The relationship of local cerebral glucose utilization to optical density ratios

The neural basis of attentional alterations in prenatally protein malnourished rats

Protein malnutrition during gestation alters brain development and produces specific behavioral and cognitive changes that persist into adulthood and increase the risks of neuropsychiatric disorders. Given evidence for the role of the prefrontal cortex in such diseases, it is significant that studies in humans and animal models have shown that prenatal protein malnutrition specifically affects functions associated with prefrontal cortex. However, the neural basis underlying these changes is unclear. In the current study, prenatally malnourished and control rats performed a sustained attention task with an unpredictable distractor, a task that depends on intact prefrontal cortical function. Radiolabeled 2-deoxyglucose was used to measure neural and brain network activity during the task. Results confirmed that adult prenatally malnourished rats were more distractible than controls and exhibited lower functional activity in prefrontal cortices. Thus, prefrontal activity was a predictor of task performance in controls but not prenatally malnourished animals. Instead, prenatally malnourished animals relied on different brain networks involving limbic structures such as the hippocampus. These results provide evidence that protein reduction during brain development has more wide-reaching effects on brain networks than previously appreciated, resulting in the formation of brain networks that may reflect compensatory responses in prenatally malnourished brains.

Prenatal protein malnutrition decreases KCNJ3 and 2DG activity in rat prefrontal cortex

Prenatal protein malnutrition (PPM) in rats causes enduring changes in brain and behavior including increased cognitive rigidity and decreased inhibitory control. A preliminary gene microarray screen of PPM rat prefrontal cortex (PFC) identified alterations in KCNJ3 (GIRK1/Kir3.1), a gene important for regulating neuronal excitability. Follow-up with polymerase chain reaction and Western blot showed decreased KCNJ3 expression in the PFC, but not hippocampus or brainstem. To verify localization of the effect to the PFC, baseline regional brain activity was assessed with (14)C-2-deoxyglucose. Results showed decreased activation in the PFC but not hippocampus. Together these findings point to the unique vulnerability of the PFC to the nutritional insult during early brain development, with enduring effects in adulthood on KCNJ3 expression and baseline metabolic activity.

Prenatal malnutrition leads to deficits in attentional set shifting and decreases metabolic activity in prefrontal subregions that control executive function

Globally, over 25% of all children under the age of 5 years experience malnutrition leading to cognitive and emotional impairments that can persist into adulthood and beyond. We use a rodent model to determine the impact of prenatal protein malnutrition on executive functions in an attentional set-shifting task and metabolic activity in prefrontal cortex (PFC) subregions critical to these behaviors. Long-Evans dams were provided with a low (6% casein) or adequate (25% casein) protein diet 5 weeks before mating and during pregnancy. At birth, the litters were culled to 8 pups and fostered to control dams on the 25% casein diet. At postnatal day 90, prenatally malnourished rats were less able to shift attentional set and reverse reward contingencies than controls, demonstrating cognitive rigidity. Naive same-sexed littermates were assessed for regional brain activity using the metabolic marker (14)C-2-deoxyglucose (2DG). The prenatally malnourished rats had lower metabolic activity than controls in prelimbic, infralimbic, anterior cingulate, and orbitofrontal cortices, but had comparable activity in the nearby piriform cortex and superior colliculus. This study demonstrates that prenatal protein malnutrition in a well-described animal model produces cognitive deficits in tests of attentional set shifting and reversal learning, similar to findings of cognitive inflexibility reported in humans exposed to early childhood malnutrition.

Regional (14C) 2-deoxyglucose uptake during forelimb movements evoked by rat motor cortex stimulation: cortex, diencephalon, midbrain

The caudal forelimb region of right "motor" cortex was repetitively stimulated in normal, conscious rats. Left forelimb movements were produced and (14C) 2-deoxyglucose (2DG) was injected. After sacrifice, regions of increased brain (14C) 2DG uptake were mapped autoradiographically. Uptake of 2DG increased about the stimulating electrode in motor (MI) cortex. Columnar activation of primary (SI) and second (SII) somatosensory neocortex occurred. The rostral or second forelimb (MII) region of motor cortex was activated. Many ipsilateral subcortical structures were also activated during forelimb MI stimulation (FLMIS). Rostral dorsolateral caudate-putamen (CP), central globus pallidus (GP), posterior entopeduncular nucleus (EPN), subthalamic nucleus (STN), zona incerta (ZI), and caudal, ventrolateral substantia nigra pars reticulata (SNr) were activated. Thalamic nuclei that increased (14C) 2DG uptake included anterior dorsolateral reticular (R), ventral and central ventrolateral (VL), lateral ventromedial (VM), ventral ventrobasal (VB), dorsolateral posteromedial (POm), and the parafascicular-centre median (Pf-CM) complex. Activated midbrain regions included ventromedial magnocellular red nucleus (RNm), posterior deep layers of the superior colliculus (SCsgp), lateral deep mesencephalic nucleus (DMN), nucleus tegmenti pedunculopontinus (NTPP), and anterior pretectal nucleus (NCU). Monosynaptic connections from MI or SI to SII, MII, CP, STN, ZI, R, VL, VM, VB, POm, Pf-CM, RNm, SCsgp, SNr, and DMN can account for ipsilateral activation of these structures. GP and EPN must be activated polysynaptically, either from MI stimulation or sensory feedback, since there are no known monosynaptic connections from MI and SI to these structures. Most rat brain motor-sensory structures are somatotopically organized. However, the same regions of R, EPN, CM-Pf, DMN, and ZI are activated during FLMIS compared to VMIS (vibrissae MI stimulation). Since these structures are not somatopically organized, this suggests they are involved in motor-sensory processing independent of which body part is moving. VB, SII, and MII are activated during FLMIS but not during VMIS.

Investigations of the cholinergic deficit hypothesis in the hippocampus of the aged rat brain with physostigmine and scopolamine

Using histochemically demonstrated acetylcholinesterase activity and (14)C-2-deoxyglucose uptake as the respective indices, a study was set up to determine whether cerebral (hippocampal) metabolism was stimulated by a cholinergic agonist and/or inhibited by a cholinergic antagonist. For this 36 12-month-old (adult) and 48 27-month-old (aged) Fischer 344 rats were given intraperitoneal injections of physostigmine 0.05, 0.1 or 0.2 mg/kg or scopolamine 0.01, 0.03 or 0.1 mg/kg for 5 days. In the aged rats there was a slight increase in acetylcholinesterase activity after physostigmine but no convincing evidence of enhanced (14)C-2-deoxyglucose uptake. In neither age group was glucose uptake significantly reduced by scopolamine; it was in fact increased, as was - slightly but significantly - acetylcholinesterase activity. Findings for acetylcholinesterase activity and (14)C-2-deoxyglucose uptake in aged Fischer 344 rats thus do not provide firm corroboration of physostigmine-induced stimulation of mental performance found in behavioural studies, while scopolamine did not adversely affect the hippocampal variables studied. It is concluded that cholinergic agents such as physostigmine and scopolamine have only a marginal effect on the functional and metabolic deficits associated with cerebral aging.

Functional impact of primary visual cortex deactivation on subcortical target structures in the thalamus and midbrain

The functional relationships between the primary visual cortex and its major subcortical target structures have long been a subject of interest. We studied these relationships by using localized cooling deactivation to silence portions of primary visual cortex and measuring 2-deoxyglucose (2DG) uptake to assess neural activity in subcortical and midbrain targets. We focused analysis on the largest subcortical targets of primary visual cortex: the superior colliculus (SC), the dorsal lateral geniculate nucleus of the thalamus (dLGN), and the lateral division of the lateral posterior nucleus of the thalamus (LPL). We found that localized cooling of different regions of primary visual cortex caused specific decreases in 2DG uptake in target structures such that the location of 2DG decrease varied according to joint retinotopy, and the magnitude of the decreases in target structures was associated with the amount of cooled cortex. In addition, we found that the impact of cortical cooling was more profound on the SC than on the dLGN. The functional impact of cortical deactivations on the LPL was weak for small deactivations but approximated the impact on the SC when deactivations were large. We discuss these findings in terms of neural circuits and in terms of drivers and modulators.

Amyloid-beta deposition is associated with decreased hippocampal glucose metabolism and spatial memory impairment in APP/PS1 mice

In Alzheimer disease (AD) patients, early memory dysfunction is associated with glucose hypometabolism and neuronal loss in the hippocampus. Double transgenic (Tg) mice co-expressing the M146L presenilin 1 (PS1) and K670N/M671L, the double "Swedish" amyloid precursor protein (APP) mutations, are a model of AD amyloid-beta deposition (Abeta) that exhibits earlier and more profound impairments of working memory and learning than single APP mutant mice. In this study we compared performance on spatial memory tests, regional glucose metabolism, Abeta deposition, and neuronal loss in APP/PS1, PS1, and non-Tg (nTg) mice. At the age of 2 months no significant morphological and metabolic differences were detected between 3 studied genotypes. By 8 months, however, APP/PS1 mice developed selective impairment of spatial memory, which was significantly worse at 22 months and was accompanied by reduced glucose utilization in the hippocampus and a 35.8% dropout of neurons in the CA1 region. PS1 mice exhibited a similar degree of neuronal loss in CA1 but minimal memory deficit and no impairment of glucose utilization compared to nTg mice. Deficits in 22 month APP/PS1 mice were accompanied by a substantially elevated Abeta load, which rose from 2.5% +/- 0.4% at 8 months to 17.4% +/- 4.6%. These findings implicate Abeta or APP in the behavioral and metabolic impairments in APP/PS1 mice and the failure to compensate functionally for PS1-related hippocampal cell loss.

Functional consequences of neuropeptide FF receptors stimulation in mouse: a cerebral glucose uptake study

The brain substrates involved in the pharmacological effects of neuropeptide FF (NPFF, Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2) including interactions with opioid systems, were investigated with the [14C]-2-deoxyglucose ([14C]-2-DG) autoradiography technique in mouse. The changes in cerebral activity were mapped after i.p. administration of 1DMe ([D-Tyr1,(NMe)Phe3]NPFF; 70 mg/kg), a neuropeptide FF analogue partially resistant to peptidases, alone or in combination with morphine (15 mg/kg). 1DMe induced a rapid decrease in the cerebral activity in the thalamus, the pontine reticular nuclei and the cerebellar cortex, brain regions involved in the control of motor activity and/or the processing of sensory data. This decrease, observed when 1DMe was administered 5 min before [14C]-2-DG, was reversed by morphine, which was devoid of significant effect at this time. When administered 30 min before the radioisotope, 1DMe was without effect, whereas morphine induced a significant increase in cerebral glucose utilization in the caudate putamen, the primary somatosensory cortex, the thalamus, the superior colliculus, the pontine reticular nuclei and the spinal cord. The association of morphine and 1DMe significantly increased cerebral glucose utilization in the same regions as morphine alone and also in three additional regions: the auditory cortex, the inferior colliculus and the dorsomedial periaqueductal gray. Following systemic administration, 1DMe and morphine modulated cerebral activity in brain regions involved in pain transmission and motor control, but their effects were temporally shifted, as were their effects on horizontal locomotor activity. However, neuropeptide FF-induced changes in brain activity were modulated in part by opioid receptors activation.

Comparative analysis of acute and chronic administration of haloperidol and clozapine using [3H] 2-deoxyglucose metabolic mapping

In an effort to compare and contrast the mechanisms of action of typical and atypical antipsychotic drugs, [3H] 2-deoxyglucose metabolic mapping was employed following acute and chronic administration of haloperidol (1 mg/kg i.p. acute and 0.5 mg/kg i.p. chronic) and clozapine (20 mg/kg i.p., both acute and chronic). Optical density ratios (ODR) were measured in 62 brain structures. An overall decrease in ODR was observed in many of the regions analyzed. Acute haloperidol elicited significant decreases, particularly in the thalamus and hippocampus. Acute clozapine decreased glucose uptake in the caudate putamen, hippocampus, central gray, locus coreleus, and the thalamus. In both chronically treated haloperidol and clozapine animals, significant decreases in ODR were seen in the thalamus and hippocampal areas most dramatically, with other changes in the superior colliculus, retrospenial cortex, and the cerebellum. Clozapine caused significant effects in 32 nuclei acutely and only 19 nuclei chronically. Haloperidol caused significant effects in 23 nuclei acutely and 15 nuclei chronically. The pattern of change induced by haloperidol and clozapine were remarkably similar when considering their pharmacology is somewhat different. Both antipsychotics elicited fewer significant changes upon chronic administration.

Cerebral glucose utilization in transgenic mice overexpressing heat shock protein 70 is altered by dizocilpine

Heat shock protein (HSP70), a member of the 70 kDa HSP superfamily, has been widely implicated in the cellular stress response to numerous insults. HSP70 may be a significant factor in cell survival following stresses such as cerebral ischaemia. The precise mechanisms by which HSP70 facilitates cell survival remain unclear. The aim of this study was to ascertain whether any differences in local cerebral glucose utilization (LCGU) existed between transgenic mice overexpressing HSP70 (HSP70 Tg) and wild- type littermate (WT) mice. LCGU was assessed using (14)C-2-deoxyglucose in HSP70 Tg and WT mice under basal conditions (intraperitoneal injection of saline) and during metabolic activation produced by NMDA receptor blockade (intraperitoneal injection of dizocilpine, 1 mg/kg). No significant alterations in LCGU were observed between saline injected HSP70 Tg and WT mice in any of the 35 brain regions analyzed. Dizocilpine injection produced significant heterogeneous alterations in LCGU in HSP70 Tg mice (24 of 35 brain regions) and in WT mice (22 of 35 brain regions) compared with saline injected mice. The distribution of altered LCGU produced by dizocilpine was similar in HSP70 Tg and WT mice. However in five brain regions, dizocilpine injected HSP70 Tg mice displayed significantly altered LCGU compared to dizocilpine injected WT mice (anterior thalamic nucleus +27%, dorsal CA1 stratum lacunosum molecularae +22%, dorsal CA1 stratum oriens + 14%, superior olivary body -26%, and the nucleus of the lateral lemniscus -16%). These data highlight that while overexpression of HSP70 transgene does not significantly alter LCGU in the basal state, mice overexpressing the HSP70 transgene respond differently to metabolic stress produced by NMDA receptor blockade in some important brain regions.

Differentially altered cerebral metabolism in ischemic rats by alpha2-adrenoceptor blockade and its relation to improved limb-placing reactions

The selective alpha2-adrenoreceptor antagonist, atipamezole, improves behavioural performance of rats subjected to focal cerebral ischemia. The aim of the present study was to investigate whether the facilitatory effect of atipamezole on behaviour is related to altered neuronal activity in specific brain areas. The right middle cerebral artery of rats was occluded for 120 min using the intraluminal filament method. Starting on day 2 after induction of ischemia, atipamezole (1mg/kg, s.c.) or 0.9% NaCl was administered to ischemic or sham-operated rats once a day 30 min before the limb-placing test. [14C]Deoxyglucose ([14C]DG) uptake was used to measure neuronal activity 30 min after atipamezole or 0.9% NaCl administration on day 6 after ischemia. Ischemia induced a significant decrease in [14C]DG uptake in several cortical areas ipsilateral and contralateral to the lesion, in the ipsilateral thalamus, and bilaterally in the cerebellum and spinal cord. Administration of atipamezole normalised [14C]DG uptake particularly in the cerebellum and spinal cord both in sham-operated and ischemic rats and to a lesser extent in the thalamus in sham-operated rats. The pattern of altered cerebral [14C]DG uptake following alpha2-adrenoceptor blockade suggests that plasticity in the cerebellum and spinal cord contributes to the improved performance of ischemic rats in tests assessing tactile/proprioceptive limb-placing reactions.

Brain regional substrates for the actions of the novel wake-promoting agent modafinil in the rat: comparison with amphetamine

Modafinil is a novel wake-promoting compound for which the mechanism and sites of action are unknown. We examined the neural substrates in the brain for the actions of modafinil using 2-deoxyglucose autoradiography and compared the findings to those obtained with amphetamine. Modafinil showed a relatively restricted pattern of changes in brain regional metabolic activity, while amphetamine altered glucose utilization in a wide variety of brain regions. Both modafinil and amphetamine increased glucose utilization in all subregions of the hippocampus (subiculum, CA1-CA3 and dentate gyrus) and in the centrolateral nucleus of the thalamus. Modafinil also increased glucose utilization in the central nucleus of the amygdala, but amphetamine had no effect in this region. Brain structures in which amphetamine increased metabolic rate but modafinil had no effect included regions of the basal ganglia, other nuclei of the thalamus, the frontal cortex, the nucleus accumbens, the ventral tegmental area and the pontine reticular fields. These findings suggest that, while both modafinil and amphetamine promote wakefulness, they act via distinctly different mechanisms. Modafinil appears to act on a specific subset of brain pathways which regulate sleep and wakefulness, whereas amphetamine affects a greater number of cerebral structures involved in the regulation of these behavioral states. Modafinil also lacks the pronounced effects on the extrapyramidal motor system which are characteristic of amphetamine and other psychomotor stimulants, implying that the effects of modafinil are not mediated by the dopamine system and that modafinil may selectively increase wakefulness with fewer side effects.

Functional development of the vibrissae somatosensory system of the rat: (14C) 2-deoxyglucose metabolic mapping study

Functional development of the rat whisker somatosensory system was studied by using the (14C) 2-deoxyglucose (2DG) metabolic mapping technique. Restrained rat pups had their left mystacial vibrissae stroked for 30 minutes and their brains harvested, sectioned, and autoradiographed from the level of the lower medulla to the frontal cortex. Subjects were tested at postnatal days (PNDs) 0-9 and 21. At birth, all subjects exhibited a significant increase of 2DG uptake in the left spinal trigeminal nuclei, the principal trigeminal sensory nucleus, and a portion of the right ventral posteromedial thalamic nucleus. The primary somatosensory cortex exhibited significant 2DG uptake contralateral to stimulation by PND 6, followed by the secondary somatosensory cortex at PND 7. The pattern of 2DG uptake in the somatosensory cortices became more intense and well defined by PND 9. Given that the somatosensory system develops in an orderly fashion from the periphery to higher brain structures, the present results show that brain structures mediating whisker sensory input are not metabolically active until projections from lower somatosensory centers are established. Neurons become responsive to whisker stimulation in the subcortical structures at birth and in the somatosensory cortex a few days later. This cortical activity follows the organization of the upper tier of thalamocortical fibers into a "barrelfield." Moreover, there is a gradual enhancement in functional activity of the vibrissa neurons at different somatosensory nuclei as rats mature. The present study elucidates the time course of functional development in the rat somatosensory system.

Metabotropic glutamate agonist-induced rotation: a pharmacological, FOS immunohistochemical, and [14C]-2-deoxyglucose autoradiographic study

Metabotropic glutamate receptors (mGluRs) are a major class of excitatory amino acid receptors. Eight mGluR subtypes, coupled to a variety of effector systems, have been cloned. These receptors have been classified into three groups based on amino acid sequence homology, effector systems, and pharmacological profile. Group I mGluRs increase phosphoinositide turnover, whereas groups II and III mGluRs are negatively coupled to adenylyl cyclase. The striatum possesses a high density of mGluR binding sites, and several mGluR mRNAs and proteins are expressed by striatal neurons. In rats, unilateral striatal injection of the nonsubtype selective mGluR agonist 1-aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD) results in contralateral rotation with delayed onset, thought to be secondary to an increase in dopamine release. We sought to determine the mGluR subtype(s) involved, the modulation of the rotation by other basal ganglia neurotransmitter systems, and the functional anatomy underlying the rotational behavior. The group I mGluR agonist 3,5-dihydroxyphenylglycine (DHPG) induced contralateral rotation in a dose-dependent manner, whereas group II and group III agonists were ineffective. Rotation induced by DHPG or 1S,3R-ACPD was attenuated by group I antagonists, but not by group II or group III antagonists. This suggests that the rotation is mediated by group I mGluRs. Rotation induced by DHPG or 1S,3R-ACPD was attenuated by pretreatment with antagonists at muscarinic cholinergic, adenosine A2, dopamine D2, or dopamine D1 receptors. Examination of FOS-like immunoreactivity after group I and group II mGluR agonist administration suggests increased activity in the striatopallidal pathway. However, [14C]-2-deoxyglucose uptake studies indicate increased activity in nuclei of the striatopallidal (indirect) pathway, particularly in the subthalamic nucleus, only after group I mGluR activation.

A metabolic mapping study of orientation discrimination and detection tasks in the cat

Increasing evidence suggests that a large number of distinct cortical areas and associated subcortical structures participate in the processing of visual information and that different aspects of visual scenes are evaluated in different areas. This necessitates identification of cortical and subcortical regions cooperating in particular visual tasks. Using the 2-deoxyglucose technique, we monitored the differential activation of areas in the cat visual cortex participating in an orientation discrimination and a detection task. Concordant with previous lesion studies, we found increased activity levels in area 17 in the discrimination condition relative to the detection condition. In addition, the 2-deoxyglucose technique revealed discrimination-related increased activations in the claustrum, the putamen and in parts of the anteromedial, anterolateral and posterolateral lateral suprasylvian visual areas. Regions activated differentially with the detection task comprised subdivisions of areas 17, 18, 19 and 21, posterior area 7 (7p), several areas of the posterior part of the middle and posterior suprasylvian sulcus, the pulvinar complex and the superior colliculus. These results show that the 2-deoxyglucose technique is useful to investigate cognitive brain functions, and that different sets of cortical and subcortical regions are activated during two visual tasks with similar visual stimulation.

Intensity and frequency functions of [14C]2-deoxyglucose labelling in the central nucleus of the inferior colliculus in the cat

The frequency organization of the central nucleus of the inferior colliculus (ICC) in the anesthetised cat was quantitatively mapped using [14C]2-deoxyglucose. From a standardised rostrocaudal region of the ICC, the position of peak selective labelling along the tonotopic axis closely conformed to the reported tonotopic organization of this nucleus. The position of the peak was found not to significantly change its position along the tonotopic axis with increasing stimulus intensity. However, the amplitude of peak uptake and width of selective labelling were shown to monotonically increase with increase in stimulus intensity. The increase in width of selective labelling, about the position of peak uptake, showed a slight asymmetry toward the high-frequency regions of the ICC. A 2-DG frequency-position function for the ICC, similar to that for the cochlea, enabled the width of 2-DG bands to be expressed in terms of their frequency spread along the tonotopic axis. This inturn enabled 2-DG tuning curves to be plotted which, when compared to electrophysiologically determined tuning curves, showed marked similarities. The minimum threshold and width (Q10) of these 2-DG tuning curves fell within the range reported for single units in the cat auditory pathway.

Fetal alcohol syndrome: early olfactory learning as a model system to study neurobehavioral deficits

The goal of basic research examining the deficits underlying fetal alcohol syndrome is to develop an animal model which allows investigation and assessment of the neural and cognitive impairments resulting from prenatal alcohol exposure. The following review focuses on animal models and their relationship to human deficits following prenatal alcohol exposure. In addition, this review examines a unique, well-established model system which may permit an increased understanding of the role of alcohol on the developing brain and cognitive behavior. Specifically, large metabolic, neurochemical, neuropharmacological, morphological and neurophysiological changes in young rats have been reported as a consequence of early olfactory preference conditioning, a form of learning that normally occurs during both human and rat development. This olfactory odor preference training paradigm can be used to assess changes in learning as well as the neural substrates underlying this learning. Olfactory preference training has been used to examine: 1) learning, as demonstrated by a behavioral preference for an odor previously paired with stimulation which mimics maternal care; 2) metabolism, by measuring 2-deoxyglucose uptake and distribution in response to the trained odor; 3) neurotransmitter levels, by using in vivo microdialysis, to examine changes in neurotransmitter levels in the olfactory bulb in response to a trained odor. Using in vivo microdialysis enables measurement of both baseline responsiveness of alcohol-exposed pups as well as learned responses at several different developmental ages. The established neural features of this olfactory model include an increase in behavioral preference for a trained odor, increases in 2-DG uptake in specific foci within the olfactory bulb in response to the odor, and increases in dopamine in response to olfactory preference training stimuli, as well as conditioned increases in norepinephrine following olfactory preference training. Using these known behavioral, metabolic and neurochemical indices in control pups allows identification of some of the neurotransmitter systems involved in deficits and the neurobiological basis for impairments induced by prenatal alcohol exposure.

Differential temporal evolution of post-training changes in regional brain glucose metabolism induced by repeated spatial discrimination training in mice: visualization of the memory consolidation process?

The present study analyses the effects of the stage of learning on the spatial patterns and time-course of [14C]glucose uptake in BALB/c mice brain regions produced by spatial discrimination training in an eight-arm radial maze. Our particular approach was designed to follow, during the post-training period, the level of functional activity in individual brain areas which may underlie the memory consolidation process. Regional mapping of relative [14C]glucose uptake was assessed at three post-training time intervals (5 min, 1 and 3 h) after either the first (Day 1), the fourth (Day 4) or the last (Day 9) daily training session of the discrimination task and compared with sham-conditioned animals placed in the same experimental environment. The results indicated that numerous subcortical and cortical brain regions exhibit metabolic alterations following the acquisition of the spatial discrimination task. These alterations, which were specifically related to learning since they did not appear in sham-conditioned animals, were functions both of the post-training interval studied and of the degree of mastery of the task. On Day 1, a progressive, time-dependent and sequential increase in labelling was found from subcortical (5 min post-training) to cortical regions (3 h post-training). On Day 4, a peak of cortical metabolic activation was identified at 1 h post-training. In contrast, on Day 9, maximum labelling was found 5 min post-training in all subcortical and cortical regions followed by a general monotonic decline at 1 and 3 h post-training. These findings, which show widely distributed changes of metabolic activity in the brain, are consistent with the hypothesis that learning involves distributed neural networks. The sequential activation from subcortical to cortical regions seems to indicate a general mechanism whose function would ultimately be to store cortical memory representations. The acquisition-dependent shifts in the patterns of post-training metabolic labelling observed as a function of task mastery may be taken to represent a visualization of the spatio-temporal evolution of the networks of brain structures actively engaged in the memory consolidation process. In particular, the present data suggest that the duration of post-acquisition memory processing is a function of the quantity of new information which has to be dealt with by the central nervous system.

Reduction of regional brain glucose metabolism following different durations of chronic ethanol consumption in mice: a selective effect on diencephalic structures

The effects of chronic alcohol consumption on regional brain glucose metabolism were examined in Balb/c mice using the [14C]2-deoxyglucose autoradiographic technique. Animals were given a solution of 12% v/v ethanol as their only source of fluid for either 6, 12 or 18 months and compared to control groups receiving either an isocaloric solution or saccharose or tap water. Alterations of cerebral brain glucose metabolism were assessed in mice who were returned to a non-alcoholic diet and allowed to freely explore a T-maze. The results showed that chronic ethanol consumption induced reductions of regional metabolic activity which were functions both of the duration of alcohol treatment and of the structure studied. Whereas a six month period of alcoholization did not induce any significant effects on metabolic activity, 12 months of treatment were necessary to induce the first observable and significant reductions in [14C]2-deoxyglucose labelling. These effects were mainly limited to diencephalic structures such as the lateral mammillary nuclei and the anterodorsal thalamic nuclei. The cerebellum was also affected but to a lesser degree. After 18 months of alcoholization, a generalized spread of the metabolic reduction to the entire mammillary complex (lateral, medial and posterior nuclei) and to the thalamic nuclei was observed. This same duration of treatment was necessary to induce the first detectable decrease of metabolic activity in the hippocampus. In agreement with data from human neuropathology, these findings confirm the particular vulnerability of diencephalic structures to ethanol and suggest that damage limited to diencephalic regions rather than to hippocampal or cortical areas could be primarily responsible for the memory disorders observed in Korsakoff's syndrome.

Anti-ataxic effects of TRH and its analogue, TA-0910, in Rolling mouse Nagoya by metabolic normalization of the ventral tegmental area

1. The mechanism of the anti-ataxic action of thyrotropin-releasing hormone (TRH) and its analogue. TA-0910, in the Rolling mouse Nagoya (RMN), an ataxic mutant mouse, has been investigated. 2. TRH (30 mg kg-1, i.p.) and TA-0910 (3 mg kg-1, i.p.) reduced the fall index (number of falls/spontaneous motor activity), an index of ataxia, 10-30 and 10-60 min after administration, respectively. 3. Relative local cerebral glucose utilization (LCGU) in the cerebellum and ventral tegmental area (VTA) of the rolling mouse was significantly smaller than that in normal animals. TRH (30 mg kg-1, i.p.) and TA-0910 (3 mg kg-1, i.p.) increased the relative LCGU value of the VTA but not of the cerebellum in rolling mice to the level of normal animals. 4. These results suggest that the ataxia of the rolling mouse may be due to dysfunction of the cerebellum and VTA, and that amelioration by TRH and TA-0910 could result from metabolic normalization of the VTA.

Age-related CNS disorder and early death in transgenic FVB/N mice overexpressing Alzheimer amyloid precursor proteins

Transgenic FVB/N mice overexpressing human (Hu) or mouse (Mo) Alzheimer amyloid precursor protein (APP695) die early and develop a CNS disorder that includes neophobia and impaired spatial alternation, with diminished glucose utilization and astrogliosis mainly in the cerebrum. Age at onset of neophobia and age at death decrease with increasing levels of brain APP. HuAPP transgenes induce death much earlier than MoAPP transgenes expressed at similar levels. No extracellular amyloid was detected, indicating that some deleterious processes related to APP overexpression are dissociated from formation of amyloid. A similar clinical syndrome occurs spontaneously in approximately 20% of nontransgenic mice when they reach mid- to late-adult life, suggesting that APP overexpression may accelerate a naturally occurring age-related CNS disorder in FVB/N mice.

Radioactive 2-DG incorporation patterns in the mesial frontal cortex of task-performing monkeys

The pattern of radioactive 2-deoxy-D-glucose (2-DG) uptake in the rostral mesial cortex was investigated in seven hemispheres of four task-performing monkeys (a delayed-response task performed with a forelimb). A two-dimensional 2-DG map was constructed from frontal sections. Blob-like 2-DG incorporation sites (2-DG active sites) were observed in single frontal sections, e.g., in the anterior cingulate gyrus (CiG) and supplementary and primary motor cortices in the mesial surface, and around the superior precentral sulcus in the premotor area. Blob-like 2-DG incorporation sites were also observed in the medial part of the dorsal frontal cortex near the midline. However, most of these blob-like 2-DG active sites were revealed in fact not to be blobs. They formed rostrocaudally continuous streaks when they were constructed in a two-dimensional map. Streaks fused with one another in some areas, and gave off branches in other areas. These 2-DG uptake patterns were similar between the paired left and right hemispheres of three brains. It is highly probable that these 2-DG active streaks (or blobs) reflected neuronal activity related to somatomotor and/or eye movements, because the 2-DG-labeled areas included motor, premotor, supplementary motor, and possibly part of the supplementary eye fields. It is also probable that this 2-DG incorporation was related to cognitive or memory functions, because neuronal activity related to performance of a delayed-response was reported in the rostral mesial cortex and in the CiG.

Development of metabolic response in male quail brain during sexual maturation

Seasonal reproductive activities of Japanese quail Coturnix japonica are induced most obviously by stimulatory effects of long-day photoperiod. This study addressed the metabolic response, as measured by 2-deoxyglucose (2-DG), in brain of male quail during sexual maturation. At 7 weeks of age, reproductively quiescent quail exposed to a short photoperiod of 6L:18D, received 2-DG on day 0 and +3, +6, +9, +12, +15 and +18 days after onset of 16L:8D. Brains were processed for autoradiography; serum testosterone was measured to indicate reproductive response to photoperiod. Circulating testosterone remained low until day 9, then rose sharply, reaching maximum levels at day 18. Heavily labeled nuclei were identified in some discrete neural pathways: both tectofugal and thalamofugal visual pathways, ascending auditory pathway, efferent vocalization pathway, and limbic structures. Metabolic activity of the terminal nucleus (ectostriatum) of the tectofugal pathway increased significantly by day 18, but in the terminal nuclei (the Wulst) of the thalamofugal visual pathway activity did not change significantly. Energy metabolism of some nuclei of the auditory pathway rose significantly by day 3, although in the vocal pathway it did not show augmentation until days 15-18. The metabolic activity of limbic structures also increased. These results suggest that, in Japanese quail, sensory nuclei and some of their integrative areas become sensitive to environmental cues in response to long-day photoperiod. It is possible that the external environmental cues that affect the reproductive activities of quail act through sensory systems.

Discrimination training in a GO/NOGO-procedure alters the 2-deoxyglucose pattern in the Starling's forebrain

European starling's (Sturnus vulgaris L.) were used to measure differences in the glucose metabolism in the auditory forebrain between birds performing an auditory discrimination task and birds habituated to the same acoustic stimuli. One group (n = 5) of individuals was trained in an operant GO/NOGO-procedure to report 1-kHz tone signals in a background of 4-kHz stimuli. The other group (n = 5) was habituated to the experimental set-up and to the same sequence of tones presented to the trained birds. [14C]2-deoxyglucose (2DG) uptake was determined in the caudal auditory telencephalon and the nucleus ovoidalis of well trained and habituated birds by autoradiography of brain sections. The tissue areas having grey values above predefined threshold values of labelling were determined in every brain section of each bird and then combined to volumes of labelled tissue. No significant differences of the 2DG uptake in the nucleus ovoidalis were found between the two experimental groups. In the caudal auditory telencephalon, however, significant differences in 2DG-labelling were found. In the trained birds, the labelling in the caudal auditory telencephalon was confined to smaller brain regions than in the habituated birds. These results suggest a differential processing of sounds in the trained and habituated birds which is discussed in the context of sharpening of the frequency representation by GABAergic inhibition and processes of attention.

Metabolic mapping of visual areas in the behaving cat: a [14C]2-deoxyglucose study

Visually responsive cortical areas and subcortical nuclei were studied in the awake cat using the 2-deoxyglucose technique. Visual input was confined to one hemisphere by unilaterally sectioning the optic tract, the corpus callosum and the commissura anterior. Within the intact hemisphere, numerous cortical regions were distinguishable in the autoradiographs due to differential labelling. Comparison of the intact with the visually deafferented hemisphere confirmed the visual character of eighteen cortical areas (areas 17, 18, 19, 20a, 20b, 21a, 21b, the posteromedial lateral, posterolateral lateral, anteromedial lateral, anterolateral lateral, dorsal lateral, ventral lateral, and posterior suprasylvian areas, the splenial and anterior ectosylvian sylvian areas, insular visual area and posterior area 7) and revealed the visual nature of an area in the posterior cingulate gyrus which had not been described previously. We refer to this area as cingulate visual area (CVA). This area exhibits a gradient in interhemispheric differences along a caudorostral axis similar to that observed in posterior area 7 which is in keeping with the strong and topographic connections between CVA and posterior area 7. These results support the validity of metabolic mapping for the characterisation of cortical areas.

Short and long-term changes in cerebral [14C]-2-deoxyglucose uptake in the MPTP-treated marmoset: relationship to locomotor activity

The "short-term" (0.7 +/- 0.1 months post-MPTP) and "long-term" effects (36.7 +/- 4.4 months) of MPTP treatment on motor behaviour and [14C]-2DG uptake were investigated in the common marmoset. The subcutaneous administration of MPTP greatly reduced locomotor activity (-94% with respect to controls) and induced motor disability in the "short-term" MPTP-treated marmoset group. In the "long-term" MPTP group, MPTP treatment did not significantly affect locomotor activity (-27% with respect to controls) and there was partial recovery of motor disability. In the "short-term" MPTP group, there were increases in [14C]-2DG uptake in the GPl (+31 to +37%), SNc (+34 to +42%), VTA (+35%), LC (+23%), PPN (+19%) and in the VA (+19%), VL (+20%) and AM (+17%) thalamic nuclei. [14C]-2DG uptake was decreased in the STN (-15%). In the "long-term" MPTP group, [14C]-2DG uptake was increased in the GPl (+18%), SNc (+27%), VTA (+25%), PPN (+19%), ventral caudate nucleus (+18 to +23%), NAc (+22%), F.Ctx (+18%) and in the VA (+34%), VL (+28%), AV (+33%) and AM (+24%) thalamic nuclei. [14C]-2DG uptake was unchanged in the STN. The increase in metabolic activity of the surviving DA neurones and/or the reactive gliosis may account for the initial increase in [14C]-2DG uptake in the SNc and VTA. On the other hand, in the "long-term" MPTP-treated animals the increase in [14C]-2DG uptake in the SNc (though less than in the "short-term" MPTP group), ventral caudate and NAc may reflect the regenerative changes in the dopaminergic system in these areas. Despite the behavioural recovery, [14C]-2DG uptake remained elevated in the target areas for medial pallidal output (the thalamic nuclei and PPN). However, the attenuation of the changes in [14C]-2DG uptake in the GPl and STN of "long-term" MPTP-treated marmosets suggest that the striato-GPl and GPl-STN outputs closely reflect motor function in this primate model of Parkinson's disease.

Transplants of embryonic cortical tissue placed in the previously damaged frontal cortex of adult rats: local cerebral glucose utilization following execution of forelimb movements

Transplantation of fetal cortical tissue into the motor cortex of adult rats was used as an experimental model to examine the functional integration of homotopic fetal neocortical grafts into the motor pathways of adult host brain. We have employed the [14C]2-deoxy-D-glucose method to analyse the metabolic activity of the transplant and host sensorimotor cortex: (i) in animals solicited to perform specific lever-pressing movements with the limb contralateral to the transplant (experimental group); and (ii) in non-solicited animals or in animals using the limb ipsilateral to the transplant (control group). Grafts in the control group displayed homogeneous uptake of 2-deoxy-D-glucose throughout the rostrocaudal extent of the transplant. The local cerebral glucose utilization levels were low as compared to those of the surrounding cortex but were at least two-times higher than in the corpus callosum. Increase in 2-deoxy-D-glucose uptake by the transplant cells was found only in the experimental group. In this group, 2-deoxy-D-glucose uptake was higher in the caudal (AP: +3.0 to +1.7 mm, relative to Bregma) than in the rostral sectors of the transplants suggesting the existence of a topographic organization within the transplant. In addition, except in the rostral part, glucose utilization was higher in the transplant of the experimental group than in the sensorimotor areas of the non-activated cortex in the control group. Moreover, glucose utilization of the transplant cells was systematically higher in the experimental than in the control group. The transplants appear to display a certain level of metabolic integration with the host sensorimotor cortex since, in the experimental group, there was no significant differences in local cerebral glucose utilization values in the caudal sector of the transplant and in the surrounding sensorimotor cortical areas of the host. The 2-deoxy-D-glucose uptake was even higher in the caudal sector of the transplant than in some of the subfields of the contralateral sensorimotor cortex. The present findings indicate for the first time that motor activation of the contralateral forelimb produces an increase in metabolic activity in distinct transplant sectors, the topographic distribution of which matches the normal topographic organization of the forelimb somatomotor map. This suggests that transplants of embryonic frontal neocortex placed in the frontal cortex of adult hosts become functionally integrated with the host motor system.(ABSTRACT TRUNCATED AT 400 WORDS)

Host resets phase of grafted suprachiasmatic nucleus: a 2-DG study of time course of entrainment

The object of the present experiment was to examine whether in an intact animal implanted with a hypothalamic graft, the phase of the host and grafted suprachiasmatic nucleus (SCN) would become synchronized. To this end, we first established the time at which daily fluctuations in local cerebral glucose utilization were maximal in the SCN in our population of adult hamsters. Next, we verified that rhythms of (14C)2-deoxyglucose uptake could be measured on the day after birth in pups that were to provide donor tissue. Host and donor animals were housed in opposite light:dark cycles. We then transplanted fetal SCN tissue into the third ventricle of intact hamsters, placed the grafted animals in constant darkness with access to running wheels and examined the phase of metabolic activity in host and donor SCN. For several days after grafting, there was no circadian fluctuation in the metabolic activity of either the host SCN or of the grafted SCN. During this time, the circadian locomotor rhythms were not disrupted, suggesting that pacemaker activity was not interrupted. By day 14 after transplantation, metabolic activity in the host SCN was elevated during subjective day and host and donor SCN were in synchrony, invariably with the phase of the host animal. We conclude that a signal from the host SCN resets the grafted SCN and not vice versa and that pacemaker cells communicate with each other rather than exerting independent effects on target sites.

Functional mapping of the rat brain during drinking behavior: a fluorodeoxyglucose study

Autoradiographic techniques using the radiolabeled glucose analog [14C]2-fluoro-2-deoxy-D-glucose (FDG) were used to map the functional activity in the CNS during drinking behavior. Rats were trained to drink water during a 1-h session each day. Half of the rats were injected with FDG and allowed to drink, while the other half were satiated prior to FDG injection. Uptake of FDG for drinking and control groups of rats was quantified in 60 brain structures from frontal cortex to cervical spinal cord. The largest percent increase in activity (96%) during drinking was in the lateral hypothalamus. Limbic structures with significant metabolic increases included the lateral septum (48%), lateral habenula (44%), and nucleus accumbens (32%). Thalamic nuclei activated included intralaminar (60%), zona incerta (51%), ventroposteromedial (50%), anterior ventral (47%), and dorsal medial (40%). Other structures with increases were the caudal caudate nucleus (53%) and the spinal trigeminal nucleus (45%). The findings were interpreted in light of related metabolic mapping studies of the effects of orofacial stimulation, dehydration, ingestion, arousal, and reward. It was concluded that this FDG study revealed primarily the involvement of structures linked to rewarding and arousal components of motivated drinking behavior, as well as sensorimotor correlates of the orofacial stimulation. The findings provide the first comprehensive functional map of brain systems related to drinking behavior in adult animals.

Metabolic activity of the central auditory structures following prolonged deafferentation

The goal of this work was to evaluate, using autoradiographic techniques, the effects of variable periods of deafness on resting and evoked metabolic activity in central auditory structures elicited by direct electrical cochlear nucleus (CN) stimulation. Thirty-five pigmented guinea pigs, divided into five groups, underwent acute implantation of bipolar electrodes in the CN. One group was not deafened and served as hearing controls. The other four groups were deafened using an established protocol of sequential kanamycin/ethacrynic acid treatment and were tested at 4 weeks, 9 weeks, 16 weeks, and 15 months after deafening. Threshold currents for eliciting evoked middle latency responses (EMLRs) with direct CN stimulation were not significantly different between hearing and deafened groups. Autoradiographic data showed progressive reduction of the evoked metabolic response with incremental periods of deafferentation. Nevertheless, central auditory structures remained responsive to direct electrical stimulation of the CN. These data indicate that direct CN stimulation remains capable of activating the auditory tract despite prolonged periods of deafness.

Hippocampal and entorhinal glucose metabolism in relation to cholinergic theta rhythm

Hippocampal and entorhinal cortex glucose metabolism were studied by 14C-2-deoxyglucose (2-DG) autoradiography in anesthetized rats with and without continuous theta rhythm (theta). 2-Deoxyglucose changes in specific cytoarchitectonic regions were precisely assessed by n innovative approach. In the absence of theta there were areas with a higher glucose metabolism corresponding to neuropile regions at CA3, dentate gyrus, and subiculum, while the cellular layers always showed lower values. In the presence of theta, provoked by intraventricular injections of anticholinesterases (i.e., physostigmine) or curarimimetics (i.e., d-tubocurarine), 2-DG uptake showed two opposite significant changes in relation to controls: a) it increased in the outer zone of the molecular layer (inner blade) of the dentate gyrus, and in the stratum lacunosum-moleculare of CA3, suggesting an increase in perforant path input during theta rhythm; b) it decreased in the hilar dentate region. This noteworthy decrease in metabolic activity probably reflects an hilar inhibition by local circuits during theta rhythm generation.

Cerebral glucose utilization during conditioned sexual arousal

Local cerebral glucose utilization was investigated in male rats during conditioned sexual arousal. Increased glucose utilization was found in three amygdaloid nuclei after exposure to a stimulus associated with exposure to a sexually active female. No changes were observed in areas known to be of crucial importance for the expression of consummatory aspects of sexual behavior. These results corroborate and extend previous results showing a dissociation between the expression of appetitive and consummatory aspects of sexual behavior at a neural level.

Central auditory metabolic activity induced by intense noise exposure

Neural activity in the central auditory system was mapped by measuring 2-deoxyglucose (2-DG) uptake during a one hour exposure to a two-octave (1414-5656 Hz) band of noise. Gerbils were exposed to 100, 110 or 120 dB SPL, intensities which can produce only temporary (100 dB) or both temporary and permanent (120 dB) hearing loss. Exposure to 100 dB SPL evoked high levels of neural activity throughout responsive regions of auditory nuclei. At 110 dB SPL, a central region of low neural activity was surrounded by areas exhibiting increased activity. At 120 dB SPL, neural activity was low in almost all areas of auditory nuclei. To study the effects of permanent hearing loss on auditory neuronal activity, other animals were given 2-DG during exposure to 65 dB SPL broad band noise as a test stimulus, two months after exposure to the noise band at 110 dB SPL. Central auditory nuclei showed a tonotopic region of low neural activity corresponding to an approximately 3 kHz pure tone, surrounded by regions of evoked activity. The deficits in evoked metabolic activity observed both during and long after noise exposure appear to exceed those predicted from the degree of temporary and permanent threshold shift produced by the same noise exposures.

Cochleotopic selectivity of a multichannel scala tympani electrode array using the 2-deoxyglucose technique

The 2-deoxyglucose (2-DG) technique was used to study the cochleotopic selectivity of a multichannel scala tympani electrode array in four cats with another acting as an unstimulated control. Each animal was unilaterally deafened and a multichannel electrode array inserted 6 mm into the scala tympani. Thresholds to electrical stimulation were determined by recording electrically evoked auditory brainstem responses (EABRs). Each animal was injected with 2-DG, and electrically stimulated using bipolar electrodes located either distal or proximal to the round window. The contralateral ear was stimulated with acoustic tone pips at frequencies that matched the electrode place. Stimulation of both distal and proximal bipolar electrodes at 3 x EABR threshold, evoked localized 2-DG labelling in both ipsilateral cochlear nucleus (CN) and the contralateral inferior colliculus (IC), which was very similar in orientation and breadth to labelling evoked by the contralateral tone pips. The cochleotopic position of labelling to proximal stimulation was located in the 24-26 kHz region of each structure, whereas the distal labelling was located around 12 kHz. Distal stimulation at 10 x EABR threshold produced very broad 2-DG labelling in IC centered around the 12 kHz place. The present 2-DG results clearly illustrate cochleotopic selectivity using multichannel bipolar scala tympani electrodes. The extent of this selectivity is dependent on electrical stimulus levels. The 2-DG technique has great potential in evaluating the efficacy of new electrode array designs.

Regional changes in 2-deoxyglucose uptake associated with neuroleptic-induced tardive dyskinesia in the Cebus monkey

The neural mechanisms that mediate a primate model of tardive dyskinesia have been investigated using the 2-deoxyglucose (2-DG) uptake technique. Three groups of Cebus monkeys were used. Some of the animals received long-term neuroleptic treatment. These animals were allotted to one of two groups depending on whether they developed tardive dyskinesia or not. A third group of animals served as untreated controls. The neuroleptic-treated dyskinetic animals showed reduced uptake of 2-DG in the medial segment of the globus pallidus and in the ventral anterior (VA) and ventral lateral (VL) nuclei of the thalamus relative to that seen in the equivalent structures in the neuroleptic-treated nondyskinetic and untreated control animals. The data are interpreted as suggesting that tardive dyskinesia is mediated by underactivity of the pathways from the subthalamic nucleus to the medial pallidal segment and the substantia pars nigra pars reticulata, which in turn result in a loss of gamma-aminobutyric acid-ergic inhibition of the VA and VL thalamic nuclei. This suggests that tardive dyskinesia shares a common underlying neural mechanism with other hyperkinesias such as chorea and ballism.

Long experimental durations are required for double label [14C]- and [3H]2-deoxyglucose autoradiographic methods

Double-label 2-deoxyglucose (2-DG) studies using sequential [14C]- and [3H]2-DG injections demonstrate increased [14C]2-DG uptake during the first and second stimulation periods. To understand why this occurs, the rat mystacial vibrissae were stimulated at various times following [14C]2-DG injection. Local cerebral glucose utilization (LCGU) increased when whisker stimulation was performed at 0-90 min following [14C]2-DG injection. LCGU did not increase when whisker stimulation was performed at 90-150 min following [14C]2-DG injection. To minimize contamination of the two tracers in double label 2-DG mapping studies, the time between [14C]- and [3H]2-DG administration should be increased to 90 min.

Direct electrical stimulation of the cochlear nucleus: surface vs. penetrating stimulation

Prosthetic stimulation of the cochlear nucleus (CN) has been used for rehabilitation of profoundly deaf patients who are not suitable candidates for cochlear implants. The goal of this article was to assess the relative effectiveness of surface vs. penetrating stimulation of the CN. Electrophysiologic and autoradiographic measures were used to study central auditory system activation elicited by direct stimulation of the CN. Eighteen pigmented guinea pigs, divided into three groups, underwent acute implantation of bipolar electrodes in the CN. One group was not stimulated and acted as a control (n = 7). Electrodes were placed on the surface of the CN in one test group (n = 4) and within the CN in a second test group (n = 7). Thresholds for electrically evoked middle latency responses (EMLR) were determined and input/output (I/O) functions were obtained. The two test groups were then pulsed with [14C]-2-Deoxyglucose (2-DG) intramuscularly and stimulated for 1 hour with biphasic; charge-balanced pulses having a total duration of 400 microseconds, a repetition rate of 100/sec, and an amplitude of 200 microA. After stimulation, animals were killed and brains were harvested and prepared for autoradiography using standard techniques. Threshold current for EMLRs in the surface-stimulated group had a mean of 67.5 +/- 23.9 microA (range, 40 to 100 microA). Thresholds for in-depth stimulated group had a mean of 11.4 +/- 3.5 microA (range, 10 to 20 microA). The saturation level of the I/O function for the surface-stimulated group had a mean of 287.5 +/- 41.5 microA (range, 250 to 350 microA). The saturation level for the in-depth stimulated group had a mean of 192.9 +/- 49.5 mciroA (range, 100 to 250 microA). The dynamic range for the surface electrodes had a mean of 13.1 +/- 2.7 dB (range, 9.9 to 15.9 dB), whereas the dynamic range for the penetrating electrodes had a mean of 24.5 +/- 2.6 dB (range, 20 to 28.0 dB). Autoradiographs generated by CNS tissue from stimulated animals demonstrated no significant difference in metabolic activity of the CN between surface and in-depth stimulated groups. However, there were highly significant differences in 2-DG uptake in the contralateral superior olivary complex, contralateral inferior colliculus, and ipsilateral and contralateral lateral lemniscus, with greater uptake in in-depth stimulated preparations. Electrophysiologic and autoradiographic data suggest that a penetrating CN prosthesis is capable of activating the auditory tract at a lower threshold, with a relatively wider dynamic range than a surface prosthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Delta 9-tetrahydrocannabinol alters cerebral metabolism in a biphasic, dose-dependent manner in rat brain

delta 9-tetrahydrocannabinol (THC)-induced alterations in limbic and neocortical function are associated with deficiencies in short-term memory and recall. The 2-deoxy-D-glucose (2DG) autoradiographic method was used to examine the effect of acute THC administration (0, 0.2, 0.5, 2.0, 10.0 mg/kg) on regional brain metabolism in limbic and cortical brain regions of male rats. THC altered 2DG uptake in a biphasic, dose-dependent manner in most limbic and cortical structures, however most diencephalic and brainstem structures examined were unaffected. The 0.2 mg/kg THC dose significantly increased 2DG uptake relative to vehicle treatment in all cortical and selected limbic regions, whereas the 2.0 and 10.0 mg/kg THC doses decreased 2DG uptake in most of these regions. Certain limbic regions, particularly the hippocampus, are more sensitive to THC suggesting a selective regional action of the drug at lower doses. The incidence of enhanced metabolic activity in limbic and cortical regions is consistent with the occurrence of high density cannabinoid receptors in these regions.

Afferent influences on brainstem auditory nuclei of the chick: nucleus magnocellularis neuronal activity following cochlea removal

Elimination of presynaptic elements often results in marked changes, such as atrophy and death, in postsynaptic neurons in the central nervous system. These transneuronal changes are particularly rapid and profound in young animals. In order to understand the cellular events underlying transneuronal regulation it is necessary to explore changes in the local environment of neurons following manipulations of their afferents. In previous investigations we have documented a variety of rapid and marked cellular changes in neurons of the cochlear nucleus of neonatal chicks (n. magnocellularis) following cochlea removal. In adult chickens, however, these transneuronal changes are either absent or minor. The goals of the studies presented here were to examine changes in the electrical activity of nucleus magnocellularis cells and their afferents following removal of the cochlea and to determine if these changes were similar in adult and neonatal animals. Two measures of electrical activity were used; multiunit recording with microelectrodes and incorporation of radiolabeled 2-deoxyglucose (2-DG). Microelectrode recordings revealed high levels of spontaneous activity in n. magnocellularis and n. laminaris, the binaural target of n. magnocellularis neurons. Neither puncturing of the tympanic membrane nor removal of the columella causes significant changes in spontaneous activity, although the latter results in a profound hearing loss (40-50 dB). Removal of the cochlea, on the other hand, results in immediate cessation of all extracellular electrical activity in the ipsilateral n. magnocellularis. Recordings from the same location for up to 6 h failed to reveal any return of spontaneous activity. When the electrode tip was placed in n. laminaris, unilateral cochlea removal had no discernible effect on extracellularly recorded spontaneous activity, probably due to the high levels of excitatory input from the intact ear. Bilateral cochlea removal, however, completely eliminated activity in n. laminaris. 2-DG studies conducted 1 h to 8 days following unilateral cochlea removal revealed marked decreases in 2-DG incorporation in the ipsilateral n. magnocellularis and bilaterally in the n. laminaris target of the ablated cochlea. No compensatory return of 2-DG incorporation was observed for up to 8 days. Comparisons of adult and neonatal chicks failed to reveal significant differences in the effects of cochlea removal on multiunit activity or 2-DG incorporation, suggesting that age differences in transneuronal regulation are due to intrinsic biochemical differences in young and adult neurons rather than differences in the proportion of synaptic input that has been abolished.

Adult rat barrel cortex plasticity occurs at 1 week but not at 1 day after vibrissectomy as demonstrated by the 2-deoxyglucose method

Stimulation of a single facial vibrissa in rats receiving [14C]2-deoxyglucose leads to increased local cerebral glucose utilization in the corresponding contralateral barrel of lamina IV of the first somatosensory cortex (SmI). In the adult rat, the metabolic representation of such a barrel enlarges 2 months after removal of all other vibrissal follicles but enlargement is prevented by prior removal of SmI norepinephrine. Here, the early time course of such enlargement and how this was affected by cortical norepinephrine manipulations were examined in adult rats. One day after total vibrissal follicle removal with sparing of the central (C3) vibrissa, neither the areal extent nor absolute glucose utilization in the stimulated, spared C3 cortical barrel were changed. However, 7 days after follicle removal, the spared C3 barrel was enlarged by 41%, although absolute glucose utilization remained constant. This delayed onset of enlargement is compatible with either a structural or neurochemical change in barrel circuitry following vibrissal deafferentation. With ipsilateral locus coeruleus lesions but intact vibrissae, there was progressive enlargement of stimulated C3 barrel areas with increasing cortical norepinephrine depletion (r = 0.864) suggesting a suppressive effect of norepinephrine on activity spread in barrels with intact vibrissal afferents. Previously shown blockade of chronic (2 month) vibrissectomy-induced barrel enlargement by norephinephrine depletion suggested an additional effect on plasticity. Even though acute (1 day) follicle removal here produced no change in spared C3 barrel area, addition of norepinephrine depletion produced a surprising 40% decrease in barrel area. Thus, barrel plasticity assessed by 2-deoxyglucose reflects a complex interaction between barrel metabolic activity and the extent of vibrissal and noradrenergic afferent input.

Analysis of 2-DG autoradiograms using image-averaging and image-differencing procedures for systems-level description of neurobehavioral function

Computer assisted 2-deoxyglucose (2-DG) autoradiography has been used to provide functional maps of areas of altered neural activity related to changes in an animal's behavior or state. The standard procedure for comparison of autoradiograms between different treatment groups has been to take measurement samples from predefined neuroanatomical regions and to average these across brains to attain statistical sensitivity for detecting treatment effects. Unfortunately, when sampling is restricted to predefined areas, important topographic information is lost along with the ability to reveal an unexpected change in neural activity. To preserve the rich topographical detail of metabolic information and to enhance the capacity to uncover novel areas of altered metabolic activity, we have developed a system for averaging entire images from 2-DG autoradiograms and for comparing the average images from two experimental groups by creating an image of differences. This procedure does not rely on sampling only preselected regions, but still allows statistical comparisons between experimental groups. The procedures we describe can be readily and inexpensively adapted for use in individual laboratories and are based on modifications of preexisting image analysis software. We show that, when average and difference images are created using standardized protocols for sectioning brain tissue and editing section images, they are impressively resolved and realistic and can serve as effective topographic descriptions of group differences in neural activity of functional and behavioral relevance.

Norepinephrine-induced plasticity and one-trial olfactory learning in neonatal rats

The influence of norepinephrine (NE) on the acquisition of a conditioned odor preference and enhanced focal uptake of [14C]2-deoxyglucose (2-DG) within the olfactory bulb was assessed in neonatal rat pups. On postnatal day (PN) 6, pups were injected with either an NE receptor agonist (isoproterenol), NE receptor antagonist (propranolol or timolol), or saline before one-trial odor conditioning. The experimental conditioning group received a 10-min exposure to an odor (peppermint) and reinforcing tactile stimulation similar to that received from the dam. Control groups received only the odor, only the tactile stimulation, backwards presentation of the odor and tactile stimulation or neither of these stimuli. The next day, pups were either tested for an olfactory preference (Expts. 1 and 2) or assessed for differential olfactory bulb activity using the 2-DG technique (Expt. 3). The results indicate that early odor experience with either tactile stimulation or isoproterenol is sufficient to produce a learned behavioral preference and enhanced focal 2-DG uptake within the olfactory bulb. Moreover, an NE receptor blocker injected prior to training with odor and tactile stimulation blocks the acquisition of both behavioral preference and the enhanced 2-DG uptake. In Expt. 4, the effects of tactile stimulation and isoproterenol were further assessed. An odor paired with a moderate level of either of these stimuli produces learning. However, the simultaneous presentation of a moderate level of these stimuli paired with an odor does not result in an odor preference. An odor preference may be reinstated by simultaneous presentation of these stimuli, provided the level of each of these stimuli is too low to produce an odor preference when presented alone with an odor. These data suggest that exogenous NE and tactile stimulation are additive in their effect on learning. These results are discussed in terms of the neural mechanisms underlying reinforcement in infant rats.

Spatial distribution of neural activity evoked by electrical stimulation of the cochlea

Activity in the central auditory system was mapped with 2-deoxyglucose (2-DG) autoradiography, using either pure tones or electrical stimulation of the normal cochlea. Electrical stimulation with both monopolar (distant reference electrode) and bipolar prostheses near threshold increased 2-DG uptake in auditory nuclei in a manner similar to that seen with a pure tone: increased 2-DG uptake was restricted to a small frequency region of brainstem and mid-brain auditory nuclei. The position of this area was related to the cochlear location of the prosthesis. At higher current amplitudes only the bipolar prosthesis retained spatial restriction of evoked neural activity, while stimulation through a monopolar prosthesis produced evoked activity in all frequency regions of auditory nuclei, and in non-auditory nuclei. Activation of non-auditory structures was consistent with spread of current through the brainstem, rather than activation of peripheral nerves. At all current amplitudes, a monopolar prosthesis evoked higher levels of 2-DG uptake than a bipolar prosthesis. The results suggest that while a bipolar prosthesis provides greater spatial restriction of evoked neural activity and a greater dynamic range, a monopolar prosthesis produces higher levels of evoked activity.

Tritium quench in autoradiography during postnatal development of rat forebrain

Quantitative autoradiography of tritium-labeled brain tissue requires correction for regional and age-dependent changes in tritium quenching. Correction values are determined using chloroform extraction of brain sections labeled with tritiated 2-deoxyglucose ([3H]2DG) in adult rats and rats at postnatal ages of 5, 14 and 21 days. Conditions are described for intraperitoneal injection of [3H]2DG for labeling neonatal animals which maximize the formation of [3H]2-deoxyglucose-6-phosphate. Tritium quench correction coefficients are determined in 65 brain regions at each age. Autoradiographic tritium quench increases during postnatal development in all brain regions, with the rate and extent of change corresponding to the development of myelination in different structures. Quench coefficients range from 6 to 45% in 5 day animals and from 21 to 108% in adult animals. Gray matter structures have a major increase in tritium quenching between postnatal days 5 and 14. Quench coefficients in white matter-containing structures increase throughout postnatal development at region-specific rates. These data may be used to correct regional differences in tritium quenching for autoradiographic studies of postnatal development.

Metabolic activation of the fetal rat brain

In the present study, we tried to examine whether the 2-deoxy-D-[14C]glucose (2-DG) technique is useful to investigate the metabolic activity of fetal rat brain in the maternal uterus. The result shows that metabolic mapping of the fetal brain was clearly obtained by means of the 2-DG technique.

Norepinephrine and learning-induced plasticity in infant rat olfactory system

Postnatal olfactory learning produces both a conditioned behavioral response and a modified olfactory bulb neural response to the learned odor. The present report describes the role of norepinephrine (NE) on both of these learned responses in neonatal rat pups. Pups received olfactory classical conditioning training from postnatal days (PN) 1-18. Training consisted of 18 trials with an intertrial interval of 24 hr. For the experimental group, a trial consisted of a pairing of unconditioned stimulus (UCS, stroking/tactile stimulation) and the conditioned stimulus (CS, odor). Control groups received either only the CS (Odor only) or only the UCS (Stroke only). Within each training condition, pups were injected with either the NE beta-receptor agonist isoproterenol (1, 20, or 4 mg/kg), the NE beta-receptor antagonist propranolol (10, 20, 40 mg/kg), or saline 30 min prior to training. On day 20, pups received one of the following tests: (1) behavioral conditioned responding, (2) injection with 14C-2-deoxyglucose (2-DG) and exposed to the CS odor, or (3) tested for olfactory bulb mitral/tufted cell single-unit responses to the CS odor. The results indicated that training with either: (1) Odor-Stroke-Saline, (2) Odor-Stroke-Isoproterenol-Propranolol, or (3) Odor only-Isoproterenol (2 mg/kg) was sufficient to produce a learned behavioral odor preference, enhanced uptake of 14C-2-DG in the odor-specific foci within the bulb, and a modified output signal from the bulb as measured by single-cell recordings of mitral/tufted cells. Moreover, propranolol injected prior to Odor-Stroke training blocked the acquisition of both the learned behavior and olfactory bulb responses. Thus, NE is sufficient and may be necessary for the acquisition of both learned olfactory behavior and olfactory bulb responses.

Effects of aging and vincamine derivatives on pericapillary microenvironment: stereological characterization of the cerebral capillary network

Changes in the pericapillary microenvironment of adult (18-month-old) and senescent (27 1/2-month-old) Fischer-344 rats treated for 6 weeks with daily IP injections of brovincamine or apovincamine (0, 2.5, 5, 10 mg/kg) were correlated with spontaneous locomotor activity and [14C]-2-deoxyglucose uptake of the brain. The animals were tested for spontaneous locomotor activity in a tunnel maze. Twenty-four hr after behavioral testing and subsequently after a [14C]-2-deoxyglucose injection, brains were removed and capillaries stained with alkaline phosphatase reaction, being later measured with an optical-electronic image analysis technique. Results revealed an increase in intercapillary distance, as a sensitive parameter for capillary density, in the hippocampus (CA1) and in the parietal cortex (area 39) in association with aging. Capillary diameter in the parietal cortex was found to be increased age dependently. A similar age-related increase was also observed in the CA1 field but this age trend was not significant. Chronic treatment with the vincamines produced a dose-dependent reduction in intercapillary distance in senescent animals which approached the level of untreated adult control rats. Significant negative correlations were found between maze locomotion and intercapillary distance among senescent rats. Furthermore, intercapillary distance and local relative 2-deoxyglucose uptake tended to be negatively correlated in both age groups. These findings provide evidence for the working hypothesis that mean intercapillary distance can be considered as an indicator of neuronal activity in the pericapillary microenvironment.

Cochlear ablation in deafness mutant mice: 2-deoxyglucose analysis suggests no spontaneous activity of cochlear origin

Deafness mutant mice show no stimulus-related cochlear potentials as well as abnormal electrically-evoked responses recorded from the inferior colliculus. Abnormal spontaneous activity in the auditory periphery could result in abnormal development and/or maintenance of the central auditory pathways. We therefore assessed spontaneous activity of cochlear origin in the central nuclei of the mutants by ablating one cochlea and subsequently using the 2-deoxyglucose (2DG) technique to study metabolic activity. Any asymmetries in labeling in a given nucleus should be due to spontaneous activity in the cochlear nerve on the unoperated side. In control animals (+/dn mice undergoing unilateral cochlea ablation), statistically significant decreased 2DG labeling was observed in the ipsilateral PVCN and AVCN, and contralateral MNTB and IC; all receive primary excitatory input from the ablated ear. No significant differences in labeling between right and left sides were observed in any of the nuclei studied in the mutant animals. These findings suggest that there is no spontaneous activity of cochlear origin in these mutants, even though many cochlear nerve fibers and spiral ganglion cells survive.

Learning-related activation in the auditory system of the rat produced by long-term habituation: a 2-deoxyglucose study

Autoradiography with [14C]2-deoxyglucose (2-DG) was used to examine the functional activity of the rat auditory system during long- and short-term habituation of the acoustic startle reflex. The data showed that presentation of the acoustic stimulus to long-term habituated rats resulted in a learning-related metabolic enhancement that was significantly greater than the response evoked by the same acoustic stimulus in the inexperienced rats. This enhancement was localized to brainstem and midbrain auditory nuclei and no significant changes occurred at thalamocortical levels of the auditory pathway. The largest difference in 2-DG uptake between long- and short-term habituated rats was in the lateral superior olivary nucleus (LSO). The LSO activation suggests that olivocochlear efferents may operate in a central feedback control of peripheral auditory input during long-term habituation. Findings of enhanced metabolism from the cochlear nuclei to the central nucleus of the inferior colliculus indicated that active processes of neuronal plasticity take place in the lower auditory system during long-term habituation. The results provide the first demonstration of how a nonassociative learning experience such as long-term habituation modifies the metabolic activity of the auditory system. The findings support the conclusion that auditory responses of behaving animals to acoustic stimuli are dependent not only on the physical parameters of a stimulus, but also on its learned behavioral significance.