Direct evidence for the link between monoaminergic descending pathways and motor activity:: II. A study with microdialysis probes implanted in the ventral horn of the spinal cord

In order to define precisely the relation between descending monoaminergic systems and the motor system, we measured in the ventral horn of spinal cord of adult rats the variations of extracellular concentrations of 5-HT, 5-HIAA, DA and MHPG. Measurements were performed during rest, endurance running on a treadmill, and a post-exercise period, with microdialysis probes implanted permanently for 45 days. We found a slight decrease in both 5-HT and 5-HIAA during locomotion with a more marked decrease during the post-exercise period compared to the mean of rest values. In contrast, the concentration of DA and MHPG increased slightly during the exercise and decreased thereafter. These results, when compared with those of a previous study, which measured monoamines in the spinal cord white matter [C. Gerin, D. Bécquet, A. Privat, Direct evidence for the link between monoaminergic descending pathways and motor activity: I. A study with microdialysis probes implanted in the ventral funiculus of the spinal cord, Brain Res. 704 (1995) 191–201], highlight the complex regulation of the release of monoamines that occurs in the ventral horn.     

Role of vasopressin on excitatory amino acids mediated pressor responses in the periaqueductal gray area

In order to evaluate the role played by vasopressin on pressor responses elicited by stimulation of the periaqueductal gray (PAG) area by excitatory amino acids we carried out in vivo studies in genetically vasopressin deficient rats (Brattleboro). Microinjections of l-glutamic acid (glutamate, 0.6 to 60 nmol/rat) or N-methyl-d-aspartic acid (NMDA, 0.07 to 7 nmol/rat) into the PAG area of freely moving Brattleboro rats induced increases of arterial blood pressure values significantly lower than those obtained in Long Evans rats (control) (glutamate in Brattleboro rats: from +2±1 mmHg to 16±3 mmHg; glutamate in Long Evans rats: from +16±2 mmHg to +36±4 mmHg; NMDA in Brattleboro rats: from +5±2 mmHg to +34 ±8 mmHg; NMDA in Long Evans rats: from +18±7 mmHg to 80±9 mmHg; n=5). Similarly, in anaesthetized Brattleboro rats (urethane 1.2 g/kg i.p.) pressor responses to NMDA microinjections (0.7 nmol/rat) into the PAG area were significantly lower than in Long Evans rats (controls) (+15±3 mmHg vs +24±4 mmHg). In Long Evans rats NMDA injection also reversed blood pressure decrease induced by ganglionic blocker, hexamethonium and/or losartan (3 mg/kg i.v.), an AT1 receptor antagonist. In Brattleboro rats, NMDA injection did not reverse blood pressure decreases induced by hexamethonium (5 mg/kg i.v.). Moreover, hexamethonium induced blood pressure decrease was not reversed by acetylcholine injection (137 nmol/rat) into the PAG area of anaesthetized Long Evans rats, but if injected before hexamethonium, acetylcholine was able to increase blood pressure (+25±3 mmHg). Our results document: i) the importance of the PAG area in the control of cardiovascular system; ii) the involvement of excitatory amino acids in the neural control of vasopressin release; iii) the close relationship between glutamate and vasopressin in the central blood pressure regulation. Received: 1 April 1997 / Accepted: 2 February 1998     

Somatostatin- and enkephalin-like immunoreactivities are frequently colocalized in neurons in the caudal brain stem of rat

Summary The medulla oblongata and pons of colchicine treated rats were analyzed with a doublestaining technique using mouse monoclonal antibodies to somatostatin and rabbit polyclonal antibodies raised against methionine-enkephalin. Numerous cells reacted with both antisera but cells reacting with only one antiserum were also observed. Double-stained cells were most frequently encountered at all levels of the nucleus tractus solitarii, in a well defined group in the caudal medullary reticular formation, along the lateral ventral surface of the medulla oblongata, dorsolateral to the inferior olive and in the nucleus raphe magnus. These findings provide further examples of coexistence of two peptides and indicate the possibility that somatostatin-and enkephalin-like peptides are co-released.     

Recovery from short term intense exercise: Its relation to capillary supply and blood lactate concentration

Summary Muscle force recovery from short term intense exercise was examined in 16 physically active men. They performed 50 consecutive maximal voluntary knee extensions. Following a 40-s rest period five additional maximal contractions were executed. The decrease in torque during the 50 contractions and the peak torque during the five contractions relative to initial torque were used as indices for fatigue and recovery, respectively. Venous blood samples were collected repeatedly up to 8 min post exercise for subsequent lactate analyses. Muscle biopsies were obtained from m. vastus lateralis and analysed for fiber type composition, fiber area, and capillary density. Peak torque decreased 67 (range 47–82%) as a result of the repeated contractions. Following recovery, peak torque averaged 70 (47–86%) of the initial value. Lactate concentration after the 50 contractions was 2.9±1.3 mmol·l⁻¹ and the peak post exercise value averaged 8.7±2.1 mmol·l⁻¹. Fatigue and recovery respectively were correlated with capillary density (r=−0.71 and 0.69) but not with fiber type distribution. A relationship was demonstrated between capillary density and post exercise/peak post exercise blood lactate concentration (r=0.64). Based on the present findings it is suggested that lactate elimination from the exercising muscle is partly dependent upon the capillary supply and subsequently influences the rate of muscle force recovery. Dr. Tesch was on leave from Department of Clinical Physiology, Karolinska Hospital, Stockholm, Sweden     

Sex differences in estradiol-induced progestin receptor immunoreactivity in the guinea pig preoptic area and hypothalamus

Progesterone exerts on the central nervous system a number of effects, some of which are estrogen dependent mostly in the preoptic area and the mediobasal hypothalamus. In these regions, an immunocytochemical study was used to evaluate differences in progesterone receptor (PR) immunoreactivity between the male and the female guinea pig in response to 10 μg/day estradiol benzoate (EB) for 5 consecutive days. Compared to EB-treated females, EB-treated males showed a slightly lower number of PR-immunoreactive cells in the preoptic area whereas PR-immunoreactivity appeared in more cells in the anterior part of the ventrolateral nucleus. The numbers of PR-immunoreactive cells in the arcuate nucleus did not differ significantly between males and females. These results show that regionally localized sex differences exist in the induced PR system after 5 days exposure to EB.     

Influence of transcranial magnetic stimulation on the execution of memorised sequences of saccades in man

Memorised sequences of saccades are cortically controlled by the supplementary motor area (SMA), as shown in animal experiments and in humans with isolated SMA lesions. We applied transcranial magnetic stimulation (TMS) in eight healthy subjects executing memorised sequences of saccades. Sequences of three targets were presented. Then, upon a go-signal, the subjects had to execute the appropriate sequences. Ten to fifteen sequences were performed in each experiment, and the number of errors were counted. The number of errors increased significantly if TMS was given 80 ms before or 60 ms after the go-signal, with the stimulation coil overlying the SMA. There was no significant increase in errors if different stimulation intervals were chosen (160ms and 120ms before the go-signal; 100 ms, 140 ms or 240 ms after the go-signal), if the coil was positioned inappropriately (e.g. over the occipital cortex), or if the stimulator output was too low. We conclude that TMS can interfere specifically with the function of the SMA during a critical time interval close to the go-signal.     

Axonal projection of descending pathways responsible for eliciting forelimb stepping into the cat cervical spinal cord

Summary The descending pathways responsible for eliciting forelimb stepping are located in the lateral funiculus (Yamaguchi 1986). In order to determine into which spinal segments the descending pathways project and to know the projections and functions of the other descending system, the ventral funicular pathways, we placed various lesions in the cervical spinal cord of decerebrate cats with the lower thoracic cord transected and studied their effects on forelimb stepping evoked by stimulation of the midbrain locomotor region. (1) The lateral funiculus was transected on one side. The operation removes descending input to all the segments caudal to the lesion. Experiments with serial transections from the caudal to rostral segment revealed that stepping activity of the limb on the lesioned side is reduced when the lesion is placed at the level between the C6 and C7 segment and then between C5 and C6. A slight reduction of activity was also observed after a lesion placed between C7 and C8. (2) Consistently, bilateral transection of the lateral funiculus at the level between C5 and C6 abolished stepping movements of both forelimbs. (3) The cervical cord was split in the parasagittal plane through the dorsal root entry. The operation removes the descending input to the segment in which the lesion is placed. The parasagittal lesions from the C1 to C6 did not abolish stepping activity, although a lesion placed between C5 and C6 could slightly affect stepping. The results, (1)–(3) suggest that the lateral funicular pathways project into the spinal segments mainly at the C6–C7 level with some rostrocaudal extension into C5 and C8. (4) Complete transections of the medial part of the spinal cord cut extensor bursts short and raised stepping frequency. Nevertheless, if the lesion at C1–C5 spared the ventromedial part of the ventral funiculus, it did not result in such high-frequency stepping or in weakened extensor activity. In the case of segments caudal to C6, medial transections which spared the corresponding region could result in such stepping. It is suggested that the pathways descending through the ventromedial part of the ventral funiculus in the rostral segments provide extensor activity during stepping. They may change their course in the more dorsal part of the ventral funiculus below the C6 and presumably project into the grey matter of more caudal segments.     

Adrenaline turnover rates in the medial preoptic area and mediobasal hypothalamus in relation to the release of luteinizing hormone in female rats

The turnover rates of adrenaline in the medial preoptic area and mediobasal hypothalamus, areas which, respectively, include the cell bodies and terminals of luteinizing hormone-releasing hormone neurons, have been measured in female rats on pro-oestrus, the day of the preovulatory surge of luteinizing hormone, and on dioestrus, the preceding day. A rise in the rate of turnover was found in the medial preoptic area coinciding with the surge of luteinizing hormone in the late afternoon of pro-oestrus; the rate of turnover at this time was higher than at the same time on dioestrus. No changes in turnover rate were found in the mediobasal hypothalamus within either of these days.The results indicate that the adrenaline-containing projections to the preoptic area may be actively involved in the production of the spontaneous preovulatory surge of luteinizing hormone in rats.     

Corticospinal projections from areas 4 and 6 in the raccoon

Summary The corticospinal projections from areas 4 and 6 were investigated in the raccoon using the horseradish peroxidase (HRP) retrograde tracing technique. Multiple injections of lectin bound HRP and HRP were made into either the cervical or lumbar cord in 7 anesthetized raccoons. Retrogradely labeled neurons were observed throughout a wide extent of areas 4 and 6a. The HRP positive cells were most numerous within the dorsal bank of the cruciate sulcus within area 4 and continued around the fundus to occupy the lateral two-thirds of the ventral bank of the cruciate sulcus within area 6a. No labeled cells were observed in the more medially located area 6a. Although the HRP positive cells observed following the lumbar cord injections were situated slightly more medial and caudal to those observed following the cervical cord injections, considerable overlap between the two projections was noted. The corticospinal projections arising from areas 4 and 6a in the raccoon largely correspond in location to the regions functionally defined as the primary motor cortex and the supplementary motor area, respectively.