Ka. Young et al., BEHAVIORAL AND FRONTAL CORTICAL METABOLIC EFFECTS OF APOMORPHINE AND MUSCIMOL MICROINJECTIONS INTO THE MEDIODORSAL THALAMIC NUCLEUS, Journal of neural transmission, 98(2), 1994, pp. 119-132
To study sensorimotor correlates of dopamine (DA) and gamma-amino buty
ric acid (GABA) neurotransmission in the thalamus, we microinjected th
e DA agonist apomorphine (APO), the GABA agonist muscimol and vehicle
into the mediodorsal thalamic nucleus (MdT) of rats and monitored cata
lepsy, sensorimotor asymmetries and the acoustic startle response. Uni
lateral MdT muscimol microinjections (50 ng) produced a lateralization
of the removal of adhesive disks placed simultaneously on both forele
gs in a tactile extinction task, but did not measurably influence any
aspects of startle behavior. The sensorimotor asymmetry consisted of p
referential orientation to the adhesive disk on the side ipsilateral t
o the microinjection. Vehicle and APO microinjections produced no sign
ificant behavioral results. In a follow-up study, unilateral MdT musci
mol microinjections significantly depressed medial prefrontal cortical
metabolism (measured by 2-fluorodeoxyglucose uptake) by 24%, but did
not affect nucleus accumbens metabolic activity. Together, these findi
ngs are consistent with the concept that GABA-mediated inhibition of t
halamocortical neurons in the MdT influences tactile extinction behavi
or, most likely by selectively suppressing excitatory input to the fro
ntal cortex. The sensorimotor asymmetry observed in the present study
resembles attentional and spatial memory deficits associated with fron
tal cortical lesions, and in conjunction with the 2-fluorodeoxyglucose
results, suggests that elevated GABA neurotransmission in the thalamu
s may be involved in attentional and functional metabolic deficits in
humans.