FAST and SLOW amygdala kindling rat strains: comparison of amygdala, hippocampal, piriform and perirhinal cortex kindling

In our companion paper, we selectively bred offspring of a Long Evans Hooded and Wistar rat cross for either fast or slow rates of amygdala kindling (Racine et al., 1999. Development of kindling-prone and kindling resistant rats: Selective breeding and electrophysiological studies, Epilepsy Res. 35, 183-195). Within 10 generations, there was no overlap in the distribution of kindling rates between these newly developed FAST and SLOW kindling strains. In the present report, we compared the local excitability, kindling rates, and convulsion profiles of kindling sites in either the amygdala, dorsal hippocampus, piriform cortex or perirhinal cortex in the two strains. Local excitability, measured as the local afterdischarge (AD) threshold and its duration, showed varied effects between structures and strains. Before kindling, the AD threshold was lower in the FAST than the SLOW rats in the hippocampus, piriform and perirhinal cortices, but not the amygdala (the selection structure). Also, the duration of the AD threshold duration was significantly longer in the FAST than in the SLOW rats in all structures, except the CA1 hippocampus. Most of these differences were maintained after kindling. Kindling itself was significantly faster in the FAST compared with the SLOW rats in all structures; however, the different structural kindling rates showed proportional differences between strains that were about five times different in the amygdala compared with only about two times different in the hippocampus. This suggested a selection bias for the amygdala and its networks. As in other rat strains, the fastest kindling rates were seen in the perirhinal cortex followed by the piriform cortex, amygdala and hippocampus in both FAST and SLOW rats. Other important differences between strains and structures occurred in the stage-5 convulsion profiles, including latency to forelimb clonus, clonus duration and duration of associated local afterdischarges. The differences in kindling profiles between strains and structures were discussed with respect to possible underlying mechanisms, significance for epileptogenesis, and impact on other normal behaviours.

Cortical spreading depression reversibly disrupts convulsive motor seizure expression in amygdala-kindled rats

To determine the role of the frontal cortex in the generalization of limbic seizures, we first produced unilateral cortical spreading depression to reversibly suppress neuronal activity in the motor cortex and then triggered an amygdala-kindled seizure. Three minutes following induction of unilateral spreading depression, stimulation of the ipsilateral kindled amygdala produced only a brief electrographic seizure, and completely failed to produce the bilateral electrographic and clonic convulsive seizures that were normally present during control trials. A very different outcome occurred when unilateral spreading depression was induced in the cortex contralateral to the kindled amygdala. In these cases, the electrographic amygdala seizures were normal and bilateral like control trials, yet the clonic convulsive seizures were lateralized and appeared to be controlled by the non-depressed, kindled hemisphere. These lateralized convulsions were identical to those observed following forebrain commissurotomy, when direct communication between the frontal cortices was permanently severed. The results of the present study further define the pathways of temporal lobe seizure propagation, and highlight the important contribution frontal cortical regions provide to both the electrographic and convulsive expression of amygdala-kindled seizures by amplifying local seizures and projecting them into downstream brainstem and spinal cord circuits.

Acute effects of lead, steel, tungsten-iron, and tungsten-polymer shot administered to game-farm mallards

Sixteen-bird groups (sexes equal) of adult mallards (Anas platyrhynchos) were orally dosed with eight #4 steel short, eight #4 lead shot, eight BB-size tungsten-iron shot, eight BB-size tungsten-polymer shot, or were sham-dosed and maintained for 30 days (16 January 1996 to 15 February 1996). Half of the lead-dosed ducks (five males, three females) died during the study, whereas no ducks died in the other dosage groups. For lead-dosed ducks, hematocrit and hemoglobin concentration were decreased on day 15 of the trial, but not on day 30. Delta aminolevulinic acid dehydratase activity in lead-dosed ducks was lower when compared to steel-dosed ducks only. Plasma activities of selected enzymes were elevated in lead-dosed ducks when compared to enzyme activities of ducks in the other groups. For lead-dosed ducks, relative heart, liver, and kidney weights increased in comparison to relative weights of those organs of ducks in other groups. Histology of tissues indicated that renal nephrosis accompanied by biliary stasis was present in the eight lead-dosed ducks that died. For the eight lead-dosed ducks that survived, six had mild to severe biliary stasis. Mild biliary stasis was noted in five tungsten-iron dosed ducks and three tungsten-polymer dosed ducks. Amounts of lead in the femur, liver, and kidneys were higher in lead-dosed ducks than in ducks of the other four groups. Small amounts of tungsten were detected in the femur and kidneys of two tungsten-polymer dosed ducks. Higher concentrations of tungsten were detected in the femur, liver, and kidneys of all tungsten-iron dosed ducks. The rate of shot erosion was highest (80%) for the tungsten-polymer shot, followed by tungsten-iron (55%), lead (50%), and steel shot (33%). Results indicated that tungsten-iron or tungsten-polymer shot (8 shot/duck) orally administered to mallards did not adversely affect them during a 30-day trial.

Adrenergic regulation of calcium-activated potassium current in cultured rabbit pigmented ciliary epithelial cells

1. The effects of adrenergic agonists on K+ currents were studied in cultured rabbit pigmented ciliary epithelial (PCE) cells. 2. Outward K+ current (IK) was reduced by tetraethylammonium chloride, the Ca2+-activated K+ (K(Ca)) channel blocker iberiotoxin (IbTX), or Ca2+-free external Ringer solution. The calcium ionophore ionomycin increased an IbTX-sensitive IK in PCE cells. 3. The adrenergic agonists adrenaline and phenylephrine increased IK in PCE cells. The induced current was blocked by IbTX and the alpha1-antagonist prazosin, suggesting that adrenergic agonists activate IK(Ca) via alpha1-adrenoreceptors. 4. Internal dialysis of D-myo-inositol 1,4, 5-trisphosphate (IP3) increased IK, whilst pre-incubation of PCE cells with thapsigargin or the phospholipase C (PLC) inhibitor U-73122 reduced phenylephrine-induced increases in IK(Ca). Adrenergic increases in IK(Ca) were mediated by a pertussis toxin-insensitive G protein. 5. These results demonstrate that IK(Ca) channels in rabbit PCE cells are coupled to alpha1-adrenergic receptors and a PLC/IP3 signalling pathway. Activation of these channels may modulate fluid secretion by the ciliary epithelium.

Activation of a nonspecific cation current in rat cultured retinal pigment epithelial cells: involvement of a G(alpha i) subunit protein and the mitogen-activated protein kinase signalling pathway

1. Whole-cell patch-clamp recording techniques were used to investigate the G protein subtype and related signalling molecules involved in activation of a nonspecific cation (NSC) current in rat cultured retinal pigment epithelial (RPE) cells. 2. Under control conditions, in 130 mM NaCl with K+ aspartate in the pipette, cytosolic dialysis with guanosine-5'-O-(3-triphosphate) (GTPgammaS, 0.1 mM) activated a large non-inactivating NSC current in 80% of the cells recorded from. 3. Loading RPE cells with antibodies (10 microg-ml(-1)) against the alpha subunit of all PTX-sensitive G proteins (G(alpha i/o/t/z)) reduced NSC current activation to 11%, while loading RPE cells with antibodies directed specifically against the alpha subunits of the Gi subclass (G(alpha i-3)) completely abolished current activation. In RPE cells loaded with anti-G(alpha s) activation of the NSC current was unaffected. 4. Investigation of the potential downstream mediators in the G(alpha i) NSC channel pathway revealed that activation of the cation conductance was unaffected by treatment of RPE cells with the selective protein kinase C inhibitor GF 109203X (3 microM) or the selective CaM kinase II inhibitor KN-93 (50 microM). However, NSC current activation was delayed and the current amplitude reduced in the presence of the nonselective kinase inhibitor H-7 (100 microM) or the selective inhibitor of MAPKK (MEK) activation, PD 98059 (50 microM). 5. In the absence of GTPgammaS, the NSC current was not activated by superfusion of the cells with the cyclic GMP kinase activator dibutyryl-cyclic GMP or with the adenylate cyclase activator forskolin. 6. These results support the involvement of a G protein of the G(alpha i) subclass in the activation of a NSC current in rat RPE cells, and suggest a potential modulatory role for MAP kinase-dependent phosphorylation in current regulation.

Identification of a novel Lymantria dispar nucleopolyhedrovirus mutant that exhibits abnormal polyhedron formation and virion occlusion

In previous studies on the formation of Lymantria dispar nuclear polyhedrosis virus (LdMNPV) few polyhedra (FP) mutants, several polyhedron formation mutants (PFM) were identified that appeared to be unique. These viral mutants are being characterized to investigate the processes of polyhedron formation and virion occlusion. LdMNPV isolate PFM-1 is one of these mutants, and is described in this report. Genetic techniques were used to determine if isolate PFM-1 contained a mutation in the polyhedrin or 25K FP gene. Wild-type viruses were recovered after coinfection of Ld652Y cells with isolate PFM-1 and a FP mutant, and with isolates PFM-1 and PFM-C (isolate PFM-C contains a mutation in the polyhedrin gene). These viruses were analyzed by genomic restriction endonuclease digestion and found to be chimeras of the original PFMs used in the coinfections. Marker rescue studies mapped the mutation in isolate PFM-1 to a genomic region that does not include the polyhedrin or 25K FP genes. Isolate PFM-1 produced approximately 14-fold fewer polyhedra than LdMNPV isolate A21-MPV, an isolate that produces wild-type levels of polyhedra, and approximately 2-fold more polyhedra compared to the FP isolate 122-2. Polyhedra generated by isolate PFM-1 were normal in size and shape but contained very few viral nucleocapsids. The same amount of budded virus (BV) was released from cells infected with isolates PFM-1 and A21-MPV. In contrast, isolate 122-2 yielded significantly more BV than isolates PFM-1 and A21-MPV.

Actions of substance P on membrane potential and ionic currents in guinea pig stellate ganglion neurons

Neuropeptides are known to modulate the excitability of mammalian sympathetic neurons by their actions on various types of K+ and Ca2+ channels. We used whole cell patch-clamp recording methods to study the actions of substance P (SP) on dissociated adult guinea pig stellate ganglion (SG) neurons. Under current-clamp conditions, SG neurons exhibited overshooting action potentials followed by afterhyperpolarizations (AHP). The K+ channel blocker tetraethylammonium (1 mM), the Ca2+ channel blocker Cd2+ (0.1-0.2 mM), and SP (500 nM) depolarized SG neurons, decreased the AHP amplitude, and increased the action potential duration. In the presence of Cd2+, the effect of SP on membrane potential and AHP was reduced. Under voltage-clamp conditions, several different K+ currents were observed, including a transient outward K+ conductance and a delayed rectifier outward K+ current (IK) consisting of Ca(2+)-sensitive [IK(Ca)] and Ca(2+)-insensitive components. SP (500 nM) inhibited IK. Pretreatment with Cd2+ (20-200 microM) or the high-voltage-activated Ca2+ channel blocker omega-conotoxin (10 microM) blocked SP's inhibitory effects on IK. This suggests that SP reduces IK primarily through the inhibition of IK(Ca) and that this may occur, in part, via a reduction of Ca2+ influx through voltage-dependent Ca2+ channels. SP's actions on IK were mediated by a pertussis toxin-insensitive G protein(s) coupled to NK1 tachykinin receptors. Furthermore, we have confirmed that 500 nM SP reduced an inward Cd(2+)- and omega-conotoxin-sensitive Ba2+ current in SG neurons. Thus the actions of SP on IK(Ca) may be due in part to a reduction in Ca2+ influx occurring via N-type Ca2+ channels. This study presents the first description of ionic currents in mammalian SG neurons and demonstrates that SP may modulate excitability in SG neurons via inhibitory actions on K+ and Ca2+ currents.

Mitogen-activated protein and tyrosine kinases in the activation of astrocyte volume-activated chloride current

Astrocytes swell during neuronal activity as they accumulate K+ to buffer the increase in external K+ released from neurons. This swelling activates volume-sensitive Cl- channels, which are thought to be important in regulatory volume decrease and in the response of the CNS to trauma and excitotoxicity. Mitogen-activated protein (MAP) kinases also are activated by cell volume changes, but their roles in volume regulation are unknown. We have investigated the role of tyrosine and MAP kinases in the activation of volume-activated Cl- channels in cultured astrocytes, using whole-cell patch-clamp recording and Western immunoblots. As previously described, hypo-osmotic solution induced an outwardly rectifying Cl- current, which was blocked by NPPB and SITS. This Cl- current did not depend on [Ca2+ ]i because it was still observed when 20 mM BAPTA was included in the pipette, but it did exhibit rundown when ATP was omitted. Inhibition of tyrosine kinases with genistein or tyrphostin A23 (but not the inactive agents daidzein and tyrphostin A1) blocked the Cl- current. The MAP kinase kinase (MEK) inhibitor PD 98059 reversibly inhibited activation of the Cl- current by hypo-osmotic solution. Western immunoblots showed that genistein or PD 98059 blocked activation of Erk-1 and Erk-2 by hypo-osmotic solution in astrocytes. Therefore, activation of tyrosine and MAP kinases by swelling is a critical step in the opening of volume-sensitive Cl- channels.

The selective sigma2-ligand Lu 28-179 has potent anxiolytic-like effects in rodents

The anxiolytic potential of the selective sigma2 ligand 1-[4-[1-(4-Fluorophenyl)-1H-indol-3-yl]-1-butyl]spiro[isobenzofuran-1(3H),4-piperidine] [corrected] (Lu 28-179) was assessed in various animal models of anxiety in rodents. Lu 28-179 facilitated the exploratory behavior of mice and rats in the black and white two-compartment box over a large dose range. In the rat, the minimal effective dose (MED) was 0.18 nmol/kg (0.1 microg/kg), and in the mouse, the MED was 0.00018 nmol/kg (0.1 ng/kg). The anxiolytic-like effect was maintained after treatment with 1 microg/kg/day for up to 14 days, and no anxiogenic-like effects were seen upon withdrawal from repeated treatment. Lu 28-179 increased the time that pairs of rats spent in active social interaction (unfamiliar high-light conditions), MED = 0.1 ng/kg. Daily treatment with Lu 28-179 (1.8 nmol/kg = 1 microg/kg/day) for up to 4 weeks increased the social interaction time significantly compared with controls, and no anxiogenic-like effects were seen upon withdrawal. Furthermore, Lu 28-179 reversed shock-induced suppression of drinking in the rat (MED = 18,000 nmol/kg = 10 mg/kg). Lu 28-179 did not inhibit footshock-induced ultrasonic vocalization in the rat or isolation-induced aggressive behavior in the mouse. Lu 28-179 was over 100 times more potent than diazepam in the rat and mouse black and white test box and the rat social interaction test, whereas the potency of Lu 28-179 was comparable to that of lorazepam in reversal of shock-induced suppression of drinking. Lu 28-179 neither induced sedation nor impaired motor coordination, even at high doses (70,000 nmol/kg = 40 mg/kg). In conclusion, Lu 28-179 exerts potent and long-lasting anxiolytic-like effects in rodents without inducing sedation and withdrawal anxiogenesis.

Buspirone fails to affect cocaine-induced conditioned place preference in the mouse

The conditioned place preference (CPP) procedure was employed to examine the effects of the 5-hydroxytryptamine1A (5-HT1A) receptor agonist, buspirone, on cocaine reinforcement. Cocaine (5.0 mg/kg, S.C., 30 min) produced a significant place preference whereas buspirone (0.5-2.0 mg/kg, I.P., 30 min) per se failed to induce a CPP. Buspirone pretreatment (0.5-2.0 mg/kg, I.P.) 30 min prior to cocaine (5.0 mg/kg, S.C., 30 min) conditioning had no effect on the acquisition of cocaine-induced CPP. Pretreatment with buspirone on the postconditioning test day also failed to affect the expression of an already established place preference response to cocaine. These results demonstrate an inability of buspirone to block both the acquisition and the expression of cocaine reward, as modeled in the CPP paradigm.

The effect of several putative cognition enhancers on a water maze acquisition deficit produced by pCPA + scopolamine combination treatment

A combined treatment of a 3-day regimen of pCPA and low-dose scopolamine produced a significant deficit in the acquisition of a water maze task, which has been suggested as a model for the cognitive deficits of Alzheimer's disease. The putative cognition enhancers oxotremorine, captopril, ondansetron, and tacrine were used in attempts to alleviate the water maze impairment. The effects of oxotremorine were difficult to determine due to nonspecific motor effects causing alterations in swimming speed. No evidence for cognition-enhancing properties of captopril was found. Ondansetron showed a cognition-enhancing effect on one of 4 days, but only at a relatively high dose (1 mg/kg i.p.). Tacrine, however, alleviated the pCPA + scopolamine-induced cognitive deficit. This study may thus provide evidence for the usefulness of tacrine in treating spatial deficits in dementia.

Mammalian retinal pigment epithelial cells in vitro respond to the neurokines ciliary neurotrophic factor and leukemia inhibitory factor

We examined whether primary cultures of rat retinal pigment epithelial (RPE) cells and RPE cells of an immortalized rat cell line, BPEI-1, would be responsive to the neurokines ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF), which are known to be potent trophic factors for neuronal cells. Primary RPE cell cultures were characterized by indirect immunofluorescence and exhibited positive immunoreactivity for RET-PE2, a monoclonal antibody that recognizes RPE cells, and for the intermediate filaments cytokeratin and vimentin. The survival of cultured RPE cells in serum-free defined medium in the presence of CNTF or LIF was investigated during a 0- to 5-day period. Both CNTF and LIF, at concentrations of 1-50 ng/mL (4-200 pM), markedly enhanced RPE cell survival. Bromodeoxyuridine labelling of RPE cells revealed an increased mitotic activity in cell cultures treated with either CNTF or LIF in comparison to untreated serum-free cultures. Increases in cell survival and proliferation after neurokine treatment were also observed with the BPEI-1 cell line. However, in comparison to the primary RPE cultures, LIF was more effective than CNTF in promoting survival of the cell line over a 5-day treatment period. These studies demonstrate that the neurokines CNTF and LIF are potent trophic factors for mammalian RPE cells in vitro and may serve as candidate therapeutic agents in degenerative conditions that affect the retina and RPE.

Perirhinal cortex involvement in limbic kindled seizures

Investigations into the anatomical substrate of temporal lobe epilepsy have yielded a number of important observations regarding the involvement of the piriform and perirhinal cortical areas in temporal lobe seizure propagation. Although early reports indirectly suggested that the circuits of the piriform cortex might act as a critical conduit for limbic seizure discharges to access motor systems, recent reports more strongly implicate the perirhinal cortex in this process. In the following report, we provide a brief summary of the earlier work involving the piriform cortex and its potential involvement in kindled limbic seizures. This is followed then by the results of several recent in vivo and in vitro electrophysiological studies that ascribe a critical importance for the perirhinal cortex in convulsive limbic seizures. Finally, since our anatomical studies indicated that the perirhinal cortex densely innervates the frontal motor cortex, we examined the involvement of this latter region in amygdala kindled seizures using the reversible functional lesion of cortical spreading depression. Based on these findings we suggest that the circuits of the perirhinal cortex may be important in the amplification and distribution of temporal lobe seizure discharges, providing access to structures that are capable of driving a convulsive response.

Seizure-induced differential expression of messenger RNAs for neurotrophins and their receptors in genetically fast and slow kindling rats

Levels of messenger RNAs for brain-derived neurotrophic factor, nerve growth factor and neurotrophin-3, and their high-affinity receptors, TrkB and TrkC, were analysed in the brains of genetically fast and slow kindling rats using in situ hybridization. Basal expression of neurotrophins and Trk messenger RNAs in the hippocampal formation, amygdala, frontoparietal and piriform cortices did not differ between the two strains. At 2 h after the third generalized grade 5 seizure, induced by kindling stimulations in the amygdala, increased expression of brain-derived neurotrophic factor messenger RNA was detected in the dentate gyrus granule cell layer, amygdala, frontoparietal and piriform cortices of the fast kindlers. Similar seizure-evoked increases of brain-derived neurotrophic factor messenger RNA levels were also observed in the amygdala and piriform cortex of slow kindlers. However, in these animals, brain-derived neurotrophic factor messenger RNA expression was not significantly altered by the seizures in the dentate gyrus granule cell layer and frontoparietal cortex. Furthermore, the seizure-induced increase of nerve growth factor, TrkB and TrkC messenger RNAs and decrease of neurotrophin-3 messenger RNA levels in the dentate gyrus granule cell layer was only observed in fast, but not in slow, kindlers. The neurotrophins are believed to regulate synaptic plasticity and efficacy and to facilitate long-term potentiation and kindling epileptogenesis. The present data suggest that the slow and fast kindling rates in the two strains studied here might partly be due to differences in seizure-evoked neurotrophin and Trk synthesis.

G protein-mediated activation of a nonspecific cation current in cultured rat retinal pigment epithelial cells

We used whole-cell patch-clamp recording techniques to investigate G protein-activated currents in cultured rat retinal pigment epithelial (RPE) cells. Using 140 mM KCl intracellular and 130 mM NaCl extracellular solutions, rat RPE cells possessed both inward and outward K+ currents. Upon addition of the nonhydrolyzable guanine triphosphate analogue, guanosine-5'-O-(3-thiophosphate) (GTPgammaS, 0.1 mM), to the recording electrode, a nonspecific cation (NSC) current was elicited. The NSC current had a mean reversal potential of +5.7 mV in 130 mm extracellular NaCl with Cs+-aspartate in the pipette, and was not affected by alterations in the extracellular Ca2+ or Cl- concentration. The GTPgammaS-activated current was found to be permeable to several monovalent cations (K+, Na+, choline, TRIS, and NMDG). Addition of fluoroaluminate, an activator of large molecular weight heterotrimeric GTP-binding proteins (G proteins), to the intracellular recording solution activated the NSC current. The G protein involved was pertussis toxin (PTX)-sensitive, since GTPgammaS failed to activate the NSC current in cells pretreated with PTX. Further investigation of second messenger molecules suggested that activation of the NSC current was not affected by alterations in intracellular Ca2+ or ATP. From these results, we conclude that a G protein-regulated NSC current is present in rat RPE cells. Activation of the NSC current may sufficiently depolarize RPE cells to activate outward K+ currents. This would provide a mechanism by which these cells could rid themselves of accumulated K+.

Combined pCPA and muscarinic antagonist treatment produces a deficit in rat water maze acquisition

A 3-day treatment with p-chlorophenylalanine (pCPA, 100 mg/kg/day) produced a significant decrease (63-89%) in 5-HT levels in both the hippocampus and the cortex of rats, while noradrenaline, adrenaline, and dopamine levels were unaffected. Treatment with pCPA alone did not affect the acquisition of a spatial learning task in the water maze. Treatment with low doses of either scopolamine (0.25 mg/kg) or atropine (10 mg/kg) was also insufficient to cause a significant impairment of water maze acquisition. However, a combined treatment of a 3-day pCPA regimen with the low dose of atropine or scopolamine produced a significant deficit in the acquisition of a water maze task.

Efferent projections of the anterior perirhinal cortex in the rat

Because convulsive seizures develop very rapidly from kindling sites in the anterior perirhinal cortex, we studied perirhinal efferents by using the anterograde tracer Phaseolus vulgaris leucoagglutinin (PhAL). PhAL injections into the anterior perirhinal cortex labelled a prominent network of fibers within the frontal cortex that was most dense within layers I and II and layer VI. As individual PhAL injection sites within the perirhinal cortex were restricted to one or two adjacent laminae, we were able to determine that layer V was the main source of the perirhinofrontal projection. This was confirmed by frontal cortex injections of the retrograde tracer Fluorogold (FG). Other cortical areas with densely labelled fibers following perirhinal PhAL injections included the agranular insular, infralimbic, orbital, parietal, and entorhinal cortices. Moderate to mild fiber labelling was also noted in the posterior piriform, temporal and occipital cortices, and the claustrum. Subcortical labelling was seen in the nucleus accumbens; fundus striati; basal and lateral amygdala nuclei; the "acoustic thalamus"; and the central grey. Several of these cortical and subcortical projections were bilateral. The different laminar origin of these perirhinal efferents is discussed. These results confirmed our prediction of extensive direct projections from the anterior perirhinal cortex to the frontal cortex in the rat. The significance of this projection is discussed with special reference to the anatomical basis of convulsive limbic seizures.

Selective effects of 8-OH-DPAT on social competition in the rat

Previous research has demonstrated that dominant-subordinate relationships measured in small groups of rats competing for access to palatable food or fluids can be disrupted by both anxiolytic and anxiogenic drugs, and it has been proposed as a possible animal model of anxiety. The present study investigated the effects of the selective 5-HT1A agonist 8-OH-DPAT on the rank order of triads of rats measured in terms of access to sweetened milk. The effect of 8-OH-DPAT on locomotor activity and intake of sweetened milk was also determined. 8-OH-DPAT (25 and 37.5 micrograms/kg) significantly increased the subordinate animals position in the social hierarchy without effect on the individual intakes of sweetened milk or locomotor activity. The same doses administered to dominant animals had no effect on any of the parameters measured. The 8-OH-DPAT-induced increase in social competition in subordinate rats was dissociable from effects on feeding behavior and locomotor activity. The results from this study provide further evidence that social competition in groups of rats may represent a model that can be used to detect drugs acting via receptor mechanisms believed to be implicated in anxiety.

Differential sensitivity of various temporal lobe structures in the rat to kindling and status epilepticus induction

Using focal brain stimulation (kindling), discrete seizures can be triggered from many neuroanatomic sites with varying degrees of facility. From several of these sites, protracted seizures or status epilepticus (SE) also can be triggered. To date, no comparison has been made between different brain sites in their sensitivity both to kindling and to SE development. In this report, we have compared the kindling profiles of three amygdala nuclei, namely the basal (BL), central (CE), and medial (ME) nuclei, to the adjacent piriform (PIR) and perirhinal (PRH) cortices. In addition, three weeks following kindling, the susceptibility of each kindled site to status epilepticus (SE) was assessed by exposing the site to 60 min of electrical stimulation. We observed that (a) during the course of daily kindling, the afterdischarge threshold dropped progressively and significantly in all structures, (b) the rate of kindling in the PRH and PIR cortices and the CE amygdala was significantly faster than either the BL or ME amygdala, (c) when discrete convulsions were triggered, the latency to forelimb clonus in the PRH cortex and CE amygdala was significantly shorter than the other three structures, and (d) despite being slower to kindle than most other sites, stimulation of the BL nucleus most readily triggered SE. The kindling data suggest that discharges triggered from the PRH and CE more readily access motor systems supporting limbic convulsions than discharges triggered from the BL, ME nuclei or the PIR cortex. On the other hand, the SE data indicate that the mechanisms and circuits associated with the development of discrete kindled seizures are not identical to those associated with the induction of limbic SE.

Calcium-activated potassium current in cultured rabbit retinal pigment epithelial cells

Calcium-activated potassium current was studied in cultured rabbit retinal pigment epithelial (RPE) cells using whole-cell and single channel patch-clamp recording techniques. When K+ was the principal cation in the electrode, depolarizing voltage steps from a holding potential of -60 mV activated outwardly rectifying current. Outward K+ current was increased by the Ca2+ ionophore ionomycin and reduced when the extracellular Ca2+ concentration was decreased from 2.5 mM to 100 nM in the presence of ionomycin. Outward K+ current recorded in the presence of ionomycin was blocked by iberiotoxin and by charybdotoxin. Single channel recording from cell-attached and excised membrane patches revealed a large conductance Ca2+-activated K+ (K(Ca)) channel. Identification of K(Ca) channels was based on: 1) the voltage-dependence of channel opening; 2) the large unitary conductance (> 200 pS with symmetrical 130 mM K+); 3) the dependence of the reversal potential on the K+ gradient; and 4) increased channel opening after exposure of the cytosolic surface of excised membrane patches to elevated Ca2+. These results demonstrate that Ca2+-activated K+ channels are present in rabbit RPE cells and may play an essential role in the regulation of membrane potential and ion transport.

Acute and chronic arecoline: effects on a scopolamine-induced deficit in complex maze learning

These studies tested the effect of arecoline, a nonselective muscarinic agonist, administered either acutely or by chronic peripheral infusion via osmotic minipumps, on a scopolamine-induced deficit in a Stone (14 unit) T-maze task in rats. Scopolamine alone (0.125-1.0 mg/kg, IP) dose-dependently impaired maze acquisition, increasing maze run-times and to a lesser extent, the number of errors committed. Neither acute administration of arecoline (5.0 and 10.0 mg/kg, IP), when tested against a deficit induced by scopolamine (0.25 mg/kg, IP), nor chronic arecoline administration (30 and 50 mg/kg per 24 h), when tested against a deficit induced by scopolamine (0.5 mg/kg), were able to ameliorate the decrements in maze performance. In fact, the higher dose of arecoline (50 mg/kg per 24 h) infused over 10 days potentiated the scopolamine-induced deficit, with respect to latency. These data indicate that dose selection is of great importance when employing arecoline in tests of learning and memory and that the influence of the method of administration of arecoline on the behavioural outcome warrants further study.

Differential expression of the electrophysiological responses to axotomy in bullfrog sympathetic neurons following nerve injury at 15°C

In frogs maintained at 15°C, there is a partial failure of the cell body reaction (CBR) to axotomy. We investigated, in the sympathetic B-cells of the bullfrog, the effects of axotomy at 15°C on the changes in electrophysiological properties which we found previously to follow axotomy at 21°C. While the increase in action potential (AP) duration was delayed by about 14 days, it increased by the normal amount. In contrast, the reduction in after-hyperpolarization (AHP) duration was both delayed and attenuated. These results show that there is a differential expression of these two components of the CBR, with changes in AHP duration more sensitive to lowered temperature. In attempts to determine if the effect of reduced temperature was on the signalling of axotomy or on the cell body response to the signal, we performed experiments where the 15°C frogs were maintained at 21°C for 7 days, immediately after axotomy, or after various delays. These results suggest that at 15°C, there is an increased delay in signalling that the injury has occurred, but we were not able to show conclusively that maintained expression of the CBR requires an ambient temperature of 21°C. This study emphasizes that the CBR to axotomy is not a unitary response to a single signal, but can be dissected, by lowered ambient temperature, into differentially regulated components.

Patch-clamp recording from identified rat ciliary ganglion neurons in primary culture

Adult rat parasympathetic ciliary ganglion (CG) neurons were retrogradely labelled by intraocular injection of the carbocyanine fluorescent dye 1,1-dioleyl-3,3,3',3'-tetramethylindocarbocyanine methanesulfonate (DiI). Whole-cell and nystatin perforated patch recording techniques were then used to examine the electrophysiological properties of labelled CG neurons growing in primary culture. The resting membrane potential of CG neurons in dissociated cell culture was -50 +/- 8 mV, and isolated neurons fired overshooting action potentials in response to depolarizing current injection. Voltage-clamp recordings of membrane currents revealed a transient tetrodotoxin-sensitive Na+ inward current and both sustained and transient outward K+ currents. Sustained outward K+ current was reduced (55-77%) by 5 mM tetraethylammonium and to a lesser extent (42-46%) by superfusion with nominally Ca2+ free external solution. Transient outward current was blocked by 100 microns 4-aminopyridine and exhibited steady-state inactivation at potentials depolarized to -50 mV. These data demonstrate that identified adult mammalian CG neurons can be successfully maintained in culture. Cultured CG neurons retain electrical excitability, with voltage-sensitive Na+ and K+ currents giving rise to action potentials.

Apolipoprotein E restricts interleukin-dependent T lymphocyte proliferation at the G1A/G1B boundary

Apolipoprotein E (apoE), a lipid transport protein important in cholesterol homeostasis, inhibits the proliferation of interleukin-dependent lymphocytes. Growth factor-responsive cells are blocked in the G1A phase of the cell cycle. Suppression by apoE is independent of growth factor, as evidenced by the fact that interleukin-2 (IL2)- and IL4-dependent proliferation of HT-2 T lymphocytes is equally inhibited. apoE has no effect on IL2-augmented killing of target cells by cytotoxic T cells, indicating that it has no direct effect on signaling via interleukin receptors. The data are consistent with inhibition by apoE of an event or pathway distal to receptor signaling and required for G1A transition, or G1B entry.

Aged Stone maze-impaired rats exhibit reduced striatal muscarinic receptor densities

Muscarinic receptor densities, measured by saturation radioligand binding using the muscarinic antagonist [3H]QNB, were compared in the striatum, frontal cortex and hippocampus between two populations of young (3 month) and aged (12-20 month) Hooded Lister rats which had previously been tested in a complex maze task. Aged rats were impaired in their performance of a Stone (14-unit T-maze) task and were less spontaneously active than young rats. Muscarinic receptor numbers were significantly decreased in the striatum of aged rats, whilst numbers in the hippocampus and frontal cortex and receptor affinities in all three areas were unaltered. These results indicate that the age-associated depletion of striatal muscarinic receptors may contribute to deficits in cognitive processing and/or motor behaviour which underlie impairments in the performance of complex spatial tasks.

Complications of plombage in a Cuban exile

Collapse of the affected lung, or plombage, was a common operative treatment for tuberculosis in the United States in the 1930s and 40s. Due to the lack of antitubercular drugs, this practice continued in Cuba into the 1950s. After 41 years the plombage material in an exile patient was found to be infected. This resulted in the bronchopleural fistula which required a pectoralis muscle flap to close. Physicians should be aware that many Cuban exiles have been treated for tuberculosis via plombage and are at risk for similar complications.

Apolipoprotein E inhibition of proliferation of mitogen-activated T lymphocytes: production of interleukin 2 with reduced biological activity

Apolipoprotein E (apoE), but not apoAI or apoCIII, suppresses mitogen-activated T lymphocyte proliferation, independent of the type of activation signal. Both CD4 and CD8 T cells are inhibited. ApoE inhibits T cell proliferation, in part, by reducing the production of bioactive interleukin 2 (IL2). IL2 activity is reduced by approximately 50-65% in cultures of mitogen-stimulated T cells when apoE is present. ApoE does not significantly alter levels of IL2 mRNA or the mass of secreted IL2 protein, quantitated by enzyme immunoassay. Reduced IL2 activity was not a consequence of induction of IL2 inhibitors in response to apoE or effects of apoE on the bioassay. These results suggest that apoE antagonizes post-translational events in mitogen-activated T lymphocytes that are required for the secretion of a bioactive IL2 protein.

Functional consequences of posttranslational isomerization of Ser46 in a calcium channel toxin

The venom of the funnel-web spider Agelenopsis aperta contains several peptides that paralyze prey by blocking voltage-sensitive calcium channels. Two peptides, omega-Aga-IVB (IVB) and omega-Aga-IVC (IVC), have identical amino acid sequences, yet have opposite absolute configurations at serine 46. These toxins had similar selectivities for blocking voltage-sensitive calcium channel subtypes but different potencies for blocking P-type voltage-sensitive calcium channels in rat cerebellar Purkinje cells as well as calcium-45 influx into rat brain synaptosomes. An enzyme purified from venom converts IVC to IVB by isomerizing serine 46, which is present in the carboxyl-terminal tail, from the L to the D configuration. Unlike the carboxyl terminus of IVC, that of IVB was resistant to the major venom protease. These results show enzymatic activities in A. aperta venom being used in an unprecedented strategy for coproduction of necessary neurotoxins that possess enhanced stability and potency.

Ondansetron fails to attenuate a scopolamine-induced deficit in a Stone maze task

The 5-HT3 receptor antagonist ondansetron has previously been reported to improve cognition in the mouse, rat and marmoset in a variety of behavioural paradigms. The present study used the Stone maze to test the effect of ondansetron on the deficit caused by scopolamine in the performance of a highly complex spatial memory task in the rat. Ondansetron administered over a large dose range (1.0 ng kg-1-1.0 micrograms kg-1, i.p., b.d.) for a period of 10-15 days failed to attenuate the scopolamine deficit. Indeed at one dose level ondansetron (100 ng kg-1, i.p., b.d.) administered in combination with scopolamine (0.5 mg kg-1, i.p.) significantly potentiated the deficit, compared with the performance of rats receiving scopolamine alone.

Potassium currents in cultured rabbit retinal pigment epithelial cells

Membrane potential and ionic currents were studied in cultured rabbit retinal pigment epithelial (RPE) cells using whole-cell patch clamp and perforated-patch recording techniques. RPE cells exhibited both outward and inward voltage-dependent currents and had a mean membrane capacitance of 26 +/- 12 pF (SD, n = 92). The resting membrane potential averaged -31 +/- 15 mV (n = 37), but it was as high as -60 mV in some cells. When K+ was the principal cation in the recording electrode, depolarization-activated outward currents were apparent in 91% of cells studied. Tail current analysis revealed that the outward currents were primarily K+ selective. The most frequently observed outward K+ current was a voltage- and time-dependent outward current (IK) which resembled the delayed rectifier K+ current described in other cells. IK was blocked by tetraethylammonium ions (TEA) and barium (Ba2+) and reduced by 4-aminopyridine (4-AP). In a few cells (3-4%), depolarization to -50 mV or more negative potentials evoked an outwardly rectifying K+ current (IKt) which showed more rapid inactivation at depolarized potentials. Inwardly rectifying K+ current (IKI) was also present in 41% of cells. IKI was blocked by extracellular Ba2+ or Cs+ and exhibited time-dependent decay, due to Na+ blockade, at negative potentials. We conclude that cultured rabbit RPE cells exhibit at least three voltage-dependent K+ currents. The K+ conductances reported here may provide conductive pathways important in maintaining ion and fluid homeostasis in the subretinal space.

A justification for high resolution hematocrit measurement

The purpose of this study was to determine the feasibility of using a 6" digital caliper and a 20x viewing microscope to measure hematocrit (HCT) from microhematocrit tubes. The reliability and validity of the digital caliper technique (DC) was simultaneously compared with that of the conventional "turntable" style microhematocrit method (MC) and the Coulter Counter hematocrit (CC) for a comprehensive comparison of the three methods. The reliability of the three methods was assessed by computing the standard error of the measurement (SEm) on triplicate readings of human blood samples. The SEm for MC, CC, and DC methods were 0.3555, 0.3004, and 0.1491, respectively. Validity was assessed by comparing the average of the triplicate HCT readings for each method with HCT determined by densitometry. Average HCT values (+/- SE) for the MC, CC, DC, and densitometry methods were 42.3 +/- 3.2, 42.4 +/- 3.4, 43.1 +/- 3.4, 43.7 +/- 3.3, respectively. Only the DC HCT values were not different from the densitometry HCT (P > 0.05). The MC and CC values were significantly lower (P < 0.01). It is concluded that accurate, highly precise measurements of HCT are obtainable using the digital caliper. The significance for this is the increased ability to perform extremely accurate measurement of changes in plasma volume. With this information, research labs can reliably measure smaller changes in plasma than was previously possible with commercial procedures.

Actions of 5-hydroxytryptophan to inhibit and disinhibit mouse behaviour in the light/dark test

The involvement of 5-HT receptors in behavioural responding to an aversive situation was investigated in the mouse light/dark test. The administration of 5-hydroxytryptophan (5-HTP) (12.5-50 mg/kg i.p.) increased brain 5-HT turnover and inhibited mouse behaviour in the light/dark test box. The 5-HT2C/5-HT2A receptor antagonists methysergide (1.0 and 5.0 mg/kg i.p.) and ritanserin (0.1-1.0 mg/kg i.p.) antagonised (methysergide) or reversed (ritanserin) the effects of 5-HTP to an increased exploration of the light compartment; a low dose of the 5-HT3 receptor antagonist ondansetron (0.01 mg/kg i.p.) had a similar effect. The disinhibitory effect of the 5-HTP/ritanserin interaction was antagonised by the 5-HT3/5-HT4 receptor antagonists SDZ205-557 (0.001-0.1 mg/kg) and a high dose of tropisetron (1.0 mg/kg i.p.) but not by ondansetron (1.0 mg/kg i.p.). At these doses tropisetron and ondansetron had no effect in their own right. Thus the dominant effect of 5-HTP in the mouse is to inhibit behaviour, a response mediated via 5-HT2C/5-HT2A and 5-HT3 receptors. A 5-HT4 receptor may effect an opposing disinhibitory potential as revealed by ritanserin.

Outwardly rectifying chloride current in rabbit osteoclasts is activated by hyposmotic stimulation

1. We characterized chloride currents in freshly isolated rabbit osteoclasts using whole-cell and single channel patch-clamp recording configurations. Depolarization activated an outwardly rectifying current in 40-50% of cells, distinct from the inwardly rectifying K+ current we have previously reported in osteoclasts. 2. The outwardly rectifying current persisted under conditions where all K+ currents were blocked. Furthermore, the outward current was reversibly inhibited by Cl- transport blockers 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS); 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS); 4,4'-dinitrostilbene-2,2'-disulphonic acid (DNDS); and niflumic acid. The blocked current had a reversal potential close to the predicted chloride equilibrium potential and was dependent on the chloride concentration gradient. 3. In those osteoclasts in which outwardly rectifying current was not initially apparent, exposure to hyposmotic extracellular solution resulted in its reversible activation. The induced current was due to Cl-, based on its reversal close to the chloride equilibrium potential and sensitivity to blockade by Cl- channel inhibitors. The hyposmotically induced current could be activated in Ca(2+)-free solutions containing 0.2 mM EGTA. 4. When studied in the current-clamp configuration, hyposmotic stimulation caused depolarization from -76 +/- 5 to -5 +/- 6 mV (mean +/- S.D., n = 7). 5. Unitary Cl- currents were recorded in the cell-attached patch configuration at positive potentials. Single channels had a slope conductance of 19 +/- 3 pS (n = 5). Reduction of the external [Cl-] shifted the current-voltage relationship in the positive direction, supporting the conclusion that these were Cl- currents. Like the whole-cell currents, single channel Cl- currents were activated by exposure of cells to hyposmotic bathing solution. 6. We conclude that rabbit osteoclasts express an outwardly rectifying Cl- current that can be activated by osmotic stress. Cl- channels may play a role in cell volume regulation and may also provide conductive pathways for dissipating the potential difference that arises from electrogenic proton transport during bone resorption.

Hippocampal kindling protects several structures from the neuronal damage resulting from kainic acid-induced status epilepticus

In an attempt to study the effects of piriform cortex damage on kindled seizure propagation, we administered kainic acid (12 mg/kg; i.p.) to rats previously kindled from the dorsal hippocampus. Unexpectedly, the ensuing status epilepticus (SE) in the kindled rats did not result in the piriform cortex damage normally observed in naive rats. As a result of this surprising finding, a more comprehensive investigation was undertaken to compare dorsal hippocampal kindled and control rats on their electrographic and behavioral SE development and subsequent brain damage. The SE induction profile and the pattern of brain damage observed in our control rats was similar to previous reports [Neuroscience, 14 (1985) 375-403; Brain Res., 218 (1981) 299-318]. By contrast, although fewer kindled rats than controls responded to the initial dose of kainic acid with electrographic and behavioral seizures, those many kindled rats that did respond, showed a pattern of SE induction that was different from controls. Kindled rats manifested fewer 'wet dog shakes', more generalized convulsions and a faster development of severe limbic status (SLS) than controls. In addition, without pharmacological intervention, the SLS continued longer in kindled rats than in controls. Histological examination revealed brain damage in kindled rats that was markedly different from controls. Unlike controls, kindled rats had no damage in the piriform cortex or substantia nigra reticulata and minimal hippocampal damage, yet showed midline thalamic and anterior olfactory nuclei damage similar to controls. These differences were observed from 1 to 28 days after kindling. Although the mechanism(s) of this kindling-based neuroprotection is not known, its discovery should add importantly to our understanding of epilepsy-induced alterations of subsequent neuronal function.

Kindling in the perirhinal cortex

In vitro experiments have indicated that the perirhinal cortex is highly excitable and its relationship to the basolateral amygdala and piriform cortex is altered by previous amygdala or dorsal hippocampal kindling. As a result, we felt it was important to assess the excitability of the perirhinal cortex in vivo by comparing its kindling profile to that of the basal amygdala, piriform cortex or dorsal hippocampus. We observed that the after-discharge (AD) threshold of the perirhinal cortex was higher than the other 3 structures but the AD duration was not different. Subsequently, the perirhinal cortex kindled more rapidly than the other 3 structures, and with extremely short latencies to onset of forelimb clonus. With the view that synchronized discharge in the perirhinal-piriform area provides the critical trigger for limbic kindled convulsions, the relationship of kindling rate and convulsion latencies and durations between the 4 structures was discussed.

The effect of the 5-HT3 receptor antagonist, RS-42358-197, in animal models of anxiety

The S-isomer of the novel 5-HT3 receptor antagonist RS-42358 ((S)-N-(1-azabicyclo[2.2.2]oct-3-yl)-2,4,5,6-tetrahydro-1-H- benzo[de]isoquinolin-1-one, RS-42358-197) disinhibited behaviour in the mouse suppressed by the aversive situation of the light/dark test box. RS-42358-197 was effective at sub-ng/kg dose levels and the efficacy was maintained over a 100 million-fold dose range. In contrast, the R-isomer was ineffective at all doses studied. The S-isomer also disinhibited a suppressed behaviour in social interaction and elevated X-maze tests in the rat and reduced anxiety-related behaviours in a marmoset human threat test. RS-42358-197 prevented the exacerbation of the suppression of behaviour in the mouse light/dark test following withdrawal from treatment with alcohol, nicotine, cocaine and diazepam. Thus, the S-isomer of RS-42358 has a consistent non-sedating anxiolytic profile in rodent and primate models. It is exceptionally potent and a maintained efficacy at high doses distinguishes its actions from many other 5-HT3 receptor antagonists.

Are differences in dorsal hippocampal kindling related to amygdala-piriform area excitability?

It has been suggested that several structures associated with the amygdala-piriform (A-P) area are important, if not critical, for convulsive generalization of limbic seizures. In experiment 1, when examining the development of convulsive seizures kindled from the dorsal hippocampus (cornus ammonis; DH), a broad range of kindling rates was observed. Independent of electrode location within the hippocampus, kindling rates were correlated positively with both local and, more dramatically, distant excitability (measured by the duration of the primary and secondary hippocampal afterdischarges, respectively) at all stages of epileptogenesis. Because kindling rates were bimodally distributed, we bisected the distribution into 'faster' and 'slower' kindling rats. Here we examined the magnitude of both electrophysiological and behavioral differences between 'faster' and 'slower' rats and their changes over time. The 'faster' rats had longer primary and secondary afterdischarge (AD) durations than 'slower' rats throughout all stages of kindling. With the appearance of generalized convulsions, the 'faster' rats showed longer latencies to clonus onset, with longer clonus and AD durations than 'slower' rats. Also, the generalized convulsions of 'faster' rats appeared during a much enlarged secondary AD period, while 'slower' rats convulsed during primary AD. In both groups, convulsions were invariably associated with increased discharge in A-P associated structures. We interpreted the differences between 'faster' and 'slower' DH rats to reflect genetic differences in excitability in both local and A-P associated structures. If the DH kindling profile of the 'faster' rats differed from 'slower' rats largely because of naturally greater excitability in A-P associated structures, then experimentally increased excitability in those structures (via amygdala kindling) in a random sample of rats should duplicate much of the 'faster' DH kindling profile. In experiment 2, this outcome was observed. In conclusion, we suggest that either natural or induced differences in the excitability of A-P associated structures affect both the genesis and the profile of convulsive generalization of limbic kindled seizures.

The interaction of R(+)- and S(-)-zacopride with PCPA to modify rodent aversive behaviour

The interaction of R(+)- and S(-)zacopride (0.00001-10 mg/kg i.p.) with parachlorophenylalanine (PCPA, 3 day treatment 100 mg/kg i.p.) to modify behaviour in an aversive situation was investigated in the mouse black and white test box and rat social interaction test. R(+)-Zacopride (but not S(-)zacopride) and PCPA had an anxiolytic profile of action to reduce aversive responding in both species. Their established anxiolytic profiles were abolished by a subsequent treatment with S(-)zacopride. In contrast, S(-)-zacopride was less or ineffective if administered simultaneously with R(+)-zacopride. A co-treatment of PCPA with R(+)-zacopride also inhibited the anxiolytic profiles observed to the individual treatments. It is concluded that there is a complex interaction between the isomers of zacopride to modify responding to an aversive situation that is dependent on the temporal sequence of drug administration, and which may be modified by changes in basal 5-hydroxytryptamine (5-HT) tone and agonist, partial agonist and antagonist effects at the 5-HT3 receptor.

Effect of charybdotoxin and leiurotoxin I on potassium currents in bullfrog sympathetic ganglion and hippocampal neurons

The effects of charybdotoxin and leiurotoxin I were examined on several classes of K+ currents in bullfrog sympathetic ganglion and hippocampal CA1 pyramidal neurons. Highly purified preparations of charybdotoxin selectively blocked a large voltage- and Ca(2+)-dependent K+ current (IC) responsible for action potential repolarization (IC50 = 6 nM) while leiurotoxin I selectively blocked a small Ca(2+)-dependent K+ conductance (IAHP) responsible for the slow afterhyperpolarization following an action potential (IC50 = 7.5 nM) in bullfrog sympathetic ganglion neurons. Neither of the toxins had significant effects on other K+ currents (M-current [IM], A-current [IA] and the delayed rectifier [IK]) present in these cells. Leiurotoxin I at a concentration of 20 nM had no detectable effect on currents in hippocampal CA1 pyramidal neurons. This lack of effect on IAHP in central neurons suggests that the channels underlying slow AHPs in those neurons are pharmacologically distinct from analogous channels in peripheral neurons.

Profiles of interaction of R(+)/S(-)-zacopride and anxiolytic agents in a mouse model

The mouse black and white test box was used to measure changes in behaviour in an aversive situation where the administration of R(+)-zacopride (but not S(-)-zacopride) alone decreased aversive responding to the white area. A similar anxiolytic profile of action was observed using parachlorophenylalanine (PCPA), whose effects were antagonised by a co-treatment with R(+)-zacopride and reversed by S(-)-zacopride to an exacerbation of the aversive response. An anxiolytic profile of action was also observed using ondansetron, granisetron, chlordiazepoxide, diazepam, ritanserin, 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), E4424 (2-[4-[4-(4-chloro-l-pyrazoyl)butyl]-l-piperazinyl]-pyrimidine), umepsirone, DuP753 (2-n-butyl-4-chloro-5-hydroxy-methyl-1-[2(1H-tetrazol-5-yl) biphenyl-4-yl)methyl)]-imidazole), SQ29,852 ((S)-1-[6-amino-2[hydroxy)(4-phenyl-butyl)phosphinyl]-oxy)-1- nexy]-2-proline), devazepide and guanfacine, and this was retained following co-treatment with PCPA. The anxiolytic profile of action of PCPA was also retained following co-treatment with renzapride which when administered alone failed to modify behaviour. However, the ability of chlordiazepoxide, diazepam, ondansetron and E4424 (but not devazepide, DuP753 or SQ29,852) to reduce aversive responding was inhibited by co-treatment with R(+) and/or S(-)-zacopride. It is concluded that the reduction in aversive responding caused by pharmacological manipulation at the benzodiazepine, 5-HT receptor subtypes 5-HT1A, 5-HT1C/5-HT2 and 5-HT3 (but not at the cholecystokin CCKA or angiotensin receptors or inhibition of angiotensin converting enzyme) can be inhibited by R(+) and S(-)-zacopride. The data is discussed in terms of zacopride having an agonist or partial agonist effect at the 5-HT3 receptor.

Profile of action of a novel 5-hydroxytryptamine1A receptor ligand E-4424 to inhibit aversive behavior in the mouse, rat and marmoset

E-4424 (2-(4-[4-(4-chloro-1-pyrazolyl)butyl]-1-piperazinyl)pyrimidine) was shown to be a 5-hydroxytryptamine1A receptor ligand in radioligand binding assays and in an in vitro guinea pig ileum preparation had both 5-hydroxytryptamine1A antagonist and agonist effects. The antagonist/agonist ratio of E-4424 was greater than in the case of buspirone and ipsapirone. E-4424 was compared to diazepam, buspirone and ipsapirone to inhibit the behavioral response to an aversive situation in the mouse black and white test box, the rat social interaction test and a marmoset human threat test. The acute administration of E-4424 (0.0001-0.5 mg/kg, i.p.) to the mouse decreased aversion to the white area of the test box and was as effective as diazepam (0.125-1.0 mg/kg, i.p.) and much more potent than buspirone (0.25-1.0 mg/kg, i.p.) or ipsapirone (0.5-5.0 mg/kg, i.p.). E-4424 was also effective in enhancing rat social interaction and reducing anxiety-related behaviors in the marmoset and was again more potent than diazepam, buspirone or ipsapirone. Withdrawal from a 14-day administration of diazepam, cocaine, nicotine or alcohol exacerbated the response to the aversive situation in the mouse test. This was not observed after withdrawal from a chronic treatment with E-4424, buspirone or ipsapirone. However, E-4424 administered during drug withdrawal prevented the response caused by withdrawal from cocaine, alcohol, nicotine and diazepam: buspirone was ineffective and ipsapirone only attenuated that syndrome after alcohol withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Anxiolytic-like actions of anpirtoline in a mouse light-dark aversion paradigm

The anxiolytic-like potential of anpirtoline was assessed in a mouse light/dark aversion test. Anpirtoline (1.0 ng kg(-1)-1.0 micrograms kg-1 i.p.) reduced the aversive responding of mice. This was detected as an increase in the latency to locate the non-aversive compartment and by decreases in the percentage of the time spent in the dark compartment, and the numbers of rears and line crossings in the dark compartment. In radioligand binding studies anpirtoline displayed submicromolar affinity for 5-HT1A, 5-HT1B and 5-HT3 receptor recognition sites (Ki = 151, 28 and 30 nM, respectively) and more modest affinity for 5-HT2 receptor recognition sites (Ki = 1.48 microM). It is concluded that anpirtoline has a unique spectrum of affinity for 5-HT receptor subtypes, its interaction with which may account for its anxiolytic-like activity.

Inwardly rectifying potassium current in rabbit osteoclasts: a whole-cell and single-channel study

Ionic conductances of rabbit osteoclasts were investigated using both whole-cell and cell-attached configurations of the patch-clamp recording technique. The predominant conductance found in these cells was an inwardly rectifying K+ conductance. Whole-cell currents showed an N-shaped current-voltage (I-V) relation with inward current activated at potentials negative to EK. When external K+ was varied, I-V curves shifted 53 mV/10-fold change in [K+]out, as predicted for a K(+)-selective channel. Inward current was blocked by Ba2+ and showed a time-dependent decline at negative potentials, which was reduced in Na(+)-free external solution. Inward single-channel currents were recorded in the cell-attached configuration. Single-channel currents were identified as inward-rectifier K+ channels based on the following observations: (i) Unitary I-V relations rectified, with only inward current resolved. (ii) Unitary conductance (gamma) was 31 pS when recorded in the cell-attached configuration with 140 mM K+ in the pipette and was found to be dependent on [K+]. (iii) Addition of Ba2+ to the pipette solution abolished single-channel events. We conclude that rabbit osteoclasts possess inwardly rectifying K+ channels which give rise to the inward current recorded at negative potentials in the whole-cell configuration. This inwardly rectifying K+ current may be responsible for setting the resting membrane potential and for dissipating electrical potential differences which arise from electrogenic transport of protons across the osteoclast ruffled border.

Angiotensin-converting enzyme inhibition, angiotensin, and cognition

In these studies, we have investigated possible cognition-enhancing effects of angiotensin-converting enzyme (ACE) inhibition, and putative neurochemical correlates for these actions. In a mouse habituation model, ACE inhibitors improved basal performance and antagonized scopolamine-induced deficits. The performance of aged mice and those with lesions of the nucleus basalis was also improved. ACE inhibition also improved scopolamine-impaired performance of rats in a swim-maze model. Neurochemical studies showed that a low dose (10 micrograms/kg i.p.) of ceranapril caused significant alterations in ex vivo rat brain catecholamine levels in the nucleus accumbens, amygdala, and septum. In further studies, angiotensin II (Ang II) was shown to decrease potassium-stimulated [3H] acetylcholine release from slices of rat entorhinal and human temporal cortex, an effect that could be antagonized by the angiotensin receptor antagonist [1-sar,8-thr]Ang II. It is concluded that ACE inhibition can improve both basal and impaired performance in animal models of learning, and that this improvement may be in part a consequence of the removal by ACE inhibition of an inhibitory tone on central acetylcholine release, and/or an effect on central catecholaminergic function.

Suppression of amygdala kindling with massed stimulation: effect of noradrenaline antagonists

Afterdischarge (AD) triggered by brief, daily stimulation of the amygdala progressively increases in complexity and duration and, over days, develops into generalized convulsions. This progression, called kindling, is delayed by noradrenaline (NA). When brief stimulation of the amygdala occurs too frequently (massed), there is a suppression of AD growth and little evidence of kindling. Previously we showed that depletion of NA before massed amygdala stimulation prevented the suppression of AD growth described above, and readily precipitated generalized seizures. In the present report, we examined the role of NA in maintaining this suppression of AD growth, after it was well established. We showed that suppression of AD development during the first 15 massed stimulations (interstimulus interval of 5 min) was reduced by subsequent injection of the NA alpha 2 antagonist, yohimbine, with most rats exhibiting occasional generalized convulsions. Conversely, rats exposed to the beta antagonist, propranolol, like controls, not only showed suppressed AD growth, but also elevated AD thresholds. Three weeks later, only a small positive transfer to daily kindling was observed in all groups. We conclude that alpha 2 NA receptors help maintain suppression of AD growth induced by massed stimulation of the amygdala, while beta receptors provide only a small proepileptic influence. These results and those from the 'rapid' kindling model (Lothman et al., Brain Research, 360 (1985) 83-91) are compared, and related to NA receptor subtype variations in the amygdala and hippocampus.

K+ and Cl- currents in freshly isolated rat osteoclasts

Membrane electrical properties of freshly isolated rat osteoclasts were studied using patch-clamp recording methods. Characterization of the passive membrane properties indicated that the osteoclast cell membrane behaved as an isopotential surface. The specific membrane capacitance was 1.2 +/- 0.3 microF/cm2 (mean +/- SD), with no difference between cells plated on glass and those adhering to a permeable collagen substrate. The current/voltage (I/V) relationship of all cells showed inward rectification and I/V curves shifted 51 mV positive per tenfold increase of [K+]out, indicating an inwardly rectifying K+ conductance. The voltage dependence of the K+ chord conductance (gK) also shifted positive along the voltage axis, and the maximum conductance increased, with elevation of [K+]out. gK for cells bathed in 4.7 mM [K+]out increased e-fold per 12 mV hyperpolarization, and half-maximal activation was at -89 mV. Approximately 18% (50 pS/pF) of the maximum gK was active at -70 mV. Inward single-channel currents were recorded in cell-attached patches at hyperpolarizing potentials. With symmetrical K+, channel conductance was 25 +/- 3 pS and reversal was close to the K+ equilibrium potential, consistent with this K+ channel underlying the whole-cell K+ currents. With both conventional whole-cell and perforated-patch recording, no voltage-activated Ca2+ current was detected. In approximately 30% of osteoclasts studied, an outwardly rectifying current was observed, which was reversibly blocked by 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS). This DIDS- and SITS-sensitive current reversed direction at the chloride equilibrium potential. We conclude that an inwardly rectifying K+ current is present in all rat osteoclasts and that some osteoclasts also exhibit an outwardly rectifying Cl- current. Both these membrane conductances may play an important physiological role by dissipating the potential that arises from the electrogenic transport of H+ across the ruffled membrane of the osteoclast.

The effects of umespirone as a potential anxiolytic and antipsychotic agent

Umespirone was compared to buspirone, diazepam and clozapine as a potential anxiolytic and antipsychotic agent. In the mouse black and white test box, umespirone was considerably more potent than diazepam or buspirone to reduce aversive responding, tolerance to its effects was not observed and sedation was absent, a chronic treatment and withdrawal was not associated with an anxiogenic profile, and umespirone prevented the behavioural consequences of withdrawal from diazepam. Umespirone also had an anxiolytic profile of action in the tests of rat social interaction and in the marmoset exposed to a human threat. Both umespirone and clozapine reduced the hyperactivity induced by the infusion of dopamine into the nucleus accumbens of rat. In radioligand binding assays umespirone demonstrated nanomolar affinity for the alpha 1-adrenoceptor and the 5-HT1A and dopamine D2 receptors. It is concluded that umespirone may present as a novel psychotropic agent with anxiolytic and antipsychotic potential.