A prolonged post-tetanic hyperpolarization in rat hippocampal pyramidal cells in vitro

The post-tetanic sequelae of trains of synaptic stimuli (50 pulses at 5 or 10 Hz) were studied with intracellular recordings from rat hippocampal neurons in vitro. In a large proportion of CA1 neurons, stimulation of afferent fibers was followed by a prolonged membrane hyperpolarization (peak amplitude approximately 6 mV) that was associated with a decrease in neuronal input resistance (approximately 33%) that lasted from tens of seconds to over 1 min. Antidromic stimulation or activation of cells with intracellular current injection did not elicit this post-tetanic hyperpolarization (PTH). The PTH could be elicited in chloride (Cl-)-loaded cells, its null potential shifted in response to changes in extracellular potassium ([K+]o), and it was significantly reduced by 5-10 mM extracellular cesium (Cs+). The K(+)-dependent PTH may also be calcium (Ca2+) dependent as its amplitude and associated conductance increase were sensitive to changes in [Ca2+]o. The PTH was enhanced by treatments that increase Ca2+ entry into cells including perfusion with elevated [Ca2+]o, with picrotoxin or with tetraethylammonium ion (TEA). The K+ conductance blocker 4-AP had no consistent effect on the PTH. The PTH was potently blocked by the membrane-permeant forms of cAMP, dibutyryl- and 8-bromo-cAMP. However, phorbol esters that activate protein kinase C and carbachol, which usually block the same potential that is blocked by cAMP, did not depress the PTH. The cardiac glycosides dihydro-ouabain and strophanthidin had only small and variable effects on the PTH.(ABSTRACT TRUNCATED AT 250 WORDS)

Tinnitus

Although tinnitus is usually a benign finding, it can have an extremely adverse effect on a patient's life. Tinnitis is a symptom that can have many different etiologies. This communication deals with the etiology, diagnosis, and available treatment of the condition.

Characterization of an early afterhyperpolarization after a brief train of action potentials in rat hippocampal neurons in vitro

1. In rat hippocampal pyramidal cells in vitro, a brief train of action potentials elicited by direct depolarizing current pulses injected through an intracellular recording electrode is followed by a medium-duration afterhyperpolarization (mAHP) and a longer, slow AHP. We studied the mAHP with the use of current-clamp techniques in the presence of dibutyryl cyclic adenosine 3',5'-monophosphate (cAMP) to block the slow AHP and isolate the mAHP. 2. The mAHP evoked at hyperpolarized membrane potentials was complicated by a potential generated by the anomalous rectifier current, IQ. The mAHP is insensitive to chloride ions (Cl-), whereas it is sensitive to the extracellular potassium concentration ([K+]o). 3. At slightly depolarized levels, the mAHP is partially Ca2+ dependent, being enhanced by increased [Ca2+]o and BAY K 8644 and depressed by decreased [Ca2+]o, nifedipine, and Cd2+. The Ca2(+)-dependent component of the mAHP was also reduced by 100 microM tetraethylammonium (TEA) and charybdotoxin (CTX), suggesting it is mediated by the voltage- and Ca2(+)-dependent K+ current, IC. 4. Most of the Ca2(+)-independent mAHP was blocked by carbachol, implying that IM plays a major role. In a few cells, a small Ca2(+)- and carbachol-insensitive mAHP component was detectable, and this component was blocked by 10 mM TEA, suggesting it was mediated by the delayed rectifier current, IK. The K+ channel antagonist 4-aminopyridine (4-AP, 500 microM) did not reduce the mAHP. 5. We infer that the mAHP is a complex potential due either to IQ or to the combined effects of IM and IC. The contributions of each current depend on the recording conditions, with IC playing a role when the cells are activated from depolarized potentials and IM dominating at the usual resting potential. IQ is principally responsible for the mAHP recorded at hyperpolarized membrane potentials.

Opioid peptides (DAGO-enkephalin, dynorphin A(1-13), BAM 22P) microinjected into the rat brainstem: comparison of their antinociceptive effect and their effect on neuronal firing in the rostral ventromedial medulla

The highly mu-selective agonist Tyr-D-Ala-Gly-MePhe-Gly-ol-enkephalin (DAGO) produces potent, dose-dependent naloxone-reversible antinociception when microinjected into the ventrolateral periaqueductal gray (PAG) (ED50 = 0.72 nmol) or rostral ventromedial medulla (RVM) (ED50 = 0.05 nmol) as measured on the rat tail flick (TF) assay. In single-unit recording experiments, DAGO microinjected into the PAG also affected On- and Off-Cell firing in the RVM in the same way as previously demonstrated by our group for morphine. PAG-microinjected DAGO inhibits spontaneous and noxious-evoked On-Cell firing (attenuating the characteristic On-Cell burst) (n = 19), and excites spontaneous Off-Cell firing, preventing the characteristic Off-Cell pause (n = 12) at doses which suppress the TF. These results support a major role for the mu receptor in PAG and RVM mechanisms of opiate antinociception. In our experiments using BAM22P, an endogenous weakly mu-selective opioid peptide, we could not demonstrate a dose-dependent antinociceptive effect, whether the peptide was microinjected supraspinally into the PAG (n = 9) or RVM (n = 11), or intrathecally at the lumbar cord (n = 4). In two animals, a naloxone-reversible antinociceptive effect was observed following the microinjection of 10 nmol BAM 22P into the RVM; however, no effect was seen in 3 animals microinjected with 20 nmol. Dyn A(1-13), a putative endogenous ligand for the kappa receptor, had no antinociceptive effect when microinjected into the ventrolateral PAG, and no effect on the firing (spontaneous or noxious-evoked) of RVM On (n = 3)- or Off (n = 2)-Cells.

Convergence and divergence of neurotransmitter action in human cerebral cortex

The postsynaptic actions of acetylcholine, adenosine, gamma-aminobutyric acid, histamine, norepinephrine, and serotonin were analyzed in human cortical pyramidal cells maintained in vitro. The actions of these six putative neurotransmitters converged onto three distinct potassium currents. Application of acetylcholine, histamine, norepinephrine, or serotonin all increased spiking by reducing spike-frequency adaptation, in part by reducing the current that underlies the slow after hyperpolarization. In addition, application of muscarinic receptor agonists to all neurons or of serotonin to middle-layer cells substantially reduced or blocked the M-current (a K+ current that is voltage and time dependent). Inhibition of neuronal firing was elicited by adenosine, baclofen (a gamma-aminobutyric acid type B receptor agonist), or serotonin and appeared to be due to an increase in the same potassium current by all three agents. These data reveal that individual neuronal currents in the human cerebral cortex are under the control of several putative neurotransmitters and that each neurotransmitter may exhibit more than one postsynaptic action. The specific anatomical connections of these various neurotransmitter systems, as well as their heterogeneous distribution of postsynaptic receptors and responses, allows each to make a specific contribution to the modulation of cortical activity.

Some characteristics of a retrovirus isolated from transformed bovine cells

A novel retrovirus has been isolated from bovine cells transformed after cocultivation with leukocytes from an animal suffering from sheep-associated bovine malignant catarrhal fever. Morphologically and in its morphogenesis the virus resembles the type D Mason-Pfizer monkey virus (MPMV) as well as the ovine jaagsiekte retrovirus (JSRV). It is also serologically related to these two viruses, whereas a relationship to other known bovine retroviruses was not detected. However, its density of 1.16 g/ml in sucrose and the preference of its reverse transcriptase for manganese ions are closer to the characteristics of type C retroviruses. Unsuccessful attempts at transmission suggest that the virus may be defective in some function affecting its infectivity.

A transient calcium-dependent potassium component of the epileptiform burst after-hyperpolarization in rat hippocampus

1. The epileptiform burst potential produced by picrotoxin is a model of the interictal spike potential seen in epilepsy. We have studied the epileptiform burst after-hyperpolarization (epileptiform burst AHP) using intracellular recording from rat CA1 hippocampal pyramidal cells in the slice preparation. In most experiments burst potentials were induced by electrical stimulation of afferent fibres, but in some experiments bursts that arose spontaneously were also investigated. 2. Previous evidence suggested that the epileptiform burst AHP has two slow K+-dependent components and that both components would be blocked by phorbol esters that activate protein kinase C. We found that phorbol esters indeed blocked the slow components, but also uncovered a transient hyperpolarizing component of the epileptiform burst AHP. This phorbol-ester-insensitive component (the transient AHP) peaked approximately 65 ms after the onset of the stimulus and lasted approximately 150 ms. The transient AHP is K+ dependent since its reversal potential shifted in elevated [K+]o, whereas Cl- loading of the cell had no effect on either its development or reversal potential. 3. The transient AHP was either greatly reduced or abolished by 5-10 mM-tetraethylammonium (TEA) and by 15-20 nM-charybdotoxin (CTX), both of which block a particular Ca2+-dependent K+ current. Concomitant with the block of the transient AHP was a significant increase in burst duration. The transient AHP was not blocked by up to 1 mM-4-aminopyridine (4-AP), 1 mM-N'-2'-O-dibutyryl-adenosine 3':5'-cyclic monophosphate (dBcAMP) or 50 microM-carbamylcholine (carbachol), and burst duration was relatively unaffected by these agents. 4. The transient AHP is Ca2+ dependent: (1) it was often associated with the occurrence of a slow, Ca2+-dependent spike; (2) its amplitude was increased in either elevated [Ca2+] saline or in (3) Bay K 8644 (5-10 microM), a compound that prolongs the open time of certain Ca2+ channels. 5. We conclude that a Ca2+-dependent K+ conductance is transiently activated by the epileptiform burst potential. Its distinctive pharmacological profile indicates that it is fundamentally different from the slow Ca2+-dependent K+ conductance. The Ca2+-dependent K+ current, IC, may mediate the transient AHP. Our data also suggest that the transient AHP conductance plays an important role in repolarizing the membrane after bursts of action potentials.

Assessment of the use of transfusion therapy perioperatively in patients with sickle cell hemoglobinopathies

During the period of 1978 to 1986, 66 patients (31 men, 35 women) with a mean age of 28.4 years and various sickle cell hemoglobinopathies underwent 82 surgical procedures; 28 were emergencies. Fifty of the 66 patients had HbSS, 13/66 had HbSC, and 3/66 had HbS-thalassemia. All 66 patients received transfusions, although not for all procedures. In 48 patients, transfusion therapy was only administered preoperatively. Simple transfusions (1 to 10 units) were administered in 31 of 48 procedures. Exchange transfusions (1 to 6 units) were performed in nine of 48 procedures. Preoperative hematocrit ranged from 7.0% to 54.2%; of those receiving transfusions the hematocrit ranged from 22.6% to 53.7%. Intraoperative transfusions (1 to 10 units) were performed in 14 of 82 procedures; postoperative transfusions (1 to 6 units) were performed in 13 of 82 procedures. No advantage was noted in preoperative exchange transfusion as measured by a decrease in postoperative complications; a slight increase was seen in atelectasis in this group of patients with preoperative transfusions. An increase was reported in the complication rate of patients with an hematocrit of less than 30%. The type of transfusion (preoperative, intraoperative, or postoperative) administered did not appear to be related to postoperative morbidity rates. The complication rate for simple transfusions was 51.6% and for multiple transfusions, 55.6%. HbSS hemoglobinopathy had the higher complication rate. The hepatitis B surface antigen was demonstrated in four of 66 (6.1%) patients; ten of 66 (15.2%) developed alloantibodies. The benefits of transfusion therapy should be judged according to clinical needs; not all sickle cell patients need exchange or preoperative transfusion.

Temperament in Australian infants

A convenience sample of 240 infants aged 4-8 months was studied to evaluate the suitability of a revised version of Carey's Infant Temperament Questionnaire (ITQ) for an Australian population. Data analyses indicated all item/dimension correlations significant at P less than 0.01 or better, satisfactory internal consistency of the instrument as measured by alpha coefficients, and test retest reliability of 0.79. Infants rated as having a 'difficult' temperament were significantly more likely to be reported as having problem behaviours. Significant differences were found between Australian and American infants on three of the nine temperament dimensions - rhythmicity, activity and intensity. The results of this study indicate that this revised ITQ is suitable for use with Australian infants.

The ability to see solid form in early infancy

The perception of three-dimensional attributes of solid objects by twelve-week-old infants was studied. In the first experiment the rates of habituation of fixation to a cube in a fixed orientation, to one which changed in orientation between presentations, and to a sequence of photographs of cubes in different orientations were determined. Habituation rate was also determined for a photograph of a cube in a fixed orientation. No difference was found between the initial fixation times for solids and photographs, or between the habituation curves for the solids in fixed and varying orientation. For the photographs habituation was much greater for the fixed orientation than the varying orientation condition. These data were interpreted as providing strong evidence that the infants were responding to the stimuli on the basis of their three-dimensional attributes. In the second experiment the same discriminations were examined by a recovery-from-habituation technique. One group was habituated to a cube in a fixed orientation and tested for recovery of fixation to a new orientation. A second group was habituated to a photograph of a cube in a single orientation and tested for recovery to a photograph of a new orientation. Both groups showed recovery and the recovery was the same for both conditions. These data demonstrated that the subjects were, after all, capable of discriminating between different orientations of a solid cube, and they provided no further evidence that the infants were perceiving three-dimensional attributes of the stimuli.