Agonistic-like responses from the torus semicircularis dorsalis elicited by GABA A blockade in the weakly electric fish Gymnotus carapo

Findings by our group have shown that the dorsolateral telencephalon of Gymnotus carapo sends efferents to the mesencephalic torus semicircularis dorsalis (TSd) and that presumably this connection is involved in the changes in electric organ discharge (EOD) and in skeletomotor responses observed following microinjections of GABA A antagonist bicuculline into this telencephalic region. Other studies have implicated the TSd or its mammalian homologue, the inferior colliculus, in defensive responses. In the present study, we explore the possible involvement of the TSd and of the GABA-ergic system in the modulation of the electric and skeletomotor displays. For this purpose, different doses of bicuculline (0.98, 0.49, 0.245, and 0.015 mM) and muscimol (15.35 mM) were microinjected (0.1 æL) in the TSd of the awake G. carapo. Microinjection of bicuculline induced dose-dependent interruptions of EOD and increased skeletomotor activity resembling defense displays. The effects of the two highest doses showed maximum values at 5 min (4.3 ± 2.7 and 3.8 ± 2.0 Hz, P < 0.05) and persisted until 10 min (11 ± 5.7 and 8.7 ± 5.2 Hz, P < 0.05). Microinjections of muscimol were ineffective. During the interruptions of EOD, the novelty response (increased frequency in response to sensory novelties) induced by an electric stimulus delivered by a pair of electrodes placed in the water of the experimental cuvette was reduced or abolished. These data suggest that the GABA-ergic mechanisms of the TSd inhibit the neural substrate of the defense reaction at this midbrain level.

The pedunculopontine nucleus: its role in the genesis of movement disorders

The pedunculopontine nucleus (PPN) is located in the dorso-lateral part of the ponto-mesencephalic tegmentum. The PPN is composed of two groups of neurons: one containing acetylcholine, and the other containing non-cholinergic neurotransmitters (GABA, glutamate). The PPN is connected reciprocally with the limbic system, the basal ganglia nuclei (globus pallidus, substantia nigra, subthalamic nucleus), and the brainstem reticular formation. The caudally directed corticolimbic-ventral striatal-ventral pallidal-PPN-pontomedullary reticular nuclei-spinal cord pathway seems to be involved in the initiation, acceleration, deceleration, and termination of locomotion. This pathway is under the control of the deep cerebellar and basal ganglia nuclei at the level of the PPN, particularly via potent inputs from the medial globus pallidus, substantia nigra pars reticulata and subthalamic nucleus. The PPN sends profuse ascending cholinergic efferent fibers to almost all the thalamic nuclei, to mediate phasic events in rapid-eye-movement sleep. Experimental evidence suggests that the PPN, along with other brain stem nuclei, is also involved in anti-nociception and startle reactions. In idiopathic Parkinson's disease (IPD) and parkinson plus syndrome, overactive pallidal and nigral inhibitory inputs to the PPN may cause sequential occurrences of PPN hypofunction, decreased excitatory PPN input to the substantia nigra, and aggravation of striatal dopamine deficiency. In addition, neuronal loss in the PPN itself may cause dopamine-r esistant parkinsonian deficits, including gait disorders, postural instability and sleep disturbances. In patients with IPD, such deficits may improve after posteroventral pallidotomy, but not after thalamotomy. One of the possible explanations for such differences is that dopamine-resistant parkinsonian deficits are mediated to the PPN by the descending pallido-PPN inhibitory fibers, which leave the pallido-thalamic pathways before they reach the thalamic targets.

Participation of nitric oxide in the nucleus isthmi in CO2-drive to breathing in toads

The nucleus isthmi (NI) is a mesencephalic structure of the amphibian brain. It has been reported that NI plays an important role in integration of CO2 chemoreceptor information and glutamate is probably involved in this function. However, very little is known about the mechanisms involved. Recently, it has been shown that nitric oxide synthase (NOS) is expressed in the brain of the frog. Thus the gas nitric oxide (NO) may be involved in different functions in the brain of amphibians and may act as a neurotransmitter or neuromodulator. We tested the hypothesis that NO plays a role in CO2-drive to breathing, specifically in the NI comparing pulmonary ventilation, breathing frequency and tidal volume, after microinjecting 100 nmol/0.5 µl of L-NAME (a nonselective NO synthase inhibitor) into the NI of toads (Bufo paracnemis) exposed to normocapnia and hypercapnia. Control animals received microinjections of vehicle of the same volume. Under normocapnia no significant changes were observed between control and L-NAME-treated toads. Hypercapnia caused a significant (P<0.01) increase in ventilation only after intracerebral microinjection of L-NAME. Exposure to hypercapnia caused a significant increase in breathing frequency both in control and L-NAME-treated toads (P<0.01 for the control group and P<0.001 for the L-NAME group). The tidal volume of the L-NAME group tended to be higher than in the control group under hypercapnia, but the increase was not statistically significant. The data indicate that NO in the NI has an inhibitory effect only when the respiratory drive is high (hypercapnia), probably acting on tidal volume. The observations reported in the present investigation, together with other studies on the presence of NOS in amphibians, indicate a considerable degree of phylogenetic conservation of the NO pathway amongst vertebrates.

Heterogeneity of median and lateral midbrain radial glia and astrocytes

In the developing mammalian midbrain, radial glial cells are divided into median formations and lateral radial systems with differential properties including rate and timing of cell proliferation, expression of cytoskeletal and calcium-binding proteins, storage of glycogen and relations to afferent fiber systems. To test hypothesis that radial glial cells of median and lateral midbrain sectors and/or their derivatives are heterogeneous in their relations with local neurons, an in vitro system has been developed and has also been characterized in terms of extracellular matrix (ECM) components. Confluent astrocyte cultures, derived from median (M) or lateral (L) embryonic mouse midbrain sectors, were used as substrates for culturing dissociated cells from median (m) or lateral (l) sectors of embryonic midbrains. In spite of the morphological invariance of glial substrates at confluency, cells that were plated onto these substrates and that were immunoreactive for neuronal markers (MAP2, polysialylated N-CAM or betaIII tubulin) showed differences in the aggregation of somata and in the length, caliber and branching of neurites. These differences, which depend mostly on the sector of origin of astrocytes (L: permissive, M: non-permissive for neuronal growth), suggest that the substrates may differ in adhesiveness and/or their carrying of growth-promoting vs. growth-interfering molecules. Indeed, L and M cultures differ in laminin deposition patterns (L: fibrillar, M: punctate pattern). Furthermore, sulfated glycosaminoglycans (s-GAGs) isolated from the pericellular (P), intracellular (I) and extracellular (E) compartments of these sectoral cultures also showed correlations with the ability to support neurite growth. The total amount of s-GAGs in M cultures was twice that in L cultures and was particularly high in the P compartment, with about 3 times as much heparan sulfate (HS) and about 15 times as much chondroitin sulfate (CS) in this fraction of M than in the corresponding compartment of L glia. Our results indicate that cultured astrocytes have heterogeneous properties including different organizatio of their extracellular matrix that reflect the roles played by their parent radial glia in regions favorable to axonal growth or barrier regions of the developing brain.

Effects of diazepam on fentanyl-induced epileptoid EGG activity and increase of multineuronal firing in limbic and mesencephalic brain structures

Electroencephalographic and clinical signs of epileptoid activity have been associated with the administration offentanyl during surgery in patients. These phenomena have been in turn related to changes in metabolic rate, oxygen consumption, and blood flow in specific brain structures both in humans and experimental animals. However, direct evidence showing changes in neuronal firing in specific brain regions during fentanyl-induced epileptoid activity has not been reported. Eight adult male cats with chronically implanted bipolar electrodes in the mesencephalic reticular formation, hippocampus, amygdala, and parieto-occipital cortex were included in the study. Different treatments i.e., vehicle-fentanyl or diazepam-fentanyl, were administered to the experimental animals at 7-day intervals under neuromuscular blockade and assisted ventilation. Electroencephalographic (EEG) seizures, grouped and isolated spikes, and significant increases of multineuronal activity (MUA) were elicited by fentanyl, 50 µg/kg iv, in these brain structures. Both EEG and MUA changes reached their maximal values within 6 min of fentanyl administration, and then diminished as time elapsed. Diazepam, 100, 200, or 400 µg/kg, but not 50 µg/kg iv, significantly reduced or prevented the fentanyl-induced epileptoid EEG activity and MUA increases. The present results show that both entanyl- induced epileptoid EEGactivity as wel as the concomitant increase in MUA of brain subcortical structures are part of the same epileptogenic phenomenon, mainly generated at limbic structures. In addition, the effects of fiazepamagainst both epileptoid EEG activity and increase of MUA of brain subcortical structures support the use of benzodiazepine as premedicants for fentanyl anesthesia in order to prevent or to reduce epileptoid phenomena that can results from opioid administration during the anesthetic procedures

Brain stem auditory evoked responses during the cold pressor test.

This study was conducted to determine changes, if any, in Brain stem auditory evoked responses (BAEP's) during the cold pressor test (CPT) in healthy human subjects. Thirteen subjects (age 18-25 yrs) were selected for the study. Their BAEP's were recorded using standardized technique employing 10-20 international electrode placement system and sound click stimuli of specified intensity, duration and frequency. The standard CPT was performed in the non-dominant hand and the BAEP's, heart rate and blood pressure were recorded before and during the CPT. The values of absolute peak latencies and amplitude of evoked responses were statistically analysed. The amplitude of wave V showed a significant increase (P < 0.05) during the CPT (0.47 +/- 0.203 and 0.37 +/- 0.174 mu v before and during CPT respectively). This could be due to interaction of activated central ascending monoaminergic pathways or nociceptive afferents with the midbrain auditory generator so as to increase it's activity.

Effect of lesions of areas of brain--stimulation reward of one region of brain on operant behaviour for receiving electrical stimulation into sites of another region and on operant behaviour for food reward.

It was aimed to study the effects of lesions of a self-stimulation (SS) area of one region of brain on the SS of another region, and on feeding behaviour in adult Wistar rats (males). The two regions proposed for study were the lateral hypothalamus (LH) and the substantia nigra-ventral tegmental area (SN-VTA). The objective was to elucidate whether each region had its own neural organization for SS behaviour or not, and whether the neural substrates of SS behaviour and feeding behaviour were one, or separate. Four bipolar electrodes were implanted bilaterally in LH and SN-VTA in each rat, and their SS pedal press rates for rewarding electrical stimulations were characterised. The rats were also trained in operant conditioning paradigm for receiving reward of food grains in FR-30 schedule. Their free-field food intake in home cages was measured. Later, electrolytic lesions of the four electrode sites were made one after another at 2-day intervals through the same biopolar electrodes. After each lesioning, the SS of the same and of the other electrode sites, and the operant performance of FR-30 food reward schedule, and daily free-field food intake (in home cage) were determined. Lesions of the LH SS site always disrupted SS-of contralateral LH but not of SN-VTA SS. Lesions of SN-VTA had not modified contralateral SN-VTA SS. A study of effects of ipsilateral lesions of LH SS site on SN-VTA SS, or of lesions of SN-VTA SS site on LH SS, revealed a range of changes, as were also effects on the FR-30 operant performance and daily food intake. Medium size lesions of SS area made in one region affected the SS of that area but not usually the SS of the other region. Large lesions of one region affected the SS of the other regions also. With large lesions, feeding behaviour also was affected, firstly of the operant type and secondly the free-field type.

Comparative assessment of pedal pressing rates of self-stimulation of hypothalamus and midbrain with both square wave and sine wave stimulus parameters.

In Wistar rats, the regional differences of pedal pressing rates of self-stimulation (SS) of lateral hypothalamus (LH) and substantia nigra-ventral tegmental area (SN-VTA) were assessed with electrodes implanted in both regions in each subject. Average of SS rates of SN-VTA sites was significantly higher than that of LH sites, tested with both sine wave and square wave types of stimuli. There was no significant difference in SS rates between males and females, and also in the females between different days of oestrus cycles. The high rates of robust SS observed in this study relative to SS rates reported in past literature were probably due not only to the placements of electrodes in the main substrates of SS, but also to the parameters of stimulus used (0.25 sec trains of sine waves through bipolar electrodes).

"Off" and "On" cell of the medulla oblongata as possible mediators of analgesia produced by mesencephalic and diencephalic stimulation in rats / Las celulas \"OFF\" y \"ON\" del bulbo raquideo como posibles mediadoras de la analgesia producida por estimulacion mesencefalica y diencefalica en ratas

The present study shows the effects of electrical`stimulation of mesencephalic and diencephalic structures on the activity of two types of neuron from the rostral ventromedial medulla,which are related to the nocifensive reflex known as tail flick response (TF). One type of neuron, the off-cell abruptly stops firing immediately before the tail is flicked, while the other type, the on-cell, increases firing just before tyhe flick. When electrical stimulation was applied to mesencephalic and diencephalic structure the TF was inhibited and, simultancously, both kinds of cell showed increment in their activities. On average,this increment was 81ñ22.09%for the off-cell, and 1563ñ257.66%for the on cell. Quantitative analysis showed a directly proportional relationship between the activation of the firing rate of both kinds of cell and the intensy of the simulation currents. Also, when the simulation electrode was positioned more rostrally in the brain, greater currents were needed to reach the threshold of analgesia. The present work contributes to a large body of evidence indicating that off-cell, or both, are involved in the complex mechanism of the control of nociceptive tranmission and nicifensive reflexes

Effects of mesencephalic lesion on the histomorphology of testis and spermatogenesis.

Mesencephalic reticular formation lesions were produced bilaterally by using two epoxy-coated stainless steel electrodes. Electrolytic lesions resulted in atrophy of testes, and decreased spermatogenesis. Seminiferous tubules of lesioned rats were characterised by a general decrease in the number of cells from different generation of germinal epithelium, empty spaces, degeneration of spermatogonia, degeneration of spermatocytes I and of young spermatids. There were significant reductions in weights of the testes (P less than 0.01). Similarly the areas of cross-sections of seminiferous tubules were significantly reduced (P less than 0.05). Another note-worthy feature was a gross reduction in the complete cross section count of interstitial cells. The study strongly suggests that the mesencephalic reticular formation influences the testes and spermatogenesis.

Brain-pituitary-adrenal interrelationship in closed loop intestinal obstruction in man. Effects of stepwise removal of brain, midbrain section and frontal leucotomy in dogs after the same type of stress.

Volvulus shows high plasma 17-OHCS level and after operation there is a progressive fall. Brain-pituitary-adrenal interrelationship has been studied in experimental dogs using a different type of stressor i.e. closed loop intestinal obstruction. Midbrain section blocks the adrenocortical response. Frontal leucotomy leads to increased response after acute distension of the closed loop. Acute hypothalamectomy does not lead to blocking of the adrenocortical response to stress.