Medial forebrain bundle stimulation in rats activates glycogen phosphorylase in layers 4, 5b and 6 of ipsilateral granular neocortex

Functional activation in human brain produces an increase in glycolytic metabolism. Animal studies suggest activation-induced glycolysis is coupled to brain glycogenolysis. Medial forebrain bundle (MFB) stimulation activates the release of neurotransmitters which promote neocortical glycogenolysis in vitro. In the present study, active glycogen phosphorylase (GP), an index of glycogenolysis, is assessed histochemically in rat brain after 15 min of MFB self-stimulation. Active GP increased significantly in layers 4, 5b and 6 of granular neocortex ipsilateral to MFB self-stimulation. Restriction of increased glycogenolysis to granular neocortex suggests an important functional interaction between sensory neocortical processing and ascending MFB systems.     

Dynamics of co-infection with M. Tuberculosis and HIV-1

The functional anatomy of perceptual and semantic processings for odors was studied using positron emission tomography (PET). The first experiment was a pretest in which 71 normal subjects were asked to rate 185 odorants in terms of intensity, familiarity, hedonicity, and comestibility and to name the odorants. This pretest was necessary to select the most appropriate stimuli for the different cognitive tasks of the second experiment. The second one was a PET experiment in which 15 normal subjects were scanned using the water bolus method to measure regional cerebral blood flow (rCBF) during the performance in three conditions. In the first (perceptual) condition, subjects were asked to judge whether an odor was familiar or not. In the second (semantic) condition, subjects had to decide whether an odor corresponded to a comestible item or not. In the third (detection) condition, subjects had to judge whether the perceived stimulus was made of an odor or was just air. It was hypothetized that the three tasks were hierarchically organized from a superficial detection level to a deep semantic level. Odorants were presented with an air-flow olfactometer, which allowed the stimulations to be synchronized with breathing. Subtraction of activation images obtained between familiarity and control judgments revealed that familiarity judgments were mainly associated with the activity of the right orbito-frontal area, the subcallosal gyrus, the left inferior frontal gyrus, the left superior frontal gyrus, and the anterior cingulate (Brodmann's areas 11, 25, 47, 9, and 32, respectively). The comestibility minus familiarity comparison showed that comestibility judgments selectively activated the primary visual areas. In contrast, a decrease in rCBF was observed in these same visual areas for familiarity judgments and in the orbito-frontal area for comestibility judgments. These results suggest that orbito-frontal and visual regions interact in odor processing in a complementary way, depending on the task requirements.     

The afferent code for sensory quality.

"Many of the more recent findings in sensory psychology and physiology derive from the application of electrophysiology to the study of sensory processes." Experiments involving the taste sense and utilizing the recording and amplifying of nerve impulse traffic in sensory fibers "en route" to the brain are reviewed, and their general implications for the theory of afferent coding are discussed. An important principle of sensory coding is that "the same afferent fiber may convey different information depending upon the amount of activity in another parallel fiber." The relative rather than the absolute amount of activity in any one set of afferent fibers may determine the quality of sensation. "It is not only the activity in parallel fibers that is important, it is the relative amount of such parallel activity. Studies of the other senses indicate that these principles are not unique to taste." 21 refs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Does the MFB convey functionally different reward signals?

Pulse frequencies that sustain the same % of the maximum self-stimulation rate (equipotent frequencies) are equipreferred by rats because they elicit identical reward signals. However, when two equipotent frequencies are delivered through different electrodes, lack of equipreference can be expected if the resulting neural signals belong to different rewarding processes and if these signals are differentially ranked on the animal's decisional scale. We used this rationale to test the possibility that the MFB conveys functionally different signals. Rats were implanted with an electrode near the anterior MFB (aMFB) and another near the posterior MFB (pMFB). The rate of self-stimulation, as a function of the pulse frequency, was first obtained for each electrode, separately. Rats were then allowed to press for aMFB or pMFB stimulation in a double-lever box. One of the levers delivered a fixed aMFB frequency whereas the other delivered a variable pMFB frequency. In the following session, this situation was reversed. The time spent bar-pressing for each stimulus was plotted as a function of the variable frequency. Equipreference for equipotent stimuli (i.e. for frequencies that supported the same % of the maximum rate in the single-lever box) was noted for 6 out of 11 electrode pairs. However, in 3 cases, the subjects preferred the pMFB stimulus over an aMFB equipotent stimulus and in two other cases they preferred the aMFB stimulus. The data from these five subjects suggest the presence of functional heterogeneity within the MFB reward pathway, a view already supported by a variety of other studies.     

Destruction of the medial forebrain bundle caudal to the site of stimulation reduces rewarding efficacy but destruction rostrally does not.

Rats with an electrode in the medial forebrain bundle (MFB) in or near the ventral tegmental area and another at the level of the rostral hypothalamus sustained large electrolytic lesions at either the rostral or the caudal electrode. The rewarding efficacy of stimulation through the other electrode was determined before and after the lesion. Massive damage to the MFB in the rostral lateral hypothalamus (LH) generally had little effect on the rewarding efficacy of more caudal stimulation, whereas large lesions in the caudal MFB generally reduced the rewarding efficacy of LH stimulation by 35–60%. Similar reductions were produced by knife cuts in the caudal MFB. These results appear to be inconsistent with the hypothesis that the reward fibers consist either of descending or ascending fibers coursing in or near the MFB. It is suggested that the reward fibers are collaterals from neurons with both their somata and their behaviorally significant terminals located primarily in the midbrain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Correction to Thomas.

Reports an error in the article "Delayed Alternation in Rats After Pre- or Postcommissural Fornicotomy" by Garth J. Thomas (Journal of Comparative and Physiological Psychology, 1978, Vol. 92, No. 6, pp. 1128-1136), on p. 1128, line 3 in the abstract, "text" should read "test." On p. 1130, the right-hand column should begin as follows: "on a deprivation regimen of about 7 g of wet mash once a day." (This abstract originally appeared in the following article see record 1980-09224-001) Investigated the contribution of the pre- and postcommissural fornices to short-term spatial memory in 15 male Long-Evans rats by evaluating the effect of small electrolytic lesions, located stereotaxically, with texts of reinforced alternation in a T-maze. Lesions in the postcommissural fornix were without behavioral effect. Ss with lesions that damaged the precommissural fornix were temporarily impaired in alternation with massed trials. They largely recovered their efficiency by the end of 5 postoperative sessions. Both the interpolation of irrelevant vestibular input (rotation) and lengthened intertrial intervals (1-4 min) reinstated an alternation deficit that had recovered in the massed-trial condition of testing. It is suggested that the recovery did not represent relearning to alternate but represented experience-dependent switching to parallel neural circuits that also mediate short-term spatial memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sniffing and smelling: separate subsystems in the human olfactory cortex

The sensation and perception of smell (olfaction) are largely dependent on sniffing, which is an active stage of stimulus transport and therefore an integral component of mammalian olfaction. Electrophysiological data obtained from study of the hedgehog, rat, rabbit, dog and monkey indicate that sniffing (whether or not an odorant is present) induces an oscillation of activity in the olfactory bulb, driving the piriform cortex in the temporal lobe, in other words, the piriform is driven by the olfactory bulb at the frequency of sniffing. Here we use functional magnetic resonance imaging (fMRI) that is dependent on the level of oxygen in the blood to determine whether sniffing can induce activation in the piriform of humans, and whether this activation can be differentiated from activation induced by an odorant. We find that sniffing, whether odorant is present or absent, induces activation primarily in the piriform cortex of the temporal lobe and in the medial and posterior orbito-frontal gyri of the frontal lobe. The source of the sniff-induced activation is the somatosensory stimulation that is induced by air flow through the nostrils. In contrast, a smell, regardless of sniffing, induces activation mainly in the lateral and anterior orbito-frontal gyri of the frontal lobe. The dissociation between regions activated by olfactory exploration (sniffing) and regions activated by olfactory content (smell) shows a distinction in brain organization in terms of human olfaction.     

The hypothalamus: Neural systems involved in feeding, irritability, aggression, and copulation in male rats.

In 3 experiments with a total of 58 male hooded rats, cuts of the ventral amygdalofugal pathway resulted in slight aphagia, and cuts anterior to the medial preoptic area resulted in transient hyposexuality. A unilateral posterior medial forebrain bundle (MFB) cut combined with a contralateral parasagittal cut resulted in severe hyposexuality if the parasagittal cut lay lateral to the anterior hypothalamic nucleus, and in irritability if the parasagittal cut lay lateral to the ventromedial hypothalamic nucleus. It is concluded that (a) the medial hypothalamic nuclei exert their effects on irritability and copulation through their lateral connections with those components of the MFB that descend on, or ascend from, the lower brain stem; and (b) the neural pathways mediating the consummatory aspects of feeding, irritability, aggression, and copulation are distinct. (58 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transection of direct anterior thalamic afferents from the hippocampus: Effects on activity and active avoidance in rats.

Demonstrated the importance of the direct hippocampo-anterior thalamic component of the postcommissural fornix in the control of general locomotion and active avoidance; 40 adult male Sprague-Dawley rats were Ss in 3 experiments. Transection of anterior thalamic afferents from the hippocampal formation (subicular cortex), at the point where they exit from the fornix posterior to the septum, enhanced bidirectional active avoidance acquisition and increased general activity. This transection may also interrupt fibers to or from other thalamic nuclei and the anterior septum. However, destruction of connections of the anterior septum with the hippocampus, habenula, and thalamus by transection in the coronal plane anterior to the descending fornix columns, without damage to the subiculothalamic fibers, increased general activity levels without affecting active avoidance behavior. The activity increase in this case resembled that seen after septal lesions rather than that seen after hippocampal lesions. Thus, destruction of a single fornix component contributing afferents to the anterior thalamic nuclei reproduces at least part of the hippocampal syndrome. This suggests that these fibers contribute significantly to the control of these behaviors and may mediate active avoidance changes resulting from hippocampal and fornix damage. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Review of Child neuropsychology: An introduction to theory, research, and clinical practice.

Reviews the book, Child neuropsychology: An introduction to theory, research, and clinical practice by Byron P. Rourke, Dirk J. Bakker, John L. Fisk, and John D. Strang (1983). With the arrival of this landmark text, there is now an established child neuropsychology literature that suggests more clearly than ever before that injury to the growing brain is often accompanied by strikingly different behavioural sequelae than a similar injury to the mature brain. This volume opens with a repudiation of the "nature-nurture" controversy. The second chapter includes a relevant and well-communicated account of the embryonic and foetal development of the nervous system. Chapters on brain asymmetry and plasticity combine to form the scholarly core of the text. Methodological problems in the study of cerebral asymmetry are highlighted. Chapters on assessment and remediation together with individual case studies illustrate how theory and research affect the manner in which one performs as a clinician. A review of behaviour modification strategies and insight-oriented psychotherapy is one of the few areas of weakness in this otherwise excellent volume. Child neuropsychology is one of the first books of its kind and is recommended highly for anyone interested in the study of brain/behaviour relationships in children. Its use as a textbook for senior undergraduate or graduate courses in child neuropsychology is strongly endorsed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of perirhinal cortex ablation and crossed unilateral lesions of the medial forebrain bundle from the inferior temporal cortex in the rhesus monkey: Effects on learning and retrieval.

Seven monkeys learned new object-reward associations and scene problems and were overtrained on 100 problems of each type. Four monkeys received crossed lesions of the medial forebrain bundle (MFB) and inferior temporal cortex, with the later addition of a fornix section ipsilateral to the MFB lesion. The remaining 3 monkeys received bilateral perirhinal cortex ablation. Disconnection of the MFB from the inferior temporal cortex impaired postoperative new learning, but the retrieval of problems overtrained preoperatively was relatively preserved. Subjects with perirhinal cortex ablation were severely impaired in new learning and at the retrieval of scene problems, but retention of object-reward associations was relatively well preserved. The results support the hypothesis that isolation of the inferior temporal cortex from basal forebrain and midbrain afferents results in dense anterograde amnesia, whereas the role of the perirhinal cortex in learning is dependent on the perceptual difficulty of the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrical stimulation of precentral cortical area in the treatment of central pain: electrophysiological and PET study

The clinical, electrophysiological and haemodynamic effects of precentral gyrus stimulation (PGS) as a treatment of refractory post-stroke pain were studied in 2 patients. The first patient had a right hemibody pain secondary to a left parietal infarct sparing the thalamus, while the second patient had left lower limb pain developed after a right mesencephalic infarct. In both cases, spontaneous pain was associated with hyperpathia, allodynia and hypoaesthesia in the painful territory involving both lemniscal and extra-lemniscal sensory modalities in patient 1, extra-lemniscal sensory modality only in patient 2. Both patients were treated with electrical PGS by means of a 4-pole electrode, the central sulcus being per-operatively located using the phase-reversal of the N20 wave of somatosensory evoked potentials. No sensory side effect, abnormal movement or epileptic seizure were observed during PGS. The analgesic effects were somatotopically distributed according to the localization of electrode on motor cortex. A satisfactory long-lasting pain control (60-70% on visual analog scale) as well as attenuation of nociceptive reflexes were obtained during PGS in the first patient. Pain relief was less marked and only transient (2 months) in patient 2, in spite of a similar operative procedure. In this patient, in whom PGS eventually evoked painful dysethesiae, no attenuation of nociceptive RIII reflex could be evidenced during PGS. Cerebral blood flow (CBF) was studied using emission tomography (PET) with O-labeled water. The sites of CBF increase during PGS were the same in both patients, namely the thalamus ipsilateral to PGS, cingulate gyrus, orbito-frontal cortex and brainstem. CBF increase in brainstem structures was greater and lasted longer in patient 1 while patient 2 showed a greater CBF increase in orbito-frontal and cingular regions. Our results suggest that PGS-induced analgesia is somatotopically mediated and does not require the integrity of somatosensory cortex and lemniscal system. PGS analgesic efficacy may be mainly related to increased synaptic activity in the thalamus and brainstem while changes in cingulate gyrus and orbito-frontal cortex may be rather related to attentional and/or emotional processes. The inhibitory control on pain would involve thalamic and/or brainstem relays on descending pathways down to the spinal cord segments, leading to a depression of nociceptive reflexes. Painful dysesthesiae during stimulation have to be distinguished from other innocuous sensory side effects, since they may compromise PGS efficacy.     

Conditioned suppression of medial forebrain bundle and septal intracranial self-stimulation in the rat: Evidence for a fear-relief mechanism of the septum.

In 3 experiments, a conditioned emotional response (CER) paradigm was presented to 2 groups of male albino Sprague-Dawley rats (N?=?20) during intracranial self-stimulation (ICSS). One group barpressed for medial forebrain bundle (MFB) stimulation reward; the other group barpressed for septal stimulation reward. The MFB ICSS was found to be suppressed by the CER procedure, but this procedure failed to suppress septal ICSS. The difference between the 2 sites was found only when both MFB and septal ICSS current intensities were available at their optimal levels. When ICSS current intensities were lowered to either threshold or medium level, both groups exhibited the CER suppression effect. Ss were also tested for a possible analgesic effect produced by the ICSS. MFB stimulation was found to produce some degree of analgesia, but septal stimulation failed to produce any analgesic effect. Thus, the possibility that the attenuation of the CER suppression effect in the septal group was due to analgesia was excluded. The difference in MFB and septal ICSS behavior during the presentation of the aversive stimulus suggests a possible qualitative distinction between the reward functions of the 2 sites, and a possible fear-reduction property of the septal area. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of pontomesencephalic cholinergic nuclei do not substantially disrupt the reward value of medial forebrain bundle stimulation

This study examines the effects of lesioning the pedunculopontine tegmentum (PPTg) and laterodorsal tegmentum (LDTg) on the reward effectiveness of medial forebrain bundle (MFB) stimulation. Although the focus is on the effects of unilateral lesions made ipsilateral to stimulation sites in the hypothalamic and ventral tegmental MFB, the effects of contralateral lesions of both targets are also investigated. Reward effectiveness was assessed using the rate-frequency curve shift paradigm. In nine rats with unilateral PPTg lesions and five rats with unilateral LDTg lesions, the frequency required to maintain half-maximal response rats was generally not changed by more than 0.1 log units relative to prelesion baseline mean. In three rats with contralateral PPTg lesions and four rats with contralateral LDTg lesions, required frequency was also not substantially changed. The results are interpreted in terms of a previously proposed hypothesis regarding the role in MFB self-stimulation of ascending cholinergic input from the pontomesencephalon to ventral tegmental dopaminergic neurons.     

Running-wheel avoidance behavior following septal area lesions in rats.

Studied acquisition of a running-wheel avoidance response in 52 male Wistar rats with (a) septal lesions, (b) septal and postcommissural fornix lesions, or (c) septal, postcommissural fornix, and anterior thalamic damage. Ss with lesions confined to the septum were deficient in acquiring the avoidance response compared with both normal Ss and Ss with the more posterior lesions. Ss sustaining combined septal-fornical and septal-fornical-thalamic lesions did not differ from normal Ss or from each other in their acquisition scores. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delayed alternation in rats after pre- or postcommissural fornicotomy.

Investigated the contribution of the pre- and postcommissural fornices to short-term spatial memory in 15 male Long-Evans rats by evaluating the effect of small electrolytic lesions, located stereotaxically, with texts of reinforced alternation in a T-maze. Lesions in the postcommissural fornix were without behavioral effect. Ss with lesions that damaged the precommissural fornix were temporarily impaired in alternation with massed trials. They largely recovered their efficiency by the end of 5 postoperative sessions. Both the interpolation of irrelevant vestibular input (rotation) and lengthened intertrial intervals (1–4 min) reinstated an alternation deficit that had recovered in the massed-trial condition of testing. It is suggested that the recovery did not represent relearning to alternate but represented experience-dependent switching to parallel neural circuits that also mediate short-term spatial memory. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-stimulation of the habenular complex in the rat.

65 male hooded Long-Evans rats learned to barpress for rewarding electrical stimulation of the medial or lateral habenular nucleus or the fasciculus retroflexus, but not the surrounding thalamic nuclei. Response rates were moderate and steady and were not influenced by food or water deprivation. Habenular self-stimulation was significantly facilitated by placing lesions in the ipsilateral anterior part of the medial forebrain bundle (MFB). Similarly, MFB self-stimulation was enhanced by ipsilateral habenular lesions. Lesions centered in the region of median raphe nucleus suppressed habenular self-stimulation for more than 4 wks. Self-stimulation of median raphe was not affected by habenular lesions. Results show that habenular stimulation can produce a rewarding effect by exciting neurons in the region of the raphe nuclei but apparently without requiring the participation of the well-known MFB reward system. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brain stimulation reward following chronic lead exposure in rats.

Adult male rats were exposed to drinking water containing either 500 parts per million (ppm) lead acetate or an equal concentration of sodium acetate for 80 days. Bipolar electrodes were then implanted into the medial forebrain bundle (MFB), and rats were allowed to recover for 7 days. On Day 8 postsurgery, control and lead-treated rats were placed in an operant chamber and shaped to press a lever to receive 200-msec trains of current. Data from a range of current intensities and frequencies were recorded to obtain threshold values for each rat, defined as the stimulation needed to support half-maximal lever responding. Results indicated that chronic lead exposure attenuated the reinforcing effect of brain stimulation. Because of the large number of reward systems mediated by the MFB nucleus accumbens pathway, these data suggest that a variety of motivational phenomena may be affected by contaminant exposure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A portrait of the substrate for self-stimulation.

Quantitative properties of the neural system mediating the rewarding and priming effects of medial forebrain bundle (MFB) stimulation in the rat have been determined by experiments that trade one parameter of the electrical stimulus against another. The 1st order neurons in this substrate are generally long, thin, myelinated axons, coursing in the MFB and ventral tegmentum, with absolute refractory periods in the range .5–2.2 msec and conduction velocities of 2–8 m/sec. Local potentials in these axons decay with a time constant of about .1 msec. A supernormal period follows the recovery from refractoriness. These axons integrate current over exceptionally long intervals, accommodate slowly, and fire on the break of prolonged anodal pulses. These properties rule out the hypothesis that catecholamine pathways constitute the 1st-order axons. The 2nd-order (postsynaptic) part of the substrate shows surprisingly simple spatial and temporal integrating characteristics. The authors examine the logic that permits conclusions of this sort to be derived from behavioral data and the role of these derivations in establishing neurobehavioral linkage hypotheses. (78 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)