Biomedical subjects

A L Mueller

Publications and source records attributed to A L Mueller.

36 records · Page 2Linked to original sources

PubMed1989

Intracellular recording from putative dopamine-containing neurons in the ventral tegmental area of Tsai in a brain slice preparation.

Coronal slices of rat mesencephalon containing the ventral tegmental area of Tsai (VTA) and the substantia nigra were prepared. Stable intracellular recordings were obtained from presumed dopamine (DA)-containing neurons in the VTA. Both silent and spontaneously active cells were encountered; spontaneously active neurons fired in an extremely regular pacemaker-like fashion. These neurons had resting membrane potentials ranging from -45 to -75 mV and input resistances ranging from 80-400 M omega. DA-containing neurons in the VTA demonstrated marked anomalous rectification in response to hyperpolarizing current pulses. Application of DA or the GABAB agonist, baclofen, to the bathing medium produced suppression of spontaneous firing, sometimes accompanied by membrane hyperpolarization. Neuronal input resistance was not changed consistently by DA and was generally reduced by baclofen.

Action Potentials↗

PubMed1987

Local circuit interactions between oriens/alveus interneurons and CA1 pyramidal cells in hippocampal slices: electrophysiology and morphology.

Electrophysiological and anatomical techniques were used to determine the role, in the hippocampal circuitry, of local circuit neurons located at the oriens/alveus border (O/A interneurons). Intracellular recording from these cells showed that their response characteristics were clearly nonpyramidal: high input resistance, short membrane time constant, short-duration action potential, pronounced, brief afterhyperpolarizations (AHP), and nondecremental firing during intrasomatic depolarizing current pulses. Intracellular Lucifer yellow (LY) injection and subsequent fluorescence microscopy confirmed their nonpyramidal nature. O/A interneuron somata were bipolar or multipolar; their dendrites projected mostly parallel to the alveus, except for 1 or 2 processes that turned perpendicularly, and ascended through stratum oriens and pyramidale and into radiatum. Their axons were seen to branch profusely in stratum oriens and pyramidale. Simultaneous intracellular recordings from O/A interneurons and CA 1 pyramidal cells showed that pyramidal cells directly excite these interneurons. Major hippocampal afferents also directly excited the O/A interneurons. In a small number of interneuron-pyramidal pairs, stimulation of the O/A interneuron directly inhibited pyramidal cells. In one case, reciprocal connections were observed: The pyramidal cell excited the interneuron, and the interneuron inhibited the pyramidal cell. In 1 interneuron-to-interneuron pair, an inhibitory connection from O/A interneuron to stratum pyramidale interneuron was also observed. With intracellular HRP injections into O/A interneurons and subsequent electron microscopy, we observed that O/A interneuron axons made contacts with pyramidal and nonpyramidal cells. HRP-filled symmetric synaptic contacts were found on pyramidal cell dendrites and somata. HRP-filled axons also made contacts with pyramidal cell initial segments. HRP-filled O/A interneuron axon contacts were also found on nonpyramidal cell dendrites in stratum oriens. These electrophysiological and anatomical results suggest that O/A interneurons make synaptic contact with pyramidal cells and may mediate feedforward and feedback inhibition onto CA 1 pyramidal cells.

Animals↗

PubMed1986

Electrophysiological actions of somatostatin (SRIF) in hippocampus: an in vitro study.

The electrophysiological actions of somatostatin (somatotropin release inhibiting factor; SRIF) were investigated in the in vitro hippocampal slice preparation. Intracellular recordings were obtained from pyramidal neurons in area CA1 in slices of hippocampus from guinea pigs and rabbits. Somatostatin, applied via micropressure ejection to CA1 pyramidal-cell somata, was primarily excitatory. The effects, however, were quite variable, with nearly all cells displaying pronounced tachyphylaxis. A majority of cells was depolarized by SRIF, but hyperpolarizations or biphasic depolarization/hyperpolarization responses were also recorded. Only minimal conductance changes were associated with the SRIF-induced voltage changes. Depletion of SRIF, by injection of the intact animal with cysteamine several hours before preparing slices, resulted in no obvious abnormalities in hippocampal slice electrophysiology. Our results obtained with application of exogenous SRIF are consistent with the concept that SRIF acts as an excitatory neurotransmitter/neuromodulator in hippocampus. However, our attempts to demonstrate endogenous SRIF action have thus far been unsuccessful.

Animals↗

PubMed1984

Development of hyperpolarizing inhibitory postsynaptic potentials and hyperpolarizing response to gamma-aminobutyric acid in rabbit hippocampus studied in vitro.

The postnatal development of IPSPs and response to locally applied GABA were examined using intracellular recording techniques in region CA1 of rabbit hippocampal slices maintained in vitro. Pyramidal neurons in slices from mature rabbits demonstrated an EPSP-IPSP sequence following stimulation of stratum radiatum. In these same slices, pressure application of GABA into stratum pyramidale and stratum radiatum produced membrane hyperpolarization and depolarization, respectively. Pyramidal neurons in slices from immature rabbits (age 6 to 10 days) responded differently. Stimulation of stratum radiatum produced a prolonged depolarizing postsynaptic potential; few IPSPs were observed. Ejection of GABA into either stratum pyramidale or stratum radiatum evoked a depolarizing response. The GABA agonist, 4,5,6,7-tetrahydroisoxazolo [5,4-c] pyridine-3-ol (THIP), which has been reported to activate "hyperpolarizing" GABA receptors selectively, primarily produced membrane hyperpolarization when applied to the somata of mature neurons, but it evoked a depolarization when applied to immature neurons. Bicuculline, a GABA antagonist which may have a preferential selectivity for "depolarizing" GABA receptors, was somewhat more efficacious (at 50 microM concentration) at antagonizing GABA-evoked depolarization in immature cells than GABA-evoked hyperpolarization in mature cells. This same concentration of bicuculline partially antagonized IPSPs in mature cells, and it markedly potentiated depolarizing PSPs in immature cells. Taken together, these results suggest that the late development of synaptic inhibition in rabbit hippocampus is due, at least in part, to an immaturity in the GABAergic system.

Action Potentials↗

PubMed1983

Actions of GABA in developing rabbit hippocampus: an in vitro study.

The development of neuronal responses to gamma-aminobutyric acid (GABA) was examined using intracellular recording techniques in area CA1 of rabbit hippocampal slices maintained in vitro. Microapplication of GABA (via pressure ejection) in stratum pyramidale in slices from mature rabbits (age 1 month) evoked a hyperpolarization of CA1 pyramidal neurons. The reversal potential (Erev) for this response was approximately -70 mV. In contrast, local application of GABA into stratum pyramidale in slices from immature rabbits (age 7-10 days) produced a depolarizing response with an Erev of approximately -54 mV. The relationship between these findings and the development of inhibitory synaptic activity in rabbit hippocampus is discussed.

Action Potentials↗

PubMed1983

Electrophysiological and biochemical sequelae of the destruction of hippocampal noradrenergic afferents by DSP4.

The effects of DSP4 lesions were examined 20-53 days postlesion in the rat hippocampus. A single treatment with DSP4 produced decreases of 42-94% in the norepinephrine (NE) content of this brain region. There was, however, no effect of DSP4 treatment on either the number or affinity of beta-adrenergic receptor sites as determined by radioligand binding studies with (-)-[125I]pindolol; furthermore, there was no relationship between the concentrations of NE and the number of receptor sites in individual hippocampi. The DSP4-induced depletion of functionally releasable NE was confirmed by the loss of electrophysiological responsiveness to amphetamine in the in vitro hippocampus following such lesions. In contrast, electrophysiological responses to direct acting beta-adrenergic or alpha-adrenergic agonists were unchanged following DSP4 treatment. This finding again suggests the lack of any change in postsynaptic sensitivity. The results of this study demonstrate that while the potent noradrenergic neurotoxin DSP4 is able to reduce NE concentrations significantly in noradrenergic target regions in brain, these lesions are not necessarily associated with postsynaptic changes in adrenergic systems.

Afferent Pathways↗

PubMed1983

Anticonvulsant and proconvulsant actions of alpha- and beta-noradrenergic agonists on epileptiform activity in rat hippocampus in vitro.

The ability of l-norepinephrine to influence epileptiform activity was examined in an in vitro rat hippocampal slice preparation. Exogenously applied norepinephrine (NE) had anticonvulsant properties in that it slowed or stopped spontaneous interictal discharges which had been initiated by superfusion of slices with medium containing penicillin and elevated levels of potassium. This anticonvulsant property of NE was shared by the alpha receptor agonists 6-fluoro-norepinephrine, l-alpha-methyl-norepinephrine, and clonidine, but not by d-alpha-methyl-norepinephrine or l-phenylephrine. The beta receptor agonists 2-fluoro-norepinephrine and l-isoproterenol, on the other hand, were proconvulsant in that they increased interictal discharge rate. The alpha receptor antagonist phentolamine selectively blocked anticonvulsant responses, whereas the beta receptor antagonist timolol selectively blocked proconvulsant activity. These results suggest that activation of alpha or beta receptors has opposing inhibitory or excitatory effects respectively on epileptiform discharges in the rat hippocampus.

Adrenergic alpha-Antagonists↗

PubMed1982

Hippocampal noradrenergic responses in vivo and in vitro. Characterization of alpha and beta components.

Pressure ejection of l-norepinephrine (NE) in the in vivo rat hippocampus generally produced depression of pyramidal cell spontaneous activity. In addition, both excitation and biphasic responses were observed. NE-induced inhibition of firing rate was effectively antagonized by concurrent administration of the alpha antagonist phentolamine, but was largely unaltered by the beta antagonist timolol. On the other hand, NE-induced elevation in spontaneous firing rate was effectively blocked by timolol, and largely unaffected by phentolamine. Another beta antagonist, sotalol, did not selectively antagonize either NE-induced inhibition or NE-induced excitation. The beta agonist 2-fluoro-NE produced increases in pyramidal cell firing rates in most cells studied, while the alpha agonist 6-fluoro-NE inhibited the majority of cells examined. The effects of sotalol were also examined on alpha and beta receptor-mediated field responses in the in vitro hippocampal slice. Sotalol was shown to be a selective beta antagonist in this system, blocking excitation evoked by the beta agonist isoproterenol while having no effect on inhibition elicited by the alpha agonist clonidine; however, the potency of sotalol (Ki = 3.5 microM) was considerably less than that of timolol (Ki = 50 nM). Taken together, these results suggest that NE-induced depression and elevation in hippocampal pyramidal cell spontaneous discharge in vivo are mediated via alpha and beta adrenoceptors, respectively.

Animals↗

PubMed1982

Noradrenergic responses in rat hippocampus: electrophysiological actions of direct- and indirect-acting sympathomimetics in the in vitro slice.

The effects of perfusion of postulated direct- and indirect-acting sympathomimetics on evoked potentials in the CA1 region of the in vitro rat hippocampus were examined. A selective alpha agonist, 6-fluoronorepinephrine, produced depressions of population spike amplitude which were antagonized by the alpha antagonist phentolamine, but not by the beta antagonist timolol. The selective beta agonist, 2-fluoronorepinephrine, produced increases in population spike amplitude which were antagonized by timolol but not by phentolamine. Weak and variable responses were seen to the indirect-acting sympathomimetic tyramine, with lower doses producing increases and higher doses producing decreases in population spike amplitude, respectively. As with 2-fluoronorepinephrine, increases in spike amplitude elicited by tyramine were blocked by timolol but not by phentolamine. Another indirect-acting sympathomimetic, d-amphetamine, produced only increases in population spike amplitude which were blocked by timolol. Phencyclidine, an agent which may produce some of its central effects via noradrenergic synapses, was virtually ineffective in producing catecholamine-like responses in this system. Only nonspecific, local anesthetic effects were observed. Taken together with previous studies, these results support the hypothesis that activation of alpha and beta receptors decreases and increases, respectively, pyramidal cell excitability. Furthermore, although both alpha and beta receptors appear to be capable of interacting with endogenously released norepinephrine, the beta response may predominate.

Action Potentials↗

PubMed1981

Noradrenergic responses in rat hippocampus: evidence for medication by alpha and beta receptors in the in vitro slice.

The effect of perfused norepinephrine (NE) on evoked potentials in CA1 of the in vitro rat hippocampus was examined. Weak and variable effects on population spike amplitude were observed, with lower doses of NE generally producing excitations and higher doses more often producing inhibitions. Clonidine, an alpha-receptor agonist, produced a dose-dependent inhibition of population spike amplitude; this inhibition was effectively antagonized by the alpha-antagonist, phentolamine. Isoproterenol (ISO), a beta-agonist, produced marked increases in population spike amplitude which could be antagonized by timolol, a beta-receptor antagonist. Phentolamine did not antagonize the excitations produced by ISO, and timolol had no effect on the inhibitions seen with clonidine. After pretreatment with either phentolamine or timolol, NE perfusion elicited robust and consistent elevations or reductions in the population spike, respectively. A potent cyclic AMP derivative, 8-p-chlorophenylthio cyclic AMP, produced large increases in population spike amplitude which appeared similar to the responses seen with beta-agonists. No changes in field EPSP amplitudes were observed with any of the drugs tested. Taken together, these results suggest that NE may interact with alpha-adrenergic receptors to decrease pyramidal cell excitability, and the beta-adrenergic receptors to increase pyramidal cell excitability; the beta-effect may involve cAMP.

Animals↗

PubMed1981

Surface characteristics of carbonic-anhydrase-rich cells in turtle urinary bladder.

Addition of a disulfonic stilbene, 4-acetamido 4'-isothiocyano-2,2'-disulfonic stilbene (SITS), to the serosal side of the turtle bladder blocks the efflux of bicarbonate ions from the acidifying cells and thereby inhibits hydrogen ion secretion into the luminal solution. Because SITS has little effect on other transport systems, we used it to define the relationship between hydrogen ion secretion (JH) and the different cell types facing the luminal surface. Cells were identified by scanning and transmission electron microscopy (SEM and TEM) and by histochemical localization of carbonic anhydrase (CA). SEM revealed that SITS caused marked alterations in luminal surface characteristics of a cell population with prominent microplicae. Two hours after the serosal addition of SITS, cells with identifiable microplicae had decreased from 12.7 to 0.5% of total cells. TEM studies and CA histochemistry showed that the number of cells rich in CA (CA cells) remained the same, whereas the individual luminal surface areas of a subpopulation of CA cells had decreased markedly. A comparison of the distribution of individual surface areas of cells with microplicae and CA cells revealed that the CA cells with large surface areas corresponded to the cells with microplicae and that both were affected by the serosal addition of SITS. Acetazolamide, which also inhibits JH, caused similar changes. The luminal addition of SITS and an inactive analogue of acetazolamide, which have no effect on JH, did not alter surface morphology, These results indicate that the CA cell with microplicae represents the active state of the hydrogen ion secreting cell.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗

PubMed1979

Effects of adenosine on neurally mediated norepinephrine release from the cat spleen.

The effects of adenosine on the release of 3H-norepinephrine (3H-NE) from the isolated, perfused cat spleen consequent to nerve stimulation were evaluated. Electrical stimulation of the splenic nerve (5 Hz/100 impulses total) caused a release of 3H-NE and a rise in perfusion pressure. Adenosine added to the perfusion fluid (final concentrations 1 X 10(-6), 1 X 10(-5), and 1 X 10(-4) M) significantly reduced the pressure response elicited by nerve stimulation. In addition, adenosine (1 X 10(-4) M) slightly increased the release of total 3H consequent to nerve stimulation. Theophylline (1 X 10(-4) M) produced both a slight increase in the release of total 3H and a diminished pressure response. The effects of adenosine were effectively antagonized by this concentration of theophylline. Neither substance had any effect on the spontaneous release of total 3H. Adenosine (1 X 10(-4) M) also antagonized the pressure response elicited by perfusion of NE.

Adenosine↗

PubMed1979

Fetal hemoglobin (HbF) synthesis in baboons, Papio cynocephalus. Analysis of fetal and adult hemoglobin synthesis during fetal development.

Fetal hemoglobin (HbF) and adult hemoglobin (HbA) synthesis was studied in fetal baboons, Papio cynocephalus, to determine the normal pattern of hemoglobin production during fetal development. Fetuses ranging from 53 to 180 days gestation (term gestation 184 days) were used. Erythroid cells were incubated with 3H-L-leucine, and the rates of globin chain synthesis and the distribution of radioactivity into hemoglobin intermediates and completed hemoglobin molecules were determined. Gamma chain synthesis accounted for approximately 97% of the total nonalpha chain synthesis up to 140 days gestation; beta chain synthesis accounted for the remainder. After 140 days gestation, approximately equal quantities of gamma and beta chain were synthesized in the bone marrow. Prior to 140 days gestation, total alpha chain synthesis was 30% greater than total non-alpha chain synthesis, while there was balanced chain synthesis after 140 days gestation. During the period of excess alpha chain synthesis, fetal erythrocytes contained a large pool of alpha-hemoglobin (alpha chain with heme attached) molecules uncombined with beta or gamma chains. In view of the possibility that alpha chains may have a lower affinity for gamma chains than beta chains, excess alpha chain synthesis may be required to maintain low levels of free gamma chains.

Animals↗

PubMed1978