Effect of estradiol benzoate microinjection into the median raphe nucleus on contextual conditioning

Estrogen deficiency has been associated with stress, anxiety and depression. Estrogen receptors have been identified in the median raphe nucleus (MRN). This structure is the main source of serotonergic projections to the hippocampus, a forebrain area implicated in the regulation of defensive responses and in the resistance to chronic stress. There is reported evidence indicating that estrogen modulates 5-HT(1A) receptor function. In the MRN, somatodendritic 5-HT(1A) receptors control the activity of serotonergic neurones by negative feedback. The present study has evaluated the effect of intra-MRN injection of estradiol benzoate (EB, 600 or 1200 ng/0.2 mu l) on the performance of ovariectormized rats submitted to contextual conditioning. Additionally, the same treatment was given after intra-MRN injection of Way 100635 (100 ng/0.2 mu l). a 5-HT(1A) receptor antagonist. Both doses of EB decreased freezing and increased rearing, indicating an anxiolytic effect. Pretreatment with Way 100635 antagonized the anxiolytic effect of estradiol. On the basis of these results, it may be suggested that estrogens modulate anxiety by acting on 5-HT(1A) receptors localized in the MRN. (C) 2009 Elsevier B.V. All rights reserved.

Role of N-Methyl-D-Aspartate and Non-N-Methyl-D-Aspartate Receptors in the Cardiovascular Effects of L-Glutamate Microinjection Into the Hypothalamic Paraventricular Nucleus of Unanesthetized Rats

We report on the cardiovascular effects of L-glutamate (L-glu) microinjection into the hypothalamic paraventricular nucleus (PVN) as well as the mechanisms involved in their mediation. L-glu microinjection into the PVN caused dose-related pressor and tachycardiac responses in unanesthetized rats. These responses were blocked by intravenous (i.v.) pretreatment with the ganglion blocker pentolinium (PE; 5 mg/kg), suggesting sympathetic mediation. Responses to L-glu were not affected by local microinjection of the selective non-NMDA receptor antagonist NBQX (2 nmol) or by local microinjection of the selective NMDA receptor antagonist LY235959 (LY; 2 nmol). However, the tachycardiac response was changed to a bradycardiac response after treatment with LY235959, suggesting that NMDA receptors are involved in the L-glu heart rate response. Local pretreatment with LY235959 associated with systemic PE or dTyr(CH(2))(5)(Me)AVP (50 mu g/kg) respectively potentiated or blocked the response to L-glu, suggesting that L-glu responses observed after LY235959 are vasopressin mediated. The increased pressor and bradycardiac responses observed after LY + PE was blocked by subsequent i.v. treatment with the V(1)-vasopressin receptor antagonist dTyr(CH(2))(5)(Me)AVP, suggesting vasopressin mediation. The pressor and bradycardiac response to L-glu microinjection into the PVN observed in animals pretreated with LY + PE was progressively inhibited and even blocked by additional pretreatment with increasing doses of NBQX (2, 10, and 20 nmol) microinjected into the PVN, suggesting its mediation by local non-NMDA receptors. In conclusion, results suggest the existence of two glutamatergic pressor pathways in the PVN: one sympathetic pathway that is mediated by NMDA receptors and a vasopressinergic pathway that is mediated by non-NMDA receptors. (C) 2009 Wiley-Liss, Inc.

Anxiolytic-like effect of noradrenaline microinjection into the dorsal periaqueductal gray of rats

The brain noradrenergic system has been implicated in the expression of defensive behaviors elicited by acute stress. The dorsal periaqueductal gray area (dPAG) is a key structure involved in the behavioral and cardiovascular responses elicited by fear and anxiety situations. Although there are noradrenergic terminals in the dPAG, few studies have investigated the role of noradrenaline (NA) in the dPAG on anxiety modulation. The aim of this study was to evaluate the effect of NA microinjection into the dPAG of rats subjected to two animal models of anxiety, the elevated plus-maze and the Vogel conflict test. Male Wistar rats implanted with a guide cannula aimed at the dPAG received microinjections of NA (3, 15, or 45 nmol/0.05 mu l) or artificial cerebral spinal fluid into the dPAG immediately before being exposed to the elevated plus-maze or the Vogel conflict test. NA increased the exploration of the open arms and the number of enclosed arm entries in the elevated plus-maze. The increase in open arm exploration remained significant after being subjected to an analysis of covariance using the latter variable as covariate. Moreover, the NA microinjection into the dPAG did not increase general exploratory activity of animals subjected to the open-field test, indicating that the increase in open arm exploration cannot be attributed to a nonspecific increase in exploratory activity. In the Vogel test, the NA microinjection into the dPAG increased the number of punished licks without changing the number of nonpunished licks or interfering with the tail-flick test. The results, therefore, indicate that the NA microinjection into the dPAG produces anxiolytic-like effects, suggesting its possible involvement in the anxiety modulation. Behavioural Pharmacology 20:252-259 (C) 2009 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.

Mechanisms involved in the pressor response to noradrenaline microinjection into the supraoptic nucleus of unanesthetized rats

We report on the cardiovascular effects of noradrenaline (NA) microinjection into the hypothalamic supraoptic nucleus (SON) as well as the central and peripheral mechanisms involved in their mediation. Microinjections of NA 1, 3, 10, 30 or 45 nmol/100 nL into the SON caused dose-related pressor and bradycardiac response in unanesthetized rats. The response to NA 10 nmol was blocked by SON pretreatment with 15 nmol of the alpha(2)-adrenoceptor antagonist RX821002 and not affected by pretreatment with equimolar dose of the selective alpha(1)-adrenoceptor antagonist WB4101, suggesting that local alpha(2)adrenoceptors mediate these responses. Pretreatment of the SON with the nonselective beta-adrenoceptor antagonist propranolol 15 nmol did not affect the pressor response to NA microinjection of into the SON. Moreover, the microinjection of the 100 nmol of the selective alpha(1)-adrenoceptor agonist methoxamine (MET) into the SON did not cause cardiovascular response while the microinjection of the selective alpha(2)adrenoceptor agonists BHT920 (BHT, 100 nmol) or clonidine (CLO, 5 nmol) caused pressor and bradycardiac responses, similar to that observed after the microinjection of NA. The pressor response to NA was potentiated by intravenous pretreatment with the ganglion blocker pentolinium and was blocked by intravenous pretreatment with the V(1)-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP, suggesting an involvement of circulating vasopressin in this response. In conclusion, our results suggest that pressor responses caused by microinjections of NA into the SON involve activation of local alpha(2)-adrenoceptor receptors and are mediated by vasopressin release into circulation. (c) 2008 Published by Elsevier B.V.

Cardiovascular responses to microinjection of noradrenaline into the medial amygdaloid nucleus of conscious rats result from alpha(2)-receptor activation and vasopressin release

The medial amygdaloid nucleus (MeA) is involved in the modulation of physiological and behavioral processes, as well as regulation of the autonomic nervous system. Moreover, MeA electrical stimulation evokes cardiovascular responses. Thus, as noradrenergic receptors are present in this structure, the present study tested the effects of local noradrenaline (NA) microinjection into the MeA on cardiovascular responses in conscious rats. Moreover, we describe the types of adrenoceptor involved and the peripheral mechanisms involved in the cardiovascular responses. Increasing doses of NA (3, 9, 27 or 45 nmol/100 nL) microinjected into the MeA of conscious rats caused dose-related pressor and bradycardic responses. The NA cardiovascular effects were abolished by local pretreatment of the MeA with 10 nmol/100 nL of the specific alpha(2)-receptor antagonist RX821002, but were not affected by local pretreatment with 10 nmol/100 nL of the specific alpha(1)-receptor antagonist WB4101. The magnitude of pressor response evoked by NA microinjected into the MeA was potentiated by intravenous pretreatment with the ganglion blocker pentolinium (5 mg/kg), and blocked by intravenous pretreatment with the selective V(1)-vasopressin antagonist dTyr(CH(2))(5)(Me)AVP (50 mu g/kg). In conclusion, our results show that microinjection of NA into the MeA of conscious rats activates local alpha(2)-adrenoceptors, evoking pressor and bradycardic responses, which are mediated by vasopressin release.

Cardiovascular responses to noradrenaline microinjection in the ventrolateral periaqueductal gray of unanesthetized rats

The periaqueductal gray area (PAG) is a mesencephalic area involved in cardiovascular modulation. Noradrenaline (NA), a neurotransmitter involved in central blood pressure control, is present in the rat PAG. We report here on the cardiovascular effects caused by NA microinjection into the ventrolateral PAG (vlPAG) of unanesthetized rats and the peripheral mechanism involved in their mediation. NA microinjection in the vlPAG of unanesthetized rats evoked dose-related pressor and bradycardiac responses. No significant cardiovascular responses were observed in urethane-anesthetized rats. The pressor response was potentiated by pretreatment with the ganglion blocker pentolinium (5 or 10 mg/kg, intravenously). Pretreatment with the vasopressin antagonist dTyr(CH(2))(5) (Me)AVP (50 mu g/kg, intravenously) blocked the pressor response evoked by the NA microinjection into the vlPAG. Additionally, circulating vasopressin content was found to be significantly increased after NA microinjection in the vlPAG. The results suggest that activation of noradrenergic synapses within the vlPAG modulates vasopressin release in unanesthetized rats. (c) 2007 Wiley-Liss, Inc.

The ventrolateral periaqueductal gray is involved in the cardiovascular response evoked by L-glutamate microinjection into the lateral hypothalamus of anesthetized rats

Microinjection Of L-glutamate (L-glu: 1, 3, 10 and 30nmol/100nL) into the lateral hypothalamus (LH) caused dose-related depressor and bradycardiac responses. The cardiovascular response to L-glu stimulation of the LH was blocked by pretreatment of the ventrolateral portion of the periaqueductal gray matter (vIPAG) with CoCl(2) (1 mM/100nL), indicating the existence of a synaptic relay of the hypotensive pathway in that area. Furthermore, the response to L-glu Was blocked by pretreatment of the vIPAG with 2 nmol/100 nL of the selective NMDA-receptor antagonist LY235959 and was not affected by pretreatment with 2 nmol/100 nL of the selective non-NMDA-receptor antagonist NBQX, suggesting a mediation of the hypotensive response by NMDA receptors in the APAG. In conclusion, our results indicate that the hypotensive pathway activated by microinjection Of L-glu into the LH involves a NMDA synaptic relay in the vIPAG. (c) 2007 Elsevier Ireland Ltd. All rights reserved.

Cardiovascular effects of acetylcholine microinjection into the ventrolateral and dorsal periaqueductal gray of rats

In the present study, we describe the cardiovascular effects of local acetylcholine (Ach) microinjection into both the ventrolateral (vlPAG) and dorsal (dPAG) periaqueductal gray areas of anesthetized rats and the possible local receptors involved with these responses. Microinjection of Ach (9, 27, 45 or 81 nmol/50 nL) into the vlPAG caused dose-related depressor responses. These hypotensive responses were blocked by local pretreatment with increasing doses of the nonselective muscarinic antagonist atropine (1, 3 or 9 nmol/50 nL). The microinjection of Ach into the dPAG caused no significant cardiovascular responses in anesthetized rats. In conclusion, the present findings suggest that a cholinergic system present in the vlPAG, but not in the dPAG, is involved with cardiovascular system control. Moreover, these cardiovascular responses evoked by Ach are mediated by muscarinic receptors. (C) 2010 Elsevier B.V. All rights reserved.

Cardiovascular effects of noradrenaline microinjection into the medial part of the superior colliculus of unanesthetized rats

The superior colliculus (SC) is a mesencephalic area involved in the mediation of defensive movements associated with cardiovascular changes. Noradrenaline (NA) is a neurotransmitter with an important role in central cardiovascular regulation exerted by several structures of the central nervous system. Although noradrenergic nerve terminals have been observed in the SC, there are no reports on the effects of local NA injection into this area. Taking this into consideration, we studied the cardiovascular effects of NA microinjection into the SC of unanesthetized rats. Microinjection of NA into the SC evoked a dose-dependent blood pressure increase and a heart rate decrease in unanesthetized rats. The pressor response to NA was not modified by intravenous pretreatment with the vasopressin v(1)-receptor antagonist dTyr(CH(2))(5) (Me)AVP, indicating a lack of vasopressin involvement in the response mediation. The effect of NA microinjection into the SC was blocked by intravenous pretreatment with the ganglionic blocker pentolinium, indicating its mediation by the sympathetic nervous system. Although the pressor response to NA was not affected by adrenal demedullation, the accompanying bradycardia was potentiated, suggesting some involvement of the sympathoadrenal system in the cardiovascular response to NA microinjection into the SC. In summary, results indicate that stimulation of noradrenergic receptors in the SC causes cardiovascular responses which are mediated by activation of both neural and adrenal sympathetic nervous system components. (C) 2009 Elsevier B.V. All rights reserved.

Microinjection molding of polyamide 6/carbon nanotube composites

Microinjection molding of polymer composites with carbon nanotubes (CNT) requires previous production of the nanocomposites, often by melt extrusion. Each processing step has a thermo-mechanical effect on the polymer melt, conveying different properties to the final product. In this work, polyamide 6 and its composites with pristine and functionalized CNT (f-CNT) were processed by a mini twin-screw extrusion, followed by microinjection molding. The morphology induced on the polymer by each process was analyzed by differential scanning calorimetry and wide angle X-ray diffraction. Calorimetric analysis showed a secondary crystallization for the microinjected materials, absent for the extruded materials. The characterization of microinjected polyamide 6 by X-ray diffraction revealed a large contribution of the c phase to the total crystallinity, mainly in the skin region, while the nanocomposites and extruded materials were characterized by a larger contribution of the a phase. Functionalization of CNT did not affect significantly the polymer morphology compared to composites with pristine CNT.

The vasodilatory effect of juxta-arteriolar microinjection of endothelinA receptor inhibitor in healthy and acute branch retinal vein occlusion minipig retinas.

Purpose. To investigate the effect of the endothelin(A) receptor inhibitor BQ-123 on the retinal arteriolar vasculature in minipig retinas in normal eyes and eyes with acute branch retinal vein occlusion (BRVO). Methods. Seven healthy eyes of seven minipigs and six eyes of six minipigs with experimental BRVO were evaluated under systemic anesthesia. An intravitreal juxta-arteriolar microinjection of 30 microL BQ-123 0.61 microg/mL (pH 7.4) was performed in all but one eye from each group, into which the physiologic saline vehicle alone was injected. Vessel-diameter changes were measured with a retinal vessel analyzer. Results. In healthy minipig retinas (n = 6), arteriolar diameter (+/-SD) increased 6.19% +/- 3.55% (P < 0.05), 25.98% +/- 2.37% (P < 0.001), 23.65% +/- 1.2% (P < 0.001), and 16.84% +/- 1.95% (P < 0.001), at 1, 5, 10, and 15 minutes, respectively, after BQ-123 microinjection. Two hours after experimental BRVO (n = 5), the retinal arteriolar diameter had decreased (13.07% +/- 5.7%; P < 0.01). One, 5, 10, and 15 minutes after BQ-123 microinjection, retinal arteriolar diameter had increased by 7.14% +/- 3.3% (P < 0.01), 26.74% +/- 7.63% (P < 0.001), 23.67% +/- 6.4% (P < 0.001), and 16.09% +/- 3.41% (P < 0.001), respectively. Vehicle only injection had no vasoactive effect on physiologic or BRVO retinas. Conclusions. A significant increase in retinal arteriolar diameter was demonstrated after juxta-arteriolar BQ-123 microinjection in healthy and in acute BRVO minipig retinas. The results suggest a role for endothelin-1 in maintaining retinal basal arteriolar tone. Reversing the BRVO-related vasoconstriction by juxta-arteriolar BQ-123 microinjection could bring a new perspective to the management of BRVO.

Fate of cadmium in rat renal tubules: a microinjection study.

109Cd was injected into the lumen of superficial proximal or distal tubules of rat kidneys, and recovery in the pelvic urine from the ipsilateral kidney was measured. Fractional recovery of labeled inulin always exceeded 90%. About 70% of injected inorganic Cd (CdCl2) was taken up by the epithelium of proximal tubules, while more than 90% of the injected amount was recovered after distal microinjection. The proximal fractional Cd uptake of a 1:1 (molar) Cd-L-cysteine complex was 82%, but was below 60% for a 5-10:1 molar ratio of cysteine:Cd. The chelate Cd-pentetic acid was recovered in final urine nearly quantitatively after proximal or distal microinjection. Fractional uptake of 109Cd from a Cd-metallothionein (Mt) complex, following proximal microinjection, ranged between 17 (Cd-Mt 0.19 mM) and 8% (Cd-Mt 1.5 mM). It is concluded that luminal Cd uptake by the tubular epithelium depends markedly on the chemical form of Cd and, when present, occurs mostly or exclusively in proximal tubules.

Cardiovascular responses to microinjection of trans-(±)-ACPD into the NTS were similar in conscious and chloralose-anesthetized rats

The changes in mean arterial pressure (MAP) and heart rate (HR) in response to the activation of metabotropic receptors in the nucleus tractus solitarii (NTS) with trans-(±)-1-amino-1,3-cyclopentanedicarboxylic acid (trans-(±)-ACPD) were evaluated in conscious and anesthetized Wistar, male rats weighing 240-260 g (N = 8). The responses obtained with trans-(±)-ACPD were compared with the responses to L-glutamate (1 nmol/100 nl), since in a previous study we showed that anesthesia converted a pressor response to L-glutamate microinjected into the NTS of conscious rats to a depressor response in the same rats under urethane or chloralose anesthesia. Microinjection of 3 doses of trans-(±)-ACPD (100, 500 and 1000 pmol/100 nl) produced a dose-dependent fall in MAP (range, -20 to -50 mmHg) and HR (range, -30 to -170 bpm) under both conscious and chloralose anesthesia conditions. These data indicate that the cardiovascular responses to the activation of metabotropic receptors by trans-(±)-ACPD are not affected by chloralose anesthesia while the cardiovascular responses to the activation of excitatory amino acid (EAA) receptors by L-glutamate are significantly altered

Cardiovascular and respiratory responses to microinjection of L-glutamate into the caudal pressor area in conscious and anesthetized rats

The role of the caudal pressor area (CPA) in the maintenance of vasomotor tonus in anesthetized and decerebrate animals has been clearly established. In conscious animals, however, the participation of CPA in the cardiovascular control remains to be fully elucidated. In the present study, unilateral L-glutamate (L-Glu) (10 and/or 20 nmol/70 nl) microinjection into CPA, in conscious male Wistar rats (250-280 g) caused a significant increase in mean arterial blood pressure (MAP; control: 112 ± 1.9 mmHg; after 20 nmol L-Glu: 139 ± 4.5 mmHg, N = 12, P<0.05) and respiratory rate (control: 81 ± 3.5 breaths/min; after 10 nmol L-Glu: 92 ± 3 breaths/min, P<0.05; after 20 nmol L-Glu: 104 ± 5 breaths/min, N = 6, P<0.05). The subsequent anesthesia with urethane caused a significant increase in basal respiratory frequency (conscious: 81 ± 3.5 breaths/min; under urethane: 107 ± 1.3 breaths/min, N = 6, P<0.05). Anesthesia also significantly attenuated L-Glu-evoked pressor (conscious: deltaMAP = +27 mmHg; anesthetized: deltaMAP = +18 mmHg, P<0.05) and respiratory responses. These results suggest that glutamatergic receptors in the CPA are involved in cardiovascular and respiratory modulation in conscious rats.

Effect of estradiol benzoate microinjection into the median raphe nucleus on contextual conditioning

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