[Entry pathways of painful afferent pathways into the spinal cord].
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Afferent Pathways↗
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Positive feedback action of pituitary beta-endorphin on acupuncture analgesia afferent pathway.
Potentials in the final sector of the afferent pathway from the acupuncture point (AP) were enhanced by intraperitoneal 0.5 mg/kg morphine without changing the threshold of AP stimulation and greatly decreased by hypophysectomy. The decreased potentials were restored to the control level by morphine (0.5 mg/kg, IP). Potentials evoked in the final sector of the afferent pathway from the nonacupuncture point (NAP) by NAP stimulation after lesion of the analgesia inhibitory system were greatly enhanced by corticotropin (ACTH) (0.25 mg/kg, IP) and greatly decreased by hypophysectomy. Diminished potentials were restored to the control level by ACTH (0.25 mg/kg, IP). Both morphine (0.5 mg/kg, IP) and ACTH (0.25 mg/kg, IP) produced analgesia, but morphine did not affect acupuncture analgesia (AA) and ACTH did not affect nonacupuncture point stimulation-produced analgesia (NAA). All analgesia, that due to 0.5 mg/kg morphine or 0.25 mg/kg ACTH, AA, and NAA were abolished by hypophysectomy. The abolished AA and NAA were restored by 0.5 mg/kg morphine and 0.25 mg/kg ACTH, respectively. Hence, beta-E and ACTH liberated from the pituitary gland by stimulation of an AP and NAP may act as positive feedback on the AA and NAA afferent pathways, respectively.
Acupuncture Analgesia↗
[Effects of morphine on evoked potential recorded from pain-afferent pathways (author's transl)].
Effects of morphine (1 mg/kg i.v.) were examined on evoked potential of somatosensory afferent pathways elicited by tooth pulp stimulation in cats. Results were as follows: In central gray (CG) of the midbrain which has a triphasic evoked potential with a short latency, morphine decreased the amplitude. In nucl. lateralis posterior(LP) and nucl. medialis dorsalis(MD) of the thalamus, association relay nuclei, which have a late component followed by a fast component with a relatively short latency, morphine decreased the amplitude of the late component but not that of fast component of the evoked potential. In nucl. centralis lateralis(CL) of the thalamus, intralaminar nuclei, and pre-central association area(PCA) of the cortex, which have monophasic and triphasic evoked potentials with a long latency, respectively, morphine markedly decreased the amplitude of both evoked potentials. In nucl. ventralis posteromedialis(VPM) and somatic sensory area I (SI), lemniscal system, which has biphasic and mutiphasic evoked potentials with a short latency, respectively, morphine had no effect on these evoked potentials. As these depressant effects of morphine on evoked potentials were antagonized by naloxone (0.2mg/kg i.v.), a specific morphine action is suggested.
Afferent Pathways↗
The negative potential wave evoked in cuneate nucleus by stimulation of afferent pathways: its origins and susceptibility to inhibition.
1. The negative (N)-wave evoked at various depths in the cuneate nucleus by stimulation of afferents in the ipsilateral forepaw or dorsal column has been studied in the rat. 2. Micro-iontophoretic applications of gamma-aminobutyric acid (GABA) into the vicinity of the recording electrode markedly reduced the amplitude of the negative wave, but only when recordings were made near the base of the cuneate nucleus. Nearer the surface of the medulla, GABA was much less effective. 3. A similar depth distribution obtained for the depression of the negative wave by micro-iontophoretic Mg2+ and enhancement by Ca2+. 4. Depression of the negative wave by conditioning stimulation of the afferent pathway also showed a similar depth distribution. The conditioned depression of the negative wave was most marked during the first 30 ms after the conditioning stimulus and this early depression could be antagonized by iontophoretic (+)-bicuculline methochloride. A lesser degree of conditioned inhibition of the negative wave persisted up to 80-200 ms but this was resistant to (+)-bicuculline methochloride. Thus, conditioned depression of the negative wave appeared to be mediated only in part by a GABA-like transmitter. 5. It is concluded that the negative wave recorded near the base of the cuneate nucleus has some of the predicted properties of a post-synaptic potential. These properties are not seen when the negative wave is recorded more superficially, near the surface of the medulla.
Afferent Pathways↗
[Sources of the afferent pathways of the motor cortex in cats revealed by using the peroxidase method].
By means of the method based on the retrograde axonal transport of exogenic horse-radish peroxidase, there have been stated the sources of afferent pathways of the motor cortex and the structure of neurons sending their axons to the given region. The marked neurons have been found in ipsilateral (SI, SII, Pr, Limb.) and contralateral cortex (MI, Limb.), as well as in the diencephalon (LP, VPL, Hp), the mesencephalon (NR, SN, TM) and the pons (TP). The complex investigation (the peroxidase method and electron microscopy) allowed to get an idea on morphological substrate of disynaptic pathways.
Animals↗
[Analgesic effect of pentazocine and its action on nociceptive afferent pathway].
Nociceptive stimulus was applied to the skin of adult cats by pinching with a serrated forceps or by radiant heat with Pain meter. This stimulation caused motor or emotional responses such as movements of the head and trunk, vocalization, escape and attack. After the administration of pentazocine, these responses disappeared and the animals behaved normally. Analgesic action appeared approximately 15 min after the administration and lasted more than 90 min. Effects of pentazocine on pain-afferent pathways were studied and the evoked potential was recorded by tibial nerve stimulation. Though pentazocine did not influence the evoked potential recorded from somatic sensory area I and mesencephalic central gray, the evoked potential in pre-central association area, nucleus centralis lateralis, nucleus suprageniculatus-limitans and reticularis pontis caudalis was reduced by pentazocine.
Afferent Pathways↗
The rubro-bulbospinal path. A descending system known to influence dynamic fusimotor neurones and its interaction with distal cutaneous afferents in the control of flexor reflex afferent pathways.
The inhibitory effect of electrical stimulation in the near-rubral region on polysynaptic segmental as well as ascending pathways activated by the flexor reflex afferents (FRA) in hind limb nerves was studied in chloralose anaesthetized cats. The effective stimulating region totally coincided with the one from which a D zone climbing fibre response may be elicited in the contralateral cerebellar cortex. The descending path was dependent upon an intact dorsolateral spinal funiculus, where also a characteristic volley could be recorded with a surface electrode on short train central stimulation. The suppressive action on the transmission through the FRA pathways was evoked in the absence of a lower lumbar dorsal root potential, and it was concluded that the effect was exerted by postsynaptic inhibition. It was suggested that this descending path, the effects of which resemble those elicited from the dorsal reticulospinal system, is identical to the rubro-bulbospinal path, previously known to influence dynamic fusimotor neurones. The transmission through the FRA pathways was also suppressed by conditioning stimulation of ipsilateral, low threshold distal cutaneous afferents. The time course of this effect was the same as that with central conditioning stimulation. Facilitatory interaction was revealed with double conditioning and it was suggested that the descending path and the distal cutaneous afferents converge upon a common group of interneurones, which postsynaptically inhibit an early (possibly the first one) interneurone in the FRA pathways. As low threshold distal cutaneous afferents supply the primary peripheral input via climbing fibres to the cerebello-cortical D zone, it was concluded that the different stimuli (central or peripheral) which activate a common group of inferior olivary neurones destined for the D zone also activate a common group of segmental inhibitory interneurones. The results are discussed in relation to current concepts of segmental motor control, and it is suggested that the mechanisms studied could be involved in the regulation of stepping.
Afferent Pathways↗
On the possible functional role of afferent pathways in skin sensation.
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Animals↗
Inhibitory actions from low and high threshold cutaneous afferents on groups II and III muscle afferent pathways in the spinal cat.
The inhibitory effects caused by volleys in cutaneous afferents on the transmission through some polysynaptic segmental pathways activated by high threshold muscle afferents were studied in chloralose anesthetized, spinal cats. Pathways studied were groups II and III to motoneurones as well as group II to primary afferents. The results suggested that two different mechanisms were involved. One mechanism, with a very slow time course (duration more than 400 ms), is suggested to be an example of presynaptic inhibition between different primary afferent systems. This mechanism required high threshold (greater than or equal to 1.6T) conditioning shocks, and appeared simultaneously with the component II dorsal root potential being evoked by the cutaneous afferent volley. The other mechanism, with a faster time course (duration always below 300 ms), was dependent upon low threshold (less than or equal to 1.5T) cutaneous conditioning volleys. This inhibitory interaction could not be ascribed to the same presynaptic mechanism, but is suggested to be an example of postsynaptic inhibition at an interneuronal level. The presumed disynaptic excitatory pathway from group II muscle afferents to flexor motoneurones was not inhibited by cutaneous conditioning shocks, but could on the contrary be facilitated by activity in low threshold cutaneous afferents, probably at the only interneurone involved in this group II pathway.
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Convergence in a thermal afferent pathway in the rat.
1. In anaesthetized rats, unit activity was recorded in the afferent somatosensory pathway leading from the scrotum. Recording sites were in the dorsal horn near the entry zone of the scrotal nerve, in the ventrobasal complex of the thalamus and in the somatosensory (SI) cortex. During recording, the temperatures of the left and right sides of the scrotum were varied independently. 2. Almost all (64/67) the units in dorsal horn, thalamus and cortex responding specifically to scrotal temperature were equally affected by temperature changes on either side of the scrotum. The receptive fields of these units were bilateral and large, implying a massive convergence of fibres from thermoreceptors on to each central unit. In contrast, mechanosensitive units responded only to unilateral stimulation. 3. As a consequence of the convergence in the thermal pathway, the firing rate of each central unit was a function of an additive combination, often simply the sum, of the temperatures of the two sides of the scrotum. 4. The relationship between firing rate and the temperature of one side of the scrotum was sigmoid, the position, but not the shape, of the curve depending on the temperature at which the opposite side was maintained. An increase in the maintained temperature shifted the sigmoid response curve towards lower temperatures and vice versa. 5. The convergence which this pathway exhibits would be well suited to integration of the temperature of the scrotal skin, but not to spatial discrimination.
Action Potentials↗
Afferent pathways of the blink reflex.
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Afferent Pathways↗
[The role of vestibular and proprioceptive afferent pathways in the reaction to pushing (author's transl)].
The reaction to pushing was studied in 6 normal subjects and 3 patients with bilateral peripheral vestibular lesions. The reaction to pushing was tested on the anterior tibial and soleus, by modifying the proprioceptive afferent impulses. The respective parts of the vestibular, proprioceptive, visual components, and of a sudden, start are analyzed; the afferent impulses obtain information from the initial posture and modulate the relative importance of these different factors at a supra-segmentary level.
Afferent Pathways↗
Contributions of different afferent pathways to the catecholamine and 5-hydroxytryptamine-innervation of the amygdala: a neurochemical and histochemical study.
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Afferent Pathways↗
A critical review of the afferent pathways and the potential chemical mediators involved in cardiac pain.
There is considerable evidence that on the anterior surface of the heart (which is usually supplied by the left anterior descending and the proximal part of the left circumflex coronary arteries), sympathetic efferent reflexes characterized by tachycardia and/or hypertension predominate following experimental or pathological perturbations. These cardiovascular reflexes are accompanied by an increase in presumed nociceptive afferent traffic and, in pathological condition, by pain. In these experiments, there is generally no effect of vagotomy on afferent nerve traffic, and lower cervical and upper thoracic sympathectomies help provide relief from angina. On the other hand, experimental or pathological perturbations involving the inferior-posterior surface of the heart (supplied by the right and distal parts of the left circumflex coronary arteries), are characterized by vagal efferent reflexes, resulting in bradycardia and/or hypotension. These reflexes are accompanied by an increase in vagal afferent nerve traffic and, in pathological conditions, by pain. In these experiments, vagotomy generally abolishes such cardiovascular reflexes, and lower cervical and upper thoracic sympathectomies are not effective in the relief from angina. Although cardiac sympathetic afferents are unquestionably involved in the central transmission of nociceptive information from the heart, it is also likely that there is a contributing role from the vagus in cardiac pain. It is important experimentally to understand the natural stimulus that gives rise to angina. In the clinical situation, a decrease in coronary blood flow or an increase in the metabolic demands of the myocardium due to increased work are obvious precipitating factors which lead to myocardial ischemia. In the experimental situation, occlusion of the coronary arteries is often used as a stimulus which mimics myocardial ischemia. As people who frequently experience angina have varying degrees of coronary artery disease, it is difficult to accept that the state of the coronary arteries of the normal experimental animal bear any resemblance to the state of the coronary arteries under pathological conditions. That is, the gain of homeostatic reflexes, the basal concentrations of neuroactive substances in the plasma, the myocardium and the afferent terminals, the excitability of the afferents, access of chemical mediators (e.g. bradykinin, 5-HT, adenosine, histamine, prostaglandins, potassium, lactate), to afferents, and the overall function of the animal are all significantly different. We have no idea how control mechanisms have been altered in the person with severe coronary artery disease compared to the normal patient or the "normal" experimental animal.(ABSTRACT TRUNCATED AT 400 WORDS)
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[Restoration of instrumental movements in cats after section of spinal cord afferent pathways].
Instrumental fore-leg movements (pedal pressing) were studied in the course of recovery of motor functions after section of the posterior columns and the spino-cervical tract at the cervical level. Recovery of supporting-locomotor functions reached a high level. Instrumental reactions connected with inborn forms of motor activity (running etc.) were being restored parallel to the locomotion restoration. Complex instrumental movements were restored slower and didn't reach a high degree of accuracy. A more simple instrumental movement (pressing on the open pedal) had a more rapid and more complete recovery. It is concluded that the possibilities of substitution of different channels, transmitting afferent somatic impulses to the sensorimotor cortex, are very limited for elaborated instrumental movements.
Afferent Pathways↗
[Effect of narcotic analgesics on the cortical control process of impulse transmission in the afferent pathways of the sciatic nerve].
The effect produced by narcotic analgetics with their intravenous administration on the process of cortical control over the transmission of impulses along specific routes of the sciatic nerve was studied. The conditioning stimulation of the cortex was effected by using a monopolar electrode through single electric impulses. The interval between conditioning and test (on sciatic nerve) impulses was of 80-120 ms. Morphine (1-2 mg/kg), promedol (trimeperidin) (1-2 mg/kg) and phentanyl (100 gamma/kg) potentiated the inhibition of evoked potentials in the nucleus gracilis and in VPL, observed upon stimulation of the cortex of optic lobuses. The intensification of inhibitory corticifugal mechanisms occurring under the effect of narcotic analgetics takes place both on the level of the medulla oblongata and of the thalamic one.
Afferent Pathways↗
The seventh cranial nerve of the rat. Visualization of efferent and afferent pathways by cobalt precipitation.
The cobalt sulphide precipitation technique, in conjunction with Timm's intensification procedure, was used to delineate the afferent and efferent intramedullary pathways of the seventh cranial nerve complex in the rat. The branchial motor nucleus with the accompanying first part, genu, and second part of the root are described. The motor branches to the superficial facial musculature do not contain fibres of geniculate ganglion origin or fibres which terminate in the spinal trigeminal nucleus. The motor branches to the deep facial muscles arise from the dorsal part of the branchial motor nucleus and traverse to the midline medial to the genu, then project under the genu into the lateral reticular formation before exiting with the facial nerve. The salivatory and lacrimal nuclei and their intramedullary pathways are described. Sensory fibres from the cutaneous auricular branch enter the spinal trigeminal tract and most of the chorda tympani gustatory fibres enter the fasciculus solitarius. A smaller number of gustatory fibres extend medially to the region of the salivatory nucleus. Fibres of greater superficial petrosal origin also enter the fasciculus solitarius as well as the medial reticular formation. These findings are discussed in relation to previous anatomical, physiological and clinical reports.
Animals↗
Expression of D2 dopamine receptor mRNA in the arterial chemoreceptor afferent pathway.
Dopamine is a major neurotransmitter in the arterial chemoreceptor pathway. In the present study we wished to determine if messenger RNAs for dopamine D1 and D2 receptor are expressed in carotid body (type I cells), in sensory neurons of the petrosal ganglion which innervate the carotid body and in sympathetic neurons of the superior cervical ganglion. We failed to detect D1 receptor mRNA in any of these tissues. However, we found that D2 receptor mRNA was expressed by dopaminergic carotid body type I cells. D2 receptor mRNA was also found in petrosal ganglion neurons that innervated the carotid sinus and carotid body. In addition, a large number of sympathetic postganglionic neurons in the superior cervical ganglion expressed D2 receptor mRNA.
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