Role of prefrontal cortex glucocorticoid receptors in stress and emotion.

BACKGROUND: Stress-related disorders (e.g., depression) are associated with hypothalamic-pituitary-adrenocortical axis dysregulation and prefrontal cortex (PFC) dysfunction, suggesting a functional link between aberrant prefrontal corticosteroid signaling and mood regulation. METHODS: We used a virally mediated knockdown strategy (short hairpin RNA targeting the glucocorticoid receptor [GR]) to attenuate PFC GR signaling in the rat PFC. Adult male rats received bilateral microinjections of vector control or short hairpin RNA targeting the GR into the prelimbic (n = 44) or infralimbic (n = 52) cortices. Half of the animals from each injection group underwent chronic variable stress, and all were subjected to novel restraint. The first 2 days of chronic variable stress were used to assess depression- and anxiety-like behavior in the forced swim test and open field. RESULTS: The GR knockdown confined to the infralimbic PFC caused acute stress hyper-responsiveness, sensitization of stress responses after chronic variable stress, and induced depression-like behavior (increased immobility in the forced swim test). Knockdown of GR in the neighboring prelimbic PFC increased hypothalamic-pituitary-adrenocortical axis responses to acute stress and caused hyperlocomotion in the open field, but did not affect stress sensitization or helplessness behavior. CONCLUSIONS: The data indicate a marked functional heterogeneity of glucocorticoid action in the PFC and highlight a prominent role for the infralimbic GR in appropriate stress adaptation, emotional control, and mood regulation.

Effect of liver ischemia-reperfusion injury on the activity of neurons in the rat brain.

Liver ischemia-reperfusion injury (LIRI) influences different body cells. Little is known about the effect of LIRI on the activity of neurons. Response of neurons to: (1) single ligation of hepatic artery (LIRIa) for 30 min and (2) combined ligation of portal triade (common hepatic artery, portal vein, common bile duct, LIRIb) for 15 min was investigated in Wistar rats. Ninety minutes, 5 h, and 24 h after liver reperfusion, alanine aminotransferase (ALT) and aspartate aminotransferase (AST), interleukin 1alpha (IL-1alpha), and tumor necrosis factor alpha (TNFalpha) serum levels were analyzed and Fos-immunolabeled cells counted in subfornical organ (SFO), suprachiasmatic (SCH), paraventricular (PVN), supraoptic (SON), arcuate (ARC), and ventromedial (VMN) hypothalamic nuclei, locus coeruleus (LC), nucleus of the solitary tract (NTS), and A1/C1 catecholaminergic cell groups. LIRIb increased ALT serum level after 90 min and 24 h while AST activity only after 24 h in all experimental groups. IL-1alpha serum level was increased only after 90 min of LIRIb while TNFalpha level did not change. Ninety minutes after surgeries more Fos-immunostained cells occurred in both LIRIs than sham-operated animals in all structures studied. More distinct Fos expression occurred after LIRIb than LIRIa in SON, PVN, VMN, and NTS. Five hours after both LIRIs, Fos increased in the parabrachial nucleus (PBN) and NTS. Twenty-four hours after both LIRIs Fos incidence decreased in all groups. Although the present data indicate that increased neuronal activity after both LIRIs is mainly a consequence of the liver damage itself partial impact of non-specific factors can not be excluded. However, the anatomical distribution of Fos occurrence detected after LIRIs gives great opportunity to perform a targeted phenotypic identification of the activated neurons by LIRIs in the subsequent experiments.

Brain response to induced peripheral cancer development in rats: dual fos-tyrosine hydroxylase and fos-oxytocin immunohistochemistry.

OBJECTIVE: During last few decades a considerable number of data has emerged supporting the hypothesis that central nervous system might monitor and modulate tumor growth. This assumption is based on two facts: 1. immune system plays a crucial role in the development and progression of cancer; 2. immune and nervous systems communicate tightly and bidirectionally. The aim of present study was to elucidate whether tumor growth may induce detectable changes in brain structures that are involved in the response to immune challenges. METHODS: Using Fos immunohistochemistry, we investigated whether the advanced stage of cancer, induced by a single intraperitoneal injection of BP6-TU2 fibrosarcoma cells to male Wistar rats, could activate Fos expression in the nucleus of the solitary tract (NTS), amygdala and parabrachial nuclei (PBN) and also activate some of neuronal phenotypes including tyrosine hydroxylase (TH) neurons in the brainstem noradrenergic cell groups and hypothalamic oxytocinergic neurons. RESULTS: Twenty eight days after the initiation of tumor process we found increased Fos expression in NTS/A2, A1 noradrenergic cells, PBN as well as in the hypothalamic paraventricular, supraoptic and accessory oxytocinergic neurons. These structures are involved in the transmission of signals related to immune challenges within the brain and consequent elaboration of neuro-endocrine responses. CONCLUSIONS: The data obtained are supporting the view that the information on peripheral tumor development might be transmitted to the brain. However, further studies are necessary to be performed to reveal whether our findings can be attributed to specific effect of cancer or whether observed changes in the activity of brainstem and hypothalamic neurons reflex processes that only accompany the cancer progression.

Alpha2-adrenergic impact on hypothalamic magnocellular oxytocinergic neurons in long evans and brattleboro rats: effects of agonist and antagonists.

We have previously demonstrated that alpha2-adrenoceptors regulate hypothalamic magnocellular oxytocinergic (OXY) neurons in Sprague Dawley rats. Here we investigated whether activation/inhibition of alpha2-adrenoceptors may similarly trigger/downregulate the activity of OXY neurons in control Long Evans (+/+) and permanently osmotically stressed Brattleboro (di/di) rats. The effect of alpha2-adrenoceptor agonist, xylazine (XYL) and alpha2-adrenoceptor antagonists, atipamezole (ATIP), and idazoxan (IDX) were evaluated in the supraoptic (SON) and paraventricular (PVN) hypothalamic nuclei. Saline (SAL, 0.1 ml/100 g), XYL (10 mg/kg), ATIP, (1 mg/kg), and IDX (10 mg/kg) and IDX or ATIP followed by XYL were applied intraperitoneally. Rats were sacrificed 90 min later and Fos/OXY co-labelings analyzed in microscope. In control +/+ rats no or few Fos/OXY co-labelings occurred in SON and PVN. XYL significantly increased Fos incidence in OXY neurons in both nuclei. ATIP significantly suppressed the effect of XYL in both nuclei and IDX only in SON. In di/di controls 81% of OXY neurons in SON and 44% in PVN revealed Fos presence and XYL did not further elevate Fos number in SON OXY neurons and slightly increased Fos number in PVN. ATIP or IDX only partially reduced Fos in SAL or XYL treated di/di rats. Our data indicate that: (1) XYL stimulation is not effective in di/di rats because of sustained upregulation of OXY neurons activity and (2) neither ATIP nor IDX reduced significantly the OXY activity in control di/di rats. These findings suggest that alpha2-adrenoceptors have only a limited impact in maintaining OXY cells activity upregulation in PVN and SON of di/di rats.

Fos expression in hypocretinergic neurons in C57B1/6 male and female mice after long-term consumption of high fat diet.

OBJECTIVE: It is generally known that hypocretin (Hcrt) neurons in lateral hypothalamus (LH) are involved in feeding behaviour. The aim of this study was to reveal the activity response of Hcrt neurons, as measured by Fos protein incidence, to prolonged high fat (HF) diet in the LH of both genders of C57B1/6 mice. METHODS: Standard (St) and high fat (HF) diets were available to mice for 16 weeks and thereafter the animals were perfused transcardially with fixative. Then the brains were removed, soaked with 15 % sucrose in 0.1 M phosphate buffer (PB), and cryo-sectioned throughout the hypothalamus into 35 microm thick coronal sections. Fos/Hcrt co-localizations were processed by employing avidin-biotin-peroxidase (ABC) complex and diaminobenzidine chromogen for Hcrt labeling. Fos immunoproduct was intensified by nickel chloride as a black color inducer. Evaluation of the incidence of Fos/Hcrt co-labeled perikarya was performed using a computerized Leica light microscopy. RESULTS: The effect of of mice gender, applied diet, and gender plus applied diet on the activation of Hcrt neurons was found. Turkey s test revealed significant (p<0.05) rise in Fos labeled Hcrt neurons in male vs. female mice after consumption of both types of diets: St (44.64 +/- 2.28 % vs. 1.47 +/- 0.195 %, resp.) and HF (44.15 +/- 3.77 % vs. 24.32 +/- 0.7 %, resp.). This showed that HF diet significantly elevated the number of activated Hcrt neurons only in female mice (24.32 +/- 0.7 % in HF fed vs. 1.47 +/- 0.195 % in St fed, p<0.05). The body weight and accumulation of body fat in animals (body fat weight expressed as % of body weight) were influenced by gender and applied diet, although the body fat weight was influenced by HF diet (more noticeably in females). CONCLUSION: The data indicated a positive correlation between body weight, fat gain, and Hcrt activities in females but not in males, thus accentuating the importance of the gender impact.

Response of substances co-expressed in hypothalamic magnocellular neurons to osmotic challenges in normal and Brattleboro rats.

The intention of this review is to emphasize the current knowledge about the extent and importance of the substances co-localized with magnocellular arginine vasopressin (AVP) and oxytocin (OXY) as potential candidates for the gradual clarification of their actual role in the regulation of hydromineral homeostasis. Maintenance of the body hydromineral balance depends on the coordinated action of principal biologically active compounds, AVP and OXY, synthesized in the hypothalamic supraoptic and paraventricular nuclei. However, on the regulation of water-salt balance, other substances, co-localized with the principal neuropetides, participate. These can be classified as (1) peptides co-localized with AVP or OXY with unambiguous osmotic function, including angiotensin II, apelin, corticotropin releasing hormone, and galanin and (2) peptides co-localized with AVP or OXY with an unknown role in osmotic regulation, including cholecystokinin, chromogranin/secretogranin, dynorphin, endothelin-1, enkephalin, ferritin protein, interleukin 6, kininogen, neurokinin B, neuropeptide Y, vasoactive intestinal peptide, pituitary adenylate cyclase-activating polypeptide, TAFA5 protein, thyrotropin releasing hormone, tyrosine hydroxylase, and urocortin. In this brief review, also the responses of these substances to different hyperosmotic and hypoosmotic challenges are pointed out. Based on the literature data published recently, the functional implication of the majority of co-localized substances is still better understood in non-osmotic than osmotic functional circuits. Brattleboro strain of rats that does not express functional vasopressin was also included in this review. These animals suffer from chronic hypernatremia and hyperosmolality, accompanied by sustained increase in OXY mRNA in PVN and SON and OXY levels in plasma. They represent an important model of animals with constantly sustained osmolality, which in the future, will be utilizable for revealing the physiological importance of biologically active substances co-expressed with AVP and OXY, involved in the regulation of plasma osmolality.

Activity of brain stem groups of catecholaminergic cells in tumor-bearing rats: response to immobilization stress.

The aim of the present study was to investigate the activity of tyrosine hydroxylase (TH) immunopositive neurons, measured by Fos protein expression, in the hindbrain noradrenergic (NA) cell groups in animals exposed to visceral tumor growth for 28 days induced by intraperitoneal implantation of fibrosarcoma cells. We were also interested in determining whether brain stem NA neurons of tumor-bearing and intact animals exhibit similarities in their response to a strong heterotypic stimulus-immobilization (IMO) stress. We found increased Fos expression in NA cells of the nucleus tractus solitarii (A2 cell group) and of the A1 cell group of tumor-bearing rats. However, Fos expression in other brain stem NA cell groups, including A5, locus ceruleus, and A7, were similar to control rats. The effect of 60 min of IMO was evident in both groups, but there were no differences between Fos expression in brain stem NA cell groups in control and tumor-bearing rats. This indicates that the sensitivity of NA cells in tumor-bearing animals was not altered by the IMO-induced stress challenge. However, whether the increased Fos expression in NA cells in tumor-bearing animals is a consequence of a specific visceral response activated by cancer development or just a nonspecific event accompanying the cancer progression requires further study.

Activity of oxytocinergic neurons in the supraoptic nucleus under stimulation of alpha2-adrenoceptors in Brattleboro rats.

Vasopressin (AVP) deficient homozygous Brattleboro rats exhibit severe osmotic challenges due to waterless chronic hypernatremia and hyperosmolality. We investigated the effect of xylazine, an alpha2-adrenoceptor agonist, on the activity of oxytocinergic (OXY) neurons in the supraoptic nucleus (SON) of homozygous (di/di), heterozygous (di/+), and control (+/+) rats. Ninety minutes after saline (0.1 mL/100 g b.w., i.p.) or xylazine injection (10 mg/kg, i.p.) rats were anaesthetized with pentobarbital (50 mg/kg i.p.) and sacrificed by transcardial perfusion with fixative. Activity of OXY neurons was evidenced by nuclear Fos protein immunoreactivity. Fos/OXY colabelings were analyzed on 40-mum thick coronal sections using computerized light microscope. As expected, plasma osmolality and water intake revealed high heterogenity within the di/di group of rats. Fos expression in SON of di/di rats was correlated with osmolality of each rat. In saline-treated rats, maximum activation of Fos reached around 4% in +/+, 20% in di/+ rats, and as much as 60% in di/di rats. Xylazine activated in SON about 70% of OXY-ergic neurons in +/+, 60% in di/+ rats, and more than 80% in di/di rats. The present findings indicate that in spite of the high spontaneous activity of SON OXY-ergic neurons due to the AVP deficiency in di/di rats, many of the silent OXY-ergic neurons in the SON remained acceptable for alpha2-adrenoceptor stimulation.

GABA regulates the rat hypothalamic-pituitary-adrenocortical axis via different GABA-A receptor alpha-subtypes.

The control of the corticotropin-releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus (PVN) is balanced by excitatory and inhibitory inputs. The GABA-A receptor, which is a major target for the inhibitory control, is composed of five subunits. The presence of an alpha(1)-, alpha(2)-, alpha(3)-, or alpha(5)-subunit in the GABA-A receptor protein complex is necessary for benzodiazepines to exert their potentiating effect on the receptor. We postulate that the effect of nonselective benzodiazepines on the hypothalamo-pituitary adrenocortical (HPA) axis is critically dependent on the composition of the GABA-A receptor subunits through which they act. We show here that positive modulators of alpha(1)-subtype containing GABA-A receptors with zolpidem (10 mg/kg) increase HPA activity in terms of increase in plasma corticosterone and induction of Fos in the PVN, whereas activation of non-alpha(1)-subtype GABA-A receptors using L-818,417 (10 mg/kg) likely inhibits the activity. We also show that the alpha(2)-subunit gene is highly expressed in the PVN, but its expression is not affected by chronic mild stress. These results show that the stimulatory effect on HPA activity after positive modulation of GABA-A receptors composed of alpha(1)-subunit(s) affects a selective afferent system than the PVN, which is distinct from another afferent system(s) activated by non alpha(1)-containing GABA-A receptors.

Improvement in the evaluation of Fos-neuropeptide colocalization by employing free-floating cryosections of delicate thickness: double and triple colored immunohistochemistry.

OBJECTIVE: The present study was aimed to select a methodical approach to optimize the thickness of cryo-processed free-floating sections for precise recognition between a single Fos signal and Fos/neuropeptide colocalizations in sequential double or triple colored immunohistochemical stainings. For this purpose brain sections of variable (5-20 microm) thickness were tested utilizing enzyme-substrate detection system employing oxytocin (OXY) and vasopressin (AVP) antisera. METHODS: The animals were perfused by fixative 90 min after i.p. administration of 5 ml of hypertonic saline (1.5 M NaCl) which was used to stimulate the hypothalamic osmosensitive neurons. The brains were removed, soaked with 30% sucrose in 0.1 M PBS, cryo-sectioned throughout the hypothalamus into 5, 10, 15, and 20 microm thick coronal sections, collected and washed in 0.2 M glycine buffer for 10-15 min, and finely stored in 0.1 M PBS. Single Fos and Fos/OXY and Fos/ OXY/AVP colocalizations were processed employing avidin-biotin-peroxidase (ABC) complex and diaminobenzidine chromogen with or without adding Nickel chloride salt as a black and blue color inducer. Evaluation of the Fos-neuropeptide co-labeled perikarya manifestation was performed on a computerized Leica light microscopy. RESULTS: The present data demonstrate that cryoprocessing enables generate free- floating sections of 5, 10, 15, and 20 microm thickness. Except the 5 microm thickness, all the other sections sizes tested exhibited well preserved tissue stability and excellent immunohistochemical properties either for single Fos reaction or double Fos/OXY and triple Fos/OXY/AVP costainings. CONCLUSIONS: We adapted and optimized Fos immunohistochemistry for use of fixed and cryocut processed free-floating brain sections. The present data indicate that except 5 mum thickness all the other sorts of cryosections tested were sufficiently resilient for performing a sequential double or triple colored immunohistochemical stainings. However, 10 mum thickness reached the borderline of the handling safety, therefore, 15 mum section thickness will be the thickness of the choice recommended, which gave relevant immunoreaction, retained good tissue preservation, and ensured an appropriate clarity for accurate recognition between a single and colocalized Fos signals.

Zolpidem, a selective GABA(A) receptor alpha1 subunit agonist, induces comparable Fos expression in oxytocinergic neurons of the hypothalamic paraventricular and accessory but not supraoptic nuclei in the rat.

Functional activation of oxytocinergic (OXY) cells in the hypothalamic paraventricular (PVN), supraoptic (SON), and accessory (ACC) nuclei was investigated in response to acute treatment with Zolpidem (a GABA(A) receptor agonist with selectivity for alpha(1) subunits) utilizing dual Fos/OXY immunohistochemistry. Zolpidem was administered intraperitoneally in dose 10 mg/kg of BW and 60 min later the animals were sacrificed by transcardial perfusion with fixative. The Fos/OXY co-labelings were analyzed on 40 microm thick serial coronal sections using computerized light microscopy. Zolpidem elicited a concordant Fos/OXY staining in all four PVN sub-areas investigated, including the anterior (15.71+/-2.35%), middle (14.52+/-2.53%), dorsal (13.34+/-2.61%), and periventricular (18.21+/-4.75%) ones, however, had no significant stimulatory effect on OXY cells in the SON. In response to Zolpidem, statistically significant activations were also seen in certain groups of accessory structures including the circular nucleus (13.99+/-3.43%), small clusters of accessory neurons (10.55+/-1.94%), and the lateral hypothalamic perivascular nucleus (9.42+/-2.74%). Between the naive and vehicle controls, the dual Fos/OXY labelings did not elicit any significant differences. Our data provide insight into the topographic patterns of brain activity within the clusters of magnocellular OXY cells in the hypothalamus associated with stimulation of GABA(A) benzodiazepine receptors and for the first time illustrate the triggering contemporaneousness within the cells of the principal and accessory magnocellular nuclei in response to Zolpidem treatment. The present study provides a comparative background that may help in the further understanding of a possible extend of Zolpidem effect on the brain.