Modifications in basal and stress-induced hypothalamic AMP-activated protein kinase (AMPK) activity in rats chronically treated with an angiotensin II receptor blocker

5' adenosine monophosphate-activated protein kinase (AMPK) plays a prominent role as a metabolic stress sensor. The role of hypothalamic AMPK in response to restraint and surgical stress has not been previously investigated. It has been recently suggested that the renin-angiotensin system, in addition to its role in stress regulation, may play a significant role in regulating metabolic pathways including the regulation of the AMPK system. This study was thus aimed to evaluate the effects of candesartan, an angiotensin II AT1 receptor blocker drug, on hypothalamic AMPK activity under basal conditions and after restraint in conscious rats or after surgical stress under general anesthesia. Male Wistar rats were treated with 5 mg/kg/day candesartan in the drinking water for 2 weeks. The hypothalamic AMPK activity was determined under basal and stress conditions, using a kinase activity assay. Chronic administration of candesartan significantly increased hypothalamic AMPK activity. Hypothalamic AMPK activity was also increased by restraint stress whereas no change was observed during surgical stress under anesthesia. The high levels of hypothalamic AMPK activation observed in candesartan-treated rats were not changed by restraint stress but were reduced to control levels by anesthesia and surgery. In conclusion, chronic candesartan treatment and restraint stress in conscious rats stimulate the hypothalamic AMPK activity, whereas surgical stress under anesthesia inhibits pathways regulating the AMPK activity even in candesartan-treated rats.     

Conditioning,sensations, and the ergotropic-trophotropic balance

Analysis of Pschonik’s work on conditioning and sensation, in the light of Gellhorn’s studies on the tuning of the central nervous system through changes in the ergotropic-trophotropic balance, leads to the following results. Vasomotor and sensory reactions (VSR) induced by stimulation of cutaneous warmth and pain receptors (US), or by the conditional stimulus (CS) reinforced by the US, show parallel changes in a variety of circumstances: 1) anesthesia of the skin abolishes the effect of the US but not that of the CS; 2) various procedures lead to a reversal of VSR in the conditioned state in response to the US; 3) in a near-neurotic state VSR may be abolished while the plethysmogram gives evidence that ergotropic and trophotropic discharges occur at the same time. Changes in the ergotropic-trophotropic balance at the hypothalamic level alter VSR quantitatively and qualitatively. In an ergotropicallytuned state not only ergotropically-acting stimuli, but also trophotropically-acting stimuli lead to vasoconstriction and pain. Thus, stimulation of pain receptors, as well as stimulation of warmth receptors, produces vasoconstriction and pain. Similarly, these stimuli effect vasodilatation and warmth in the trophotropically-tuned state. It is concluded that the ergotropic-trophotropic balance has a profound influence on sensations and perceptions. It is of clinical significance that this balance can be altered through a conditional reflex mechanism,i.e., on the basis of individual experience.     

The effects of reversible lidocaine-induced lesion of the tissue surrounding the anterior ventral wall of the third ventricle on drinking in rats.

The local anesthetic lidocaine (XILOCAINA), 2%, was injected into the tissue surrounding the anterior region of the third cerebral ventricle (AV3V) of the rat, through a permanently implanted cannula, to produce a temporary and reversible disruption of the nervous connections of this area with other cellular nuclei while leaving the vascular connections intact. Following 24 h water deprivation, lidocaine was injected, and after 20 min water intake decreased; subsequently, the lidocaine-injected rats behaved similarly to control rats injected with artificial cerebrospinal fluid. Osmotic drinking was not affected. Prolonged adipsia or hyperdipsia did not occur. In nondeprived rats, lidocaine prevented angiotensin II-induced drinking. Following 24 h sodium depletion by peritoneal dialysis, lidocaine decreased the specific sodium appetite by 50% in animals with different levels of body sodium depletion. The data indicate that the integrity of the neural tissue of the AV3V is essential for a correct body water-salt regulation. Temporary "ablation" with lidocaine, which blocked neural activity but maintained the blood supply, produced responses different from most of those reported after electrolytic lesions. Therefore, lidocaine may be used as a tool to assess the response of this neural tissue to body fluid regulation.     

Analysis of systems influencing renal hemodynamics and sodium excretion. I. Biochemical systems theory

In this article we present a new methodology—Biochemical Systems Theory and Analysis—as an alternative to traditional parametric statistical procedures for investigating differences between risk groups in a population. We review the systems theory and how it can be used to represent a model of processes influencing renal hemodynamics and sodium (Na⁺) excretion. We also discuss the potential for new measures of the biology of common diseases that can emerge from a synergism between systems theory and population-based statistical approaches. This work was supported in part by grants from the Public Health Service, RO1-HL30428, R01-HL39107 and General Clinical Research Center Grant RR0585.     

Dopamine D2 receptors mediate reversal learning in male C57BL/6J mice

Dopamine is critical for directing goal-oriented behavior. We investigated dopamine D₂ receptor involvement in reversal learning and reinforcement efficacy in mice lacking functional dopamine D₂ receptors and their heterozygous and wild-type littermates. Mice discriminated between two odors to receive a food reinforcer: One odor signaled a reinforcer (S⁺); the other odor signaled no reinforcer (S⁻). After mice learned the S⁺/S⁻ relationship, we inverted the reinforcement contingencies. The necessary number of trials to relearn the new reinforcement contingencies served as our index of reversal learning. Mice lacking functional dopamine D₂ receptors repeatedly failed to inhibit previously reinforced responses during reversal trials. In a separate experiment, mice responded for reinforcers on a progressive ratio schedule of reinforcement. Mice lacking functional dopamine D₂ receptors earned significantly fewer reinforcers than did heterozygous mice. Our results suggest that dopamine D₂ receptors regulate reversal learning and influence the reinforcing efficacy of natural rewards.     

Mouse genetic approaches to feeding regulation: serotonin 5-HT2C receptor mutant mice

Neural mechanisms underlying the regulation of ingestive behavior and energy balance are well conserved among mammals. Many neural pathways, each reflecting the function of many genes, interact to regulate these processes. Systematic genetic perturbations are not feasible in humans--the examination of gene functions relevant to feeding regulation must be performed in other species. Many advances in this field have been made through molecular genetic studies of mice, the most genetically tractable of mammalian species. The relevance of mouse ingestive behavior to the mechanisms underlying the regulation of feeding in humans is discussed. Approaches for evaluating the contributions of genes to the regulation of energy balance and to the actions of anorectic drugs are described in the context of studies focused on a line of mice lacking the serotonin 5-HT2C receptor subtype. These animal display reduced responsiveness to serotonergic anorexic drugs and a late-onset obesity syndrome associated with features reminiscent of common forms of human obesity. Developmental studies of energy balance uncovered a novel age-dependent physiological process that may contribute generally to the predisposition of humans and other mammals to accumulate fat stores during "middle-age." These findings are presented to illustrate considerations in the use of mouse molecular genetic technologies to investigate genetic influences on ingestive behavior and energy balance.     

Brain and peripheral angiotensin II play a major role in stress

Angiotensin II (Ang II), the active principle of the renin-angiotensin system (RAS), was discovered as a vasoconstrictive, fluid retentive circulating hormone. It was revealed later that there are local RAS in many organs, including the brain. The physiological receptor for Ang II, the AT(1) receptor type, was found to be highly expressed in many tissues and brain areas involved in the hypothalamic-pituitary-adrenal axis response to stress and in the sympathoadrenal system. The production of circulating and local Ang II, and the expression of AT(1) receptors increase during stress. Blockade of peripheral and brain AT(1) receptors with receptor antagonists administered peripherally prevented the hormonal and sympathoadrenal response to isolation stress, the stress-related alterations in cortical CRF(1) and benzodiazepine receptors, part of the GABA(A) complex, and reduced anxiety in rodents. AT(1) receptor blockade prevented the ulcerations of the gastric mucosa produced by cold-restraint stress, by preservation of the gastric blood flow, prevention of the stress-induced inflammatory response of the gastric mucosa, and partial blockade of the sympathoadrenal response to the stress. Our observations demonstrate that Ang II is an important stress hormone, and that blockade of AT(1) receptors could be proposed as a potentially useful therapy for stress-induced disorders.     

Why Dexamethasone Poorly Penetrates in Brain

Dexamethasone poorly penetrates in brain. A tracer amount of [3H]-dexamethasone administered to adrenalectomized rats or mice is poorly retained by glucocorticoid receptors in brain, while pituitary corticotrophs containing equivalent amounts of these receptors accumulate and retain large amounts of this synthetic steroid. However, adrenalectomized mice with a genetic disruption of the multiple drug resistance (mrd1a) gene have a tenfold increase of [3H]-dexamethasone uptake in brain glucocorticoid target sites reaching levels observed in the pituitary. These data demonstrate that dexamethasone is extruded from brain by the mrd1a-encoded P-glycoproteins. The data support the concept of a pituitary site of action of dexamethasone in blockade of stress-induced ACTH release, which implies that chronic dexamethasone treatment does not replace the endogenous corticosteroids depleted from brain mineralocorticoid (MRs) and glucocorticoid receptors (GRs). Dexamethasone, therefore, causes a profound disturbance in the balance of these two receptor types in hippocampus, which is an unfavourable condition threatening the neuronal integrity of this brain structure through the expression of noxious genes.     

Taste rejection of nonnutritive sweeteners in cats.

Cats reject saccharin and cyclamate and are indifferent to dulcin, although they, like other mammals, prefer sucrose. The rejection threshold for saccharin found in this experiments, .0001 M, is about 2 log steps lower than a previously reported rejection threshold for sodium saccharin. Water produces a taste in cats adapted to their own saliva. The high sodium saccharin threshold may have resulted because the taste of the sodium saccharin was masked by the taste of the water solvent; however, saccharin may also be somewhat more aversive to the cat than sodium saccharin. Saccharin may produce an aversive taste because it stimulates receptor sites sensitive to substances bitter to man as well as those sensitive to sugars. In addition, saccharin may not be an effective stimulus for all sugar-sensitive sites.     

The Solubility of Salt: A Divine Action Account

In the burgeoning literature on dispositions, solubility is a standard example. In this paper we give a rigorous theistic divine action account of the simple mechanism of the dissolving of salt, NaCl, into the ions Na⁺ and Cl^?. We explore this reaction in terms of an alternative view of divine action, Divine Compositionalism, which holds that the functioning of every physical, chemical, and biological mechanism in the universe is a manifesting complex disposition, which is nothing other than ways God acts according to plan.     

Reply to Stuart and Lovegrove's question, "visual processing deficits in dyslexia: receptors or neural mechanisms?".

Recently Stuart and Lovegrove questioned the receptor hypothesis of Grosser and Spafford which these authors used to account for the findings that dyslexic individuals have superior peripheral color discrimination to normal readers but also have poorer peripheral brightness discrimination than normal readers. Stuart and Lovegrove hypothesized that dyslexics instead have an impaired transient visual system. The receptor hypothesis is an attempt by Grosser and Spafford to link the functioning of the rods and cones to transient and sustained visual system functioning in a more specific manner than has been tried heretofore by suggesting that, while the parvocellular system is almost entirely fed by cones, both kinds of receptors drive magnocellular cells (but with the rapid onset of early transient system responding being due to the highly light sensitive rods). The rods are proposed to be the receptors initiating the rapid onset of responding in the magnocellular, transient pathway. In dyslexic individuals, they maintain, there are relatively fewer rods to provide for the rapid onset of transient system responses, resulting in a diminished capacity of the transient system to inhibit sustained system activity (as occurs with normal readers). Their receptor hypothesis supplements the concept of transient-vs-sustained system differences.     

Intracerebroventricular Administration of Mineralocorticoid Receptor Antisense Oligonucleotides Attenuates Salt Appetite in the Rat

The anterior ventral third ventricle (AV3V) region of the brain contains high concentrations of mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) that are important in the maintenance of body fluid and electrolyte balance as well as other physiological processes. Daily intracerebroventricular pulse injections of MR antisense oligonucleotides significantly suppressed deoxycorticosterone acetate (DOCA) induced salt appetite in a dose-related manner. Similar administration of GR antisense or scrambled/sense oligonucleotide into the third ventricle failed to inhibit salt appetite. Salt appetite aroused after adrenalectomy was not suppressed by MR antisense oligonucleotide treatments but was suppressed by an antisense oligonucleotide directed against the angiotensin II AT1 receptor subtype. Receptor binding analysis demonstrated that MR and GR oligonucleotide treatments each reduced their respective receptor subtypes. Finally, although GR antisense oligonucleotide treatment was ineffective in suppressing DOCA-induced salt appetite, this treatment did increase stress induced corticosterone release as well as delayed the recovery of corticosterone to basal levels after stress.     

Enkephalins and learning and memory: a review of evidence for a site of action outside the blood-brain barrier

A series of studies indicate that enkephalins exert dramatic influences on learning and memory in rats and mice, when studied with conditioning tasks that are both negatively and positively motivated. Pharmacological analysis of these enkephalin actions on conditioning suggests that the [leu]enkephalin acts through a delta opioid receptor which is located outside the blood-brain barrier. Control studies indicate that enkephalins do not simply affect the performance of a conditioned response through actions on shock sensitivity or locomotor activity. Characterization of the peripheral enkephalin mechanism that affects behavior suggests an action through an enzymatic system that controls the concentrations of enkephalin present at its receptors in the periphery. This enzymatic mechanism is sensitive to experience, since its activity changes following conditioning, which suggests that it may be a regulatory mechanism for behavior.     

Effect of extrinsic noise on vibrotactile information processing channels

Cutaneous receptors sensitive to high-frequency vibration produce spatial summation at threshold levels of stimulation, whereas the response of the receptor population sensitive to low frequencies appears to be independent of contactor size at threshold. Reports have been made of a phenomenon in which the presumably nonsummating population of mechanoreceptors produce spatial summation at suprathreshold levels. A possible explanation concerns the relative signal-to-noise ratios of cutaneous mechanoreceptor systems. By selectively masking the systems with narrow-band and wide-band noise, it can be shown that any combination of signal frequency, masking noise, and contactor size that predominantly activates either system results in a linear effect of the masker on the threshold of the signal. Combinations of the experimental variables that activate both receptor systems simultaneously reduce the effect of the masking by one-half. This is interpreted as evidence of an interactive process between receptor systems within the central nervous system. The effects of signal-to-noise ratio and intrasensory interactions are discussed.     

The brain prolactin system: involvement in stress response adaptations in lactation

This review focuses on prolactin as a potential candidate for the regulation of emotional and neuroendocrine stress responses in the brain. In particular, we summarise evidence for a brain prolactin receptor-mediated anxiolytic action both in female and male rats, and for inhibitory actions on the reactivity of the hypothalamic-pituitary-adrenal (HPA) axis and the neurohypophysial oxytocin system. These physiological functions of the brain prolactin system are especially relevant in the peripartum period, as an attenuation of behavioural and neuroendocrine stress responses has been described during pregnancy and lactation. At this time, there is an increase in brain prolactin receptor expression and binding, and an increase in hypothalamic prolactin gene expression. In the absence of a selective prolactin receptor antagonist, complementary approaches including chronic intracerebral infusion of prolactin, and antisense targeting of the long form of the brain prolactin receptor were used to investigate the actions of prolactin. The hypothesis of a brain prolactin system activated in the peripartum period which contributes to the adaptive changes in stress responsiveness in order to support reproductive functions is strongly emphasised.     

Chronic effects of high salt intake and conflict stress on blood pressure in primates

The effects of combined behavioral stress and high dietary salt on blood pressure were examined in baboons (N=4) over the course of 1 year. Either high salt diet (240 mEq Na⁺/day) or conflict stress were administered for 8 to 16 weeks, followed by high salt intake and stress combined. Mean arterial pressure (MAP) increased by 8 mmHg during high dietary salt alone, by 4 mmHg during stress alone, and increased further to 14 mmHg above baseline during combined salt and stress. Control baboons (N=2) had no change in MAP across 47 weeks. The data indicate additive effects of chronic high dietary salt intake and behavioral stress on blood pressure in non-human primates.     

Brain Oxidative Damage Following Acute Immobilization and Mild Emotional Stress

We studied the role of free radicals on brain oxidative damage in rats after acute immobilization stress (restraint) and mild emotional stress (handling). To investigate brain oxidative damage, CuZn and Mn dependent superoxide dismutase (CuZn SOD, Mn SOD) activities, lipid peroxidation (TBARs), Na ⁺ K ⁺ ATPase activity, protein carbonyl (PrC), and reduced and oxidized glutathione (GSH, GSSG) levels were measured in the cerebral cortex (CTX), hippocampus (HIP), and striatum (ST) of the animals after the two different stress stimuli. Because stress produces abnormalities in the hypothalamic-pituitary-adrenal axis, the intensity of the two stress conditions were measured by plasmatic corticosteroid (COR) levels: particularly, COR levels doubled in handled rats and increased 15-fold in restrained animals. The SOD activities increased in CTX and decreased in HIP of the handled rats, while in ST a significant decrease in handled animals but an increase in restrained animals occurred. TBARs, GSH, and GSSG levels remained unchanged, while an index of glutathione redox decreased significantly in ST of handled animals and in CTX of restrained ones. Na ⁺ K ⁺ ATPase activity increased significantly in the HIP and ST of both groups of stressed rats. The stress induced a remarkable increase in PrC levels in all studied cerebral areas. These findings provide evidence to support the idea that stress produces oxidants but that the oxidative damage in stress differs in cerebral areas and could contribute to the degenerative mechanism of aging.     

Biobehavioral effects of extended salt loading and conflict stress in intact baboons.

Behavioral stressors may inhibit sodium excretion, potentially increasing plasma volume and elevating blood pressure during chronic exposure. Blood pressure regulation may be especially deranged during manipulations that further challenge the kidney, such as a diet high in salt content. The effects on blood pressure and other variables of combined behavioral stress (food/shock conflict) and dietary salt (12 g NaCl per day; 218 mEq Na+ per day) were examined in adult male baboons over the course of 1 year. Mean arterial pressure was not significantly elevated over baseline after 5 months of high dietary salt alone (6 +/- 5 mmHg) but was maximally elevated by an average of 17 (+/- 3 SEM) mmHg after 5 months of combined salt and conflict stress. Control baboons showed no significant trends in mean arterial pressure across the same time period. Individual subjects whose blood pressure was "salt+stress resistant" or "salt+stress sensitive" were differentiated by their degree of pressure diuresis and natriuresis, urinary free cortisol, and a behavioral index of stress sensitivity. The data indicate additive effects of chronic high dietary salt intake and behavioral stressors on blood pressure in nonhuman primates that are dependent on renal function and pituitary-adrenocortical activity.