Functional neuroanatomy of the auditory cortex studied with [2-14C]deoxyglucose

The functional neuroanatomy of the auditory cortex during sound stimulation was studied in 16 cats using a labeled tracer, [2-¹⁴C]deoxyglucose. In individual experiments the effect of anesthesia and of stimulation with pure tones, narrow- or broad-band noise, and binaural or monaural input was examined. The results indicate that glucose utilization in the auditory cortex during barbiturate anesthesia was negligiable compared with that seen in paralyzed-awake cats. Narrow-band or broad-band noise stimulation produced activity in the auditory cortex in two dimensions, radially from white matter to pia and as bands of activity running in a dorsoventral orientation on the cortex. No activity could be elicited by pure-tone stimuli. The findings have implications for the more traditional anatomic and physiologic observations of the auditory cortex and for the utility of measuring glucose consumption in the cortex with the [2-¹⁴C]deoxyglucose tracer.     

Stimulus-dependent labeling of cultured ganglionic cell with [14C]2-deoxyglucose

We prepared cultures of dissociated cells from the ciliary (CG) and dorsal root ganglion (DRG) of 10–12-day-old chick embryos, and applied [¹⁴C]2-deoxyglucose ([¹⁴C]2-DG) to the cultured cells to examine the effects of stimulation on the labeling with [¹⁴C]2-DG at the single cell level. Electrical current stimulation increased [¹⁴C]2-DG uptake in CG and DRG neurons. The increase depended on frequency of the stimulation. These effects were potentiated by the application of tetraethylammonium, but suppressed by tetrodotoxin. Externally applied potassium ions increased the [¹⁴C]2-DG uptake in the CG cell, depending logarithmically on the concentration of applied KC1. The concentration-dependent increase agreed with potassium effect on the equilibrium potential. For CG cells, acetylcholine (ACh), glutamate, γ-aminobutyric acid (GABA) and glycine induced remarkable increases of the [¹⁴C]2-DG uptake, while dopamine did not induce any change. For DRG cells, GABA and glycine facilitated the [¹⁴C]2-DG uptake, while ACh, glutamate and dopamine did not have any significant effects on it. These facilitatory actions of neurotransmitters on the [¹⁴C]2-DG uptake are mostly consistent with the excitatory effects of the substrates on both CG and DRG cells in culture. The results suggest that the [¹⁴C]2-DG uptake in single cells is intimately correlated with action potential generation and change in the resting potential.     

Positron Emission Tomography with [11C]Deuterium-Deprenyl in Temporal Lobe Epilepsy

Summary: We performed positron emission tomography (PET) with [¹¹C]deuterium-deprenyl in 9 patients with temporal lobe epilepsy (TLE) undergoing evaluation for possible epilepsy surgery. Seven patients had unilateral and 2 had bilateral mesiotemporal epileptic foci based on the preoperative investigation including ictal EEG discharges and PET with 2-[¹⁸F]fluoro-2-deoxyglucose (FDG). Deprenyl is an irreversible inhibitor of mono-amine oxidase type B (MAO-B) with a very high affinity for the enzyme. In the brain, MAO-B is preferentially located in astrocytes, and a previous in vitro study showed increased binding of the ligand in sclerotic hippocampi. Dynamically acquired N-[methyl-¹¹C]-a, a-di-deutero-L-deprenyl distributions in PET images were analyzed graphically, and the focus regions were assessed visually on the PET images. In addition, the accumulation rate and distribution volume of the tracer relative to the cerebellar cortex were measured in standardized homologous temporal regions by semiquantitative methods. Uptake of [¹¹C]deuterium-deprenyl was significantly increased in the epileptogenic temporal lobes, both apparently and semiquantitatively. By calculating mean inter-lobar ratios, we identified the temporal lobe containing the epileptic focus in six unilateral cases. One case was ambiguous but was not falsely localized. The two bilateral cases were correctly identified as such. Our results suggest that PET with [¹¹C]deuterium-deprenyl might be a useful method for identification of epileptogenic temporal lobes.     

[11C]Flumazenil Positron Emission Tomography Visualizes Frontal Epileptogenic Regions

Summary: Presently available noninvasive methods correctly localize epileptogenic regions in only ε50% of patients with frontal lobe epilepsy (FLE). Earlier studies have shown that temporal lobe epileptogenic regions may be identified readily by positron emission tomography (PET) measurements of regional benzodiazepine (BZD) receptor binding. We tested the specific applicability of this method in patients with FLE. Six patients with frontal partial seizures and 7 healthy men were investigated with PET and the BZD receptor ligand [¹¹C]flumazenil. All patients had magnetic resonance (MR) brain scans. The independent assessment of seizure–onset region was based on seizure semiology, intra– and extracranial EEG and, in 4 cases, also on [¹⁸F]fluorodeoxyglucose (FDG) PET. The epileptic focus/seizure-generating region was correctly identified by [¹¹C]flumazenil PET in all patients. This region was characterized by a significant reduction in BZD receptor density. The area with reduced BZD receptor density was better delimited than the corresponding hypometabolic region, which was observed in 50% of patients investigated with [¹⁸F]FDG–PET. MRI was normal in 5 patients. Visualization of BZD receptors with [¹¹C]flumazenil PET appears to be a promising approach for noninvasive identification of frontal lobe epileptogenic regions.     

Striatal kinetics of [11C]-(+)-nomifensine and 6-[18F]fluoro-L-dopa in Parkinson''s disease measured with positron emission tomography

The kinetics in brain of the dopamine reuptake blocking agent [11C]-(+)-nomifensine and the L-dopa analogue 6-[18F]fluoro-L-dopa were compared in 3 patients with idiopathic Parkinson's disease and age-matched healthy volunteers using positron emission tomography. Regional uptake was analyzed and quantified according to a 3-compartment model. Retention of both tracers in striatal regions of the parkinsonian patients were reduced compared with the healthy volunteers mainly in the putamen, while the caudate nucleus was only mildly affected. The reductions were considerably less than the decrease previously reported postmortem for striatal dopamine content in the basal ganglia of patients with Parkinson's disease. A fairly constant ratio between 6-[18F]fluoro-L-dopa utilization and [11C]-(+)-nomifensine binding in the caudate nucleus and the putamen were found in both groups unrelated to the size of the estimated parameters. This indicates that a limiting factor for the utilization of exogenous levodopa in Parkinson's disease may be a reduced transport capacity for the amino acid into the dopaminergic terminals.     

Benzodiazepine-GABAA Receptors in Idiopathic Generalized Epilepsy Measured with [11C]Flumazenil and Positron Emission Tomography

Summary The neurochemical basis of absence seizures and the mechanism of their suppression by valproate (VPA) are uncertain. We used positron emission tomography (PET) to determine whether an abnormality of [¹¹C]flumazenil binding to benzodiazepine (BZD)-GABA_A receptors exists in patients with childhood and juvenile absence epilepsy and to examine the effects of VPA on [¹¹C] flumazenil binding. The regional cerebral volume of distribution ( V _d) of [¹¹C]flumazenil in patients not treated with VPA was not different from that in normal controls; V _d was lower in patients treated with VPA, and the number of receptors available for binding was significantly reduced in such patients as compared with normal controls. There was no evidence of a primary abnormality of the BZD-GABA, receptor in childhood and juvenile absence epilepsy (CAE/JAE), but the data suggest that treatment with VPA is associated with a reduction in [¹¹C]flumazenil binding that may be relevant to its mode of action in CAE/JAE.     

Differential blood-brain barrier permeabilities to [14C]sucrose and [3H]inulin after osmotic opening in the rat

The blood-brain barrier (B-BB) in 3-month-old rats was opened unilaterally by infusing 1.8 ml(+)arabinose in water into the internal carotid artery through a catheter in the external carotid. Two poorly penetrating uncharged test radiotracers of differing molecular weight and size, [¹⁴C]sucrose (340 daltons, radius 5 Å) and [³H]inulin (5500 daltons, radius 15 Å), were simultaneously injected i.v. in untreated rats, or in rats at 1, 30, or 50 min after infusion of hypertonic arabinose solution. Evans-blue solution was injected 5 min prior to osmotic treatment as a visual indicator of barrier integrity. In regions of uninfused control brains, the [¹⁴C]sucrose permeability-surface area (PA) product approximated 10^?5 s^?1, whereas PA was not measurable for [³H]inulin. In arabinose-infused animals, PA products on the ipsilateral hemisphere for both [¹⁴C]sucrose and [³H]inulin were markedly elevated 6 min after infusion, but decreased by 35 and 55 min. In nearly all regions, statistically significant differences were not found between 6-min [¹⁴C]sucrose- and [³H]inulin-PA values (P > 0.05). However, at 35 and 55 min in most regions, the PA for [³H]inulin was significantly lower (P < 0.05) than PA for [¹⁴C]sucrose. The results indicated that the B-BB closed more rapidly to larger than to smaller molecules after osmotic treatment and were consistent with a pore model for osmotic B-BB opening.     

Species difference in circadian [14C]2-deoxyglucose uptake by suprachiasmatic nuclei

Hamsters exhibited a circadian variation in metabolic activity determined by [¹⁴C]2-deoxyglucose uptake in the suprachiasmatic nuclei, as has been previously reported for rats. The 13-line ground squirrel, a diurnal rodent, did not show a circadian variation in metabolic activity. The data are consistent with the hypothesis that there is a basic difference in the functional organization of the suprachiasmatic nuclei in nocturnal and diurnal animals.     

EFFECTS OF HYPERTONIC SOLUTIONS AND OF MERCURIC CHLORIDE ON THE UPTAKE OF [14C]GLUCOSE ANALOGUES BY RABBIT BRAIN

Intracarotid perfusion of hypertonic solutions of urea, NaCl or acetamide increased the brain uptake index (BUI) of glucose analogues by rabbit brain, while isotonic urea was without effect. Lactamide, whether isotonic or hypertonic, decreased the BUI of glucose analogues. The increased BUI produced by the other hypertonic solutions could be inhibited by unlabeled substrate, unlabeled glucose or by phloridzin, and may reflect stimulated carrier-mediated transport of monosaccharides into brain. Although the increases could also have been due to altered cerebral blood flow, radioautography showed no gross evidence of such alterations. The BUI of 2-2-deoxy-D-[1-¹⁴C]glucose was decreased by intracarotid injection of 0.01mM HgCl₂, to the same level seen following maximal inhibition with unlabeled 2-deoxy-D-glucose, while 0.08mM HgCl₂ gave BUI's above this level. The lower concentration of HgCl₂ probably inhibited carrier-mediated monosaccharide transfer, while the higher concentration appeared to increase passive diffusion into the brain as well.     

PET visualization of microglia in multiple sclerosis patients using [11C]PK11195

Activated microglia are involved in the immune response of multiple sclerosis (MS). The peripheral benzodiazepine receptor (PBR) is expressed on microglia and up-regulated after neuronal injury. [11C]PK11195 is a positron emission tomography (PET) radioligand for the PBR. The objective of the present study was to investigate [11C]PK11195 imaging in MS patients and its additional value over magnetic resonance imaging (MRI) concerning the immuno-pathophysiological process. Seven healthy and 22 MS subjects were included. Semiquantitative [11C]PK11195 uptake values were assessed with normalization on cortical grey matter. Uptake in Gadolinium-lesions was significantly increased compared with normal white matter. Uptake in T2-lesions was generally decreased, suggesting a PBR down-regulation. However, uptake values increased whenever a clinical or MR-relapse was present, suggestive for a dynamic process with a transient PBR up-regulation. During disease progression, an increase of normal-appearing white matter (NAWM) uptake was found, propagating NAWM as the possible real burden of disease. In conclusion, [11C]PK11195 and PET are able to demonstrate inflammatory processes with microglial involvement in MS.     

2-deoxy[14C]glucose uptake in the rat hypoglossal nucleus after nerve transection

We studied glucose utilization by measuring 2-deoxy[¹⁴C]glucose uptake in the rat hypoglossal nucleus after nerve transection, using the contralateral nucleus with intact nerve for comparison. There was increased glucose use on the side of nerve transection 24 h after axotomy. The difference between the two sides increased until at 14 days after nerve transection there was a 62% greater density on the transected side. The rapidity of onset of the accelerated glucose metabolism suggests that it may be among the first metabolic events to occur during regeneration.     

Chronic Lithium Treatment Decreases [3H]-Imipramine Binding in Rat Brain

Abstract: The effect of a chronic lithium treatment on the [3H]-imipramine binding in rat brain regions was investigated. In the striatum, an oral administration of lithium for 30 days induced a decrease in the [3H]-imipramine binding at the concentration of [3'H]-imipramine, 1.0 nM, compared to the control. Lithium did not affect the [3H]-imipramine binding in the cerebral cortex and hypothalamus. A Scatchard analysis in the striatum revealed a decrease in the number of [3H]-imipramine binding sites with no changes in the binding affinity. These results suggest that the chronic lithium treatment may produce subsensitivity of the [3H]-imipramine binding in man and that this effect of the ion may be closely related to the established effect of lithium in the treatment of affective disorders.     

Increased subcortical and laminar cortical 2-deoxy[14C]glucose uptake during cerebellar stimulation

2-Deoxy[¹⁴C]glucose (2DG) uptake was mapped in brains of conscious rats during cerebellar hemisphere electrical stimulation and compared with sham-operated controls. The 2DG uptake increased bilaterally in cerebellar cortex and deep nuclei, the largest increases being ipsilateral to the stimulating electrode. Structures which increased 2DG uptake bilaterally but had larger contralateral increases included the red nucleus, inferior olive, zona incerta, substantia nigra, globus pallidus, deep mesencephalic nucleus, habenula, reticular tegmental nucleus of the pons, ventroanterolateral and ventromedial nuclei of thalamus, several other thalamic nuclei, and motor-somatosensory cortex. Most of these structures receive efferent fibers from cerebellar nuclei. Cerebellar stimulation produced two bands of 2DG uptake bilaterally in rat motor-somatosensory neocortical laminae IV and Vc-VIa. Shamoperated controls had one band of 2DG uptake in neocortical lamina IV. We postulate that cerebellar stimulation increased 2DG uptake polysynaptically in lamina Vc-VIa by the following pathway: Purkinje cells → deep cerebellar nuclei → ventrolateral and/or ventromedial nuclei of thalamus → lamina Vc-VIa of neocortex. Activation of these cortical laminae could affect cortical seizure foci.     

Absence of microwave effect on blood-brain barrier permeability to [14C]sucrose in the conscious rat

The permeability-capillary surface area product (PA) for [¹⁴C]sucrose was examined at the blood-brain barrier of unanesthetized rats, after their exposure to continuous wave or pulsed wave microwave energy at a frequency of 2.8 gHz. The PA was calculated by a dual compartment (plasma-brain) model of S. I. Rapoport, K. Ohno, W. R. Fredericks, and K. D. Pettigrew (1979, Radio Sci.14, 345–348). After the intravenous injection of[¹⁴C]sucrose, plasma radioactivity was measured until the rats were decapitated at 30 min, when brain radioactivity was determined in 11 separate brain regions. Regardless of the power density level (10 to 40 mW/cm², continuous wave; 1 to 15 mW/cm², pulsed wave) of the microwaves, the PA for [¹⁴C]sucrose in any brain region was not significantly different from that in sham-irradiated control animals. The findings indicate that microwave irradiation under the given experimental conditions does not damage the blood-brain barrier.