Saralasin increases activity of hippocampal neurons inhibited by angiotensin II

Long-term intracerebroventricular infusion of angiotensin II after kainate-induced status epilepticus: Effects on epileptogenesis, brain damage, and diurnal behavioral changes

Our previous studies revealed that Angiotensin (Ang) II has anticonvulsant effects in acute seizure models. However, data on its role in experimental models of epilepsy are missing. In the present study, we tested whether posttreatment with Ang II after kainate (KA)-induced status epilepticus (SE) can affect epileptogenesis, concomitant behavioral changes, and brain damage. The Wistar rats were intracerebroventricularly infused via osmotic mini-pumps with Ang II (1.52μg/μl/day for 28days) after SE. Spontaneous motor seizures (SMS) were video-recorded for up to three months. Locomotor activity, anxiety, and depression-like behavior were evaluated during the last week of drug infusion, while spatial memory was assessed during the 3rd month after SE. Angiotensin II decreased the latency for onset of the first SMS and increased the frequency of SMS two months after SE. The continuous peptide infusion exacerbated the KA-induced hyperactivity and caused depression-like behavior. The reduced anxiety of KA-treated rats was alleviated by Ang II exposure. The KA-induced deficit in the hippocampal-dependent spatial memory was not influenced by Ang II. However, Ang II partially prevented the neuronal damage in the hippocampus, specifically in the CA1 area. The role of AT1 and AT2 receptor activation in the effects of the octapeptide is discussed.

Angiotensin peptides modulatory system: how is it implicated in the control of seizure susceptibility?

Accumulated studies support the concept that angiotensin peptides, ANG II, ANG III, and ANG IV act as neurotransmitters or neuromodulators in specific neuronal pathways in the brain stem, the hypothalamus, and the forebrain. They have been implicated in the regulation of several physiological processes, particularly in excitable brain structures that express high concentration of their receptors. With the help of pharmacological approaches it was shown that angiotensin peptides appear to be anticonvulsant in a variety of experimental seizure models. Thus, ANG II increases the threshold for pentylenetetrazol (PTZ)-, bicuculline-and picrotoxin-induced seizures in mice. It also attenuates the intensity of clonic seizures evoked by PTZ and 3-mercaptopropionic acid and is effective in the maximal electroshock test. Furthermore, ANG II, ANG III, and ANG IV protect against the clonic convulsions in the PTZ kindling model of epilepsy in mice. From the accumulated results it could be assumed that the angiotensin peptides appear to realize their effects acting directly on their receptors (AT(1), AT(2) and AT(4)) and through close interaction with different neurotransmitter/neuromodulator systems as dopamine (DA)-, gamma-aminobutyric acid (GABA)-and adenosine. This may contribute to a new potential use of angiotensin drugs either alone or in combination with other neuroprotective agents acting through the above mentioned systems, thus providing a more rational strategy for the treatment of neurodegenerative disorders such as epilepsy.

Brain renin angiotensin system (RAS) in stress-induced analgesia and impaired retention

Physiological stress is known to produce analgesia and memory disruption. Brain renin angiotensin system (RAS) has been reported to participate in stress response and plays a role in the processing of sensory information. Angiotensin receptors (AT), particularly AT1 subtypes have been reported to be distributed in brain areas that are intimately associated with stress response. The purpose of present study was to examine the modulation of AT1 receptor in the immobilization stress and angiotensin II (AngII)-induced analgesia and impaired retention, and to determine whether resultant behavioral changes involve common sensory signals. Result of present experiments showed that immobilization stress in mice and rats, and intracerebroventricular (ICV) administration of AngII (10 and 20 ng) in rats produced an increase in tail-flick latency. Similarly, post training administration of AngII or immobilization stress produced impairment of retention tested on plus-maze learning and on passive avoidance step-down task. Both these responses were sensitive to reversal by prior treatment with losartan (10 and 20 mg/kg), an AT1 AngII receptor antagonist. On the other hand, naloxone, an opiate antagonist preferentially attenuated the stress and AngII-induced analgesia and retention deficit induced by immobilization stress, but failed to reverse the AngII induced retention deficit. These results suggest immobilization stress-induced analgesia and impaired retention involves the participation of brain RAS. Further, failure of naloxone to reverse AngII-induced retention impairment shows. AngII-induced behavioral changes are under control of different sensory inputs.

Excitatory action of angiotensins II and IV on hippocampal neuronal activity in urethane anesthetized rats

The renin-angiotensin system of the mammalian brain seems to interfere with the process of cognition and has been associated with the hippocampal function in relation to mechanisms of learning and memory. In our investigation, the effects of angiotensin II (Ang II) and angiotensin IV (Ang II) on neuronal activity have been studied in the hippocampus of adult rats anesthetized with urethane. Excitatory effects of both angiotensins predominated over inhibitory effects. Angiotensins also induced an enhancement of burst discharges. These angiotensin-induced effects were blocked by the specific angiotensin antagonists. Our findings showed that the different effects of Ang II and Ang IV in behavioral studies are not similarly reflected in a different change of the discharge rate and/or pattern of hippocampal neurons after microiontophoretic administration of both substances.

Lateral hypothalamic stimulation inhibits dentate granule cell LTP: direct connections

We discovered that angiotensin II (Ang II) applied directly to the dentate gyrus inhibited LTP induction in medial perforant path-dentate granule cell synapses and that the inhibition can be blocked by losartan, an Ang II AT1 receptor specific antagonist. In the first part of this study we found that electrical stimulation of the lateral hypothalamus (LH) inhibits LTP in these synapses and the inhibition can be blocked by pretreating the animals with losartan, indicating that LH angiotensin-containing neurons project to the dentate gyrus. Results of the second part of the study demonstrate clearly that some angiotensin-containing LH neurons project directly to dentate granule cells. LH neurons were identified by retrograde tracers applied to the granule cell layer. Double-labeled neurons containing angiotensin and HRP were sparsely distributed and both fusiform and multipolar LH neurons appeared in a small cluster lateral and ventral to the fornix at the level of the paraventricular nucleus. Large numbers of angiotensin staining neurons were observed in the hypothalamus. Results support our hypothesis that some angiotensin containing LH neurons project directly to the dentate gyrus.

Modulation of membrane potential and ionic currents by the AT1 and AT2 receptors of angiotensin II

Angiotensin II, the principal effector of the renin-angiotensin system, modulates various ionic currents. Its effects on potassium currents, including outward transient potassium current, the inward or outward rectifiers, as well as Ca(2+)- activated potassium currents, is well described. Other ionic currents, such as voltage-dependent calcium currents, cationic or chloride currents, are also altered by the hormone. All these effects provoke changes in membrane potential, such as modulation of action potential firing or resting membrane potential and control intracellular calcium concentration. Summarized here are the results obtained on these membrane electrical properties using electrophysiological recordings.

Angiotensin II type 2 receptor-mediated regulation of rat neuronal K+ channels

We have previously shown that angiotensin II (Ang II), via AT2 receptors, increases whole-cell K+ current in cultured rat hypothalamus and brain stern neurons. We have now investigated the AT2 receptor-mediated effects of Ang II on the activity of single delayed rectifier K+ channels in cell-attached membrane patches. In control recordings (bath, 5.4 mmol/L K+; pipette, 140 mmol/L K+), two voltage-dependent channels were recorded with conductances of 34 +/- 4 and 56 +/- 6 pS, respectively (n = 6). When patches were excised, the channels reversed near a membrane potential expected for a K+ channel. In cell-attached patches (-40 mV), Ang II (100 nmol/L) increased open probability of the 56-pS K+ channel from 0.03 +/- 0.01 to 0.21 +/- 0.05 (n = 3). The selective AT2 receptor antagonist PD 123319 (1 mumol/L) but not the AT1 receptor antagonist losartan (1 mumol/L) blocked the actions of Ang II (n = 3). The selective AT2 receptor agonist CGP 42112 (100 nmol/L) produced similar effects to Ang II. Kinetic analysis of the Ang II effect showed that open-time histograms were best fit by two exponential functions. Ang II increased both open-time constants relative to control (control, tau 1 = 0.9 +/- 0.1 milliseconds, tau 2 = 2.3 +/- 0.3 milliseconds; Ang II, tau 1 = 3.1 +/- 0.4 milliseconds, tau 2 = 12.1 +/- 2.4 milliseconds), and PD 123319 blocked this effect (n = 3). The closed-time histogram was not affected by Ang II PD 123319, or losartan. These results suggest that activation of AT2 receptors modulates rat hypothalamus and brain stern neuronal whole-cell K+ current by increasing the open probability of a 56-pS K+ channel.

Angiotensin II blockade of long-term potentiation at the perforant path--granule cell synapse in vitro

Field recordings of evoked excitatory postsynaptic potentials (pEPSPs) were carried out in the granule cell stratum moleculare following stimulation of the perforant path in rat hippocampal slices. Under control conditions tetanic stimulation produced long-term potentiation (LTP) as measured by an increase in the initial slope of the pEPSPs that lasted for at least 1 h. LTP experiments were repeated with 0.5, 5.0, 50, or 500 nM angiotensin II (AII) present in the bath at the time of tetanization. Induction of LTP was blocked by 50 nM AII; however, normal baseline responses were not affected. At the highest dose tested, 500 nM, a decrease in the amplitude and slope of baseline pEPSPs was observed. When the AII AT1 receptor antagonist losartan was present in the bath AII inhibition of LTP was blocked. The application of losartan alone had no effect on LTP expression. These findings support previous results from in vivo studies demonstrating that activation of AT1 receptors in the dentate gyrus blocks the induction of LTP at the perforant path-granule cell synapse.

Differential effects of angiotensin II on the activities of suprachiasmatic neurons in rat brain slices

The effects of angiotensin II (AII) on the firing rates of suprachiasmatic neurons were determined in rat brain slices. AII in pmol ranges stimulated 25% and inhibited another 25% of 52 irregular firing neurons, while it stimulated 23% and inhibited 4% of 30 regular firing neurons. Three "oscillating" neurons whose firing rates oscillated with rather constant amplitudes and periods were recorded. AII induced the occurrence of oscillation in one unit and modulated the oscillation amplitude of the other two. Pretreatment with saralasin, an AII antagonist, effectively blocked (100%) the actions of AII (n = 5). The present findings suggest that AII may act as an important mediator in the suprachiasmatic nucleus and its mode of action may be variable in different neurons.

Angiotensin II depresses glutamate depolarizations and excitatory postsynaptic potentials in locus coeruleus through angiotensin II subtype 2 receptors

A previously reported depression of glutamate responses by angiotensin II was investigated to define the nature of this neuromodulatory effect. Studies were carried out in an vitro brain slice preparation containing the locus coeruleus, using intracellular recordings, and iontophoretic, micropressure and bath perfusion methods for application of drugs. The angiotensin action was found to be blocked by a non-peptide antagonist specific for the angiotensin type 2 receptor, and not by an antagonist selective for the type 1 receptor. Excitatory postsynaptic potentials mediated primarily by excitatory amino acids were also depressed by angiotensin II. The angiotensin II depressions of glutamate were shown to be strong and highly specific. The low effectiveness of bath-applied compared with iontophoretically or micropressure-applied angiotensin II was found to be at least partly explained by a rapid degradation by peptidases. Ammonium ions and hydrogen ions were also able to depress glutamate responses, but these effects were not specific for locus coeruleus neurons and were mediated independently of the angiotensin actions. Strong depression by angiotensin II of excitatory postsynaptic potentials as well as exogenously applied glutamate strengthens the strong possibility of a physiological role for this neuromodulatory mechanism. The identification of the type 2 angiotensin receptor subtype as the mediator of this effect indicates a novel functional role for this receptor, since previously recognized functions of angiotensin II in the brain, such as vascular and body fluid regulation, have been associated with the type 1 receptor.

Brain angiotensin receptor subtypes in the control of physiological and behavioral responses

This review summarizes emerging evidence that supports the notion of a separate brain renin-angiotensin system (RAS) complete with the necessary precursors and enzymes for the formation and degradation of biologically active forms of angiotensins, and several binding subtypes that may mediate their diverse functions. Of these subtypes the most is known about the AT1 site which preferentially binds angiotensin II (AII) and angiotensin III (AIII). The AT1 site appears to mediate the classic angiotensin responses concerned with body water balance and the maintenance of blood pressure. Less is known about the AT2 site which also binds AII and AIII and may play a role in vascular growth. Recently, an AT3 site was discovered in cultured neoblastoma cells, and an AT4 site which preferentially binds AII(3-8), a fragment of AII now referred to as angiotensin IV (AIV). The AT4 site has been implicated in memory acquisition and retrieval, and the regulation of blood flow. In addition to the more well-studied functions of the brain RAS, we review additional less well investigated responses including regulation of cellular function, the modulation of sensory and motor systems, long term potentiation, and stress related mechanisms. Although the receptor subtypes responsible for mediating these physiologies and behaviors have not been definitively identified research efforts are ongoing. We also suggest potential contributions by the RAS to clinically relevant syndromes such as dysfunctions in the regulation of blood flow and ischemia, changes in cognitive affect and memory in clinical depressed and Alzheimer's patients, and angiotensin's contribution to alcohol consumption.

The renin-angiotensin system in the brain: an update 1993

The renin-angiotensin system is considered to be one of the most important hormonal systems in the regulation of blood pressure and body fluid homeostasis. Ever since this system has been demonstrated to be present also in the brain, vast efforts have been made in investigating its central impact and function. The last few years, and especially the development of non-peptidic angiotensin II receptor subtype specific antagonists and the subsequent pharmacological characterization of these subtypes, brought this field of research a large step forward. This progress also might have opened up new avenues of developing highly specific anti-hypertensive drugs and thereby new ways of treating hypertension. This paper intends to provide a summary of the knowledge about the brain renin-angiotensin system accumulated during recent years; an update 1993.

Angiotensin II in the spinal cord of the rat and its sympatho-excitatory effects

Immunohistochemical studies have shown there is a dense angiotensin-like immunoreactivity of terminals in the sympathetic region of the thoracic and lumbar spinal cord. In the present study measurements were made of the concentration of angiotensin in the spinal cord of rats using radioimmunoassay following two different extraction procedures. These gave concentrations of angiotensin as mean of 108 and 161 pg.g-1 tissue wet weight. Angiotensin II given intrathecally or microinjected into the spinal cord caused an increase in postganglionic sympathetic nerve activity which was blocked by prior application of saralasin. Angiotensin III was without effect. Intracellular recordings from sympathetic preganglionic neurones in-vitro in slices of neonate rat spinal cord showed that angiotensin II produced an increase of excitability of the neurones by a slow depolarisation without the generation of action potentials. This effect still occurred in the presence of TTX. Angiotensin II also could increase synaptic activity, both EPSPs and IPSPs as well as a synaptically induced slow depolarisation being observed suggesting that presympathetic interneurones are also sensitive to the peptide. The evidence indicates that if angiotensin is released from nerve terminals surrounding sympathetic neurones it will enhance the gain of the neurone so that it could more easily be discharged by other excitatory inputs.

Role of angiotensin II and AT1 receptors in hippocampal LTP

Results of a previous study showed that angiotensin II (AII) inhibited the induction of long-term potentiation (LTP) in hippocampal granule cells in response to dorsomedial perforant path stimulation in urethane-anesthetized rats. The results of present experiments demonstrate a dose-dependent inhibition of LTP induction under the same conditions due to ethanol (EtOH) administered by stomach tube and diazepam (DZ) injected IP. The inhibition of LTP induction by EtOH and DZ can be blocked by saralasin (SAR) applied directly to the dorsal hippocampus and by lorsartan (DuP 753) administered IP. Lorsartan or a metabolite crosses the blood-brain barrier because it also blocks the inhibition of LTP induction due to AII administration directly into the dorsal hippocampus. Lorsartan is a competitive antagonist of the AT1 subtype AII receptor. Therefore, the AII and the EtOH and DZ inhibition of LTP induction are mediated by the AII subtype receptor AT1. AIII and the AT2 antagonist PD123319 did not produce any significant effects. These in vivo effects can be reproduced in brain slices and therefore cannot be attributed to other factors, such as the urethane. In addition, electrical stimulation of the lateral hypothalamus (LH) inhibits LTP induction, and the inhibition can be blocked by SAR. These data on LH stimulation indicate that LH AII-containing neurons send axons into the hippocampus that inhibit the induction of LTP. These results not only provide new information on a neurotransmitter involved in the amnesic effects of benzodiazepines and ethanol-induced memory blackouts, but also testable hypotheses concerning recent observations that angiotensin converting enzyme (ACE) inhibitors elevate mood and improve certain cognitive processes in the elderly.

Angiotensin II blocks hippocampal long-term potentiation

We have found that injection of angiotensin II (AII) above the hippocampus in the intact rat blocks the induction of long-term potentiation (LTP) in perforant path-stimulated dentate granule cells. A minimum dose of 4.78 pmol AII was required for the complete blockade of LTP and this blockade was entirely prevented if the AII-specific antagonist saralasin was co-injected at a 50-fold molar excess. AII thus appears to act via AII receptors and does not cause non-specific inhibition. The injection of saralasin alone yielded LTP comparable to that obtained when vehicle was injected. Angiotensin III was found to be 40-50 fold less potent than AII in blocking LTP. Both AII and AII receptors of unknown function occur in the hippocampal formation. The results reported here suggest a role for these molecules in the control of hippocampal LTP.

Angiotensin II modulation of glutamate excitation of locus coeruleus neurons

The effects of iontophoretically applied angiotensin II (AII) have been tested on intracellularly recorded locus coeruleus neurons in an in vitro brain slice preparation. In most neurons, AII strongly depressed the depolarizing effect of L-glutamate in the absence of other effects on membrane properties. This action was specific, in that AII had no effect on depolarizations caused by current injection or application of acetylcholine, and it was blockable by the AII antagonist saralasin. These results appear to demonstrate a potent and previously unreported neuromodulatory action of AII in the central nervous system.

Sensitivity to angiotensin II of neurons in the circumventricular organs of polydipsic inbred mice

The polydipsic inbred mice, STR/N, are known to possess an extremely strong appetite for drinking but no abnormality in the vasopressin system and renal functions. In brain slice preparations the sensitivity of neurons in the anteroventral region of the third ventricle (AV3V) and the subfornical organ (SFO) to angiotensin II (ANG II) was investigated using extracellular recordings in the STR/N and its control, Swiss/Webster (S/W) mice. In the AV3V, less proportion of neurons (15 out of 168; 9%) of the STR/N than that in the S/W (49/206; 24%) was excited by ANG II added to the medium. In the SFO, a proportion of neurons excited by ANG II was again lower in the STR/N (27/104; 26%) than in the S/W mice (64/118; 54%). The threshold concentration of ANG II for excitation of the AV3V and SFO neurons was, however, similar for both strains, 10(-9) M or less. Only one neuron in the SFO of a S/W mouse was inhibited by ANG II application. The excitatory effect of ANG II on AV3V and SFO neurons of both strains of mice persisted under synaptic blockade and was reversibly antagonized by an ANG II antagonist, saralasin. Such differences in sensitivity to ANG II of neurons in the SFO and AV3V, the regions thought to be involved in drinking behavior, suggest the involvement, at least in part, of the central angiotensin system in the polydipsia of the STR/N mice.

Alpha 1 and alpha 2-adrenergic receptor blockade influences angiotensin II facilitation of avoidance behavior and stereotypy in rats

Pretreatment of rats with prazosin (PRA), an alpha 1-adrenergic receptor blocker, abolished the increased rate of learning of conditioned avoidance responses stimulated by intracerebroventricular angiotensin II (AII) administration. Yohimbine (YOH), an alpha 2-receptor blocker, reversed the effect of AII. PRA did not affect, and YOH abolished, the improvement of recall of a passive avoidance behavior caused by AII. The stereotypies produced by apomorphine (APO) and amphetamine (AMP) were enhanced by AII. PRA changed neither stereotypy, but it abolished the AII effect in both cases. YOH did not alter APO stereotypy and abolished the enhancement of that behavior caused by AII. YOH increased AMP stereotypy and had an additive effect with AII. No significant changes of exploratory motor activity were caused by PRA, YOH, or their combination, with AII. These findings indicate that functioning alpha 1- and alpha 2-adrenergic receptors are necessary for the facilitation of learning by AII, while only alpha 2-receptors appear to be involved in AII improvement of recall. The central dopaminergic system may in part be responsible for the modulation by PRA and YOH of the effects of AII on learning and recall.

Dose-response testing of peptides by hippocampal brain slice recording

The brain slice chamber described offers a method of studying, with intracellular electrodes, the relationship of response to dose of peptides. By raising the level of the slices 1 mm above the level of flowing perfusion medium, we can test substances in known concentrations, free from artifacts, during long duration, stable intracellular recordings. Manipulation of Ca2+/Mg2+ ratios in the medium can help to define synaptic and second messenger mediation of the responses. The addition of substances to the perfusion medium in this system could be combined with iontophoresis and/or micropressure techniques. Pathways in the slices may also be stimulated electrically and analyzed for the involvement of various synaptic transmitters. The results with the method so far show distinct differences among the peptides studied. Thus, there are several advantages to this method in establishing the physiological role of peptides in the brain.

Angiotensin II receptors in the lumbar spinal cord of the rat

Locations of cells responsive to microiontophoretically applied angiotensin II (AII) were compared to distributions of AII receptor binding sites identified by autoradiography in the lumbar enlargement region of the rat spinal cord. Angiotensin II receptor binding sites were densely concentrated in the superficial layers of the dorsal horn. Considerably lower densities of binding sites were present in the remaining gray matter. Effects of microiontophoretically applied AII on lumbar spinal cord cells did not vary with location within the gray matter. AII facilitated firing of most cells in the lumbar cord whether the cells were in superficial or deeper laminae of the dorsal horn or in the ventral horn. The distribution of AII binding sites and the distribution of cells that were responsive to AII suggest that AII may play a role in modulating both sensory and motor functions of the spinal cord.

Pitfalls in the use of brain slices

In vitro brain slices are the preparation of choice for the detailed examination of local circuit properties in mammalian brain. However it is the investigator's responsibility to verify that the circuits under investigation are indeed confined within the boundaries of the functional region of the slice used. The medium in which the slice is maintained is under the full control of the investigator. This places the burden on the investigator to ensure that: (1) the properties of the medium are fully under control; (2) the effects of the medium on the slice are known; (3) the conditions under which the slice is being maintained bear some reasonable relation to those it enjoys (or endures) in vivo. Generalizations to in vivo conditions must be made with caution. If at all possible, similar studies (perhaps less extensive, due to the greater technical difficulties) should be done in vivo to provide a basis for comparison. Investigators using drugs should be aware of, and respect, the basic pharmacological principles cited in the text. In particular, the substantial freedom the investigator has in defining the extracellular medium should not be abused.

Cellular organization of the brain renin-angiotensin system

A model of intracellular Ang II formation (Figure 1) implies that angiotensinogen neurons exist and that CNS Ang II acts both as a neurotransmitter as well as a neurohormone. Such a mechanism is consistent with the immunocytochemical localization of a fraction of brain Ang II in neurosecretory vesicles. To date, several dozen peptide neurotransmitters and neurohormones have been studied. Those assigned to peptidergic systems follow the generalized pathway of biosynthesis shown in Figure 1. In peptidergic systems, a prohormone and all of its processing enzymes are synthesized in the rough endoplasmic reticulum of a cell and move into the Golgi apparatus (Figure 1: #1-3). In the Golgi the prohormone and processing enzymes are packaged into the same vesicle (#3). These secretory vesicles then migrate toward the plasma membrane, frequently via axonal or dendritic projections to terminals. Within these cytoplasmic vesicles and prior to release, the processing enzymes are activated (#4) and the prohormone enzymatically processed, yielding the active peptide (#5-6). Only then do the vesicles fuse with the plasma membrane (in a calcium-dependent process), releasing their contents (#7-8). Once released, the active peptide migrates across the extracellular space and interacts with specific cell surface receptors to initiate a response (#9). Finally, receptor-bound peptide degradation is initiated by receptor-mediated endocytosis (#10-11). For angiotensin peptides to be produced intracellularly, the cell must present only one secretory pathway for Golgi packaging of renin and angiotensinogen; otherwise current theories of protein sorting would predict that these two proteins would be segregated even if synthesized within the same cell. Small quantities of co-packaged renin and angiotensinogen occurring via "spill-over" between compartments seems an unsatisfactory process for a regulated hormone system. Figure 2, depicting an extracellular mechanism for producing Ang II in the brain, has also been proposed. The mechanism of extracellular angiotensin formation is consistent with the molecular information encoded within the component proteins, known mechanisms of protein secretio, well-defined systemic renin-angiotensin enzymatic cascades, and demonstration of all the components of the renin-angiotensin system in the extracellular compartments of the brain. This model (Figure 2) allows independently coordinated gene expression and synthesis of renin (#1R), angiotensinogen (#1A), and angiotensin-converting enzyme (# 1C) in the same or different cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Angiotensin II sensitive neurons in the supraoptic nucleus, subfornical organ and anteroventral third ventricle of rats in vitro

The angiotensin II (AII) sensitivity of neurons in the supraoptic nucleus (SON), subfornical organ (SFO) and the region near the anteroventral part of the third ventricle (AV3V) was investigated using extracellular recording in the rat brain slice preparation by adding AII (10(-10)-10(-6) M) to the perfusion medium. Forty seven (44%) of 106 SON neurons, 62 (66%) of 94 SFO neurons and 28 (33%) of 86 AV3V neurons were excited by AII. One cell was inhibited by AII in the SON and one in the SFO. The threshold concentration to evoke responses in the SON neurons was approximately 10(-9) M, but neurons in the SFO and AV3V showed clear excitatory responses to AII at 10(-10) M. In the SON, 18 (40%) of 45 phasic firing neurons (putative vasopressin neurons) and 29 (48%) of 61 nonphasic firing neurons (including putative oxytocin neurons) were excited by AII. The excitatory effect of AII was reversibly antagonized by a specific antagonist saralasin and persisted after synaptic blockade in medium with low [Ca2+] and high [Mg2+]. We conclude that AII can stimulate both vasopressin and oxytocin release, acting directly upon SON neurons and also that both the SFO and AV3V are important receptive sites for AII (although the SFO is relatively more sensitive) which contributes SON input and modulates release of these hormones.

A constant perfusion slice chamber for stable recording during the addition of drugs

A new design for a brain slice chamber is described. This chamber has the following features: slices are maintained in a stable condition for long-term (3-4 h) intracellular recording; drugs may be injected into the flowing perfusion medium in known concentrations without disturbing intracellular penetration; a wide range of concentrations may be used to test a single cell, highly repeatable results may be obtained; only minute amounts are required of substances to be tested, and the apparatus is easy to use and clean since all parts are removable. The chamber may also be easily modified to allow for the requirements of different experiments. The chamber has been used successfully to test the effects of Ang II, carbachol, insulin and gonadotropin releasing hormone.