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High fat diet induced-obesity facilitates anxiety-like behaviors due to GABAergic impairment within the dorsomedial hypothalamus in rats.

HighlightsHFD facilitates the development of anxiety‐related behavior.Muscimol intra‐dorsomedial hypothalamus has an anxiogenic effect in obese rats.BMI intra‐dorsomedial hypothalamus does not cause an anxiogenic effect in obese rats.Memory acquisition and locomotor activity are not altered by GABAergic manipulation. ABSTRACT Overweight and obesity are conditions associated with an overall range of clinical health consequences, and they could be involved with the development of neuropsychiatric diseases, such as generalized anxiety disorder (GAD) and panic disorder (PD). A crucial brain nuclei involved on the physiological functions and behavioral responses, especially fear, anxiety and panic, is the dorsomedial hypothalamus (DMH). However, the mechanisms underlying the process whereby the DMH is involved in behavioral changes in obese rats still remains unclear. The current study further investigates the relation between obesity and generalized anxiety, by investigating the GABAA sensitivity to pharmacological manipulation within the DMH in obese rats during anxiety conditions. Male Wistar rats were divided in two experimental groups: the first was fed a control diet (CD; 11% w/w) and second was fed a high fat diet (HFD; 45% w/w). Animals were randomly treated with muscimol, a GABAA agonist and bicuculline methiodide (BMI), a GABAA antagonist. Inhibitory avoidance and escape behaviors were investigated using the Elevated T‐Maze (ETM) apparatus. Our results revealed that the obesity facilitated inhibitory avoidance acquisition, suggesting a positive relation between obesity and the development of an anxiety‐like state. The injection of muscimol (an anxiolytic drug), within the DMH, increased the inhibitory avoidance latency in obese animals (featuring an anxiogenic state). Besides, muscimol prolonged the escape latency and controlling the possible panic‐like behavior in these animals. Injection of BMI into the DMH was ineffective to produce an anxiety‐like effect in obese animals opposing the results observed in lean animals. These findings support the hypotheses that obese animals are susceptible to develop anxiety‐like behaviors, probably through changes in the GABAergic neurotransmission within the DMH.

Amygdalar neuronal activity mediates the cardiovascular responses evoked from the dorsolateral periaqueductal gray in conscious rats

There is ample evidence that both lateral/dorsolateral periaqueductal gray (l/dlPAG) and basolateral amygdala (BLA) are essential for the regulation of the autonomic responses evoked during innate reactions to threatening stimuli. However, it is not well established to what extent the BLA regulates the upstream functional connection from the l/dlPAG. Here we evaluated the role of the BLA and its glutamatergic receptors in the cardiovascular responses induced by l/dlPAG stimulation in rats. We examined the influence of acute inhibition of the BLA, unilaterally, by injecting muscimol on the cardiovascular responses evoked by the injection of N-methyl D-aspartate (NMDA) into the l/dlPAG. We also evaluated the role of BLA ionotropic glutamate receptors in these responses by injecting antagonists of NMDA and AMPA/kainate receptor subtypes into the BLA. Our results show that the microinjection of NMDA in the BLA increased the mean arterial pressure (MAP) and heart rate (HR). Injection of NMDA into the l/dlPAG caused similar increases in these variables, which was prevented by the prior injection of muscimol, a GABAA agonist, into the BLA. Moreover, injection of glutamatergic antagonists (2-amino-5-phosphonopentanoate (AP5) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)) into the BLA reduced the increase in MAP and HR induced by l/dlPAG activation. Finally, the inhibition of the central amygdala neurons failed to reduce the cardiovascular changes induced by l/dlPAG activation. These results indicate that physiological responses elicited by l/dlPAG activation require the neuronal activity in the BLA. This ascending excitatory pathway from the l/dlPAG to the BLA might ensure the expression of the autonomic component of the defense reaction.

New insights on amygdala: Basomedial amygdala regulates the physiological response to social novelty.

The amygdala has been associated with a variety of functions linked to physiological, behavioral and endocrine responses during emotional situations. This brain region is comprised of multiple sub-nuclei. These sub-nuclei belong to the same structure, but may be involved in different functions, thereby making the study of each sub-nuclei important. Yet, the involvement of the basomedial amygdala (BMA) in the regulation of emotional states has yet to be defined. Therefore, the aim of our study was to investigate the regulatory role of the BMA on the responses evoked during a social novelty model and whether the regulatory role depended on an interaction with the dorsomedial hypothalamus (DMH). Our results showed that the chemical inhibition of the BMA by the microinjection of muscimol (γ-aminobutyric acid (GABAA) agonist) promoted increases in mean arterial pressure (MAP) and heart rate (HR), whereas the chemical inhibition of regions near the BMA did not induce such cardiovascular changes. In contrast, the BMA chemical activation by the bilateral microinjection of bicuculline methiodide (BMI; GABAA antagonist), blocked the increases in MAP and HR observed when an intruder rat was suddenly introduced into the cage of a resident rat, and confined to the small cage for 15min. Additionally, the increase in HR and MAP induced by BMA inhibition were eliminated by DMH chemical inhibition. Thus, our data reveal that the BMA is under continuous GABAergic influence, and that its hyperactivation can reduce the physiological response induced by a social novelty condition, possibly by inhibiting DMH neurons.

Increased α1-adrenoreceptor activity is required to sustain blood pressure in female rats under food restriction

AIMS We evaluated the effect of food restriction (FR) on the various reflexes involved in short term cardiovascular regulation; we also evaluated the contribution of the sympathetic nervous systemand of the plasmatic nitric oxide (NO) in the development of the counterregulatory cardiovascular changes triggered by FR. MAIN METHODS Female rats were subjected to FR for 14 days, and after this period biochemical measurements of biochemical parameters were performed. For physiological tests, animals were anaesthetised, and a catheter was inserted into the femoral artery and vein for the acquisition of blood pressure and heart hate, and drug infusion, respectively.We then tested the Bezold–Jarisch reflex, the baroreflex and chemoreflex and the effect of the infusion of adrenergic receptor antagonists in control and food restricted animals. KEY FINDINGS The rats subjected to severe FR presented biochemical changes characteristic of malnutrition with a great catabolic state. FR also led to hypotension and bradycardia besides reducing the plasmatic concentration of NO. Moreover, activation of the Bezold–Jarisch reflex induced a more pronounced hypotensive response in animals subjected to FR. Intravenous infusion of a α1-adrenoreceptor antagonist induced a greater hypotensive response and a more pronounced tachycardic response in animals under food restriction,while the infusion of β-adrenoreceptor antagonist induced lower increases in blood pressure in these animals. SIGNIFICANCE Our results suggest that an increased α1-adrenoreceptor activity in the resistance arteries coupled with a reduction of plasmatic NO contributes in a complementary manner to maintain the blood pressure levels in animals under FR.

PSD95 and nNOS interaction as a novel molecular target to modulate conditioned fear: relevance to PTSD

Stimulation of N-methyl-D-aspartic acid receptors (NMDARs) and the resulting increase of nitric oxide (NO) production are critical for fear memory formation. Following NMDAR activation, efficient production of NO requires linking the 95 kDa postsynaptic density protein (PSD95), a scaffolding protein to neuronal nitric oxide synthase (nNOS). A variety of previously studied NMDAR antagonists and NOS inhibitors can disrupt fear conditioning, but they also affect many other CNS functions such as motor activity, anxiety, and learning. We hypothesized that disrupting nNOS and PSD95 interaction in the amygdala, a critical site for fear memory formation, will reduce conditioned fear. Our results show that systemic treatment with ZL006, a compound that disrupts PSD95/nNOS binding, attenuates fear memory compared to its inactive isomer ZL007. Co-immunoprecipitation after fear conditioning showed a robust increase in the amygdala PSD95/nNOS binding, which was blocked by systemic pre-administration of ZL006. Treatment of amygdala slices with ZL006 also impaired long-term potentiation (LTP), a cellular signature of synaptic plasticity. Direct intra-amygdala infusion of ZL006 also attenuated conditioned fear. Finally, unlike NMDAR antagonist MK-801, ZL006 does not affect locomotion, social interaction, object recognition memory, and spatial memory. These findings support the hypothesis that disrupting the PSD95/nNOS interaction downstream of NMDARs selectively reduces fear memory, and highlights PSD95/nNOS interaction as a novel target for fear-related disorders, such as posttraumatic stress disorder.

Role of the Renin Angiotensin System in Blood Pressure Allostasis-induced by Severe Food Restriction in Female Fischer rats

Severe food restriction (FR) is associated with blood pressure (BP) and cardiovascular dysfunction. The renin-angiotensin system (RAS) regulates BP and its dysregulation contributes to impaired cardiovascular function. Female Fischer rats were maintained on a control (CT) or severe FR (40% of CT) diet for 14 days. In response to severe FR, BP allostasis was achieved by up-regulating circulating Ang-[1–8] by 1.3-fold through increased angiotensin converting enzyme (ACE) activity and by increasing the expression of AT1Rs 1.7-fold in mesenteric vessels. Activation of the RAS countered the depressor effect of the severe plasma volume reduction (≥30%). The RAS, however, still underperformed as evidenced by reduced pressor responses to Ang-[1–8] even though AT1Rs were still responsive to the depressor effects of an AT1R antagonist. The aldosterone (ALDO) response was also inadequate as no changes in plasma ALDO were observed after the large fall in plasma volume. These findings have implications for individuals who have experienced a period(s) of severe FR (e.g., anorexia nervosa, dieters, natural disasters) and suggests increased activity of the RAS in order to achieve allostasis contributes to the cardiovascular dysfunction associated with inadequate food intake.

Role of Medial Hypothalamic Orexin System in Panic, Phobia and Hypertension

Orexin has been implicated in a number of physiological functions, including arousal, regulation of sleep, energy metabolism, appetitive behaviors, stress, anxiety, fear, panic, and cardiovascular control. In this review, we will highlight research focused on orexin system in the medial hypothalamic regions of perifornical (PeF) and dorsomedial hypothalamus (DMH), and describe the role of this hypothalamic neuropeptide in the behavioral expression of panic and consequent fear and avoidance responses, as well as sympathetic regulation and possible development of chronic hypertension. We will also outline recent data highlighting the clinical potential of single and dual orexin receptor antagonists for neuropsychiatric conditions including panic, phobia, and cardiovascular conditions, such as in hypertension.

Estrogen receptor β activation within dorsal raphe nucleus reverses anxiety-like behavior induced by food restriction in female rats

&NA; Severe food restriction (FR), as observed in disorders like anorexia nervosa, has been associated to the reduction of estrogen levels, which in turn could lead to anxiety development. Estrogen receptors, mainly ER&bgr; type, are commonly found in the dorsal raphe nucleus (DRN) neurons, an important nucleus related to anxiety modulation and the primary source of serotonin (5‐HT) in the brain. Taking together, these findings suggest an involvement of estrogen in anxiety modulation during food restriction, possibly mediated by ER&bgr; activation in serotonergic DRN neurons. Thus, the present study investigated the relationship between food restriction and anxiety‐like behavior, and the involvement of DRN and ER&bgr; on the modulation of anxiety‐like behaviors in animals subjected to FR. For that, female Fischer rats were grouped in control group, with free access to food, or a FR group, which received 40% of control intake during 14 days. Animals were randomly treated with 17&bgr;‐estradiol (E2), DPN (ER&bgr; selective agonist), or their respective vehicles, PBS and DMSO. Behavioral tests were performed on Elevated T‐Maze (ETM) and Open Field (OF). Our results suggest that FR probably reduced the estrogen levels, since the remained in the non‐ovulatory cycle phases, and their uterine weight was lower when compared to control group. The FR rats showed increased inhibitory avoidance latency in theETM indicating that FR is associated with the development of an anxiety‐like state. The injections of both E2 and DPN into DRN of FR animals had an anxiolytic effect. Those data suggest thatanxiety‐like behavior induced by FR could be mediated by a reduction of ER&bgr; activation in the DRN neurons, probably due to decreased estrogen levels.