Demonstration of competition between endogenous dopamine and [¹¹C]raclopride binding in in vitro brain slices using a dynamic autoradiography technique

Abstract

To elucidate the mechanism of in vivo binding competition between radioligand and endogenously released transmitter, we examined the influence of depolarization-induced dopamine (DA) release on [11C]raclopride-specific binding to D2 receptors in slices of living brain tissues using dynamic positron autoradiography. Rat brain slices were incubated in a chamber with [11C]raclopride in oxygenated medium at 34 degrees C for 150 min. Two-dimensional images of radioactivity in the slices were recorded on a storage phosphor screen and dynamic changes were measured. When the brain slices were exposed to the depolarization agents (25 mM K+, 50 mM K+, and 20 microM veratridine), the percentage inhibition of striatal [11C]raclopride-specific binding was 22 +/- 4%, 44 +/- 8% and 54 +/- 7% of the control, respectively. The percentage inhibition of [11C]raclopride-specific binding during each depolarization treatment agreed proportionally with the amount of DA released into the medium. However, preexposure of brain slices to the same depolarization treatment (50 mM K+) did not affect the [11C]raclopride-specific binding, suggesting that the reduction in receptor density and/or affinity was not involved in the decrease of [11C]raclopride-specific binding. [11C]Raclopride-specific binding decreased dose-dependently in the presence of exogenously added DA (range 0.005-3mM). The synaptic DA concentration during each depolarization treatment estimated using three different methods. These results suggest that the decrease of [11C]raclopride-specific binding to striatal slices following evoked DA release is due to competition between endogenous DA and raclopride. It is unlikely that changes in D(2) receptor density or in affinity of the receptors for raclopride are involved. These results provide supportive evidence for in vivo binding competition between radioligand and endogenous neurotransmitter.

In vitro and ex vivo storage phosphor imaging of short-living radioisotopes

“…Although not evaluated in the present experiments, the positron emitter 11 C is used often in PET-radiotracers that are used for neuroimaging, for instance as [ 11 C]Raclopride. Earlier studies have evaluated the storage phosphor imaging for this particular radioisotope (Sihver et al, 1997) and the imaging technique was used successfully in several preclinical studies using this isotope (Sasaki et al, 2002;Wang et al, 2000). In the future 68 Ga may also be used as the positron emitting radioisotope in tracers for PET-studies.…”

Age‐related increase of reactive oxygen generation in the brains of mammals and birds: Is reactive oxygen a signaling molecule to determine the aging process and life span?

“…13 This imaging technique has several advantages: (i) dynamic changes in radioactivity can be followed in living tissue; (ii) physiological conditions in tissue slices can be easily controlled and changed; and (iii) radioligand distribution into tissue regions is not influenced by blood flow. Application studies of bioradiography were carried out to evaluate the glucose metabolism, [13][14][15][16][17][18] neuroreceptors, [19][20][21] neurotransmitter synthesis and release, 13,22,23 synaptic neurotransmitter concentration, 21 and mitochondrial function 24,25 using brain slices. However, momentary image acquisition is not possible using this method, because the acquisition of bioradiography is carried out by repeated exposure to radioluminographic plates.…”

Quantitative in vitro phosphor imaging using [3H] and [18F] radioligands: the effects of chronic desipramine treatment on serotonin 5-HT2 receptors

“…Besret et al, 1998;Passchier et al, 2000;Doze et al, 2002). Phosphor imaging with PET tracers has also been used with live tissue preparations, where the tissue is removed from the animal but maintained in biological buffer solutions with oxygenation during incubation with the PET compound (Matsumura et al, 1995;Sasaki et al, 2002). Very few studies have used in vitro phosphor imaging with PET tracers for quantitative autoradiography (Gatley et al, 1998;Nikolaus et al, 2001Nikolaus et al, , 2003.…”