Gene structure and differential regulation of the Rhizobium-induced peroxidase gene rip1.

Primary expression of the Rhizobium meliloti-induced peroxidase gene rip1 occurs prior to nodule morphogenesis, specifically at the site of impending rhizobial infection (D. Cook, D. Dreyer, D. Bonnet, M. Howell, E. Nony, K. VandenBosch [1995] Plant Cell 7: 43-55). We examined the distribution and structure of rip1 transcript throughout nodule development. We determined that expression of rip1 in root tips is correlated with the competence of this zone for symbiotic association, whereas after rhizobial infection rip1 transcript is specifically associated with the zone of nodule development, including nascent nodule primordia. rip1 transcripts are characterized by multiple polyadenylation sites distributed within 200 to 400 bp of the translation stop site, and a single major transcription initiation site in close proximity to the rip1 open reading frame. Thus, rip1 expression is likely to be mediated through effects on a single transcription unit. Immediately 5' of the rip1 transcription unit DNA sequence analysis identified a 377-bp DNA element containing extensive repeat structure that is widely distributed in the Medicago truncatula genome.

Acute repeated nicotine injections increase enkephalin and decrease AP-1 DNA binding activity in rat adrenal medulla.

Previously we reported that a single injection of nicotine decreased AP-1 DNA binding activity in adrenal medullae, although chronic bidaily nicotine (and saline) injections increased this binding activity [15]. Repeated acute nicotine injections (3 mg/kg i.p., 7 injections equi-spaced over a 3 h period) effectively increased adrenal tyrosine hydroxylase [3] and [Met5]enkephalin levels and also profoundly decreased adrenal medulla AP-1 DNA binding activity for over 8 h.

Dependence of subjective traverse length on velocity of moving tactile stimuli.

Two series of experiments were performed to assess the effects of stimulus velocity on human subjects' perception of the distance traversed by a moving tactile stimulus. In all experiments, constant-velocity stimuli were applied to the dorsal surface of the left forearm; velocities ranging between 1.0 and 256 cm/sec were used. In some experiments the stimuli moved from distal to proximal over the skin, and in others they moved from proximal to distal. The length of skin contacted by the moving stimulus was defined by a plate having an aperture of 4.0 X 0.5 cm. In the first series of experiments, subjects were required to compare the distance traversed by a test stimulus delivered 2 sec after a standard stimulus, and also to report the on-locus and the off-locus of the brushing stimulus. In the second series of experiments, the subjects rated the perceived distance on the skin using a free-magnitude-estimation procedure. The data from both series of experiments defined the same relationship between stimulus velocity and perceived stimulus distance. More specifically, although the length of skin contacted by the stimulus was the same at all velocities, subjects' estimates of stimulus distance decreased with increasing stimulus velocity. In addition, the function relating estimates of stimulus distance to velocity was flat for velocities between 5 and 20 cm/sec, but possessed an appreciable negative slope at lower and higher velocities. It is interesting that the plateau of the relationship between perceived stimulus distance and velocity occurred within the range of velocities that human subjects employ to scan textured surfaces; it also corresponded precisely with the range of stimulus velocities at which the directional sensitivity of somatosensory cortical neurons and human subjects is optimal.

Factors influencing capacity to judge direction of tactile stimulus movement on the face.

The influence of stimulus velocity and traverse length on a subject's ability to indicate direction of brush movement across perioral skin was determined using a forced-choice procedure. The data show that correct identification of brush direction increases with traverse length and is optimal for velocities between 3 and 25 cm/sec.

Representation of moving stimuli by somatosensory neurons.

The findings obtained in neurophysiological and psychophysical investigations using tactile stimuli that move at constant velocity across the skin are reviewed. For certain neurons in the postcentral gyrus of the cerebral cortex (S-I) of macaque monkeys, direction of stimulus motion is a "trigger feature"" i.e., moving tactile stimuli evoke vigorous discharge activity in these neurons only if the stimuli are moved in a particular direction across the receptive field. This directional selectivity is maximal when stimulus velocity is between 5 and 50 cm/sec, and falls off rapidly at lower or higher velocities. The capacity for human subjects to correctly identify the direction of stimulus motion on the skin exhibits a similar dependence on stimulus velocity. The similar effects of velocity on neural and psychophysical measures of directional sensitivity support the idea that direction of stimulus motion on the skin can only be recognized if the moving stimulus optimally activates the group of S-I neurons for which that directions of simulus motion is the trigger feature.

Factors influencing cutaneous directional sensitivity.

The influence of stimulus velocity and traverse length on the ability of human subjects to indicate in which of two opposite directions a brush moved along the skin was determined using a forced choice procedure. Stimulus velocities ranged from 0.75 to 250 cm/sec, and traverse lengths ranged from 0.5 to 6 cm; measurements were made on both the thenar eminence and the preaxial upper arm. Performance was expressed in terms of "critical traverse length" i.e., that traverse length at which, for a given velocity, the subject would correctly identify the direction of brush motion on 75% of the trials. The data indicate that the capacity to identify direction of tactile stimulus motion increases with traverse length and is optimal for velocities between 3 and 25 cm/sec. The overall level of performance was better on the thenar than on the upper arm.

Thalamic projections to S-I in macaque monkey.

The organization of thalamic input to functionally characterized zones in primary somatosensory cerebral cortex (S-I) of macaque monkeys (Macaca mulatta) was investigated using the method of labelling by retrograde transport of horseradish peroxidase (HRP). It was found that the cell columns positioned at the posterior margin of the band of cortex representing a given body region receive thalamic input from a posterior level of the ventroposterior thalamic nucleus (VP), and that cell columns at successively more anterior positions within that band receive input from successively more anterior levels of VP. The extreme posterior and anterior margins of the S-I hand, foot and face areas receive input from neuron populations which are not as widely separated in the anteroposterior dimension of VP as the neurons projecting to the extreme anterior and posterior margins of the proximal limb and trunk representations in S-I. These characteristics of the organization of the projections from VP to S-I are consistent with the view that the body representations in VP and S-I have the same connectivity and differential submodality distribution; and with the idea that thalamocortical conncetions only exist between functionally equivalent neuron populations in VP and S-I.

Improved voiding in response to electrical stimulation of the spinal cord of paraplegic dogs.

Bipolar electrodes were inserted into the conus medullaris and attached to the proximal urethra of paraplegic dogs. Repeated stimulus trains were delivered to the spinal cord electrodes and the urethral electrodes in an attempt to improve voiding induced by cord stimulation. The results indicate that the increased outflow resistance which often accompanies electromicturition can be significantly overcome both by repeated spinal cord stimulation and by prestimulation of the proximal urethra.

Segmental analysis of spinal cord monoamines after thoracic transection in the dog.

The noradrenaline, dopamine and serotonin content from 10 segments of the dog spinal cord before and after a T7 transection were measured. The levels of amines were highest in the conus medullaris. However, when calculated per gram cord grey matter, noradrenaline was found to be concentrated in the midthoracic and sacral cord, while serotonin was concentrated in the mid-thoracic region. Levels of dopamine were very low throughout the spinal cord. Up to 3 days after a T7 transection, the levels of all 3 amines did not change in the distal cord segments. Ten days after transection the level of all 3 amines were less than twice tissue blank distally. This segmental analysis of dog spinal cord shows some potentially important differences from previous studies of cat and rat.

Representation of head and face in postcentral gyrus of the macaque.

The receptive field and submodality characteristics of individual neurons within the cytoarchitectural and topographic subdivisions of the head and face areas of the postcentral gyrus (SI) were determined with the technique of extracellular recording. Correlation of the single-unit data with the intracortical location of the recording electrode provided a detailed description of the functional organization within each of the several cytoarchitecturally distinct regions contributing to the representation of the head and face in SI. The data indicate that the functional organization of the SI cortex which receives its principal input from trigeminal mechanoreceptors is comparable to the organization within those SI regions which receive their input from the mechanoreceptors of the limbs, trunk, and tail. In each topographic subdivision of the SI cortex 1) a single region in the periphery is represented several times in widely separated locations, each time in a context of different submodalities and peripheral receptive fields; and 2) neurons belonging to the different submodality classes are segregated so that projections from cutaneous afferents terminate mainly in cytoarchitectural area 3 in the adjacent anterior portion of area 1, while projections from the afferents innervating deep tissues terminate mainly in cytoarchitectural area 3a, area 2, and the posterior part of each 1. Although the mechanoreceptor input to SI is segregated according to submodality and the mechanoreceptors from most body regions project to multiple widely separated regions within SI, neurons with receptive fields confined to the ophthalmic division of the trigeminal peripheral innervation field are found within a restricted region of the anterior postcentral gyral crown which is positioned symmetrically about the junction of cytoarchitectural areas 1 and 3. Neurons with receptive fields confined to the maxillary division of the trigeminal innervation field are found within a ring of cortex which a) completely surrounds the representation of the ophthalmic field, and b) includes parts of cytoarchitectural area 2, 1, 3, and 3a. SI neurons with receptive fields restricted to the mandibular division of the trigeminal innervation field occupy the largest portion of the SI face area and form a ring of cortical cell columns which completely surrounds that cortical region which receives its input from the maxillary peripheral innervation field.