Defensive burying in rodents: ethology, neurobiology and psychopharmacology

Increased anxiety-like behavior is associated with the metabolic syndrome in non-stressed rats

Metabolic syndrome (MS) is a cluster of signs that increases the risk to develop diabetes mellitus type 2 and cardiovascular disease. In the last years, a growing interest to study the relationship between MS and psychiatric disorders, such as depression and anxiety, has emerged obtaining conflicting results. Diet-induced MS rat models have only examined the effects of high-fat or mixed cafeteria diets to a limited extent. We explored whether an anxiety-like behavior was associated with MS in non-stressed rats chronically submitted to a high-sucrose diet (20% sucrose in drinking water) using three different anxiety paradigms: the shock-probe/burying test (SPBT), the elevated plus-maze (EPM) and the open-field test (OFT). Behaviorally, the high-sucrose diet group showed an increase in burying behavior in the SPBT. Also, these animals displayed both avoidance to explore the central part of the arena and a significant increase in freezing behavior in the OFT and lack of effects in the EPM. Also, high-sucrose diet group showed signs of an MS-like condition: significant increases in body weight and body mass index, abdominal obesity, hypertension, hyperglycemia, hyperinsulinemia, and dyslipidemia. Plasma leptin and resistin levels were also increased. No changes in plasma corticosterone levels were found. These results indicate that rats under a 24-weeks high-sucrose diet develop an MS associated with an anxiety-like behavior. Although the mechanisms underlying this behavioral outcome remain to be investigated, the role of leptin is emphasized.

Repeated threat (without direct harm) alters metabolic capacity in select regions that drive defensive behavior

To understand the behavioral consequences of intermittent anticipatory stress resulting from threats without accompanying physiological challenges, we developed a semi-naturalistic rodent housing and foraging environment that can include threats that are unpredictable in timing. Behavior is automatically recorded while rats forage for food or water. Over three weeks, the threats have been shown to elicit risk assessment behaviors, increase defensive burying and increase adrenal gland weight. To identify brain regions activated by this manipulation, we measured cytochrome c oxidase (COX), which is tightly coupled to neural activity. Adolescent male Sprague-Dawley rats were randomly assigned to control (CT) or unpredictable threat/stress (ST) housing conditions consisting of two tub cages, one with food and another with water, separated by a tunnel. Over three weeks (P31-P52), the ST group received randomly timed (probability of 0.25), simultaneous presentations of ferret odor, an abrupt light, and sound at the center of the tunnel. The ST group had consistently fewer tunnel crossings than the CT group, but similar body weights. Group differences in COX activity were detected in regions implicated in the control of defensive burying. There was an increase in COX activity in the hypothalamic premammillary dorsal nucleus (PMD) and lateral septum (LS), whereas a decrease was observed in the periaqueductal gray (PAG) and CA3 region of the hippocampus. There were no significant differences in the anterior cingulate cortex, prefrontal cortex, striatum or motor cortex. The sites with changes in metabolic capacity are candidates for the sites of plasticity that may underlie the behavioral adaptations to intermittent threats.

Anxiolytic- and antidepressant-like effects of an aqueous extract of Tanacetum parthenium L. Schultz-Bip (Asteraceae) in mice

AIM

Tanacetum parthenium L. Schultz-Bip (Asteraceae) is widely used worldwide in traditional medicine for the treatment of convulsions and culture-bound syndromes such as susto (fear). The aim of this work was to evaluate the anxiolytic- and antidepressant-like effects of an aqueous extract of T. parthenium in behavioral paradigms in mice. The effects of T. parthenium were compared with those produced by anxiolytic and antidepressant drugs. We carried out the chemical characterization of the main constituents of T. parthenium. The involvement with the GABAergic and serotoninergic neurotransmitter systems were explored be means of synergic and antagonist experiments.

MATERIALS AND METHODS

The anxiolytic-like effect was evaluated using the Burying Behavior Test (BBT) and the Elevated Plus-Maze Test (PMT). The antidepressant-like effect was evaluated in the Forced Swimming Test (FST), and ambulatory activity was assessed in the Open Field Test (OFT). Employing the behavioral tests, synergism and antagonism experiments with Alprazolam, Muscimol, and Picrotoxin were carried out in the PMT. In a series of independent experiments, concomitant administration of T. parthenium and Alprazolam, Fluoxetine, or p-chlorophenylalanine were conducted in the FST. For chemical characterization, High-Performance Liquid Chromatography-Electro Spray Ionization-Mass Spectrometry (HPLC-ESI-MS) analysis was performed.

RESULTS

T. parthenium exerts clear anxiolytic- and antidepressant-like effects in mice, without affecting the ambulatory activity of the experimental subjects.

CONCLUSIONS

Anxiolytic- and antidepressant-like T. parthenium effects result, at least part from the involvement of the GABAergic system. Our results support the use of Tanacetum parthenium in traditional medicine and suggest its therapeutic potential in the comorbid anxiety and depression.

Prothymosin alpha-deficiency enhances anxiety-like behaviors and impairs learning/memory functions and neurogenesis

Prothymosin alpha (ProTα) is expressed in various mammalian organs including the neuronal nuclei in the brain, and is involved in multiple functions, such as chromatin remodeling, transcriptional regulation, cell proliferation, and survival. ProTα has beneficial actions against ischemia-induced necrosis and apoptosis in the brain and retina. However, characterizing the physiological roles of endogenous ProTα in the brain without stress remains elusive. Here, we generated ProTα-deficiency mice to explore whether endogenous ProTα is involved in normal brain functions. We successfully generated heterozygous ProTα knockout (ProTα^+/- ) mice, while all homozygous ProTα knockout (ProTα^-/- ) offspring died at early embryonic stage, suggesting that ProTα has crucial roles in embryonic development. In the evaluation of different behavioral tests, ProTα^+/- mice exhibited hypolocomotor activity in the open-field test and enhanced anxiety-like behaviors in the light/dark transition test and the novelty induced hypophagia test. ProTα^+/- mice also showed impaired learning and memory in the step-through passive avoidance test and the KUROBOX test. Depression-like behaviors in ProTα^+/- mice in the forced swim and tail suspension tests were comparable with that of wild-type mice. Furthermore, adult hippocampal neurogenesis was significantly decreased in ProTα^+/- mice. ProTα^+/- mice showed an impaired long-term potentiation induction in the evaluation of electrophysiological recordings from acute hippocampal slices. Microarray analysis revealed that the candidate genes related to anxiety, learning/memory-functions, and neurogenesis were down-regulated in ProTα^+/- mice. Thus, this study suggests that ProTα has crucial physiological roles in the robustness of brain.

Differential stress induced c-Fos expression and identification of region-specific miRNA-mRNA networks in the dorsal raphe and amygdala of high-responder/low-responder rats

Chronic stress triggers a variety of physical and mental health problems, and how individuals cope with stress influences risk for emotional disorders. To investigate molecular mechanisms underlying distinct stress coping styles, we utilized rats that were selectively-bred for differences in emotionality and stress reactivity. We show that high novelty responding (HR) rats readily bury a shock probe in the defensive burying test, a measure of proactive stress coping behavior, while low novelty responding (LR) rats exhibit enhanced immobility, a measure of reactive coping. Shock exposure in the defensive burying test elicited greater activation of HR rats' caudal dorsal raphe serotonergic cells compared to LRs, but lead to more pronounced activation throughout LRs' amygdala (lateral, basolateral, central, and basomedial nuclei) compared to HRs. RNA-sequencing revealed 271 mRNA transcripts and 33 microRNA species that were differentially expressed in HR/LR raphe and amygdala. We mapped potential microRNA-mRNA networks by correlating and clustering mRNA and microRNA expression and identified networks that differed in either the HR/LR dorsal raphe or amygdala. A dorsal raphe network linked three microRNAs which were down-regulated in LRs (miR-206-3p, miR-3559-5p, and miR-378a-3p) to repression of genes related to microglia and immune response (Cd74, Cyth4, Nckap1l, and Rac2), the genes themselves were up-regulated in LR dorsal raphe. In the amygdala, another network linked miR-124-5p, miR-146a-5p, miR-3068-3p, miR-380-5p, miR-539-3p, and miR-7a-1-3p with repression of chromatin remodeling-related genes (Cenpk, Cenpq, Itgb3bp, and Mis18a). Overall this work highlights potential drivers of gene-networks and downstream molecular pathways within the raphe and amygdala that contribute to individual differences in stress coping styles and stress vulnerabilities.

Tactile stimulation during different developmental periods modifies hippocampal BDNF and GR, affecting memory and behavior in adult rats

Recent studies have shown that tactile stimulation (TS) in pups is able to prevent and/or minimize fear, anxiety behaviors, and addiction to psychostimulant drugs in adult rats. In these studies, animals have been exposed to handling from postnatal day (PND) 1-21. This study was designed to precisely establish which period of preweaning development has a greater influence of TS on neuronal development. After birth, male pups were exposed to TS from PND1-7, PND8-14, and PND15-21. In adulthood, the different periods of postnatal TS were assessed through behavioral, biochemical, and molecular assessments. Animals that received TS from PND8-14 showed lower anxiety-like symptoms, as observed by decreased anxiety index in elevated plus maze. This same TS period was able to improve rats' working memory by increasing the percentage of alternation rate in Y-maze, and induce better ability to cope with stressful situations, as showed in the defensive burying test by a reduced time of burying behavior. On the other hand, animals receiving TS in the first week of life showed longest cumulative burying time, which is directly related to increased anxiety-like behavior. Moreover, TS from PND8-14 showed lower corticosterone levels and better oxidative status, as observed by decreased lipid peroxidation and increased catalase activity in the hippocampus. Brain-derived neurotrophic factor (BDNF) immunocontent was increased in the hippocampus of animals receiving TS from PND8-14, while glucocorticoid receptors immunocontent was decreased in both TS_1-7 and TS_15-21 , but not TS_8-14 . To the best of our knowledge, this study is the first to show TS can be more efficient if applied over a focused period of neonatal development (PND8-14) and this beneficial influence can be reflected on reduced emotionality and increased ability to address stressful situations in adulthood. © 2016 Wiley Periodicals, Inc.

The drug candidate, ADX71441, is a novel, potent and selective positive allosteric modulator of the GABAB receptor with a potential for treatment of anxiety, pain and spasticity

Positive allosteric modulation of the GABA_B receptor is a promising alternative to direct activation of the receptor as a therapeutic approach for treatment of addiction, chronic pain, anxiety, epilepsy, autism, Fragile X syndrome, and psychosis. Here we describe in vitro and in vivo characterization of a novel, potent and selective GABA_B positive allosteric modulator (PAM) N-(5-(4-(4-chloro-3-fluorobenzyl)-6-methoxy-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)-2-fluorophenyl)acetamide (ADX71441). In vitro, Schild plot and reversibility tests at the target confirmed PAM properties of the compound. In mice and rats ADX71441 is bioavailable after oral administration and is brain penetrant. A single dose of ADX71441 had an anxiolytic-like profile in the mouse marble burying test (minimum effective dose; MED 3 mg/kg) as well as in the elevated plus maze test in mice and rats (both MED 3 mg/kg). Also, in mice, acute administration of ADX71441 reduced visceral pain-associated behaviors in the acetic acid-induced writhing test. ADX71441 dose-dependently reduced time on rotarod in rats (MED 10 mg/kg) indicative of muscle-relaxant qualities. ADX71441 reduced locomotor activity in mice (10 mg/kg) and rats (3 mg/kg) after single dose; however, following sub-chronic administration in mice, 30 mg/kg ADX71441 was associated with normal locomotor activity. While acute administration of ADX71441 reduced body temperature in rats and mice (both MED 10 mg/kg), the effect in the former was transient, rapidly returning to normal levels despite high concentrations of the compound remaining in plasma. Thus, the GABA_B PAM ADX71441 represents a valid therapeutic approach for development of novel treatment of anxiety, pain and spasticity.

Environmental enrichment prevents anxiety-like behavior induced by progesterone withdrawal in two strains of rats

Stress vulnerability could influence the treatment response to anxiety associated with abrupt hormonal suppression. The present study explored the effects of different treatments on experimental anxiety induced by progesterone withdrawal (PW) in a stress-sensitive rat strain, Wistar Kyoto (WKY), in the burying behavior test (BBT). The following experimental series was conducted using independent groups of Wistar (control strain) and WKY ovariectomized rats: Experiment 1: Rats were treated for 5days with oil, a constant dose of progesterone (0.5mg/rat, s.c) or a combination of progesterone (0.5mg/rat, s.c) plus fluoxetine (10 mg/kg, i.p); on day 6, all rats were subjected to BBT. Experiment 2: Rats received corn oil or decreasing doses of progesterone (0.84, 0.67, 0.5, 0.33 and 0.17mg/rat; one dose daily); on day 6, the rats were subjected to BBT. Experiment 3: Rats were divided into two groups that were subjected to 30days of standard conditions or environmental enrichment (EE); from days 25 to 30, all rats received a fixed dose of progesterone (0.5mg/rat, s.c.) or vehicle. On day 31, the rats were tested with BBT. Results showed that PW increased anxiety in both strains, and fluoxetine prevented anxiety in WKY rats. In contrast, a gradual reduction of progesterone prevents the anxiety in Wistar but not in WKY. EE was preventive against the anxiety induced by PW in both strains of rats. Thus, the results suggest that anxiety induced by PW is prevented by EE while the anxiolytic effect of pharmacological treatments depends on stress vulnerability.

Perinatal exposure to the selective serotonin reuptake inhibitor citalopram alters spatial learning and memory, anxiety, depression, and startle in Sprague-Dawley rats

Selective serotonin reuptake inhibitors (SSRIs) block the serotonin (5-HT) reuptake transporter (SERT) and increase synaptic 5-HT. 5-HT is also important in brain development; hence when SSRIs are taken during pregnancy there exists the potential for these drugs to affect CNS ontogeny. Prenatal SSRI exposure has been associated with an increased prevalence of autism spectrum disorder (ASD), and peripheral 5-HT is elevated in some ASD patients. Perinatal SSRI exposure in rodents has been associated with increased depression and anxiety-like behavior, decreased sociability, and impaired learning in the offspring, behaviors often seen in ASD. The present study investigated whether perinatal exposure to citalopram causes persistent neurobehavioral effects. Gravid Sprague-Dawley rats were assigned to two groups and subcutaneously injected twice per day with citalopram (10mg/kg; Cit) or saline (Sal) 6h apart on embryonic day (E)6-21, and then drug was given directly to the pups after delivery from postnatal day (P)1-20. Starting on P60, one male/female from each litter was tested in the Cincinnati water maze (CWM) and open-field before and after MK-801. A second pair from each litter was tested in the Morris water maze (MWM) and open-field before and after (+)-amphetamine. A third pair was tested as follows: elevated zero-maze, open-field, marble burying, prepulse inhibition of acoustic startle, social preference, and forced swim. Cit-exposed rats were impaired in the MWM during acquisition and probe, but not during reversal, shift, or cued trials. Cit-exposed rats also showed increased marble burying, decreased time in the center of the open-field, decreased latency to immobility in forced swim, and increased acoustic startle across prepulse intensities with no effects on CWM. The results are consistent with citalopram inducing several ASD-like effects. The findings add to concerns about use of SSRIs during pregnancy. Further research on different classes of antidepressants, dose-effect relationships, timing of exposure periods, and mechanisms for these effects are needed. It is also important to balance the effects described here against the effects of the disorders for which the drugs are given.

GPR88 in A2AR Neurons Enhances Anxiety-Like Behaviors

GPR88 is an orphan G-protein-coupled receptor highly expressed in striatal dopamine D₁ (receptor) R- and D2R-expressing medium spiny neurons. This receptor is involved in activity and motor responses, and we previously showed that this receptor also regulates anxiety-like behaviors. To determine whether GPR88 in D2R-expressing neurons contributes to this emotional phenotype, we generated conditional Gpr88 knock-out mice using adenosine A_2AR (A_2AR)-Cre-driven recombination, and compared anxiety-related responses in both total and A_2AR-Gpr88 KO mice. A_2AR-Gpr88 KO mice showed a selective reduction of Gpr88 mRNA in D2R-expressing, but not D₁R-expressing, neurons. These mutant mice showed increased locomotor activity and decreased anxiety-like behaviors in light/dark and elevated plus maze tests. These phenotypes were superimposable on those observed in total Gpr88 KO mice, demonstrating that the previously reported anxiogenic activity of GPR88 operates at the level of A_2AR-expressing neurons. Further, A_2AR-Gpr88 KO mice showed no change in novelty preference and novelty-suppressed feeding, while these responses were increased and decreased, respectively, in the total Gpr88 KO mice. Also, A_2AR-Gpr88 KO mice showed intact fear conditioning, while the fear responses were decreased in total Gpr88 KO. We therefore also show for the first time that GPR88 activity regulates approach behaviors and conditional fear; however, these behaviors do not seem mediated by receptors in A_2AR neurons. We conclude that Gpr88 expressed in A_2AR neurons enhances ethological anxiety-like behaviors without affecting conflict anxiety and fear responses.

Enhanced anxiety in the male offspring of sires that self-administered cocaine

We previously showed that paternal cocaine exposure reduced the reinforcing efficacy of cocaine in male offspring. Here, we sought to determine whether paternal cocaine experience could also influence anxiety levels in offspring. Male rats were allowed to self-administer cocaine (controls received saline passively) for 60 days and then were bred with naïve females. Measures of anxiety and cocaine-induced anxiogenic effects were assessed in the adult offspring. Cocaine-sired male offspring exhibited increased anxiety-like behaviors, as measured using the novelty-induced hypophagia and defensive burying tasks, relative to saline-sired males. In contrast, sire cocaine experience had no effect on anxiety-like behaviors in female offspring. When challenged with an anxiogenic (but not anorectic) dose of cocaine (2.5 mg/kg, i.p.), anxiety-like behavior was enhanced in all animals to an equal degree regardless of sire drug experience. Since anxiety and depression are often co-morbid, we also assessed measures of depressive-like behavior. Sire cocaine experience had no effect on depression-like behaviors, as measured by the forced swim task, among male offspring. In a separate group of naïve littermates, select neuronal correlates of anxiety were measured. Male offspring of cocaine-experienced sires showed increased mRNA and protein expression of corticotropin-releasing factor receptor 2 in the hippocampus. Together, these results indicate that cocaine-experienced sires produce male progeny that have increased baseline anxiety, which is unaltered by subsequent cocaine exposure.

Dopamine D1 receptor activity is involved in the increased anxiety levels observed in STZ-induced diabetes in rats

Epidemiological surveys have indicated that anxiety disorders are more frequent in diabetic patients than in the general population. Similar results have been shown in animal studies using the streptozotocin (STZ)-induced diabetes model. The mechanisms underlying this relationship are not clearly understood, but it has been suggested that alterations in the dopaminergic neurotransmission, which plays an important role in the amygdaloid modulation of fear and anxiety, may be involved. The aim of this study was to ascertain whether or not the amygdaloid DA D1 receptors are involved in the increase of anxiety-like behavior observed in "diabetic" animals. Adult Wistar male rats were injected with STZ (50mg/kg, i.p.) in two consecutive days and subjected to the Shock-Probe Burying Test 10days after the beginning of treatment. STZ-treated rats showed a significant increase in immobility/freezing behavior whereas no effects were elicited in latency to bury, burying behavior itself and the number of shocks received during testing as compared with non-diabetic controls. These results suggest the triggering of a passive coping response in the STZ-treated rats. Interestingly, immobility/freezing behavior was reversed following the intra-amygdaloid dopamine D1 receptor blockade by the local microinfusion of SCH23390 (100ng/side). Autoradiographic experiments showed a selective increase of [(3)H]-SCH23390 binding in the ventral intercalated paracapsular islands of STZ-treated rats when compared to the non-treated control group. Our results suggest that a hyperdopaminergic state involving DA D1 receptors within the amygdala may have a role in the increase of anxiety observed in diabetic rats.

Young-Adult Male Rats' Vulnerability to Chronic Mild Stress Is Reflected by Anxious-Like instead of Depressive-Like Behaviors

In a previous study, we found that chronic mild stress (CMS) paradigm did not induce anhedonia in young-adult male rats but it reduced their body weight gain. These contrasting results encouraged us to explore other indicators of animal's vulnerability to stress such as anxious-like behaviors, since stress is an etiologic factor also for anxiety. Thus, in this study, we evaluated the vulnerability of these animals to CMS using behavioral tests of depression or anxiety and measuring serum corticosterone. Male Wistar rats were exposed to four weeks of CMS; the animals' body weight and sucrose preference (indicator of anhedonia) were assessed after three weeks, and, after the fourth week, some animals were evaluated in a behavioral battery (elevated plus maze, defensive burying behavior, and forced swimming tests); meanwhile, others were used to measure serum corticosterone. We found that CMS (1) did not affect sucrose preference, immobility behavior in the forced swimming test, or serum corticosterone; (2) decreased body weight gain; and (3) increased the rat's entries into closed arms of the plus maze and the cumulative burying behavior. These data indicate that young male rats' vulnerability to CMS is reflected as poor body weight gain and anxious-like instead of depressive-like behaviors.

Differential effect of the 17β-aminoestrogens prolame, butolame and pentolame in anxiety and depression models in rats

Estrogens of clinical use produce consistent antidepressant- and anxiolytic-like effects in animal models of menopause. Regulation of the hypothalamic-pituitary-adrenal (HPA) or stress axis, has been proposed as a pathway through which estrogens improve affective-like behaviors. Anticoagulant 17β-aminoestrogens (17β-AEs) butolame and pentolame mimic some effects of estradiol (E2), i.e., on female rodent sexual behavior, with opposite actions on coagulation. However, their psychoactive actions have not been explored. On the basis of similitude with E2's effects, we hypothesized that these 17β-AEs would induce anxiolytic- and antidepressant-like effects, which would be reflected in a reduction of activity in the HPA axis. In ovariectomized female rats, chronic treatment with prolame (60 μg/kg), butolame (65 μg/kg) and pentolame (70 μg/kg) reduced anxiety-like behavior in the elevated plus maze (evidenced by an increase in time in open arms, E2 (40 μg/kg) +176%; prolame +201%; butolame, +237%; and pentolame +295%, in comparison to the control vehicle group 100%). Pentolame also decreased significantly anxiety-like behavior in the burying behavior test. Prolame and E2 produced a significantly antidepressant-like action, which was not induced by butolame and pentolame. Behavioral effects of 17β-AEs (and E2) on anxiety and depression did not follow the same pattern than corticosterone or E2 levels; they also were associated to changes in locomotor activity, evaluated by the open field test. These results constitute the first evidence of specific and selective actions of butolame and pentolame as anxiolytics for females with a hypoestrogenic condition. Results also confirm the potential of prolame as an antidepressant steroid with equivalent actions to E2. Psychoactive properties of 17β-AEs in combinations with reduced adverse effects on coagulation, suggest that 17β-AEs may be a good alternative replacement therapy for women with symptoms associated with menopause.

Inflammation is increased with anxiety- and depression-like signs in a rat model of spinal cord injury

Spinal cord injury (SCI) leads to increased anxiety and depression in as many as 60% of patients. Yet, despite extensive clinical research focused on understanding the variables influencing psychological well-being following SCI, risk factors that decrease it remain unclear. We hypothesized that excitation of the immune system, inherent to SCI, may contribute to the decrease in psychological well-being. To test this hypothesis, we used a battery of established behavioral tests to assess depression and anxiety in spinally contused rats. The behavioral tests, and subsequent statistical analyses, revealed three cohorts of subjects that displayed behavioral characteristics of (1) depression, (2) depression and anxiety, or (3) no signs of decreased psychological well-being. Subsequent molecular analyses demonstrated that the psychological cohorts differed not only in behavioral symptoms, but also in peripheral (serum) and central (hippocampi and spinal cord) levels of pro-inflammatory cytokines. Subjects exhibiting a purely depression-like profile showed higher levels of pro-inflammatory cytokines peripherally, whereas subjects exhibiting a depression- and anxiety-like profile showed higher levels of pro-inflammatory cytokines centrally (hippocampi and spinal cord). These changes in inflammation were not associated with injury severity; suggesting that the association between inflammation and the expression of behaviors characteristic of decreased psychological well-being was not confounded by differential impairments in motor ability. These data support the hypothesis that inflammatory changes are associated with decreased psychological well-being following SCI.

Experimental Models of Anxiety for Drug Discovery and Brain Research

Animal models have been vital to recent advances in experimental neuroscience, including the modeling of common human brain disorders such as anxiety, depression, and schizophrenia. As mice express robust anxiety-like behaviors when exposed to stressors (e.g., novelty, bright light, or social confrontation), these phenotypes have clear utility in testing the effects of psychotropic drugs. Of specific interest is the extent to which mouse models can be used for the screening of new anxiolytic drugs and verification of their possible applications in humans. To address this problem, the present chapter will review different experimental models of mouse anxiety and discuss their utility for testing anxiolytic and anxiogenic drugs. Detailed protocols will be provided for these paradigms, and possible confounds will be addressed accordingly.

Investigation of diazepam efficacy on anxiety-like behavior in hemiparkinsonian rats

There is growing recognition that anxiety disorders have a greater impact on quality of life in Parkinson's disease than motor symptoms. Yet, little is known about the pathophysiology underlying this non-motor symptom in Parkinson's disease which poses a considerable barrier in developing effective treatment strategies. Here, we administered diazepam to hemiparkinsonian and non-parkinsonian rats and assessed its efficacy in three anxiety behavioral tests. At present, no information about this exists in preclinical research with sparse data in the clinical literature. Moreover, diazepam is an acute anxiolytic which makes this drug a suitable research tool to unmask differences in anxiety-like behavior. Using the unilateral, medial forebrain bundle 6-hydroxydopamine rat model of Parkinson's disease, we noted that hemiparkinsonian rats had more baseline anxiety-like behavior with 60% of them exhibiting high anxiety (HA) behavior in the elevated plus maze. In contrast, 41% of sham-lesioned rats and 8% of naïve rats exhibited HA behavior. Next, we employed the elevated plus maze and noted that diazepam (1.5mg/kg) was anxiolytic in low anxiety (LA) sham-lesioned (p=0.006) and HA sham-lesioned rats (p=0.016). Interestingly, diazepam was anxiolytic for LA hemiparkinsonian rats (p=0.017), but not for HA hemiparkinsonian rats (p=0.174) despite both groups having similar motor impairment and parkinsonian phenotype. Overall, diazepam administration unmasked differences in anxiolytic efficacy between HA hemiparkinsonian rats, LA hemiparkinsonian rats and non-parkinsonian rats. Our data suggests that neuro-circuits involved in anxiety-like behavior may differ within these groups and posits that diazepam may have reduced efficacy in certain individuals with PD anxiety disorders.

Involvement of nitric oxide in anticompulsive-like effect of agmatine on marble-burying behaviour in mice

In view of the reports that nitric oxide modulates the neurotransmitters implicated in obsessive-compulsive disorder (OCD), patients with OCD exhibit higher plasma nitrate levels, and drugs useful in OCD influence nitric oxide. Agmatine is a polyamine and widely distributed in mammalian brain which interacts with nitrergic systems. Hence, the present study was carried out to understand the involvement of nitrergic systems in the anticompulsive-like effect of agmatine. We used marble-burying behaviour (MBB) of mice as the animal model of OCD, and nitric oxide levels in hippocampus (HC) and cortex homogenate were measured. Results revealed that, agmatine (20 and 40mg/kg, i.p) significantly inhibited the MBB. Intraperitoneal administration of nitric oxide enhancers viz. nitric oxide precursor - l-arginine (l-ARG) (400mg/kg and 800mg/kg) increased MBB as well as brain nitrites levels, whereas treatment with N(G)-nitro-l-arginine methyl ester (l-NAME) neuronal nitric oxide synthase inhibitor (30mg/kg and 50mg/kg, i.p.) and 7-nitroindazole (7-NI) (20mg/kg and 40mg/kg) attenuated MBB and nitrites levels in brain. Further, in combination studies, the anticompulsive-like effect of agmatine (20mg/kg, ip) was exacerbated by prior administration of l-ARG (400mg/kg) and conversely l-NAME (15mg/kg) or 7-NI (10.0mg/kg) attenuated OCD-like behaviour with HC and cortex changes in the levels of NO. None of the above treatment had any significant influence on locomotor activity. In conclusion, Agmatine is effective in ameliorating the compulsive-like behaviour in mice which appears to be related to nitric oxide in brain.

Chronic stress and brain plasticity: Mechanisms underlying adaptive and maladaptive changes and implications for stress-related CNS disorders

Stress responses entail neuroendocrine, autonomic, and behavioral changes to promote effective coping with real or perceived threats to one's safety. While these responses are critical for the survival of the individual, adverse effects of repeated exposure to stress are widely known to have deleterious effects on health. Thus, a considerable effort in the search for treatments to stress-related CNS disorders necessitates unraveling the brain mechanisms responsible for adaptation under acute conditions and their perturbations following chronic stress exposure. This paper is based upon a symposium from the 2014 International Behavioral Neuroscience Meeting, summarizing some recent advances in understanding the effects of stress on adaptive and maladaptive responses subserved by limbic forebrain networks. An important theme highlighted in this review is that the same networks mediating neuroendocrine, autonomic, and behavioral processes during adaptive coping also comprise targets of the effects of repeated stress exposure in the development of maladaptive states. Where possible, reference is made to the similarity of neurobiological substrates and effects observed following repeated exposure to stress in laboratory animals and the clinical features of stress-related disorders in humans.

Stress during the gestational period modifies pups' emotionality parameters and favors preference for morphine in adolescent rats

Experimental animal studies have shown that early life periods are highly vulnerable to environmental factors, which may exert prolonged impact on HPA axis function and on subsequent neurochemical and behavioral responses in adulthood. Here we evaluated the influence of environmental stressful situations in two different early life stages on stress-related behaviors, and morphine-conditioned place preference (CPP), which is indicative of addiction. While in the gestational stress (Gest-S) dams were exposed to daily sessions of chronic mild stress (CMS) for 2 weeks, in the postnatal stress (post-NS) the offspring were exposed daily to neonatal isolation from postnatal day (PND) 2 to PND 9 for 60 min. Animals exposed to post-NS showed lesser anxiety in different behavioral paradigms (elevated plus maze-EPM and defensive burying test-DBT) as well as increased exploratory behavior (open-field task-OFT), and no preference for morphine in CPP. In contrast, animals exposed to Gest-S showed increased corticosterone plasma levels together with anxiety symptoms and greater preference for morphine following three days of drug withdrawal. Our findings indicate that the gestational period is critical for stress, whose effects may be manifest throughout life. On the other hand, post-NS can trigger neuroadaptations able to overcome emotional consequences of early life. We hypothesized that Gest-S is able to modify responses to opioids along adulthood, which may facilitate development of addiction to these drugs.

Investigation of allyphenyline efficacy in the treatment of alcohol withdrawal symptoms

We have recently demonstrated that allyphenyline, behaving as α2C-adrenoceptor/serotonin 5-HT1A receptor agonist and α2A-adrenoceptor antagonist, in mice enhanced morphine analgesia, attenuated morphine withdrawal symptoms, showed significant antidepressant-like activity and was devoid of sedative side effects. Opioid and alcohol withdrawal shares several common neurobiological and molecular mechanisms. Therefore, in this study we expanded our analysis of the pharmacological properties of allyphenyline by investigating its ability to prevent the expression of somatic withdrawal signs, anxiety-like behavior and hyperlocomotion associated with chronic ethanol intoxication. Rats were subjected to induction of ethanol dependence via repeated daily intragastric ethanol (20%) administration for 4 consecutive days. Twelve hours after the last alcohol administration, somatic alcohol withdrawal signs were scored. Results revealed a significant expression of physical withdrawal signs that were not affected by intraperitoneal (i.p.) administration of allyphenyline at the doses of 0.05, 0.275 and 0.5 mg/kg. In contrast, allyphenyline (0.05 and 0.275 mg/kg i.p.) significantly reduced hyperanxiety-like behavior observed 6 days after alcohol intoxication as measured using the defensive burying test. Allyphenyline also reduced open field hyperlocomotor activity associated with alcohol withdrawal. Notably, the anxiolytic effect of the compound, as well as the already reported antidepressant action, was observed at very low doses, suggesting the involvement of its α2C-adrenoceptor/serotonin 5-HT1A receptor agonism. Therefore, the present investigation suggests that allyphenyline might represent an interesting pharmacological tool to investigate the potential of compounds exhibiting α2C-adrenoceptor/serotonin 5-HT1A receptor agonism and α2A-adrenoceptor antagonism in the treatment of hyperanxiety and hyperlocomotion occurring during alcohol withdrawal in dependent subjects.

Monoamine Oxidase A is Required for Rapid Dendritic Remodeling in Response to Stress

BACKGROUND

Acute stress triggers transient alterations in the synaptic release and metabolism of brain monoamine neurotransmitters. These rapid changes are essential to activate neuroplastic processes aimed at the appraisal of the stressor and enactment of commensurate defensive behaviors. Threat evaluation has been recently associated with the dendritic morphology of pyramidal cells in the orbitofrontal cortex (OFC) and basolateral amygdala (BLA); thus, we examined the rapid effects of restraint stress on anxiety-like behavior and dendritic morphology in the BLA and OFC of mice. Furthermore, we tested whether these processes may be affected by deficiency of monoamine oxidase A (MAO-A), the primary enzyme catalyzing monoamine metabolism.

METHODS

Following a short-term (1-4h) restraint schedule, MAO-A knockout (KO) and wild-type (WT) mice were sacrificed, and histological analyses of dendrites in pyramidal neurons of the BLA and OFC of the animals were performed. Anxiety-like behaviors were examined in a separate cohort of animals subjected to the same experimental conditions.

RESULTS

In WT mice, short-term restraint stress significantly enhanced anxiety-like responses, as well as a time-dependent proliferation of apical (but not basilar) dendrites of the OFC neurons; conversely, a retraction in BLA dendrites was observed. None of these behavioral and morphological changes were observed in MAO-A KO mice.

CONCLUSIONS

These findings suggest that acute stress induces anxiety-like responses by affecting rapid dendritic remodeling in the pyramidal cells of OFC and BLA; furthermore, our data show that MAO-A and monoamine metabolism are required for these phenomena.

GABAA/benzodiazepine receptor complex mediates the anxiolytic-like effect of Montanoa tomentosa

ETHNOPHARMACOLOGICAL RELEVANCE

Montanoa tomentosa also named Cihuapatli is a native plant of Mexico that has been used in traditional medicine for the last five centuries mainly as a remedy for reproductive impairments. However, there are reports indicating that this plant was also consumed by Mexican ancient people for its relaxing properties. In order to corroborate this information, the present study was conducted to evaluate the effect of Montanoa tomentosa lyophilisate (MT) on rat׳s anxiety-like behavior and to analyze its mechanism of action.

MATERIALS AND METHODS

The anxiolytic-like action of MT (1.5, 3.0, 6.0 and 12.0 mg/kg) was investigated in male Wistar rats tested in three animal models of anxiety: the burying behavior, the elevated plus maze and the hole-board tests. As a positive control, the anti-anxiety effects of different doses of the selective GABAA receptor agonist muscimol were also analyzed. In order to evaluate the participation of the GABAA and oxytocin receptors in the anxiolytic-like actions of MT, the GABAA receptors blockers picrotoxin (0.25 and 0.50 mg/kg), bicuculline (2.0 mg/kg) and flumazenil (5.00 and 10.0 mg/kg), the neurosteroid inhibitor finasteride (50.0 and 100 mg/kg) and the oxytocin receptor antagonist atosiban (0.25 µg) were used. Finally, to evaluate general activity, and motor coordination, the open field and rota-rod tests were used.

RESULTS

MT at 3.0 mg/kg showed anxiolytic-like effects in the three anxiety paradigms without affecting reactivity, general motor activity or motor coordination; however, at higher doses sedative effects were observed. Picrotoxin (0.25 and 0.50 mg/kg), flumazenil (10.0 mg/kg) and finasteride (100 mg/kg) antagonized the anxiolytic-like actions of MT in the burying behavior test. In the plus maze and hole-board tests bicuculline (2.0 mg/kg) blocked the effects of the plant as well. Atosiban (0.25 µg) did not antagonize the anxiolytic-like actions of MT.

CONCLUSIONS

The results corroborate the anxiolytic-like actions of Montanoa tomentosa and suggest that this effect is mediated through GABAA receptors but not oxytocin receptors.

Behavioral changes following a single episode of early-life seizures support the latent development of an autistic phenotype

We probed the developmental and behavioral consequences of a single episode of kainic acid-induced early-life seizures (KA-ELS) in the rat on postnatal day 7. Correlates of developmental trajectory were not altered, demonstrating that long-term consequences following KA-ELS are not initiated by secondary causes, such as malnourishment or alterations in maternal care. We report reduced marble burying in adult rats, suggestive of restricted interests, a trait common to experimental and clinical autism. We did not detect increased repetitive grooming during habituated cage behavior. However, we did detect reduced grooming in adult KA-ELS rats in the presence of an unfamiliar rat, supporting altered social anxiety following KA-ELS. Reanalysis of a social approach task further indicated abnormal social interactions. Taken together with previous physiological and behavioral data, these data support the hypothesis that KA-ELS lead to a latent autistic phenotype in adult rats not attributable to other early alterations in development.

Polymorphism in the corticotropin-releasing factor receptor 1 (CRF1-R) gene plays a role in shaping the high anxious phenotype of Marchigian Sardinian alcohol-preferring (msP) rats

INTRODUCTION

Marchigian Sardinian alcohol-preferring (msP) rats exhibit innate preference for alcohol along with anxious phenotype. In these animals, two single-nucleotide polymorphisms in position -1,836 and -2,097 from the first start codon of the CRF1-R transcript have been found.

MATERIALS AND METHODS

Here, we examined whether these point mutations account for the heightened anxiety-like behavior and stress responsiveness of msP rats. We rederived the msP rats to obtain two distinct lines carrying the wild-type (GG) and point mutations (AA), respectively.

RESULTS

CRF1-R gene expression analysis revealed significant dysregulation of the system in the extended amygdala of AA rats. At the behavioral level, using the elevated plus maze, we found that both AA and GG lines had higher basal anxiety compared to Wistar rats. In the defensive burying test, AA rats showed decreased burying behavior compared to the GG and the unselected Wistar lines. Freezing/immobility did not differ among AA and GG but was higher than that of Wistars. The selective CRF1-R antagonist antalarmin (0, 10, and 20 mg/kg) reduced burying behavior in Wistar animals. However, antalarmin (10 mg/kg) tended to increase rather than reducing this behavior when tested in the msP lines, an effect that appeared more marked in the GG as compared to the AA line.

CONCLUSION

The present data suggest that rats with msP genetic background are more anxious and show different sensitivity to stress and CRF1-R blockade than Wistars. The point mutations occurring in the CRF1-R gene do not seem to influence basal anxiety while they appear to affect active responses to stress.

Individual differences in the effects of prenatal stress exposure in rodents

Exposure to prenatal stress alters the phenotype of the offspring in adulthood. When the prenatal and adult environments do not match, these alterations may induce pathology risk. There are, however, large individual differences in the effects of prenatal stress. While some individuals seem vulnerable, others appear to be relatively resistant to its effects. In this review we discuss potential mechanisms underlying these individual differences with a focus on animal models. Differences between rodent models selected for stress coping traits are discussed. In addition, the role of circulating factors, like glucocorticoids and cytokines, factors involved in brain development and influences of epigenetic and genetic factors in prenatal stress induced phenotype are covered.

The amount of cage bedding preferred by female BALB/c and C57BL/6 mice

In order to improve the welfare of laboratory mice, a number of different environmental enrichment strategies have been developed to provide opportunities for mice to engage in naturalistic behaviors. Providing sufficient cage bedding for mice to use as a burrowing substrate could be considered an environmental enrichment strategy, but few studies have considered the welfare aspects of cage bedding amount. The authors compared the preferences of group-housed female BALB/c and C57BL/6 mice for three different volumes of cage bedding (0.5 l, 1.5 l and 6 l). Mice of both strains but especially C57BL/6 mice showed strong preferences for cages with more bedding. The results highlight the importance of providing a sufficient amount of cage bedding to laboratory mice.

Central insulin signaling modulates hypothalamus-pituitary-adrenal axis responsiveness

Objective

Obesity is often accompanied by hyperactivity of the neuroendocrine stress axis and has been linked to an increased risk of psychiatric disorders. Insulin is reciprocally regulated with the stress hormone corticosterone (CORT), raising the possibility that insulin normally provides inhibitory tone to the hypothalamus-adrenal-pituitary (HPA) axis. Here we examined whether disrupting signaling via the insulin receptor (InsR) in hypothalamic subpopulations impacts the neuroendocrine response to acute psychological stress.

Methods

We used Nkx2.1-Cre, Sim1-Cre and Agrp-Cre transgenic driver lines to generate conditional knockouts of InsR signaling throughout the hypothalamus, paraventricular nucleus of the hypothalamus (PVH) and in neurons expressing Agouti-related peptide (AgRP) in the arcuate nucleus of the hypothalamus (ARH), respectively. We used a combination of molecular, behavioral and neuroendocrine criteria to evaluate the consequences on HPA axis responsiveness.

Results

Endpoints related to body weight and glucose homeostasis were not altered in any of the conditional mutant lines. Consistent with observations in the neuronal Insr knockout mice (NIRKO), baseline levels of serum CORT were similar to controls in all three lines. In male mice with broad disruptions of InsR signals in Nkx2.1-expressing regions of the hypothalamus (IR^Nkx2.1 KO), we observed elevated arginine vasopressin (AVP) levels at baseline and heightened neuroendocrine responses to restraint stress. IR^Nkx2.1 KO males also exhibited increased anxiety-like behaviors in open field, marble burying, and stress-induced hyperthermia testing paradigms. HPA axis responsivity was not altered in IR^Sim1 KO males, in which InsR was disrupted in the PVH. In contrast to observations in the IR^Nkx2.1 KO males, disrupting InsR signals in ARH neurons expressing Agrp (IR^Agrp KO) led to reduced AVP release in the median eminence (ME).

Conclusions

We find that central InsR signals modulate HPA responsivity to restraint stress. InsR signaling in AgRP/NPY neurons appears to promote AVP release, while signaling in other hypothalamic neuron(s) likely acts in an opposing fashion. Alterations in InsR signals in neurons that integrate metabolic and psychiatric information could contribute to the high co-morbidity of obesity and mental disorders.

Defensive burying test in postweaning rats: use of a small round chamber

The defensive burying test is an experimental model that is used to explore anxiety-like behavior in adult rats. Because the expression of anxiety-like behavior may differ between infant and adult rats, we tested the impact of chambers with different sizes and shapes on defensive burying in 28-day-old Wistar rats. The first two chambers had base areas of 560 cm, but one was rectangular and the other round. The base areas of the other two chambers were 282 cm, also with one rectangular and one round. We examined the effects of vehicle and 1 mg/kg diazepam on defensive burying in the various chambers. Locomotor activity was also measured to identify or exclude any sedative effects. Independent of the treatments used, the infant rats showed a shorter burying latency in the three modified chambers and a longer cumulative burying time compared with the original apparatus. The effects of diazepam (i.e. increased latency and decreased burying time) were only significant in the small round chamber, without significant effects on general motor activity. These results suggest that a small round chamber that is used to test burying behavior is sensitive to the anxiolytic actions of diazepam when the experimental subjects are very young rats.

Developmental alterations in anxiety and cognitive behavior in serotonin transporter mutant mice

RATIONALE

A promoter variant of the serotonin transporter (SERT) gene is known to affect emotional and cognitive regulation. In particular, the "short" allelic variant is implicated in the etiology of multiple neuropsychiatric disorders. Heterozygous (SERT(+/-)) and homozygous (SERT(-/-)) SERT mutant mice are valuable tools for understanding the mechanisms of altered SERT levels. Although these genetic effects are well investigated in adulthood, the developmental trajectory of altered SERT levels for behavior has not been investigated.

OBJECTIVES

We assessed anxiety-like and cognitive behaviors in SERT mutant mice in early adolescence and adulthood to examine the developmental consequences of reduced SERT levels. Spine density of pyramidal neurons was also measured in corticolimbic brain regions.

RESULTS

Adult SERT(-/-) mice exhibited increased anxiety-like behavior, but these differences were not observed in early adolescent SERT(-/-) mice. Conversely, SERT(+/-) and SERT(-/-) mice did display higher spontaneous alternation during early adolescence and adulthood. SERT(+/-) and SERT(-/-) also exhibited greater neuronal spine densities in the orbitofrontal but not the medial prefrontal cortices. Adult SERT(-/-) mice also showed an increased spine density in the basolateral amygdala.

CONCLUSIONS

Developmental alterations of the serotonergic system caused by genetic inactivation of SERT can have different influences on anxiety-like and cognitive behaviors through early adolescence into adulthood, which may be associated with changes of spine density in the prefrontal cortex and amygdala. The altered maturation of serotonergic systems may lead to specific age-related vulnerabilities to psychopathologies that develop during adolescence.

Myristic acid produces anxiolytic-like effects in Wistar rats in the elevated plus maze

A mixture of eight fatty acids (linoleic, palmitic, stearic, myristic, elaidic, lauric, oleic, and palmitoleic acids) at similar concentrations identified in human amniotic fluid produces anxiolytic-like effects comparable to diazepam in Wistar rats. However, individual effects of each fatty acid remain unexplored. In Wistar rats, we evaluated the separate action of each fatty acid at the corresponding concentrations previously found in human amniotic fluid on anxiety-like behaviour. Individual effects were compared with vehicle, an artificial mixture of the same eight fatty acids, and a reference anxiolytic drug (diazepam, 2 mg/kg). Myristic acid, the fatty acid mixture, and diazepam increased the time spent in the open arms of the elevated plus maze and reduced the anxiety index compared with vehicle, without altering general locomotor activity. The other fatty acids had no effect on anxiety-like behaviour, but oleic acid reduced locomotor activity. Additionally, myristic acid produced anxiolytic-like effects only when the concentration corresponded to the one identified in human amniotic fluid (30 μg/mL) but did not alter locomotor activity. We conclude that of the eight fatty acids contained in the fatty acid mixture, only myristic acid produces anxiolytic-like effects when administered individually at a similar concentration detected in human amniotic fluid.

Memory reconsolidation, emotional arousal, and the process of change in psychotherapy: New insights from brain science

Since Freud, clinicians have understood that disturbing memories contribute to psychopathology and that new emotional experiences contribute to therapeutic change. Yet, controversy remains about what is truly essential to bring about psychotherapeutic change. Mounting evidence from empirical studies suggests that emotional arousal is a key ingredient in therapeutic change in many modalities. In addition, memory seems to play an important role but there is a lack of consensus on the role of understanding what happened in the past in bringing about therapeutic change. The core idea of this paper is that therapeutic change in a variety of modalities, including behavioral therapy, cognitive-behavioral therapy, emotion-focused therapy, and psychodynamic psychotherapy, results from the updating of prior emotional memories through a process of reconsolidation that incorporates new emotional experiences. We present an integrated memory model with three interactive components - autobiographical (event) memories, semantic structures, and emotional responses - supported by emerging evidence from cognitive neuroscience on implicit and explicit emotion, implicit and explicit memory, emotion-memory interactions, memory reconsolidation, and the relationship between autobiographical and semantic memory. We propose that the essential ingredients of therapeutic change include: (1) reactivating old memories; (2) engaging in new emotional experiences that are incorporated into these reactivated memories via the process of reconsolidation; and (3) reinforcing the integrated memory structure by practicing a new way of behaving and experiencing the world in a variety of contexts. The implications of this new, neurobiologically grounded synthesis for research, clinical practice, and teaching are discussed.

Imidazoline binding sites mediates anticompulsive-like effect of agmatine in marble-burying behavior in mice

Agmatine is a cationic amine formed by decarboxylation of l-arginine by the mitochondrial enzyme arginine decarboxylase and widely distributed in mammalian brain. Although the precise function of endogenous agmatine has been largely remained unclear, its exogenous administration demonstrated beneficial effects in several neurological and psychiatric disorders. This study was planned to examine the role of imidazoline binding sites in the anticompulsive-like effect of agmatine on marble-burying behavior. Agmatine (20 and 40mg/kg, ip), mixed imidazoline I1/α2 agonists clonidine (60µg/kg, ip) and moxonidine (0.25mg/kg, ip), and imidazoline I2 agonist 2- BFI (10mg/kg, ip) showed significant inhibition of marble burying behavior in mice. In combination studies, the anticompulsive-like effect of agmatine (10mg/kg, ip) was significantly potentiated by prior administration of moxonidine (0.25mg/kg, ip) or clonidine (30µg/kg,) or 2-BFI (5mg/kg, ip). Conversely, efaroxan (1mg/kg, ip), an I1 antagonist and idazoxan (0.25mg/kg, ip), an I2 antagonist completely blocked the anticompulsive-like effect of agmatine (10mg/kg, ip). These drugs at doses used here did not influence the basal locomotor activity in experimental animals. These results clearly indicated the involvement of imidazoline binding sites in anti-compulsive-like effect of agmatine. Thus, imidazoline binding sites can be explored further as novel therapeutic target for treatment of anxiety and obsessive compulsive disorders.

Similarities and differences between "proactive" and "passive" stress-coping rats in responses to sucrose, NaCl, citric acid, and quinine

A stress-coping style describes a set of behavioral and physiological measures that characterize an individual's response to stressful stimuli. It would follow that different stress-coping styles are associated with differential sensitivity for taste stimuli. Animals with stress-coping characteristics better suited to an environment in which new foods are more frequently encountered may show enhanced orosensitivity to cues that signal toxins and/or nutritional value. Here, rats were categorized as "proactive" or "passive" based on results from a defensive burying test. Next, the brief-access taste procedure was used to compare unconditioned licking responses to a concentration array of compounds that humans describe as "sweet" (sucrose), "salty" (NaCl), "sour" (citric acid), and "bitter" (quinine) across the 2 groups. Both groups displayed concentration-dependent lick responses to sucrose, NaCl, citric acid, and quinine. The passive group initiated significantly fewer trials to sucrose than the proactive rats, but the groups did not significantly differ in trial initiation for the other 3 test compounds. Thus, differences in food intake, body weight, and glucose homeostasis between the stress-coping styles are not likely driven by alterations in orosensory responsivity. However, the current findings lend support to the hypothesis that the 2 groups differ in reward-related signaling mechanisms.

Restoration of dopamine signaling to the dorsal striatum is sufficient for aspects of active maternal behavior in female mice

Striatal dopamine (DA) is important for motivated behaviors, including maternal behavior. Recent evidence linking the dorsal striatum with goal-directed behavior suggests that DA signaling in the dorsal striatum, not just the nucleus accumbens, could be involved in maternal behavior. To investigate this question, we tested the maternal behavior of mice with DA genetically restricted to the dorsal striatum. These mice had a mild deficit in pup retrieval but had normal licking/grooming and nursing behavior; consequently, pups were weaned successfully. We also tested a separate group of mice with severely depleted DA in all striatal areas. They had severe deficits in pup retrieval and licking/grooming behavior, whereas nursing behavior was left intact; again, pups survived to weaning at normal rates. We conclude that DA signaling in the striatum is a part of the circuitry mediating maternal behavior and is specifically relevant for active, but not passive, maternal behaviors. In addition, DA in the dorsal striatum is sufficient to allow for active maternal behavior.

Mapping brain circuits of reward and motivation: in the footsteps of Ann Kelley

Ann Kelley was a scientific pioneer in reward neuroscience. Her many notable discoveries included demonstrations of accumbens/striatal circuitry roles in eating behavior and in food reward, explorations of limbic interactions with hypothalamic regulatory circuits, and additional interactions of motivation circuits with learning functions. Ann Kelley's accomplishments inspired other researchers to follow in her footsteps, including our own laboratory group. Here we describe results from several lines of our research that sprang in part from earlier findings by Kelley and colleagues. We describe hedonic hotspots for generating intense pleasure 'liking', separate identities of 'wanting' versus 'liking' systems, a novel role for dorsal neostriatum in generating motivation to eat, a limbic keyboard mechanism in nucleus accumbens for generating intense desire versus intense dread, and dynamic limbic transformations of learned memories into motivation. We describe how origins for each of these themes can be traced to fundamental contributions by Ann Kelley.