Search PubMed⌕ Search

Biomedical subjects

R J Nelson

Publications and source records attributed to R J Nelson.

At least 253 records · Page 14Linked to original sources
PubMed1983

Topographic reorganization of somatosensory cortical areas 3b and 1 in adult monkeys following restricted deafferentation.

Two to nine months after the median nerve was transected and ligated in adult owl and squirrel monkeys, the cortical sectors representing it within skin surface representations in Areas 3b and 1 were completely occupied by 'new' and expanded representations of surrounding skin fields. Some occupying representations were 'new' in the sense that (1) there was no evidence that these skin surfaces were represented in this region prior to median nerve transection; and (2) these skin surfaces retained their normal representation elsewhere within these two cortical representations of hand surfaces. Large 'new' representations of the dorsal surfaces of digits 1 and 2 (innervated by the radial nerve) and large 'new' representations of the hypothenar eminence (innervated by the ulnar nerve) were consistently recorded. Some surrounding skin surface representations expanded into the former median nerve zone, so that bordering skin surfaces (the ulnar insular palmar pad, the third digital palmar pad, glabrous ulnar digit 3, radial hand dorsum) were represented over far larger than normal cortical areas. These expanded representations of always-innervated skin sometimes appeared to move in entirety into the former median nerve representational zone (e.g. in the zone of representation of glabrous digit 4) were also consistently recorded. Reorganizational changes following median nerve sections were much more variable in Area 1 than in Area 3b. The topographic order of the reorganized cortical zone was comparable to normal. In at least most cortical sectors, there was a consistent, maintained relationship between receptive field size and magnification, i.e. as representations enlarged, receptive fields were correspondingly reduced in size. These studies indicate that topographic representations of the skin surface in adult monkeys are maintained dynamically. They clearly reveal that this projection system retains a self-organizing capacity in adult monkeys. They suggest that processes perhaps identical to a part of the original developmental organizing processes (by which details of field topographics are established) are operational throughout life in this projection system in primates. Some of the implications of these studies for the neural origins of tactile perception are discussed.

Afferent Pathways↗
PubMed1983

Progression of change following median nerve section in the cortical representation of the hand in areas 3b and 1 in adult owl and squirrel monkeys.

In an earlier study (Neuroscience 8, 33-55, 1983), we found that the cortex representing the skin of the median nerve within parietal somatosensory fields 3b and 1 was completely occupied by 'new' inputs from the ulnar and radial nerves, 2-9 months after the median nerve was cut and tied in adult squirrel and owl monkeys. In this report, we describe the results of studies directed toward determining the time course and likely mechanisms underlying this remarkable plasticity. Highly detailed maps of the hand surface representation were derived in monkeys before, immediately after, and at subsequent short and intermediate time stages after median nerve section. In one monkey, maps were derived before nerve section, immediately after nerve section, and 11, 22 and 144 days later. Thus, direct comparisons in cortical map structure could be made over time in this individual monkey. In other experiments, single maps were derived at given post-section intervals. These studies revealed that: (1) large cortical sectors were 'silenced' by median nerve transection. (2) Significant inputs restricted to the dorsum of the radial hand and the dorsum of digits 1, 2 and 3 were immediately 'unmasked' by median nerve transection. (3) These immediately 'unmasked' regions were topographically crude, and represented only fragments of this dorsal skin. They were transformed, over time, into very large, highly topographic and complete representations of dorsal skin surfaces. (4) Representations of bordering glabrous skin surfaces progressively expanded to occupy larger and larger portions of the former median nerve cortical representational zone. (5) These 'expanded' representations of ulnar nerve-innervated skin surfaces sometimes moved, in entirety, into the former median nerve representational zone. (6) Almost all of the former median nerve zone was driven by new inputs in a map derived 22 days after nerve section. At shorter times (3, 6 and 11 days), 'reoccupation' was still incomplete. (7) Very significant changes in map dimensions within and outside of the former median skin cortical field were seen after the 'reoccupation' of the deprived cortex by 'new' inputs was initially completed. (8) Progressive changes were recorded within the original ulnar and radial nerve cortical representational zones, as skin surfaces originally overtly represented wholly within these regions expanded into the former median nerve zone. (9) Throughout the studied period, the cortical representational loci of many skin sites appeared to change continually and often markedly. (10) The locations of map discontinuities also shifted significantly over time. (11) Concomitant with changes in representational magnification over time, inverse changes in receptive field sizes were recorded.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1983

Influence of photoperiod, nutrition and water availability on reproduction of male California voles (Microtus californicus).

Male California voles were maintained in long (14L:10D) or short photoperiods (10L:14D) for 10 weeks and fed a standard diet of rabbit chow and water ad libitum. One additional group in each photoperiod received the standard diet plus supplements of spinach 3 times weekly. A fifth group was housed in 14L:10D and fed the standard diet, but for 10 weeks water availability was restricted to several hours each morning. Testes and seminal vesicles were heaviest in long-day voles fed spinach supplements and lightest in short-day voles fed only the standard diet; the latter animals manifested reduced testicular spermatogenesis. Testicular weights were also depressed in voles with restricted access to water. It is suggested that photoperiods that simulate those of winter induce regression of the reproductive organs of male California voles but the availability of green vegetation counteracts the inhibitory effects of short daylengths.

Animals↗
PubMed1983

Neovascularity of a tracheal prosthesis/tissue complex.

Permanent bioincorporation of a microporous tracheal prosthesis will require a stable blood supply to connective tissue supporting an epithelial surface. In experience with over 80 tracheal implants in dogs, we have observed that end-on ingrowth and epithelialization does not occur in the absence of lateral ingrowth, epithelialization is marked by the appearance of a subepithelial network of vessels, and this process must be well advanced by 6 to 8 weeks for long-term stability. These observations were extended by using microangiography to delineate the blood supply of the prosthesis/tissue complex. Six implants of bioelectric polyurethane with 10% gentamicin (3 cm length, 2 cm diameter, 1 to 1.25 mm wall thickness, 60 to 120 mu micropore diameter) were interposed in the dog thoracic trachea and wrapped with an omental pedicle. The aorta was perfused with a barium suspension at elective sacrifice between 10 weeks and 21 months. Radiographs of specimens were correlated with bronchoscopic, gross, and histopathological findings. Neovascularity of the prosthesis/tissue complex can be described in three categories: outer capsule, prosthetic wall, and inner lining. Outer capsule vessels were oriented circumferentially immediately adjacent to the prosthetic wall. They resembled arteries up to 75 mu diameter on microscopy and appeared to develop from the omentum with connections developing to the bronchial circulation. Prosthetic wall vessels up to 75 mu with thin muscular walls were noted to traverse the porous prosthetic wall. The inner lining had a network of subepithelial vessels that connected to the lamina propria vasculature of the native trachea across the anastomoses with vessels up to 120 mu in diameter. We conclude that the omentum provides an immediate blood supply and a base for early connective tissue ingrowth. Epithelialization occurs as early as 3 weeks on the favorable bed, accompanied by vascular connections to the existing lamina propria tracheal vessels. This dual organization of blood supply with connections across the prosthetic wall is probably important to long-term stability of healing.

Animals↗
PubMed1982

Representations of the body surface in cortical areas 3b and 1 of squirrel monkeys: comparisons with other primates.

Microelectrode multiunit mapping techniques were used to determine the somatotopic organization of postcentral parietal cortex in the squirrel monkey Saimiri sciurus. Recordings were largeLy confined to architectonic areas 3b and 1. Results were compared to those from similar studies of owl (Merzenich et al., '78) and macaque (Nelson et al., '80) monkeys. As in these previous investigations, separate representations of the body surface were found in areas 3b and 1 of squirrel monkeys. These representations were organized in parallel, so that both proceeded from the tail on the medial wall of the cerebral hemisphere, to the lips and oral cavity on the lateral margin of these areas along the sylvian fissure. The representations were also roughly mirror images of each other so that whatever skin surface was represented rostrally in area 3b was represented caudally in area 1, and similar skin surfaces were represented along the common border. However, the representations were not identical. For example, the split representations of the leg differed so that the distal leg was represented in cortex lateral to that devoted to the foot in area 1 and medial to the foot in area 3b. Remarkably, the representations of some body parts were reversed in orientation in both area 3b and area 1 in squirrel monkeys as compared to owl and macaque monkeys. The face, arm, trunk, and leg representations were all reversed in squirrel monkeys, while the orientations of the hand and foot representations were the same. For example, the dorsal trunk is trunk is represented at the 3b/1 border in owl and macaque in area the ventral trunk is represented at th 3b/1 border in squirrel monkeys. These reversals of somatotopic organization in part but not all of the representations in areas 3b and 1 suggest that both fields are divided into sectors where the basic somatotopic orientation is independently determined, that the orientation of some of these sectors is subject to reversal in evolution, and that matching sectors in areas 3b and 1 are not independent in somatotopic organization.

Animals↗
PubMed1982

Effect of suture technique on arterial anastomotic compliance.

To determine the immediate effect of running and interrupted suture on anastomotic compliance, catheters were positioned in both femoral arteries of ten dogs for pressure measurement and introduction of an electromagnetic rheoangiometry loop probe. Changes in the area of the loop allowed simultaneous determination of the static and pulsatile internal diameter of the vessel when the loop was in an externally induced magnetic field. After dynamic diameter compliance (Cd) of the undisturbed femoral arteries was obtained, they were exposed, stripped of their adventitia, and divided. They were subsequently anastomosed with 6-0 polypropylene suture using a running anastomosis for one femoral artery and an interrupted anastomosis for the other; Cd was then measured 1 cm proximal to the anastomoses, at the anastomoses, and 1 cm distal to the anastomoses. The Cd significantly decreased with both running and interrupted anastomoses; running anastomoses showed significantly greater decrease in compliance than did interrupted.

Animals↗
PubMed1982

Diagnosis and management decisions in infections of the deep fascial spaces of the head and neck utilizing computerized tomography.

Infections of the deep spaces of the head and neck may still result in major consequences despite the advent of antibiotics. Abscesses in these areas merit special consideration by today's head and neck surgeon because of their relative rarity and the life-threatening complications that may follow inadequate treatment. Diagnosis and management decisions are enhanced by use of computerized tomography (CT) as an adjunctive study. The EMI scan may demonstrate either cellulitis of the neck requiring no surgery or a space abscess displacing the adjacent structures thus requiring surgical drainage. Anatomy of the significant fascial planes and spaces of the neck will reviewed employing CT utilizing 3 mm cuts. Specific case presentations feature early diagnosis and management.

Abscess↗
PubMed1982

Photoperiodic regulation of testis function in rats: mediation by a circadian mechanism.

Laboratory rats traditionally are classified as nonphotoperiodic because variations in daylength have little or no effect on their gonadal function. After olfactory bulbectomy, however, rats show clear evidence of photoperiodic regulation of the gonads. The present study demonstrates, by means of resonance experiments, that the testicular response to daylength in rats is mediated by a circadian photoperiodic time measurement system similar to that of photoperiodic rodents. Olfactory-bulbectomized rats were maintained in fixed photoperiods in which a 6 h light period was coupled with dark periods of 18, 30, 42, or 54 h (6L:18D, 6L:30D, etc.); a fifth group was maintained in a 45L:10D photoperiod. Rats from the 6L:30D, 6L:54D and 14L:10D photoperiods had testes and seminal vesicle weights, plasma testosterone titers and spermatogenesis indices indicative of functional reproductive status. Rats exposed to the 6L:18D and 6L:42D photoperiods had reduced testicular and seminal vesicle weights, lower testosterone levels and reduced spermatogenesis. We hypothesize that photo- and nonphotoperiodic rodent species use similar mechanisms for distinguishing long from short photoperiods, but differ in the extent to which discrimination of short daylengths is transduced into altered gonadal activity.

Animals↗
PubMed1981

Connections of the ventroposterior nucleus of the thalamus with the body surface representations in cortical areas 3b and 1 of the cynomolgus macaque, (Macaca fascicularis).

The somatotopic pattern of the connections of the ventroposterior nucleus of the thalamus with the representations of the body surface in somatic cortical Areas 3b and 1 were investigated in macaque monkeys using the anatomical tracers horseradish peroxidase (HRP), and 3H-proline. These tracers, in combination or separately, were injected into one or more cortical sites, after the skin surface capable of activating neurons at each site had been defined with microelectrode mapping methods. These injection sites were later related to the overall organizations of the two cutaneous representations as determined in more extensive mapping experiments (Nelson et al, '80). Finally, zones of anterograde and retrograde label in the thalamus were located with reference to architectonically defined subnuclei in the ventroposterior nucleus (VP). The results led to the following conclusions. (1) Zones of cells in VP projecting to a given location in either Area 3b or 1 also receive reciprocal projections from the cortical target. (2) A given cortical location typically relates to a disc-shaped or lamellar region in VP with the disc extending rostrocaudally and dorsoventrally, being most narrow in the mediolateral dimension. (3) The representations of the same body surface in Area 1 and Area 3b relate to the same region of VP. However, since fewer cells were generally labeled after Area 1 injections, less dense terminations are suggested from VP to Area 1 than to Area 3b. (4) VP is the major or exclusive relay of somatosensory information to the two cutaneous representations from the thalamus. Labeled neurons or zones of terminations were found outside VP in other parts of the somatosensory thalamus only when injection sites extended into cortex outside Areas 3b and 1. (5) The face, hand, limbs, and foot are represented in a mediolateral sequence of subnuclei within VP. A dorsal capping subnucleus is apparently largely devoted to the axial trunk and perhaps other hairy skin surfaces such as some parts of the proximal surfaces of the limbs. (6) While anterior and posterior surfaces of the hind limb are widely separated by the glabrous foot in the cortical representations, they appear to be represented in adjacent zones in the thalamus.

Animals↗
PubMed1981

Histopathologic observations after short-term implantation of two porous elastomers in dogs.

This report describes the effects of pore size and material on soft tissue ingrowth of two medical-grade elastomers. Using the replamineform process, silicone rubber (SR) and bioelectric polyurethane (BEP) were rendered microporous with essentially the same microstructural pore configuration. Implants were prepared in each material having five pore size ranges: 18-25 microns, 30-45 microns, 75-95 microns, 60-120 microns, and 120-180 microns. Implants 1 cm X 1 cm X 1 mm were harvested at 1, 2, 4 and 12 weeks following subcutaneous implantation in mongrel dogs. Ingrowth of the 18-25 microns and 30-45 microns implants in both polymers consisted of histiocytes and dispersed fibrocytic proliferation during the first two weeks. By 12 weeks, the fibrocytic component had increased, but histiocytes remained the principal component of ingrown tissue. In contrast, initial ingrowth of the 75-95 microns, 60-120 microns and 120-180 microns implants showed increased fibrocytic proliferation and minimal histiocytic reaction. By 12 weeks, ingrowth into the larger-pore implants had progressed to broad bands of well organized collagenous stroma. Differences in the rate of tissue ingrowth were found to be related to both material and pore size. Less than 15% of the void spaces were infiltrated by 4 weeks in 18-25 microns and 30-45 microns SR implants, although this increased to approximately 50% by 12 weeks. In contrast, the 3 larger-pore SR implants and all pore sizes in the BEP implants were almost completely ingrown by 4 weeks.

Animals↗
PubMed1981

Hamster activity and estrous cycles: control by a single versus multiple circadian oscillator(s).

Running activity onset and estrous onset were recorded for hamsters exposed to progressively shorter daily light/dark (T) cycles. The period of the estrous cycle was a quadruple multiple of the period of the activity rhythm during entrainment to T cycles of 23.5-21.5 hr. There was no evidence of desynchronization of the activity and estrus rhythms. The very short estrous periods shown during exposure to short T cycles indicate that an intrinsic 96-hr interval for ovarian follicular maturation does not determine the period of the estrous cycle. Dissociation of estrous and running activity onsets occurred for all hamsters: estrous onset generally preceded running activity onset for T greater than or equal to 23.0 hr; for shorter T cycles, estrous onset generally lagged behind running activity onset. Wheel-running activity was intermittently split into entrained and free-running components for one female: at T = 22.0 hr, estrous onset was coupled first with one and then with the other of the split activity components. These findings suggest that two or more separate circadian oscillators may control timing of the activity and estrous rhythms.

Animals↗
PubMed1981

Photoperiodic control of reproduction in olfactory-bulbectomized rats.

30-day-old male rats were (1) sham-operated or subjected to (2) removal of the olfactory bulbs, (3) olfactory bulbectomy and blinding (4) olfactory bulbectomy and pinealectomy or (5) olfactory bulbectomy, blinding and pinealectomy. Animals were exposed from 30 to 110 days of age to long-day (14 h of light per day) or short-day (8 h of light per day) photoperiods. The reproductive system of neurologically-intact rats was not affected by exposure to short days. Nor did bulbectomy affect the reproductive system of rats exposed to long days. However, bulbectomized, short-day rats had significantly lower body weights, reduced testicular and seminal vesicle weights and lower plasma testosterone levels than did bulbectomized, long-day rats. The effects of short-day exposure on bulbectomized rats were prevented by pinealectomy. Short-day exposure and blinding exerted similar effects in bulbectomized rats. The testes of rats from all groups contained elongated spermatids; blinding and short-day treatment had no effect on spermatogenesis. Neither mating behavior nor the number of young sired was influenced by photoperiod in bulbectomized or intact rats. Removal of the olfactory bulbs unmasks photoperiodic responsiveness in rats; the antigonadal effects of short-day exposure are mediated by the pineal gland in bulbectomized rats as in species traditionally designated photoperiodic. The mechanisms by which bulbectomy renders rats responsive to short days are considered.

Animals↗
PubMed1980

Representations of the body surface in postcentral parietal cortex of Macaca fascicularis.

The somatotopic organization of the postcentral parietal cortex of the Old World monkey, Macaca fascicularis, was determined with multi-unit microelectrode recordings. The results lead to the following conclusions: 1) There are at least two complete and systematic representations of the contralateral body surface in the cortex of the postcentral gyrus. One representation is contained within Area 3b, the other within Area 1. 2) While there are important differences in the organization of the two representations, they are basically mirror-images of each other. 3) Each representation maintains body-surface adjacency by cortical adjacency in some mediolateral regions. In other regions, two types of discontinuities can be described: first, in which adjacent body surfaces are represented in separate cortical loci; second, in which adjacent cortical regions represent disparate body-surface regions. The internal organization of each representation is better described as a composite of somatotopic regions (Merzenich et al., '78) than as a serial array of dermatomal bands, or as a "homunculus." 4) While architectonic Area 2 responds to stimulation of deep body tissue, at least parts of Area 2 also respond to cutaneous stimulation. The organiation of the cutaneous representation of the hand in Area 2 is basically a mirror-image of the hand representation in Area 1. 5) Area 3a is activated by deep body tissue stimulation, suggesting the possibility of a fourth body representation within the traditional "S-I" region of somatosensory cortex in macaques. In accord with a previous study in a New World monkey (Merzenich et al., '78), we suggest that the cutaneous representation in Area 3b be considered as SI proper, and that the cutaneous representation in Area 1 be termed the posterior cutaneous field. Furthermore, based on the orientation of the representations of the body surface, as well as other factors, we suggest that the representation in Area 3b is homologous to "SmI" (or "SI") in non-primates.

Animals↗