Delayed Treatment of Capsaicin Produces Partial Motor Recovery by Enhancing Dopamine Function in MPP⁺-lesioned Rats via Ciliary Neurotrophic Factor

Transient receptor potential vanilloid subtype 1 (TRPV1) on astrocytes prevents ongoing degeneration of nigrostriatal dopamine (DA) neurons in MPP⁺-lesioned rats via ciliary neurotrophic factor (CNTF). The present study determined whether such a beneficial effect of astrocytic TRPV1 could be achieved after completion of injury of DA neurons, rather than ongoing injury, which seems more relevant to therapeutics. To test this, the MPP⁺-lesioned rat model utilized here exhibited approximately 70~80% degeneration of nigrostriatal DA neurons that was completed at 2 weeks post medial forebrain bundle injection of MPP⁺. TRPV1 agonist, capsaicin (CAP), was intraperitoneally administered. CNTF receptor alpha neutralizing antibody (CNTFRαNAb) was nigral injected to evaluate the role of CNTF endogenously produced by astrocyte through TRPV1 activation on DA neurons. Delayed treatment of CAP produced a significant reduction in amphetamine-induced rotational asymmetry. Accompanying this behavioral recovery, CAP treatment increased CNTF levels and tyrosine hydroxylase (TH) activity in the substantia nigra pars compacta (SNpc), and levels of DA and its metabolites in the striatum compared to controls. Interestingly, behavioral recovery and increases in biochemical indices were not reflected in trophic changes of the DA system. Instead, behavioral recovery was temporal and dependent on the continuous presence of CAP treatment. The results suggest that delayed treatment of CAP increases nigral TH enzyme activity and striatal levels of DA and its metabolites by CNTF endogenously derived from CAP-activated astrocytes through TRPV1, leading to functional recovery. Consequently, these findings may be useful in the treatment of DA imbalances associated with Parkinson's disease.

Spectral Modification by Operant Conditioning of Cortical Theta Suppression in Rats

OBJECTIVE: Brain activity is known to be voluntarily controllable by neurofeedback, a kind of electroencephalographic (EEG) operant conditioning. Although its efficacy in clinical effects has been reported, it is yet to be uncovered whether or how a specific band activity is controllable. Here, we examined EEG spectral profiles along with conditioning training of a specific brain activity, theta band (4–8 Hz) amplitude, in rats. METHODS: During training, the experimental group received electrical stimulation to the medial forebrain bundle contingent to suppression of theta activity, while the control group received stimulation non-contingent to its own band activity. RESULTS: In the experimental group, theta activity gradually decreased within the training session, while there was an increase of theta activity in the control group. There was a significant difference in theta activity during the sessions between the two groups. The spectral theta peak, originally located at 7 Hz, shifted further towards higher frequencies in the experimental group. CONCLUSION: Our results showed that an operant conditioning technique could train rats to control their specific EEG activity indirectly, and it may be used as an animal model for studying how neuronal systems work in human neurofeedback.

Electroacupuncture Alleviates Motor Symptoms and Up-Regulates Vesicular Glutamatergic Transporter 1 Expression in the Subthalamic Nucleus in a Unilateral 6-Hydroxydopamine-Lesioned Hemi-Parkinsonian Rat Model / 神经科学通报·英文版

Previous studies have shown that electroacupuncture (EA) promotes recovery of motor function in Parkinson's disease (PD). However the mechanisms are not completely understood. Clinically, the subthalamic nucleus (STN) is a critical target for deep brain stimulation treatment of PD, and vesicular glutamate transporter 1 (VGluT1) plays an important role in the modulation of glutamate in the STN derived from the cortex. In this study, a 6-hydroxydopamine (6-OHDA)-lesioned rat model of PD was treated with 100 Hz EA for 4 weeks. Immunohistochemical analysis of tyrosine hydroxylase (TH) showed that EA treatment had no effect on TH expression in the ipsilateral striatum or substantia nigra pars compacta, though it alleviated several of the parkinsonian motor symptoms. Compared with the hemi-parkinsonian rats without EA treatment, the 100 Hz EA treatment significantly decreased apomorphine-induced rotation and increased the latency in the Rotarod test. Notably, the EA treatment reversed the 6-OHDA-induced down-regulation of VGluT1 in the STN. The results demonstrated that EA alleviated motor symptoms and up-regulated VGluT1 in the ipsilateral STN of hemi-parkinsonian rats, suggesting that up-regulation of VGluT1 in the STN may be related to the effects of EA on parkinsonian motor symptoms via restoration of function in the cortico-STN pathway.

Desynchronization of Theta Oscillations in Prefrontal Cortex during Self-stimulation of the Medial Forebrain Bundles in Mice

Stimulation of the medial forebrain bundle (MFB) can reinforce intracranial self-stimulation (ICSS) in rodents (i.e., reward-seeking behavior). The MFB stimulation produces a highly reliable behavioral output that enabled a clear distinction of the animal behavioral states between the non-ICSS and ICSS periods. However, the cortical states during these reward-seeking behaviors are not fully characterized in comparison to those during volitional behavior. This study was designed to characterize the cortical rhythms of and coherence between prefrontal cortex and hippocampus during the wheel-turning behavior reinforced by the ICSS in comparison to the wheel-turning without ICSS. We used a wheel for freely moving mice, which was programmed to deliver cathode currents through an electrode in the MFB at each one-quarter turn of the wheel to induce ICSS. The wheel-turning epochs were extracted from the pre-ICSS, ICSS and post-ICSS sessions and the prefrontal EEGs and the hippocampal LFPs in the epochs were analyzed with power and synchronization analyses. During the ICSS, the EEG power decreased at 6~10 Hz in the prefrontal cortex, while was not significantly altered in the hippocampus. Furthermore, we found that the phase synchrony between the prefrontal cortex and the hippocampus corresponding to information transmission between the two regions during reward-seeking motion decreased preceding MFB stimulation reinforced by ICSS. Our findings suggest that theta-activity can be reliably dissociated from active behavior if the animal is involved in self-stimulation.

Impaired Voluntary Wheel Running Behavior in the Unilateral 6-Hydroxydopamine Rat Model of Parkinson's Disease

OBJECTIVE: The aim of this study was to investigate voluntary wheel running behavior in the unilateral 6-hydroxydopamine (6-OHDA) rat model. METHODS: Male Sprague-Dawley rats were assigned to 2 groups : 6-OHDA group (n=17) and control group (n=8). The unilateral 6-OHDA rat model was induced by injection of 6-OHDA into unilateral medial forebrain bundle using a stereotaxic instrument. Voluntary wheel running activity was assessed per day in successfully lesioned rats (n=10) and control rats. Each behavioral test lasted an hour. The following parameters were investigated during behavioral tests : the number of running bouts, the distance moved in the wheel, average peak speed in running bouts and average duration from the running start to the peak speed. RESULTS: The number of running bouts and the distance moved in the wheel were significantly decreased in successfully lesioned rats compared with control rats. In addition, average peak speed in running bouts was decreased, and average duration from the running start to the peak speed was increased in lesioned animals, which might indicate motor deficits in these rats. These behavioral changes were still observed 42 days after lesion. CONCLUSION: Voluntary wheel running behavior is impaired in the unilateral 6-OHDA rat model and may represent a useful tool to quantify motor deficits in this model.

Enhanced Efficacy of Human Brain-Derived Neural Stem Cells by Transplantation of Cell Aggregates in a Rat Model of Parkinson's Disease

OBJECTIVE: Neural tissue transplantation has been a promising strategy for the treatment of Parkinson's disease (PD). However, transplantation has the disadvantages of low-cell survival and/or development of dyskinesia. Transplantation of cell aggregates has the potential to overcome these problems, because the cells can extend their axons into the host brain and establish synaptic connections with host neurons. In this present study, aggregates of human brain-derived neural stem cells (HB-NSC) were transplanted into a PD animal model and compared to previous report on transplantation of single-cell suspensions. METHODS: Rats received an injection of 6-OHDA into the right medial forebrain bundle to generate the PD model and followed by injections of PBS only, or HB-NSC aggregates in PBS into the ipsilateral striatum. Behavioral tests, multitracer (2-deoxy-2-[18F]-fluoro-D-glucose ([18F]-FDG) and [18F]-N-(3-fluoropropyl)-2-carbomethoxy-3-(4-iodophenyl)nortropane ([18F]-FP-CIT) microPET scans, as well as immunohistochemical (IHC) and immunofluorescent (IF) staining were conducted to evaluate the results. RESULTS: The stepping test showed significant improvement of contralateral forelimb control in the HB-NSC group from 6-10 weeks compared to the control group (p<0.05). [18F]-FP-CIT microPET at 10 weeks posttransplantation demonstrated a significant increase in uptake in the HB-NSC group compared to pretransplantation (p<0.05). In IHC and IF staining, tyrosine hydroxylase and human beta2 microglobulin (a human cell marker) positive cells were visualized at the transplant site. CONCLUSION: These results suggest that the HB-NSC aggregates can survive in the striatum and exert therapeutic effects in a PD model by secreting dopamine.

A Rat Model of Striatonigral Degeneration Generated by Simultaneous Injection of 6-Hydroxydopamine into the Medial Forebrain Bundle and Quinolinic Acid into the Striatum

A double toxin-double lesion strategy is well-known to generate a rat model of striatonigral degeneration (SND) such as multiple system atrophy-parkinsonian type. However, with this model it is difficult to distinguish SND from Parkinson's disease (PD). In this study, we propose a new rat model of SND, which is generated by simultaneous injection of 6-hydroxydopamine into the medial forebrain bundle and quinolinic acid into the striatum. Stepping tests performed 30 min after intraperitoneal L-dopa administration at 6 weeks post-surgery revealed an L-dopa response in the PD group but not the SND group. Apomorphine-induced rotation tests revealed no rotational bias in the SND group, which persisted for 2 months, but contralateral rotations in the PD group. MicroPET scans revealed glucose hypometabolism and dopamine transporter impairment on the lesioned striatum in the SND group. Tyrosine hydroxylase immunostaining in the SND group revealed that 74.7% of nigral cells on the lesioned side were lost after lesion surgery. These results suggest that the proposed simultaneous double toxin-double lesion method successfully created a rat model of SND that had behavioral outcomes, multitracer microPET evaluation, and histological aspects consistent with SND pathology. This model will be useful for future study of SND.

Push-in Head Restraining Apparatus for Intracranial Self Stimulation Tasks in Rats

Head restraining is an experimental technique that firmly secures the animal's head to a fixation apparatus for the precise control and sensing of behaviors. However, procedural and surgical difficulties and limitations have been obstructing the use of the technique in neurophysiological and behavioral experiments. Here, we propose a novel design of the head-restraining apparatus which is easy to develop and convenient for practical use. Head restraining procedure can be completed by sliding the head mounter, which is molded by dental cement during implantation surgery, into the port, which serves as matching guide rails for the mounter, of the fixation bar. So neither skull-attached plates nor screws for fixation are needed. We performed intracranial self stimulation experiment in rats using the newly designed device. Rats were habituated to acclimatize the head-restraint environment and trained to discriminate two spatially distinguished cues using a customized push-pull lever as an operandum. Direct electrical stimulation into the medial forebrain bundle served as reward. We confirmed that head restraining was stable throughout experiments and rats were able to learn to manipulate the lever after successful habituation. Our experimental framework might help precise control or sensing of behavior under head fixed rats using direct electrical brain stimulation as a reward.

Relationship between Microglial Activation and Dopaminergic Neuronal Loss in 6-OHDA-induced Parkinsonian Animal Model / 체질인류학회지

This study assessed the dynamics of morphological and immunophenotypic properties of activated microglia in a 6-hydroxydopamine (6-OHDA) induced Parkinsonian animal model. Neurodegeneration in the substantia nigra pars compacta (SNc) was induced by unilateral injection of 6-OHDA into the medial forebrain bundle. Parkinsonian animal model were sacrificed at 1, 2, 4 and 8 weeks after 6-OHDA injection. Changes in the functional activity of activated microglia were identified using different monoclonal antibodies: OX6 for major histocompatibility complex (MHC) class II, ED1 for phagocytic activity. Phagocytic microglia, characterized by ED1- or OX6-immunoreactivity, appeared in the SNc at 1 week after 6-OHDA injection, activated microglia selectively adhered to degenerating axons, dendrites and dopaminergic neuron somas in the SNc. This was followed by significant loss of these fibers and nigral dopaminergic neurons. Activation of microglia into phagocytic stage was most pronounced at 2 week after 6-OHDA injection and gradually subsided, but phagocytic microglia persisted until 8 weeks after 6-OHDA injection. Taken together, our results indicate that activated microglia is lead to persistently neuron cell death and promotes loss of dopaminergic neuron by degeneration of the dopaminergic neurons.

Lesion of Subthalamic Nucleus in Parkinsonian Rats: Effects of Dopamine D1 and D2 Receptor Agonists on the Neuronal Activities of the Substantia Nigra Pars Reticulata

OBJECTIVE: It was hypothesized that dopamine agonist administration and subthalamic nucleus (STN) lesion in the rat might have a synergistic effect on the neuronal activities of substantia nigra pars reticulata (SNpr) as observed in patients with Parkinson's disease. The effects of SKF38393 (a D1 receptor agonist) and Quinpirole (a D2 receptor agonist) were compared in parkinsonian rat models with 6- hydroxydopamine (6-OHDA) after STN lesion. METHODS: SKF38393 and Quinpirole were consecutively injected intrastriatally. SNpr was microrecorded to ascertain the activity of the basal ganglia output structure. The effect of SKF38393 or Quinpirole injection on the firing rate and firing patterns of SNpr was investigated in medial forebrain bundle (MFB) lesioned rats and in MFB+STN lesioned rats. RESULTS: The administration of SKF38393 decreased SNpr neuronal firing rates and the percentage of burst neurons in the MFB lesioned rats, but did not alter them in MFB+STN lesioned rats. The administration of Quinpirole significantly decreased the spontaneous firing rate in the MFB lesioned rats. However, after an additional STN lesion, it increased the percentage of burst neurons. CONCLUSION: This study demonstrated that dopamine agonists and STN lesion decreased the hyperactive firing rate and the percentage of burst neurons of SNpr neurons in 6-OHDA lesioned rats, respectively. Quinpirole with STN lesion increased a percentage of burst neurons. To clear the exact interactive mechanism of D1 and D2 agonist and the corresponding location, it should be followed a study using a nonselective dopamine agonist and D1, D2 selective antagonist.

A remote controlled multimode micro-stimulator for freely moving animals / 生理学报

This paper presents a remote controlled multimode micro-stimulator based on the chip nRF24E1, which consists mainly of a micro-control unit (MCU) and a radio frequency (RF) transceiver. This micro-stimulator is very compact (18 mmx28 mm two layer printed circuit board) and light (5 g without battery), and can be carried on the back of a small animal to generate electrical stimuli according to the commands sent from a PC 10 meters away. The performance and effectiveness of the micro-stimulator were validated by in vitro experiments on the sciatic nerve (SN) of the frog, where action potentials (APs) as well as artifacts were observed when the SN was stimulated by the micro-stimulator. It was also shown by in vivo behavioral experiments on operant conditioned reflexes in rats which can be trained to obey auditory instruction cues by turning right or left to receive electrical stimulation ('virtual' reward) of the medial forebrain bundle (MFB) in a maze. The correct response for the rats to obey the instructions increased by three times and reached 93.5% in an average of 5 d. This micro-stimulator can not only be used for training small animals to become an 'animal robot', but also provide a new platform for behavioral and neurophysiological experiments.

The Effect of 1, 25-Dihydroxyvitamin D3 on Dopaminergic Neurons and Microglial Activation in Parkinsonian Rat Model Induced by 6-Hydroxydopamine

BACKGROUND: Recent studies have shown increasing evidence for microglial activation in neuronal degeneration in Parkinson's disease (PD), although the cause of PD remains unclear. Recent studies have also shown that 1alpha, 25-dihydroxyvitamin D3 (vitamin D3) exert neuroprotective effects by inducing an increased expression of neurotrophic factors, suggesting the possibility of vitamin D3 for the treatment of PD and other neurodegenerative diseases. The purpose of this study was to investigate the effect of vitamin D3 on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity and microglial activation in adult rats. METHODS: Adult male Sprague-Dawley rats were subcutaneously injected with vitamin D3 or 0.1% ethanol for seven consecutive days and then infused unilaterally with 6-OHDA in the medial forebrain bundle. After 7 days of injection with 6-OHDA, the substantia nigra was examined by immunohistochemistry. RESULTS: The number of tyrosine hydroxylase (TH)-positive neurons in the lesioned substantia nigra pars compacta of vitamin D3 and ethanol groups was 84.8 +/- 18.84 and 52.6 +/- 13.23, respectively, fewer than that of the contralateral side (122.35 +/- 9.79 and 123.81 +/- 12.11, respectively) (P<0.05). The vitamin D3 group showed significantly higher numbers of the TH-positive neurons than that of the ethanol group (P<0.05). CD11b-positive microglial immunoreactivity was stronger in the lesion side than that of the normal side, and it was much weaker in the vitamin D3 group than that of the ethanol group (P<0.05). CONCLUSIONS: These results indicate that vitamin D3 protects dopaminergic neurons from the neuronal injury induced by 6-OHDA, possibly by the mechanism involving microglial activation.

Differential Activation of Microglia in the Substantia Nigra and Lesioned Site Following Medial Forebrain Bundle Transection / 대한해부학회지

Medial forebrain bundle (MFB) transmits the nigrostriatal dopaminergic (DA) axons, and previously we reported that transection of the MFB causes apotosis-like neurodegeneration of nigral DA neurons. On the other hand, it is likely to occur necrosis at the lesioned site where MFB is cut, due to direct mechanical transection of the brain tissue. To clarify the pathological dynamics of microglia reacting to the two different types of neuronal cell death, immunophenotypic and morphological features of microglia were compared and analyzed in the substantia nigra (SN) and lesioned site of the MFB axotomized rat brain. OX42 (mouse anti-rat CD 11b; pan-microglia marker), ED1 (mouse anti-rat lysosomal enzyme; phagocytic marker), and OX6 (mouse anti-rat MHC II) were used as primary antibodies for immunohistochemical localization of microglia, ED2 (mouse anti-rat macrophage) for macrophages, and anti-tyrosine hydro-xylase (TH) antibody for DA neurons. Quite numerous activated microglia with strong OX42 immunoreactivity were found in the SN at 1 day post-lesion (dpl), but most of them were ED1-and OX6-negative except only a few which were ED1-positive. This phenomenon was thought to be related with the stage of alert, the first step of microglial activation. It could be presumed that microglial phagocytosis may precede MHC II expression, because ED1-positive microglia appeared from 1 dpl while OX6-positive ones from 3 dpl. Number of activated microglia showing strong ED1, OX6 and OX42 immunoreactivity increased significantly by 7 ~14 dpl, and they specifically stick to various parts of dendrites and somas of TH-immunoreactive neurons of the SN. The phagocytic microglia of the SN maintained ramified form although they retained enlarged soma and shortened, thickened processes. The lesioned site was surrounded by numerous microglia showing strong OX42 and ED1 immunoreactivity as early as 1 dpl, indicating that microglial phagocytosis starts earlier in the lesioned site than in the SN. OX42-positive microglia of the lesioned site were ED2-negative, and showed amoeboid morphology already from 1 dpl. The amoeboid microglia became to be enlarged in their soma size by 3 dpl, and fused each other to form clumps within the necrotic zone by 5 ~7 dpl. The entire necrotic zone was completely filled with microglia of obscure outline with strong OX42 and ED1 immuno-reactivity. However, the majority of amoeboid microglia of the lesioned site were OX6-negative except a few. These results clearly demonstrate that activated microglia reacting to apoptotic neurodegeneration show different pathodynamic characteristics in terms of immunological phenotypes and morphology from those reacting to necrotic, mechanical lesion.

Neuroglial Proliferative Activity Following Medial Forebrain Bundle Axotomy / 대한해부학회지

Changes in morphology, immunophenotypes and proliferative activity of neuroglia are key features in most forms of CNS pathology. We compared proliferative activity of neuroglial cells in response to two different types of brain injury induced by medial forebrain bundle (MFB) axotomy. In the cannula track where acute necrosis occurs due to mechanical lesion caused by cannula inserted to incise the MFB, many BrdU-immunoreactive (ir) cells appeared around the cannula track already at 1 day post-lesion (1 dpl). Their number significantly increased by 7 dpl and then decreased, but considerable number of BrdU-ir cells was still found at 14 dpl. Some of the BrdU-ir cells were double-labeled with either OX-42 or GFAP. This finding suggests that both microglia and astrocytes are activated and proliferate immediately after the mechanical damage, and the proliferative activity is maintained in a considerable number of these cells by 14 dpl. In general, the main cell type showing BrdU immunoreactivity was amoeboid microglia within the necrotic zone immediately surrounding the cannula track, and was astrocytes in the periphery of the necrotic zone more or less apart from the cannula track. Previously, we reported that MFB axotomy induces apoptosis of dopaminergic (DA) neurons in the substantia nigra (SN). In the SN where axotomized DA neurons undergo apoptosis, only a few BrdU-ir cells were found at 1 dpl. Their number increased gradually from 3 dpl and peaked at 7 dpl, then significantly reduced at 14 dpl. Most of them were double-labeled with OX -42-positive ramified microglia but not with GFAP. This data indicates that microglia but not astrocyte are the cell type that proliferate in response to apoptotic neuronal cell death, and their morphology and proliferative activity are different from those observed in the cannula track. Meanwhile, in the both cannula track and SN, some BrdU-ir cells were thought to be neither GFAP-positive nor OX-42-positive, and thus they were presumed to be infiltrated peripheral immune cells. These results demonstrate that different types of neuronal cell death are accompanied with different neurogilal proliferative activities.

Correlation between iron levels and degeneration of dopaminergic neurons in rat nigrostriatal system during the early 6-OHDA lesions in medial forebrain bundle / 生理学报

In the present study, using fast cyclic voltammetry (FCV), atomic absorption/flame emission spectrophotometry and immunohistochemistry, we investigated the correlation between iron levels and degeneration of dopaminergic neurons in rat nigrostriatal system during the early 6-OHDA lesions in the medial forebrain bundle (MFB). The results showed that 1 d or 3 d after lesions in MFB, there was a 45% or 66% reduction, respectively, in the density of tyrosine hydroxylase (TH) immunoreactive cells in the substantia nigra (SN) of the lesioned side accompanied by an increase in iron staining intensity and iron concentration; while there was no change in dopamine (DA) release in the striatum (Str) of the lesioned side compared with the unlesioned side and the normal rats. There was no difference in the iron staining and concentration of SN and DA release of Str on the lesioned side between one-day group and three-days group. These results suggest that an iron level elevation in SN may be involved at the early stage of degeneration of DA neurons in SN. However, DA release in Str was unchanged due to the immense compensatory mechanism of DA system.

Morphological Changes in the Striatum after Dopaminergic Cell Transplantation to Parkinson's Disease Rat Model / 대한해부학회지

Parkinson's disease animal model was developed by the destruction of the striatonigral dopaminergic system. The morphological changes in the dopamine depleted striatum after the transplantation of the fetal mesencephalic dopaminergic neurons or tyrosine hydroxylase cDNA transfected human neural stem cells (C4-TH cells) were studied. Male Sprague-Dawley rats, weighting 250~300 gm, were used. To make unilateral lesion of nigrostriatal tract, 6-OHDA (6 microgram/microliter) was injected into the medial forebrain bundle. Two weeks after the lesion surgery, the effect of the 6-OHDA lesion was assessed by monitoring apomorphine (0.5 mg/kg, s.c)-induced turning behavior and confirmed by the lack of TH-immunoreactivity on tissue sections. Either cell suspension from ventral mesencephalic tissue obtained from embryonic day 14 fetus or C4-TH cells was grafted into the rostral striatum. After grafting, rats were tested with apomorphine every 2 weeks for 6 weeks. The grafted rats showing behavioral recovery were sacrificed and analysed by TH, neuropeptide Y (NPY), and parvalbumin (PV) immuno- histochemistry. TH-immunoreactive (ir) neurons were located around the graft and their processes extended into the striatum. The TH-ir axon terminals made a symmetrical synapse with the dendrites of the striatal neuron. Cell bodies either NPY- or PV-ir striatal neuron were observed around the graft and extended their processes into the graft. TH-ir C4-TH cells were also distributed along the needle track such as the transplanted fetal dopaminergic neurons, but had smaller soma and fewer processes than those. It is concluded that the grafted dopaminergic cells are survived in the dopamine depleted striatum and recovered the rotational behavior of Parkinson's disease animal model.

Dose-response functions of apomorphine, SKF 38393, LY 171555, haloperidol and clonidine on the self-stimulation evoked from lateral hypothalamus and ventral tegmentum.

The experimental animals were implanted with two bipolar electodes, one in the lateral hypothalamus including medial forebrain bundle (LH-MFB) and other in ipsilateral ventral tegmental area-substantia nigra (VTA-SN) and were trained to press a pedal for self-stimulation. This provided the scope to compare directly the effect of a given dose of a drug on the two reward regions in the same animal in the same testing situation. The current intensity was set to produce intracranial self-stimulation (ICSS) response rates of 50% less than the maximal shaping response rates for the respective animals (M60). Following systemic (intraperitoneal) administration of apomorphine (a dopamine receptor D1/D2 mixed agonist), SKF 38393 (D1 > D3 > D2 agonist), LY 17155 or quinpirole (D3 > D2 and D1) agonist), haloperidol (a DA-D2 antagonist), and clonidine (noradrenaline receptor alpha 2 agonist), the ICSS response rates evoked from LH-MFB and VTA-SN were compared with vehicle or saline-treated animals on the basis of dose-response functions. A dose-dependent inhibitory effect at M50 was observed with apomorphine (0.01-1.00 mg/kg) and haloperidol (0.05-0.30 mg/kg) for both the sites of stimulation. These doses of haloperidol did not produce any motor deficits like catalepsy and muscular rigidity. The dose-response and time-effect functions of SKF 38393 and LY 171555 at M50 showed the facilitation and suppression of ICSS of VTA-SN and LH-MFB respectively. Clonidine (0.05-0.25 mg/kg) also produced inhibitory effect on ICSS rates, but this suppression was of different magnitude with respect to the site of stimulation. These doses of clonidine were in the range that did not prevent active pedal pressing responses. ED50 (the dose required to reduce the ICSS response rate 50% of the rate after administration of vehicle) for LY 171555 was 0.8 and 4.4 mg/kg for the ICSS of VTA-SN and LH-MFB respectively and thus statistically different ED50 for apomorphine was 0.27 and 0.36 mg/kg; and for haloperidol was 0.75 and 0.90 mg/kg for LH-MFB and VTA-SN respectively and thus not different significantly. ED50 for clonidine was 0.25 and 0.08 mg/kg for VTA-SN and LH-MFB respectively and thus statistically different. The two-way analysis of variance (ANOVAR) of interaction of dose-response function of alpha 2 agonist with respect to LH-MFB and VTA-SN showed significant independence in their suppressive effects.

Contractions of the gastric antrum induced by stimulation of the medial forebrain bundle in the rat

Glucoreceptors sensitive to cytoglucopenia exist in the medial forebrain bundle of the rat. The selective activation of these receptors provokes an increase in glycemia and gastric secretion. In the present work, we found that stimulation of this diencephalic area in rats also provokes potent gastric contractions. Stimulation with high voltage usually inhibited this effect