Self-motion signals in vestibular nuclei neurons projecting to the thalamus in the alert squirrel monkey.

Sixty vestibular nuclei neurons antidromically activated by electrical stimulation of the ventroposterior thalamus were recorded in two alert squirrel monkeys. The majority of these neurons were monosynaptically activated by vestibular nerve electrical stimulation. Forty-seven neurons responded to animal rotations around the earth-vertical axis; 16 of them also responded to translations in the horizontal plane. The mean sensitivity to 0.5-Hz rotations of 80 degrees /s velocity was 0.40 +/- 0.31 spikes.s(-1).deg(-1).s(-1). Rotational responses were in phase with stimulus velocity. Sensitivities to 0.5-Hz translations of 0.1 g acceleration varied from 92.2 to 359 spikes.s(-1).g(-1) and response phases varied from 10.1 degrees lead to -98 degrees lag. The firing behavior in 28 neurons was studied during rotation of the whole animal, of the trunk, and voluntary and involuntary rotations of the head. Two classes of vestibulothalamic neurons were distinguished. One class of neurons generated signals related to movement of the head that were similar either when the head and trunk move together or when the head moves on the stationary trunk. A fraction of these neurons fired during involuntary head movements only. A second class of neurons generated signals related to movement of the trunk. They responded when the trunk moved alone or simultaneously with the head, but did not respond to head rotations while the trunk was stationary.

Coding of self-motion signals in ventro-posterior thalamus neurons in the alert squirrel monkey.

The firing behavior of 47 ventro-posterior thalamus neurons was studied in two alert squirrel monkeys during rotations of whole body, head and trunk. A total of 27 of these neurons (57%) were sensitive to spatial motion of the head irrespective of the mode of motion. These neurons responded similarly when the head moved simultaneously with the trunk, and when the head voluntarily or involuntarily moved on the stationary trunk. These neurons did not respond to rotation of the trunk when the spatial position of the head was fixed. Five neurons (11%) responded only to involuntary movement of the head produced by external force, but were insensitive to voluntary spatial head movement. They also did not respond to spatial motion of the trunk. Totally 15 neurons (32%) were sensitive to spatial motion, which included rotation of the trunk. These neurons responded when the trunk moved alone, and when the trunk moved simultaneously with the head, but were not responsive to spatial movement of the head while the trunk was stationary. We suggest that the vestibulo-thalamo-cortical pathway comprises two distinct functional channels. In one of these channels, cephalokinetic, spatial motion of the head is coded. In the other channel, somatokinetic, motion of the body in space is coded. Each of these channels further consists of two divisions. In the principal division the motion signal is conveyed continuously, irrespective of the behavioral context of motion. In the other auxiliary division the signal only codes movement caused by externally applied force.

PCBs, PBDEs and pesticides released to the Arctic Ocean by the Russian rivers Ob and Yenisei.

The Ob and Yenisei Rivers contribute 37% of riverine freshwater inputs to the Arctic Basin and thus represent an important pathway for the land-Arctic ocean exchange of contaminants. Sampling was carried out in the Yenisei (2003) and Ob (2005) River estuaries and Kara Sea to address the general lack of reliable dissolved contaminant flux data for these major rivers. Contaminant analyses were performed by high resolution mass spectrometry on sample extracts taken from filtered large volume water samples (50-100 L) and concentrated in situ onto XAD-2 resin columns. Hexachlorocyclohexanes (HCHs), the polychlorinated biphenyl (PCB) mixtures Sovol and trichlorodiphenyl, dichlorodiphenyltrichloroethane (DDT), as well as "penta" brominated technical mixtures of polybrominated diphenyl ethers (PBDEs) are important contributors to persistent organohalogen contamination for these waterways. Dissolved fluxes to the Kara Sea were estimated at sigmaHCH 246 kg/yr, sigmaPCB 63 kg/yr, sigmaDDT 16 kg/yr, hexachlorobenzene 8 kg/yr, alpha-endosulfan 8 kg/ yr, dieldrin 5 kg/yr, sigmaPBDE 4 kg/yr, and chlordanes 4 kg/yr. Contaminant fluxes from these rivers are similar to those reported for major Canadian rivers, confirming expectations that the Ob and Yenisei are also major point sources for the Arctic basin.

Activity of ventroposterior thalamus neurons during rotation and translation in the horizontal plane in the alert squirrel monkey.

The firing behavior of 107 vestibular-sensitive neurons in the ventroposterior thalamus was studied in two alert squirrel monkeys during whole body rotation and translation in the horizontal plane. Vestibular-sensitive neurons were distributed primarily along the anterior and posterior borders of ventroposterior nuclei; three clusters of these neurons could be distinguished based on their location and inputs. Eighty-four neurons responded to rotation; 66 (78%) of them responded to rotation only and 18 (22%) to both rotation and translation. Forty-one neurons were sensitive to linear translation; 23 (56%) of them responded to translation only. The population rotational response to 0.5-Hz sinusoids with a peak velocity of 40 degrees /s showed a gain of 0.23 +/- 0.15 spike.s(-1).deg(-1).s(-1) and phase lagging behind the angular velocity by -9.3 +/- 34.1 degrees . Although rotational response amplitude increased with the stimulus velocity across the range 4-100 degrees /s, the rotational sensitivity decreased with and was inversely proportional to the stimulus velocity. The rotational response amplitude and sensitivity increased with the stimulus frequency across the range 0.2-4.0 Hz. The population response to sinusoidal translation at 0.5 Hz and 0.1 g amplitude had a gain of 111.3 +/- 53.7 spikes.s(-1).g(-1) and lagged behind stimulus acceleration by -71.9 +/- 42.6 degrees . Translational sensitivity decreased as acceleration increased and this was inversely proportional to the square root of the acceleration. Results of this study imply that changes in the discharge rate of vestibular-sensitive thalamic neurons can be approximated using power functions of the angular and linear velocity of spatial motion.

Nucleus prepositus.

The cytoarchitecture and the histochemistry of nucleus prepositus hypoglossi and its afferent and efferent connections to oculomotor structures are described. The functional significance of the afferent connections of the nucleus is discussed in terms of current knowledge of the firing behavior of prepositus neurons in alert animals. The efferent connections of the nucleus and the results of lesion experiments suggest that it plays a role in a variety of functions related to the control of gaze.

Signal processing of semicircular canal and otolith signals in the vestibular nuclei during passive and active head movements.

The vestibular nerve sends signals to the brain that code the movement and position of the head in space. These signals are used by the brain for a variety of functions, including the control of reflex and voluntary movements and the construction of a sense of self-motion. If many of these functions are to be carried out, a distinction must be made between sensory vestibular signals related to active head movements and those related to passive head movements. Current evidence is that the distinction occurs at an early stage of sensory processing in the brain, and the results are evident in the firing behavior of neurons in the vestibular nuclei that receive direct inputs from the vestibular nerve. Several specific examples of how sensory information related to passive and active head movements is transformed in the vestibular nuclei are discussed.

Firing behaviour of squirrel monkey eye movement-related vestibular nucleus neurons during gaze saccades.

The firing behaviour of vestibular nucleus neurons putatively involved in producing the vestibulo-ocular reflex (VOR) was studied during active and passive head movements in squirrel monkeys. Single unit recordings were obtained from 14 position-vestibular (PV) neurons, 30 position-vestibular-pause (PVP) neurons and 9 eye-head-vestibular (EHV) neurons. Neurons were sub-classified as type I or II based on whether they were excited or inhibited during ipsilateral head rotation. Different classes of cell exhibited distinctive responses during active head movements produced during and after gaze saccades. Type I PV cells were nearly as sensitive to active head movements as they were to passive head movements during saccades. Type II PV neurons were insensitive to active head movements both during and after gaze saccades. PVP and EHV neurons were insensitive to active head movements during saccadic gaze shifts, and exhibited asymmetric sensitivity to active head movements following the gaze shift. PVP neurons were less sensitive to on-direction head movements during the VOR after gaze saccades, while EHV neurons exhibited an enhanced sensitivity to head movements in their on direction. Vestibular signals related to the passive head movement were faithfully encoded by vestibular nucleus neurons. We conclude that central VOR pathway neurons are differentially sensitive to active and passive head movements both during and after gaze saccades due primarily to an input related to head movement motor commands. The convergence of motor and sensory reafferent inputs on VOR pathways provides a mechanism for separate control of eye and head movements during and after saccadic gaze shifts.