Infusion Of Artificial Cerebrospinal Fluid Research Articles

Enhanced pressor response to increased CSF sodium concentration and to central ANG I in heterozygous α2Na+-K+-ATPase knockout mice

Intracerebroventricular (ICV) infusion of NaCl mimics the effects of a high-salt diet in salt-sensitive hypertension, raising the sodium concentration in the cerebrospinal fluid (CSF [Na]) and subsequently increasing the concentration of an endogenous ouabain-like substance (OLS) in the brain. The OLS, in turn, inhibits the brain Na(+)-K(+)-ATPase, causing increases in the activity of the brain renin-angiotensin system (RAS) and blood pressure. The Na(+)-K(+)-ATPase alpha (catalytic)-isoform(s) that mediates the pressor response to increased CSF [Na] is unknown, but it is likely that one or more isoforms that bind ouabain with high affinity are involved (e.g., the Na(+)-K(+)-ATPase alpha(2)- and/or alpha(3)-subunits). We hypothesize that OLS-induced inhibition of the alpha(2)-subunit mediates this response. Therefore, a chronic reduction in alpha(2) expression via a heterozygous gene knockout (alpha(2) +/-) should enhance the pressor response to increased CSF [Na]. Intracerebroventricular (ICV) infusion of artificial CSF containing 0.225 M NaCl increased mean arterial pressure (MAP) in both wild-type (+/+) and alpha(2) +/- mice, but to a greater extent in alpha(2) +/-. Likewise, the pressor response to ICV ouabain was enhanced in alpha(2) +/- mice, demonstrating enhanced sensitivity to brain Na(+)-K(+)-ATPase inhibition per se. The pressor response to ICV ANG I but not ANG II was also enhanced in alpha(2) +/- vs. alpha(2)+/+ mice, suggesting an enhanced brain RAS activity that may be mediated by increased brain angiotensin converting enzyme (ACE). The latter hypothesis is supported by enhanced ACE ligand binding in the organum vasculosum laminae terminalis. These studies demonstrate that chronic downregulation of Na(+)-K(+)-ATPase alpha(2)-isoform expression by heterozygous knockout increases the pressor response to increased CSF [Na] and activates the brain RAS. Since these changes mimic those produced by the endogenous brain OLS, the brain alpha(2)-isoform may be a target for the brain OLS during increases in CSF [Na], such as in salt-dependent hypertension.

Macelignan attenuates LPS-induced inflammation and reduces LPS-induced spatial learning impairments in rats

Previous studies have shown that macelignan has anti-inflammatory and neuroprotective effects. Subsequently, in the current study, we demonstrate that oral administrations of macelignan reduce the hippocampal microglial activation induced by chronic infusions of lipopolysaccharide (LPS) into the fourth ventricle of Fisher-344 rat brains. A Morris water maze was used to evaluate the status of the hippocampal-dependent spatial learning in control rats with an artificial cerebrospinal fluid infusion, rats with chronic LPS infusions, and rats with chronic LPS infusions and oral administrations of macelignan. The rats with chronic LPS infusions showed spatial memory impairments relative to the control rats in the performance of the memory task. Daily administration of macelignan reduced the spatial memory impairments induced by the chronic LPS infusions. The results indicate that macelignan may possess therapeutic potential for the prevention of Alzheimer’s disease.

O.016 Resonance and intracranial pressure pulsations: An experimental study

s of the Hydrocephalus 2008 Congress / Clinical Neurology and Neurosurgery 110S (2008), S1–S41 S5 O.015 New model of cervical stenosis in cats: Effects on size of brain ventricles and cerebrospinal fluid pressure M. Klarica1 , I. Jurjevic1 , T. Jukic2, D. Oreskovic3, M. Bulat 1 1Department of Pharmacology and Croatian Institute for Brain Research, School of Medcine University of Zagreb, Zagreb, Croatia; 2Department of Ophtalmology, Clinical Hospital center Rebro, Zagreb, Croatia; 3Rudjer Boskovic Institute, Zagreb, Croatia It was shown that cervical obstruction of physiological cranio-spinal displacement of cerebrospinal fluid (CSF), which is developed during inflammating process after kaolin application, may lead to development of hydrocephalus and hydromyelia. We have tested this hypothesis on new experimental model of cervical stenosis without inflammation. Acute and subacute experiments were performed in cats in which plastic semiring was positioned in epidural space at C2 vertebrae separating spinal from cranial cerebrospinal fluid. CSF pressures were recorded in lateral ventricle (LV) and lumbar subarahnoid space (LSS). Size of both the brain ventricles and central canal was determined by planimetric method. In all experiments the CSF pressures were normal. However, in acute experiments with infusion of artificial CSF, the transmission of the increased CSF pressure from LV to LSS was limited. After 3 or 6 weeks, an atrophy of spinal cord was observed at the site of cervical stenosis and pressure transmission from LV to LSS was improved. Planimetric measurement of surface of coronal brain slice and ventricles showed that ventricular surface was 0.6±;0.1% (n=5) in control and 1.6±;0.2% (n=4) in animals with cervical stenosis (p<0.002). Change in size of central canal was not detected. These results support the hypothesis claiming that impairment of cranio-spinal displacement of CSF volume can lead to development of hydrocephalus. However, changes in size of brain ventricle and central canal are relatively limited, probably due to atrophy of spinal cord at the stenosis site, and improvement of physiological CSF cranio-spinal displacement. O.016 Resonance and intracranial pressure pulsations: An experimental study M.E. Wagshul1,2,3, M.R. Egnor 2, E.J. Kelly4, H.J. Yu3 1Department of Radiology, 2Department of Neurosurgery, 3Department of Biomedical Engineering, Stony Brook University, Stony Brook, NY, USA; 4Toshiba Medical Systems, Tustin, CA, USA While the existence of a coupling between intravascular and intraparenchymal pressure is undisputed, the nature of this coupling and how it changes under conditions of decreased intracranial compliance has not been carefully investigated. We used transfer function analysis between the intracarotid and intraparenchymal pulse pressure waveforms in twelve healthy mongrel dogs, under conditions of normal and decreased intracranial compliance, to characterize the relationship between arterial and intracranial pulsations. Compliance was manipulated via infusions of isotonic saline into the spinal subarachnoid space. We find that under normal conditions, the intracranial pressure wave leads the arterial wave and there is a relative minimum in the intracranial pulse pressure amplitude near the frequency of the heart rate. Under conditions of decreased intracranial compliance, the intracranial pressure wave begins to lag behind the arterial wave and increases significantly in amplitude. Most interestingly, in many animals the pulse pressure exhibits a minimum in amplitude at a particular mean pressure which coincides with the transition from a leading to lagging ICP wave. This transfer function behavior is characteristic of a resonant notch system, in which the portion of the arterial pulsations near the heart rate are optimally dissipated, and may explain the importance of altered pulse pressure in the pathophysiology of hydrocephalus. New models of intracranial dynamics are needed to explain these results and may open the path for development of new therapies geared toward addressing the pulsation dysfunction in hydrocephalus. Session 2A 10:30–12:30, Room A

Continuous Measurement of Autoregulation by Spontaneous Fluctuations in Cerebral Perfusion Pressure

Clinical application of continuous autoregulation monitoring would benefit from a comparison of curves generated by online monitoring with standard autoregulation curves in animal models. We characterized the accuracy of 3 continuous monitors of autoregulation in a piglet model of hypotension. Piglets 5 to10 days old with intracranial pressure (ICP) at naïve or elevated (20 mm Hg) levels had gradual arterial hypotension induced by a balloon catheter in the inferior vena cava. Elevated ICP was maintained by a continuous infusion of artificial cerebrospinal fluid. Three indices of autoregulation were simultaneously and continuously calculated. A moving, linear Pearson's coefficient between spontaneous slow waves of cerebral perfusion pressure and slow waves of laser-Doppler flux or cortical oxygenation rendered the laser-Doppler index and cerebral-oximetry index, respectively. Similar correlation between slow waves of arterial blood pressure and ICP rendered the pressure-reactivity index. The lower limit of autoregulation was determined directly for each animal by plotting laser-Doppler cortical red blood cell flux as a function of cerebral perfusion pressure. Receiver-operator characteristics were determined for the 3 indices. The areas under the receiver-operator characteristics curves for discriminating the individual lower limit of autoregulation at low and high ICP were 0.89 and 0.85 for the laser-Doppler index, 0.89 and 0.84 for the cerebral-oximetry index, and 0.79 and 0.79 for the pressure-reactivity index. The pressure-reactivity index performed equally well at low and high ICPs. Continuous monitoring of autoregulation by spontaneous slow waves of cerebral perfusion pressure can accurately detect loss of autoregulation due to hypotension in piglets by all 3 modalities.

New method of bone reconstruction designed for skull base surgery

The direct endonasal or transoral transclival approaches to the skull base permit effective, minimally invasive surgery along the clivus. Developing long-term, effective techniques to prevent cerebrospinal fluid (CSF) leaks and their consequences (infection and delayed healing) remains a major challenge. In this study we describe a method of bone reconstruction newly developed by us, which uses a custom designed silicone plug for bone replacement after minimally invasive skull base surgery with a low incidence of postoperative CSF leaks. German Landrace pigs were used to test the efficiency of the new technique. Twelve craniotomies were performed in six pigs using a subtemporal approach and subsequently the dura was opened. After these preparations the craniotomy defects were occluded with a silicone ball, which had a near spherical shape. The ball elastically adapts to the bone defect. Each pig also received an intracranial pressure (ICP) catheter and a subdural catheter for later fluorescein injection. Then we increased ICP by infusion of artificial CSF and detected fluorescein leaks from the craniotomy using ultraviolet illumination and a photomacroscope equipped with appropriate filters and a charge-coupled device camera. In all pigs we increased ICP to 75–80 mmHg by infusing 25–30 mL saline containing 0.05% sodium fluorescein. For the first four craniotomies infusions were interrupted after CSF leaks occurred due to technical failures, which were subsequently rectified. The following eight craniotomies were watertight without CSF leakage. This novel medical device allows a leak-proof closure of bone defects after minimally invasive craniotomies; no additional surgery or other therapies were necessary. The application of the silicone plug, which is made of a cost-effective and biocompatible material, is easy and fast, making use of a specially developed toolkit.

Intrathecal Glycine Significantly Decreases the Minimum Alveolar Concentration of Isoflurane in Rats

To evaluate the effect of intrathecal administration of glycine on the minimum alveolar concentration (MAC) of isoflurane in rats. Intrathecal catheters were implanted in 40 adult male rats anesthetized with isoflurane. Baseline MAC of isoflurane was measured during the infusion of artificial cerebrospinal fluid (CSF) alone. Subsequently, 10, 40, 80, 160, and 300 mmol/L of glycine dissolved in artificial CSF were infused for two hours at the same rate as under control conditions, and MAC for isoflurane was re-determined. Intrathecal administration of glycine produced a significant, dose-dependent decrease in MAC for isoflurane (up to -65.2% +/- 16.2%). Intrathecal administration of glycine decreases anesthetic requirement This result supports the idea that glycine receptors may be important to the immobilizing effect of anesthetics that enhance glycine receptor function such as isoflurane.

Brain Metabolism During a Decrease in Cerebral Perfusion Pressure Caused by an Elevated Intracranial Pressure in the Porcine Neocortex

Cranial hypertension coincides with a reduction in cerebral blood flow as well as in oxygen delivery and influences outcome. In this study, we monitored changes in energy-related metabolites in the porcine cortex during an increase of intracranial pressure (ICP) and to determine the level at which damage occurs. Male domestic pigs (32-40 kg) were anesthetized, mechanically ventilated, and randomly assigned to either the experimental (n = 6) or control groups (n = 5). A microdialysis probe (CMA 70) was inserted into the cortex to measure extracellular dialysate concentrations of lactate, pyruvate, glucose, glutamate, and glycerol. Every hour an increase of 10 mm Hg in ICP was preformed in the experimental group by infusion of artificial cerebrospinal fluid into the ventricular system of the brain until a maximum ICP of 50 mm Hg was reached. We demonstrated a significant increase of lactate and glycerol compared with control at ICP values > or =30 mm Hg and cerebral perfusion pressure (CPP) below 50 mm Hg. The increase of ICP to > or =40 mm Hg in conjunction with a reduction in CPP below 40 mm Hg led to a significant increase in the lactate/pyruvate-ratio and glutamate, as well as a decrease of glucose in relation to control. Our data strongly suggest that, during a defined ICP increase, lower CPP values may be tolerable until severe damage occurs. Borderline ICP and CPP values of 30 and 40 mm Hg, respectively, could be advised.

Intravenous hypertonic NaCl acts via cerebral sodium‐sensitive and angiotensinergic mechanisms to improve cardiac function in haemorrhaged conscious sheep

Acute NaCl loading as resuscitation in haemorrhagic hypovolaemia is known to induce rapid cardiovascular recovery. Besides an osmotically induced increase in plasma volume the physiological mechanisms of action are unknown. We hypothesized that a CNS mechanism, elicited by increased periventricular [Na(+)] and mediated by angiotensin II type 1 receptors (AT(1)), is obligatory for the full effect of hypertonic NaCl. To test this we investigated the cardiovascular responses to haemorrhage and subsequent hypertonic NaCl infusion (7.5% NaCl, 4 ml (kg BW)(-1)) in six conscious sheep subjected to intracerebroventricular (i.c.v.) infusion of artificial cerebrospinal fluid (aCSF; control), mannitol solution (Man; 75 mmol l(-1) [Na(+)], total osmolality 295 mosmol kg(-1)) or losartan (Los; 1 mg ml(-1), AT(1) receptor antagonist) at three different occasions. Man normalized (144 +/- 6 mmol l(-1), mean +/- s.d.) the increase in i.c.v. [Na(+)] seen after aCSF (161 +/- 2 mmol l(-1)). Compared with control, both Man and Los significantly (P < 0.05) attenuated the improvement in mean arterial blood pressure (MAP), cardiac index and mesenteric blood flow (SMBF) in response to intravenous hypertonic NaCl: MAP, rapid response +45 mmHg versus +38 mmHg (Man) and +35 mmHg (Los); after 180 min, +32 mmHg versus +21 mmHg (Man) and +19 mmHg (Los); cardiac index after 180 min, +1.9 l min(-1) (m(2))(-1) versus +0.9 l min(-1) (m(2))(-1) (Man) and +0.9 l min(-1) (m(2))(-1) (Los); SMBF rapid response, +981 ml min(-1) versus +719 ml min(-1) (Man) and +744 ml min(-1) (Los); after 180 min, +602 ml min(-1) versus +372 ml min(-1) (Man) and +314 ml min(-1) (Los). The results suggest that increased periventricular [Na(+)] and cerebral AT(1) receptors contribute, together with plasma volume expansion, to improve systemic haemodynamics after treatment with hypertonic NaCl in haemorrhagic hypovolaemia.

Mechanisms Controlling Feed Intake in Large-type Goats Fed on Dry Forage

An intracerebroventricular (ICV) infusion of somatostatin 1-28 (SRIF) was used as a thirst-controlling peptide antagonist to investigate whether or not thirst-controlling peptides are involved in the significant decrease in feed intake during the initial stages of feeding large-type goats on dry forage. A continuous ICV infusion of SRIF was conducted at a small dose of 4 μg/0.2 ml/h for 27 h from day 1 to day 2. Goats (n 5) were fed roughly crushed alfalfa hay cubes for 2 h twice daily and water was given ad libitum. Feed intake was measured during ICV infusion of artificial cerebrospinal fluid (ACSF) and SRIF. The feed intake during SRIF infusion increased significantly compared to that during ACSF infusion. In comparison to the ACSF treatment, plasma osmolality during the SRIF treatment significantly decreased during the first half of the 2 h feeding period. The factor causing the decrease in plasma osmolality during the ICV infusion of SRIF was a decrease in plasma Na, K, Cl, and Mg concentrations. In comparison to the ACSF infusion treatment, parotid saliva secretion volumes during the 2 h feeding period in the SRIF infusion treatment were significantly larger. While there was no significant difference in cumulative water intake (thirst levels) between the SRIF and the ACSF treatments upon conclusion of the 2 h feeding period, based on the plasma osmolality results it is thought that thirst level increases brought about by alfalfa hay cube feeding in the first half of the feeding period were reduced. It is thought that the somatostatin-induced increases in feed intake during the 2 h feeding period in the present experiment were caused by decreases in plasma osmolality brought about by the somatostatin infusion. As a result, it is suggested that the significant decrease in feed intake during the initial stages of feeding in large-type goats given roughly crushed alfalfa hay cubes, was due to the actions of thirst-controlling peptides.

Neuronal Responsiveness to Central Na + in 2 Congenic Strains of Dahl Salt-Sensitive Rats

Dahl salt-sensitive rats show increased Na(+) entry into the brain on high salt intake and increased sympathetic and pressor responses to central Na(+). We examined C10QTL2 and C17QTL to test whether they contribute to these phenotypes. In Dahl salt-sensitive, Lewis, and C10S.L16, and C17S.L2 congenic rats on a high salt diet for 8 to 10 days, blood pressure and heart rate were higher in Dahl salt-sensitive versus others and in C10S.L16 and C17S.L2 versus Lewis rats. Cerebrospinal fluid [Na(+)] increased by approximately 5 mmol/L in Dahl salt-sensitive, C10S.L16, and C17S.L2 compared with Lewis rats. In rats on a regular salt diet, 8-minute intracerebroventricular infusions of artificial cerebrospinal fluid with increasing [Na(+)] caused increases in blood pressure, heart rate, and renal sympathetic nerve activity, which were approximately 90% larger in Dahl salt-sensitive and C17S.L2 versus Lewis rats and only 35% to 45% larger in C10S.L16 versus Lewis rats. In another set of rats on regular salt, blood pressure and heart rate were recorded by telemetry before and during intracerebroventricular infusion of Na(+)-rich cerebrospinal fluid for 14 days. Na(+)-rich cerebrospinal fluid caused significantly larger increases in blood pressure and heart rate, larger responses to air stress and more impairment of baroreflex in Dahl salt-sensitive and C17S.L2 rats versus Lewis rats. In contrast, responses in C10S.L16 rats were similar to those in Lewis rats. These data suggest that, in Dahl salt-sensitive rats, genetic variants in C10QTL2 but not C17QTL contribute to increased neuronal responsiveness to cerebrospinal fluid [Na(+)]. However, neither of them contributes to the increase in cerebrospinal fluid [Na(+)] induced by high salt.

Interaction of AT1 receptors and V1a receptors-mediated effects in the central cardiovascular control during the post-infarct state

Experimental objectives. Because myocardial infarct is associated with overactivation of brain angiotensin II (ANG II) and vasopressin (AVP) V1a receptors we decided to determine whether AT1 and V1a receptors-mediated effects of ANG II and AVP interact in central cardiovascular control during the post-infarct state. Four groups of infarcted and four groups of sham-operated conscious rats entered the study. Results. In the infarcted rats cerebroventricular infusion of AT1 (AT1ANT, losartan) and V1a antagonist {V1aANT,d(CH 2) 5[Tyr(Me) 2Ala-NH 2 9]VP} and combined infusion of both these compounds performed 4 weeks after induction of the infarct significantly and comparably reduced mean arterial blood pressure (MABP) in comparison to control experiments (artificial cerebrospinal fluid infusion). In the sham rats MABP was not affected by any of the infusions. In control experiments MABP and HR responses to an alarming air jet stress were significantly higher in the infarcted than in the sham rats. Both responses were normalized with the same effectiveness by administration of AT1ANT, V1aANT and AT1ANT+V1aANT. In the sham rats administration of these compounds did not affect MABP and HR responses to stress. Conclusion: The results provide evidence for interaction of AT1 and V1a receptors-mediated effects of ANG II and AVP in the central cardiovascular control during the post-infarct state.

COMPARISON BETWEEN THE EFFECTS ON HEMODYNAMIC RESPONSES OF CENTRAL AND PERIPHERAL INFUSIONS OF HYPERTONIC NACL DURING HEMORRHAGE IN CONSCIOUS AND ISOFLURANCE-ANESTHETIZED SHEEP

The i.v. infusion of hypertonic NaCl solutions, as in small volume hypertonic NaCl resuscitation, improves cardiovascular function in hypovolemic shock. The mechanism(s) of action of this treatment is(are) not fully elucidated. In this study, we investigate the possible importance of fully functional neurocardiovascular regulation for the effect of intracerebroventricular (i.c.v.) and i.v. administration of hypertonic NaCl on the hemodynamic responses to hemorrhage. Six groups (each n = 6) of adult ewes were subjected to hypotensive hemorrhage during treatment with i.c.v. infusion (20 microL/min) of either artificial cerebrospinal fluid (controls) or 0.5 mol/L NaCl, or i.v. infusion of 1.2 mol/L NaCl (4 mL/kg) when conscious, respectively anesthetized with isoflurane. Thirty minutes into infusion, treatment blood was withdrawn at 0.7 mL/kg per minute from a jugular vein until the mean arterial pressure dropped to a value just below 50 mmHg. In conscious animals, the amount of blood loss needed to lower the mean arterial pressure to less than 50 mmHg was increased by the i.c.v. and i.v. infusions of hypertonic NaCl (24.0 +/- 4.6 and 22.4 +/- 3.3 mL/kg, respectively), compared with controls receiving i.c.v. infusion of artificial cerebrospinal fluid (14.2 +/- 1.4 mL/kg). Isoflurane anesthesia, as such, severely compromised the cardiovascular compensatory mechanisms activated by hemorrhage and reduced the blood loss necessary to cause hypotension (10.2 +/- 2.5 mL/kg). Furthermore, anesthesia totally abolished the effect of i.c.v. hypertonic NaCl (10.4 +/- 2.2 mL/kg) and blunted the response to i.v. hypertonic NaCl (15.9 +/- 2.1 mL/kg) seen in conscious animals. The results show that an intact autonomic cardiovascular control is crucial for the effect of i.c.v. hypertonic saline and indicate that i.v. hypertonic saline exerts some of its action through the central nervous system.

Prolonged Increase in the Sensitivity of the Posterior Ventral Tegmental Area to the Reinforcing Effects of Ethanol following Repeated Exposure to Cycles of Ethanol Access and Deprivation

The posterior ventral tegmental area (VTA) is a neuroanatomical substrate mediating the reinforcing effects of ethanol in rats. Repeated alcohol deprivations produce robust ethanol intakes of alcohol-preferring (P) rats during relapse and increase the reinforcing effects of oral alcohol self-administration. The objective of this study was to test the hypothesis that alcohol drinking and repeated alcohol deprivations will increase the reinforcing effects of ethanol within the posterior VTA of P rats. Groups of female P rats were used (alcohol-naive, continuous access, and repeatedly deprived). Each rat was implanted with a guide cannula aimed at the posterior VTA. Depression of the active lever produced the infusion of 100 nl of artificial cerebrospinal fluid (CSF) or ethanol (25-300 mg%). Each rat was given only one ethanol concentration during the 4-h sessions conducted every other day. Compared with the infusions of artificial CSF, the alcohol-naive group reliably self-infused 75 and 150 mg% ethanol, but not the lower or higher concentrations. On the other hand, the continuous access group had significantly higher self-infusions of 50, 75, 150, and 300 mg% ethanol compared with artificial CSF infusions. The repeatedly deprived group also self-infused significantly more of 50, 75, 150, and 300 mg% ethanol than artificial CSF; moreover, the number of infusions for all four concentrations was higher in the repeatedly deprived versus the continuous access group. Chronic alcohol drinking by P rats increased the reinforcing effects of ethanol within the posterior VTA, and repeated alcohol deprivations produced a further increase in these reinforcing effects of ethanol.

Chronic Ethanol Drinking by Alcohol‐Preferring Rats Increases the Sensitivity of the Posterior Ventral Tegmental Area to the Reinforcing Effects of Ethanol

The ventral tegmental area (VTA) is involved in regulating ethanol drinking, and the posterior VTA seems to be a neuroanatomical substrate that mediates the reinforcing effects of ethanol in ethanol-naive Wistar and ethanol-naive alcohol-preferring (P) rats. The objective of this study was to test the hypothesis that chronic ethanol drinking increases the sensitivity of the posterior VTA to the reinforcing effects of ethanol. Two groups of female P rats (one given water as its sole source of fluid and the other given 24-hr free-choice access to 15% ethanol and water for at least 8 weeks) were stereotaxically implanted with guide cannulae aimed at the posterior VTA. One week after surgery, rats were placed in standard two-lever (active and inactive) operant chambers and connected to the microinfusion system. Depression of the active lever produced the infusion of 100 nl of artificial cerebrospinal fluid (CSF) or ethanol. The ethanol-naive and chronic ethanol-drinking groups were assigned to subgroups to receive artificial CSF or 25, 50, 75, or 125 mg/dl of ethanol (n = 6-9/dose/group) to self-infuse (FR1 schedule) during the 4-hr sessions given every other day. Compared with the infusions of artificial CSF, the control group reliably (p < 0.05) self-infused 75 and 125 mg/dl of ethanol but not the lower concentrations. The ethanol-drinking group had significantly (p < 0.05) higher self-infusions of 50, 75, and 125 mg/dl of ethanol than artificial CSF during the four acquisition sessions; the number of infusions of all three doses was higher in the ethanol-drinking group than in the ethanol-naive group. Both groups decreased responding on the active lever when artificial CSF was substituted for ethanol, and both groups demonstrated robust reinstatement of responding on the active lever when ethanol was restored. Chronic ethanol drinking by P rats increased the sensitivity of the posterior VTA to the reinforcing effects of ethanol.

Efecto de la lesión de la sustancia negra parte compacta sobre la liberación de glutamato y GABA en el núcleo pedunculopontino

The pedunculopontine nucleus (PPN), co-localized with the mesencephalic locomotor region, has been proposed as a key structure in the physiopathology of Parkinson's disease. The goal of the present study was to assess if the aminoacid neurotransmitter release in the PPN is modified by the degeneration of dopaminergic cells, from substantia nigra pars compacta in 6-hydroxidopamine (6-OHDA)-lesioned rats. In addition, it was studied the aminoacid neurotransmitter release in the PPN of rats with lesion of the subthalamic nucleus by quinolinic acid (QUIN) (100 nmol) intracerebral injection. Rats were assigned to five groups: untreated rats (I) (n = 13), 6-OHDA lesion (II) (n = 11), 6-OHDA + QUIN lesion (III) (n = 9), sham-operated (IV) (n = 10), QUIN, STN (V) lesioned (n = 9). The extracellular concentrations of glutamic acid (GLU) and gamma-aminobutyric acid (GABA) were determined by brain microdialysis and high performance liquid chromatography (HPLC). RESULTS. GLU released in PPN from 6-OHDA lesioned rats (group II), was significantly increased in comparison with the others groups (F(4, 47) = 18.21, p < 0.001). GABA released shows significant differences between experimental groups (F(4, 45) = 12.75, p < 0.001). It was detected a higher valour (p < 0.05) in-group II. The groups III and IV exhibited intermeddle valour (p < 0.001) and groups I and IV (p < 0.001) showed the lower GABA extracellular concentrations. The infusion of artificial cerebrospinal fluid with higher potassium (100 mmol) induced an increase in the GLU and GABA released in all groups, which confirm the neuronal origin of the extracellular content. These results are in agreement with the current model of basal ganglia functioning and suggest the role of STN-PPN projection in the physiopathology of Parkinson's disease.

Enhanced involvement of brain vasopressin V1 receptors in cardiovascular responses to stress in rats with myocardial infarction

Stress is one of the factors provoking cardiovascular complications. The purpose of the study was to explore the role of vasopressin (VP) in central control of arterial blood pressure and heart rate under resting conditions and during stimulation by an alarming stress (air jet stress) in myocardial infarct-induced cardiac failure. Six groups of male Sprague Dawley (SD) rats were subjected either to sham surgery (sham rats) or to ligation of a left coronary artery (infarcted rats). After 5 weeks both infarcted and sham rats were subjected either to intracerebroventricular infusion of artificial cerebrospinal fluid (aCSF) (sham aCSF and infarcted aCSF), [Arg8]-VP (sham VP and infarcted VP) or VP V1a receptor antagonist (d(CH2)5[Tyr(Me)2Ala-]VP, sham V1ANT and infarcted V1ANT). Air jet stress elicited significantly greater increases in mean arterial blood pressure (MABP) and heart rate in the infarcted aCSF than in the sham aCSF rats. Intracerebroventricular infusion of V1ANT significantly reduced resting MABP and MABP and heart rate increases in response to stress in the infarcted but not in the sham rats. Intracerebroventricular infusion of VP elicited a significant increase in resting MABP in the infarcted VP but not in the sham VP rats. The results provide evidence for enhanced engagement of the brain V1 VP receptors in regulation of resting MABP and in generation of exaggerated cardiovascular responses to air jet stress during the post-infarct state.

Cortical and medial amygdala are both involved in the formation of olfactory offspring memory in sheep

Ewes form a selective olfactory memory for their lambs after 2 h of mother-young interaction following parturition. Once this recognition is established, ewes will subsequently reject any strange lamb approaching the udder (i.e. maternal selectivity). The present study tested the functional contribution of different amygdala nuclei to lamb olfactory memory formation. Using the anaesthetic lidocaine, cortical, medial or basolateral nuclei of the amygdala were transiently inactivated during lamb odour memory formation. Reversible inactivation of either cortical or medial amygdala during the first 8 h postpartum impaired lamb olfactory recognition, whereas inactivation of the basolateral nucleus or infusion of artificial cerebrospinal fluid did not. Control experiments indicate that inactivation of the cortical and medial nuclei of the amygdala specifically disrupt memory formation rather than olfactory perception or memory retrieval. These findings show that both nuclei of the amygdala are required for the formation of a lamb olfactory memory and suggest functional interaction between these two nuclei.

Inhibition of intercellular adhesion molecule-1 protein expression by antisense oligonucleotides is neuroprotective after transient middle cerebral artery occlusion in rat.

The present study was performed to determine whether antisense inhibition of intercellular adhesion molecule-1 (ICAM-1) protein expression decreases focal ischemic brain damage. Male spontaneously hypertensive rats underwent 1-hour middle cerebral artery occlusion (MCAO) and 24-hour reperfusion. Rats were infused with ICAM-1 antisense or control oligodeoxynucleotides (ODNs) (48 nmol/d ICV) or vehicle, starting 24 hours before MCAO and continuing until the time of death. ICAM-1 and vascular cell adhesion molecule-1 (VCAM-1) mRNA levels were measured by real-time polymerase chain reaction. ICAM-1 protein knockdown was confirmed by Western blotting. Infarct volume was quantified by the use of cresyl violet-stained brain sections. Neurological deficits were evaluated. Mean arterial blood pressure was recorded by laser Doppler. Tissue penetration of antisense was confirmed by the use of fluorescent ODNs. Transient MCAO upregulated ICAM-1, but not VCAM-1, mRNA expression in the ipsilateral cortex between 3 and 72 hours of reperfusion. ICAM-1 antisense infusion prevented ischemia-induced ICAM-1 protein expression and reduced total infarct volume (by 53%; P<0.05; 226+/-35 mm3 in control ODN group and 104+/-27 mm3 in antisense ODN group; n=8 each) and mean neurological deficit score (by 44%; P<0.05; 2.4 in control ODN group and 1.3 in antisense ODN group; n=8 each). Neither control nor antisense ODN had any effect on mean arterial blood pressure and the physiological parameters monitored during MCAO. Compared with noninfused control, intracerebroventricular infusion of artificial cerebrospinal fluid or antisense or sense ODN had no significant effect on the regional cerebral blood flow changes that accompanied ischemia and reperfusion. Increased ICAM-1 expression is implicated in the pathogenesis of focal ischemia since ICAM-1 protein knockdown decreased ischemic brain damage. The mechanism by which ICAM-1 inhibition offers neuroprotection is independent of blood pressure modulation.

Forebrain sites of NPY action on estrous behavior in Syrian hamsters

Food deprivation and similar metabolic challenges inhibit estrous behavior in female Syrian hamsters. The relevant metabolic cues appear to be detected in the hindbrain, and this information is then relayed synaptically to the forebrain circuits controlling estrous behavior. Neuropeptide Y (NPY) may be one of the neuropeptides/neurotransmitters serving this function. Infusion of NPY or the Y2/Y5 agonist, peptide YY3-36 (PYY3-36), into the lateral ventricles rapidly inhibits estrous behavior in ovariectomized, steroid-primed hamsters. This experiment sought to determine the neural loci where NPY acts to inhibit estrous behavior. Steroid-primed animals received infusions of artificial cerebrospinal fluid (aCSF) vehicle, 0.024 nmol PYY3-36 and 0.24 nmol PYY3-36 in separate tests 30 min prior to testing for sexual receptivity. Infusion of 0.24 nmol, but not 0.024 nmol, of PYY3-36 reduced lordosis duration when infused into the paraventricular nucleus of the hypothalamus (PVN), the caudal part of the medial preoptic area (MPO), the anterior hypothalamus (AH) or the lateral ventricles. Placements in the ventromedial hypothalamus (VMH), the arcuate nucleus (ARC) and the fourth ventricle were generally without effect. These data suggest that increased endogenous release of NPY into the caudal MPO–AH–PVN continuum during food deprivation could contribute to the observed inhibition of sexual receptivity. The possible contributions of other neuropeptides and neural estrogen receptors to this action of NPY are discussed.

Glycine receptors mediate part of the immobility produced by inhaled anesthetics.

Many inhaled anesthetics potentiate the effect of glycine on inhibitory strychnine-sensitive glycine receptors in vitro, supporting the view that this receptor could mediate the immobility produced by inhaled anesthetics during noxious stimulation (i.e., would underlie minimum alveolar anesthetic concentration [MAC]). There are quantitative differences between anesthetics in their capacity to potentiate glycine's effect in receptor expression systems: halothane (most potentiation), isoflurane (intermediate), and cyclopropane (minimal). If glycine receptors mediate MAC, then their blockade in the spinal cord should increase the MAC of halothane more than that of isoflurane and isoflurane MAC more than cyclopropane MAC; the increases in MAC should be proportional to the receptor potentiation produced in vitro. Rats with chronically implanted intrathecal catheters were anesthetized with halothane, isoflurane, or cyclopropane. During intrathecal infusion of artificial cerebrospinal fluid, MAC was determined. Then MAC was re-determined during an infusion of 3, 12, 24, or 48 (isoflurane only) micro g/min of strychnine (strychnine blocks glycine receptors) in artificial cerebrospinal fluid. Strychnine infusion increased MAC in proportion to the enhancement of glycine receptors found in vitro. The maximum effect was with an infusion of 12 micro g/min. For the combined results at 12 and 24 micro g/min of strychnine, the increase in MAC correlated with the extent of in vitro potentiation (r(2) = 0.82). These results support the hypothesis that glycine receptors mediate part of the immobilization produced by inhaled anesthetics. In vitro, halothane potentiates glycine's effect on strychnine-sensitive glycine receptors more than isoflurane and isoflurane more than cyclopropane. The present in vivo work indicates that antagonism of the glycine receptor with strychnine increases minimum alveolar anesthetic concentration for halothane more than isoflurane and isoflurane more than cyclopropane. Such results support the notion that glycine receptors may mediate part of the immobility produced by inhaled anesthetics.