Lateral Reticular Formation Research Articles

Origin of the preganglionic visceral efferent fibers to the glands in the rat tongue as demonstrated by the horseradish peroxidase method

A study was made to identify the cells which give origin to the preganglionic visceral efferent fibers to the ‘intralingual’ glands in the tongue of the albino rat by the horseradish peroxidase (HRP) method. The medium-sized multipolar neurons whose cell bodies were filled with HRP were located in the lateral reticular formation at the level between the facial motor nucleus and the superior olivary nucleus. These HRP-labeled neurons were identified as belonging to the superior salivatory nuclear complex. There was no discernible topographical separation within the superior salivatory nucleus for the submandibular glands and ‘intralingual’ glands.

Cyclobenzaprine: Studies on its site of muscle relaxant action in the cat

Vibration (150 μ × 300 Hz) of the gastrocnemius-soleus muscle was used to elicit a reflex muscle contraction (tonic vibration reflex) which was facilitated or inhibited by electrical stimulation of various areas within the central nervous system. The results obtained support previous suggestions that the principal site of action of cyclobenzaprine as a skeletal muscle relaxant agent is upon neurons of the brain stem reticular formation. Vestibular nerve and medial reticular formation-elicited responses were more sensitive to the action of cyclobenzaprine than those induced through activation of Deiters' vestibular nucleus or its spinal projection through the lateral reticular formation. Least sensitive to the action of cyclobenzaprine were responses elicited through activation of these pathways at the level of the spinal cord. It may be noted that vestibular nerve afferents as well as vestibular nuclei project to the medial reticular formation including reticulospinal neurons within the nucleus pontis oralis and caudalis. Further, stereotaxic coordinates for electrical stimulation of the medial reticular formation impinged upon these pontine nuclei. This would suggest that in the present study the muscle relaxant action of cyclobenzaprine resulted from its suppression of these latter pontine reticulospinal pathways.

Comparative effects of pentylenetetrazol on the sensory responsiveness of lateral geniculate and reticular formation neurons

The responses of bulbar and mesencephalic reticular formation (MRF) neurons to visual, auditory and/or somatosensory stimuli were considerably enhanced after subconvulsant doses of pentylenetetrazol (PTZ) in a similar fashion suggesting a general action of PTZ on reticular formation (RF) neurons. PTZ enhanced MRF responses evoked by electrical stimuli in the lateral geniculate nucleus (LGN) or cochlear nucleus but only modestly enhanced LGN neuronal responses. These findings indicate that the effects of this convulsant on the first brain sensory ‘relay’ nuclei and primary sensory receptors do not appear to be sufficient to account for the extensive PTZ-induced enhancement of RF neuronal responses, and direct effects of PTZ on the reticular formation may play a major role in this enhancement.

Autonomic innervation of the tongue: A horseradish peroxidase study in the dog

Autonomic ganglia have been found along the lingual nerve in the rostral two-thirds of the canine tongue and along the glossopharyngeal nerve in the caudal glandular third of the tongue [4,17,18]. A 30% horseradish peroxidase (HRP) solution was injected throughout these ganglionated areas in order to identify the origin of the preganglionic fibers to the lingual ganglia. These injections resulted in ipsilateral retrograde labeling of small multipolar neurons in the lateral reticular formation of the medulla oblongata. The same injections labeled neurons in the ipsilateral cranial cervical ganglion, but preganglionic sympathetic neurons in the thoracic spinal cord were not labeled. These findings indicated that the lingual ganglia consist of parasympathetic neurons which receive preganglionic projections from the medulla. The lingual preganglionic neurons were located within the nucleus reticulatis parvicellularis and, in this location, were co-extensive with salivatory neurons that labeled after HRP injections in the mandibular and sublingual salivary glands. A degree of somatotopic organization within the lingual preganglionic group was indicated by the results of regional injections of enzyme and was confirmed by performing unilateral chorda tympani and glossopharyngeal neurectomies prior to extensive biliateral injections of HRP.

Brain stem blood vessels and the organization of the lateral reticular formation in the medulla oblongata of the cat

Brain stem blood vessels and the organization of the lateral reticular formation in the medulla oblongata of the cat

Motor and sensory centers for the innervation of mandibular and sublingual salivary glands: A horseradish peroxidase study in the dog

Horseradish peroxidase was injected at multiple sites in the mandibular and sublingual salivary glands in order to label the preganglionic salivatory neurons in the brain stem. The same injections resulted in retrograde labeling of the sympathetic and sensory neurons that project to these glands. Labeled fusiform and multipolar salivatory neurons were found ipsilaterally in the lateral reticular formation of the medulla where they extended over the rostral four-fifths of the facial nucleus and the caudal one-third of the dorsal nucleus of the trapezoid body. The vast majority of the small and medium-sized, labeled neurons appeared in the nucleus reticularis parvocellularis. Labeled neurons also appeared occasionally at the ventral and lateral aspects of the facial nucleus. Enzyme injections into these glands labeled sympathetic neurons that were concentrated in the caudal one-third of the ipsilateral cranial cervical ganglion. Labeled sensory neurons were distributed randomly in the ipsilateral proximal vagal and geniculate ganglia. Large numbers of sensory neurons were concentrated ventromedially within the mandibular zone of the trigeminal ganglion.

Differential inhibitory effects of medial and lateral midbrain stimulation on spinal neuronal discharges to noxious skin heating in the cat.

1. The inhibitory effects of electrical stimulation in midbrain periaqueductal gray (PAG) and lateral reticular formation (LRF) on spinal dorsal horn neuronal responses to noxious skin heating were investigated in cats anesthetized with Nembutal and N2O. 2. Thirty-one dorsal horn units driven by electrical stimulation of the posterior tibial and/or superficial peroneal nerves at A- and C-fiber strength responded to noxious radiant heating (e.g., 50 degrees C) of the skin of the hindpaw. All units tested were inhibited by electrical stimulation (100-Hz trains, 3/s) of both PAG and LRF. 3. Systematic tracking with the stimulating electrode revealed that descending inhibition is generated at sites throughout the mediolateral extent of the midbrain. Particularly effective sites were in LRF and PAG. 4. More powerful descending inhibition was generated from LRF than from PAG sites, based on quantitative comparison in the same unit of a) degree of inhibition of spinal unit heat-evoked discharges by PAG and LRF stimulation at the same current intensity, b) current threshold for inhibition by PAG and LRF stimulation, and c) slope of curves plotting degree of inhibition in relation to intensity of PAG and LRF stimulation. 5. Dorsal horn neurons show a linear relationship between response magnitude and temperature of skin heating during a series of heat stimuli (42-50 degrees C) applied at 3-min intervals. When the series is repeated during PAG stimulation, the slope of the linear temperature-response curve is reduced without a change in the response threshold. In contrast, repetition of the heating series during LRF stimulation produced a parallel rightward shift in the linear temperature-response curve, with commensurate increase in response threshold. 6. The results indicate that functionally separate descending inhibitory systems are activated by stimulation of PAG and LRF. Possible inhibitory mechanisms and the functional significance of descending inhibition from PAG and LRF are discussed.

Abolition of hypoxic vagal bradycardia by lateral mesencephalic lesions in spinal cats.

To examine central sites that integrate the vagal bradycardia induced by hypoxia, heart rates were recorded continuously in spinal, precollicular, decerebrated cats during transient hypoxia induced by ventilation with 100% nitrogen. Bilateral lesions in the lateral mesencephalic reticular formation either decreased the extent of bradycardia or caused a reversal to tachycardia; anesthesia induced the same change. In contrast, bilateral lesions in the medial mesencephalic reticular formation failed to alter the bradycardia. Hence, the lateral mesencephalic reticular formation is essential for the appearance of hypoxia-induced vagal bradycardia.

Gradual increase in self-stimulation response rates: Effect of electrode loci

Nine male rats, each with electrodes implanted in a telencephalic region and seven of them also with successful placements in a more caudal brain reward region, were taught to self-stimulate. Rates in the caudate nucleus and medial frontal cortex showed a gradual increase over daily sessions, but self-stimulation in lateral hypothalamus, substantia nigra, and reticular formation did not have this property. In the telencephalon, rates in the first five testing sessions were low, averaging 138 barpresses/10-min session. ICSS rates gradually rose during approximately the next 15 sessions, leveling off at an average of 453/10 min. Seizures were sometimes observed as rates increased at telencephalic points. Cumulative recordings showed that the long-term overall increase in response rate was partly due to a rate increase that occurred within some individual sessions, although during the last test days, a fast, steady rate dominated the entire session. The possibilities are discussed that the plasticity in ICSS is related to the kindling phenomenon or to dyskinesias which result from chronic administration of drugs presumed to have their main locus of action in the corpus striatum.

Tectal projections in the goldfish (Carassius auratus): A degeneration study

Efferents revealed by degeneration staining following tectal lesions in goldfish are presented. Four major projections were found. Ascending ipsilateral projections to pretectal-diencephalic areas exit the tectum rostrally and laterally and terminate in the area pretectalis (AP), lateral geniculate (LGN), nucleus pretectalis (NP), and nucleus rotundus (NR). Ascending contralateral projections exit rostrally and possibly laterally, enter the posterior and postoptic commissures and terminate in the contralateral AP, LGN, NP, NR, and rostral tectum. A medially directed projection enters the intertectal commissure, and some of these fibers may terminate sparsely in an area of the contralateral tectum homotopic to the lesion. A descending projection exits the tectum laterally and projects ipsilaterally to a dorsolateral tegmental nucleus (DLT) and the lateral reticular formation of the tegmentum and pons, and contralaterally to the medial reticular formation of the tegmentum and pons.

Efferent projections from temperature sensitive recording loci within the marginal zone of the nucleus caudalis of the spinal trigeminal complex in the cat.

The efferent projections from nucleus caudalis of the spinal trigeminal complex in cats were studied with retrograde and anterograde axonal transport techniques combined with localization of recording sites in the thalamus and marginal zone of nucleus caudalis to innocuous skin cooling. Results showed brainstem projections from nucleus caudalis to rostral levels of the spinal trigeminal complex, to the ventral division of the principal trigeminal nucleus, the parabrachial nucleus, cranial motor nuclei 7 and 12, solitary complex, contralateral dorsal inferior olivary nucleus, portions of the lateral reticular formation, upper cervical spinal dorsal horn and, lateral cervical nucleus. Projections to the thalamus included; a dorsomedial region of VPM (bilaterally) and to the main part of VPM and PO contralaterally. Neuronal activity was recorded in the dorsomedial region of VPM to cooling the ipsilateral tongue. HRP injections in this thalamic region retrogradely labeled marginal neurons in nucleus caudalis. These results show that marginal neurons of nucleus caudalis provide a trigeminal equivalent of spinothalamic projections to the ventroposterior nucleus in cats.

Effects of brain-stem and thalamic lesions on the corneal reflex: an electrophysiological and anatomical study.

In 9 patients with Wallenberg's lateral medullary syndrome, one patient with a midbrain lesion involving the right side of the tegmentum, and 2 patients with a thalamic lesion, corneal reflexes were investigated by a new electromyographic technique. The electrophysical results were compared with the results obtained by clinical observation. In the lateral medullary lesions the electrophysiologically obtained reflex responses showed four types of abnormality. Type A consisted of a bilateral delay and type B a bilateral absence of the corneal reflex response to stimulation on the affected side in combination with a normal reflex response on both sides when the cornea on the normal side was stimulated. Type C, which was present in one case, and type D which was seen in 3 cases, consisted of a bilateral absence of the corneal reflex upon stimulation on the affected side; stimulation on the unaffected side produced a normal reflex response on the intact side in combination with, respectively, a delay or absence of the corneal reflex response on the affected side. Comparison of the clinical observations with the electrophysiological findings revealed minor discrepancies in type A and B abnormalities. However, the electrophysiological type C and D abnormalities were not detected by clinical observation. These findings demonstrate that electrophysiological recording of the corneal reflex may reveal clinically undetectable abnormalities. From the electrophysiological findings it is concluded that the corneal reflex is conducted along medullary pathways running both ipsilaterally and contralaterally from the stimulated side before connecting, respectively, with the ipsilateral and contralateral facial nucleus. From the anatomical findings it is suggested that the ascending pathways from the spinal fifth nerve complex to the facial nuclei are located in the lateral reticular formation of the lower brain-stem. The normal corneal reflex responses in the presence of thalamic and midbrain lesions involving nociceptive fibres in the trigeminothalamic tract do not support a previously postulated long-loop reflex arc passing through this tract. The suprabulbar influence upon the corneal reflex is discussed.

Regional distribution of angiotensinogen in rat brain

The regional distribution of angiotensinogen, the prohormone of angiotensin I, was examined in rat brain. Quantification of brain angiotensinogen concentration was difficult because of the presence of an endogenous angiotensin I degrading (i.e. angiotensinase) activity which was active at the pH of the renin-angiotensinogen incubation. This degrading activity was unequally distributed throughout the brain, and its presence in homogenates invalidated measured levels of angiotensinogen. Only following removal of the angiotensinase activity by ammonium sulfate precipitation of the prohormone could the distribution of the prohormone be determined. Angiotensinogen was widely distributed throughout 31 brain regions; however there was an approximate 12-fold variation in concentration. Highest levels of the prohormone were found in the dorsal and ventral periventricular hypothalamus, area postrema, organum vasculosum lamina terminalis, periventricular thalamus, dorsal raphe and lateral reticular formation. Significantly lower amounts were found in the parietal cortex, cerebellum, septum and pituitaries. While the majority of regions examined exhibited similar concentrations of angiotensinogen, the demonstration of regions containing either significantly low or high amounts of prohormone is consistent with a topographical distribution of angiotensinogen in rat brain.

Spinal and medullary input to the lateral cervical nucleus.

The distributions of spinal and medullary cells projecting to the lateral cervical nucleus (LCN) have been investigated in young cats and dogs using the retrograde horseradish peroxidase (HRP) technique. Labeled spinal cells, whose axons contribute to the spinocervical tract (SCT), were found at all levels of the spinal cord ipsilateral to the injection sites. No significant differences were found between cat and dog, nor between cases with single injections at different levels of the LCN. SCT cells were found predominantly, if not exclusively, within lamina IV, with some extension into medial lamina V. No apparent mediolateral or dorsoventral density gradient was observed within lamina IV; cells of all sizes were labeled. Cells in cervical laminae I and V-VII were occasionally labeled; these, however, were considered to be propriospinal, supplying afferent fibers to the C1-2 dorsal horn. Cells of origin of spinocerebellar fibers consistently remained unlabeled in cases with restricted HRP injections and minimal fiber damage in the dorsolateral funiculus (DLF) around the injection sites. These results, therefore, corroborate and refine the findings of electrophysiological studies of the SCT and the LCN. Labeled medullary cells were located in the caudoventral and rostral portions of the dorsal column nuclei (DCN; stellate and fusiform cells), the underlying n. medullae oblongatae centralis, subnucleus dorsalis (parvicellular medullary reticular formation), the marginal and magnocellular layers (both large and small cells) of the n. trigeminalis spinalis pars caudalis and also in pars interpolaris; a cluster of cells was also consistently labeled in the lateral reticular formation just ventral to pars caudalis. The projection from the DCN to the LCN was confirmed with the anterograde Nauta technique. Fiber degeneration was observed in the entire ipsilateral LCN, although it was less abundant than that observed in the adjacent C1-2 dorsal horn. These results indicate that neurons in the rostral portions of the DCN not only may affect the input to the LCN (at the level of the dorsal horn), but also the output of the LCN itself. These data also suggest the possibility of both noxious and non-noxious facial input to the LCN.

Axonal transport of HRP in descending tectal fibers of the pit viper

Micro injections of 30% HRP were made into the superficial layers of the rattlesnake's optic tectum. The results demonstrate the presence of: an intertectal connection, a tectal → contralateral medial reticular formation projection, a reciprocal tectal ↔ ipsilateral lateral reticular formation projection, and a direct trigemino → contralateral tectal projection. This latter projection may be related to the relay of infrared information from the trigeminal system to the contralateral tectum in pit vipers.

Intratrigeminal and thalamic projections of nucleus caudalis in the squirrel monkey (Saimiri sciureus): A degeneration and autoradiographic study,

AbstractIn order to test the hypothesis that thalamic efferents of trigeminal nucleus caudalis (NC) are the cranial analogue of the spinothalamic system, lesion and autoradiographic studies were carried out in the squirrel monkey, and the terminal projection fields in thalamus were noted. Results showed that NC, including lateral reticular formation (LRF), projects to contralateral VPM, the VPM‐VPL border and medial VPL, and a region dorsal to ventroposterior nucleus (VP) proper which contains cells larger than those in VPM yet which stain as darkly as VPL neurons; this latter zone of termination may be homologous with VPLo (Vim) in other species, which is that area receiving lemniscal and cerebellar afferents (Mehler, '71; Walsh and Ebner, '73; Boivie, '74). In addition, a small projection is noted in an area intercalated between dorsomedial MG, limitans nucleus and posterior VP which closely agrees with the medial division of Posterior nucleus (Po) described in rhesus and squirrel monkey (Burton and Jones, '76). No terminations were observed in the gustatory nucleus medial to VPM.Bilateral, terminal projection fields were observed in posterior mediodorsal nucleus (MD), and a paralaminar area (PL) which lies in the ventrolateral strip of MD and is particularly prominent in primates; other bilateral fields were noted in CL, particularly the more medial segment of the nucleus. A sparse projection was noted in contralateral CM. Ipsilateral, intratrigeminal connections between NC and main sensory nucleus (MSV) also were observed.We conclude that, in the squirrel monkey, NC efferents, probably including LRF, may be considered analagous to the spinothalamic system by virtue of terminations in older medial and newer ventroposterior thalamus. Terminations in posterior MD may be specific to Primates. Moreover, projections to an area just dorsal to VP proper in squirrel monkey may be included within the broader definition of a neo‐spinothalamic area as reflected in spinothalamic tract projections to the ventrolateral complex in cat (Boivie, '71b; Jones and Burton, '74). The small NC projection to a part of Po is consistent with spinothalamic terminations to a “posterior” thalamic area in other primates (Mehler, '69), and with the suggestion that medial Po transmits pain information (Burton and Jones, '76).

Movement induced in cataleptic rats: Differential effects produced by electrical stimulation of the lateral hypothalamus, substantia nigra, and reticular formation

Haloperidol catalepsy can be countered by electrical stimulation of the lateral hypothalamus (LH) and, to a lesser extent, the reticular formation (RH). Substantia nigra (SN) stimulation proved to be least effective in this regard. Dissociation between behavioral arousal and cortical EEG during stimulation of the RF in cataleptic rats was observed.

Analysis of the circuitry responsible for primary afferent depolarization in the trigeminal spinal nucleus caudalis of cats.

Depth analysis was performed on the field potential evoked by stimulation of the infraorbital nerve in the trigeminal spinal nucleus caudalis and the subjacent lateral reticular formation of cats. It was shown by dye marking of the recording positions that each subnucleus of the nucleus caudalis (subnucleus marginalis, gelatinosus and magnocellularis) and the reticular formation could be differentiated from one another by the characteristics of the peripherally evoked field potentials. Responses of neurons were extracellularly recorded in the subnuclei gelatinosus and magnocellularis of the nucleus caudalis and in the reticular formation to stimulation of the trigeminal sensory branches (the frontal, infraorbital and lingual nerves), the nucleus ventralis posteromedialis of the thalamus and the cerebral cortex. The properties of the neurons were studied in relation to their thresholds, latencies, receptive fields (sensory branches effective for spike generation) and frequency-following capacities. These responses were then compared with properties of the PAD induced in the fibers terminating in the nucleus caudalis by similar peripheral and central stimulation. It was found that the neurons in the subnucleus magnocellularis were the most likely candidates for the interneurons mediating the peripherally evoked disynaptic PAD in the trigeminal nerve fibers terminating in the nucleus caudalis.

Investigation of the functional role of the septum.

A spectral-correlation analysis was made of the EEG recorded from the motor and visual cortex, hippocampus, and septum (in some series of experiments, the lateral geniculate body and mesencephalic reticular formation also) of rabbits in the presence or absence (background) of sensory stimulation. To investigate the functional role of the septum as a pacemaker the method of "rhythm binding" by electrical stimulation of the septum (lateral and medial nuclei) was used. By electrical stimulation of the medial nucleus of the septum at a frequency of 4-30 Hz rhythm binding was successfully obtained in all regions studied. Maximal rhythm binding was observed in cortical potentials. It is postulated that cortical rhythmic activity is generated as a result of physiological interaction between cortex and septum.

Intracranial self-stimulation and escape by EEG-derived instrumental responses in cerveau isolé rats

In 14 of the 25 unanesthetized postcollicular, pretrigeminal cerveau isole rats studied, intracranial self-stimulation or escape, or both, were demonstrated using EEG-derived instrumental responses. Stimulus trains (0.5-sec, 40-cps trains of 0.5-msec cathodal pulses at 600 μA) were delivered in a continuous reinforcement schedule in series of tests for each of 55 diencephalic and mesencephalic sites. Medial forebrain bundle stimulation consistently elicited self-stimulation, but never evoked escape. Stimulation of known aversive regions, lateral reticular formation, medial lemniscus, and meninges, elicited escape, but not self-stimulation. Both self-stimulation and escape were obtained by two types of EEG responses: high and low voltage, which triggered reinforcements when EEG amplitude increased and decreased, respectively. These data extend previous concepts of the integrative capability of cerveau isole animals to include phenomena related to reward, pain, and neural plasticity. The cerveau isole technique presented may offer significant advantages for several types of experiments for which the paralyzed encephale isole preparation has been the traditional choice.