Single-cell recordings: a method for investigating the brain's activation pattern during exercise.

The precision of human movements to generate skills as accurate as the exercises performed by athletes are the consequence of a long and complex learning process. These processes involve a great amount of the nervous system's structures. Electrophysiological techniques have been largely used to highlight brain functions related to the control of these kinds of movements. These methods cover invasive and non-invasive techniques which have been applied to humans and experimental animals. We describe here electrophysiological techniques that are used in behaving animals. Especially, we will focus on the analysis and results obtained from single-cell recording in the prefrontal cortex to explain the relationship between single neuronal activity and movement during locomotion. In addition, we will show how, analyzing these results, that we can characterize the integrative role of neurons involved in the control of locomotion. The objective is to demonstrate single-cell recording techniques as suitable methods to study, in experimental animals, the brain's activation pattern during exercise.

Immunocytochemical visualization of D-glutamate in the rat brain.

Using highly specific antisera directed against conjugated d-amino acids, the distribution of d-glutamate-, d-tryptophan-, d-cysteine-, d-tyrosine- and d-methionine-immunoreactive structures in the rat brain was studied. Cell bodies containing d-glutamate, but not d-glutamate-immunoreactive fibers, were found. Perikarya containing this d-amino acid were only found in the mesencephalon and thalamus of the rat CNS. Thus, the highest density of cell bodies containing d-glutamate was observed in the dorsal raphe nucleus, the ventral part of the mesencephalic central gray, the superior colliculus, above the posterior commissure, and in the subparafascicular thalamic nucleus. A moderate density of immunoreactive cell bodies was observed in the dorsal part of the mesencephalic central gray, above the rostral linear nucleus of the raphe, the nucleus of Darkschewitsch, and in the medial habenular nucleus, whereas a low density was found below the medial forebrain bundle and in the posterior thalamic nuclear group. Moreover, no immunoreactive fibers or cell bodies were visualized containing d-tryptophan, d-cysteine, d-tyrosine or d-methionine in the rat brain. The distribution of d-glutamate-immunoreactive cell bodies in the rat brain suggests that this d-amino acid could be involved in several physiological mechanisms. This work reports the first visualization and the morphological characteristics of conjugated d-glutamate-immunoreactive cell bodies in the rat CNS using an indirect immunoperoxidase technique. Our results suggest that the immunoreactive neurons observed have an uptake mechanism for d-glutamate.

Overexpression of kynurenic acid in stroke: An endogenous neuroprotector?

It is known that kynurenic acid (KYNA) exerts a neuroprotective effect against the neuronal loss induced by ischemia; acting as a scavenger, and exerting antioxidant action. In order to study the distribution of KYNA, a highly specific monoclonal antibody directed against KYNA was developed. This distribution was studied in control rats and in animals in which a middle cerebral artery occlusion (stroke model) was induced. By double immunohistochemistry, astrocytes containing KYNA and GFAP were exclusively found in the ipsilateral cerebral cortex and/or striatum, at 2, 5 and 21days after the induction of stroke. In control animals and in the contralateral side of the stroke animals, no immunoreactivity for KYNA was found. Under pathological conditions, the presence of KYNA is reported for the first time in the mammalian brain from early phases of stroke. The distribution of KYNA matches perfectly with the infarcted regions suggesting that, in stroke, this overexpressed molecule could be involved in neuroprotective/scavenger/antioxidant mechanisms.

NO-tryptophan: a new small molecule located in the rat brain.

A highly specific monoclonal antibody directed against nitric oxide-tryptophan (NO-W) with good affinity (10-9 M) and specificity was developed. In the rat brain, using an indirect immunoperoxidase technique, cell bodies containing NO-W were exclusively found in the intermediate and dorsal parts of the lateral septal nucleus. No immunoreactive fibres were found in the rat brain. This work reports the first visualization and the morphological characteristics of cell bodies containing NO-W in the mammalian brain. The restricted distribution of NO-W in the rat brain suggests that this molecule could be involved in specific physiological mechanisms.

3-hydroxi-anthranilic acid is early expressed in stroke.

Using an immunohistochemical technique, we have studied the distribution of 3-OH-anthranilic acid (3-HAA) in the rat brain. Our study was carried out in control animals and in rats in which a stroke model (single transient middle cerebral artery occlusion) was performed. A monoclonal antibody directed against 3-HAA was also developed. 3-HAA was exclusively observed in the infarcted regions (ipsilateral striatum/cerebral cortex), 2, 5 and 21 days after the induction of stroke. In control rats and in the contralateral side of the stroke animals, no immunoreactivity for 3-HAA was visualized. Under pathological conditions (from early phases of stroke), we reported for the first time the presence of 3-HAA in the mammalian brain. By double immunohistochemistry, the coexistence of 3-HAA and GFAP was observed in astrocytes. The distribution of 3-HAA matched perfectly with the infarcted regions. Our findings suggest that, in stroke, 3-HAA could be involved in the tissue damage observed in the infarcted regions, since it is well known that 3-HAA exerts cytotoxic effects.

Randomized controlled trial comparing the effectiveness of the ultrasound-guided galvanic electrolysis technique (USGET) versus conventional electro-physiotherapeutic treatment on patellar tendinopathy.

BACKGROUND: Patellar tendinopathy has a high prevalence rate among athletes. Different therapeutic options can be found in the current literature, but none of them has been clearly established as the gold standard. The purpose of this study is to compare, in a randomized controlled trial, the clinical efficacy of eccentric exercise combined with either an ultrasound-guided galvanic electrolysis technique (USGET) or conventional electrophysiotherapy to treat patellar tendinopathy. METHODS: Sixty patients diagnosed with patellar tendinopathy were randomized into two groups. Group 1 (n = 30) received electrophysiotherapy treatment consisting of ultrasound, laser and interferential current techniques. Group 2 (n = 30) received USGET. Both groups did the same standardized eccentric exercise program. Periodic assessments of the subjects were carried out with the Victorian Institute of Sport Assessment-Patella (VISA-P) score. An analysis of means and a survival study were performed. RESULTS: There were statistically significant differences in the VISA-P between the baseline and final follow-up in each treatment group. Group 1 (conventional electrophysiotherapy) went from 52.5 ± 18.8 to 61.9 ± 13.7 (in VISA-P < 90 subgroup) and from 69.1 ± 9.1 to 95.2 ± 2.5 (in VISA-P > 90 subgroup). Group 2 (USGET) went from 51.4 ± 17.9 to 63.3 ± 14.3 (in VISA-P < 90 subgroup) and from 66.3 ± 13.1 to 97.1 ± 1.7 (in VISA-P > 90 subgroup). There were statistically significant correlations between the baseline and final score in the VISA-P > 90 subjects upon completing the study but no statistically significant correlations between subjects with VISA-P < 90. The mean number of sessions applied was 22.6 ± 2.5 in Group 1 and 3.2 ± 0.9 in Group 2. The success probability in Group 1 was 36.1% versus 72.4% in Group 2. The difference was statistically significant. CONCLUSION: The results obtained with the combination of USGET and eccentric exercise reported better outcomes than with the conventional electrophysiotherapy techniques in the treatment of patellar tendinopathy.

Beta-Amyloid peptide25-35 depresses excitatory synaptic transmission in the rat basolateral amygdala "in vitro".

The effects of beta-amyloid peptide25-35 on resting membrane potential, spontaneous and evoked action potential and synaptic activity have been studied in basolateral amygdaloid complex on slices obtained from adult rats. Intracellular recordings reveal that perfusion with beta-amyloid peptide25-35 at concentrations of 400 nM and less did not generate any effect on resting membrane potential. However, concentrations in the range of 800-1200 nM produced an unpredictable effect, depolarization and/or hyperpolarization, which were blocked by tetrodotoxin or 6-cyano-7-nitroquinoxaline-2,3-dione+D-(-)-2-amino-5-phosphonopentanoic acid together with bicuculline. Excitatory and inhibitory evoked responses mediated by glutamic acid or gamma-aminobutyric acid decreased in amplitude after beta-amyloid peptide25-35 perfusion. Additionally, results obtained using the paired-pulse protocol offer support for a presynaptic mode of action. To determine which type of receptors and/or channels are involved in the presynaptic mechanism of action, a specific blocker of alpha-7 nicotinic receptors (methyllycaconitine citrate) or L-type calcium channel blockers (calcicludine or nifedipine) were used. beta-amyloid petide25-35 decreased excitatory postsynaptic potentials amplitude in control conditions and also in slices permanently perfused with methyllycaconitine citrate. However, this effect was blocked in slices perfused with calcicludine or nifedipine suggesting the involvement of the L-type calcium channels. On the whole, these experiments provide evidence that beta-amyloid peptide25-35 affects neurotransmission in basolateral amygdala and its action is mediated through L-type calcium channels.

Simultaneous depletion of neurokinin A, substance P and calcitonin gene-related peptide from the caudal trigeminal nucleus of the rat during electrical stimulation of the trigeminal ganglion.

The central terminals of the primary sensory trigeminal ganglion (TG) neurons projecting into the caudal trigeminal nucleus (CTN) of the rat exhibit neurokinin A (NKA)-, substance P (SP)-, and calcitonin gene-related peptide (CGRP)-immunoreactivities (IRs). We stimulated the TG in the rat to induce some of the alterations which might occur during migraine (neurogenic inflammation). Under a stereotaxic apparatus and by means of a bipolar electrode, one-side TG of the animals were electrically stimulated (7.5 Hz, 5 ms, 0.8-1. 4 mA) with square pulses for 5 min. Then, using immunohistochemical methods, the lower medulla of each rat was studied for NKA-, SP- and CGRP-IRs. Light microscopic examination of brain-stem sequencial sections revealed a simultaneous decrease in the immunoreactivities of all neuropeptides (NKA, SP and CGRP) in the CTN ipsilateral to TG stimulation in comparison with the other (not stimulated) side CTN. It is suggested that this decrease in immunoreactivity would be due to the co-release of neuropeptides following noxious stimuli and that NKA, SP and CGRP might therefore act as co-transmitters or co-modulators at the first central synapses of the trigeminal sensory pathway.

Muscarinic activation of a non-selective cationic conductance in pyramidal neurons in rat basolateral amygdala.

In the present study, a cationic membrane conductance activated by the acetylcholine agonist carbachol was characterized in vitro in neurons of the basolateral amygdala. Extracellular perfusion of the K+ channel blockers Ba2+ and Cs+ or loading of cells with cesium acetate did not affect the carbachol-induced depolarization. Similarly, superfusion with low-Ca2+ solution plus Ba2+ and intracellular EGTA did not affect the carbachol-induced depolarization, suggesting a Ca2+-independent mechanism. On the other hand, the carbachol-induced depolarization was highly sensitive to changes in extracellular K+ or Na+. When the K+ concentration in the perfusion medium was increased from 4.7 to 10 mM, the response to carbachol increased in amplitude. In contrast, lowering the extracellular Na+ concentration from 143.2 to 29 mM abolished the response in a reversible manner. Results of coapplication of carbachol and atropine, pirenzepine or gallamine indicate that the carbachol-induced depolarization was mediated by muscarinic cholinergic receptors, but not the muscarinic receptor subtypes M1, M2 or M4, specifically. These data indicate that, in addition to the previously described reduction of a time- and voltage-independent K+ current (IKleak), a voltage- and time-dependent K+ current (IM), a slow Ca2+-activated K+ current (sIahp) and the activation of a hyperpolarization-activated inward rectifier K+ current (IQ), carbachol activated a Ca2+-independent non-selective cationic conductance that was highly sensitive to extracellular K+ and Na+ concentrations.

Cholinergic responses of morphologically and electrophysiologically characterized neurons of the basolateral complex in rat amygdala slices.

The electrophysiological properties, the response to cholinergic agonists and the morphological characteristics of neurons of the basolateral complex were investigated in rat amygdala slices. We have defined three types of cells according to the morphological characteristics and the response to depolarizing pulses. Sixty-six of the recorded cells (71%) responded with two to three action potentials, the second onwards having less amplitude and longer duration (burst). In a second group, consisting of 21 cells (22%), the response to depolarization was a train of spikes, all with the same amplitude (multiple spike). Finally, seven neurons (7%) showed a single action potential (single spike). Burst response and multiple-spike neurons respond to the cholinergic agonist carbachol (10-20 microM) with a depolarization that usually attained the level of firing. This effect was accompanied by decreased or unchanged input membrane resistance and was blocked by atropine (1.5 microM). The depolarizing response to superfusion with carbachol occurred even when synaptic transmission was blocked by tetrodotoxin, indicating a direct effect of carbachol. Similarly, the depolarization by carbachol was still present when the M-type conductance was blocked by 2 mM Ba2+. The carbachol-induced depolarization was prevented by superfusion with tetraethylammonium (5 mM). Injection of biocytin into some of the recorded cells and subsequent morphological reconstruction showed that "burst" cells have piriform or oval cell bodies with four or five main dendritic trunks; spines are sparse or absent on primary dendrites but abundant on secondary and tertiary dendrites. This cellular type corresponds to a pyramidal morphology. The "multiple-spike" neurons have oval or fusiform somata with four or five thick primary dendritic trunks that leave the soma in opposite directions; they have spiny secondary and tertiary dendrites. Finally, neurons which discharge with a "single spike" to depolarizing pulses are round with four or five densely spiny dendrites, affording these neurons a mossy appearance. The results indicate that most of the amygdaloid neurons respond to carbachol with a depolarization. This effect was concomitant with either decrease or no change in the membrane input resistance and was not blocked by the addition of Ba2+, an M-current blocker, indicating that a conductance pathway other than K+ is involved in the response to carbachol.

Depletion of substance P, neurokinin A and calcitonin gene-related peptide from the contralateral and ipsilateral caudal trigeminal nucleus following unilateral electrical stimulation of the trigeminal ganglion; a possible neurophysiological and neuroanatomical link to generalized head pain.

Primary trigeminal neurons of the trigeminal ganglion (TG) innervate major parts of the face and head, including the dura. Electrical stimulation of the TG at specific parameters, can activate its nociceptive neurons and may serve as an experimental pain model. Markowitz [J. Neurosci. 7 (1987) 4129] reported that electrical stimulation of the trigeminal ganglion (TG) causes extravasation of plasma proteins from venules of the trigeminally innervated domain possibly due to the release of vasoactive substances. Neurogenic inflammation (vasodilatation, plasma protein extravasation, release of vasoactive peptides) in dura may serve as one of the possible pathomechanisms underlying vascular head pain [Moskowitz, Ann. Neurol. 16 (1984) 157]. We performed a unilateral electrical stimulation (7.5 Hz, 5 ms, 0.8-1.4 mA for 5 min) of the TG in rat, to induce a neurogenic inflammation in the peripheral trigeminal domain including the dura, looking for calcitonin gene related peptide (CGRP), substance P (SP) and neurokinin A (NKA) immunoreactivity (IR) in the caudal trigeminal nucleus (CTN) into which massive central trigeminal processes terminate. Here, we show patchy depletion(s) of CGRP-, SP- and NKA-IRs in the contralateral CTN of the rat in addition to their ipsilateral depletion. Such depletion is due to the release of these neuropeptides in the CTN leading to the activation of bilateral trigeminal nociceptive pathway. These data afford the possibility that under specific frequencies (which may roughly correlate to the intensity of the painful stimulus) and/or specific intensities (may correlate to specific areas of the peripheral trigeminal domain) of stimulation, activation of one side of the TG may activate bilateral trigeminal nociceptive pathway leading to the perception of an ill localized/generalized pain or headache rather than a unilateral one.

Effects of cooling parietal cortex on prefrontal units in delay tasks.

The effects of cooling posterior parietal cortex (areas 5 and 7) on behavior and on the activity of prefrontal neurons were assessed in monkeys performing two visual discrimination tasks with delayed choice. In both tasks, the visual cue for each trial was displayed for 0.5 s by rear projection through colored filters on a central 2.5-cm translucid button. After a variable delay, the choice stimuli were presented on two lower stimulus-response buttons; to obtain a reward, the animal had to press the correct button in accord with the cue. In one task, a red or a green cue called for the choice of that color when the two colors appeared after the delay; in the other task, a yellow or blue cue called for the choice of, respectively, the right or the left of the two white-illuminated choice buttons. Prefrontal single-unit activity (sulcus principalis area) and eye movements were recorded during task performance while parietal areas were at normal or subnormal (6-20 degrees C) temperature. Two-thirds of the units investigated showed significant spontaneous firing changes, most commonly a decrease, as a result of bilateral parietal cooling. A similar proportion of units showed cooling-related changes, excitatory or inhibitory, of their firing activity during the task; such firing changes could occur in any trial-epoch. Parietal cooling also induced misreaching, slow and inaccurate ocular movements, and longer choice reaction time, but did not alter performance in terms of correct responses. Our results suggest the involvement of posterior parietal cortex in spatial aspects of task performance (reaching speed and accuracy, eye movements, reaction time). They also suggest the existence of functional influences from parietal upon prefrontal cortex. Those influences, however, seem not essential for the basic role of the prefrontal cortex in the temporal integration of behavior.

Prefrontal representation of stimulus attributes during delay tasks. I. Unit activity in cross-temporal integration of sensory and sensory-motor information.

The activity of 294 single units was recorded from the dorsolateral prefrontal cortex of monkeys performing two visual discrimination tasks with delayed response. One task, delayed matching-to-sample (DMS), required memory of a colored cue for later (18 s) matching and choice of color; the cue did not connote the location of the delayed response. The other task, delayed conditional position discrimination (DCPD), required memory of a colored cue for later (18 s) choice of spatial response; the cue did connote delayed-response location. All 4 cues (red and green in DMS, yellow and blue in DCPD) were isoluminous and appeared in identical location at trial start. Differential unit reactions to the two DCPD cues were more common than those to the two DMS cues (samples). During the delay period, 15% of all units showed, in one task or the other, differential discharge depending on the cue. In DCPD, a large proportion of the units showing direction-related activity at the time of motor response also reacted with a firing frequency change to one or both (spatially identical) trial-initiating cues. Some units showed coherence of cue-related and response-related changes in accord with the behavioral association between color and direction of response (i.e., yellow-right, blue-left). The reactivity of some units was correlated with the behavioral performance of the tasks in terms of correctness or incorrectness of response. The results indicate that, during visual delay tasks, neurons in the dorsolateral prefrontal cortex may process both spatial and non-spatial information. Because of their protracted differential discharge between cue and response (i.e., during the delay), some units seem involved in the transfer of sensory information across time. These findings suggest the role of prefrontal neurons in the representation of multiple attributes of sensory stimuli, including their associated motor connotations, and the overlap of the cortical representations of different attributes. They are also consistent with the role of the prefrontal cortex in the cross-temporal mediation of sensory-motor contingencies and, therefore, the temporal organization of behavior.

Prefrontal representation of stimulus attributes during delay tasks. II. The role of behavioral significance.

Rhesus monkeys were trained to perform two visual discrimination tasks with delayed response. In both tasks, the response depended on the color of the cue, a lighted circle in the center of a panel. Red and green guided one task, yellow and blue the other. In the course of performance, a fifth color (violet), non-relevant and inconsequential, was presented at random in the same location as the cues. All 5 stimuli were of equal brightness. Many cells in the dorsolateral prefrontal cortex (sulcus principalis and superior convexity) treated the relevant cues differently than the irrelevant stimulus. In general, cellular reactions to that stimulus were of lesser magnitude than the reactions to the cues. Cell reaction differences as a function of stimulus significance outnumbered and overshadowed differences as a function of cue-color or any other task variable. The results indicate that, during visual delay tasks, units in the dorsolateral prefrontal cortex differentiate stimuli by their behavioral significance, as well as by other stimulus attributes, including color. Because the motivational evaluation of sensory stimuli is an integral part of the cognitive processes in delay tasks (together with short-term memory and motor set), these results support the notion that the prefrontal cortex integrates motivational inputs into the structure of behavioral action.

Alterations in neurokinin A-, substance P- and calcitonin gene-related peptide immunoreactivities in the caudal trigeminal nucleus of the rat following electrical stimulation of the trigeminal ganglion.

We have carried out an immunohistochemical study on the presence of neurokinin A (NKA) and substance P (SP) in the rat caudal trigeminal nucleus (CTN) after electrical stimulation of the trigeminal ganglion (TG), used as an experimental model to induce alterations, some of which may occur during migraine attacks (release of vasoactive peptides from perivascular trigeminal axons and neurogenic inflammation). Both unilateral, 30 min electrical stimulation (5 Hz, 5 ms, 0.1-1 mA) of the TG and 5 min stimulation with a slight increase in the stimulating parameters (7.5 Hz, 5 ms, 1.4 mA) caused a significant depletion of the NKA and SP immunoreactivities (-IR) of the TG nerve central terminals in the ipsilateral CTN. Calcitonin gene-related peptide (CGRP)-IR of the ipsilateral CTN was also studied in the CTN using the increased stimulating parameters and a marked depletion of CGRP-IR was also observed following TG stimulation. Such depletion may be due to the release of neuropeptides from the trigeminal central terminals. These findings suggest that NKA, SP and CGRP could act as neurotransmitters at the first central synapses of the trigeminal nociceptive pathway to transmit the sensory stimuli to the higher brain centers.

[Implication of the neuropeptides methionine enkephalin, neurotensin and somatostatin of the caudal trigeminal nucleus in the experimental migraine]. / Implicación de los neuropéptidos metionina-encefalina, neurotensina y somatostatina del núcleo caudal del trigémino en la migraña experimental.

INTRODUCTION: Primary peptidergic sensory neurons of the trigeminal ganglion that innervate the cerebral dura have been involved in the pathogenesis of headache, including the migraine. In addition, it is known that nociceptive central processes of the trigeminal neurons terminate in the caudal trigeminal nucleus. Moreover, the electrical stimulation of the trigeminal ganglion has been used as an experimental model in order to study the vascular headache, including the migraine. AIM: To study whether there is or not a decrease of the immunoreactivity for methionine enkephalin, somatostatin and neurotensin in the caudal trigeminal nucleus after electrical stimulation of the trigeminal ganglion. MATERIAL AND METHODS: The trigeminal ganglia of Wistar albino rats of both sexes were electrically stimulated (frequency, 5 Hz; duration, 5 ms; intensity, 0,8 1.4 mA) and unilaterally for five minutes. Sections of the medulla oblongata containing the caudal trigeminal nucleus were obtained and processed for immunocytochemistry, in which specific antibodies were used against methionine enkephalin, neurotensin and somatostatin 28. RESULTS: In stimulated animals, we observed a decrease in the immunoreactivity for the three neuropeptides studied in the stimulated (ipsilateral) side, in comparison with the not stimulated side (contralateral). In control animals (not stimulated) the degree of the immunoreactivity was the same on both sides. CONCLUSIONS: 1. The decrease of the immunoreactivity in the ipsilateral side (stimulated) suggests that methionine enkephalin, neurotensin and somatostatin 28 are released in the caudal trigeminal nucleus after electrical stimulation of the trigeminal ganglion; 2. Methionine enkephalin and somatostatin 28 could act in the caudal trigeminal nucleus as inhibitors (with antinociceptive action) of another released exciters neuropeptides (with nociceptive action); and 3. These data will allow in the future to try new therapeutic strategies (e.g., the inhibition of the receptors implicated.), in order to alleviate certain headaches.

Early growth hormone (GH) treatment promotes relevant motor functional improvement after severe frontal cortex lesion in adult rats.

A number of studies, in animals and humans, describe the positive effects of the growth hormone (GH) treatment combined with rehabilitation on brain reparation after brain injury. We examined the effect of GH treatment and rehabilitation in adult rats with severe frontal motor cortex ablation. Thirty-five male rats were trained in the paw-reaching-for-food task and the preferred forelimb was recorded. Under anesthesia, the motor cortex contralateral to the preferred forelimb was aspirated or sham-operated. Animals were then treated with GH (0.15 mg/kg/day, s.c) or vehicle during 5 days, commencing immediately or 6 days post-lesion. Rehabilitation was applied at short- and long-term after GH treatment. Behavioral data were analized by ANOVA following Bonferroni post hoc test. After sacrifice, immunohistochemical detection of glial fibrillary acid protein (GFAP) and nestin were undertaken in the brain of all groups. Animal group treated with GH immediately after the lesion, but not any other group, showed a significant improvement of the motor impairment induced by the motor lesion, and their performances in the motor test were no different from sham-operated controls. GFAP immunolabeling and nestin immunoreactivity were observed in the perilesional area in all injured animals; nestin immunoreactivity was higher in GH-treated injured rats (mainly in animals GH-treated 6 days post-lesion). GFAP immunoreactivity was similar among injured rats. Interestingly, nestin re-expression was detected in the contralateral undamaged motor cortex only in GH-treated injured rats, being higher in animals GH-treated immediately after the lesion than in animals GH-treated 6 days post-lesion. Early GH treatment induces significant recovery of the motor impairment produced by frontal cortical ablation. GH effects include increased neurogenesis for reparation (perilesional area) and for increased brain plasticity (contralateral motor area).

Direct visualization of retinoic acid in the rat hypothalamus: an immunohistochemical study.

In order to increase our knowledge about the distribution of vitamins in the mammalian brain, we have developed a highly specific antiserum directed against retinoic acid with good affinity (10(-8) M), as evaluated by ELISA tests. In the rat brain, no immunoreactive fibers containing retinoic acid were detected. Cell bodies containing retinoic acid were only found in the hypothalamus. This work reports the first visualization and the morphological characteristics of cell bodies containing retinoic acid in the mammalian paraventricular hypothalamic nucleus and in the dorsal perifornical region, using an indirect immunoperoxidase technique. The restricted distribution of retinoic acid in the rat brain suggests that this vitamin could be involved in very specific physiological mechanisms.

Angiotensin II effects on plasmatic renin activity.

Intravenous infusion of angiotensin II into the cat (4.13 microng/45 min) produces a decrease of plasmatic renin activity. This reduction was not modified after the bilateral denervation of the kidneys or section of both carotid and aortic nerves. The reserpinization of the cats does not modify the angiotensin effects on the renin plasmatic concentration. These observations suggest that the sympathetic nervous system and the catecholamines do not alter significantly the effects of angiotensin II on the renin secretion.

Effects of sympathetic stimulation on carotid and aortic baroreceptors in the cat.

Variations in the discharge of baroreceptor units in the left aortic nerve were investigated during stimulation of the stellate ganglion both in the intact cat and in vitro perfusion of the aortic arch. The effects of stimulation of the peripheral cervical sympathetic trunk of the baroreceptor discharge in the carotid nerve during in vitro perfusion of the carotid artery were further studied. Stimulation of the stellate ganglion or the aortic nerve in the intact cat caused a simultaneous increase in arterial pressure, heart rate and number of baroreceptor impulses in a filament to the left aortic nerve. In the in vitro studies, decreases in the number of baroreceptor impulses both in the aortic and carotid nerves were produced in most cases during the stimulation of the sympathetic nerves. These effects were only observed during low pressure perfusion of the isolated artery and in low frequency changes. The infusion of norepinephrine caused a more marked decrease.