Differential projections from the lateral habenula to the rostromedial tegmental nucleus and ventral tegmental area in the rat

The mesopontine rostromedial tegmental nucleus (RMTg) is a mostly ?-aminobutyric acid (GABA)ergic structure believed to be a node for signaling aversive events to dopamine (DA) neurons in the ventral tegmental area (VTA). The RMTg receives glutamatergic inputs from the lateral habenula (LHb) and sends substantial GABAergic projections to the VTA, which also receives direct projections from the LHb. To further specify the topography of LHb projections to the RMTg and VTA, small focal injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin were aimed at different subdivisions of the LHb. The subnuclear origin of LHb inputs to the VTA and RMTg was then confirmed by injections of the retrograde tracer cholera toxin subunit b into the VTA or RMTg. Furthermore, we compared the topographic position of retrogradely labeled neurons in the RMTg resulting from VTA injections with that of anterogradely labeled axons emerging from the LHb. As revealed by anterograde and retrograde tracing, LHb projections were organized in a strikingly topographic manner, with inputs to the RMTg mostly arising from the lateral division of the LHb (LHbL), whereas inputs to the VTA mainly emerged from the medial division of the LHb (LHbM). In the RMTg, profusely branched LHb axons were found in close register with VTA projecting neurons and were frequently apposed to the latter. Overall, our findings demonstrate that LHb inputs to the RMTg and VTA arise from different divisions of the LHb and provide direct evidence for a disynaptic pathway that links the LHbL to the VTA via the RMTg. J. Comp. Neurol. 520:12781300, 2012. (C) 2011 Wiley Periodicals, Inc.

Activity of brainstem cholinergic neurons during 22 kHz ultrasonic vocalization in rats /

Adult rats emit 22 kHz ultrasonic alann calls in aversive situations. This type of call IS a component of defensive behaviour and it functions predominantly to warn conspecifics about predators. Production of these calls is dependent on the central cholinergic system. The laterodorsal tegmental nucleus (LDT) and pedunculopontine tegmental nucleus (PPT) contain largely cholinergic neurons, which create a continuous column in the brainstem. The LDT projects to structures in the forebrain, and it has been implicated in the initiation of 22 kHz alarm calls. It was hypothesized that release of acetylcholine from the ascending LDT terminals in mesencephalic and diencephalic areas initiates 22 kHz alarm vocalization. Therefore, the tegmental cholinergic neurons should be more active during emission of alarm calls. The aim of this study was to demonstrate increased activity of LDT cholinergic neurons during emission of 22 kHz calls induced by air puff stimuli. Immunohistochemical staining of the enzyme choline acetyltransferase identified cell bodies of cholinergic neurons, and c-Fos immunolabeling identified active cells. Double labeled cells were regarded as active cholinergic cells. There were significantly more (pnucleus. Results suggest that there are cholinergic and non-cholinergic cells, which are selectively active in the LDT during emission of 22 kHz alarm calls.

Melanin-concentrating hormone projections to areas involved in somatomotor responses

The lateral hypothalamic area (LHA) participates in the integration of sensory information and somatomotor responses associated with hunger and thirst. Although the LHA is neurochemically heterogeneous, a particularly high number of cells express melanin-concentrating hormone (MCH), which has been reported to play a role in energy homeostasis. Treatment with MCH increases food intake, and MCH mRNA is overexpressed in leptin-deficient (ob/ob) mice. Mice lacking both MCH and leptin present reduced body fat, mainly due to increased resting energy expenditure and locomotor activity. Dense MCH innervation of the cerebral motor cortex (MCx) and the pedunculopontine tegmental nucleus (PPT), both related to motor function, has been reported. Therefore, we postulated that a specific group of MCH neurons project to these areas. To investigate our hypothesis, we injected retrograde tracers into the MCx and the PPT of rats, combined with immunohistochemistry. We found that 25% of the LHA neurons projecting to the PPT were immunoreactive for MCH, and that 75% of the LHA neurons projecting to the MCx also contained MCH. Few MCH neurons were found to send collaterals to both areas. We also found that 15% of the incerto-hypothalamic neurons projecting to the PPT expressed MCH immunoreactivity. Those neurons preferentially innervated the rostral PPT. In addition, we observed that the MCH neurons express glutamic acid decarboxylase mRNA, a gamma-aminobutyric acid (GABA) synthesizing enzyme. We postulate that MCH/GABA neurons are involved in the inhibitory modulation of the innervated areas, decreasing motor activity in states of negative energy balance. (C) 2007 Published by Elsevier B.V.

Segregated anatomical input to sub-regions of the rodent superior colliculus associated with approach and defense

The superior colliculus (SC) is responsible for sensorimotor transformations required to direct gaze toward or a way from unexpected, biologically salient events. Significant changes in the external world are signaled to SC through primary multisensory afferents, spatially organized according to a retinotopic topography. For animals, where anunexpected event could indicate the presence of either predator or prey, early decisions to approach or avoid are particularly important. Rodents' ecology dictates predators are most often detected initially as movements in upper visual field (mapped in medial SC), while appetitive stimuli are normally found in lower visual field (mapped in lateral SC). Our purpose was to exploit this functional segregation to reveal neural sites that can bias or modulate initial approach or avoidance responses. Small injections of Fluoro-Gold were made into medial or lateral sub-regions of intermediate and deep layers of SC (SCm/SCl). A remarkable segregation of input to these two functionally defined areas was found. (i) There were structures that projected only to SCm (e.g., specific cortical areas, lateral geniculate and suprageniculate thalamic nuclei, ventromedial and premammillary hypothalamic nuclei, and several brain-stem areas) or SCl (e.g., primary somatosensory cortex representing upper body parts and vibrissae and parvicellular reticular nucleus in the brainstem). (ii) Other structures projected to both SCm and SCl but from topographically segregated populations of neurons (e.g., zona incerta and substantia nigra pars reticulata). (iii) There were a few brainstem areas in which retrogradely labeled neurons were spatially overlapping (e.g., pedunculopontine nucleus and locus coeruleus). These results indicate significantly more structures across the rat neuraxis are in a position to modulate defense responses evoked from SCm, and that neural mechanisms modulating SC-mediated defense or appetitive behavior are almost entirely segregated.

Antinociceptive effect of stimulating the zona incerta with glutamate in rats

The zona incerta (ZI) is a subthalamic nucleus connected to several structures, some of them known to be involved with antinociception. The 21 itself may be involved with both antinociception and nociception. The antinociceptive effects of stimulating the ZI with glutamate using the rat tail-flick test and a rat model of incision pain were examined. The effects of intraperitoneal antagonists of acetylcholine, noradrenaline, serotonin, dopamine, or opioids on glutamate-induced antinociception from the ZI in the tail-flick test were also evaluated. The injection of glutamate (7 mu g/0.25 mu l) into the ZI increased tail-flick latency and inhibited post-incision pain, but did not change the animal performance in a Rota-rod test. The injection of glutamate into sites near the ZI was non effective. The glutamate-induced antinociception from the ZI did not occur in animals with bilateral lesion of the dorsolateral funiculus, or in rats treated intraperitoneally with naloxone (1 and 2 m/kg), methysergide (1 and 2 m/kg) or phenoxybenzamine (2 m/kg), but remained unchanged in rats treated with atropine, mecamylamine, or haloperidol (all given at doses of 1 and 2 m/kg). We conclude that the antinociceptive effect evoked from the ZI is not due to a reduced motor performance, is likely to result from the activation of a pain-inhibitory mechanism that descends to the spinal cord via the dorsolateral funiculus, and involves at least opioid, serotonergic and a-adrenergic mechanisms. This profile resembles the reported effects of these antagonists on the antinociception caused by stimulating the periaqueductal gray or the pedunculopontine tegmental nucleus. (C) 2012 Elsevier Inc. All rights reserved.

Immunohistochemical study of laterodorsal tegmental neurons active during 22kHz vocalization /

An ascending cholinergic projection, which originates in the laterodorsal tegmental nucleus (LDT), was implicated in the initiation of ultrasonic vocalization. The goal of this study was to histochemically examine the activity the LDT following ultrasonic calls induced by two methods. It was hypothesized that cholinergic LDT cells would be more active during air puffinduced vocalization than carbachol-induced one. Choline acetyltransferase (ChAT), and cFos protein were visualized histochemically as markers of cholinergic calls and cellular activity, respectively. Results indicated that animals vocalizing after carbachol, but not after air puff, had a significantly higher number of Fos labeled nuclei within the LDT than non vocalizing controls. A significantly higher number of doublelabeled neurons were discovered in the LDT of vocalizing animals (in both groups) as compared to control conditions. Thus, there were significantly more active cholinergic cells in the LDT of vocalizing than non-vocalizing rats for both methods of call induction.

Influência de gênero e do ciclo estral no reflexo auditivo de sobressalto em ratos Wistar

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A susceptibilidade à nicotina e etanol é afetada pela exposição à nicotina, fumaça de cigarro e etanol durante o período gestacional: alterações comportamentais e eletrofisiológicas no período pós-natal de camundongos

Uma questão particularmente relevante é o fato de exposições precoces a drogas de abuso durante o desenvolvimento potencialmente aumentarem a susceptibilidade a estas drogas posteriormente durante o desenvolvimento. No presente estudo utilizando estudos comportamentais e eletrofisiológicos, investigamos efeitos tardios da exposição de camundongos à fumaça de cigarro, à nicotina e ao etanol durante o período que corresponde à gestação em humanos. Para tal, esta tese foi dividida em 2 estudos. No Estudo 1, submetemos camundongos durante o período que corresponde à gestação de humanos à fumaça de cigarro e/ou etanol visando investigar se a estas drogas de abuso, separadamente ou quando combinadas, programam maior susceptibilidade aos efeitos da nicotina durante a adolescência (PN30) ou idade adulta (PN90). Para avaliar a susceptibilidade, utilizamos 3 testes: campo aberto (CA), preferencia pela nicotina (PPN) e preferencia condicionada por lugar (CPP). No Estudo 2, os animais foram expostos a nicotina durante o período gestacional e, no período que corresponde à infância (PN9 a PN20), fatias de cérebro contendo o núcleo tegumental laterodorsal (LDT) foram expostas a etanol. Este núcleo foi escolhido uma vez que estudos recentes indicam sua participação em mecanismos de toxicodependência. Foram realizados registros eletrofisiológicos de uma única célula. No Estudo 1, identificamos maior sensibilidade para os efeitos da reexposição à nicotina na adolescência quando comparada com a idade adulta . Em animais testados no CA durante a adolescência, a nicotina foi capaz de causar aumento da atividade locomotora nos animais controle, previamente expostos à fumaça de cigarro e ao etanol. Contudo, em animais expostos à fumaça combinada com etanol, não houve aumento da locomoção. Na idade adulta, a nicotina causou um aumento da atividade locomotora no CA somente nos animais expostos à fumaça de cigarro. Quanto ao CPP, a exposição prévia à fumaça de cigarro e ao etanol causaram aumento da resposta condicionada à nicotina em fêmeas adolescentes. Nos animais previamente expostos à combinação entre fumaça de cigarro e etanol, a resposta condicionada à nicotina não atingiu significância estatística. Não houve alterações na idade adulta. A exposição a fumaça de cigarro e/ou etanol não afetou a PPN. No Estudo 2, os dados eletrofisiológicos mostraram que a exposição pré-natal à nicotina foi capaz de alterar as correntes de despolarização basais e o potencial de repouso de células do LDT A nicotina também foi capaz de alterar as respostas deste núcleo ao etanol reduzindo as correntes de despolarização e aumentando, embora que não de forma significativa, as correntes inibitórias. De acordo com estes dados, injurias causadas pela exposição à fumaça do cigarro, à nicotina isoladamente, e ao etanol durante o desenvolvimento são capazes de perdurar por um logo tempo na vida do individuo, alterando as respostas a comportamentais e celulares a uma exposição tardia à nicotina e ao etanol.

Pedunculopontine nucleus deep brain stimulation produces sustained improvement in primary progressive freezing of gait

Objective: To assess the efficacy of bilateral pedunculopontine nucleus (PPN) deep brain stimulation (DBS) as a treatment for primary progressive freezing of gait (PPFG). ------ ----- Methods: A patient with PPFG underwent bilateral PPN-DBS and was followed clinically for over 14 months. ------ ----- Results: The PPFG patient exhibited a robust improvement in gait and posture following PPN-DBS. When PPN stimulation was deactivated, postural stability and gait skills declined to pre-DBS levels, and fluoro-2-deoxy-d-glucose positron emission tomography revealed hypoactive cerebellar and brainstem regions, which significantly normalised when PPN stimulation was reactivated. ------ ----- Conclusions: This case demonstrates that the advantages of PPN-DBS may not be limited to addressing freezing of gait (FOG) in idiopathic Parkinson's disease. The PPN may also be an effective DBS target to address other forms of central gait failure.

A spatiotemporal analysis of gait freezing and the impact of pedunculopontine nucleus stimulation

Gait freezing is an episodic arrest of locomotion due to an inability to take normal steps. Pedunculopontine nucleus stimulation is an emerging therapy proposed to improve gait freezing, even where refractory to medication. However, the efficacy and precise effects of pedunculopontine nucleus stimulation on Parkinsonian gait disturbance are not established. The clinical application of this new therapy is controversial and it is unknown if bilateral stimulation is more effective than unilateral. Here, in a double-blinded study using objective spatiotemporal gait analysis, we assessed the impact of unilateral and bilateral pedunculopontine nucleus stimulation on triggered episodes of gait freezing and on background deficits of unconstrained gait in Parkinson’s disease. Under experimental conditions, while OFF medication, Parkinsonian patients with severe gait freezing implanted with pedunculopontine nucleus stimulators below the pontomesencephalic junction were assessed during three conditions; off stimulation, unilateral stimulation and bilateral stimulation. Results were compared to Parkinsonian patients without gait freezing matched for disease severity and healthy controls. Pedunculopontine nucleus stimulation improved objective measures of gait freezing, with bilateral stimulation more effective than unilateral. During unconstrained walking, Parkinsonian patients who experience gait freezing had reduced step length and increased step length variability compared to patients without gait freezing; however, these deficits were unchanged by pedunculopontine nucleus stimulation. Chronic pedunculopontine nucleus stimulation improved Freezing of Gait Questionnaire scores, reflecting a reduction of the freezing encountered in patients’ usual environments and medication states. This study provides objective, double-blinded evidence that in a specific subgroup of Parkinsonian patients, stimulation of a caudal pedunculopontine nucleus region selectively improves gait freezing but not background deficits in step length. Bilateral stimulation was more effective than unilateral.