Evolution of the reticular formation

The reticular formation of mammals contains numerous nuclei which can be recognized by their projection patterns, cytoarchitectonics, and neuropeptide/neurotransmitter content. We have identified reticular nuclei in representatives from numerous reptilian groups and ascertained presence or absence of these reticular nuclei in an attempt to use neuronal occurrence as a tool to determine phylogenetic relationships. Recently these studies have been extended to two elasmobranchs, a galeomorph shark and a ray. In this report, we concentrate on three medullary spinal projecting reticular nuclei, reticularis gigantocellularis, reticularis magnocellularis, and reticularis paragigantocellularis. We found that all three nuclei were present in rats, lizards, and elasmobranchs, but one nucleus was absent in crocodilians, and two nuclei were absent in turtles. Thus brain organization may give us clues to phylogenetic relationships. Moreover, these three reticular nuclei exhibited remarkably similar cellular morphology in mammals, reptiles, and elasmobranchs.     

Sleep duration varies as a function of glutamate and GABA in rat pontine reticular formation

The oral part of the pontine reticular formation (PnO) is a component of the ascending reticular activating system and plays a role in the regulation of sleep and wakefulness. The PnO receives glutamatergic and GABAergic projections from many brain regions that regulate behavioral state. Indirect, pharmacological evidence has suggested that glutamatergic and GABAergic signaling within the PnO alters traits that characterize wakefulness and sleep. No previous studies have simultaneously measured endogenous glutamate and GABA from rat PnO in relation to sleep and wakefulness. The present study utilized in vivo microdialysis coupled on-line to capillary electrophoresis with laser-induced fluorescence to test the hypothesis that concentrations of glutamate and GABA in the PnO vary across the sleep/wake cycle. Concentrations of glutamate and GABA were significantly higher during wakefulness than during non-rapid eye movement sleep and rapid eye movement sleep. Regression analysis revealed that decreases in glutamate and GABA accounted for a significant portion of the variance in the duration of non-rapid eye movement sleep and rapid eye movement sleep episodes. These data provide novel support for the hypothesis that endogenous glutamate and GABA in the PnO contribute to the regulation of sleep duration.     

The reticular formation differentiates heterotopic stimuli

The role of the reticular formation (RF) in discriminative functions was studied in experiments on anaesthetized cats. In this association, a) the variability of responses in the RF (bipolarly recorded potential gradients - PG) to the same stimuli, and b) the responses of the RF to different (heterotopic) stimuli were recorded. The PG pattern in electrical stimulation of the same source (a nerve, skin) was constant during the time periods studied (several tens of minutes); even when the functional state of the RF was modified with strychnine, the basic characteristics of the responses usually remained intact. The pattern of PG generated by natural stimulation (tapping) was likewise reproduced with exactness at the level of statistical significance. Responses evoked from reciprocally remote receptor areas were manifestly different, at least in one of the depths investigated. The differences in stimulation of topically close areas were small. The results show that the RF, through its reactions, can differentiate heterotopic stimuli.     

The mesencephalic reticular formation as a link in the cortical control of exploratory and goal-directed behaviour

The general accepted concept about the MRF as an unspecific ascending activating system concerns only one of its multiple functions. Investigations on more than 100 hooded rats of the Long-Evans strain with small bilateral symmetric lesions in dorsal, central and ventral subnuclei of the MRF brought out the following results pointing to further important functions: 1. Each lesion type produced a different syndrome of parameter changes of the spontaneous open field behavior with some common tendencies of reduced ambulatory and exploratory activities. 2. Visual placing responses were strongly reduced or totally abolished after lesions without tendencies of recovery. 3. Changes of locomotion and muscular tonus were quite different or even opposite in dorsal, central and ventral types of lesions. 4. In four tasks of postoperative active avoidance acquisition or retention and performance of preoperatively learned tasks the impairments were different related to the lesion type including a different loss in brightness discrimination. The results support the hypothesis that MRF subdivisions participate differently in information selection, tuning and coupling information with goal directed movements of different type. Lesions severely disturb the proper use of some information for a cue, especially visual cues when they are in the anterior part of the mesencephalon.     

The brainstem reticular formation is a small-world, not scale-free, network

Recently, it has been demonstrated that several complex systems may have simple graph-theoretic characterizations as so-called 'small-world' and 'scale-free' networks. These networks have also been applied to the gross neural connectivity between primate cortical areas and the nervous system of Caenorhabditis elegans. Here, we extend this work to a specific neural circuit of the vertebrate brain--the medial reticular formation (RF) of the brainstem--and, in doing so, we have made three key contributions. First, this work constitutes the first model (and quantitative review) of this important brain structure for over three decades. Second, we have developed the first graph-theoretic analysis of vertebrate brain connectivity at the neural network level. Third, we propose simple metrics to quantitatively assess the extent to which the networks studied are small-world or scale-free. We conclude that the medial RF is configured to create small-world (implying coherent rapid-processing capabilities), but not scale-free, type networks under assumptions which are amenable to quantitative measurement.     

Chronic pain syndromes

Brainstem-scalp discharge propagation was evaluated in 20 patients with chronic pain, of which 10 were ranked according to the frequency of involved systems making up the chronic pain syndrome. It is concluded that brainstem discharges alone were sufficient to generate the chronic pain syndrome.     

Putative nociceptive neurotransmitters in the mesencephalic reticular formation

The neurotransmitter(s) involved in the transmission of nociceptive information in the mesencephalic reticular formation (MRF) of the rat have not been identified. Acetylcholine (ACh), substance P (SP), neurotensin (NT), norepinephrine (NE) and dopamine (DA) have all been implicated as putative neurotransmitters involved in nociception. All of these compounds were microiontophoretically administered in the MRF of rats to determine which, if any, mimicked the effects produced by a nociceptive stimulus (foot pinch). This is only one of several criteria that a substance should meet to be considered a nociceptive neurotransmitter in the MRF. ACh and NE mimicked the effects of the nociceptive stimulus in 61% and 67% respectively of the cells tested; NT, DA and SP mimicked the effects of the nociceptive stimulus less frequently (33%, 30%, 23% respectively). Therefore, the nociceptive neurotransmitters in the MRF appear to be ACh and NE; NT, DA and SP may be neurotransmitters with a less important role in nociception in the MRF.     

Lamina propria of intestinal mucosa as a typical reticular tissue

Summary Information about the chemical structure of ovine submandibular glycoconjugates was obtained in situ by means of a battery of peroxidase-conjugated lectins with affinity for specific terminal or internal sugars or sugar sequences in conjunction with neuraminidase digestion and periodate oxidation. Stored secretions in all mucous acinar cells contained disaccharide side chains consisting of Nacetylneuraminic acid linked to penultimate -N-acetylgalactosamine localizing the predominant disaccharide demonstrated biochemically. A previously unrecognized disaccharide consisting of terminal N-acetylneuraminic acid and penultimate -galactose was found in 20–30% of mucous acinar cells. Occasional clusters of acini composed purely of serous cells contained an additional unrecognized glycoconjugate with oligosaccharides terminated by sialic acid with O-acetylated polyhydroxyl side chains and penultimate -galactose. Serous demilunes, however, lacked detectable complex carbohydrate other than glycogen. Terminal sialic acid--galactose dimers were present on the apical surface of all ducts except for intercalated ducts coated only with neutral glycoconjugate. Fucose assayed biochemically as a minor component occurred in abundance in glycoconjugates at the apical surface of all intercalated and most striated duct cells and within some striated duct cells. Terminal -galactose not previously detected biochemically was localized at the apex of all duct cells. These results provide new knowledge concerning the structure of ovine submandibular glycoconjugates. They also illustrate the value of histochemical methods for elucidating the diversity of complex carbohydrates in an organ, locating different glycoconjugates in different types or subtypes of epithelial cells and demonstrating intracellular sites that contain complex carbohydrate.This research was supported by National Institute of Health Grants HL-29775 and AM-10956     

Neurons of the rabbit midbrain reticular formation during a defensive conditioned reflex]

Analysis of unit activity of the midbrain reticular formation was carried out on alert rabbits during defensive conditioning. Most of the examined neurones exhibited phasic responses corresponding in time to the components of the evoked potential (EP) recorded in the cortical visual area in response to the "indifferent" stimulus, and to the conditioned stimulus and electric cutaneous reinforcement. The data obtained are considered from the standpoint of the Anokhin functional systems theory. A conclusion has been made regarding the participation of reticular units in providing all the basic mechanisms of the functional system of the behavioral act. Discharges of one and the same neurone may correspond to different components of the EPs to conditioned and unconditioned stimuli. In different behavioral acts a neurone may apparently participate in different systemic mechanisms.     

Evoked potentials in the reticular formation of the rabbit midbrain during formation of a dominant focus in it

During creation of a dominant focus in the midbrain reticular formation (RF) by its multiple stimulation with a high-frequency current (stimulation frequency 200 Hz, pulse duration 0.1-0.5 ms, voltage 1-3 V, duration 5 s) a statistically significant increase of the amplitude of the evoked potential (EP) in RF to light flashes was revealed in comparison with background data. Significant increase of EP amplitude was also observed in RF in response to the same stimuli applied in successive experiments without RF stimulation, which pointed to the existence of a latent dominant focus in the CNS.