Coordination of eye and head components of movements evoked by stimulation of the paramedian pontine reticular formation.

Constant frequency microstimulation of the paramedian pontine reticular formation (PPRF) in head-restrained monkeys evokes a constant velocity eye movement. Since the PPRF receives significant projections from structures that control coordinated eye-head movements, we asked whether stimulation of the pontine reticular formation in the head-unrestrained animal generates a combined eye-head movement or only an eye movement. Microstimulation of most sites yielded a constant-velocity gaze shift executed as a coordinated eye-head movement, although eye-only movements were evoked from some sites. The eye and head contributions to the stimulation-evoked movements varied across stimulation sites and were drastically different from the lawful relationship observed for visually-guided gaze shifts. These results indicate that the microstimulation activated elements that issued movement commands to the extraocular and, for most sites, neck motoneurons. In addition, the stimulation-evoked changes in gaze were similar in the head-restrained and head-unrestrained conditions despite the assortment of eye and head contributions, suggesting that the vestibulo-ocular reflex (VOR) gain must be near unity during the coordinated eye-head movements evoked by stimulation of the PPRF. These findings contrast the attenuation of VOR gain associated with visually-guided gaze shifts and suggest that the vestibulo-ocular pathway processes volitional and PPRF stimulation-evoked gaze shifts differently.

On the role of the reticular formation in vocal pattern generation.

This review is an attempt to localize the brain region responsible for pattern generation of species-specific vocalizations. A catalogue is set up, listing the criteria considered to be essential for a vocal pattern generator. According to this catalogue, a vocal pattern generator should show vocalization-correlated activity, starting before vocal onset and reflecting specific acoustic features of the vocalization. Artificial activation by electrical or glutamatergic stimulation should produce artificially sounding vocalization. Lesioning is expected to have an inhibitory or deteriorating effect on vocalization. Anatomically, a vocal pattern generator can be assumed to have direct or, at least, oligosynaptic connections with all the motoneuron pools involved in phonation. A survey of the literature reveals that the only area meeting all these criteria is a region, reaching from the parvocellular pontine reticular formation just above the superior olive through the lateral reticular formation around the facial nucleus and nucleus ambiguus down to the caudalmost medulla, including the dorsal and ventral reticular nuclei and nucleus retroambiguus. It is proposed that vocal pattern generation takes place within this whole region.

Electrocortical and behavioral responses elicited by acute electrical stimulation of inferior thalamic peduncle and nucleus reticularis thalami in a patient with major depression disorder.

OBJECTIVE: Our aim was to study electrocortical and behavioral responses elicited by 6, 60 and 3/s stimulation of the inferior thalamic peduncle (ITP) and nucleus reticularis thalami (Re) in a patient with of major depression disorder resistant to psychotherapy, pharmacotherapy and electroconvulsive therapy and candidate to be treated by electrical stimulation of the ITP. METHODS: In this patient, two multicontact electrodes were implanted bilaterally through frontal coronal parasagittal burr-holes with oblique trajectories aiming ITP and Re. Stimulation was performed through externalized systems. Referential scalp electroencephalographic (EEG) recordings were performed and subjective sensations and clinical symptoms reported by patient and changes in responsiveness in single response tasks during stimulation trials were systematically recorded. RESULTS: Unilateral, low (6/s) and high (60/s) frequency stimulation of either ITP or Re produced identical recruiting-like responses or desynchronization-DC shift changes predominant at frontopolar region, bilaterally. Billateral, high intensity 3/s stimulation or either ITP or Re produced electrocortical responses that consisted in generalized 3/s spike-wave complexes predominant at frontopolar, frontocentral and frontotemporal regions. However, while ITP responses were accompanied by all symptoms described for a spontaneous absence attack, Re responses were behaviorly accompanied only by delayed reaction time. CONCLUSION: These data suggests that in humans as in cats, ITP and Re are both part of a non-specific thalamo-orbitofrontal system normally engaged in cortical synchronization, selective attention and sleep. SIGNIFICANCE: Under abnormal conditions, ITP and RE may play a role in the physiopathology of typical absence attacks and depression disorders.

Anterior cingulate cortex contributes to the descending facilitatory modulation of pain via dorsal reticular nucleus.

Supraspinal centres biphasically modulate spinal nociceptive transmission, including descending inhibition and facilitation. Recent studies have revealed that descending facilitatory modulation is a key mechanism underlying induction and maintenance of neuropathic and inflammatory pain. The anterior cingulate cortex (ACC) is not only involved in the transmission of pain sensation but also plays a role in processing pain-related emotion. The ACC also widely connects with relevant regions of the descending modulation system. Here we used electrophysiological and behavioural techniques to study the possible pathways behind the modulation of spinal nociceptive transmission from the ACC. C-fibre-evoked field potentials in the spinal dorsal horn were produced by electrical stimulation of the sciatic nerve at an intensity high enough to excite C fibres, and paw withdrawal latencies (PWLs) to noxious heating were recorded. The results showed that high-frequency tetanic electrical stimulation of the ACC both unilaterally enhanced the C-fibre-evoked field potentials in the spinal dorsal horn and bilaterally shortened PWLs, indicating a facilitation of spinal nociception. A similar effect was observed after microinjection of N-methyl-d-aspartic acid (NMDA; 10 nm, 1 microL) or homocysteic acid (HCA; 0.1 m, 1 microL) into the ACC. When the dorsal reticular nucleus (DRt) was electrolytically lesioned, ACC-induced facilitation of spinal nociception was blocked. These results imply that: (i) activation of the ACC may facilitate spinal nociception; (ii) NMDA receptors in the ACC may be involved in descending facilitation; and (iii) the DRt plays a crucial role in mediating ACC-induced facilitation of spinal nociception.

Visual orienting response in goldfish: a multidisciplinary study.

The neural basis underlying the orienting response has been thoroughly studied in frontal-eyed mammals. However, in non-mammalian species, including fish, it remains almost unknown. Therefore, we studied the contribution of the optic tectum and the mesencephalic reticular formation to the performance of the orienting response in goldfish, using behavioural, physiological, and anatomical tracer techniques. The appearance of a visual stimulus (a pellet of food) in the environment of a goldfish evoked a turn of the body to reorient the line of sight. Left-tectal lobe ablation abolished the orienting turn response towards the contralateral hemifield. Electrical microstimulation of the optic tectum suggested the presence of a motor map, which is in correspondence with the overlying visual representation, as previously reported in other vertebrates. The tracer biotin-dextran amine was injected into different functionally identified tectal zones. The results showed that rostral and caudal poles of the mesencephalic reticular formation receive outflow mainly from the rostral and caudal tectal poles, respectively. This suggests that the tectal wiring with downstream structures is site-dependent. Furthermore, the electrical activation of rostral and caudal mesencephalic reticular formation revealed a different contribution to vertical and horizontal orienting eye movements. We conclude that the basic neural system coding the orienting response appears early in phylogenesis, although some specific characteristics are selected by adaptive pressure.

Lack of monosynaptic corticomotoneuronal EPSPs in rats: disynaptic EPSPs mediated via reticulospinal neurons and polysynaptic EPSPs via segmental interneurons.

In the rat, some findings have been taken to suggest the existence of monosynaptic corticomotoneuronal (CM) connections. Because this connection is believed to be largely responsible for the ability to make independent digit movements in primates and man, it has been inferred that the monosynaptic CM connection in the rat is likewise important for skilled prehension. Comparison of intra- and extracellular recordings from forelimb motoneurons in anesthetized rats, revealed no monosynaptic CM excitatory postsynaptic potentials (EPSPs). The fastest descending excitation in forelimb motoneurons was disynaptically mediated via a corticoreticulospinal pathway and slowly conducted excitation via corticospinal fibers and segmental interneurons. The findings stress the importance of di- and trisynaptic excitatory corticofugal pathways to forelimb motoneurons in the control of skillful digit movements.

[Functional action of nonfocused ultrasound on the somatosensory cortex and striatum in rats]. / Funktsional'noe vozdeistvie nefokusirovannym ul'trazvukom na somatosensornuiu koru i striatum krys.

Evoked potentials of the simmetric points of the striatum and the medullar reticular formation were investigated in immobilized albino rats under the ultrasound action on the cortical representation of one of the stimulated forepaws. It is found that the doze of the flat continuously radiated ultrasound which reversiblly depresses the functional activity in the cortex and in the ipsilateral striatum depends on the intensity and duration of the influence (intensity 3 w/sm2--time up to 15 s; time 120 s--intensity up to 1.2 w/sm2). Repeated application of the same doze ultrasound reduces the amplitude of the evoked potential and evoked significantly less effect than the previous one. The amplitude decrease of evoked potentials in the contralateral striatum and the reticular formation occurs only in response to the stimuli applied to the foriepaw the cortical representation of which is affected by ultrasound. The amplitude of all the potentials decreases in the ipsilateral striatum. The border between reversible and irreversible potential changes is individual for every animal.

[Heterogeneity of neurocytes of different brain regions to repeated superhigh-frequency irradiation]. / Geterogennost' reaktsii neirotsitov razlichnykh otdelov golovnogo mozga na mnogokratnoe sverkhvysokochastotnoe obluchenie.

The study was based on the analysis of morphological changes in the brain of 45 rats exposed for 10 days to ultrahigh frequency field of moderate gravity. Detailed studies of the state of the basophilic substance and the volume of the nuclei in the course of the neurocyte swelling were undertaken. The response of the neurocytes of various brain divisions was found to be heterogenous. The most pronounced were dystrophic changes in the sincipital area of the cortex. A lack of correlation between the character of the nuclear swelling and the degree of chromatolysis in the thalamic neurocytes was noted.