Multimodality imaging in a depressed patient with violent behavior and temporal lobe seizures.

Patients suffering from epilepsy commonly experience behavioral symptoms. Behavioral manifestations are especially prevalent in patients with seizures originating in the limbic system. This case report illustrates how an objective, multimodality work-up can guide the clinician in the diagnosis and the treatment of a patient with a complex presentation. After the discontinuation of some medications, the patient underwent a multimodality work-up that consisted of MRI, SPECT, and conventional and quantitative EEG (LORETA). In this case, the functional imaging studies showed a convergence of findings across the three modalities: MRI, SPECT and qEEG. Because of these findings, we supported more aggressive treatment of the seizure disorder. Ultimately this treatment resulted in resolution of the aggression and the depression. In summary, when applied routinely, a comprehensive, systematic, diagnostic approach will minimize treatment false starts and failures, may reduce costs, and also, potentially decrease the severity and the duration of symptoms.

Similar or disparate brain patterns? The intra-personal EEG variability of three women with multiple personality disorder.

Quantitative EEG was used to assess the intra-personal variability of brain electrical activity for 3 women diagnosed with Multiple Personality Disorder (MPD). Two separate control groups (within-subject and between-subject) were used to test the hypothesis that the intra-personal EEG variability between 2 alters would be less than the interpersonal EEG variability between 2 controls, and similar to the intra-personal EEG variability of a single personality. This hypothesis was partially supported. In general, the 2 EEG records of a MPD subject (alter 1 vs. alter 2) were more different from one another than the 2 EEG records of a single control, but less different from one another than the EEG records of 2 separate controls. Most of the EEG variability between alters involved beta activity in the frontal and temporal lobes.

Changes in regional cerebral blood flow after electroconvulsive therapy for depression.

Fifteen patients with major depression and normal results of magnetic resonance imaging or computed tomographic studies were treated by electroconvulsive therapy (ECT). The regional cerebral blood flow (rCBF) of these patients was imaged using Tc-99m hexamethylpropylene amineoxime single-photon emission computed tomography before and after treatment, and their images were compared with a population of 11 healthy volunteers. Before ECT treatment, the patients had hypoperfusion of the frontal region compared with the controls, and they had multiple areas of altered perfusion throughout the brain. Five of the patients had an excellent clinical response to ECT; these patients also showed changes toward normal in rCBF. The remaining patients had minimal to moderate clinical response and showed no significant change in rCBF. These results indicate that improvement in clinical status as a result of ECT is correlated with a change toward normal in rCBF.

Individual differences among cocaine users.

The present study examined whether individual differences in personality could differentiate two types of cocaine users. We hypothesized that self-medicators (SM) use cocaine as a way to alleviate their dysphoric moods, whereas sensation seekers (SS), in contrast, use cocaine primarily to engender positive mood states. Eighteen male cocaine users were classified based on two dimensions of the Tridimensional Personality Questionnaire. SM were defined by having high harm avoidance (>17) and low novelty-seeking scores (<18), and SS by high novelty-seeking (>18) and low harm-avoidance scores (<17). It was predicted that SM would report higher depression and anxiety than would SS, and would also exhibit a brain activity pattern similar to that found in clinical depression. The results showed that SM reported higher anxiety than SS, F(1, 8) = 27.5, p < .001, but did not differ in depression. SM exhibited decreased blood flow within the left frontal lobes, F(1, 10) = 6.78, p < .05, similar to what has been observed in major depressive disorder. These findings suggest the importance of attending to individual differences in the motivation for cocaine use so that treatment can be targeted more effectively.

Platelet cytosolic calcium hyperresponsivity to serotonin in patients with hypertension and depressive symptoms.

BACKGROUND: Data from recent studies indicate that the presence of depression is an independent risk factor for cardiovascular and cerebrovascular events. The mechanism by which depression increases the morbidity and mortality risks in patients with comorbid vascular disease is currently the object of considerable research interest. Platelets may be involved in this pathological process. Although many investigators have extensively evaluated platelet biochemistry in depressed patients, there currently exists very little information regarding how the biochemical alterations might relate to an increased risk of cardiovascular events. In this study, we examined the responsivity of platelet cytosolic calcium concentrations ([Ca++]i) to serotonin stimulation in populations of hypertensive patients with or without comorbid depressive symptoms. METHODS: We utilized Fura-2 loaded platelets to compare changes in intracellular calcium levels (delta [Ca++]i) following serotonin stimulation among 48 patients with hypertension and varying degrees of depressive symptomatology. RESULTS: We found that those patients with higher scores on standardized depression rating scales showed significantly greater [Ca++]i (82.82 +/- 15.88 mmol/L) increase compared with [Ca++]i (60.10 +/- 22.65 mmol/L) patients with lower depression scores. CONCLUSIONS: The results of this study support the hypothesis that the enhanced platelet reactivity seen in patients with depressive symptoms may mediate the deleterious effects of depression on cardiovascular disease.

Platelet cytosolic calcium responses to serotonin in depressed patients and controls: relationship to symptomatology and medication.

BACKGROUND: Serotonin produces an exaggerated rise in platelet cytosolic calcium (delta [Ca++]i) in patients with mood disorders. Studies on patients with bipolar disorder consistently demonstrate calcium abnormalities. By comparison, data on patients with major depression are more variable. METHODS: To determine causes of variability, we utilized Fura-2 loaded platelets to compare changes in platelet intracellular calcium levels (delta [Ca++]i) following serotonin stimulation in 24 patients with major depression and in 20 controls. We also sought relationships between the delta [Ca++]i responses and scores on clinical depression and anxiety scales. RESULTS: We found positive correlations between delta [Ca++]i responses and the clinical scales across all subjects. Furthermore, depressed patients with high anxiety had significantly increased delta [Ca++]i responses compared to depressed patients with low anxiety. In addition, patients receiving selective-serotonin reuptake inhibitors (SSRIs) demonstrated reduced delta [Ca++]i responses compared to patients not on SSRIs. CONCLUSIONS: Since elevations in [Ca++]i mediate platelet aggregation and secretion cascades, the enhanced responsivity observed in depressed, and in particular anxious, depressed patients may contribute to their increased risk for vascular disease.

Serotonin-induced increases in platelet cytosolic calcium concentration in depressed, schizophrenic, and substance abuse patients.

Exaggerated intracellular calcium responses to challenges with serotonin (5-HT) have been reported in depression. In our studies, consistent with previous reports, patients with depression exhibited an exaggerated increase in 5-HT-stimulated intracellular calcium concentration ([Ca++]i). Basal cytosolic calcium was elevated in both calcium-free and 1 mM calcium media in depressed patients. the increased responsiveness to 5-HT was seen in both conditions. Patients with schizophrenia and substance abuse did not differ from normal controls. The 5-HT response was correlated with diastolic blood pressure (r = 0.33, p = 0.02): however, this association did not fully account for the exaggerated [Ca++]i responses in the depressed group. These findings suggest that exaggerated increases in [Ca++]i in response to serotonin are a characteristic of depressed patients not shared with schizophrenic and substance abuse patients. The relationship of depression to hypertension, two conditions that share abnormalities of calcium homeostasis, warrants further study.

Spontaneous transients of [Ca2+]i depend on external calcium and the activation of L-type voltage-gated calcium channels in a clonal pituitary cell line (AtT-20) of cultured mouse corticotropes.

Spontaneous transients of [Ca2+]i were recorded from single nonstimulated cells of a clonal pituitary cell line of corticotropes, AtT-20/D16v. The spontaneous [Ca2+]i transients were dependent on calcium entry from the extracellular solution because they were abolished both in the absence of extracellular calcium and with the addition of cobalt to the calcium-containing extracellular solution. Calcium entry occurred through voltage-gated (VGCC) L-type calcium channels because the [Ca2+]i transients were blocked by L-type calcium channel antagonists, e.g. nifedipine, and were unaffected by the addition of tetrodotoxin. Bay K 8644 (1 microM) induced transient increases in [Ca2+]i which were also blocked reversibly by either the absence of extracellular calcium or the addition of an L-type calcium channel antagonist (e.g. nifedipine). The resting levels of [Ca2+]i and the frequency, but not the amplitude or duration, of the spontaneous [Ca2+]i transients increased as the concentration of extracellular calcium was elevated in concentrations ranging from 1.8-7.2 mM. Potassium depolarization reversibly elevated resting levels of [Ca2+]i and initiated the spontaneous calcium transients. These results indicate that extracellular calcium modulates the frequency of spontaneous [Ca2+]i transients in AtT-20 cells which are caused by the activation of L-type calcium channels by a spontaneous increase in the permeability of the cell membrane to calcium.

Serotonin-induced changes in membrane potential and cytosolic free calcium in a clonal pituitary cell line (AtT-20) of cultured mouse corticotropes.

The effects of serotonin (5-HT) were examined on the cytosolic free calcium concentration, [Ca2+]i, in fura-2-loaded cells from a clonal cell line derived from the mouse anterior pituitary gland (AtT-20/D16v). Brief applications of 5-HT produced transient increases in [Ca2+]i. The duration and the amplitude of the 5-HT-induced increase in [Ca2+]i depended on the duration of 5-HT application. Longer duration (> 150 msec) applications of 5-HT produced a transient increase followed by a prolonged plateau phase of [Ca2+]i. Oscillations in [Ca2+]i were initiated and maintained in previously quiescent corticotropes following brief exposures to 5-HT. Addition of cobalt (500 microM-3.6 mM) to the extracellular solution abolished oscillations in [Ca2+]i and produced transient but not sustained increases in [Ca2+]i in response to 5-HT. Electrophysiological responses to 5-HT were recorded in separate experiments using the whole-cell patch clamp recording technique. Application of 5-HT to single cells produced a depolarization which was accompanied by a decrease in membrane conductance when measured under voltage clamp. The duration of the depolarizing response also increased with the duration of the 5-HT application. With longer duration 5-HT applications, the 5-HT-induced depolarizing response resembled the spontaneous action potential responses recorded in the same cell. However, the 5-HT-induced depolarizations were unaltered in the presence of extracellular cobalt. This suggests that the transient increase in [Ca2+]i recorded when 5-HT was applied in the presence of cobalt may represent intracellular release of calcium. These results demonstrate that 5-HT activates single cultured corticotropes directly by producing an increase in [Ca2+]i and cell depolarization.

Bethanechol-induced responses in mudpuppy parasympathetic neurons.

The effect of bethanechol on membrane potential and excitability was determined in mudpuppy parasympathetic postganglionic neurons. Bethanechol induced a large amplitude hyperpolarization, which was followed by a smaller amplitude depolarization, in 115 out of 135 cells tested. In approximately 20% of these cells, a brief depolarization preceded the hyperpolarization. During the bethanechol-induced hyperpolarization, the membrane input resistance decreased markedly, whereas the input resistance was increased during the subsequent depolarization. The hyperpolarization and depolarization were blocked by atropine and were unaffected by d-tubocurarine, thus, both appeared to be mediated by muscarinic receptors. The bethanechol-induced hyperpolarization was inhibited by the M2 muscarinic receptor antagonist AF-DX 116, whereas the bethanechol-induced depolarization was unaffected. Both a nonselective increase in membrane conductance and a decrease in membrane potassium conductance appeared to be involved in the generation of the bethanechol-induced depolarization. Evidence for the first mechanism was obtained in barium-treated cells in which bethanechol initiated a rapid onset depolarization, which was reversed at membrane potentials near 0 mV. Evidence for the second mechanism was obtained when the hyperpolarization was inhibited by AF-DX 116. In AF-DX 116-treated cells, the membrane input resistance was increased during most of the bethanechol-induced depolarization. Mudpuppy neurons initiate repetitive action potential activity in response to long depolarizing current pulses. Following application of bethanechol, with the hyperpolarization negated electrotonically, the number of action potentials produced by a depolarizing current pulse was greater than that produced prior to application of bethanechol. It is suggested that activation of muscarinic receptors on mudpuppy cardiac neurons influences multiple conductance systems and determines the excitability of these neurons.

Galanin-like innervation of rat submandibular and sublingual salivary glands: origin and effect on acinar cell membranes.

The distribution and source of a galanin-like innervation of rat salivary glands has been examined. Additionally, submandibular and sublingual acinar cell membrane responses to galanin or a cholinergic agonist were studied. Galanin-immunoreactive fibers were observed throughout the submandibular and sublingual glands in association with ducts and acini. A subset of submandibular ganglion cells expresses galanin immunoreactivity. Parasympathectomy resulted in a marked decrease in galanin immunoreactivity in the glands. Sympathectomy resulted in marked reduction of dopamine beta-hydroxylase immunoreactivity with no appreciable change in galanin immunoreactivity. Retrograde labeling experiments demonstrated that galanin-immunoreactive sensory neurons in the trigeminal ganglion do not innervate the submandibular or sublingual gland. These results indicate that the galanin-like innervation of rat salivary glands is derived from parasympathetic nerves to the glands. Since rat sublingual glands contain largely mucous acini while rat submandibular gland acini are seromucous, electrophysiological responses to galanin and the muscarinic agonist, bethanechol, were compared. Agonist-induced voltage shifts varied between the two glands. The galanin-induced response at the level of the resting membrane potential in submandibular acinar cells was a hyperpolarization, while that in sublingual acinar cells was a depolarization. There was also a greater voltage dependence to the galanin-induced submandibular response than to the sublingual response. Differences were also noted in the acinar cell response to cholinergic stimulation between these glands. These results demonstrate the existence of a galanin-like innervation to salivary glands that may be functionally relevant. Moreover, the results challenge the idea that agonist-induced membrane responses are similar among acinar cells of different glands.

Aminergic and peptidergic elements and actions in a cardiac parasympathetic ganglion.

Correlated histochemical, immunocytochemical, and electrophysiological experiments have been undertaken to identify putative neurotransmitter-neuromodulator substances in cells and fibers in the parasympathetic cardiac ganglion of the mudpuppy, Necturus maculosus, and to determine the action of these agents on the properties of the parasympathetic postganglionic neurons. The mudpuppy cardiac ganglion contains two neuron types: large parasympathetic postganglionic neurons and smaller intrinsic neurons initially identified as small intensely fluorescent cells. We have shown that the postganglionic neurons contain both acetylcholine and a galanin-like neuropeptide. Also, we have demonstrated that the intrinsic neurons contain a number of different biogenic amines such as dopamine and serotonin, as well as neuropeptides including a substance P-like peptide and a galanin-like peptide. The results of these studies indicate that the anatomical and histochemical organization of the mudpuppy cardiac ganglion is more complex than that seen in other amphibians and is very similar to that found in most mammalian species. Previously, we showed that galanin has actions that make it of interest as a potential inhibitory neurotransmitter in the mudpuppy cardiac ganglion. Galanin hyperpolarizes and decreases membrane excitability in most parasympathetic neurons. Here we show that galanin initiates membrane hyperpolarization by activating a voltage- and time-dependent potassium conductance. We also present the initial results of ongoing studies which indicate that calcitonin gene-related peptide can depolarize some of the parasympathetic neurons as well as evidence that serotonin initiates depolarization in many parasympathetic neurons. This serotonin-induced depolarization consists of an initial transient depolarization followed by a longer, more slowly developing depolarization. Action potential activity is stimulated during the initial period of depolarization, but depressed during the later, slow depolarization. The results of these electrophysiological experiments suggest that many of the bioactive substances that have been identified in the different cells and nerve fibers within the cardiac ganglion affect the excitability of the postganglionic neurons. In conclusion, we suggest that the results of the studies summarized in this review demonstrate that the cardiac ganglion in the mudpuppy is not simply a relay station. Rather, the cardiac ganglion has a complex organization and exhibits a diversity of physiological responses, indicating that it very likely is another site of integration for control of cardiac function.

Analysis of the galanin-induced decrease in membrane excitability in mudpuppy parasympathetic neurons.

Previously, we showed that the neuropeptide galanin hyperpolarizes and decreases membrane excitability of mudpuppy parasympathetic neurons [Konopka L. M., McKeon T. W. and Parsons R. L. (1989) J. Physiol. 410, 107-122]. We also demonstrated that membrane excitability remains depressed when the agonist-induced potential change is negated electrotonically. We hypothesized that galanin inhibits the membrane conductances associated with spike generation. However, we cannot rule out the possibility that the decreased excitability is due to a galanin-induced increase in membrane potassium conductance which reduces the effectiveness of subsequent depolarizing stimuli. Therefore, in the present study we tested, with the galanin-induced hyperpolarization negated, whether the galanin-induced increased membrane potassium conductance was responsible for the decreased excitability. The results showed that the galanin-induced decreased excitability was not dependent on the peak amplitude of the galanin-induced hyperpolarization. Furthermore, the decreased excitability occurred in cells in which there was no measurable galanin-induced hyperpolarization. Moreover, in most cells the galanin-induced decrease in input resistance, measured at the peak of the hyperpolarization (3-25 mV), was less than 15% and when the hyperpolarization was negated electronically, the decrease was even less (approximately 2%). These results indicated that when the hyperpolarization was negated, the galanin-induced increase in potassium conductance was not responsible for the decreased excitability. In preparations pretreated with 5 mM tetraethylammonium, galanin decreased excitability which indicated that a galanin-induced decrease in the calcium-dependent potassium current was not necessary for the decreased excitability. Galanin also decreased excitability in preparations exposed to either 1-3 microM tetrodotoxin or 100-200 microM cadmium. Following galanin application, the threshold for initiation of tetrodotoxin-insensitive spikes was shifted to more positive membrane potentials. Galanin also decreased the amplitude and hyperpolarizing afterpotential of barium spikes in the absence of any agonist-induced hyperpolarization. These observations confirmed that galanin decreased the voltage-dependent calcium conductance. In the present study, we showed that when the hyperpolarization was negated, galanin decreased excitability by shifting the threshold for spike generation regardless of whether voltage-dependent sodium or calcium currents were primarily responsible for the depolarizing component of the action potential.

Galanin-induced hyperpolarization of mudpuppy neurons is calcium dependent.

The calcium dependence of the hyperpolarization produced by galanin has been studied in parasympathetic postganglionic neurons of the mudpuppy. Necturus maculosus. The galanin-induced hyperpolarization, but not the bethanechol-induced hyperpolarization, was reduced when manganese or magnesium were substituted for external calcium. Also, the galanin-induced, but not the bethanechol-induced hyperpolarization, was decreased in the presence of cadmium or nitrendipine. Because the inhibition of the galanin-induced hyperpolarization developed gradually and reversed slowly in the absence of extracellular calcium or presence of the voltage-gated calcium channel blockers, it is suggested that an intracellular pool rather than an extracellular pool of calcium is involved in the generation of the galanin-induced hyperpolarization.

Frog sympathetic ganglion cells have local axon collaterals.

Amphibian autonomic ganglia have been used as simple models for studies involving the physiology of synaptic transmission. These models assume an anatomical simplicity where the ganglion is a simple relay for central nervous system output to peripheral autonomic targets. Cholinergic preganglionic fibers innervate the soma and proximal axon of the unipolar ganglion cells, which were thought to relay the information to the periphery with little ganglionic processing. However, several different types of synaptic potentials occur in response to preganglionic stimulation. Also, a variety of neuropeptides are found in both preganglionic fibers and ganglion cells; at least one of the peptides found in preganglionic fibers is known to act as a neurotransmitter in the ganglion. Finally, there may be communication between ganglion cells. In the present study, we have explored the morphology of lumbar sympathetic chain ganglion cells by intracellular injection with horseradish peroxidase to determine whether an anatomical substrate exists for processing information within these ganglia. We have shown that 39% of these cells have axons that branch within the ganglion. While both major classes of ganglion cells (B cells and C cells) had intraganglionic axon collaterals, there was a marked difference in the frequency: 65% of the C cell axons had collaterals while only 19% of the B cell axons collateralized within the ganglion. Ultrastructural examination of labeled axon collaterals indicated that these collaterals receive synaptic input; whether the collaterals also make synapses has not been definitively established.

Characteristics of the galanin-induced depolarization of mudpuppy parasympathetic postganglionic neurons.

The depolarization of mudpuppy parasympathetic cardiac neurons, produced by pressure application of the neuropeptide galanin, has been characterized. The amplitude and duration of the depolarization were dependent on the duration of the galanin application. The amplitude of the depolarization increased with hyperpolarization and the reversal potential determined by extrapolation was approximately +10 mV. The amplitude and time course of the galanin-induced depolarization were not changed by substitution of either manganese or magnesium for extracellular calcium, but were decreased by exposure to 50-100 microM d-tubocurarine. It is proposed that the galanin-induced depolarization results from a receptor-activated, nonselective, cation channel; and further, that the receptor initiating depolarization differs from the galanin receptor mediating hyperpolarizing responses in these parasympathetic neurons.

Galanin-induced hyperpolarization and decreased membrane excitability of neurones in mudpuppy cardiac ganglia.

1. Membrane hyperpolarization and decreased excitability produced by galanin were investigated in vitro on parasympathetic postganglionic neurones in the cardiac ganglion of the mudpuppy, Necturus maculosus. 2. Galanin produced a slowly developing hyperpolarization which, in 2.5 mM-KCl, reversed at -105.4 +/- 2.7 mV. The reversal potential was shifted by 38.7 +/- 4.9 mV following a fourfold elevation of the extracellular potassium concentration. 3. Galanin inhibited action potential firing in spontaneously active neurones and decreased the number of spikes in a train produced by long (500-680 ms) depolarizing current pulses. Both effects were independent of the galanin-induced hyperpolarization. 4. Galanin increased the threshold for spike generation, prolonged the spike hyperpolarizing after-potential and decreased the maximum rate of rise, amplitude and maximum rate of fall of the sodium spike. These effects occurred independently of the galanin-induced hyperpolarization. 5. Galanin decreased the amplitude and duration of TTX-insensitive spikes initiated in cells maintained in a solution containing 9 mM-calcium, 20 mM-TEA and 1.5 microM-TTX. 6. These results suggest that a galanin-like peptide may act as an inhibitory transmitter in the mudpuppy cardiac ganglion.

The presence and possible role of a galanin-like peptide in the mudpuppy heart.

A correlated histochemical and pharmacological study was undertaken to establish the presence, origin, and possible function of nerve fibers containing a galanin-like peptide in the mudpuppy (Necturus maculosus) heart. Whole mount preparations of septum-sinus venosus or atria and sections of ventricular muscle were prepared for immunocytochemistry. Galanin-immunoreactive fibers were found coursing diffusely across the septum-sinus venosus to form complex networks over cardiac muscle strands. Individual atrial muscle strands were densely innervated by galanin-immunoreactive fibers and galanin-immunoreactive fibers were also observed in the epicardial and myocardial layers of the ventricle. Most of the parasympathetic postganglionic neurons in the cardiac ganglion and many of the small intensely fluorescent-like cells exhibited galanin immunoreactivity. Galanin-immunoreactive fibers were present in the nerve trunks connecting clusters of parasympathetic postganglionic neurons. Close associations between galanin-positive fibers and individual parasympathetic postganglionic neurons were also observed. The presence of the galanin-immunoreactive fibers was similar in preparations taken from animals pretreated with 6-hydroxydopamine to that seen in preparations taken from control animals, indicating that the galanin-positive fibers were not sympathetic postganglionic axons. Moreover, the galanin-immunoreactive nerve fibers were separate from fibers containing substance P and/or calcitonin gene-related peptide that have previously been shown to be processes of afferent fibers. In twitch-tension experiments, galanin in the range 1 x 10(-7) to 1 x 10(-6) M caused cardioinhibition of spontaneously beating isolated septal-sinus venosus preparations. Galanin also produced a concentration-dependent (1 x 10(-7) to 1 x 10(-6) M) decrease in the twitch-tension development of electrically stimulated atrial or ventricular preparations. Local application of galanin produced hyperpolarization of cardiac muscle fibers in both isolated septal-sinus venosus preparations and atrial preparations. The response of individual parasympathetic ganglion cells to local application of galanin varied between neurons; some neurons were depolarized whereas others were hyperpolarized. We conclude that a galanin-like peptide is contained in both the parasympathetic postganglionic neurons and small intensely fluorescent-like cells and their processes. Further, we hypothesize that in the case of the parasympathetic postganglionic neurons, the galanin-like peptide may work in conjunction with acetylcholine to regulate cardiac activity.

Clindamycin-induced alteration of ganglionic function. II. Effect of nicotinic receptor-channel function.

The postsynaptic effects of clindamycin have been analyzed in bullfrog sympathetic ganglion B cells using single electrode current and voltage clamp recordings and two electrode voltage clamp measurements. Clindamycin added to the bathing solution in the concentration range, 2.5 x 10(-4) to 5 x 10(-4) M, inhibited fast ganglionic transmission. In addition, local application of clindamycin decreased depolarizations produced by direct application of acetylcholine and decreased the amplitude of miniature excitatory postsynaptic potentials (MEPSPs) evoked by tetanic stimulation of the preganglionic trunk. In contrast, clindamycin did not change the amplitude or time course of the slow EPSP elicited by preganglionic stimulation (30 Hz for 10 s) or muscarinic depolarizations produced by local acetylcholine application to preparations pretreated with 25-50 microM (+)-tubocurarine. In voltage-clamped ganglion cells, excitatory postsynaptic current (EPSC) amplitude initially was increased and then decreased with increasing concentrations of clindamycin (0.5 x 10(-5) to 2.5 x 10(-4) M). The EPSC time course in control cells was exponential. After exposure to clindamycin, the EPSC decay was composed of two exponential components. The time constant of the fast component decreased and the time constant of the slow component increased with increasing concentrations of clindamycin. The two time constants of EPSCs obtained in clindamycin were independent of membrane voltage between -50 and -100 mV. We concluded that the block of fast ganglionic transmission is primarily due to a postsynaptic site of action, at least part of which is due to a concentration-dependent, but voltage-independent blockade of open nicotinic receptor channel complexes.

Clindamycin-induced alteration of ganglionic function. I. Direct effects on ganglion cell properties.

The influence of the lincosamide antibiotic, clindamycin, on the properties of bullfrog sympathetic ganglion B cells has been determined in vitro using conventional voltage recording methods or single microelectrode voltage-clamp recording techniques. Individual neurons were depolarized with both bath application or local perfusion of clindamycin. The amplitude of the depolarization was not altered by pretreatment with 50 microM (+)-tubocurarine, 10-microM atropine, or 1.5 microM tetrodotoxin (TTX), indicating that the clindamycin-induced depolarization does not result from either the activation of (1) nicotinic receptors, (2) muscarinic receptors, or (3) voltage-gated sodium channels. Clindamycin partially inhibited IM, an action which accounts for part of the clindamycin-induced depolarization. The duration of the hyperpolarizing afterpotential (HAP) following the action potential was decreased in the presence of clindamycin. Clindamycin decreased the amplitude and maximum rate of rise (MRR) of TTX-insensitive action potentials. As calcium influx is thought to contribute to the depolarizing phase of the TTX-insensitive spikes, we suggest that the decrease in HAP duration by clindamycin results from a decrease in the somal calcium current. Further, it is suggested that a decrease in IM and HAP duration may be responsible for the increased excitability exhibited during exposure to clindamycin.