1,721,015 research outputs found
Substantia nigra control of basal ganglia nuclei
No full textAbstract. The substantia nigra, located in the ventral mesencephalon,
is one of the five nuclei that constitute the basal
ganglia circuit, which controls voluntary movements.
It is divided into the pars compacta and the pars reticulata,
which mainly contain dopaminergic and GABAergic
cells respectively. Here we overview the electrophysiological
properties of these substantia nigra neurons in the pars
compacta and reticulata, together with their synaptic connections,
and discuss the functional effects of dopaminergic
and GABAergic inputs within the basal ganglia. We also
examine the phenomenon that when a deficiency of dopamine
(DA) occurs (e.g. in Parkinson’s disease), there is an
aberrant synaptic plasticity in the basal ganglia.
Moreover, we point out that the appearance of an altered
pattern of neuronal firing (beta-oscillations) and synchrony
among neurons in the subthalamic nucleus, the internal
globus pallidus, and the substantia nigra pars reticulata has
been related to motor symptoms and possibly, persistent
degeneration of DA-containing neurons.
Finally, we believe that, based on pathophysiological
data, new and significant targets for therapeutic intervention
can be identified and tested
A dynamic model of the blood-brain barrier "in vitro"
No full textCell culture models have been widely used for screening of neurotoxicants and represent a viable alternative to direct in vivo experiments. We have developed a dynamic in vitro blood-brain barrier model designed to allow for extensive toxicological, pharmacological and physiological testing. Induction of blood-brain barrier properties in a tri-dimensional hollow fiber culturing apparatus was investigated by co-culturing a bovine aortic endothelial cell line (or rat brain endothelial cells) with rat brain astrocytes (or C6 rat glioma cells) under pulsatile flow conditions to mimic intraluminal blood flow. Cell growth was monitored over time by measuring glucose consumption and lactate production: these experiments confirmed that the hollow fiber cell culturing systems can maintain viable cells in culture for extended (> 1 month) periods of time. Cells were visually inspected after culturing and dissociation from the hollow fiber cartridge and identified as endothelial (by fluorescent Dil-Ac-LDL uptake) or glial (by GFAP immunoreactivity). Blood-brain barrier properties were tested by intraluminal injection of horse-radish peroxidase (HRP, mol. weight 44,000), glucose (m.w. 180) or potassium. Either procedure demonstrated that aortic cells co-cultured with astrocytes (or C6 cells) developed a selective barrier with an estimated electrical resistance of 2,900 omega/cm2. The electrophysiological and morphological properties of BAEC were also affected by the co-culturing process, suggesting that astrocytes induced CNS properties in these cells. These results demonstrate that the hollow fiber cell co-culturing system may be used as a dynamic model of the mammalian blood-brain barrier
Hyperpolarization-activated ion currents in cultured rat cortical and spinal cord astrocytes
No full textHyperpolarization-activated currents were recorded f r om r a t b r a i n c o r t i cal
and spinal cord astrocytes maintained i n culture. Spinal cord astrocytes expressed
pr i m a r i l y an i n w a r d rectifier potassium current characterized by time-dependent inactivation,
a strong dependence on extracellular N a + and insensitivity to i n t r a c e l l u l a r GTP-
-y-S ( 0 . 2 mM). I n cortical astrocytes voltage clamp protocols aimed to elicit currents
activated at, or negative to cell membrane potentials led to the development of two
distinct ion currents. The most prominent current resembled the inwar d rectifier potassium
current. This component was sensitive to blockade by extracellular cesium and
was greatly reduced d u r i n g recordings performed w i t h GTP-7-S ( 0 . 2 Mm) added to the
pipette solutions. The remaining current component was similar to the endothelial I h a
current. I h a conductance was enhanced by extracellular potassium and the current reversal
potential behaved as expected for a mixed cation, N a 7 K + current. I h a was nearly
abolished after removal of extracellular Na". These results are consistent w i t h the
expression of a novel mixed cation conductance i n g l i a l cells, possibly involved i n extracell
u l a r potassium bufferin
The weaver mutation reverses the function of dopamine and GABA in mouse dopaminergic neurons
No full textIn the present study, we characterized the intrinsic electrophysiological properties and the membrane currents activated by dopamine (DA) D(2) and GABA(B) receptors in midbrain dopaminergic neurons, maintained in vitro in a slice preparation, from wild-type and homozygous weaver (wv/wv) mice. By using patch-clamp techniques, we found that membrane potential, apparent input resistance, and spontaneous firing of wv/wv dopaminergic neurons were similar to those of dopamine-containing cells recorded from nonaffected (+/+) animals. More interestingly, the wv/wv neurons were excited rather than inhibited by dopamine and the GABA(B) agonist baclofen. This neurotransmitter-mediated excitation was attributable to the activation of a G-protein-gated inward current that reversed polarity at a membrane potential of approximately -30 mV. We suggest that the altered behavior of the receptor-operated wv G-protein-gated inwardly rectifying K(+) channel 2 (GIRK2) might be related to the selective degeneration of the dopaminergic neurons. In addition, the wv GIRK2 would not only suppress the autoreceptor-mediated feedback inhibition of DA release but could also establish a feedforward mechanism of DA release in the terminal fields
Molecular and Epigenetic Aspects of Opioid Receptors in Drug Addiction and Pain Management in Sport
No full textOpioids are substances derived from opium (natural opioids). In its raw state, opium is a gummy latex extracted from Papaver somniferum. The use of opioids and their negative health consequences among people who use drugs have been studied. Today, opioids are still the most commonly used and effective analgesic treatments for severe pain, but their use and abuse causes detrimental side effects for health, including addiction, thus impacting the user’s quality of life and causing overdose. The mesocorticolimbic dopaminergic circuitry represents the brain circuit mediating both natural rewards and the rewarding aspects of nearly all drugs of abuse, including opioids. Hence, understanding how opioids affect the function of dopaminergic circuitry may be useful for better knowledge of the process and to develop effective therapeutic strategies in addiction. The aim of this review was to summarize the main features of opioids and opioid receptors and focus on the molecular and upcoming epigenetic mechanisms leading to opioid addiction. Since synthetic opioids can be effective for pain management, their ability to induce addiction in athletes, with the risk of incurring doping, is also discussed
Group I mGluRs coupled to G proteins are regulated by tyrosine kinase in dopamine neurons of the rat midbrain
No full textGroup I mGluRs coupled to G proteins are
regulated by tyrosine kinase in dopamine neurons of the rat midbrain.
J Neurophysiol 85: 2490–2497, 2001. Metabotropic glutamate receptors
(mGluRs) modulate neuronal function via different transduction
mechanisms that are either dependent or independent on G-protein
function. Here we investigated, using whole cell patch-clamp recordings
in combination with fluorimetric measurements of intracellular
calcium concentration ([Ca21]i), the metabolic pathways involved in
the responses induced by group I mGluRs in dopamine neurons of the
rat midbrain. The inward current and the [Ca21]i increase caused by
the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG,
100 mM) were permanently activated and subsequently abolished in
cells loaded with the nonhydrolizable GTP-analogue GTP-g-S (600
mM). In addition, when GDP-b-S (600 mM) was dialyzed into the
cells to produce the blockade of the G proteins, the DHPG-dependent
responses were reduced. When the tissue was bathed with the phospholipase
C inhibitor 1-[6[[(17b)-3-methoxyestra-1,3,5(10)-trien-17-
yl]amino]exyl]-1H-pyrrole-2,5-dione (10 mM), the DHPG-induced
calcium transients slightly diminished but the associated inward currents
were not affected. Interestingly, a substantial depression of the
DHPG-induced inward current and transient increase of [Ca21]i was
caused by the protein tyrosine kinase inhibitors tyrphostin B52 (40
mM) and 49,5,7-trihydroxyisoflavone (genistein; 40 mM), whereas
genistein’s inactive analogue 49,5,7-trihydroxyisoflavone-7-glucoside
(40 mM) was ineffective. The blockade of the Src family of tyrosine
kinase by 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]-
pyrimidine (20 mM), mitogen-activated protein kinase by 29-amino-39
methoxyflavone (50 mM), and protein kinase C by staurosporine (1
mM) had no effect on the cellular responses caused by DHPG. The
mGluR5-selective antagonist 2-methyl-6-(phenylethynyl)-pyridine
(10–100 mM) did not affect the actions of DHPG. Thus our results
indicate that the responses, mainly mediated by mGluRs1 in dopamine
neurons, are activated by intracellular mechanisms coupled to G
proteins and regulated by tyrosine kinases
Voltage-gated calcium channels mediate intracellular calcium increase in weaver dopaminergic neurons during stimulation of D2 and GABAB receptors.
No full textVoltage-gated calcium channels mediate intracellular calcium
increase in weaver dopaminergic neurons during stimulation of
D2 and GABAB receptors. J Neurophysiol 92: 3368–3374, 2004. First
published July 7, 2004; doi:10.1152/jn.00602.2004. The weaver (wv)
mutation affects the pore-forming region of the inwardly rectifying
potassium channel (GIRK) leading to degeneration of cerebellar
granule and midbrain dopaminergic neurons. The mutated channel
(wvGIRK) loses its potassium selectivity, allowing sodium (Na) and
possibly calcium ions (Ca2) to enter the cell. Here we performed
whole cell patch-clamp recordings combined with microfluorometry
to investigate possible differences in calcium ([Ca2]i) dynamics in
native dopaminergic neurons (expressing the wvGIRK2 subunits) in
the midbrain slice preparation from homozygous weaver (wv/wv) and
control (/) mice. Under resting conditions, [Ca2]i was similar in
wv/wv compared with / neurons. Activation of wvGIRK2 channels
by D2 and GABAB receptors increased [Ca2]i in wv/wv neurons,
whereas activation of wild-type channels decreased [Ca2]i in /
neurons. The calcium rise in wv/wv neurons was abolished by antagonists
of the voltage-gated calcium channels (VGCC); voltage clamp
of the neuron at 60 mV; and hyperpolarization of the neuron to 80
mV or more, in current clamp, and was unaffected by TTX. Therefore
we propose that wvGIRK2 channels in native dopamine neurons are
not permeable to Ca2, and when activated by D2 and GABAB
receptors they mediate membrane depolarization and an indirect Ca2
influx through VGCC rather than via wvGIRK2 channels. Such
calcium influx may be the trigger for calcium-mediated excitotoxicity,
responsible for selective neuronal death in weaver mic
Neurons dissociated from neocortex fire with 'burst' and 'regular' trains of spikes
No full textNeurons acutely dissociated from neocortex slices of 14-16-day-old rats were patch-clamped in physiological conditions. Different pyramidal cells, spontaneously or in response to current steps, generate regular spiking and intrinsically bursting behaviour during long periods of time. We show that typical firing properties recorded in somatosensory neocortex slices are preserved in dissociated pyramidal neurons originating from the slices themselves, thus, providing a way for the related characterization of biophysical properties of currents in identified subtypes of pyramidal neurons
Action potentials recorded with patch-clamp amplifiers: are they genuine?
No full textA growingnumber of experimental studieshaveusedpatch-clampamplifiers(PCAS) in the currentclamp
(CC) mode to investigateclassicalexcitability.In this paperweshowthat the measurements
obtained in this way are affectedby errors due to the electronic design of the PCA input section.
We present experimental evidence of such errors, and demonstrate that they derive from PCA
current absorption. Moreover,wepropose a new PCA input-circuit configuration for the CC mode,
which is suitablefor accuratelyrecording physiologicalvoltage signalsand is perfectly compatible
with the standard voltage-clamp mode
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