The temperature dependence of intrinsic membrane conductances and synaptic potentials in guinea pig hippocampal CA1 pyramidal neurons were examined in vitro as they were cooled from 37°C to between 33 and 27%. Cooling reversibly increased resting input resistance in a voltage-independent manner (Go = 0.58 to 0.75). The amplitude and duration of orthodromically evoked action potentials were increased by cooling (Cl0 = 0.87 and 0.52 to 0.53, respectively), whereas the maximum rates of rise and fall were reduced (Q,,, =

1. Single-electrode voltage-clamp recordings were made from CA3 pyramidal cells in organotypic hippocampal slice cultures for measurement of membrane currents underlying both the gamma-aminobutyric acid (GABA)-mediated, Cl- -dependent inhibitory postsynaptic potential (IPSC), evoked in response to stimulation of the mossy fiber pathway, and responses to iontophoretically applied GABA. Their reversal potentials are presumed to equal the equilibrium potential for Cl- (37). Mechanisms underlying activity-dependent increases in the intracellular concentration of Cl- ([Cl-]i) were investigated by describing active and passive pathways for Cl- influx and efflux. 2. During 99-s applications of GABA, driving force declined by 51% due to increases in [Cl-]i; thus passive Cl- influx through GABA-activated pathways can significantly affect [Cl-]i. 3. Decreasing the extracellular K+ concentration ([K+]o) from 5.8 to 1 mM caused a rapid hyperpolarizing shift in the mean IPSC reversal potential (EIPSC) from -67.6 to -81.9 mV, even when membrane potential (Vm) was maintained constant and depolarized with respect to EIPSC. 4. Decreasing [K+]o from 5.8 to 1 mM caused a rapid hyperpolarizing shift in the mean GABA reversal potential (EGABA) from -64.7 to -81.1 mV, even when Vm was maintained constant and depolarized with respect to EGABA. Reducing the extracellular Cl- concentration from 153 to 89 mM, while maintaining [K+]o constant at 1 mM, shifted the mean EGABA from -81.1 to -66.2 mV, an amount close to that predicted by the Nernst equation for Cl-. We conclude that reducing [K+]o caused a hyperpolarizing shift in EGABA and EIPSC by decreasing [Cl-]i. 5. The shift of EIPSC and EGABA upon alteration of [K+]o did not result from contamination of the responses by additional K+-mediated components because it was unaffected by block of K+ channels with intracellular Cs+. 6. Reducing the extracellular Na+ concentration from 141 to 70 mM had no effect on EGABA. 7. Furosemide, bath-applied at 5 X 10(-4) M while holding Vm depolarized with respect to EIPSC, caused a rapid, reversible decrease in IPSC driving force averaging 69%, consistent with the presence of a furosemide-sensitive outward Cl- -transport system. 8. Reducing [K+]o from 5.8 to 1 mM in the presence of 5 X 10(-4) M furosemide produced a smaller shift of EIPSC from -61.0 to -71.2 mV, however, after washout of furosemide from [K+]o = 1 mM saline, EIPSC shifted further to -89.8 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

The protein kinase C activator phorbol 12,13-dibutyrate (0.5 microM, PDBu) and the protein kinase A activator forskolin (20 microM) each increased evoked monosynaptic inhibitory postsynaptic current (IPSC) amplitude, without affecting its reversal potential, and increased the frequency of miniature IPSCs (mIPSCs), without affecting their amplitude or kinetics, as assessed with whole-cell recording form CA3 pyramidal cells in hippocampal slice cultures. The effects of forskolin and PDBu on both evoked IPSC amplitude and mIPSC frequency were additive and were antagonized by inhibitors of protein kinases A and C, respectively. The kinase activator-induced increases in mIPSC frequency were quantitatively comparable to the increases in evoked IPSC amplitude. The increases in mIPSC frequency were not attenuated by the voltage-dependent calcium channel blocker Cd2+ (100 microM). We conclude that stimulation of protein kinases A and C potentiates hippocampal inhibitory synaptic transmission through independent presynaptic mechanisms of action. Kinase-induced potentiation of spontaneous release does not require modulation of axon terminal Ca2+ channels. This mechanism may also contribute substantially to the potentiation of evoked release.

1. Intracellular recording techniques were used to investigate the mechanisms underlying the activity-dependent lability of inhibitory synaptic potentials indirectly evoked in CA3 pyramidal neurons by stimulation of the mossy fiber afferent pathway in organotypic slice cultures of hippocampus. 2. Repetitive stimulation (3-10 Hz, 30-60 s) was found to reduce the amplitude of the inhibitory postsynaptic potential (IPSP) and occasionally lead to repetitive, epileptiform discharge. 3. Under single-electrode voltage-clamp, the current underlying the inhibitory postsynaptic potential (IPSC) was found to have the same reversal potential (EIPSC) as the response to iontophoretically applied gamma-aminobutyric acid (EGABA), and both were blocked by bicuculline. Reducing the extracellular Cl- concentration from 153 to 89 mM shifted EGABA in the depolarizing direction by 9 mV from -64.7 to -55.6 mV, an amount close to that predicted by the Nernst equation. We therefore presume that the IPSC is mediated by GABA and that the reversal potentials of both are equal to ECl-. 4. Under single-electrode voltage-clamp, repetitive stimulation (3-10 Hz, 30-60 s) was found to cause a mean decrease in the conductance underlying the IPSC (gIPSC) of 22%. This decrease was independent of the membrane potential at which stimuli were delivered. 5. Under single-electrode voltage-clamp, repetitive stimulation (3-10 Hz, 30-60 s) was found to cause a 2-8 mV depolarizing shift in EIPSC when the membrane potential was held constant 5-15 mV depolarized from EIPSC. The mean decrease in IPSC driving force was 49%. If membrane potential was held 10-20 mV hyperpolarized from EIPSC, there was no change in driving force. 6. Currents activated by iontophoretically applied GABA were decreased in amplitude following repetitive stimulation at depolarized, but not hyperpolarized, holding potentials. 7. The decrease in IPSC driving force following repetitive stimulation at depolarized holding potentials was less after decreasing the extracellular K+ concentration from 5.8 to 1 mM. 8. We conclude that the decrease in driving force following repetitive stimulation results from an increase in the intracellular Cl- concentration, and that the activity-dependent decrease in gIPSC results from a decrease in presynaptic release rather than from postsynaptic receptor desensitization.

1. The effects of the gamma-aminobutyric acid (GABA) uptake blocker tiagabine on inhibitory synaptic potentials (IPSPs) were examined with microelectrode and whole-cell recording from CA3 pyramidal cells in rat hippocampal slice cultures. 2. Tiagabine (10-25 microM) greatly prolonged the duration of monosynaptic IPSPs elicited in the presence of excitatory amino acid antagonists but had no effect on their amplitude. Part of the prolonged time course resulted from a GABAB receptor-mediated component that was not detectable under control conditions. 3. The mean decay time constant of the underlying GABAA receptor-mediated synaptic current was increased from 16 to 250 ms. Spontaneous miniature IPSPs recorded with whole-cell clamp were unaffected by tiagabine. Pentobarbital sodium, in contrast, increased the decay time constant of both evoked and spontaneous GABAA-mediated currents. 4. Tiagabine (25 microM) inhibited spontaneous and evoked epileptiform bursting induced by increasing the extracellular potassium concentration to 8 mM. 5. We conclude that GABA uptake plays a significant role in determining the time course of evoked IPSPs and also limits the likelihood that GABAB receptors are activated.

SUMMARY1. Intracellular microelectrode recordings were used to study the cellular location, pharmacology, and mechanism of action of y-aminobutyric acidB (GABAB) receptors on pyramidal cells and presynaptic axonal endings in area CA3 of organotypic hippocampal slice cultures.2. Baclofen (bath applied at 10 /tM) caused a 10-15 mV hyperpolarization of CA3 cells and a 75-100 % decrease in the amplitude of excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs). Baclofen reduced the amplitude of monosynaptic IPSPs elicited in the presence of excitatory amino acid receptor antagonists, as well as the amplitude of EPSPs elicited after blocking GABAA receptors and reducing subsequent epileptic bursts with excitatory amino acid receptor antagonists. These data indicate that GABAB receptors are located on both excitatory and inhibitory presynaptic elements.3. The GABAB receptor antagonist CGP 35 348 blocked the postsynaptic action of baclofen, the late IPSP, and the reduction of EPSPs and monosynaptic IPSPs by baclofen. 3-Aminopropylphosphinic acid (3-APA) mimicked all the pre-and postsynaptic actions of baclofen, and its effects were fully antagonized by CGP 35 348.4. Incubation of cultures with pertussis toxin (500 ng/ml for 48 h) prevented both the postsynaptic hyperpolarization and the block of monosynaptic IPSPs induced by baclofen. The action of baclofen on isolated EPSPs, however, was not affected by pertussis toxin treatment. Stimulation of protein kinase C with phorbol ester (phorbol 12, 13 dibutyrate, 1 /,M for 10 min) reduced all pre-and postsynaptic effects of GABAB receptor activation.5. Barium (bath applied at 1 mM) prevented both the baclofen-induced hyperpolarization of pyramidal cells and the block of monosynaptic IPSPs by baclofen. In the presence of barium, however, baclofen was fully capable of blocking EPSPs.6. We conclude that pre-and postsynaptic GABAB receptors are pharmacologically indistinguishable, at present, and that all actions of GABAB receptors are inhibited by stimulation of protein kinase C. Both the postsynaptic action of baclofen and the block of GABA release from interneurons are mediated by pertussis toxin-sensitive G proteins which can be inactivated by stimulation of protein kinase C. Baclofen acts at postsynaptic sites and on the axon terminals of inhibitory MS 9606

1. Paired intracellular recordings were made in rat hippocampal slice cultures, with the use of either sharp microelectrodes or the whole cell configuration of the patch-clamp technique. Unitary synaptic connections were studied between pyramidal and nonpyramidal cells within and between areas CA1 and CA3. 2. Monosynaptic excitatory synaptic responses between CA3 pyramidal neurons were found in 56% of cell pairs (n = 91, 28 postsynaptic cells). Monosynaptic connections from a CA3 cell to a CA1 cell were observed in 76% of cell pairs (n = 125, 26 postsynaptic cells), but from CA1 to CA3 neurons in only 8% of cell pairs (n = 13, 13 postsynaptic cells). Monosynaptic excitatory connections were found in only 16% of CA1/CA1 cell pairs (n = 25, 10 postsynaptic cells). 3. Disynaptic inhibition was commonly observed between CA3 cell pairs (43%), but rarely found between CA3-CA1 pyramidal cell pairs (2%). In 50% of CA3 pyramidal cell pairs, synchronous inhibitory postsynaptic potentials (IPSPs) in both cells could be triggered by an action potential in one pyramidal cell. Reciprocal monosynaptic connections were found between 75% of interneuron and pyramidal cell pairs within area CA3. 4. The latency of monosynaptic CA3- to CA1-cell responses was significantly longer than for responses between two CA3 cells. Within area CA3 the latencies for inhibitory synaptic responses between interneurons and pyramidal cells were significantly shorter than those for excitatory responses between pyramidal cells. Monosynaptic excitatory postsynaptic potentials (EPSPs) in interneurons had a significantly shorter time-to-peak than those recorded in pyramidal neurons. 5. 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX)- and D-2-amino-5-phosphonovalerate (AP5)-sensitive components were identified in unitary monosynaptic EPSPs in CA3-CA3 and CA3-CA1 pyramidal cell pairs. The CNQX-sensitive component had a mean time-to-peak and duration of 6.2 +/- 0.3 (SE) ms and 61.2 +/- 2.0 ms, respectively, and an amplitude of approximately 1 mV (n = 93). The AP5-sensitive component of EPSPs was only detected when the cell was depolarized with respect to the resting potential, had a mean time-to-peak of 41 +/- 5 ms and duration of 121 +/- 11 ms (n = 6), and increased in amplitude with postsynaptic depolarization. 6. Unitary monosynaptic IPSPs between an interneuron and a pyramidal cell had a mean amplitude of approximately 1 mV and were fully blocked by gamma-aminobutyric acid-A (GABAA) receptor antagonists (n = 3). 7. Unitary inhibitory responses were found only within, but not between, areas CA3 or CA1.(ABSTRACT TRUNCATED AT 400 WORDS)

Sex differences have been observed across many psychiatric diseases, especially mood disorders. For major depression, the most prevalent psychiatric disorder, females show a roughly two-fold greater risk as compared to males. Depression is sexually dimorphic with males and females exhibiting differences in clinical presentation, course, and response to antidepressant treatment. In this review, we first discuss sex differences observed in depressed patients, as well as animal models that reveal potential underlying mechanisms. We then discuss antidepressant treatments including their proposed mechanism of action and sex differences observed in treatment response. We include possible mechanisms underlying these sex differences with particular focus on synaptic transmission.