Normalized affective responsiveness following deep brain stimulation of the medial forebrain bundle in depression

Deep brain stimulation (DBS) of the supero-lateral medial forebrain bundle (slMFB) is associated with rapid and sustained antidepressant effects in treatment-resistant depression (TRD). Beyond that, improvements in social functioning have been reported. However, it is unclear whether social skills, the basis of successful social functioning, are systematically altered following slMFB DBS. Therefore, the current study investigated specific social skills (affective empathy, compassion, and theory of mind) in patients with TRD undergoing slMFB DBS in comparison to healthy subjects. 12 patients with TRD and 12 age- and gender-matched healthy subjects (5 females) performed the EmpaToM, a video-based naturalistic paradigm differentiating between affective empathy, compassion, and theory of mind. Patients were assessed before and three months after DBS onset and compared to an age- and gender-matched sample of healthy controls. All data were analyzed using non-parametric Mann-Whitney U tests. DBS treatment significantly affected patients' affective responsiveness towards emotional versus neutral situations (i.e. affective empathy): While their affective responsiveness was reduced compared to healthy subjects at baseline, they showed normalized affective responsiveness three months after slMFB DBS onset. No effects occurred in other domains with persisting deficits in compassion and intact socio-cognitive skills. Active slMFB DBS resulted in a normalized affective responsiveness in patients with TRD. This specific effect might represent one factor supporting the resumption of social activities after recovery from chronic depression. Considering the small size of this unique sample as well as the explorative nature of this study, future studies are needed to investigate the robustness of these effects.

Anatomical characterisation of three different psychosurgical targets in the subthalamic area: from the basal ganglia to the limbic system

Effective neural stimulation for the treatment of severe psychiatric disorders needs accurate characterisation of surgical targets. This is especially true for the medial subthalamic region (MSR) which contains three targets: the anteromedial STN for obsessive compulsive disorder (OCD), the medial forebrain bundle (MFB) for depression and OCD, and the "Sano triangle" for pathological aggressiveness. Blocks containing the subthalamic area were obtained from two human brains. After obtaining 11.7-Tesla MRI, blocks were cut in regular sections for immunohistochemistry. Fluorescent in situ hybridisation was performed on the macaque MSR. Electron microscopic observation for synaptic specialisation was performed on human and macaque subthalamic fresh samples. Images of human brain sections were reconstructed in a cryoblock which was registered on the MRI and histological slices were then registered. The STN contains glutamatergic and fewer GABAergic neurons and has no strict boundary with the adjacent MSR. The anteromedial STN has abundant dopaminergic and serotoninergic innervation with very sparse dopaminergic neurons. The MFB is composed of dense anterior dopaminergic and posterior serotoninergic fibres, and fewer cholinergic and glutamatergic fibres. Medially, the Sano triangle presumably contains orexinergic terminals from the hypothalamus, and neurons with strong nuclear oestrogen receptor-alpha staining with a decreased anteroposterior and mediolateral gradient of staining. These findings provide new insight regarding MSR cells and their fibre specialisation, forming a transition zone between the basal ganglia and the limbic systems. Our 3D reconstruction enabled us to visualize the main histological features of the three targets which should enable better targeting and understanding of neuromodulatory stimulation results in severe psychiatric conditions.

A connectomic analysis of deep brain stimulation for treatment-resistant depression

OBJECTIVE

Deep brain stimulation (DBS) has been used as a treatment of last resort for treatment-resistant depression (TRD) for more than a decade. Many DBS targets have been proposed and tested clinically, but the underlying circuit mechanisms remain unclear. Uncovering white matter tracts (WMT) activated by DBS targets may provide crucial information about the circuit substrates mediating DBS efficacy in ameliorating TRD.

METHODS

We performed probabilistic tractography using diffusion magnetic resonance imaging datas from 100 healthy volunteers in Human Connectome Project datasets to analyze the structural connectivity patterns of stimulation targeting currently-used DBS target for TRD. We generated mean and binary fiber distribution maps and calculated the numbers of WMT streamlines in the dataset.

RESULTS

Probabilistic tracking results revealed that activation of distinct DBS targets demonstrated modulation of overlapping but considerably distinct pathways. DBS targets were categorized into 4 groups: Cortical, Striatal, Thalamic, and Medial Forebrain Bundle according to their main modulated WMT and brain areas. Our data also revealed that Brodmann area 10 and amygdala are hub structures that are associated with all DBS targets.

CONCLUSIONS

Our results together suggest that the distinct mechanism of DBS targets implies individualized target selection and formulation in the future of DBS treatment for TRD. The modulation of Brodmann area 10 and amygdala may be critical for the efficacy of DBS-mediated treatment of TRD.

Deep brain stimulation for psychiatric disorders: From focal brain targets to cognitive networks

Deep brain stimulation (DBS) is a promising intervention for treatment-resistant psychiatric disorders, particularly major depressive disorder (MDD) and obsessive-compulsive disorder (OCD). Up to 90% of patients who have not recovered with therapy or medication have reported benefit from DBS in open-label studies. Response rates in randomized controlled trials (RCTs), however, have been much lower. This has been argued to arise from surgical variability between sites, and recent psychiatric DBS research has focused on refining targeting through personalized imaging. Much less attention has been given to the fact that psychiatric disorders arise from dysfunction in distributed brain networks, and that DBS likely acts by altering communication within those networks. This is in part because psychiatric DBS research relies on subjective rating scales that make it difficult to identify network biomarkers. Here, we overview recent DBS RCT results in OCD and MDD, as well as the follow-on imaging studies. We present evidence for a new approach to studying DBS' mechanisms of action, focused on measuring objective cognitive/emotional deficits that underpin these and many other mental disorders. Further, we suggest that a focus on cognition could lead to reliable network biomarkers at an electrophysiologic level, especially those related to inter-regional synchrony of the local field potential (LFP). Developing the network neuroscience of DBS has the potential to finally unlock the potential of this highly specific therapy.

Medial forebrain bundle structure is linked to human impulsivity

Comparative research indicates that projections from midbrain dopamine nuclei [including the ventral tegmental area (VTA)] to the ventral striatum [including the nucleus accumbens (NAcc)] critically support motivated behavior. Using diffusion-weighted imaging and probabilistic tractography in humans, we characterized the trajectory and structure of two tracts connecting the VTA and NAcc, as well as others connecting the substantia nigra and dorsal striatum. Decreased structural coherence of an inferior VTA-NAcc tract was primarily and replicably associated with increased trait impulsivity and also distinguished individuals with a stimulant use disorder from healthy controls. These findings suggest that decreased coherence of the inferior VTA-NAcc tract is associated with increased impulsivity in humans and identify a previously uncharacterized structural target for diagnosing disorders marked by impulsivity.

Genetic silencing of striatal CaV1.3 prevents and ameliorates levodopa dyskinesia

BACKGROUND

Levodopa-induced dyskinesias are an often debilitating side effect of levodopa therapy in Parkinson's disease. Although up to 90% of individuals with PD develop this side effect, uniformly effective and well-tolerated antidyskinetic treatment remains a significant unmet need. The pathognomonic loss of striatal dopamine in PD results in dysregulation and disinhibition of striatal CaV1.3 calcium channels, leading to synaptopathology that appears to be involved in levodopa-induced dyskinesias. Although there are clinically available drugs that can inhibit CaV1.3 channels, they are not adequately potent and have only partial and transient impact on levodopa-induced dyskinesias.

METHODS

To provide unequivocal target validation, free of pharmacological limitations, we developed a CaV1.3 shRNA to provide high-potency, target-selective, mRNA-level silencing of striatal CaV1.3 channels and examined its ability to impact levodopa-induced dyskinesias in severely parkinsonian rats.

RESULTS

We demonstrate that vector-mediated silencing of striatal CaV1.3 expression in severely parkinsonian rats prior to the introduction of levodopa can uniformly and completely prevent induction of levodopa-induced dyskinesias, and this antidyskinetic benefit persists long term and with high-dose levodopa. In addition, this approach is capable of ameliorating preexisting severe levodopa-induced dyskinesias. Importantly, motoric responses to low-dose levodopa remained intact in the presence of striatal CaV1.3 silencing, indicating preservation of levodopa benefit without dyskinesia liability.

DISCUSSION

The current data provide some of the most profound antidyskinetic benefit reported to date and suggest that genetic silencing of striatal CaV1.3 channels has the potential to transform treatment of individuals with PD by allowing maintenance of motor benefit of levodopa in the absence of the debilitating levodopa-induced dyskinesia side effect. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Research on the synchronous detection of neuronal signals under a nerve stimulation system control

Deep brain stimulation (DBS) provides a recognized research intervention for neurological disease currently. However, there is a lack of traditional electrical stimulator to observe neuronal firing activity synchronously. The aim of the present study was to realize concurrent detection of neuronal signals better under a nerve stimulation system control. Herein, we designed an integrated software, which could control not only neuro-stimulator but also detection instrument at the same time. Moreover, the actual stimulation signals applied to the experiment object could be collected back to data acquisition card and in consistent with the electrophysiological signals. As to basic performance of self-building stimulator, the accuracy of output square signal was verified to be greater than 99.05 % with the change of voltage amplitude. Practicably, combined with homemade microelectrode array (MEA) detecting device, medial forebrain bundle (MFB) DBS effects were observed significantly through the changes of electrophysiological signals in caudate putamen (CPu) of Sprague-Dawley (SD) rat, and the signal-to-noise ratio (SNR) was 5:1 after stimulation. Therefore, the comprehensive nerve stimulation system, which consists of neuro-stimulator and integrated software, could be widely used in the field of neuroscience research with high precision and synchronization.

Neuroprotective Effects of Ellagic Acid in a Rat Model of Parkinson's Disease

Antioxidants have protective effects against free radicals-induced neural damage in Parkinson's disease (PD). We examined the effects of ellagic acid (EA) on locomotion, pallidal local EEG, and its frequency bands' power and also cerebral antioxidant contents in a rat model of PD induced by 6-hydroxidopamine (6-OHDA). 6-OHDA (16 µg/2µ l) was injected into the right medial forebrain bundle (MFB) in MFB-lesioned rat's brain. Sham group received vehicle instead of 6-OHDA. PD-model was confirmed by rotational test using apomorphine injection. EA (50 mg/kg/2 ml, by gavages) was administered in PD+EA group. One group of MFB-lesioned rats received pramipexole (PPX; 2 mg/kg/2 ml, by gavages) as a positive control group (PD+PPX group). Motor activity was assessed by stride length, rotarod, and cylinder tests. Pallidal local EEG was recorded in freely moving rats. The levels of malondialdehyde (MDA) besides Glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities were measured in both striatum and hippocampus tissues. MFB lesion caused significant reduction of stride-length (P<0.001), bar decent latency (P<0.001) and frequency bands' power of pallidal EEG (P<0.001). Use of 6-OHDA caused a reduction in the GPx (P<0.001) and SOD (P<0.001) activities while increased significantly the levels of MDA (P<0.001) in MFB-lesioned rats. EA significantly restored all above parameters. The results show that EA can improve the motor impairments and electrophysiological performance in the MFB-lesioned rats via raising the cerebral antioxidant contents. Therefore, EA can protect the brain against free radicals-induced neural damage and may be beneficial in the treatment of PD.

Optogenetic Activation of a Lateral Hypothalamic-Ventral Tegmental Drive-Reward Pathway

Electrical stimulation of the lateral hypothalamus can motivate feeding or can serve as a reward in its own right. It remains unclear whether the same or independent but anatomically overlapping circuitries mediate the two effects. Electrical stimulation findings implicate medial forebrain bundle (MFB) fibers of passage in both effects, and optogenetic studies confirm a contribution from fibers originating in the lateral hypothalamic area and projecting to or through the ventral tegmental area. Here we report that optogenetic activation of ventral tegmental fibers from cells of origin in more anterior or posterior portions of the MFB failed to induce either reward or feeding. The feeding and reward induced by optogenetic activation of fibers from the lateral hypothalamic cells of origin were influenced similarly by variations in stimulation pulse width and pulse frequency, consistent with the hypothesis of a common substrate for the two effects. There were, however, several cases where feeding but not self-stimulation or self-stimulation but not feeding were induced, consistent with the hypothesis that distinct but anatomically overlapping systems mediate the two effects. Thus while optogenetic stimulation provides a more selective tool for characterizing the mechanisms of stimulation-induced feeding and reward, it does not yet resolve the question of common or independent substrates.

Relationships among rat ultrasonic vocalizations, behavioral measures of striatal dopamine loss, and striatal tyrosine hydroxylase immunoreactivity at acute and chronic time points following unilateral 6-hydroxydopamine-induced dopamine depletion

Voice deficits in Parkinson disease (PD) emerge early in the disease process, but do not improve with standard treatments targeting dopamine. Experimental work in the rat shows that severe and chronic unilateral nigrostriatal dopamine depletion with 6-OHDA results in decreased intensity, bandwidth, and complexity of ultrasonic vocalizations. However, it is unclear if mild/acute dopamine depletion, paralleling earlier stages of PD, results in vocalization deficits, or to what degree vocalization parameters are correlated with other dopamine-dependent indicators of lesion severity or percent of tyrosine hydroxylase (%TH) loss. Here, we assayed ultrasonic vocalizations, forelimb asymmetry, and apomorphine rotations in rats with a range of unilateral dopamine loss resulting from 6-OHDA or vehicle control infusions to the medial forebrain bundle at acute (72 h) and chronic (4 weeks) time points post-infusion. The %TH loss was evaluated at 4 weeks. At 72 h, forelimb asymmetry and %TH loss were significantly correlated, while at 4 weeks, all measures of lesion severity were significantly correlated with each other. Call complexity was significantly correlated with all measures of lesion severity at 72 h but only with %TH loss at 4 weeks. Bandwidth was correlated with forelimb asymmetry at both time points. Duration was significantly correlated with all dopamine depletion measures at 4 weeks. Notably, not all parameters were affected universally or equally across time. These results suggest that vocalization deficits may be a sensitive index of acute and mild catecholamine loss and further underscores the need to characterize the neural mechanisms underlying vocal deficits in PD.

Motor disorders and impaired electrical power of pallidal EEG improved by gallic acid in animal model of Parkinson's disease

The aim of this study was evaluation the effect of Gallic acid on movement disorders and pallidal electrical power in animal model of Parkinson's Disease (PD). PD is clinically characterized by development of motor disturbances, such as bradykinesia, resting tremors, rigidity and a later loss ofpostural reflexes. Oxidative stress is a hallmark factor where the oxidation of dopamine generates Reactive Oxygen Species (ROS) and an unbalanced production ROS induces neuronal damage, therefor leading the neuronal death. Gallic Acid (GA) and its derivatives are present in the plant kingdom and acts as a potent antioxidant. Wistar male rats divided into seven groups randomly with 8 in each. Animals in all groups except control received 8 microg/2 microL 6-hydroxydopamine dissolved in normal saline contains 0.01% ascorbate or vehicle in right Medial Forbrain Bundle (MFB) and a bipolar wire electrode was implanted in the left globus pallidus nucleus of all animals under stereotaxic surgery. Two weeks later PD was approved by contralateral rotation signs induced by apomorphine and then movements and electrical power of pallidal were evaluated. Motor functions and pallidal electrical power were impaired and GA could improve motor dysfunctions and gamma wave power in parkinsonian rats' significantly with higher dose of GA (200 mg kg(-1)). Present result showed that GA may act as a potent antioxidant and free radical scavenger to reverse motor disorders and pallidal gamma wave power after 6-OHDA neurotoxicity in brain.

DtiStudio: resource program for diffusion tensor computation and fiber bundle tracking

A versatile resource program was developed for diffusion tensor image (DTI) computation and fiber tracking. The software can read data formats from a variety of MR scanners. Tensor calculation is performed by solving an over-determined linear equation system using least square fitting. Various types of map data, such as tensor elements, eigenvalues, eigenvectors, diffusion anisotropy, diffusion constants, and color-coded orientations can be calculated. The results are visualized interactively in orthogonal views and in three-dimensional mode. Three-dimensional tract reconstruction is based on the Fiber Assignment by Continuous Tracking (FACT) algorithm and a brute-force reconstruction approach. To improve the time and memory efficiency, a rapid algorithm to perform the FACT is adopted. An index matrix for the fiber data is introduced to facilitate various types of fiber bundles selection based on approaches employing multiple regions of interest (ROIs). The program is developed using C++ and OpenGL on a Windows platform.

Protective effect of 1-methyl-1,2,3,4-tetrahydroisoquinoline against dopaminergic neurodegeneration in the extrapyramidal structures produced by intracerebral injection of rotenone

The aim of this paper was to investigate whether rotenone, a pesticide causing experimental parkinsonism, causes direct damage to dopaminergic structure when injected intracerebrally and whether this action may be prevented by peripheral administration of 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), an endogenous compound with anti-dopaminergic activity. Male Wistar rats were injected unilaterally into the median forebrain bundle with 2 microg rotenone, and received 1MeTIQ, 50 mg/kg i.p. 1 h before and then daily for 21 d. To compare the effect of intracerebral and peripheral treatment, rotenone was also given once or for 7 d in a dose of 10 mg/kg s.c. Dopamine, serotonin and their metabolites were assessed by HPLC in the substantia nigra and striatum. While a single subcutaneous rotenone dose did not produce any change in striatal dopamine metabolism, the multiple treatments resulted in changes suggesting a shift in the metabolism towards oxidative desamination and reduction of O-methylation. In contrast to systemic injections, intracerebral-administered rotenone produced a decrease in dopamine and its metabolites content in the striatum (dopamine decrease by 70%) and substantia nigra (dopamine decrease by 35%), without affecting the serotonin system. As those changes were observed 21 d after the injection of rotenone, they suggest a durable neurotoxic effect. The treatment with 1MeTIQ strongly reduced the fall of striatal dopamine concentration. The data suggest that rotenone given peripherally affects metabolic processes in dopaminergic neurons, and this seems to result from its neurotoxic action, which may be observed after an intracerebral injection. 1MeTIQ is able to counteract the damaging action of rotenone and seems to be a potential neuroprotective agent.

Modulation of photic resetting in rats by lesions of projections to the suprachiasmatic nuclei expressing p75 neurotrophin receptor

The suprachiasmatic nuclei of the hypothalamus (SCN) are the site of the master circadian clock in mammals. The SCN clock is mainly entrained by the light-dark cycle. Light information is conveyed from the retina to the SCN through direct, retinohypothalamic fibres. The SCN also receive other projections, like cholinergic fibres from basal forebrain. To test whether cholinergic afferents are involved in photic resetting, lesions of cholinergic projections were performed in rats with intracerebroventricular (i.c.v.) injections or intra-SCN microinjections of 192 IgG-saporin. When injected in the SCN, this immunotoxin destroys the cholinergic projections and retinohypothalamic afferents that express p75 low-affinity nerve growth factor (p75(NGF)) receptors. The extent of lesions in the basal forebrain and SCN was assessed by acetylcholinesterase histochemistry, p75(NGF) receptor, choline acetyl-transferase, calbindin-D28K and VIP immunocytochemistry. The intra-SCN treatment reduced light-induced phase advances by 30%, and induced a complete loss of forebrain and retinal afferents expressing p75(NGF) receptors within the SCN and a decrease of forebrain cholinergic neurons, most likely those projecting to the SCN. The i.c.v. treatment reduced light-induced phase advances by 40%, increased phase delays and led to extensive damage of forebrain p75(NGF)-expressing neurons, while sparing half of the fibres expressing p75(NGF) receptors (retinal afferents?) in the SCN. Because the integrity of forebrain p75(NGF)-expressing neurons appears to be critical in mediating the effects on light-induced phase advances, we therefore suggest that anterior cholinergic projections expressing p75(NGF) receptors modulate the sensitivity of the SCN clock to the phase advancing effects of light.

Evaluation of striatal dopamine transporter function in rats by in vivo beta-[123I]CIT pinhole SPECT

Striatal dopamine transporter (DAT) function was evaluated in rats by in vivo SPECT-MRI coregistration using the radioligand 2-beta-carbomethoxy-3-beta-(4-[123I]iodophenyl)tropane (beta-[123I]CIT). The reconstructed transaxial resolution of 3.5 mm full width at half-maximum and the system sensitivity of 0.081 c/s/kBq using a 2.0-mm pinhole collimator aperture provided adequate spatial detail and sufficient sensitivity for imaging striatal beta-[123I]CIT uptake. SPECT images, coregistered onto a MRI template, showed high accuracy in the coronal and transverse planes (maximum mismatch of 1.3 mm). Following estimation of the in vivo binding equilibrium of beta-[123I]CIT in the healthy rat striatum, we evaluated the 6-hydroxydopamine-induced loss of striatal DAT function using beta-[123I]CIT SPECT and MRI coregistration and correlated these findings with dopaminergic cell counts in the substantia nigra pars compacta using TH immunohistochemistry. A subtotal unilateral DAT deficit was detected by beta-[123I]CIT SPECT in all animals which correlated significantly with the cell counting of the remaining dopaminergic neurons. beta-[123I]CIT pinhole SPECT provides a powerful and widely available tool for in vivo investigations of rat striatal DAT function. In contrast to classical autoradiography, the present method will be helpful in imaging dynamic changes of neurotransmission in the CNS by virtue of serial study designs. Depending on SPECT ligand availability, a wide range of other CNS receptors may be imaged as well using the presented in vivo technique.

Preferential increases in nucleus accumbens dopamine after systemic cocaine administration are caused by unique characteristics of dopamine neurotransmission

In vivo voltammetry was used to investigate the preferential increase of extracellular dopamine in the nucleus accumbens relative to the caudate-putamen after systemic cocaine administration. In the first part of this study, cocaine (40 mg/kg, i.p.) was compared with two other blockers of dopamine uptake, nomifensine (10 mg/kg, i.p.) and 3beta-(p-chlorophenyl)tropan-2beta-carboxylic acid p-isothiocyanatophenylmethyl ester hydrochloride (RTI-76; 100 nmol, i.c.v.), to assess whether the inhibitory mechanism of cocaine differed in the two regions. All three drugs robustly increased electrically evoked levels of dopamine, and cocaine elevated dopamine signals to a greater extent in the nucleus accumbens. However, kinetic analysis of the evoked dopamine signals indicated that cocaine and nomifensine increased the K(m) for dopamine uptake whereas the dominant effect of RTI-76 was a decrease in V(max). Under the present in vivo conditions, therefore, cocaine is a competitive inhibitor of dopamine uptake in both the nucleus accumbens and caudate-putamen. Whether the preferential effect of cocaine was mediated by regional differences in the presynaptic control of extracellular DA that are described by rates for DA uptake and release was examined next by a correlation analysis. The lower rates for dopamine release and uptake measured in the nucleus accumbens were found to underlie the preferential increase in extracellular dopamine after cocaine. This relationship explains the paradox that cocaine more effectively increases accumbal dopamine despite identical effects on the dopamine transporter in the two regions. The mechanism proposed for the preferential actions of cocaine may also mediate the differential effects of psychostimulant in extrastriatal regions and other uptake inhibitors in the striatum.

A combined electrophysiological and video data acquisition system using a single computer

Numerous experimental paradigms in behavioral electrophysiology and neuroethology require simultaneous recording of neural signals and behavior. A computer fitted with an analog to digital converter and a frame grabber was configured to perform both tasks. The analog to digital converter collected electrophysiological data while the frame grabber recorded video images. Since spike and image information were present in one computer, arbitrary combinations of electrophysiological and behavioral parameters could be used as the basis of an operant conditioning paradigm. The system was used to record subicular cell firing in rats performing a place search task. The computer monitored the output of the analog to digital converter for supra-threshold events. When one was detected, a block of samples (pre- and post-trigger) was stored in memory. The same computer also scanned every video frame to find the rat, and recorded a image of its behavior. The location of the rat was then quickly calculated. If it satisfied the task conditions, a brain reward pathway (medial forebrain bundle) was stimulated. The recording of neural and image data was monitored in real-time by writing spike waveforms and location data directly to video card RAM.

LESIONS IN THE MEDIAL FOREBRAIN BUNDLE: DELAYED EFFECTS ON SENSITIVITY TO ELECTRIC SHOCK

Rats with bilateral lesions in the medial forebrain bundle demonstrate both an increased sensitivity to electric shock, as reflected by a lowered jump threshold, and a decrease in the concentration of serotonin in the brain. Both effects of the lesion are characterized by a delayed time of onset and gradual development, which approximates the time required for progressive nerve degeneration in the central nervous system. It is suggested that this behavioral effect of bilateral lesions in the medial forebrain bundle may be due to a central denervation supersensitivity.

Diagonal ventral forebrain continuum has overlapping telencephalic inputs and brainstem outputs which may represent loci for limbic/autonomic integration

Growing evidence indicates that three areas within the mammalian basal forebrain share many common features. Based on the similarity of connections and their adjacent spacial proximity, three forebrain nuclei are referred to as a continuum. The components of this diagonal ventral forebrain continuum (DVFC) are the central nucleus of the amygdala, the sublenticular portion of the substantia innominata, and the lateral bed nucleus of the stria terminalis. A primary concern and terminal goal of this study is to determine whether the region of this continuum which projects to the brainstem autonomic nuclei such as the vagal nuclei or the parabrachial nuclei also receives inputs from the basolateral amygdala. The first phase of this study involved determining what autonomic regions receive projections from the basal forebrain. The vagal complex and the parabrachial nuclei were found to receive the densest inputs from the DVFC. The topographic distribution of the respective retrogradely labeled cells and their collateral status is described. The second phase involved looking at afferent inputs from brainstem nuclei. The parabrachial nucleus sends reciprocal projections back to the continuum, which generally overlap the neurons which project back to the brainstem visceral nuclei. The third phase of the study indicated that the cells of the basolateral amygdala contribute a major terminal field which overlaps those cells of the basal forebrain continuum which in turn project to either the nucleus of the solitary tract or the parabrachial nucleus. The possibility that the circuits implied in this study represent the neural circuitry whereby emotional stimuli result in changes in visceral activity is addressed.

Short-term treatments with haloperidol or bromocriptine do not alter the density of the monoamine vesicular transporter in the substantia nigra

[3H]dihydrotetrabenazine ([3H]TBZOH) was used to label the monoamine vesicular transporter in the rat substantia nigra. An accumulation of neuronal vesicles in the substantia nigra pars compacta was observed after blockade of the fast axonal transport by a microinjection of colchicine (10 micrograms/2 microliters) into the medial forebrain bundle. This accumulation was measured after sustained 2-day pharmacological modifications of the central dopaminergic transmission. It was not modified after s.c. administration of either the direct dopamine (DA) receptor agonist bromocriptine (four injections of 4 or 6 mg/kg) or the DA receptor antagonist haloperidol (four injections of 0.5-1-1.5-2 mg/kg). Thus, it appears that these pharmacological modifications, imposed to the activity of the nigro-striatal dopaminergic system during 2 days, have no consequence on the rate of synthesis of its vesicles.

Does GFAP mRNA and mitochondrial benzodiazepine receptor binding detect serotonergic neuronal degeneration in rat?

Intracerebroventricularly (ICV) injected 5,7-dihydroxytryptamine (5,7-DHT), which reduced by 70-90% forebrain serotonin levels, significantly raised glial fibrillary acidic protein (GFAP) mRNA levels in the hippocampus and nucleus raphe dorsalis 5 days but not 15 days after the lesion. A significant increase of mitochondrial benzodiazepine receptors (MBR), measured by binding autoradiography of 3H-PK 11195, was found in the nucleus raphe dorsalis 5 and 15 days after the ICV 5,7-DHT and also in the hippocampus, ventral tegmental area, and substantia nigra at 15 days. No significant effect was observed in the striatum and cortex for either GFAP mRNA or MBR binding. Unlike the ICV route, bilateral injection of 5,7-DHT into the medial forebrain bundle, which caused a 65-90% reduction of serotonin levels in different forebrain regions, significantly raised GFAP mRNA and MBR binding only at the site of injection with no effect in hippocampus, striatum, and cortex. MBR binding slightly increased in the nucleus raphe dorsalis 15 days after the lesion. High doses of d-fenfluramine (10 mg/kg intraperitoneally twice daily for 4 days) caused 80-90% reduction of serotonin levels 5 days after the last injection but did not change the GFAP mRNA or the MBR binding in any of the brain regions considered. These findings suggest that the effect of 5,7-DHT on microglial and glial markers is probably related to a nonspecific interaction with other neuronal systems besides the serotonin or to direct interaction with glial cells; the use of these parameters for detecting selective degeneration of serotonin axons presents some obvious limitations.

A quantitative estimate of the role of striatal D-2 receptor proliferation in dopaminergic behavioral supersensitivity: the contribution of mesolimbic dopamine to the magnitude of 6-OHDA lesion-induced agonist sensitivity in the rat

Rats with unilateral depletions of neostriatal dopamine display increased sensitivity to dopamine agonists estimated to be 30 to 100 x in the 6-hydroxydopamine (6-OHDA) rotational model. Given that mild striatal dopamine D-2 receptor proliferation occurs (20-40%), it is difficult to explain the extent of behavioral supersensitivity by a simple increase in receptor density. This study was designed to investigate the quantitative aspects of the rotational behavior model utilizing constrained non-linear curve fitting routines. A dose-response curve for the rotational response arising from apomorphine stimulation of the normosensitive striatum was obtained in animals bearing unilateral lesions of striatal efferents (predominantly the striato-nigral pathway as previously described). After the control dose-response experiment, rats received a dopamine- (DA) depleting lesion in the contralateral hemisphere. In one group, 6-OHDA was infused into the medial forebrain bundle (MFB), a placement which is common in the literature and is known to deplete DA in both the striatum and nucleus accumbens. In a second group of rats, 6-OHDA was infused into the globus pallidus at a site which depletes caudate DA, but leaves n. accumbens DA relatively intact. The two experimental groups were tested in identical apomorphine-induced rotation dose-response experiments. The ED50's of the MFB- and caudate-lesioned rats were reduced by 36 and 5.8 fold, respectively, as compared to the control dose-response curve. The MFB and caudate lesions depleted striatal DA and produced a 30 and 36% increase in striatal D-2 binding sites, respectively. Modeling the behavioral and biochemical data with the null model for receptor occlusion indicated that increased striatal D-2 receptor density could account for the magnitude of behavioral supersensitivity in neither the MFB-lesioned group, nor even in the caudate-lesioned group. Thus simple up-regulation or D-2 receptors is unlikely to account for supersensitization as measured in the rotational model. Further, we suggest that quantitative modeling of such hypotheses is a valuable experimental technique for assessing relationships between biochemical and behavioral variables.

Stimulation of the nigrostriatal dopamine system inhibits both heat production and heat loss mechanisms in rats

The effects of stimulating the pars compacta of the substantia nigra (SNC) on thermoregulation were assessed in normal rats, in rats with chemical lesion of the SNC dopamine (DA) pathways and in rats with striatal DA receptor blockade. Electrical stimulation of the SNC produced hypothermia, decreased metabolism and/or cutaneous vasoconstriction in rats at ambient temperatures (Ta) below 22 degrees C, as well as hyperthermia and cutaneous vasoconstriction in rats at Ta of 30 degrees C. Microinjection of an excitotoxic amino acid (kainic acid) at the same brain sites also produced the same thermal responses. In vivo voltammetric studies revealed that electrical or chemical stimulation of the SNC produced an increase in striatal DA release. The enhanced striatal DA release induced by SNC stimulation was attenuated in rats after selective destruction of the nigrostriatal DA pathway by administration of 6-hydroxydopamine into the medial forebrain bundle. In addition, the magnitude of the thermal responses produced by the SNC stimulation in the cold was attenuated by selective bilateral destruction of the nigrostriatal DA pathways or selective blockade of the striatal DA produced by intrastriatal infusion of haloperidol, a DA receptor antagonist. The results indicate that stimulation of the SNC inhibits both heat production and heat loss mechanisms in the rat.

Parametric manipulations and fixed-interval self-stimulation

Three experiments investigated hypothalamic self-stimulation under a fixed-interval (FI) reinforcement schedule. An FI 20-s schedule was chosen to reduce stimulation density in order to minimize the influence of priming effects or stimulation aftereffects that can affect responding under other schedules of reinforcement. The first experiment showed that the influence of train duration is greatest at levels up to 1 s and thereafter level off over a wide range of train durations (1-32 s). The second experiment showed that altering frequency, current, or pulse width produced almost identical changes in FI responding. These findings show that the neutral network subserving hypothalamic self-stimulation simply integrates the amount of charge over time. It is relatively insensitive to the combination of stimulation parameters that make up a given waveform. In the third experiment, the chronaxies from the strength-duration curves indicate the neural substrate supporting self-stimulation has a great current-integrating capacity. Together, these experiments show that varying the amount of brain stimulation produce large and consistent changes in a number of FI response measures. These measures effectively describe different attributes of FI performance and include response rate, the postreinforcement pause, interresponse times of short duration and the temporal distribution of responses within the interval.

Behavioral effects of a dimethylsulfonium analog of dopamine after injection into the nucleus accumbens and the striatum

We have previously synthesized a chemical analog of dopamine (DA) in which the amine group has been replaced by a permanently charged dimethylsulfonium group. In the present study, we have determined whether this compound can exert DA agonist activity in the nucleus accumbens by comparing its effects with those of DA. When DA was injected into the nucleus accumbens of rats pretreated with nialamide, a monoamine oxidase inhibitor, there was marked stimulation of locomotor activity. Similarly, after intraaccumbens injection, the sulfonium analog also produced a marked stimulation of locomotor activity, and this effect was inhibited by the DA receptor antagonist, haloperidol (0.2 mg/kg, IP). However, the sulfonium analog did not stimulate locomotor activity when rats were pretreated with saline instead of nialamide. In addition, the stimulation of locomotor activity produced by the sulfonium analog in rats pretreated with nialamide was completely inhibited by the DA synthesis inhibitor, alpha-methyl-p-tyrosine. These results suggest that the stimulation of locomotor activity by the sulfonium analog is mediated indirectly through the release of DA. The sulfonium analog was able to produce marked contralateral circling after it was injected into the striatum of rats on the side of the brain in which DA nerve terminals were previously destroyed with 6-hydroxydopamine. Similarly, the sulfonium analog produced a marked stimulation of locomotor activity after it was injected into the nucleus accumbens of rats that were previously injected into this region with 6-hydroxydopamine. These results suggest that the sulfonium analog of dopamine can exert direct as well as indirect DA agonist activity.

Effect of chronic apomorphine on the development of denervation supersensitivity

We hypothesised that it would be possible to prevent the development of post-synaptic dopamine receptor supersensitivity to 6-hydroxydopamine lesions of the nigro-striatal tract in rats if they were constantly infused with the dopamine agonist apomorphine. Using osmotic minipumps to infuse apomorphine for 15 days in unilaterally lesioned rats, it was possible to delay the development of supersensitivity of the lesioned side for 9 days but not to prevent its eventual appearance. At the same time, evidence for the development of subsensitivity of presynaptic dopamine receptors of the intact side following chronic infusion of apomorphine was inferred from the production of rotations directed towards the lesioned side.

Effect of hypothalamic cooling on the tonic vibration reflex of gastrocnemius muscle in cats

The tonic vibration reflex (TVR) in a medial gastrocnemius muscle (MG) was analyzed in 28 cats anesthetized with pentobarbital sodium while the preoptic-anterior hypothalamic region (PO-AH) was locally cooled or warmed in a thermoneutral environment. Cooling of the PO-AH did not produce shivering or changes in rectal and skin temperatures, but it brought about facilitation (16/28 cats) or inhibition (9/28) of the TVR in the MG. A few cats (3/28) showed inconsistent alteration of the TVR. Warming of the PO-AH did not produce any changes in the TVR of the MG. Histological identification of thermode placements revealed that in cats having the facilitatory response of the TVR, the thermodes were localized at regions caudal to A 14.0 mm and most of the thermodes in those having the inhibitory response were rostral to A 14.0 mm, except for two cases. Bilateral microinjection of a small quantity of anesthetic agent into the medial forebrain bundle (MFB) at the level of the mamillary body abolished the facilitatory effect of PO-AH cooling on the TVR. The results suggest that the spinal motor system is influenced by the PO-AH's sensitivity to local temperature and that the MFB constitutes part of the efferent pathway of the hypothalamic influence.

Effects of serotonin neurotoxins on rotational behavior in the rat

Injections of p-CA or 5,7-DHT into the MRN caused decreases in 5-HT and 5-HIAA levels in the cortex and striatum. They also caused a decrease in 5-HT turnover in the cortex and an increase in striatal DA turnover. The unilaterally injected rats showed contralateral rotation after amphetamine or apomorphine administration. There was a significant correlation among the rate of rotation, the decrease in cortical 5-HT turnover, and the increase in striatal DA turnover. Injection of 5,7-DHT into the SN produced the same biochemical and behavioral changes as did MRN lesions, suggesting that the changes induced by MRN lesions might be due to a direct projection from the raphe to the substantia nigra. Injection of 5,7-DHT into the MFB caused ipsilateral rotation after injection of amphetamine or apomorphine and a decrease in DA turnover in the striatum. There was a significant correlation among the rate of rotation, the decrease in 5-HT turnover in the cortex, and the decrease in striatal DA turnover in the MFB-lesioned rats. These effects might be due to a projection from the DRN to cell bodies in the striatum.

The lateral hypothalamic area. An ultrastructural analysis

An ultrastructural analysis of the rat lateral hypothalamic area (LHA) was undertaken in order to provide an initial step in the characterization of this complex area which appears to participate in a number of important neural functions. The organization of the normal tuberal LHA was compared to the area following acute and chronic denervating lesions. In the normal animal, the principal features of the LHA are the presence of lateral hypothalamic neurons, a major sagittal pathway (the medial forebrain bundle, MFB) and the interposed neuropil richly populated by a variety of synaptic terminal types. Alterations in the synaptic organization of the LHA following rostral and caudal MFB lesions were most pronounced in animals with acute and chronic caudal lesions. A 10% reduction of synaptic terminals containing 800-1000 A diameter dense core vesicles and a 10% increase in terminals containing lucent core vesicles was observed in animals with caudal lesions while no significant redistribution of synaptic terminal types occurred with rostral lesions. The preliminary degeneration experiments indicate that identification of the numerous and diverse afferents to the LHA neuropil may be aided by this method but that a detailed and systematic ultrastructural analysis will be required to identify sources of input with certainty.

The effect of lesions of the accessory optic tract terminal nuclei on the gonadal response to light in ferrets

Electrolytic lesions were made in the lateral (LTN), medial (MTN) or in both terminal nuclei of the accessory optic tract in female ferrets. Either the ipsilateral or contralateral eye was removed. Complete destruction of both nuclei, as assessed by both histological and autoradiographic criteria, did not prevent the acceleration of estrus by artificial long days (L:D, 14:10) in any animal. Although the ferret has no anterior (inferior) accessory tract, lesions were also made in the medial forebrain bundle (MFB) area in ipsilaterally and contralaterally enucleated animals. Estrus still occurred in response to artificial long days in these animals. The experiments suggest that the accessory optic system in the ferret does not transmit information to the pineal regulating the annual breeding season.