Bilateral Occlusion of Carotid Artery in Awake Hypertensive Rats (SHR-SP) as a Model of Global Cerebral Ischemia

Bilateral occlusion of carotid arteries in awake hypertensive rats (SHR-SP) was used as a model of global brain ischemia (duration of occlusion — until appearance of seizures). In normotensive rats (WKY), no seizures developed over 60 min. We revealed swelling of mitochondria in dendrites of hippocampal CA1 pyramidal cells, which was more pronounced in SHP-SP than in WKY rats. Blood pressure and heart rate in SHR-SP rats increased starting from the first minutes of occlusion, while in WKY rats these parameters remained unchanged. We proved that bilateral occlusion of the carotid arteries in awake SHR-SP rats can be used as an adequate model of global cerebral ischemia. Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 146, No. 12, pp. 627–630, December, 2008     

Synaptic connectivity of serotonin graft efferents in the suprachiasmatic and supraoptic nuclei of the hypothalamus

We have previously reported that a cell suspension from the rostral part of the embryonic raphe grafted to the basal hypothalamus of 5,7-dihydroxytryptamine-denervated rats produced incomplete serotonin (5-HT) re-innervation of the suprachiasmatic nucleus (SCN) as opposed to hyper-innervation of the supraoptic nucleus (SON). We took advantage of this experimental model to investigate whether the graft-derived, 5-HT fibres retained normal ultrastructural features, and, particularly, a normal density of synaptic junctions, irrespective of the extent of target re-innervation. The intrinsic features of immunostained, graft-derived 5-HT axonal varicosities in both the SCN (ventral portion) and the SON were essentially similar to those exhibited by the respective endogenous innervation. Analysis of well-preserved varicosities in uninterrupted series of thin sections allowed us to evaluate directly the proportions of junctional to non-junctional 5-HT varicosities in both regions. Synaptic incidences were also remarkably conserved after grafting (45.5% in the SCN versus 38.5% in the SON; 48% and 38% in normal rats, respectively). Synapses were primarily reestablished on dendritic shafts, which also were identified as the major post-synaptic targets of the normal 5-HT innervations. We noted, however, a tendency toward increased numbers of symmetrical versus asymmetrical synapses in both the SCN and SON of grafted rats. Thus, irrespective of whether hypo-or hyper-innervation patterns developed post-grafting, the transplanted 5-HT neurons essentially retained normal ultrastructural features in their target territories, with a normal incidence of synaptic junctions. The data provide further support to the hypothesis that the innervation territory is the major determinant of the frequency with which ingrowing 5-HT fibres make synaptic junctions.     

Temporal response properties of lumbar-projecting vestibulospinal neurons to roll tilt in decerebrate cats

In decerebrate cats, rotation about the longitudinal axis of the animal, leading to sinusoidal stimulation of labyrinth receptors, produces a tonic contraction of limb extensors during side-down tilt ( responses) and of dorsal neck extensors during side-up tilt ( responses). These changes in posture are mediated, at least in part, by lateral vestibular nucleus (LVN) neurons, with response characteristics to stimulation of macular and/or canal receptors that have so far been evaluated at the level of either unidentified vestibulospinal (VS) neurons or vestibulo-collic neurons projecting to the upper cervical cord. In the present study we investigated the dynamics of the responses of VS neurons projecting to the lumbosacral segments of the spinal cord to increasing frequencies of tilt (from 0.026 to 0.32 Hz, ±10°). All the recorded units showed an average phase lead with respect to position of +25.6±5.5° (SE) at the tilt frequency of 0.026 Hz. Most of these neurons (n=32) were particularly activated during side-down tilt ( responses) and showed either a stable phase or an increase in phase lead of the responses with increasing frequency of tilt. At the tilt frequency of 0.026 Hz, the smaller the phase lead of the responses, the larger was the response gain. Moreover, the smaller the phase lead of the responses at that frequency of tilt, the smaller the increase in gain but the larger was the increase in lead of the responses obtained by increasing the stimulation frequency up to 0.32 Hz. Through this set of finely organized changes in unit response characteristics, the overall output of this population of neurons increased, while the phase angle of the responses reached the mean value of +64.9±2.6° (SE), thus becoming more related to the velocity than to the positional signal. The remaining units (n=7), which were mainly activated during side-up tilt ( responses), displayed an increase in phase lag of the responses to increasing frequency of stimulation, which reached the mean value of-118.9±14.5° (SE) at 0.32 Hz. The differences in the dynamic properties of these VS neurons projecting to the lumbosacral cord, with respect to those of previously recorded populations of VS neurons, are discussed.     

老年大鼠的海马神经元对微量注射Ach的敏感性

本工作观察了老年大鼠海马神经元对微量注射Ach(10μg/0.5μl)的敏感性。 实验在6只老年大鼠(大于30月龄)和5只年青大鼠(4～5月龄)上进行。结果表明:年青大鼠和老年大鼠的海马神经元对Ach的主要反应模式有所不同,前者多出现神经元放电明显增加的兴奋反应。后者多出现抑制反应,神经元的放电明显减少。此外,老年大鼠的海马神经元对Ach反应的持续时间(包括兴奋和抑制反应)也明显长于年青大鼠。本文对海马神经元敏感性和适应能力的改变可能是影响老年记忆的重要因素进行了讨论。     

Electrophysiological properties of sympathetic preganglionic neurons in the cat spinal cord in vitro

Intracellular recordings were obtained from sympathetic preganglionic neurons of the intermedio-lateral nucleus of the adult cat in slices of upper thoracic spinal cord maintained in vitro. The neurons were identified by their antidromic responses to stimulation of various ipsilateral sites. Sites from which antidromic responses could be evoked were the white ramus, the ventral root, the ventral root exit zone, the white matter between the latter and the outer edge of the tip of the ventral horn, the lateral edge of the ventral horn. Resting membrane potential was –61.3±1.6 mV (mean±SEM), input resistance 67.5±3.7 M, time constant 11.5±1.2 ms. The amplitude of the action potential generated by antidromic or direct stimulation was 77.4±2.3 mV. Threshold for direct spikes was 18.2±1.8 mV. The action potential had an average duration of 3.03±0.16 ms. It showed a prominent hump on the falling phase. The action potential had a tetrodotoxin (TTX)-sensitive and a TTX-resistant component. The latter was abolished by cobalt.Tetraethylammonium, cesium and barium prolonged the action potential duration which acquired a plateau-shape. A prolonged after-hyperpolarization (AHP) followed the sympathetic preganglionic neuron spike. Following a single spike, AHP duration and peak amplitude were 2.8±0.3 s and 16.6±0.7 mV, respectively. The AHP was abolished by cesium or barium, but enhanced by tetraethylammonium. An AHP followed the TTX-resistant spike. EPSPs and IPSPs could be generated by focal stimulation. The EPSP triggered spikes when threshold (15.0±2.0 mV) was reached. The slice of the thoracic spinal cord provides a useful experimental preparation for analysis of cellular properties and synaptic mechanisms of the sympathetic preganglionic neuron.     

Expression of voltage-dependent sodium and transient potassium currents in an identified sub-population of dorsal root ganglion cells acutely isolated from 12-day-old mouse embryos

The electrophysiological properties of a subset of dorsal root ganglion (DRG) neurons microdissected from 12-day-old (E12) mouse embryos and acutely isolated were analyzed as soon as 3 after their isolation. Two classes of neurons were defined according to their mean diameter. The larger diameter class was examined in this study. They display uniform cytoskeletal properties with co-expression of vimentin and neurofilament triplet proteins. Patch-clamp methods also revealed a homogeneous and limited repertoire of ionic channels that included (1) a TTX-sensitive Na⁺ current whose properties are similar to that reported in mature mammalian neurons, and (2) two types of K⁺ currents that can be compared with the delayed rectifier (I _k ) and the transient (I _a) potassium currents found in other mammalian preparations. It may be possible to use this in vitro model to examine the development of new types of currents, such as Ca²⁺ currents during neuronal growth and differentiation.     

The endocannabinoid system in the physiology and pathophysiology of the gastrointestinal tract

Numerous investigations have recently demonstrated the important roles of the endocannabinoid system in the gastrointestinal (GI) tract under physiological and pathophysiological conditions. In the GI tract, cannabinoid type 1 (CB1) receptors are present in neurons of the enteric nervous system and in sensory terminals of vagal and spinal neurons, while cannabinoid type 2 receptors are located in immune cells. Activation of CB1 receptors was shown to modulate several functions in the GI tract, including gastric secretion, gastric emptying and intestinal motility. Under pathophysiological conditions induced experimentally in rodents, the endocannabinoid system conveys protection to the GI tract (e.g. from inflammation and abnormally high gastric and enteric secretions). Such protective activities are largely in agreement with anecdotal reports from folk medicine on the use of Cannabis sativa extracts by subjects suffering from various GI disorders. Thus, the endocannabinoid system may serve as a potentially promising therapeutic target against different GI disorders, including frankly inflammatory bowel diseases (e.g. Crohns disease), functional bowel diseases (e.g. irritable bowel syndrome) and secretion- and motility-related disorders. As stimulation of this modulatory system by CB1 receptor agonists can lead to unwanted psychotropic side effects, an alternative and promising avenue for therapeutic applications resides in the treatment with CB1 receptor agonists that are unable to cross the blood–brain barrier, or with compounds that inhibit the degradation of endogenous ligands (endocannabinoids) of CB1 receptors, hence prolonging the activity of the endocannabinoid system.     

Equalization of asymmetries of tonus in the optomotor system of rabbits

Summary Turning a rabbit on a turn-table for a few degrees induces compensatory eye-movements and results in an asymmetry of tonus in the optomotor system. If the visual input is discontinued (darkness), this asymmetry decays and the eyes drift back to the mid-position within 12–18 sec. The equalization of such asymmetries of tonus under normal conditions and under curare is described. Tonus asymmetries induced by tilting the animals about the longitudinal axis are neither compensated under visual, nor under non-visual, conditions. Recordings were taken from oculomotor neurons, and changes of their firing frequencies were used as a measure for eye movements.A preliminary report was given at the spring meeting of the German Physiological Society 1973.Supported by the Deutsche Forschungsgemeinschaft, SFB 33.     

Comparative Analysis of the Frequency of Neuron Spike Activity in the Sensorimotor Cortex of the Right and Left Hemispheres in Conditions of Immobilization Catatonia in Rabbits

Multineuron activity was recorded from the sensorimotor cortex of the right and left hemispheres during immobilization catatonia in rabbits. The first session of immobilization of the animals was followed by changes in spike frequency in 47% of neurons in the sensorimotor cortex of the right hemisphere. Of these, 30% showed decreases in spike frequency and 17% showed increases. Spike frequency in the sensorimotor cortex of the left hemisphere changed in only 18% of cells, of which 13% showed decreases in spike frequency and 5% showed increases. The spike frequency of neighboring (recorded with the same electrode) neurons could change reciprocally. Differences in neuron activity in the two hemispheres were virtually absent after the second session of immobilization (several days after the first) – spike activity changed in 21% of neurons in the right hemisphere and 24% in the left hemisphere. The ratios of the numbers of neurons with increases and decreases in spike activity in hypnosis also became identical in the cortex of the right and left hemispheres. A hypothesis is proposed for the involvement of cortical neurons in the organization of hypnosis-like states.     

Analysis of behavioral and hippocampal variation in congenic albino and pigmented BALB mice

Mice of the BALB/c strain are widely used in behavioral research in spite of the albino condition, which can obscure brain-behavior relationships. We have developed a pigmented BALB strain, congenic to BALB/c, which could be more appropriate for neurogenetic studies that aim at identifying the effects of neurological mutations on behavior. Comparison of inbred albino and pigmented congenic BALB arising from the same litters provides a valuable tool for detecting the consequences of the albino mutation on behavioral performances. Preliminary results presented here show that the albino condition does not interfere with the development and patterns of connectivity of mossy fibers in the hippocampus. On the other hand, obvious coat color-linked differences appear for locomotor activity and defecation scores in the open field, pigmented mice being unexpectedlyl less active and more reactive than albino, as if better vision increased their reactions to a novel, anxiogenic environment. Finally, pigmented mice do not show better performances in the radial maze, which confirms that the inability of BALB mice for spatial learning in a highly demanding version of this task cannot be attributed to their inability to process visual information.