions of the root bark in rodents and the possible underlying mechanisms in rats.

Methods

A 70% ethanol extract of the root bark was successively fractionated with n-butanol, ethyl acetate, and water. Animals of both sexes received 2% Tween 80, imipramine (30 mg/kg), or various doses (50, 100, 200 mg/kg) of the fractions. Duration of immobility was determined using the tail suspension test and the forced swim test. Locomotor activity was evaluated in the open field test. Serum corticosterone levels, total phenols, flavonoids, and alkaloids were determined. Preliminary mechanistic studies were also performed to explore possible mechanisms of action of the active fraction.

Results

All fractions but the aqueous fraction significantly (p<0.001) decreased the duration of immobility in both tests, with the ethyl acetate fraction being the most active. The locomotor test revealed that the activity was not due to non-specific psycho-stimulant effects. Serum corticosterone levels were reduced by both fractions, with the ethyl acetate fraction again being the most effective. Mechanistic studies showed the involvement of multiple neurotransmission systems, including adrenergic, dopaminergic and cholinergic as well as L-Arginine-NO-cGMP pathway. Higher contents of phenols (42.42 vs 29.8 mgGAE/g), flavonoids (12.43 vs 2.07 mgQE/g), and alkaloids (0.17 vs 0.07 mgATE/g) were found in the ethyl acetate than in the n-butanol fraction.

Conclusion

The present findings collectively indicate that the ethyl acetate and n-butanol fractions are endowed with antidepressant-like activity due to the presence of phenols, flavonoids, and alkaloids, which are medium polar in nature.

Antidepressants Differentially Regulate Intracellular Signaling from α1-Adrenergic Receptor Subtypes In Vitro

Currently utilized antidepressants have limited effectiveness and frequently incur undesired effects. Most antidepressants are thought to act via the inhibition of monoamine reuptake; however, direct binding to monoaminergic receptors has been proposed to contribute to both their clinical effectiveness and their side effects, or lack thereof. Among the target receptors of antidepressants, α1‑adrenergic receptors (ARs) have been implicated in depression etiology, antidepressant action, and side effects. However, differences in the direct effects of antidepressants on signaling from the three subtypes of α1-ARs, namely, α1A-, α1B- and α1D‑ARs, have been little explored. We utilized cell lines overexpressing α1A-, α1B- or α1D-ARs to investigate the effects of the antidepressants imipramine (IMI), desipramine (DMI), mianserin (MIA), reboxetine (REB), citalopram (CIT) and fluoxetine (FLU) on noradrenaline-induced second messenger generation by those receptors. We found similar orders of inhibition at α1A-AR (IMI < DMI < CIT < MIA < REB) and α1D‑AR (IMI = DMI < CIT < MIA), while the α1B-AR subtype was the least engaged subtype and was inhibited with low potency by three drugs (MIA < IMI = DMI). In contrast to their direct antagonistic effects, prolonged incubation with IMI and DMI increased the maximal response of the α1B-AR subtype, and the CIT of both the α1A- and the α1B-ARs. Our data demonstrate a complex, subtype-specific modulation of α1-ARs by antidepressants of different groups.

Three-Dimensional Proteome-Wide Scale Screening for the 5-Alpha Reductase Inhibitor Finasteride: Identification of a Novel Off-Target

Finasteride, a 5-alpha reductase (5α-R) inhibitor, is a widely used drug for treating androgen-dependent conditions. However, its use is associated with sexual, psychological, and physical complaints, suggesting that other mechanisms, in addition to 5α-R inhibition, may be involved. Here, a multidisciplinary approach has been used to identify potential finasteride off-target proteins. SPILLO-PBSS software suggests an additional inhibitory activity of finasteride on phenylethanolamine N-methyltransferase (PNMT), the limiting enzyme in formation of the stress hormone epinephrine. The interaction of finasteride with PNMT was supported by docking and molecular dynamics analysis and by in vitro assay, confirming the inhibitory nature of the binding. Finally, this inhibition was also confirmed in an in vivo rat model. Literature data indicate that PNMT activity perturbation may be correlated with sexual and psychological side effects. Therefore, results here obtained suggest that the binding of finasteride to PNMT might have a role in producing the side effects exerted by finasteride treatment.

Potential antidepressant-like effect of piperazine derivative LQFM212 in mice: Role of monoaminergic pathway and brain-derived neurotrophic factor

Major depression disorder (MDD) is one of the most widespread and debilitating psychiatric diseases and may be associated with other mental disorders such as anxiety. Despite advances in neurobiology studies, currently no established mechanism can explain all facets of MDD, and available drugs often show therapeutic delay for clinical effectiveness and response rates in patients are around 50 %. Previous activities of piperazine derivatives on CNS are indicators of its therapeutic potential for treating mental disorders. In this regard, we have previously shown that the piperazine derivative 2,6-di-tert-butyl-4-((4-(2-hydroxyethyl)piperazin-1-yl)methyl)phenol (LQFM212) has anxiolytic-like activity which involves serotonergic pathway, nicotinic receptors and BZD-site of GABA_A receptor, without cognitive impairments. Herein, was evaluated the potential antidepressant-like effect of LQFM212 on forced swimming test (FST) after a single dose of 54 μmol/kg and after repeated treatment for 15 days in mice. Pretreatment with WAY-100635, PCPA, prazosin, SCH-23390, sulpiride or AMPT reversed the antidepressant-like effect on FST, suggesting that monoaminergic pathway contributes for effects of LQFM212. Furthermore, repeated treatment with LQFM212 increased hippocampal BDNF levels dosed by ELISA kit. In assessment of possible adverse effects, repeated treatment with LQFM212 did not alter the body weight of the animals, glutathione levels in the liver, and serum levels of AST, ALT, urea, and creatinine. Taken together, the results showed that LQFM212 has an antidepressant-like effect that involves monoaminergic pathway and increased BDNF levels. This compound represents promising candidate for prototype of psychoactive drugs for treatment of anxiety and depression disorders since these pathological conditions may exist in comorbidities.

Central norepinephrine transmission is required for stress-induced repetitive behavior in two rodent models of obsessive-compulsive disorder

RATIONALE

Obsessive-compulsive disorder (OCD) is characterized by repetitive behaviors exacerbated by stress. Many OCD patients do not respond to available pharmacotherapies, but neurosurgical ablation of the anterior cingulate cortex (ACC) can provide symptomatic relief. Although the ACC receives noradrenergic innervation and expresses adrenergic receptors (ARs), the involvement of norepinephrine (NE) in OCD has not been investigated.

OBJECTIVE

To determine the effects of genetic or pharmacological disruption of NE neurotransmission on marble burying (MB) and nestlet shredding (NS), two animal models of OCD.

METHODS

We assessed NE-deficient (Dbh -/-) mice and NE-competent (Dbh +/-) controls in MB and NS tasks. We also measured the effects of anti-adrenergic drugs on NS and MB in control mice and the effects of pharmacological restoration of central NE in Dbh -/- mice. Finally, we compared c-fos induction in the locus coeruleus (LC) and ACC of Dbh -/- and control mice following both tasks.

RESULTS

Dbh -/- mice virtually lacked MB and NS behaviors seen in control mice but did not differ in the elevated zero maze (EZM) model of general anxiety-like behavior. Pharmacological restoration of central NE synthesis in Dbh -/- mice completely rescued NS behavior, while NS and MB were suppressed in control mice by anti-adrenergic drugs. Expression of c-fos in the ACC was attenuated in Dbh -/- mice after MB and NS.

CONCLUSION

These findings support a role for NE transmission to the ACC in the expression of stress-induced compulsive behaviors and suggest further evaluation of anti-adrenergic drugs for OCD is warranted.

Pupo A. Updates in the function and regulation of α1 -adrenoceptors

α1 -Adrenoceptors are seven transmembrane domain GPCRs involved in numerous physiological functions controlled by the endogenous catecholamines, noradrenaline and adrenaline, and targeted by drugs useful in therapeutics. Three separate genes, whose products are named α1A -, α1B -, and α1D - adrenoceptors, encode these receptors. Although the existence of multiple α1 -adrenoceptors has been acknowledged for almost 25 years, the specific functions regulated by each subtype are still largely unknown. Despite the limited comprehension, the identification of a single class of subtype-selective ligands for the α1A - adrenoceptors, the so-called α-blockers for prostate dysfunction, has led to major improvement in therapeutics, demonstrating the need for continued efforts in the field. This review article surveys the tissue distribution of the three α1 -adrenoceptor subtypes in the cardiovascular system, genitourinary system, and CNS, highlighting the functions already identified as mediated by the predominant activation of specific subtypes. In addition, this review covers the recent advances in the understanding of the molecular mechanisms involved in the regulation of each of the α1 -adrenoceptor subtypes by phosphorylation and interaction with proteins involved in their desensitization and internalization. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Environmental Exposures and Depression: Biological Mechanisms and Epidemiological Evidence

Mental health and well-being are consistently influenced—directly or indirectly—by multiple environmental exposures. In this review, we have attempted to address some of the most common exposures of the biophysical environment, with a goal of demonstrating how those factors interact with central structures and functions of the brain and thus influence the neurobiology of depression. We emphasize biochemical mechanisms, observational evidence, and areas for future research. Finally, we include aspects of contextual environments—city living, nature, natural disasters, and climate change—and call for improved integration of environmental issues in public health science, policies, and activities. This integration is necessary for reducing the global pandemic of depression.

The development of depression-like behavior is consolidated by IL-6-induced activation of locus coeruleus neurons and IL-1β-induced elevated leptin levels in mice

RATIONALE

Many studies have supported the cytokine hypothesis as the underlying pathophysiology of depressive disorder.

OBJECTIVES

We previously reported that lipopolysaccharide (LPS)-induced depression-like behavior is abrogated by the α1-adrenoceptor antagonist prazosin. Since cytokines are involved in LPS effects on the brain, we investigated the effects of cytokines on noradrenergic neurons in the locus coeruleus (LC) and whether central α1-adrenoceptors can cause the development of depression-like behavior.

METHODS

Adult male CD1 mice were treated with LPS (1 mg/kg, i.p.) or saline and sacrificed 2 h later for immunofluorescence studies of c-fos and tyrosine hydroxylase (TH) expression in LC neurons. Serum cytokines were measured using enzyme-linked immunosorbent assay (ELISA). Another group of mice were implanted with intracerebroventricular (i.c.v.) cannulae and given artificial cerebrospinal fluid (CSF) (control), interleukin (IL)-1β (0.5 μg), IL-6 (1 μg), or tumor necrosis factor (TNF)-α (1 μg), and sacrificed 2 h later for c-fos and TH immunofluorescence analysis. Serum samples were analyzed for leptin levels. In addition, tail suspension test (TST), forced swimming test (FST), and sucrose preference (SP) test were conducted in a separate group of mice treated i.c.v. with cytokines, recombinant mouse leptin (5 μg) or phenylephrine (40 μg). These effects were countered by i.c.v. administration of prazosin and a leptin antagonist.

RESULTS

LPS increased c-fos expression in TH-positive neurons. Central administration of IL-6 and IL-1β increased c-fos immunoreactivity and serum leptin levels. Phenylephrine, an α1-adrenoceptor agonist, given i.c.v., increased the immobility time during FST and decreased SP, but had no effect on TST. Central leptin administration increased immobility time during FST but did not affect TST or SP. The combination of phenylephrine and leptin increased immobility time during FST and TST, and decreased SP. Induction of depression-like behavior by co-administration of IL-1β and IL-6 was prevented by pretreatment with prazosin alone.

CONCLUSION

These results suggest that IL-6-dependent LC neuronal activation induced depression-like behavior and IL-1β-induced increase in leptin levels enhanced α1-adrenoceptor-mediated depression-like behavior.

Biphasic Effects of α-Asarone on Immobility in the Tail Suspension Test: Evidence for the Involvement of the Noradrenergic and Serotonergic Systems in Its Antidepressant-Like Activity

Alpha (α)-asarone is one of the main psychoactive compounds, present in Acorus species. Evidence suggests that the α-asarone possess an antidepressant-like activity in mice. However, the exact dose-dependent effect of α-asarone and mechanism(s) involved in the antidepressant-like activity are not clear. The present study aimed to investigate the dose-dependent effect of α-asarone and the underlining mechanism(s) involved in the antidepressant-like activity of α-asarone in the mouse model of tail suspension test (TST). In this study, the acute effect of α-asarone per se at different doses (10–100 mg/kg, i.p.) on immobility in the TST was studied. Additionally, the possible mechanism(s) involved in the antidepressant-like effect of α-asarone was studied using its interaction with noradrenergic and serotonergic neuromodulators in the TST. The present results reveal that the acute treatment of α-asarone elicited biphasic responses on immobility such that the duration of the immobility time is significantly reduced at lower doses (15 and 20 mg/kg, i.p.) but increased at higher doses (50 and 100 mg/kg, i.p.) in the TST. Besides, α-asarone at higher doses (50 and 100 mg/kg, i.p.) significantly decreased the spontaneous locomotor activity. Moreover, pretreatment of mice with noradrenergic neuromodulators such as AMPT (100 mg/kg, i.p., a catecholamine synthesis inhibitor), prazosin (1 mg/kg, i.p., an α₁-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α₂-adrenoceptor antagonist) and with serotonergic neuromodulators such as PCPA (100 mg/kg, i.p., once daily for four consecutive days, a serotonin synthesis inhibitor,) and WAY100635 (0.1 mg/kg, s.c., a selective 5-HT_1A receptor antagonist) significantly reversed the anti-immobility effect of α-asarone (20 mg/kg, i.p.). Taken together, our results suggest that the acute treatment with α-asarone elicited biphasic actions in the TST in which antidepressant-like effect was seen at relatively lower doses (15 and 20 mg/kg, i.p.) and depressive-like activity at relatively higher doses (50 and 100 mg/kg, i.p.). Furthermore, it has been revealed that the antidepressant-like effect of α-asarone could be mediated through both noradrenergic (α₁ and α₂ adrenoceptors) and serotonergic (particularly, 5-HT_1A receptors) systems.

Antidepressant-like effect of the hydroethanolic leaf extract of Alchornea cordifolia (Schumach. & Thonn.) Mull. Arg. (Euphorbiaceae) in mice: involvement of monoaminergic system

ETHNOPHARMACOLOGICAL RELEVANCE

The leaf of Alchornea cordifolia (Euphorbiaceae) is used in traditional African medicine in the treatment of various neurological and psychiatric disorders including depression. Previous studies have shown its potent antidepressant-like effect in the forced swimming test (FST). Hence, this study sought to investigate the involvement of monoaminergic systems in the antidepressant-like effect elicited by hydroethanolic leaf extract of Alchornea cordifolia (HeAC) in the FST.

MATERIALS AND METHODS

HeAC (25-400mg/kg, p.o.) was administered 1h before the FST. To investigate the contribution of monoaminergic systems to antidepressant-like effect, receptors antagonists were injected 15min before oral administration of HeAC (200mg/kg) to mice and 1h thereafter, subjected to FST.

RESULTS

HeAC (200 and 400mg/kg, p.o.) produced dose dependent and significant (P<0.001) antidepressant-like effect, in the FST, without accompanying changes in spontaneous locomotor activities in the open-field test. The anti-immobility effect of HeAC (200mg/kg) in the FST was prevented by pretreatment of mice with SCH 23390 (0.05mg/kg, s.c., a dopamine D1 receptor antagonist), sulpiride (50mg/kg, i.p., a dopamine D2 receptor antagonist), prazosin (1mg/kg, i.p., an α1-adrenoceptor antagonist), yohimbine (1mg/kg, i.p., an α2-adrenoceptor antagonist), and GR 127993 (5-HT1B receptor antagonist). Similarly, 3 days intraperitoneal injection of p-chlorophenylalanine (pCPA, 150mg/kg, i.p., an inhibitor of serotonin synthesis) prevented the antidepressant-like effect elicited by HeAC. The combination of subeffective doses of imipramine (5mg/kg, p.o.) or fluoxetine (5mg/kg, p.o.), with HeAC (25mg/kg, p.o., subeffective dose) produced a synergistic antidepressant-like effect in the FST.

CONCLUSION

The hydroethanolic extract of Alchornea cordifolia possesses antidepressant-like effect mediated through interaction with dopamine (D1 and D2), noradrenergic (α1 and α2 adrenoceptors), and serotonergic (5HT1B receptors) systems. Also, the potentiation of the anti-immobility effect of conventional antidepressants (fluoxetine and imipramine) by Alchornea cordifolia suggest potential therapeutic effect in depression.

Adrenaline rush: the role of adrenergic receptors in stimulant-induced behaviors

Psychostimulants, such as cocaine and amphetamines, act primarily through the monoamine neurotransmitters dopamine (DA), norepinephrine, and serotonin. Although stimulant addiction research has largely focused on DA, medication development efforts targeting the dopaminergic system have thus far been unsuccessful, leading to alternative strategies aimed at abating stimulant abuse. Noradrenergic compounds have shown promise in altering the behavioral effects of stimulants in rodents, nonhuman primates, and humans. In this review, we discuss the contribution of each adrenergic receptor (AR) subtype (α1, α2, and β) to five stimulant-induced behaviors relevant to addiction: locomotor activity, conditioned place preference, anxiety, discrimination, and self-administration. AR manipulation has diverse effects on these behaviors; each subtype profoundly influences outcomes in some paradigms but is inconsequential in others. The functional neuroanatomy and intracellular signaling mechanisms underlying the impact of AR activation/blockade on these behaviors remain largely unknown, presenting a new frontier for research on psychostimulant-AR interactions.

Brief maternal separation affects brain α1-adrenoceptors and apoptotic signaling in adult mice

Exposure to adversity during early life is a risk factor for the development of different mood and psychiatric disorders, including depressive-like behaviors. Here, neonatal mice were temporarily but repeatedly (day 1 to day 13) separated from mothers and placed in a testing environment containing a layer of odorless clean bedding (CB). We assessed in adult animals the impact of this early experience on binding sites and mRNA expression of α1-adrenergic receptor subtypes, heat shock proteins (HSPs) and proapoptotic and antiapoptotic members of the Bcl-2 family proteins in different brain regions involved in processing of olfactory information and rewarding stimuli. We found that repeated exposure to CB experience produced anhedonic-like behavior in terms of reduced saccharin intake and α1-adrenoceptor downregulation in piriform and somatosensory cortices, hippocampus, amygdala and discrete thalamic nuclei. We also found a selective decrease of α1B-adrenoceptor binding sites in the cingulate cortex and hippocampus and an increase of hippocampal α1A and α1B receptor, but not of α1D-adrenoceptor, mRNA levels. Moreover, while a significant decrease of antiapoptotic heat shock proteins Hsp72 and Hsp90 was identified in the prefrontal cortex, a parallel increase of antiapoptotic members of Bcl-2 family proteins was found at the hippocampal level. Together, these data provide evidence that the early exposure to CB experience produced enduring downregulation of α1-adrenoceptors in the prefrontal-limbic forebrain/limbic midbrain network, which plays a key role in the processing of olfactory information and reaction to rewarding stimuli. Finally, these data show that CB experience can "prime" the hippocampal circuitry and promote the expression of antiapoptotic factors that can confer potential neuroprotection to subsequent adversity.

A mechanism for nerve cell excitation by norepinephrine via α-1 adrenoceptors: inhibition of potassium M-current

Some of the excitatory effects of norepinephrine on central neurons are mediated by alpha-1 (α1) adrenoceptors. These receptors are coupled to the Gq family of G proteins, and hence stimulate hydrolysis of the membrane phospholipid phosphatidylinositol-4,5-bisphosphate. Other receptors of this type can excite neurons by inhibiting the subthreshold voltage-gated potassium M-current. We tested this possibility using rat sympathetic neurons transformed to express α1a receptors. The α1 agonist phenylephrine strongly inhibited the M-current recorded under voltage-clamp by 72 ± 11 % (n = 4) and in an unclamped neuron dramatically increased the number of action potentials produced by a 2 s depolarizing current step from 2 to 40, without effect on control neurons devoid of α1 receptors. We suggest that this might be a potential cause of the increased excitability produced by norepinephrine in some central neurons.

Epinephrine: a short- and long-term regulator of stress and development of illness : a potential new role for epinephrine in stress

Epinephrine (Epi), which initiates short-term responses to cope with stress, is, in part, stress-regulated via genetic control of its biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT). In rats, immobilization (IMMO) stress activates the PNMT gene in the adrenal medulla via Egr-1 and Sp1 induction. Yet, elevated Epi induced by acute and chronic stress is associated with stress induced, chronic illnesses of cardiovascular, immune, cancerous, and behavioral etiologies. Major sources of Epi include the adrenal medulla and brainstem. Although catecholamines do not cross the blood-brain barrier, circulating Epi from the adrenal medulla may communicate with the central nervous system and stress circuitry by activating vagal nerve β-adrenergic receptors to release norepinephrine, which could then stimulate release of the same from the nucleus tractus solitarius and locus coeruleus. In turn, the basal lateral amygdala (BLA) may activate to stimulate afferents to the hypothalamus, neocortex, hippocampus, caudate nucleus, and other brain regions sequentially. Recently, we have shown that repeated IMMO or force swim stress may evoke stress resiliency, as suggested by changes in expression and extinction of fear memory in the fear-potentiated startle paradigm. However, concomitant adrenergic changes seem stressor dependent. Present studies aim to identify stressful conditions that elicit stress resiliency versus stress sensitivity, with the goal of developing a model to investigate the potential role of Epi in stress-associated illness. If chronic Epi over expression does elicit illness, possibilities for alternative therapeutics exist through regulating stress-induced Epi expression, adrenergic receptor function and/or corticosteroid effects on Epi, adrenergic receptors and the stress axis.

The 'resting-state hypothesis' of major depressive disorder-a translational subcortical-cortical framework for a system disorder

Major depressive disorder (MDD) has traditionally been characterized by various psychological symptoms, involvement of diverse functional systems (e.g., somatic, affect, cognition, reward, etc.), and with progress in neuroscience, an increasing number of brain regions. This has led to the general assumption that MDD is a stress-responsive brain 'system disorder' where either one or several alterations infiltrate a large number of functional systems in the brain that control the organism's somatic, affective, and cognitive life. However, while the effects or consequences of the abnormal changes in the functional systems of, for instance affect, cognition or reward have been investigated extensively, the underlying core mechanism(s) underlying MDD remain unknown. Hypotheses are proliferating rapidly, though. Based on recent findings, we will entertain an abnormality in the resting-state activity in MDD to be a core feature. Based on both animal and human data, we hypothesize that abnormal resting-state activity levels may impact stimulus-induced neural activity in medially situated core systems for self-representation as well as external stimulus (especially stress, specifically separation distress) interactions. Moreover, due to nested hierarchy between subcortical and cortical regions, we assume 'highjacking' of higher cortical affective and cognitive functions by lower subcortical primary-process emotional systems. This may account for the predominance of negative affect in somatic and cognitive functional system operations with the consecutive generation of the diverse symptoms in MDD. We will here focus on the neuroanatomical and biochemical basis of resting-state abnormalities in MDD including their linkage to the diverse psychopathological symptoms in depression. However, our 'resting-state hypothesis' may go well beyond that by being sufficiently precise to be linked to genetic, social, immunological, and endocrine dimensions and hypotheses as well as to clinical dimensions like endophenotypes and various diagnostic-prognostic biomarkers. Taken together, our 'resting-state hypothesis' may be considered a first tentative framework for MDD that integrates translational data, the various dimensions, and subcortical-cortical systems while at the same time providing the link to the clinical level of symptoms, endophenotypes and biomarkers.

The pharmacological properties of antidepressants

Antidepressant drugs represent one of the main forms of effective treatment for the amelioration of depressive symptoms. Most available antidepressants increase extracellular levels of monoamines. However, it is now recognized that monoamine levels and availability are only part of the story, and that antidepressants whose mechanism of action is mainly based on the modulation of monoaminergic systems may not be able to satisfy the unmet needs of depression. Therefore, a number of compounds, developed for their potential antidepressant activity, are endowed with putative mechanisms of action not affecting traditional monoamine targets. This article briefly reviews, within a mechanistic perspective, the pharmacological profiles of representative antidepressants from each class, including monoamine oxidase inhibitors, tricyclics, norepinephrine reuptake inhibitors, selective serotonin reuptake inhibitors, norepinephrine and serotonin reuptake inhibitors, antidepressants interacting with dopaminergic, melatonergic, glutamatergic, or neuropeptide systems. The undesirable side effects of currently used antidepressants, which can often be a reason for lack of compliance, are also considered.

The tricyclic antidepressants amitriptyline, nortriptyline and imipramine are weak antagonists of human and rat alpha1B-adrenoceptors

Although it is long known that the tricyclic antidepressants amitriptyline, nortriptyline and imipramine inhibit the noradrenaline transporter and alpha(1)-adrenoceptors with similar affinities, which may lead to self-cancelling actions, the selectivity of these drugs for alpha(1)-adrenoceptor subtypes is unknown. The present study investigates the selectivity of amitriptyline, nortriptyline and imipramine for human recombinant and rat native alpha(1)-adrenoceptor subtypes. The selectivity of amitriptyline, nortriptyline and imipramine was investigated in HEK-293 cells expressing each of the human alpha(1)-subtypes and in rat native receptors from the vas deferens (alpha(1A)), spleen (alpha(1B)) and aorta (alpha(1D)) through [(3)H]prazosin binding, and noradrenaline-induced intracellular Ca(2+) increases and contraction assays. Amitriptyline, nortriptyline and imipramine showed considerably higher affinities for alpha(1A)- (approximately 25- to 80-fold) and alpha(1D)-adrenoceptors (approximately 10- to 25-fold) than for alpha(1B)-adrenoceptors in both contraction and [(3)H]prazosin binding assays with rat native and human receptors, respectively. In addition, amitriptyline, nortriptyline and imipramine were substantially more potent in the inhibition of noradrenaline-induced intracellular Ca(2+) increases in HEK-293 cells expressing alpha(1A)- or a truncated version of alpha(1D)-adrenoceptors which traffics more efficiently towards the cell membrane than in cells expressing alpha(1B)-adrenoceptors. Amitriptyline, nortriptyline and imipramine are much weaker antagonists of rat and human alpha(1B)-adrenoceptors than of alpha(1A)- and alpha(1D)-adrenoceptors. The differential affinities for these receptors indicate that the alpha(1)-adrenoceptor subtype which activation is most increased by the augmented noradrenaline availability resultant from the blockade of neuronal reuptake is the alpha(1B)-adrenoceptor. This may be important for the behavioural effects of these drugs.

Anti-PrP Mab 6D11 suppresses PrP(Sc) replication in prion infected myeloid precursor line FDC-P1/22L and in the lymphoreticular system in vivo

The pathogenesis of prion diseases is related to conformational transformation of cellular prion protein (PrP(C)) into a toxic, infectious, and self-replicating conformer termed PrP(Sc). Following extracerebral inoculation, the replication of PrP(Sc) is confined for months to years to the lymporeticular system (LRS) before the secondary CNS involvement results in occurrence of neurological symptoms. Therefore, replication of PrP(Sc), in the early stage of infection can be targeted by therapeutic approaches, which like passive immunization have limited blood-brain-barrier penetration. In this study, we show that 6D11 anti-PrP monoclonal antibody (Mab) prevents infection on a FDC-P1 myeloid precursor cell line stably infected with 22L mouse adapted scrapie strain. Passive immunization of extracerebrally infected CD-1 mice with Mab 6D11 resulted in effective suppression of PrP(Sc) replication in the LRS. Although, a rebound of PrP(Sc) presence occurred when the Mab 6D11 treatment was stopped, passively immunized mice showed a prolongation of the incubation period by 36.9% (pb0.0001) and a significant decrease in CNS pathology compared to control groups receiving vehicle or murine IgG. Our results indicate that antibody-based therapeutic strategies can be used, even on a short-term basis, to delay or prevent disease in subjects accidentally exposed to prions.

Adrenergic responses to stress: transcriptional and post-transcriptional changes

Stress effects on adrenergic responses in rats were examined in adrenal medulla, the primary source of circulating epinephrine (Epi). Irrespective of duration, immobilization (IMMO) increased adrenal corticosterone to the same extent. In contrast, Epi changed little, suggesting that Epi synthesis replenishes adrenal pools and sustains circulating levels for the heightened alertness and physiological changes required of the "flight or fight" response. IMMO also induced the Epi-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT). The rise in its mRNA and protein was preceded by increases in Egr-1 and Sp1 mRNA, protein, and protein-DNA binding complex formation. With repeated and prolonged stress, PNMT protein did not reflect the magnitude of change in mRNA. The latter suggests that post-transcriptional, in addition to transcriptional mechanisms, regulate PNMT responses to stress. To further reveal molecular mechanisms underlying stress-induced changes in adrenergic function, the effects of hypoxia on PNMT promoter-driven gene expression are being examined in adrenal medulla-derived PC12 cells. Hypoxia activates the PNMT promoter to increase PNMT promoter-driven luciferase reporter gene expression and endogenous PNMT in PC12 cells. Induction of both appear mediated via activation of multiple signaling pathways and downstream activation of hypoxia inducible factor and PNMT transcriptional activators, Egr-1 and Sp1. Hypoxia generates both partially and fully processed forms of PNMT mRNA. The former reportedly is translated into a truncated, nonfunctional protein, and the latter into enzymatically active PNMT. Together, findings suggest that stress increases PNMT gene transcriptional activity but post-transcriptional regulatory mechanisms limit the biological end-point of functional PNMT enzyme and, thereby, Epi.

Evidence for the involvement of the monoaminergic system in the antidepressant-like action of two 4-amine derivatives of 10,11-dihydro-5H-dibenzo [a,d] cycloheptane in mice evaluated in the tail suspension test

Our previous study described the synthesis of 4-amine derivatives of 10,11-dihydro-5H-dibenzo-alkylamine-cycloheptane, 4-amine (3-N,N-dimethylpropylamine)-10,11-dihydro-5H-dibenzo[a,d] cycloheptane-5-one (ADDCH1), and 1,2,3,4,8,9-hexahydro-dibenzocycloheptane[4,4a,5-ef]1,4-diazepin (ADDCH2), and the characterization of their antidepressant-like effect in the forced swimming test in mice. This study investigated the involvement of monoaminergic pathways in the antidepressant-like effect of these compounds in mice evaluated in the tail suspension test (TST), another animal model to screen antidepressant drugs. Our results show that the immobility time in the TST was significantly reduced by ADDCH1 (15 to 50 mg/kg, i.p.) or ADDCH2 (30 and 50 mg/kg, i.p.). The antidepressant-like effect of ADDCH1 (30 mg/kg, i.p.) in the TST was prevented by pre-treatment of mice with methysergide (2 mg/kg, i.p.), a non-selective serotonin receptor antagonist, p-chlorophenylalanine methylester (pCPA, 100 mg/kg, i.p.), an inhibitor of serotonin synthesis, prazosin (62.5 microg/kg, i.p.), an alpha1-adrenoceptor antagonist, or yohimbine (1 mg/kg, i.p.), an alpha2-adrenoceptor antagonist. In contrast, the antidepressant-like effect of ADDCH2 was antagonized only by yohimbine (1 mg/kg) or haloperidol (50 microg/kg, i.p.), a dopamine D2/D3/D4 receptor antagonist, and was not affected by methysergide, pCPA or prazosin. Altogether, the present results strongly suggest the differential involvement of monoaminergic systems, serotonin/noradrenaline (ADDCH1) and noradrenaline/dopamine (ADDCH2) pathways, respectively, in the antidepressant-like effect of dibenzosuberone compounds.

Effects of ICV administration of the alpha1A-adrenoceptor antagonist 5-methylurapidil on concurrent measures of eating and locomotion after cocaine in the rat

Psychostimulants including amphetamine and cocaine induce locomotion and stereotypy and suppress eating. Although the capacity of cocaine to alter locomotion is usually viewed as related to dopamine neurotransmission, recent studies suggest that norepinephrine, acting through alpha1-adrenergic receptors (alpha1-ARs) can facilitate cocaine-stimulated locomotion. Of the three alpha1-AR subtypes (alpha(1A), alpha(1B), and alpha(1D)) identified to date, inactivation of the alpha(1B)-AR subtype diminishes cocaine-stimulated locomotion, whereas the impact of inactivation of the alpha(1A)-AR subtype on either eating or locomotion is unknown. In the present study, we assessed the relative impact of ICV administration of the alpha(1B)-AR antagonist 5-methylurapidil (5-MU) on cocaine-stimulated hyperlocomotion and hypophagia, using a concurrent method [Wellman, P.J., Ho, D.H., Davis, K.W., 2005. Concurrent measures of feeding and locomotion in rats. Physiology of Behavior 84 (5), 769-774.]. Rats were infused ICV with one of 3 doses of 5-MU (0, 3, or 30 nmol) and then injected (i.p.) with 0, 2.5, 5.0, 10.0, or 20.0 mg/kg cocaine HCl on each of five tests. Rats always received the same 5-MU dose, but a different cocaine dose on each trial. Feeding and locomotion were assessed concurrently during a 45-min postinjection period. Significant suppression of eating was noted at 2.5 mg/kg cocaine, a dose that does not alter forward locomotion in the rat. Administration of 5-MU did not alter locomotion in rats treated with saline, but did significantly increase baseline food intake. Neither cocaine-induced hypophagia nor hyperlocomotion was altered by ICV administration of 5-MU. These results suggest that the capacity of alpha1-AR agonists (e.g. phenylpropanolamine) to suppress eating may be related to activation of the alpha(1A)-AR subtype, whereas cocaine does not act through the alpha(1A)-AR subtype to suppress eating nor does this subtype modulate cocaine-induced hyperlocomotion.

Stress-induced changes in epinephrine expression in the adrenal medulla in vivo

Immobilization (IMMO) stress was used to examine how stress alters the stress hormone epinephrine (EPI) in the adrenal medulla in vivo. In rats subjected to IMMO for 30 or 120 min, adrenal corticosterone increased to the same extent. In contrast, EPI changed very little, suggesting that EPI synthesis replenishes adrenal pools and sustains circulating levels for the heightened alertness and physiological responses of the 'flight or fight' response. In part, stress activates EPI via the phenylethanolamine N-methyltransferase (PNMT) gene as single or repeated IMMO elevated PNMT mRNA. The rise in PNMT mRNA was preceded by induction of the PNMT gene activator, Egr-1, with increases in Egr-1 mRNA, protein, and protein-DNA binding complex apparent. IMMO also evoked changes in Sp1 mRNA, protein, and Sp1-DNA complex formation, although for chronic IMMO changes were not entirely coincident. In contrast, glucocorticoid receptor and AP-2 mRNA, protein, and protein-DNA complex were unaltered. Finally, IMMO stress elevated PNMT protein. However, with seven daily IMMOs for 120 min and delayed killing, protein stimulation did not attain the highly elevated levels expected based on mRNA changes. The latter may perhaps suggest initiation of adrenergic desensitization to prolonged and repeated IMMO stress and/or dissociation of transcriptional and post-transcriptional regulatory mechanisms.

The effects of norepinephrine transporter inactivation on locomotor activity in mice

BACKGROUND

Acute administration of different classes of antidepressants can enhance or reduce spontaneous locomotor activity in a novel environment, but the effects of chronic antidepressant treatment on spontaneous locomotor activity in novel and familiar environments are less well characterized. Because norepinephrine is an important regulator of spontaneous locomotor activity, we speculated that norepinephrine transporter blockade contributes to the effects of some antidepressants on spontaneous locomotor activity.

METHODS

Antidepressant drugs (reboxetine, desipramine, imipramine, venlafaxine, bupropion) were administered acutely (intraperitoneal) or chronically (via osmotic minipump) to control and norepinephrine transporter knockout mice, and spontaneous locomotor activity in novel or familiar environments was recorded.

RESULTS

Acute treatment with most norepinephrine transporter-blocking antidepressants decreased spontaneous locomotor activity in a novel environment, whereas chronic treatment decreased spontaneous locomotor activity in both novel and familiar environments. The exception was bupropion, a dual norepinephrine transporter/dopamine transporter blocker, which tended to increase spontaneous locomotor activity. Coadministration of reboxetine and the dopamine transporter blocker GBR 12909 also increased spontaneous locomotor activity. Norepinephrine transporter knockout mice had low basal spontaneous locomotor activity, which was increased by bupropion, whereas reboxetine had no effect in norepinephrine transporter knockout mice.

CONCLUSIONS

Acute or chronic inactivation of the norepinephrine transporter decreases spontaneous locomotor activity in novel and familiar environments unless coupled with dopamine transporter blockade.

Depressive behavior in mice due to immune stimulation is accompanied by reduced neural activity in brain regions involved in positively motivated behavior

BACKGROUND

Immune stimulation inhibits positively motivated behavior and induces depressive illness. To help clarify the mechanism of these effects, neural activity in response to a positive stimulus was examined in brain regions associated with positively motivated activity defined on the basis of prior behavioral studies of central alpha1-adrenoceptor action.

METHODS

Mice pretreated with either lipopolysaccharide or, for comparison, reserpine were exposed to a motivating stimulus (fresh cage) and subsequently assayed for fos expression and mitogen-activated protein kinase (MAPK) phosphorylation, two measures associated with alpha1-adrenoceptor-dependent neural activity, in several positive-activity-related (motor, piriform, cingulate cortex, nucleus accumbens, locus coeruleus) and stress-related brain regions (paraventricular hypothalamus, bed nucleus stria terminalis).

RESULTS

Both lipopolysaccharide and reserpine pretreatment abolished fresh cage-induced fos expression and MAPK activation in the positive activity-related brain regions but enhanced these measures in the stress-related areas.

CONCLUSIONS

The results support the hypothesis that immune activation reduces alpha1-adrenoceptor-related signaling and neural activity in brain regions associated with positive activity while it increases these functions in stress-associated areas. It is suggested that neural activities of these two types of brain regions are mutually antagonistic and that a reciprocal shift toward the stress regions is a factor in the loss of positively motivated behaviors in sickness behavior and depressive illness.

The 'drive for activity' and "restlessness" in anorexia nervosa: potential pathways

This paper discusses the hypothesis that a 'drive for activity" in the presence of physiological and endocrine changes consistent with starvation is a characteristic symptom of acute anorexia nervosa (AN). This 'drive for movement', along with alertness and lack of fatigue, so unlike the motor slowing and loss of energy observed in simple starvation has been recognized in AN throughout history, but has received little attention in the past fifty years. Clinical reports and experimental evidence suggest that 'restlessness' and a 'drive for activity' vary in intensity, they appears to be starvation-dependent and to wane with food intake. Central nervous system (CNS) systems known to be involved in mediating activity and arousal levels that are altered by the negative energy expenditure in AN are reviewed. Among these, the corticotropin-releasing hormone (CRH) system, the melanocyte stimulating hormone/agouti-related protein (MSH/AGRP) system and the norepinephrine/epinephrine (NE/EPI) and dopamine (DA) system may contribute to the 'drive for activity' and alertness in AN. AN appears to represent a disorder of gene/environment interaction. Future research will reveal whether in individuals predisposed to AN, the 'drive for activity' reflects the reactivation of mechanisms important in food scarcity, controlled by one or more evolutionary conserved genes including those regulating foraging behavior. Recognition of the 'drive for activity' as a diagnostic symptom of AN and its assessment prior to re-nutrition would permit clarification of its role in the etiology of AN.

Role of CNS α1-adrenoceptor activity in central fos responses to novelty

The present study investigated, by use of fos immunohistochemistry, whether the functional activity of alpha(1)-adrenoceptors is elevated during heightened behavioral activity in brain regions shown earlier to contain motoric alpha(1)-receptors. In confirmation, marked c-fos responses that were blocked by an alpha(1)-antagonist (prazosin) were found in four of these brain regions (secondary motor, cingulate, piriform cortices, and nucleus accumbens) of animals exposed to a mildly novel environment (clean cage), which elicits a high degree of sustained exploratory activity. Experimental restriction of exploratory activity in the novel cage by a small enclosure did not reduce the fos responses in these areas, and in fact, enhanced gene expression when carried out in home-caged animals suggesting that the fos response may be more closely associated with the motivation to be active rather than activity itself. Experiments with locally administered alpha(1)-agonists and antagonists in the cortex by reverse dialysis showed that the above mentioned alpha(1)-dependent-fos responses were the result of activation of local alpha(1)-receptors in these brain regions. Unlike the aforementioned brain regions, the fos response of the locus coeruleus was not blocked by prazosin, and this nucleus also showed a marked fos increase to prazosin itself possibly as a compensatory response to the blockade of forebrain alpha(1)-receptors.

Alpha(1)-adrenergic and alpha(2)-adrenergic balance in the dorsal pons and gross behavioral activity of mice in a novel environment

RATIONALE

Central alpha(1)- and alpha(2)-adrenoceptors in a number of different brain regions are known to have opposing actions on gross behavioral activity, with the former stimulating and the latter inhibiting activity. Therefore, blockade of alpha(1)-receptors may induce inactivity by leading to unopposed alpha(2) activity.

OBJECTIVE

The aim of this study was to test if central blockade of alpha(2)-receptor function restores behavioral activity in alpha(1)-receptor-blocked mice.

METHODS

Dose-response studies were undertaken on the effects of alpha(1)- and alpha(2)-agonists and antagonists microinjected into the dorsal pons on gross behavioral activity in a novel cage test.

RESULTS

The behavioral inactivity resulting from blockade of alpha(1)-receptors in the pons with the antagonist, terazosin, was reversed by either a low dose of an alpha(2)-antagonist, atipamezole, or a low dose of an alpha(2)-agonist, dexmedetomidine, but was exacerbated by a high dose of the alpha(2)-agonist.

CONCLUSION

The results support the hypothesis that blockade of alpha(1)-receptors in the dorsal pons of mice produces inactivity by causing unopposed activity of alpha(2)-receptors. This condition may be relevant to inactive states seen after stress or during depressive illness.

Recent progress in alpha1-adrenergic receptor research

Alpha1-Adrenergic receptors (AR) play an important role in the regulation of physiological responses mediated by norepinephrine and epinephrine, particularly in the cardiovascular system. The three cloned alpha1-AR subtypes (alpha1A, alpha1B, and alpha1D) are G protein-coupled receptors that signal through the Gq/11 signaling pathway, each showing distinct pharmacological properties and tissue distributions. However, due to the lack of highly subtype-selective drugs, the functional roles of individual subtypes are still not clear. Development of new subtype-specific drugs will greatly facilitate the identification of the functions of each subtype. Conopeptide rho-TIA has been found to be a new alpha1B-AR selective antagonist with different modes of inhibition at alpha1-AR subtypes. In addition, recent studies using genetically engineered mice have shed some light on alpha1-AR functions in vivo, especially in the cardiovascular system and brain. Several proteins have been shown to interact directly with particular alpha1-AR, and may be important in regulating receptor function. Receptor heterodimerization has been shown to be important for cell surface expression, signaling and internalization. These new observations are likely to help elucidate the functional roles of individual alpha1-AR subtypes.

The role of monoamines in the actions of established and "novel" antidepressant agents: a critical review

Monoaminergic pathways are highly responsive to aversive stimuli and play a crucial role in the control of affect, cognition, endocrine secretion, chronobiotic rhythms, appetite, and motor function, all of which are profoundly disrupted in depressive states. Accordingly, a perturbation of monoaminergic transmission is implicated in the aetiology of depressive disorders, and all clinically available antidepressants increase corticolimbic availability of monoamines. However, their limited efficacy, delayed onset of action, and undesirable side effects underlie ongoing efforts to identify improved therapeutic agents. Sequencing the human genome has raised the hope not only of better symptomatic control of depression, but even of the prevention or cure of depressive states. In the pursuit of these goals, there is currently a tendency to focus on selective ligands of "novel" nonmonoaminergic targets. However, certain classes of novel agent (such as neurokinin(1) receptor antagonists) indirectly modulate the activity of monoaminergic networks. Others may act "downstream" of them, converging onto common cellular substrates controlling gene expression, synaptic plasticity, and neurogenesis. Further, by analogy to the broad-based actions of currently employed drugs, multitarget agents may be better adapted than selective agents to the management of depression-a complex disorder with hereditary, developmental, and environmental origins. It is, thus, important to continue the creative exploration of clinically validated and innovative monoaminergic strategies within a multitarget framework. In this light, drugs combining monoaminergic and nonmonoaminergic mechanisms of action may be of particular interest. The present article provides a critical overview of monoaminergic strategies for the treatment of depressive states, both established and under development, and discusses interactions of novel "nonmonoaminergic" antidepressants with monoaminergic mechanisms.

The effect of combined treatment with imipramine and amantadine on the behavioral reactivity of central ??1-adrenergic system in rats

The problem of drug-resistant depression implies a strong need for alternative antidepressant therapies. Recently, it has been shown that joint administration of a tricyclic antidepressant, imipramine (IMI), with amantadine (AMA), a drug already approved for clinical use in the treatment of other diseases, induces a stronger 'antidepressant' effect in the forced swimming test in rats than treatment with either drug given separately. Combined treatment with IMI and AMA also induces up-regulation of dopamine D2 and D3 receptors in the rat brain, and appears to be effective in the treatment of patients with drug-resistant unipolar depression. In the present study, we examined the effect of IMI (5 or 10 mg/kg p.o.) and AMA (10 mg/kg p.o.) given separately or jointly, either as a single dose or repeatedly (twice daily for 14 days) on the development of adaptive changes in the behavioral reactivity of the central alpha1-adrenergic system. Following repeated administration of the higher dose of IMI together with AMA, we observed an increase in clonidine-induced aggression in mice, and significant enhancement of D-amphetamine-induced locomotor hyperactivity, as well as phenylephrine-induced exploratory behavior, in rats. In binding studies using [3H]prazosin, no changes in the density (Bmax) or affinity (Kd) of alpha1-adrenergic receptors were observed in rat brain cortex. However, competition analysis allowed us to observe an increase in the affinity of alpha1-adrenergic receptors (Ki) for an agonist (phenylephrine) upon repeated treatment with IMI, given alone or in combination with AMA. AMA appears to act through several pharmacological mechanisms, none of which has been identified as the chief mode of action. In the light of data obtained in the present study, one can supplement the postulated mechanisms of antidepressant action of AMA by adaptive changes in the reactivity of alpha1-adrenergic receptors, which develop upon repeated combined treatment with IMI.

Immobility from administration of the alpha1-adrenergic antagonist, terazosin, in the IVth ventricle in rats

Brain alpha1-adrenoceptors have been shown to be essential for motor activity and movement in mice using intraventricular injection of alpha1-antagonists. To facilitate subsequent neuroanatomical mapping of these receptors, the present study was undertaken to replicate these effects in the rat. Rats were administered the alpha1-antagonist, terazosin, in the absence and presence of the alpha1-agonist, phenylephrine, in the IVth ventricle and were tested for their motor activity responses to an environmental change. Terazosin was found to produce a dose-dependent, virtually complete cessation of behavioral activity that was reversed by coinfusion of phenylephrine. The results could not be explained by sedation. It is concluded that central alpha1-adrenoceptors are essential for behavioral activation in rats as in mice.

Role of locus coeruleus ?1-adrenoceptors in motor activity in rats

The question of whether or not the locus coeruleus (LC) participates in the control of motor activity has been controversial due to difficulties in demonstrating permanent motor deficits after neurotoxic lesions of this nucleus or of the dorsal noradrenergic bundle (DNB). In the present experiments it was shown in rats that acute local blockade (with terazosin) or stimulation (with phenylephrine) of LC alpha(1)-adrenoceptors respectively blocked or stimulated exploratory behavior in a novel cage and the home cage. Moreover, previous lesion of the DNB by i.p. DSP4 abolished the behavioral changes to local LC alpha(1)-receptor manipulation but did not affect motor activity in the novel or home cage by itself. These findings are consistent with the hypothesis that the intact LC does contribute to motor activity control, exerted in part by its alpha(1)-receptors; however, the permanent loss of this nucleus is compensated for by remaining CNS motor structures.