High-resolution mapping of neuronal activity using the lipophilic thallium chelate complex TlDDC: protocol and validation of the method.
In neurons the rate of K(+)-uptake increases with increasing activity. K(+)-analogues like the heavy metal ion thallium (Tl(+)) can be used, therefore, as tracers for imaging neuronal activity. However, when water-soluble Tl(+)-salts are injected systemically only minute amounts of the tracer enter the brain and the Tl(+)-uptake patterns are influenced by regional differences in blood-brain barrier (BBB) K(+)-permeability. We here show that the BBB-related limitations in using Tl(+) for imaging neuronal activity are no longer present when the lipophilic Tl(+) chelate complex thallium diethyldithiocarbamate (TlDDC) is applied. We systemically injected rodents with TlDDC and mapped the Tl(+)-distribution in the brain using an autometallographic (AMG) technique, a histochemical method for detecting heavy metals. We find that Tl(+)-doses for optimum AMG staining could be substantially reduced, and regional differences attributable to differences in BBB K(+)-permeability were no longer detectable, indicating that TlDDC crosses the BBB. At the cellular level, however, the Tl(+)-distribution was essentially the same as after injection of water-soluble Tl(+)-salts, indicating Tl(+)-release from TlDDC prior to neuronal or glial uptake. Upon sensory stimulation or intracortical microstimulation neuronal Tl(+)-uptake increased after TlDDC injection, upon muscimol treatment neuronal Tl(+)-uptake decreased. We present a protocol for mapping neuronal activity with cellular resolution, which is based on intravenous TlDDC injections during ongoing activity in unrestrained behaving animals and short stimulation times of 5 min.
Goldschmidt
Jürgen
J
Leibniz Institut für Neurobiologie, Abteilung Akustik LernenSprache, Brenneckestrasse 6, Magdeburg, Germany. goldschmidt@ifn-magdeburg.de
Wanger
Tim
T
Engelhorn
Achim
A
Friedrich
Hergen
H
Happel
Max
M
Ilango
Anton
A
Engelmann
Mario
M
Stuermer
Ingo W
IW
Ohl
Frank W
FW
Scheich
Henning
H
D000161:Acoustic Stimulation; D000818:Animals; D001345:Autoradiography; D001522:Behavior, Animal / Q000187:drug effects; D001921:Brain / Q000166:cytology*; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000502:physiology; D002614:Chelating Agents / Q000008:administration & dosage; D004050:Ditiocarb / Q000008:administration & dosage; D005260:Female; D005557:Formaldehyde; D018755:GABA Agonists; D005849:Gerbillinae; D007274:Injections, Intraperitoneal; D007275:Injections, Intravenous; D007601:Jugular Veins / Q000502:physiology; D008297:Male; D009118:Muscimol; D009474:Neurons / Q000502:physiology*; D010147:Pain Measurement / Q000187:drug effects; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results
D002614:Chelating Agents; D018755:GABA Agonists; D019275:Radiopharmaceuticals; D005557:Formaldehyde; D009118:Muscimol; D004050:Ditiocarb