Prolonged inhibition in burst firing neurons: synaptic inactivation of the slow regenerative inward current.

By using voltage clamping and microiontophoretic techniques, it has been found that the prolonged cholinergic and dopaminergic inhibition seen in Aplysia burst firing neurons occludes the inward current on which slow oscillations depend. It also mimics the temperature and ionic sensitivity of that inward current. This prolonged inhibition, which cannot be inverted and is insensitive to extracellular potassium changes, thus appears to result from a synaptically produced inactivation of the regenerative slow inward current underlying bursting.

A direct synaptic connection mediating both excitation and inhibition.

Neurons have generally been thought to produce only one synaptic action on any particular cell which they innervate. An identified interneuron in the abdominal ganglion of Aplysia mediates both direct excitation and inhibition to an identified follower cell. At low firing rates the interneuron produces excitatory postsynaptic potentials; however at higher firing rates these gradually diminish in size and eventually invert to inhibitory postsynaptic potentials. Electrophysiological and pharmacological evidence indicates that the connection between these cells is monosynaptic, and that a single transmitter, acetylcholine, mediates both actions. These opposite synaptic responses appear to result from the transmitter's acting on two types of postsynaptic receptors having different thresholds for activation and different susceptibilities for desensitization.

Negative resistance characteristic essential for the maintenance of slow oscillations in bursting neurons.

Voltage clamping giving step commands reveals a steady-state negative resistance characteristic in the current-voltage curves of Aplysia bursting neurons. This is observed below spike threshold in the unstable range through which the membrane potential slowly oscillates. The negative resistance characteristic underlies this instability and shapes the rapid depolarization-hyper-polarization phase of the cycle. When bursting cells are converted to silent cells (by cooling) the negative resistance is abolished; conversely, when normally silent cells are made to burst (by warming) a negative resistance develops. The presence of negative resistance thus enables the bursting cell to oscillate, whereas its absence precluldes such oscillations.

Lateralization index but not contralateral suppression at adrenal vein sampling predicts improvement in blood pressure after adrenalectomy for primary aldosteronism.

Adrenal vein sampling (AVS) is essential in differentiating unilateral from bilateral sources of aldosterone excess in primary aldosteronism (PA). However, its ability to predict blood pressure (BP) improvement after adrenalectomy has not been well studied. This is a retrospective observational study of 119 patients who underwent AVS by sequential technique followed by adrenalectomy for PA at the Hospital of the University of Pennsylvania from 1997 to 2015. Median age was 52 years (interquartile range 44-59), 67% were male and median duration of hypertension was 10 (interquartile range 6-20) years. A total of 76% and 90% of patients experienced BP improvement at 0-6 months or at any time point after surgery, respectively. Lateralization index (LI) >8, but not the presence of contralateral suppression, was significantly associated with BP improvement after surgery by multivariate logistic regression analysis adjusted for potential confounders (odds ratio (95% confidence interval): 17.1 (1.7-171.6) and 6.39 (0.06-641.8), respectively). A prediction score was created by covariates that was significantly associated with BP improvement in logistic regression analysis (duration of hypertension, body mass index, preoperative systolic BP and number of antihypertensive medications). Receiver-operating characteristic curve analyses showed that the addition of LI >8 to the score increased its ability to predict BP improvement (area under the curve 0.73-0.80). In conclusion, LI is useful in predicting improvement in BP after adrenalectomy for PA. The results of this study suggest that patients with long-standing severe hypertension may still benefit from surgery if LI >8.

Electrophysiological basis for the spatial dependence of the inhibitory coupling in the Limulus retina.

A technique for measuring, with total optical isolation, the inhibition between two individual receptor units in the Limulus lateral eye is described. The extracellular responses of pairs of units were recorded, using light piping microelectrodes. The inhibitory coupling between two units was found to be nonlinear and describable by a simple hyperbolic equation written in terms of saturation rate (S), half saturation (H), and threshold (ft). By plotting reciprocal frequencies, the data could be linearized and compared for different pairs of units. The magnitude of inhibition (in terms of S and H) was found to decrease monotonically as the anatomical distance between receptors increased. An electrical model of the inhibitory system was developed which accounts for many of the properties of the observed inhibitory interactions. Using the equations from the model and the experimental data, it is shown that the "electrical distances" (which are computed in terms of space constants lambda) of the inhibitory synapses from the impulse-generating region of the test unit are directly related to the anatomical distance between receptors. It is also shown that "synaptic strength" is relatively constant with separation. The electrical distances of the inhibitory synapses range from about 0.1lambda to 0.25lambda for adjacent units to greater than 0.5lambda for units seven to nine receptors away. It is concluded that the nonlinear character of the inhibitory coupling is attributable to synaptic effects, and that the decrease of inhibition with distance between receptors is caused primarily by an increase in the electrical distance of the inhibitory synapses from the test unit.

Potential antidepressant activity of rolipram and other selective cyclic adenosine 3',5'-monophosphate phosphodiesterase inhibitors.

Following intraperitoneal administration, the selective cAMP phosphodiesterase (PDE) inhibitors rolipram, ICI 63 197 and Ro 20-1724 were investigated in mice in comparison with imipramine for their effectiveness in two classical test models for prediction of clinical antidepressant activity: antagonism of reserpine-induced hypothermia or hypokinesia and potentiation of yohimbine lethality. Rolipram was approximately 15 times more potent than imipramine or Ro 20-1724 and approximately as potent as ICI 63 197 in antagonizing reserpine-induced hypothermia. The antihypothermic effect of the phosphodiesterase inhibitors occurred at a smaller dose than that of imipramine. In contrast to imipramine, the phosphodiesterase inhibitors reversed reserpine-induced hypokinesia. Rolipram was approximately as potent as ICI 63 197 and about 15 times more potent than Ro 20-1724. Rolipram was approx. 5 times more potent than Ro 20-1724 and approx. as potent as imipramine or ICI 63 197 in potentiating the lethality of yohimbine. In both test models the (-)-isomer of rolipram was approx. 10-15 times more potent than the (+)-isomer, indicating a stereospecific mechanism of action. The present data suggest an antidepressant action of selective cAMP phosphodiesterase inhibitors due to enhancement of central noradrenergic transmission. The hypothesis is put forward that the increase of noradrenaline turnover induced by phosphodiesterase inhibitors in conjunction with the inhibitory action of the compounds on cAMP metabolism enables more efficient adaptative changes to occur at central synapses resulting in a rapid onset of the antidepressant activity. Preliminary results with rolipram in patients with endogenous depression seem to support this assumption.

Rolipram, a novel antidepressant drug, reverses the hypothermia and hypokinesia of monoamine-depleted mice by an action beyond postsynaptic monoamine receptors.

The antidepressant potential of rolipram and inhibitors of phosphodiesterase (PDE) which are selective for cyclic AMP has previously been ascribed to enhancement of central noradrenergic transmission by the combination of two mechanisms of action: increase of synthesis of noradrenaline and release (presynaptic component) and concomitant potentiation of noradrenaline signals due to inhibition of phosphodiesterase (postsynaptic component). To examine the contribution of the latter component to the antidepressant action, rolipram, ICI 63 197 or Ro 20-1724 were given to mice which were depleted of monoamines in the brain by combined pretreatment with reserpine, alpha-methyl-p-tyrosine and p-chlorophenylalanine. Rolipram, ICI 63 197 and Ro 20-1724 dose-dependently reversed the hypothermia and hypokinesia induced by this pretreatment. Imipramine and pargyline were inactive in this respect, indicating that their antidepressant effect depends on the availability of endogenous monoamines. The antihypothermic and antihypokinetic action of rolipram was not prevented by blockade of central beta-adrenergic or dopaminergic receptors. It is concluded that an action of rolipram, beyond postsynaptic receptors, essentially contributes to its antidepressant effect. The postsynaptic adenylate cyclase/cyclic AMP phosphodiesterase system is thought to be the most likely target. The unique properties of rolipram to stimulate both presynaptic and postsynaptic components of central neurotransmission should enable more efficient transduction of postsynaptic signals by circumventing presynaptic inhibitory feedback mechanisms, responsible for the delay in the therapeutic action of conventional antidepressant drugs.

Nonsteroidal antiinflammatory agents. 14. Synthesis and pharmacological profile of 6-chloro-5-(cyclopentylmethyl)indan-1-carboxylic acid.

The preparation of 6-chloro-5-(cyclopentylmethyl)indan-1-carboxylic acid is described. This acid has good anti-inflammatory and analgesic activities without producing irritation in the gastrointestinal tract up to the highest tested dose.

The type IV phosphodiesterase specific inhibitor mesopram inhibits experimental autoimmune encephalomyelitis in rodents.

Experimental autoimmune encephalomyelitis (EAE) is an autoimmune disease with pathological features reminiscent of those seen in multiple sclerosis and thus serves as an animal model for this disease. Inhibition of type IV phosphodiesterase (PDE IV) in animals with this disease has been shown to result in amelioration of disease symptoms. Here we describe the immunomodulatory activity of the novel potent and selective PDE IV inhibitor mesopram. In vitro, mesopram selectively inhibits the activity of type 1 helper T (Th1) cells without affecting cytokine production or proliferation of type 2 helper T (Th2) cells. Administration of mesopram to rodents inhibits EAE in various models. Clinically, EAE is completely suppressed by mesopram in Lewis rats. This is accompanied by a reduction of inflammatory lesions in spinal cord and brain. RT-PCR analysis revealed a marked reduction in the expression of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in the brains of these animals. Furthermore, the ex vivo production of Th1 cytokines by activated spleen cells derived from mesopram-treated animals is significantly reduced compared to vehicle-treated controls. Amelioration of the clinical symptoms is also observed during chronic EAE in mesopram-treated SJL mice as well as in relapsing-remitting EAE in SWXJ mice using a therapeutic treatment regimen. These data demonstrate the anti-inflammatory activity of mesopram and provide a rationale for its clinical development.

Immune factors in narcolepsy.

Most but not all subjects with the narcoleptic syndrome have the human leukocyte antigen (HLA) DR2 (and DQ1). The narcolepsy-DR2 association is the highest disease-HLA linkage known, and occurs in nonfamilial as well as familial cases of the narcoleptic syndrome. In other forms of daytime drowsiness, there is no relationship with a specific HLA, although some subjects considered to have "essential" hypersomnolence probably have the narcoleptic syndrome. The cause of the narcoleptic syndrome remains unknown, although in a few instances the condition follows infection. There is no evidence for a circulating sleep factor in the blood or in the cerebrospinal fluid of narcoleptic subjects, and no unequivocal marker of cellular immunity has yet been found. However, a few subjects with the narcoleptic syndrome have oligoclonal bands or raised immunoglobulin concentration in the cerebrospinal fluid. It is highly likely that the narcoleptic syndrome is an immune-mediated disorder, occurring in a genetically susceptible (DR2/DQ1-positive) subject.

Characteristic behavioural alterations in rats induced by rolipram and other selective adenosine cyclic 3', 5'-monophosphate phosphodiesterase inhibitors.

The significance of a characteristic symptomatology (hypothermia, hypoactivity, forepaw shaking, grooming, head twitches) as a potential in vivo correlate of enhanced availability of brain adenosine cyclic 3',5'-monophosphate (cAMP) was examined in rats following systemic administration of various doses of dibutyryladenosine cAMP (dBcAMP) or of the phosphodiesterase (PDE) inhibitors rolipram, Ro 20-1724, ICI 63-197, isobutylmethylxanthine (IBMX) theophylline, cartazolate, and papaverine. The various PDE inhibitors could be assigned to three groups according to the pattern of behavioral alterations they induced. Rolipram, Ro 20-1724, and ICI 63-197 (group 1) caused hypothermia, hypoactivity, forepaw shaking, grooming, and head twitches. All behavioral effects were mimicked by dBcAMP but not dBcGMP. The order of potency and effective dosage range to induce the behavioral alterations were, in descending order, rolipram (0.09-1453 mumol/kg IP), ICI 63-197 (0.48-119 mumol/kg IP), Ro 20-1724 (5.6-1438 mumol/kg IP), corresponding with the recently reported efficacy of the drugs to elevate rat brain cAMP in vivo. Comparatively high doses of the alkylxanthine PDE inhibitors IBMX and theophylline (group 2) caused hypothermia, forepaw shaking, grooming, and head twitches concomitantly with a decline of the motor stimulatory effect, suggesting enhanced availability of brain cAMP. The order of potency and the effective dosage range to induce the behavioral alterations were, in descending order, IBMX (28.1-113 mumol/kg IP) and theophylline (139-555 mumol/kg IP). The third group, papaverine (295-1179 mumol/kg IP) and cartazolate (21.5-345 mumol/kg IP), caused only hypothermia and hypoactivity. The differences in the behavioral pattern of the two latter groups of compounds in comparison with dBcAMP and the selective cAMP PDE inhibitors are discussed with regard to their additional interference with adenosine actions besides their nonselective PDE inhibitory action.

Effects of forskolin and cyclic nucleotides in animal models predictive of antidepressant activity: interactions with rolipram.

Forskolin, a direct activator of the catalytic subunit of adenylate cyclase (AC), and the cyclic nucleotide analogs dibutyryl cAMP (dBcAMP), 8-bromo cAMP (8-BrcAMP) and dibutyryl cGMP (dBcGMP) were tested for their ability to reverse the hypothermia or hypokinesia of mice depleted of presynaptic endogenous monoamines by pretreatment with reserpine, alpha-methyl-p-tyrosine and p-chlorophenylalanine. Forskolin and the cAMP analogs decreased the rectal temperature and inhibited locomotor activity in normal mice. In mice depleted of brain monoamines forskolin reversed the hypothermia and hypokinesia; dBcAMP and 8-BrcAMP antagonized the hypothermia but were only marginally effective in reversing the hypokinesia. DBcGMP was inactive. The antihypothermic action of forskolin or salbutamol was enhanced by the novel antidepressant and cAMP selective phosphodiesterase inhibitor rolipram (4RS-[3-cyclopentyloxy-4-methoxy-phenyl]-2-pyrrolidone). As an indirect effect via release of endogenous monoamines stimulating postsynaptic receptors was precluded by the monoamine-depleting pretreatment, forskolin and the cAMP analogs are thought to exert their antidepressant action by directly increasing brain cAMP availability. This is achieved by forskolin via activation of the catalytic subunit of AC and by the cAMP analogs via substitution for cAMP. These findings suggest that antidepressant activity is crucially linked to enhanced cAMP availability within brain effector cells. The successful treatment of endogenously depressed patients with rolipram supports this assumption.

Effects of locally applied dopamine to the nucleus accumbens on the motor activity of normal rats and following alpha-methyltyrosine or reserpine.

The motor activity of rats was investigated following bilateral application of various doses (0--80 micrograms) of dopamine to the nucleus accumbens. A high dose (80 micrograms) of dopamine increased the motor activity of normal as well as alpha-methyltyrosine- and reserpine-treated rats. It also increased the late motor activity (6--9 min) of normal rats, probably due to stimulation of postsynaptic dopamine receptors. Lower doses (10--40 micrograms) of dopamine suppressed initial (0--3 min) motor activity of normal rats, perhaps due to stimulation of dopamine autoreceptors on the dopamine nerve terminals in the nucleus accumbens with a subsequent inhibition of dopamine neurotransmission. An intermediate dose (40 micrograms) of dopamine was able to restore the motor activity of alpha-methyltyrosine-treated but not of reserpine-treated rats at all time intervals. This difference, indicating a restoration of the normal pattern of habituation by dopamine only in animals pretreated with alpha-methyltyrosine, suggests that normal behaviour is dependent on release of dopamine by nerve impulses.

Close correlation between behavioural response and binding in vivo for inhibitors of the rolipram-sensitive phosphodiesterase.

The antidepressant rolipram interacts in vitro with a binding site in brain tissue labeled by 3H-rolipram. A 3H-rolipram binding assay was employed in vivo to compare the affinity of rolipram-related compounds and reference phosphodiesterase (PDE) inhibitors with their potency in behavioural measures for potential antidepressant property. In two species, mice and rats, the potency of a number of compounds to antagonise reserpine-induced hypothermia (mice) and to induce head twitches (rats) was determined, as well as their potency to displace 3H-rolipram from forebrain binding sites in vivo. The treatment schedules for the two series of experiments were identical. Significant correlations between pharmacological effects and displacement of 3H-rolipram binding in vivo were observed in both species. Since the reference PDE inhibitors closely fit into the binding-pharmacological activity relationship, the PDE inhibitory properties of the substances involved are discussed.

ZK 91296, a partial agonist at benzodiazepine receptors.

5-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate) is a potent and selective ligand for benzodiazepine (BZ) receptors. Biochemical investigations indicate that ZK 91296 may be a partial agonist at BZ receptors. Such partial agonism may explain to some extent why ZK 91296 needs higher BZ receptor occupancy than diazepam for the same effect against chemical convulsants and for behavioural effects. The lack of sedative effects, and the very potent inhibition of reflex epilepsy, spontaneous epilepsy and DMCM-induced seizures suggest, furthermore, that ZK 91296 may possess pharmacological selectivity for a particular type of BZ receptor interaction, perhaps including topographic as well as receptor subtype differentiation.

Elimination of microwave effects on the vitality of nerves after blockage of active transport.

We have previously reported that exposure to microwave fields (a specific absorption rate of 10 W/kg at 2.45-GHz continuous wave) would consistently lower the survival time of isolated frog sciatic nerves stimulated at high repetition rates (50 pulse pairs per second, ppps). The time course of the loss of excitability of the exposed nerve (as compared to its unexposed contralateral mate) is reminiscent of that seen when the active transport of sodium (Na) and potassium (K) is blocked by certain agents--such as the cardiac glycoside ouabain. To assess the role that these microwaves may have in interfering with or counteracting active transport, we performed a series of experiments in which the active Na-K pump was substantially blocked by ouabain prior to microwave exposure. The paired nerves were soaked for 5 min in a high concentration (10(-3) g/liter) of ouabain to achieve the fastest and most complete blockage of the Na-K pump prior to stimulation at 50 ppps. The "rundown time course" was, as expected, accelerated in all ouabain-treated nerves, but the microwave-exposed nerves showed no additional shortening of survival time. The experiments were repeated at a slower stimulation rate (5 ppps) so that the survival time of the nerves more closely approximated that of nerves not treated with ouabain (1 to 2 h versus 30 min or less for ouabain-treated nerves stimulated at 50 ppps). Results of these lower stimulation rates also showed that there was no significant difference in the survival time of ouabain-treated exposed and control nerves. These results lend support to the view that the relative loss of excitability in microwave-exposed nerves is related to an interference with or counteraction of the Na-K pump.

Two reciprocating current components underlying slow oscillations in Aplysia bursting neurons.

The mechanisms of the slow oscillatory potential in burst firing neurons in the abdominal ganglion of Aplysia californica (L3-L6 and R15) were studied using voltage clamp methods, including a novel tract and hold technique. The steady-state negative resistance characteristic (NRC) of these neurons is attributed to the activation of a moderately fast, persistent, inward current over a range of membrane potential below spike threshold. This inward current is quite sensitive to changes in external sodium concentration (Na)0 and insensitive to potassium (K)0. By contrast, the portion of the I-V curve below the NRC range is insensitive to (Na)0, but highly sensitive to (K)0. The results of 'track and store' voltage clamping show that there are actually two reciprocating currents whose combined action produces the slow oscillation. In addition to the inward current, there is a slow outward current which develops during the depolarized (burst) phase. The slow outward current can also be evoked, and more completely examined, with prolonged depolarizing voltage commands. The extremely slow decay of this current (tau approximately 45 sec) appears to be the factor underlying the slow, ramplike depolarization of Vm during the interburst interval. This slow outward current is insensitive to changes of (Na)0, but changes with (K)0 in a manner consistent with the Nerst equation. We conclude that the burst-inducing slow oscillations are generated as follows: a moderately fast inward sodium dependent current (INa) produces a regenerative depolarization, and this in turn, produces a much slower outward potassium current (IS) which hyperpolarizes the cell. The cycle is completed when IS has decayed sufficiently to allow Vm to depolarize enough to reactivate INa. We have used a quantitative version of this model to determine the time courses of gNa and gK throughout the oscillation, and to explain why different portions of the oscillatory cycle display 'graded' or 'all-or-none' behavior.

Do NMDA receptor antagonists protect against MPTP-toxicity? Biochemical and immunocytochemical analyses in black mice.

We investigated whether excitatory amino acids acting at the N-methyl-D-aspartate (NMDA) subtype of the L-glutamate receptor contribute to the dopaminergic neurotoxicity induced by systemic administration of the Parkinson's syndrome-inducing toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in C57Bl/6 mice. The MPTP-regimen chosen (30-40 mg/kg body weight subcutaneously) resulted a 60-70% depletion of striatal dopamine (DA) content and a 20% reduction of tyrosine hydroxylase immunoreactive (TH-IR) cells in the substantia nigra pars compacta 20 days after administration. Repeated systemic coadministration of the non-competitive NMDA receptor antagonist MK-801 or of the novel competitive NMDA receptor antagonist CGP 40116 did not protect against MPTP-induced striatal DA depletion 20 days after toxin administration. Additionally, no short-term protective effects of MK-801 on striatal DA content were observed 24, 48, and 96 h, respectively, after exposure to MPTP. A slight and non-significant attenuation (approximately 10%) of the MPTP-induced decrease in the number of nigral TH-IR cells was observed after MK-801- and CGP 40116-treatment. We conclude that neurotoxicity of systemically administered MPTP is not substantially antagonized by NMDA receptor antagonists in mice.

Direct dopaminergic action of lisuride hydrogen maleate, an ergot derivative, in mice.

Lisuride hydrogen maleate induced stereotyped behaviour in normal as well as in reserpinized mice. It antagonized the motor depression and hypothermia induced by reserpine. On i.p. administration the compound was about as effective as apomorphine and D-amphetamine. As with apomorphine and in contrast to D-amphetamine the effects of lisuride hydrogen maleate in reserpinized mice were not impaired by additional treatment with alpha-methyl-p-tyrosine methylester. In untreated mice, the substance was very potent in lowering body temperature with significant hypothermia measured after dosages as low as 0.10 mg/kg i.p. Occurrence of stereotyped behaviour and hypothermia could be prevented by the dopaminergic antagonist haloperidol. From these data it is concluded that lisuride hydrogen maleate in addition to its interaction with serotoninergic systems is a potent dopaminergic agonist with a probably direct action on dopaminergic receptors. Further arguments in support of such an action of lisuride hydrogen maleate are, in addition to biochemical data, its serum prolactin lowering effect in rats, its strong emetic action in dogs and its effects on rat behaviour.

Lamotrigine has no antiparkinsonian activity in rat models of Parkinson's disease.

In rodent models of Parkinson's disease such as reserpinized or 6-hydroxydopamine substantia nigra lesioned rats, blockade of glutamate receptors of the NMDA (N-methyl-D-aspartate) or the AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptor subtypes and concomitant treatment with L-DOPA (L-3,4-dihydroxyphenylalanine) or direct dopamine agonists restores locomotor activity and induces rotations. An alternative approach to interfere with glutamatergic transmission would involve the inhibition of glutamate release resulting in functional glutamate antagonism. The novel antiepileptic drug lamotrigine blocks the veratridine-evoked release of the excitatory transmitters L-glutamate and L-aspartate. Due to its presumed antiglutamatergic action it has been suggested that lamotrigine may be useful in the treatment of Parkinson's disease. In a preliminary open-label study in patients with Parkinson's disease some favourable effects were reported. The present study was undertaken to systematically investigate the effects of lamotrigine in rat models of Parkinson's disease. However, lamotrigine failed to exert antiparkinsonian activity in reserpinized rats when administered alone or in combination with the dopamine receptor agonist apomorphine. In rats bearing 6-hydroxydopamine lesions of the substantia nigra lamotrigine did not induce rotations when given alone and did not modify rotations induced by apomorphine or the preferential dopamine D2 receptor agonist lisuride. On the basis of these negative results it is predicted that lamotrigine will not have significant favourable effects on akinesia and rigidity in Parkinson's disease patients.