Correlation of monosynaptic field potentials evoked by single action potentials in single primary afferent axons and their bouton distributions in the dorsal horn

The relationship between structure and function of the projections of single identified primary cutaneous axons was investigated by recording cord dorsum potentials at 4 sites in response to electrical stimulation of the single axon and visualizing the boutons of the axon stained by intracellular injection of horseradish peroxidase. The rostrocaudal extent of boutons differed from fiber to fiber ranging from 4.14-11.50 mm; their location in the dorsal horn also varied in agreement with the known somatotopy of the presynaptic neuropil and dorsal horn neurons. Rostrocaudal distributions of cord dorsum potentials and boutons of individual fibers revealed good agreement. Cord dorsum potential amplitude and length of the spinal projection were positively correlated with number of boutons, but no correlation with bouton density was found. The spinal projection of afferents innervating slowly adapting type 1 mechanoreceptors exhibited a greater rostrocaudal extent (mean: 8.48 mm) than those innervating rapidly adapting mechanoreceptors (i.e., hair follicle and field receptors: mean: 5.87 mm). Although the mean total number of boutons was greater for axons with slowly adapting receptors (7,250/fiber) than for axons of rapidly adapting receptors (4,677/fiber), no differences in the longitudinal density of boutons (boutons/mm) were observed. Likewise, summed amplitudes of cord dorsum potentials at the 4 recording electrodes were larger for SA1 afferents than for those of field and hair follicle afferents. A major role for the number of boutons in determining these differences is supported by the finding that the calculated average contribution per bouton to cord dorsum potentials (expressed as an amplitude coefficient a) was similar for slowly and rapidly adapting afferents. No evidence was found for regions in which boutons did not contribute to the cord dorsum potential.

Crossed and uncrossed projections to cat sacrocaudal spinal cord: I. Axons from cutaneous receptors

Intra-axonal recording and horseradish peroxidase staining techniques were used to map terminal fields of primary afferent fibers from cutaneous receptors within the cat sacrocaudal spinal cord. It was hypothesized that projection patterns of cutaneous afferent fibers mirror the known somatotopic organization of sacrocaudal dorsal horn cells. Forty-three primary afferent fibers, innervating either slowly adapting type I receptors, hair follicles, or slowly adapting type II receptors, all on the tail, were recovered. All collaterals (N = 372) branched from parent axons in the dorsal columns. Most collaterals coursed rostromedially to the ipsilateral gray matter, penetrated the medial dorsal horn, and arborized within laminae III, IV, and to a lesser extent, V. Ipsilateral projections to dorsal horn were as follows: axons with dorsal or dorsolateral receptive fields (RFs; n = 20) to the lateral portion, axons with lateral RFs (n = 4) to the central portion, and axons with ventral or ventro-lateral RFs (n = 19) to the medial portion. Most axons (16 of 20) with dorsal or dorsolateral RFs also had contralateral projections to lateral dorsal horn and most axons (15 of 19) with ventral or ventrolateral RFs also had contralateral projections to medial dorsal horn. No axons with lateral RFs had crossed projections. These data represent the first complete mapping of the somatotopic organization of primary afferent fiber projection patterns to a spinal cord level. The findings demonstrate that ipsilateral projection patterns of sacrocaudal primary afferent fibers are in register with the somatotopic organization of the dorsal horn. Our earlier suggestion that crossed projections of primary afferent fibers give rise to crossed components of dorsal horn RFs spanning the midline is supported by these results.

Degree of cervical carotid artery stenosis and hemispheric stroke: duplex US findings

Duplex ultrasound (US) scans of 110 carotid arteries ipsilateral to hemispheric strokes were compared with scans of 90 asymptomatic vessels in the same patients to determine the relative prevalence of stenotic lesions. In addition, scans of paired carotid arteries in patients with stroke involving only one cerebral hemisphere were compared to determine whether the incriminated side demonstrated a greater degree of stenosis than the asymptomatic side. The duplex US findings demonstrated a positive correlation between stenosis and hemispheric stroke. However, only 20% of carotid arteries ipsilateral to hemispheric stroke showed a reduction in diameter greater than 70%, compared with 5% of asymptomatic vessels. A minimal difference was demonstrated between the symptomatic and asymptomatic groups with respect to lesser degrees of stenosis. In paired carotid arteries, the degree of stenosis of the symptomatic vessel exceeded that of the asymptomatic vessel in only 43% of cases. These results suggest that the prevalence of severe carotid stenosis in stroke patients has been previously overestimated. The findings also emphasize the need for further investigation of other plaque-related risk factors that may enhance stroke prevention through improved selection of surgical or medical therapy. Factors currently under investigation include plaque ulceration, intraplaque hemorrhage, plaque echogenicity, and the effects of sequential stenoses.

Somatotopy of digital nerve projections to the dorsal horn in the monkey

The dorsal horn projection patterns of finger nerves were investigated in four Macaca mulatta monkeys. Proper digital branches of the median nerves, serving the radial aspect of a digit on each hand, were loaded with wheatgerm agglutinin-horseradish peroxidase complex (WGA:HRP). The distribution of the lectin-enzyme complex was mapped in the right and left dorsal horns. The dorsal horn projections of the digital nerves were localized in segments C6-C8 in laminae I-VI, primarily in laminae I-IV. The wedge-shaped termination zones were somatotopically organized, in agreement with the projections of the digits in cats. The fingers are represented medially, as they are in the cat. This similarity suggests that there is a mediolateral gradient of dorsal horn organization similar to that of the cat, with distal skin represented medially and proximal skin represented laterally. The rostrocaudal trajectory of finger representation, with digit 1 most rostral and digit 5 most caudal, is also in agreement with the organization of hindlimb toe projections in the cat. There was a high degree of bilateral symmetry for homologous nerves, and little overlap of projections from nerves innervating adjacent fingers. The sample size was too small to permit us to assess interanimal variation. These results suggest a similar somatotopy of projections, and presumably of dorsal horn cell somatotopy, in monkey and cat.

Temporally dependent changes in response properties of dorsal horn neurons after dorsolateral funiculus lesions

Previous studies in this laboratory have shown 1) that 19% of L6 and L7 dorsal horn cells in normal cats respond only with excitatory postsynaptic potentials (EPSPs) to sural nerve stimulation, and 2) that the distribution of dorsal horn neurons responding with impulses to sural nerve stimulation is increased in cats with chronic lateral funiculus lesions. The present study was undertaken to determine whether strengthening of subliminal sural nerve projections could account for the changes seen after lateral funiculus lesions and to explore the nature of these changes in greater detail. Ipsilateral L6 and L7 dorsal horn cells of cats with T12 dorsolateral funiculus (DLF) lesions were studied electrophysiologically at less than 1-30 days postoperatively (DPO) and were compared with similar cells recorded in normal cats. The major results were as follows. 1. Responsiveness to peripheral stimulation was depressed for up to 3 DPO following the lesions. 2. The percentage of L6 and L7 dorsal horn cells showing spontaneous activity was elevated at 3 DPO and declined to normal levels by 28 DPO. 3. The percentage of cells that responded to sural nerve stimulation increased over 3-30 DPO and was significantly greater than normal at 28-30 DPO. The increase in the percentage of cells giving impulses to sural nerve stimulation at 28-30 DPO was similar to the percentage of cells with subliminal responses to sural nerve stimulation in normal cats. A subpopulation of identified postsynaptic dorsal column neurons also showed a significant increase in the percentage that responded to sural nerve stimulation after DLF lesions. 4. The percentage of cells that had a cutaneous receptive field (RF) overlapping the region of skin innervated by the sural nerve also increased over time and was significantly greater than normal at 28-30 DPO. 5. Median low-threshold or high-threshold RF areas were not significantly greater than normal ipsilateral to DLF lesions at any survival time. 6. The proportions of low-threshold (LT), high-threshold (HT), and multireceptive (MR) cells were not significantly different from normal at any survival time from less than 1 to 30 DPO.(ABSTRACT TRUNCATED AT 400 WORDS)

Dorsal horn potentials and current source densities evoked by single action potentials in single slowly adapting type I axons

The slow-wave response of cat dorsal horn, elicited by single action potentials in single slowly adapting type I (SAI) axons, was mapped by averaging the slow wave recorded from each locus in a rectangular array of recording loci in the transverse plane. Current source-density (CSD) waveforms were computed from these averages. Evoked potentials always included N-waves, with mean latency = 4.9 ms, rise time (base line to peak) = 2.3 ms, and duration (base line-peak-base line) = 13.1 ms. In some planes, the N-wave was followed by a longer P-wave. The N-wave timing corresponded to previously described excitatory postsynaptic potentials (EPSPs) recorded intracellularly and excitatory discharges recorded extracellularly from single units evoked by single SAI spikes. The P-wave timing corresponded to a previously described postexcitatory suppression of SAI spike-evoked EPSPs and discharges following single conditioning SAI action potentials. The current sink during the N-wave had the following properties: It occurred in a column of tissue, perpendicular to the laminar borders, less than 600 microns wide; this is similar to the terminal domain of a single SAI collateral. It remains stationary during the N-wave, indicating that the excited population of dorsal horn elements does not spread or shift within the transverse plane during the response. It is somatotopically organized in the mediolateral dimension, in a manner similar to the somatotopic organization of primary afferent terminations and of dorsal horn cell receptive fields.

Somatotopic organization in cat spinal cord segments with fused dorsal horns: caudal and thoracic levels

We have explored the somatotopic organization of the two cat spinal cord regions where the dorsal horns are fused (i.e., continuous across the midline): the caudal and thoracic segments. We have mapped the low-threshold component of dorsal horn cell receptive fields (RFs) in these segments and have charted the locations of dorsal root low-threshold mechanoreceptive dermatomes. We also have determined the projections of caudal and thoracic dorsal roots to laminae III and IV by using degeneration techniques. The dorsal skin of the tail or thorax is represented laterally, and ventral skin is represented at the midline, in the fused dorsal horns. Many caudal and thoracic dorsal horn units had RFs that crossed the dorsal or ventral midline of the skin; these units were encountered near the edges or the midline, respectively, of the fused dorsal horns. The tail is fully represented within dorsal root dermatomes S3 to Ca5. Roots more caudal than Ca5 represent progressively smaller skin areas of the distal tail. Adjacent dermatomes overlapped 15-65%. Thoracic dermatomes had a nearly vertical orientation; adjacent dermatomes overlapped by 30-75%. Dorsal roots in caudal and thoracic regions have crossed projections to the medial and lateral (but not middle) portions of the contralateral dorsal horn. These crossed projections are a possible anatomical substrate for RFs that cross the ventral or dorsal midline. The dorsal root projection patterns are consistent with those that would be predicted from the dorsal root dermatomes and dorsal horn cell somatotopy, assuming that the presynaptic terminals' somatotopy is in register with that of dorsal horn cells (the presynaptic somatotopy hypothesis; see Ref. 12).

Effect of temperature and length of storage on serum-stimulated and serum-independent lipolytic activities in human milk

Milk was collected from five mothers. Upon collection, serum-stimulated and serum-independent lipolytic activities were determined. The milk samples were aliquoted and stored at 25, 4, -20, and -70 degrees C. After storage for 3, 6, 12, and 24 h, serum-stimulated and -independent activities were again determined and compared with the initial activities. Storage at 25 degrees C resulted in a significant (p less than 0.05) decrease in lipolytic activity. Serum-stimulated activity decreased 83.4% and serum-independent activity decreased 66.9% over the 24-h period. Storage at 4 degrees C resulted in a significant (p less than 0.05) decrease of 22.6% in serum-stimulated activity and a 7.2% decrease in serum-independent activity. No significant changes were observed in milk stored for 24 h at -20 and -70 degrees C. Milk was stored at -20 and -70 degrees C for an additional 1, 2, and 4 weeks. Serum-stimulated lipolysis did not change significantly over the 4-week period. Serum-independent lipolysis increased significantly (p less than 0.05) with storage time. Storage at -20 degrees C resulted in an increase of 20% and storage at -70 degrees C resulted in an increase of 36% over the 4 weeks.

Two-point discriminability: relation to properties of the somatosensory system

The ability to resolve two closely spaced cutaneous stimuli presumably depends upon the degree of overlap between the two populations of responding neurons. The degree of overlap is determined by receptive field (RF) geometry and location, and by interactive factors such as lateral inhibition. In this paper, we first consider some aspects of RFs that would be expected to influence two-point acuity. In some somatosensory brain regions, relatively few RFs overlap the body midline. As would be expected, discrimination is enhanced for two points straddling the backbone. This does not simply reflect a mediolateral gradient of acuity, as we found higher acuity laterally. On the limbs, where RFs are elongated along the length of the limb, transverse two-point acuity was greater than longitudinal acuity. However, on the back, where RFs are fairly round, there was an even larger orientation effect, with two-point acuity greater for stimuli longitudinal than for stimuli transverse to the spine. Thus, the substantial variation of two-point acuity with stimulus orientation on the back cannot be explained by RF geometry alone. We discuss the possibility that differences in lateral inhibition and degree of similarity in dermatomal composition contribute to the observed stimulus orientation effects.

Projections of hindlimb dorsal roots to lumbosacral spinal cord of cat

Single dorsal roots of spinal nerves that contribute to the cat lumbosacral plexus (L3-S2) were cut to evoke degeneration of centrally projecting axons. Serial sections throughout lumbosacral cord levels were impregnated by the Fink-Heimer method (20) to permit charting of the distribution patterns of segmental dorsal root afferent fibers. Afferent fibers that enter a single dorsal root have an extensive distribution to multiple cord segments; their longitudinal extent varies with entry level and with laminar targets. Afferent projections to the ventral horn reach motor nuclei only in their entry segment and the adjacent segments just above and below their entry. Those afferent fibers projecting to intermediate gray (laminae VI and VII) have the most extensive spinal distribution of any types; they may, from a single dorsal root, reach as many as 13 or 14 cord segments. Dorsal horn projections of single roots are also longitudinally expansive. Small-diameter afferent fibers course rostrally and caudally in Lissauer's tract (LT) for up to 9-10 segments. They appear to terminate in at least laminae I and II in and near their entry segment; their endings are difficult to demonstrate at greater distances where they are probably less dense. Larger caliber axons entering the dorsal horn generate a somatotopically organized projection, especially to laminae III and IV. Collaterals of these fibers appear to course longitudinally within the gray matter and they distribute to as many as six to seven segments.

Distribution of trans-octadecenoic acid in the major glycerolipids of human milk

The intramolecular distributions of fatty acids in triacylglycerol, phosphatidylcholine, and phosphatidylethanolamine of human milk were determined. Milk donated from 10 mothers during their 2nd week of lactation was analyzed. Based on pancreatic lipase digestion of milk triacylglycerols, the 14:0 and 16:0 fatty acids were observed predominantly in the sn-2 position, while 18:0, 18:1, and 18:2 were observed predominantly in the sn-1,3 positions. The average trans-18:1 content of the triacylglycerols was 3.4% and was greater in the sn-1,3 positions. Phosphatidylcholine and phosphatidylethanolamine were digested by phospholipase A2. As in other tissues, saturated fatty acids were esterified at the sn-1 position and polyunsaturated fatty acids at the sn-2 position of the phospholipids. The proportion of trans-18:1 averaged 2.5% in phosphatidylcholine and 3.7% in phosphatidylethanolamine. The proportion of trans-18:1 was slightly greater in the sn-2 position of the phospholipids. In conclusion, there appeared to be a reverse positional distribution of saturated and polyunsaturated fatty acids in triacylglycerol compared to phosphatidylcholine and phosphatidylethanolamine. When compared to other mammalian tissues, there were only small differences observed in trans-18:1 content between positions within a glycerolipid class and between glycerolipids of human milk.

Bile salt-stimulated lipase in human milk from 2 to 16 weeks postpartum

Our objectives were to determine the change in bile salt-stimulated lipase (BSSL) activity in mature milk with time postpartum and to determine if BSSL activity was related to total lipid in the milk. Milk samples were collected from 12 mothers at 2, 6, 12 and 16 weeks postpartum. A significant (P less than .05) decrease in BSSL activity with time was observed. The average values expressed as mumol free fatty acids released/min/ml milk were 5.3, 4.5, 4.1 and 3.6 at 2, 6, 12 and 16 weeks postpartum. Total lipid in the milk increased significantly (P less than .05) from 4.1 g/dl at 2 weeks to 5.4 g/dl at 16 weeks postpartum but was not significantly correlated with BSSL activity.

Effects of dorsal root section on spinocervical tract neurones in the cat

1. In nine cats, dorsal roots L(6) and L(7) were sectioned under pentobarbitone anaesthesia using strict aseptic precautions. In two cats all lumbosacral roots except L(6) were sectioned under similar conditions. 27-75 days after the dorsal rhizotomies, under chloralose anaesthesia, neurones of the spinocervical tract (s.c.t.) were recorded electrophysiologically both extracellularly and intracellularly, their response properties and receptive fields were analysed, and they were injected with horseradish peroxidase (HRP). Twenty-five cells were recorded extracellularly and twenty were recorded intracellularly and stained with the enzyme.2. Of the twenty neurones stained with HRP, one was located in caudal L(5), eleven in L(6) and eight in L(7). Five cells had no receptive field, either before or after current injection, two cells had no field before injection but after current injection responded to either electrical stimulation of peripheral nerve or to brusque tapping on the limb; six neurones responded only to tapping before current injection and two of these showed a more clearly defined receptive field after current injection; six neurones had a receptive field and responded with impulses to hair movement and/or pressure within a well-defined area but this area was surrounded by skin from which excitatory post-synaptic potentials could be elicited; only one neurone had an apparently normal receptive field.3. Of the twenty-five neurones recorded extracellularly, eleven had no receptive field, four responded only to tapping on the limb, three had receptive fields consisting of an area of low threshold plus an area responding to brusque or noxious mechanical stimulation, and seven neurones had apparently normal receptive fields.4. Neurones with no observable receptive fields were either silent with no resting activity, or had very low rates of background activity consisting of isolated single impulses or short bursts of impulses. No neurones in de-afferented segments had high rates of background activity.5. There were no alterations in the normal somatotopy of the dorsal horn. All fifteen s.c.t. neurones injected with HRP and which had a localizable receptive field had fields appropriately located in the somatotopic map. There were no electro-physiological signs of inappropriate connexions.6. The dendritic trees of fifteen neurones injected with HRP were reconstructed. With the exception of one cell which appeared grossly disorganized (but which was the one cell with an apparently normal receptive field), there were no obvious differences between the dendritic trees of de-afferented cells and normal cells from the same and other cats. Their dendritic trees had similar rostro-caudal, medio-lateral and dorso-ventral extents to normal cells, and appeared to exhibit similar degrees of branching. There was a suggestion that de-afferented neurones had rather more of their dorsally-directed distal dendrites invading lamina II than normal cells, but the sample size was too small to make this more than a possibility.7. It is concluded that after dorsal rhizotomy, s.c.t. neurones lose part or all of their afferent input and that within 75 days do not show any signs of new or inappropriate connexions.

Receptive field organization and response properties of spinal neurones with axons ascending the dorsal columns in the cat

Micro-electrode recordings were made from single post-synaptic axons in the dorsal columns of cats anaesthetized with chloralose and paralysed with gallamine triethiodide. The recordings were made from the L5 segment and the axons were shown to project to the upper cervical level. Forty-eight units were recorded and the axons had conduction velocities of 22-61 ms-1, averaging 38.3 ms-1. Excitatory receptive fields were complex in many units, being made up of clearly defined, separate, low and high threshold areas. The receptive fields were often discontinuous. Only a few units behaved as if they received excitatory input from a single class of mechanoreceptors. A minority (13%) of units had labile, excitatory receptive fields that expanded in size during the recording period. About 40% of the units had inhibitory receptive fields. These were of two main types: either small and within or adjacent to the excitatory field, or large and separated from or adjacent to the excitatory field. The great majority of units had resting discharges upon isolation and these consisted of single impulses or bursts of impulses at short intervals separated by longer, irregular periods. The time course of inhibition produced by electrical stimulation of cutaneous nerves suggested presynaptic inhibitory components to the inhibition. Some inhibitory curves were very prolonged with maxima at about 100 ms and total durations of up to 400 ms. The complexity of the receptive field organization in these dorsal horn neurones is discussed, as is their possible significance as input neurones to the dorsal column nuclei.

Human complement activation by self-associated IgG rheumatoid factors

IgG rheumatoid factors (IgG-RFs) undergo concentration-dependent self-association into dimers and higher polymers, as previously reported. The interactions of purified IgG-RF from the plasma of 3 patients with rheumatoid arthritis, with guinea pig and human complement were studied. Self-associating IgG-RFs were isolated by affinity columns and gel filtration. These preparations contained no detectable IgM and were composed only of IgG subclasses known to fix complement. Complement utilization of IgG-RF was compared with that of monomeric IgG, heat-aggregated IgG, and soluble rabbit IgG immune complexes. Although incubation of IgG-RF or monomeric IgG with 3 units of guinea pig or human complement resulted in decreased hemolysis of sheep erythrocytes sensitized with IgM hemolysin, these substances were less than 100 times as effective as heat-aggregated IgG or soluble immune complexes. The ability of human or guinea pig complement that had been incubated with IgG-RF to restore hemolytic activity to C4-deficient guinea pig serum served to distinguish Clq binding from complement cascade activation. IgG-RFs and monomeric IgG did not activate guinea pig complement cascade in contrast to aggregated IgG. IgG-RFs, however, activated human complement cascade; monomeric IgG only bound human Clq. These results indicate that self-associated IgG-RFs can activate human complement in fluid phase, but less effectively than aggregated IgG or large-latticed immune complexes.

Somatotopic organization of hindlimb cutaneous nerve projections to cat dorsal horn

1. The dorsal horn lamina III-IV projections of 10 hindlimb nerves innervating most of the hindlimb have been studied in the cat using transganglionic transport of horseradish peroxidase (HRP). The somatotopic organization of whole cutaneous nerve projections was largely in register with the somatotopic organization of dorsal horn cells. That is, nerves projected to areas of dorsal horn where their innervation fields overlap the receptive fields of dorsal horn cells. 2. However, long-ranging projections were observed that were more extensive than predicted from the somatotopy of dorsal horn cells: these long-ranging projections may reflect the presence of normally ineffective synapses (synapses that do not cause postsynaptic discharge during receptive-field mapping of dorsal horn cells,) or a misconception of dorsal horn cell somatotopy in S2 and caudal segments, or the existence of a functionally separate cell group in ventral lamina IV and lamina V of these segments. 3. The cutaneous innervation fields of homologous nerves possessed high bilateral symmetry, as did their lamina III-IV projection fields. The degree of separation or overlap of two cutaneous nerves' projection fields was predictable from the degree of separation or overlap of their cutaneous innervation fields.

Changes in the lipids of human milk from 2 to 16 weeks postpartum

Changes in total lipid, fatty acids, total cholesterol, free cholesterol, and lipid phosphorus in mature milk with time were investigated. Milk samples were collected from 10 mothers at 2, 6, 12, and 16 weeks postpartum. During 1 day, each mother donated two complete breast expressions. Expressions were taken using an electric breast pump 1 h after the previous a.m. and p.m. nursing. For each mother, the a.m. and p.m. samples were pooled for analysis. It was observed that the amount of total lipid increased significantly (p less than 0.05) from 3.9 g/100 ml at 2 weeks to 5.2 g/100 at 16 weeks postpartum. The total fatty acid composition remained uniform during the investigation. Average total cholesterol and free cholesterol in the milk were 10.3 mg/100 ml and 8.3 mg/100 ml, respectively. These concentrations did not change significantly with time postpartum. Average lipid phosphorus was 3.9 mg/100 ml and also remained constant throughout. We conclude that the fatty acid pattern, lipid phosphorus, total cholesterol, and free cholesterol of mature milk to 16 weeks postpartum remains relatively constant while total lipid concentration increases.