Observations of cavity polaritons in one-dimensional photonic crystals containing a liquid-crystalline semiconductor based on perylene bisimide units.

We investigated the optical transmission properties of one-dimensional photonic crystal (1D-PC) microcavity structures containing the liquid-crystalline (LC) perylene tetracarboxylic bisimide (PTCBI) derivative. We fabricated the microcavity structures for this study by two different methods and observed the cavity polaritons successfully in both samples. For one sample, since the PTCBI molecules were aligned in the cavity layer of the 1D-PC by utilizing a friction transfer method, vacuum Rabi splitting energy was strongly dependent on the polarization of the incident light produced by the peculiar optical features of the LC organic semiconductor. For the other sample, we did not utilize the friction transfer method and did not observe such polarization dependence. However, we did observe a relatively large Rabi splitting energy of 187 meV, probably due to the improvement of optical confinement effect.

Activation of presynaptic 5-HT3 receptors facilitates glutamatergic synaptic inputs to area postrema neurons in rat brain slices.

Whole-cell voltage-clamp recordings were performed to investigate the serotonergic modulation of neurotransmitter release onto rat area postrema neurons in vitro. The bath application of serotonin (5-HT; 50 microM) or phenylbiguanide (PBA; 50 microM), a potent 5-HT3 receptor agonist, increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) or miniature EPSCs (mEPSCs) in 35 of 83 neurons (42%). These increases occurred in all electrophysiological cell classes. No cells exhibited a decrease in EPSC frequency. The majority of responding cells showed no inward currents during the application of serotonergic agonists (n = 34/35). However, the amplitude of mEPSCs was increased in 11/11 cells with 5-HT or 3/11 cells with PBA. ICS-205,930, a potent 5-HT3 receptor antagonist, markedly suppressed the 5-HT-induced facilitation of sEPSCs (n = 5) or mEPSCs (n = 5). An increase in the frequency of mEPSCs after PBA exposure was found, even with media containing Cd2+ (50 microM) or zero Ca2+. mEPSCs and evoked EPSCs were completely blocked in media containing the non-NMDA ionotropic receptor antagonist, CNQX (10 microM), indicating that EPSCs were glutamate events. These results suggest that glutamate release is increased in the area postrema by presynaptic 5-HT3 receptor activation. Furthermore, we present evidence that 5-HT3 receptor activation may be able to directly release glutamate from terminals, bypassing a requirement for voltage-dependent calcium entry into terminals. Such a mechanism may contribute to the chemosensitive function of area postrema neurons.

Functional electrical stimulation (FES) for spinal cord injury.

Restoration of respiratory motion by stimulation of the phrenic nerve was investigated. Respiratory motion was restored successfully by introducing a breathing pacemaker to a patient with respiratory disturbance due to upper cervical spinal cord injury. Breathing pacemakers are considered to be more similar to physiological conditions compared to mechanical ventilators. Although the system is very expensive, its cost effectiveness may be excellent, provided that it can be used for long hours each day over an extended period. The system is effective in improving patient QOL because it dramatically increases patient mobility. From these findings, it is concluded that breathing pacemakers should be used more frequently in Japan, and that various forms of support are necessary to cope with economic and other concerns.

Effects of left ventricular assist device on cardiac function: experimental study of relationship between pump flow and left ventricular diastolic function.

The left ventricular assist device (LVAD) with centrifugal pump has two characteristics. One is a pump flow wave of the centrifugal pump, consisting of the pulsatile flow of the native heart and the nonpulsatile flow of the centrifugal pump. The other is that the centrifugal pump fills from the native heart not only in the systolic phase, but also in the diastolic phase. In the case of the apex outlet LVAD with centrifugal pump, blood flows from the left atrium through the left ventricle to the pump. Pump flow is regulated by preload, and preload is regulated by diastolic hemodynamics. The aim of this study is to analyze the relationship between pump flow and the diastolic hemodynamics of the native heart. Ten anesthetized intact pigs were studied after placement of an LVAD. Data were recorded with the LVAD off (control) and the LVAD on. The assist rate was changed to 25%, 50%, and 75%. The indexes of left ventricular (LV) diastolic function included LV myocardial relaxation (time constant of isovolumic pressure decay [Tau] and maximum negative dP/dt [LV dP/dt min]) and LV filling (peak filling rate [PFR], time to peak filling rate [tPFR], and diastolic filling time [DFT]). Stroke volume decreased significantly in 75% assist. LV end-systolic pressure decreased significantly in 50% and 75% assist. LV end-diastolic volume decreased as assist rate increased, but there were no significant changes. Stroke work decreased significantly in 50% and 75% assist. LV dP/dt min decreased significantly in 50% and 75% assist. Tau prolonged as assist rate increased, but there were no significant changes. DFT shortened significantly in 75% assist. PFR increased significantly in 75% assist. tPFR shortened significantly in 50% and 75% assist. In this study, LV relaxation delayed as an increasing of pump assist rate, but it suggested a result of reduction of cardiac work. Also, it was suggested that LVAD increases the pressure difference between the left atrium and the left ventricle in the diastolic phase. This phenomenon is due to the filling of the left ventricle. In this study it was suggested that as pump assist rate increases, it is more effective to keep cardiac function in the diastolic phase.

Propofol suppresses a hyperpolarization-activated inward current in rat hippocampal CA1 neurons.

We examined the effect of propofol and thiopental, intravenous anesthetics, on the hyperpolarization-activated inward current (I(H)), whose functional role on the neuronal activity has been evaluated. Whole-cell recordings of I(H) evoked by hyperpolarizing step pulses were taken from hippocampal CA1 neurons in rat brain slices. Propofol reduced I(H) current in a dose-dependent manner. However, thiopental had no significant effect on the activation of I(H). According to the functional role of I(H), the suppression of I(H) should result in a reduction of neuronal activity. We suggest that the effectiveness of propofol as an anticonvulsant or an antiemetic is associated with the blockade of the I(H) channel.

Role of parabrachial nucleus in submandibular salivary secretion induced by bitter taste stimulation in rats.

When rats lick a bitter taste solution such as quinine-hydrochloride, they secrete profuse amounts of saliva. The salivation has a higher flow rate than that induced by other qualities of taste stimulation: sweet, salty, and sour. The present study is aimed to clarify the neural mechanism of the quinine-evoked salivation by means of behavioral, neuroanatomical, and electrophysiological experiments. Behaviorally, submandibular salivary secretion and rejection behavior (gaping) were observed in normal rats, as well as in rats chronically decerebrated at the precollicular level. In chronically decerebrate rats, these quinine-evoked reactions were strongly suppressed by destruction of the medial part of the parabrachial nucleus, including the so-called taste area, and ventral part of the parabrachial nucleus, including the pontine reticular formation. Neuroanatomical study using a retrograde tracer, Fluoro-gold, revealed that the neurons sending their axons to the superior salivatory nucleus, parasympathetic secretory center, were located mainly in the pontine reticular formation ventral to the parabrachial nucleus, not in the parabrachial taste area. Extracellular neural activity was recorded from the parabrachial region in decerebrate rats, and responsiveness to taste stimulation, jaw movements, and electrical stimulation of the superior salivatory nucleus was examined. Neurons responsive to both taste stimulation and antidromic stimulation of the superior salivatory nucleus were found in the pontine reticular formation ventral to the parabrachial nucleus, which responded well to quinine and HCl taste stimuli. Neurons in the parabrachial taste area could respond to four qualities of taste stimulation, but not to antidromic stimulation of the salivary center. These results suggest that aversive taste information from the parabrachial taste area reaches the salivary secretory center via the reticular formation ventral to the parabrachial nucleus.

Intravenous anesthetics inhibit nonadrenergic noncholinergic lower esophageal sphincter relaxation via nitric oxide-cyclic guanosine monophosphate pathway modulation in rabbits.

BACKGROUND: Nonadrenergic noncholinergic (NANC) nerves have important roles in the regulation of the lower esophageal sphincter (LES) motility and function. The effects of thiopental, ketamine, and midazolam on NANC LES relaxation were investigated. METHODS: The isometric tension of circular muscle strips from Japanese White rabbits was examined. The NANC relaxation was induced by KCl (30 mM) in the presence of atropine (3 x 10(-6) M) and guanethidine (3 x 10(-6) M). The modifications of the NANC and sodium nitroprusside (SNP; 10(-5) M)-induced relaxation by the anesthetics were examined. The content of 3',5'-cyclic guanosine monophosphate (cGMP) was measured by radioimmunoassay. RESULTS: The KCl-induced relaxation was abolished by pretreating with tetrodotoxin (10(-6) M). The NANC relaxation was inhibited in the presence of N(G)-nitro-L-arginine (L-NNA; 3 x 10(-5) M), methylene blue (10(-6) M), apamin (10(-7) M), and glibenclamide (10(-5) M). The SNP-induced relaxation was inhibited by methylene blue but was not affected by tetrodotoxin, L-NNA, apamin, or glibenclamide. Ketamine (EC50 = 8.8 x 10(-5) M) and midazolam (EC50 = 4.8 x 10(-6) M) suppressed the NANC response in a concentration-dependent manner, leaving SNP-induced response unchanged. Thiopental altered neither of the relaxations. cGMP content was decreased in the presence of ketamine and midazolam. CONCLUSION: The NANC relaxation was mediated by nitric oxide and by low-conductance calcium- and adenosine triphosphate-sensitive potassium channels of smooth muscle. The modulation of the nitric oxide-cGMP pathway was related, at least in part, to the inhibitory actions of ketamine and midazolam on the NANC LES relaxation.

MRI of disseminated developmental dysmyelination in Fukuyama type of CMD.

Whether the pathologic origin of white matter lesions in Fukuyama type of congenital muscular dystrophy (FCMD) is delayed myelination or dysmyelination is a controversial issue. This study investigated pathologic distribution in white matter with heavily T(2)-weighted images using fluid-attenuated inversion recovery (FLAIR) pulse sequence. For detection of abnormal white matter lesions, FLAIR images were approximately twice as sensitive as T(2)-weighted images and five times as sensitive as T(1)-weighted images of spin echo sequence. The distribution of the white matter lesions was disseminated and not correlated with cortical disarrangement. The distribution was not consistent with delayed myelination. These findings support the evidence found using in vitro proton-NMR spectroscopy that the pathologic origin of white matter lesions is dysmyelination. When conventional magnetic resonance imaging is used, masked white matter lesions are easy to misidentify as delayed myelination instead of disseminated developmental dysmyelination. The lesions in the white matter of FCMD are masked because of brain development.

Propagation of synchronous burst discharges from entorhinal cortex to morphologically and electrophysiologically identified neurons of rat lateral amygdala.

Intracellular and field potential recordings were taken from the lateral nucleus of the amygdala in a rat horizontal brain slice preparation that included hippocampal formation. Pyramidal cells comprised the majority of labeled cells (77%). Electrophysiological classification based on hyperpolarizing or depolarizing afterpotentials subdivided both the pyramidal and non-pyramidal cell classes, although pyramidal cells tended to have hyperpolarizing afterpotentials (70%) and non-pyramidal cells tended to have depolarizing afterpotentials (63%). Synchronous population bursts were triggered with single extracellular stimuli in the deep layers of entorhinal cortex. These events propagated from deep layers of entorhinal cortex into the lateral nucleus of the amygdala. Latencies were consistent with a direct entorhinal to amygdala projection. Individual lateral nucleus neurons exhibited responses ranging from a long burst response that included an initial period of 200 Hz firing and a tail of gamma frequency firing lasting over 100 ms (grade 1) to an epsp with no firing (grade 4). Half of pyramidal cells responding to events initiated in entorhinal cortex were found to receive epsps strong enough to trigger firing. Only one stellate neuron fired in response to entorhinal stimulation. Excitatory postsynaptic responses included NMDA and non-NMDA receptor mediated components. We demonstrate that synchronous population events can propagate from entorhinal cortex to the lateral nucleus of the amygdala and that pyramidal neurons of the lateral nucleus are more common targets than stellate neurons. We conclude that other synchronous events such as sharp waves and interictal spikes can spread from entorhinal cortex to amygdala in the same manner.

[A case report of treatment for tracheal fistula after radical esophagectomy].

We report our experience of the treatment of a 60-year-old man with upper tracheal fistula which developed on the 11th day after radical surgery for esophageal cancer. Primary treatment to close the fistula was unsuccessful, resulting in the involvement of empyema due to infection. Controlled ventilation with T-tube and drainage through a chest tube for 2 months lead to depuration of the thoracic cavity. As a strategy for secondary closure of the fistula, fenestration was performed on the 87th day postoperatively. The patient's overall condition improved thereafter and closure was being considered. However, the patient died on the 116th day postoperatively due to supervenient aspiration pneumonia. Thus, long-term controlled ventilation with a T-tube was beneficial for the treatment of central airway injury.

Sequential chemoimmunotherapy with cisplatin, interferon-beta and interleukin-2 inhibits the growth of B16-F1 melanoma in syngeneic mice.

Sequential combinations of chemotherapy with biological response modifiers has recently been evaluated as systemic treatment for patients with advanced melanoma. The response rates of the chemoimmunotherapy were reported to be higher than conventional treatment using chemotherapy or biological agents alone. To investigate the effectiveness of such chemoimmunotherapy, we evaluated the antitumour effect of sequential chemoimmunotherapy in vivo using a B16 mouse melanoma system. In this sequential regimen, administration of cisplatin (CDDP) was followed by interferon-beta (IFNbeta) and interleukin-2 (IL-2). This combination therapy synergistically inhibited the growth of B16-F1 melanoma and prolonged the survival of mice bearing B16-F1. In contrast, this therapy did not show any antitumour effect on B16-F10 melanoma. The exact mechanism of the antitumour effect is not clear, but the following results were noted: no synergistic effect of this therapy was detected in nude mice, neutralizing anti-IFNgamma antibody significantly blocked the antitumour effect of this therapy, and the number of apoptotic melanoma cells was significantly increased in melanoma tissues removed from mice treated with this therapy. These results demonstrated the potent immunological antitumour effect of this sequential chemoimmunotherapy.

Activity of neurons in the nucleus of the solitary tract of rats: effect of osmotic and mechanical stimuli.

Patch-clamp recordings were used to examine the osmosensitivity and mechanosensitivity of neurons in the caudal part of the nucleus tractus solitarius in coronal slices from rat brain. Firing rates and membrane potentials were measured as slices were exposed to perfusate which varied in its osmolality and/or sodium concentration. In all cells tested, the responses to change in the sodium concentration of perfusate were duplicated by osmolality changes of sucrose or mannitol. When nucleus tractus solitarius cells were tested with changes in pressure applied via the pipette, responses to positive or negative pressure paralleled their responses to osmotic stimulation. We suggest that a mechanosensitive receptor exists on osmosensitive neurons within the nucleus tractus solitarius, and this receptor may be responsible for changes in the firing rate and membrane potential which occur in the nucleus tractus solitarius neurons.

Application of the cell block method, utilizing mount quick mounting medium.

Our objective was to determine the applicability of cell transfer and cell block methods using Mount Quick (Daido Sangyo, Saitama, Japan) mounting medium (MQ) for hematoxylin-eosin (H&E) and immunohistochemical staining of several limited amounts of biological materials in slide preparations. The materials investigated were histopathologically confirmed malignant mesotheliomas (pleural effusions) and malignant lymphomas, a malignant melanoma, and an amelanotic melanoma in sealed slides. Monoclonal antibodies against carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA), cancer antigen 125 (CA-125), vimentin, thrombomodulin (TM), cytokeratin, UCHL-1, L-26, melanoma-specific antigen (HMB45), and S-100 protein (S-100) were applied in the investigation. The malignant mesotheliomas were found to be positive for EMA, cytokeratin, vimentin, TM, and CA-125, and negative for CEA, with no differences being observed in findings from direct contact preparations. Using T-cell-type malignant lymphomas for immunohistochemistry, UCHL-1 positivity and L-26 negativity were clearly demonstrated. The malignant melanoma and amelanotic melanoma materials stained strongly for HMB45 and S-100. Cell transfer employing MQ is a suitable approach for immunohistochemical investigations of limited materials. In addition, cell blocks derived from MQ-embedded smears can be used for both H&E and immunohistochemical staining. Diagn. Cytopathol. 2000;22:117-119.

Re-entrant activity in a presubiculum-subiculum circuit generates epileptiform activity in vitro.

The retrohippocampal cortices form the transition between neocortex and the hippocampus. Area CA3 of the hippocampus and the entorhinal cortex (EC) of the retrohippocampal region are established as brain regions that generate epileptiform activity. Interictal activity generated in EC consists of a primary population burst followed by multiple afterdischarges. The presubiculum is similar to EC in its six-layered structure, but lacks a columnar circuitry that the EC possesses. Isolated presubicular tissue cannot generate afterdischarges and isolated subicular tissue generates no spontaneous activity under some conditions. We report epileptiform activity in combined presubiculum-subiculum slices that consists of synchronous population bursts and multiple afterdischarges. Intracellular and field potential recordings reveal two re-entrant paths for interaction of presubicular and subicular neurons. We demonstrate a deep presubicular input to subiculum and separate return paths from subicular bursting neurons onto deep and superficial layer pre-/parasubicular neurons. Recordings from subicular cell apical dendrites showed repetitive burst firing during sustained depolarizing current injection. We conclude that re-entrant activity in a presubiculum-subiculum circuit generates epileptiform activity in both regions. Presubicular inputs to subiculum depolarize apical dendrites which can then burst repetitively. These bursts are transmitted back to the presubiculum. We suggest that iterations on this circuit act to prolong the dendritic depolarization of subicular bursting neurons and to entrain the activity across subicular cells resulting in multiple afterdischarges.

Noxious tooth pulp stimulation suppresses c-fos expression in the rat hippocampal formation.

Changes in the expression of immediate early gene c-fos by noxious mechanical stimulation to the mandibular incisor pulp of rats were immunohistochemically examined in the hippocampus (Ammon's horn and dentate gyrus) and the retrohippocampus (subiculum, presubiculum, parasubiculum and entorhinal cortex). The highest control levels were found in subiculum, CA1, dentate and deep medial entorhinal cortex. Lower, but substantial levels were present in the other areas. Whereas weak dentinal stimulation caused increases in c-fos expression in some regions which were not statistically significant, strong tooth pulp stimulation caused a bilateral decrease in c-fos expression in every region except contralateral subiculum. These decreases reached statistical significance in superficial layer parasubiculum bilaterally (p<0.01), bilateral CA1 and ipsilateral side of superficial layer of medial entorhinal cortex (p<0.05). We suggest that inhibitory circuitry in hippocampal formation regions may be activated by peripheral noxious somatosensory inputs and this change in activity is accompanied by a change in the expression of the immediate early gene, c-fos.

Pleiotrophin as a Swiss 3T3 cell-derived potent mitogen for adult rat hepatocytes.

Rat parenchymal liver cells were cultured in the presence of lethally treated Swiss 3T3 cells. This co-culture allowed hepatocytes to produce colonies containing more than 300 cells in 30 days. Hepatocytes in colonies appeared morphologically normal and some of them were suggested to have bipotental differentiation capacity. The initial growth stimulatory activity of the feeder cells was replaceable with their conditioned medium (CM). Biochemical analysis of an active principle in the 3T3 cell-CM identified pleiotrophin. Pleiotrophin purified from the 3T3 cell-CM, recombinant human pleiotrophin, chemically synthesized human pleiotrophin, and midkine promoted the growth of hepatocytes as well. Reverse transcription-polymerase chain reaction clearly showed that the synthesis of mRNA of pleiotrophin was stimulated in the regenerating liver induced by either partial hepatectomy or the treatment with d-galactosamine, strongly suggesting a biological significance of pleiotrophin in the proliferation of hepatocytes in vivo. From these results we concluded that pleiotrophin is a new potent growth factor for adult parenchymal hepatocytes. This study indicates the importance of mesenchymal stimulation for the growth of adult rat hepatocytes.

Presence of nuclear grooves in endometrial cytology.

Although the presence of nuclear grooving in papillary carcinomas of the thyroid has been well-described, so far the attention paid to similar structures in endometrial cell samples has been limited. In order to investigate the occurrence of nuclear grooves in endometrial specimens from patients with various pathologic conditions of the endometrium, we compared their appearance with papillary thyroid cancers. A total of 10 cases was studied (age range, 40-72 yr), all cases demonstrating nuclear grooves. In each case, 10 random high-power fields (HPFs) were investigated, and the numbers of fields in which nuclear grooving could be seen were recorded. Nuclear grooves were observed in 3-36 of each HPFs and were more often observed in atypical endometrial cells than in their normal-appearing counterparts; however, these nuclear alterations were thought to be nonspecific findings.

Induction of immediate-early genes c-fos and zif268 in the subnucleus oralis by noxious tooth pulp stimulation.

c-fos and zif268 expression were assessed by immunocytochemistry for c-Fos and Zif268 proteins in the sensory trigeminal nuclear complex following noxious mechanical stimulation of the mandibular incisor pulp of rats. Marked up-regulation of both immediate early genes was observed in the subnucleus oralis ipsilateral to the stimulation. Cavity preparation of the dentine without reaching the pulp did not cause significant up-regulation detectable by immunocytochemistry. These results provide evidence that noxious dental signals reach the ipsilateral subnucleus oralis and up-regulate the transcription of immediate early genes c-fos and zif268.

Properties of gamma-frequency oscillations initiated by propagating population bursts in retrohippocampal regions of rat brain slices.

1. In the hippocampal formation in vivo, brief periods of gamma-frequency activity follow population bursts called sharp waves. The approximately 200 Hz activity of the sharp wave itself may serve to enhance synaptic connections and the approximately 40 Hz gamma activity has been offered as a mechanism for solving the 'binding' problem. We describe epochs of gamma-frequency activity which follow population spikes evoked by low frequency repetitive extracellular stimuli in retrohippocampal neurons of horizontal rat brain slices. 2. gamma-Frequency activity recorded intracellularly from deep layer neurons of entorhinal cortex, presubiculum and parasubiculum consisted of one action potential correlated with each of the three to five gamma cycles recorded with a proximate field potential electrode. A minority of cells exhibited only sub-threshold gamma-frequency membrane potential oscillations (ranging from 5 to 10 mV). No cells fired more than one spike per gamma cycle under any conditions. 3. The range of synchrony varied from individual cells which showed gamma-frequency firing without corresponding oscillations in close field recordings to field potential recordings of oscillations which were well correlated across regions. The lead or lag between any two retrohippocampal regions was in the direction of the conduction delay for the primary population spike, but typically was less, and approached zero milliseconds for some cycles in most cells. The level of synchrony was stable for particular stimulating conditions (intensity, stimulation rate, stimulus location). 4. The duration of the period of gamma activity had the duration of a slow depolarizing potential which was mediated by NMDA receptor activation. NMDA receptor antagonists or low concentrations of AMPA receptor antagonists reduced the duration of, or completely abolished the slow potential, thereby eliminating the gamma portion of the evoked response. 5. gamma-Frequency firing was eliminated by the GABAA receptor antagonist picrotoxin but small (< 5 mV) membrane potential oscillations remained after focal picrotoxin applications, and these exhibited the voltage dependence of EPSPs. Bath application of thiopental lowered the frequency of gamma oscillations, confirming the involvement of GABAA receptors. 6. The GABAB receptor antagonist 2-hydroxy-saclofen appeared to enhance the gamma activity by increasing the duration of the gamma epoch and increasing the amplitude of individual gamma cycles in field potential recordings. These saclofen-induced cycles were, however, less well synchronized across regions. 7. We show that synchronous gamma (40-100 Hz) activity follows population bursts by deep layer retrohippocampal neurons in undrugged slices from rat brain. Responses from medial entorhinal, parasubicular or presubicular cells were not distinguishable. These events can be initiated by a propagating population spike. We suggest that an NMDA receptor mediated depolarization enables the network of deep layer retrohippocampal neurons to oscillate by providing a sustained excitation, the duration of which determines the duration of the gamma episode. gamma-Frequency firing is primarily the result of GABAA receptor dependent inhibition during this period of sustained depolarization. Recurrent excitation appears to be inconsequential for principal cell firing, but may contribute to interneuron firing.

GABA receptor-mediated post-synaptic potentials in the retrohippocampal cortices: regional, laminar and cellular comparisons.

Inhibitory post-synaptic potentials (IPSPs) were studied in neurons of presubiculum, parasubiculum and medial entorhinal cortex in horizontal slices from rat brains. Isolated IPSPs were evoked by extracellular electrical stimuli in the presence of glutamate receptor antagonists. Cellular morphology was identified using Neurobiotin labeling. IPSPs were compared: (a) across morphological cell types, (b) across laminae within regions, and (c) across regions. IPSPs were visible in stellate and pyramidal cells from layers II, III, and V of all retrohippocampal areas during bath application of glutamate antagonists. Qualitative and quantitative differences in IPSPs were only found when comparing responses by superficial layer II, III cells to responses by deep layer V cells. Responses by stellate and pyramidal cells within the same or adjacent layers did not differ, nor did responses differ from region to region. All cell types exhibited an early hyperpolarizing response. The majority (85%) of superficial layer cells in all regions, regardless of cell shape, exhibited a second hyperpolarizing component. Fewer (50%) deep layer cells exhibited the late peak with similar long latencies. IPSPs were typically larger in superficial layer cells. IPSPs were comprised of GABAA and GABAB (gamma-aminobutyric acid) receptor-mediated components. With repetitive stimulation, the peak amplitude of the GABAA receptor-mediated component decreased with successive stimuli, but stabilized during the first five or fewer stimuli to a level that did not vary with stimulation frequency. The GABAB receptor-mediated component also stabilized, but the final amplitude appeared to decrease as the stimulation frequency increased. With high-frequency repetitive stimulation, both components of the IPSP showed summation. We conclude that the most meaningful distinction for IPSPs among retrohippocampal neurons is a laminar distinction, between superficial and deep layer neurons, and not one across cell shape or retrohippocampal subregion. These laminar differences can contribute to synchronous activity by deep layer neurons and restrict the activity of superficial layer neurons.