Repeated stress induces a pro-inflammatory state,increases amygdala neuronal and microglial activation,and causes anxiety in adult male rats

A link exists between immune function and psychiatric conditions, particularly depressive and anxiety disorders. Psychological stress is a powerful trigger for these disorders and stress influences immune state. However, the nature of peripheral immune changes after stress conflicts across studies, perhaps due to the focus on few measures of pro-inflammatory or anti-inflammatory processes. The basolateral amygdala (BLA) is critical for emotion, and plays an important role in the effects of stress on anxiety. As such, it may be a primary central nervous system (CNS) mediator for the effects of peripheral immune changes on anxiety after stress. Therefore, this study aimed to delineate the influence of stress on peripheral pro-inflammatory and anti-inflammatory aspects, BLA immune activation, and its impact on BLA neuronal activity. To produce a more encompassing view of peripheral immune changes, this study used a less restrictive approach to categorize and group peripheral immune changes. We found that repeated social defeat stress in adult male Sprague-Dawley rats increased the frequencies of mature T-cells positive for intracellular type 2-like cytokine and serum pro-inflammatory cytokines. Principal component analysis and hierarchical clustering was used to guide grouping of T-cells and cytokines, producing unique profiles. Stress shifted the balance towards a specific set that included mostly type 2-like T-cells and pro-inflammatory cytokines. Within the CNS component, repeated stress caused an increase of activated microglia in the BLA, increased anxiety-like behaviors across several assays, and increased BLA neuronal firing in vivo that was prevented by blockade of microglia activation. Because repeated stress can trigger anxiety states by actions in the BLA, and altered immune function can trigger anxiety, these results suggest that repeated stress may trigger anxiety-like behaviors by inducing a pro-inflammatory state in the periphery and the BLA. These results begin to uncover how stress may recruit the immune system to alter the function of brain regions critical to emotion.     

Release of glutamate and GABA in the hippocampus under zinc deficiency

Zinc homeostasis in the brain is affected by dietary zinc deficiency, and its alteration may cause brain dysfunctions. On the basis of the previous evidence that hippocampal zinc was responsive to 12-week zinc deprivation, responsiveness of hippocampal zinc to dietary zinc deficiency was examined in rats fed a zinc-deficient diet for 4 weeks. Zinc concentration in the hippocampus was not decreased by zinc deprivation for 4 weeks. However, Timm's stain was extensively attenuated in the brain of the zinc-deficient rats. In the brain of the zinc-deficient rats, moreover, zinc concentration in the hippocampal extracellular fluid was approximately 30% of that of control rats. These results demonstrate that vesicular zinc is responsive to dietary zinc and may decrease easily under zinc deficiency. Zinc concentration in the hippocampal extracellular fluid during stimulation with high K(+) was significantly increased even in zinc-deficient rats, although the increased levels of zinc were lower than the basal levels of zinc in control rats. The basal glutamate concentration in the hippocampal extracellular fluid was not significantly different between the control and zinc-deficient rats. However, glutamate concentration in the hippocampal extracellular fluid during stimulation with high K(+) was more increased in the zinc-deficient rats than in the control rats. Gamma aminobutyric acid (GABA) concentration in the hippocampal extracellular fluid during stimulation with high K(+) was increased in the control rats, but not in the zinc-deficient rats. The present study suggests that the excitability of hippocampal glutamatergic neurons is enhanced by dietary zinc deficiency.     

Difference in distribution of glutamate-immunoreactive neurons projecting into the subretrofacial nucleus in the rostral ventrolateral medulla of SHR and WKY: a double-labeling study

Glutamate immunoreactivity was found in 19% and 21% of the neurons of the central autonomic nuclei projecting into the subretrofacial nucleus (SRF) in the rostral ventrolateral medulla of Wistar-Kyoto rat (WKY) and spontaneously hypertensive rat (SHR), respectively, using a double-labeling technique in combination with glutamate immunocytochemistry. Double-labeled neurons were distributed in 22 nuclei or subnuclei in the limbic system, hypothalamus, midbrain, pons and medulla. The average number of glutamate-immunoreactive neurons per thousand in SHR was significantly higher in the ipsilateral lateral parabrachial nucleus (P < 0.05) and Koelliker-Fuse nucleus (P < 0.01) than in WKY, while it was significantly lower in the ipsilateral medial subnucleus (P < 0.05) and the commissure subnucleus (P < 0.05) of the nucleus tractus solitarii in SHR than in WKY. The results indicate that: (1) glutamate-immunoreactive neurons (possibly glutamatergic) in many central autonomic nuclei project into the sympathetic vasomotor control neurons in the SRF; (2) the large population of glutamate-immunoreactive neurons in the lateral parabrachial nucleus and the Koelliker-Fuse nucleus of SHR is likely to increase excitatory inputs to the SRF vasomotor control neurons, while the smaller population of glutamate-immunoreactive neurons in the medial and commissure subnuclei of the nucleus tractus solitarii is likely to decrease excitatory inputs to the GABAergic neurons intrinsic to the SRF.     

Chronic, systemic treatment with a metabotropic glutamate receptor 5 antagonist produces anxiolytic-like effects and reverses abnormal firing activity of projection neurons in the basolateral nucleus of the amygdala in rats with bilateral 6-OHDA lesions

Although 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a selective metabotropic glutamate receptor 5 antagonist, improves the motor symptoms of Parkinson's disease (PD), the effects of MPEP on the psychiatric symptom of PD and the mechanism involved are still unclear. In the present study, we examined the effects of MPEP in anxiolytic-like behavior and firing activity of projection neurons in the basolateral nucleus of the amygdala (BLA) in rats with 6-hydroxydopamine (6-OHDA) injected bilaterally into dorsal striatum. Rats were divided into three groups, sham-operated group, 6-OHDA lesion with vehicle treatment group and 6-OHDA lesion with MPEP treatment group. Injection of 6-OHDA (10.5 μg) into the dorsal striatum produced 31.5% loss of tyrosine hydroxylase immunoreactive (TH-ir) neurons in the SNpc. The 6-OHDA-lesioned rats showed anxiety behavior and the firing rate of BLA projection neurons decreased significantly compared with sham-operated rats, and no difference was found in the firing pattern of these neurons. Whereas chronic, systemic treatment of MPEP (3 mg/kg/day, i.p.; 14 days) attenuated loss of TH-ir neurons, produced anxiolytic-like effect and normalized the abnormal firing rate of projection neurons of the BLA in rats with the bilateral lesions. Systemic administration of cumulative apomorphine (10-160 μg/kg, i.v.) inhibited the firing rate of BLA projection neurons in sham-operated, 6-OHDA lesion with vehicle-treated and MPEP-treated rats, but the 6-OHDA lesion decreased the response of BLA projection neurons to apomorphine stimulation, while MPEP reversed the reactivity of these neurons. These data demonstrate that the partial lesion of the nigrostriatal pathway causes anxiety symptom and decreases firing rate of BLA projection neurons in the rat. Furthermore, chronic, systemic MPEP treatment has the neuroprotective and anxiolytic-like effects, and reverses the abnormal firing rate of BLA projection neurons, suggesting that MPEP has important implication for the treatment of PD.     

Effect of treatment with choline alphoscerate on hippocampus microanatomy and glial reaction in spontaneously hypertensive rats

The influence of long term treatment with choline alphoscerate on microanatomy of hippocampus and glial reaction was assessed in spontaneously hypertensive rats (SHR) used as an animal model of cerebrovascular disease. Choline alphoscerate is a cholinergic precursor, which has shown to be effective in countering cognitive symptoms in forms of dementia disorders of degenerative, vascular or combined origin. Male spontaneously hypertensive rats (SHR) aged 6 months and age-matched normotensive Wistar-Kyoto (WKY) rats were treated for 8 weeks with an oral daily dose of 100 mg/kg of choline alphoscerate, 285 mg/kg of phosphatidylcholine (lecithin) or vehicle. On the hippocampus of different animal groups, nerve cell number and GFAP-immunoreactive astrocytes were assessed by neuroanatomical, immunochemical and immunohistochemical techniques associated with quantitative analysis. Treatment with choline alphoscerate countered nerve cell loss and glial reaction primarily in the CA1 subfields and in the dentate gyrus of the hippocampus of SHR. Phosphatidylcholine did not affect hypertension-dependent changes in hippocampal microanatomy. Both compounds did not affect blood pressure values in SHR. These data suggest that choline alphoscerate may play a role in the countering hippocampal changes induced by cerebrovascular involvement. The observation that treatment with choline alphoscerate attenuates the extent of glial reaction in the hippocampus of SHR suggests also that the compound may afford neuroprotection in this animal model of vascular brain damage.     

Inhibition of anandamide hydrolysis enhances noradrenergic and GABAergic transmission in the prefrontal cortex and basolateral amygdala of rats subjected to acute swim stress

Limbic forebrain endocannabinoid (eCB) signaling is critically involved in stress integration by modulating neurotransmitters release. The purpose of this study was to examine, by brain microdialysis, the effects of fatty acid amide hydrolase (FAAH) inhibition on noradrenergic and γ‐aminobutyric acid (GABA)‐ergic neurotransmission in the prefrontal cortex (PFC) and basolateral amygdala (BLA) of rats subjected to a 20‐min swim stress. Microdialysis started on stress‐ and drug‐naïve rats that were treated with the FAAH inhibitor URB597 (0.1 or 0.3 mg/kg) 30 min before undergoing the stress procedure. Dialysate samples were collected every 20 min from the beginning of the experiment. Concentrations of noradrenaline (NA) and GABA were determined by HPLC coupled to electrochemical and fluorescence detection, respectively. We found that neither URB597 treatment nor 20 min of swim stress exposure per se altered NA and GABA extracellular levels in PFC or BLA. Interestingly, rats treated with 0.1 mg/kg of URB597 followed by 20 min of stress showed significantly higher NA and GABA levels in PFC and BLA. These effects were absent in rats treated with 0.3 mg/kg URB597, indicating a dose‐specific effect. Moreover, we found that the pretreatment with the CB1 receptor antagonist rimonabant blocked the URB597 effects on NA and GABA release in PFC and BLA of animals subjected to forced swimming. The present study might provide an important first step toward understanding the mechanisms through which URB597 modulates stress‐induced neuroendocrine secretion and behavioral coping strategies. © 2015 Wiley Periodicals, Inc.     

Release of excitatory and inhibitory amino acids from the locus coeruleus of conscious rats by cardiovascular stimuli and various forms of acute stress

The release of amino acids in the locus coeruleus (LC) of conscious, freely moving rats was studied in time periods of 3 min by use of push-pull superfusion under basal conditions and during application of various experimental stimuli known to influence the activity of the LC-noradrenergic system. Tail pinch for 3 min led immediately to a pronounced tetrodotoxin-sensitive increase in the release rates of the excitatory amino acids (EAA) glutamate (Glu) and aspartate (Asp) and to moderate increases in GABA and taurine (Tau) outflow. Immobilization stress for 9 min elevated the release of the EAA Glu and Asp, as well as that of the inhibitory amino acid GABA to a similar extent. A fall of blood pressure (BP) by nitroprusside or haemorrhage slightly enhanced the release rates of Glu and Asp. Noradrenaline-induced rise in BP, as well as hypervolaemia increased the release rate of GABA, but did not influence the release rates of Glu, Asp, Tau and arginine (Arg). The results provide direct evidence that the amino acid release pattern in the LC of conscious rats differs in response to various stimuli, according to the modality of the stimulus. A functional significance of excitatory and inhibitory amino acids in the regulation of LC activity during stress and haemodynamic changes is suggested.     

Norepinephrine release in medial amygdala facilitates activation of the hypothalamic-pituitary-adrenal axis in response to acute immobilisation stress

Activation of the brain noradrenergic system during stress plays an important integrative function in coping and stress adaptation by facilitating transmission in many brain regions involved in regulating behavioural and physiological components of the stress response. The medial amygdala (MeA) has been implicated in modulation of stress-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis, and MeA is a target of innervation from brainstem noradrenergic neurones. However, it is not known whether, and to what extent, activation of the ascending noradrenergic innervation of MeA might modulate stress-induced adrenocorticotropic hormone (ACTH) secretion. In the first experiment in this study, we measured extracellular norepinephrine (NE) levels in MeA using in vivo microdialysis. The concentration of NE in dialysate samples collected in MeA was elevated by more than three-fold over baseline in response to acute immobilisation stress, providing evidence of a possible modulatory role for NE in the MeA during stress. This potential role was then assessed in the second experiment by measuring changes in the elevation of plasma ACTH concentration induced by acute immobilisation stress immediately following bilateral microinjections of alpha1- or beta-adrenergic receptor antagonists directly into MeA. Compared to vehicle-injected controls, the alpha1-receptor antagonist benoxathian dose-dependently and significantly attenuated the ACTH response to acute stress, whereas combined beta1/beta2-receptor blockade in MeA had only a modest effect. These results indicate that MeA does play a role in the stress response, and support the hypothesis that stress-induced activation of NE release in MeA, acting primarily through alpha1 receptors, facilitates activation of the HPA axis in response to acute stress.     

Acute effects of various GABA receptor agonists and glutamate antagonists on focal hippocampal seizures in freely moving rats elicited by low-frequency stimulation

In this study, we examined the acute anticonvulsant spectrum of (1) dizocilpine (0.03–3 mg/kg), CGS 19755 (1–10 mg/kg), and 7-chlorokynurenic acid (1–100 nmol) (NMDA receptor/ionophore complex antagonists); (2) muscimol (0.1–10 nmol; direct GABA_A agonist); (3) YM90K (3–10 mg/kg; AMPA receptor antagonist); and (4) diazepam (2 and 5 mg/kg) and carbamazepine (5 and 20 mg/kg), two standard anticonvulsants, using the partially-kindled hippocampal model for epileptic seizures in freely moving rats. The anticonvulsant effect of these compounds were assessed by determining (1) the afterdischarge (AD), which is indicative of the severity of the seizure and related to seizure maintenance, and (2) the pulse number threshold (PNT), which is indicative of the seizure threshold or initiation. In addition, ataxia, a measure of CNS dysfunction, was assessed for each compound. Overall, our results indicated that the anticonvulsant compounds examined could be classified into three categories based on effects on the AD and PNT: (1) elevation of PNT (carbamazepine, dizocilpine, CGS 19755 and 7-chlorokyurenic acid); (2) reduction of AD (diazepam and muscimol); and (3) mixed action, i.e., increased PNT and decreased AD (YM90K). Behavioral data indicated that all compounds, except carbamazepine, produced a dose- or concentration-dependent ataxia. Overall, our results suggest that NMDA receptors play a role in seizure initiation, whereas the GABA_A receptors appear to be involved in seizure maintenance and AMPA receptors may be involved in both phenomena. Synapse 28:103–109, 1998. © 1998 Wiley-Liss, Inc.     

Mortality and histological findings of the brain during and after cerebral ischemia in male and female spontaneously hypertensive rats

Mortality and pathological changes of the brain during and after cerebral ischemia induced by bilateral carotid artery occlusion (BCO) were studied in male and female spontaneously hypertensive rats (SHR). Systolic arterial blood pressure at rest was significantly higher in male SHR (228 +/- 13 mm Hg, mean +/- S.E.M.) than female (192 +/- 12) (P less than 0.05). The average survival time during permanent occlusion was 11 +/- 6 h (mean +/- S.D.) in male SHR and 17 +/- 7 in female (P less than 0.005), though the cumulative mortality during 24-h ischemia was not different between male (88%) and female SHR (84%). Severe ischemic changes of nerve cells in the brain, especially in the cortex and hippocampus, were observed in 50% of male SHR at 3-h ischemia, while only 15% was observed in female SHR even after 7-h ischemia. After the temporary ischemia followed by reperfusion for 24 h, the mortality was varied between male and female SHR; 0, 31 and 100% after 1-, 3- and 5-h ischemia, respectively, in male SHR and 0% after 1- to 3-h ischemia and 33% after 5- to 7-h ischemia, respectively, in female. Ischemic changes of the brain tissue, such as acidophilic cytoplasm, nuclear degeneration and intercellular edema, were more frequent and severe in male SHR than female after recirculation following 3- or 5-h ischemia. It is concluded that the mortality and post-ischemic viability seem to be determined by the duration of ischemia and also by the degree of the neuronal damage, and female SHR is more tolerated for ischemic insult in comparison to male SHR.     

Cerebellar nuclei and the nucleocortical projections in the rat: retrograde tracing coupled to GABA and glutamate immunohistochemistry.

The amino acids GABA and glutamate (Glu) are thought to be the principal substances in the central nervous system responsible for neuronal inhibition and excitation. Their distributions among the different neurons in a defined pathway may thus be indicative of the contributions of the cells to pathway function. Examples of such neurons are those of the cerebellar nuclei which, while regulating output from the Purkinje cells of the cerebellar cortex, are also found to project back to the cerebellar cortex. Immunohistochemical experiments were done to identify GABA and glutamate (Glu) containing cells in the adult rat cerebellar nuclei. Consecutive semithin and serial vibratome sections were incubated with antisera raised in rabbit against GABA and Glu. In semithin sections, only small neurons were intensely GABA immunoreactive (GABA-IR) (31.7%), and the majority (80.5%) were Glu immunoreactive (Glu-IR) of different sizes. Consistent with Glu being a metabolic precursor for GABA, 75.4% of the GABA-IR population colocalized Glu. In vibratome sections GABA-IR neurons showed some local differences in number, whereas the Glu-IR were uniformly distributed in the three nuclei studied. Measured mean diameters for these neurons showed a distinct size difference for the GABA- and Glu-IR with little overlap. Cerebellar nuclei neurons projecting to the cortex (nucleocortical neurons, NCN) were identified by locally preinjecting the retrograde transported WGA-apoHRP-colloidal gold complex in the cerebellar cortex. Vibratome sections of these cerebellar were silver intensified for the retrograde tracer and double labeled for GABA and Glu. Of the total number of identified NCN, 8.7% were GABA-IR (10 animals) and 47.7% Glu-IR (5 animals). Many retrograde labeled NCN in the core of the thick sections were immunonegative for both amino acids due to poor antibody penetration, thus underestimating the proportions of cells containing GABA and Glu. The size distributions for the GABA-IR and Glu-IR NCN were similar to those measured in non-retrograde labeled nuclei in thick sections. The conclusions reached are that GABA-IR neurons of the cerebellar nuclei, including the NCN, use GABA as the presumed inhibitory neurotransmitter and that Glu-IR neurons may use Glu or another excitatory neurotransmitter.     

Asymmetric time‐dependent activation of right central amygdala neurones in rats with peripheral neuropathy and pregabalin modulation

Neuropathic pain (NP) often presents with comorbidities, including depression and anxiety. The amygdala is involved in the processing of mood disorders, fear, and the emotional‐affective components of pain. Hemispheric lateralization of pain processing in the amygdala has recently been brought to light because, independently of the side of the peripheral injury, the right central nucleus of the amygdala (CeA) showed higher neuronal activity than the left in models of inflammatory pain. Although the CeA has been called the ‘nociceptive amygdala’, because of its high content of nociceptive neurones, little is known about changes in its neuronal function in vivo, under NP conditions. Herein, we quantified CeA spontaneous and evoked activity in rats subjected to spinal nerve ligation (SNL), under isoflurane anaesthesia, following application of mechanical and thermal stimuli to widespread body areas. We found that spontaneous and stimulus‐evoked neuronal activity was higher in the left CeA at 2 and 6 days after SNL induction and declined afterwards, whereas activity in the right CeA became dominant at 14 days after surgery, independently of the side of surgery. We also observed that systemic injection of pregabalin, which is widely used in patients with NP, reduced CeA spontaneous and stimulus‐evoked neuronal activity. Overall, we observed that peripheral nerve injury produced asymmetric plasticity in ongoing and evoked activity in the left and right CeA. Remarkably, at 14 days after SNL induction, enhanced evoked activity in the right CeA persisted compared to short‐term increases in activity in the left CeA. The plasticity found in ongoing and evoked activity was inhibited by pregabalin.     

Quantitation of ventricular size in normal and spontaneously hypertensive rats by magnetic resonance imaging

Magnetic resonance imaging (MRI) performed at high field (4.7 Tesla), and high spatial resolution (0.6 mm slice thickness, 0.18 mm inplane) enabled noninvasive quantitative measurement of the ventricular vol. in live rats. Comparing the results for 15 male Wistar-Kyoto (WKY) rats, aged 2.5-10 months, with those from 17 spontaneously hypertensive rats (SHR), clearly confirmed the previously reported elevated ventricular vols. in the SHR strain. A significant difference in ventricular vol. between the two strains was detected above the age of 3 months. For mature animals above the age of 6 months the mean vol. in the SHR strain was elevated by about a factor of two compared to the WKY control animals.     

Acute and chronic restraint stress: effects on [I]-galanin binding in normotensive and hypertensive rat brain

The neuropeptide galanin (GAL) has been implicated in the neural response to a number of stressors including restraint; however, the effect of restraint stress on GAL receptor density in the central nervous system (CNS) has not been investigated. Normotensive (Wistar-Kyoto; WKY) and hypertensive (spontaneously hypertensive; SHR) rats were subjected to a daily 60-min restraint stress paradigm for 0 (control), 1, 3, 5 or 10 consecutive days, and the density of [¹²⁵I]-GAL binding sites following exposure to restraint was compared between strains using quantitative autoradiography. Significant differences in basal (no stress) levels of GAL receptor density between WKY and SHR were detected in regions such as the central nucleus of the amygdala (Ce) and ventromedial hypothalamus (VMH) (P<0.05). In WKY, restraint stress (1 day) induced significant decreases in GAL receptor density in forebrain regions such as the Ce (−41%) and medial nucleus of the amygdala (−41%) (P<0.05). Chronic restraint (10 days) did not induce significant decreases in these nuclei in WKY, indicating that forebrain neurons containing GAL receptors in WKY possessed a functional ability to adapt to repeated restraint. In addition, restraint stress induced significant decreases in GAL receptor density in SHR in regions such as the lateral parabrachial nucleus (−43%; 5 days of restraint) and hypoglossal nucleus (−18% for entire restraint period) (P<0.05). In conclusion, restraint stress resulted in region- and strain-specific alterations in GAL receptor density, some of which may contribute to the altered stress response previously observed in hypertensive rats. The results clearly support the hypothesis that neuropeptides such as GAL are an integral component of the neural response to psychological stress, although the functional significance of the changes in GAL receptor density described in this study awaits elucidation.     

Extracellular glutamate and dopamine measured by microdialysis in the rat striatum during blockade of synaptic transmission in anesthetized and awake rats

We investigated the effect of high dose tetrodotoxin (TTX) on microdialysis measurements of extracellular striatal glutamate and dopamine in normal female rats. Both halothane-anesthetized rats with acutely implanted microdialysis probes and awake rats with microdialysis probes implanted for 24 h were tested. Glutamate levels in awake rats were 45% higher than those of anesthetized rats. Extracellular glutamate remained TTX-insensitive irregardless of TTX concentration, anesthesia, or time lapsed after probe implantation. In contrast, TTX reduced dialysate dopamine in all TTX concentrations tested. We speculate that the lower glutamate levels in anesthetized rats reflect the effect of anesthesia. Because glutamate is involved, either as a reactant or a product in a variety of reactions critical to intermediary metabolism in the brain, basal dialysate glutamate levels might indirectly reflect brain metabolism. Further, we conclude that extracellular glutamate collected during non-stimulated conditions is TTX-insensitive. The fact that glutamate levels are TTX-independent does not rule out that glutamate is synaptic in origin but rather demonstrates that it is not nerve impulse-dependent. However, the brain interstitial glutamate pool accessible to the microdialysis probe during control conditions is most likely isolated from the synapse, and therefore does not impose a neurotoxic potential.     

Substrate specificity and developmental aspects of a presynaptic GABA receptor regulating glutamate release in the rat cerebellum

In order to better characterize the presynaptic GABA receptors regulating glutamate release in the cerebellum [Levi and Gallo, 1981], a number of GABA agonists and GABA transport inhibitors were tested for their ability to potentiate the depolarization-induced release of the glutamate analog D-[3H]aspartate from superfused cerebellar synaptosomes. Of all the compounds tested, only those which are known to interact specifically with GABA receptors were effective when tested on synaptosomal preparations. The order of effectiveness found was the following: muscimol congruent to 3-APS greater than or equal to P4S greater than isoguvacine greater than THIP. GABA uptake inhibitors were unable to enhance D-[3H]aspartate evoked release from synaptosomes, but were effective when tested in cerebellar slices; in the latter case, the activation of the GABA receptors may be achieved indirectly, through an increase of the extracellular GABA concentrations. The substrate specificity of the presynaptic GABA receptors regulating cerebellar acidic amino acid release appears to be similar to that reported for GABA receptors in radioligand binding studies and for GABA autoreceptors. Studies on synaptosomes from immature cerebella suggested that the presence of the potentiating effect on the acidic amino acid release by GABA agonists is correlated with the development of the parallel fiber terminals, which are believed to be the main site from which glutamate is released in the adult cerebellum.     

Systemic phencyclidine administration is associated with increased dopamine,GABA, and 5-HIAA levels in the dorsolateral striatum of conscious rats: an in vivo microdialysis study

Summary In vivo microdialysis was used to study the effects of systemically administered phencyclidine (PCP, 10 mg/kg) on the extracellular levels of dopamine, dihydroxyphenylacetate (DOPAC), homovanillate (HVA), 5-hydroxy-indolacetate (5-HIAA), -aminobutyrate (GABA), glutamate, and aspartate in the rat dorsolateral striatum. In order to demarcate the effects of anesthesia, tissue trauma and gliosis, the effect of PCP was studied in both anesthetized rats with long and short probe implantation periods and in conscious rats with a long probe implantation period. PCP significantly increased the extracellular levels of dopamine in all experimental groups, though the post-implantation interval and anesthesia modulated the degree of increase. PCP increased 5-HIAA levels in both conscious and anesthetized rats after a long post-implantation period and HVA only in anesthetized rats after a long post-implantation period. Glutamate, aspartate, and DOPAC were not affected by PCP challenge but our study indicated for the first time that systemic PCP elevates extracellular GABA in conscious rats.     

Effects of stress and corticosterone on activity and plasticity in the amygdala

The basolateral amygdala (BLA) has been repeatedly shown to mediate the effects of stress on memory-related processes. However, the way in which stress influences BLA itself has not been fully explored. We studied the effects of stress and corticosterone (CORT) on activity and plasticity in the BLA in the rat, using the electrophysiological procedure of long-term potentiation (LTP) induction in vivo. Rats were exposed to an acute elevated-platform stress or administered vehicle or 5 mg/kg, 10 mg/kg, or 25 mg/kg of CORT systemically, after which they were anesthetized and prepared for field potential recording in the BLA, in response to stimulation of the entorhinal cortex. The elevated platform stress enhanced baseline responses in BLA and plasma CORT but inhibited amygdalar LTP. Systemic injections of CORT enhanced baseline responses in BLA in a dose-dependent manner but did not influence amygdalar LTP. Posttetanic potentiation (PTP) was similarly reduced in CORT- and vehicle-injected groups, possibly because of an additional stress from the injection, thus implying that PTP and LTP in the amygdala differentially react to stress. These results suggest that the increase in amygdalar baseline activity following the exposure to stress may be mediated by the concomitant increase in plasma CORT. However, the suppression of amygdalar LTP is not a result of elevated levels of CORT, suggesting that activity and plasticity in the amygdala might be mediated by different mechanisms.     

Sympathetic inhibition and attenuation of spontaneous hypertension by PVN lesions in rats

To determine whether the paraventricular nucleus (PVN) contributes to the development of hypertension in spontaneously hypertensive rats (SHR), we compared cardiovascular responses to ganglionic blockade with hexamethonium or vasopressin antagonism with dPVAVP in sham-operated or PVN lesioned SHR and Wistar-Kyoto rats (WKY). Lesions were produced electrolytically when the rats were 5 weeks old. During the next 3 weeks, tail-cuff measurements showed that the development of hypertension in SHR was inhibited, while systolic pressure in WKY was unaffected. Mean pressures recorded directly from the femoral artery at 8 weeks of age were lower in lesioned than in sham-operated SHR (141 +/- 5 vs 110 +/- 3 mm Hg, P less than 0.05), but did not differ in corresponding WKY groups (110 +/- 4 vs 112 +/- 5 mm Hg). Depressor responses to ganglionic blockade induced by i.v. injection of hexamethonium (25 mg/kg) were significantly larger in sham-operated than in lesioned SHR (-41 +/- 4% vs -28 +/- 3%, P less than 0.05). By contrast, vasopressin antagonism with dPVAVP did not alter blood pressure in all rat groups. In 24-h urine samples, excretion of vasopressin was unaffected, but that of norepinephrine was significantly reduced in lesioned SHR. These findings suggest that the PVN contributes to the development of spontaneous hypertension by sympathetic activation without increasing vasopressin secretion.     

Differential Regulation of the Renin-Angiotensin System by Nicotine in WKY and SHR Glia

Given that (1) the renin-angiotensin system (RAS) is compartmentalized within the central nervous system in neurons and glia (2) the major source of brain angiotensinogen is the glial cells, (3) the importance of RAS in the central control of blood pressure, and (4) nicotine increases the probability of development of hypertension associated to genetic predisposition; the objective of the present study was to evaluate the effects of nicotine on the RAS in cultured glial cells from the brainstem and hypothalamus of Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Ligand binding, real-time PCR and western blotting assays were used to compare the expression of angiotensinogen, angiotensin converting enzyme, angiotensin converting enzyme 2 and angiotensin II type1 receptors. We demonstrate, for the first time, that there are significant differences in the basal levels of RAS components between WKY and SHR rats in glia from 1-day-old rats. We also observed that nicotine is able to modulate the renin-angiotensin system in glial cells from the brainstem and hypothalamus and that the SHR responses were more pronounced than WKY ones. The present data suggest that nicotine effects on the RAS might collaborate to the development of neurogenic hypertension in SHR through modulation of glial cells.