A nucleus in the dorsolateral funiculus of the spinal cord of the rat

Investigations of the distribution of acetylcholinesterase in the spinal cord of the rat have revealed a group of cells in the dorsolateral funiculus which show varying degrees of enzyme activity. In cervical segments of the spinal cord this group of cells occupies a pposition similar to that described for the lateral cervical nucleus in other species. However, in the rat the nucleus is found to extend throughout the whole length of the cord, from the spinomedullary junction to sacral segments.

In cholinesterase preparations some cells within the nucleus are located ventrolateral to the extreme lateral tip of the dorsal horn, while other cells are observed more medially near the base of the dorsal horn. The main group of cells within the nucleus lies between these two extremes. Most of the cells in the nucleus are multipolar and have dimensions of 8–36 μ by 4–12 μ. Many of the cell processes pass in a medial direction towards a group of cells located at the base of the dorsal horn, although a few cell processes run in a cranio-caudal direction. The high level of acetylcholinesterase activity in many cells in the nucleus may indicate that they are cholinergic. Thionin stained preparations confirm that the nucleus extends throughout the whole length of the spinal cord.

It is suggested that this nucleus in the rat may have a function similar to the lateral cervical nucleus of other species, and that it may receive afferent fibres at all segmental levels.     

Timing and duration of dihydrotestosterone treatment affect the development of motoneuron number and morphology in a sexually dimorphic rat spinal nucleus.

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic motor nucleus in the rat lumbar spinal cord. SNB motoneurons and their perineal target muscles are present in adult males, but reduced or absent in adult females. This dimorphism is due to the presence of androgens during development. Perinatal treatment of females with testosterone (T), or a combination of dihydrotestosterone (DHT) and estrogen (E+D females) from embryonic (E) day 16 through postnatal (P) day 5, results in a masculine number of SNB motoneurons and the retention of the target muscles. Perinatal treatment with estrogen alone does not masculinize the SNB; prenatal treatment with DHT alone from E17-E22 results in a feminine number of SNB motoneurons and a significantly altered motoneuron morphology and connectivity. To determine if masculinization of the SNB involves the interaction of estrogen and DHT or results from a longer exposure to DHT alone, the number, morphology, and connectivity of SNB motoneurons in females treated with DHT both pre- and post-natally (from E16-P5) were examined. At E22, DHTP (E16-P5) females have SNB motoneuron numbers identical to E+D and normal females, but far fewer than normal males, thus indicating that T is essential for prenatal masculinization. After E22, SNB motoneuron number declines precipitously in normal females but remains stable in DHTP (E16-P5) females and E+D females, which do not differ from normal males at P10. These results demonstrate that DHT can completely masculinize SNB motoneuron number without any synergistic actions with estrogen, and suggest that the development of SNB motoneuron number is strictly an androgen-mediated event. In adulthood, horseradish peroxidase histochemistry reveals that the connectivity, dendritic length, and soma size of SNB motoneurons in DHTP (E16-P5) females are identical to those of normal males but differ significantly from those of DHTP (E17-E22) females. These data suggest that the altered connectivity in DHTP (E17-E22) females is not simply a hormone-specific effect, but the result of a truncated hormone exposure. Thus, DHT can fully masculinize SNB morphology and connectivity if given during the appropriate period of development. It is suggested that while T may be required to masculinize the SNB prenatally, DHT may be involved in masculinizing postnatal aspects of SNB development.     

Normal development and effects of deafferentation on the morphology of superior collicular neurons projecting to the lateral posterior nucleus in hamster.

Visually responsive neurons in the superficial layers of the hamster's superior colliculus (SC) can be divided into distinct morphological and functional classes. In the preceding paper (Mooney et al., '91), we showed that neonatal enucleation has only slight and insignificant effects upon the structural characteristics of cells within a given class, but results in a significant reduction of neurons (narrow and widefield vertical cells) with dorsally directed dendritic arbors. In an effort to determine whether this change reflected differential transneuronal degeneration of these cell types or alterations in the dendritic arbors of surviving cells, this study re-examined this issue by restricting the analysis to a specific and relatively homogeneous subpopulation of superficial layer neurons, those that project to the lateral posterior nucleus (LP). Physiological recordings demonstrated that most (64.7%) tecto-LP cells in neonatally enucleated hamsters develop somatosensory receptive fields. The combination of retrograde tracing and injection of cells with Lucifer yellow in a fixed slice preparation demonstrated that nearly 75% of tecto-LP cells in normal adult hamsters are widefield vertical cells while less than 25% of the neurons filled in neonatally enucleated adults are in this class. Most of the tecto-LP cells in the neonatally enucleated adult hamsters were either horizontal cells (19.5%), giant stellate cells (24.6%), or had dendrites that were directed only toward the deep SC laminae (10.3%). Differential enucleation-induced cell death could not account for all of these changes. Tecto-LP neurons were retrogradely labelled with the carbocyanine dye, Di-I, in hamsters on postnatal day (P-) 0 (the day of birth) through P-10. As early as P-0, most retrogradely labelled neurons could be identified as either widefield (44.6%) or narrowfield (18.9%) vertical cells. These results, when considered together with those from the normal adult and neonatally enucleated adult hamsters, support the conclusion that neonatal eye removal results in a reorganizaton of the dendritic arbors of some collicular neurons that have already undergone considerable development at the time of the lesion.     

Neuroprotective effects of testosterone on motoneuron and muscle morphology following spinal cord injury

Treatment with testosterone is neuroprotective/neurotherapeutic after a variety of motoneuron injuries. Here we assessed whether testosterone might have similar beneficial effects after spinal cord injury (SCI). Young adult female rats received either sham or T9 spinal cord contusion injuries and were implanted with blank or testosterone-filled Silastic capsules. Four weeks later, motoneurons innervating the vastus lateralis muscle of the quadriceps were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in three dimensions. Soma volume, motoneuron number, lesion volume, and tissue sparing were also assessed, as were muscle weight, fiber cross-sectional area, and motor endplate size and density. Contusion injury resulted in large lesions, with no significant differences in lesion volume, percent total volume of lesion, or spared white or gray matter between SCI groups. SCI with or without testosterone treatment also had no effect on the number or soma volume of quadriceps motoneurons. However, SCI resulted in a decrease in dendritic length of quadriceps motoneurons in untreated animals, and this decrease was completely prevented by treatment with testosterone. Similarly, the vastus lateralis muscle weights and fiber cross-sectional areas of untreated SCI animals were smaller than those of sham-surgery controls, and these reductions were both prevented by testosterone treatment. No effects on motor endplate area or density were observed across treatment groups. These findings suggest that regressive changes in motoneuron and muscle morphology seen after SCI can be prevented by testosterone treatment, further supporting a role for testosterone as a neurotherapeutic agent in the injured nervous system.     

Sexual dimorphism and the influence of neonatal androgen in the dorsolateral motor nucleus of the rat lumbar spinal cord

There is a sexually dimorphic motor nucleus, the spinal nucleus of the bulbocavernosus (SNB) in the fifth and sixth lumbar segments of the rat spinal cord. We now report a second sex difference in the dorsolateral nucleus (DLN) in the ventral horn of the rat lumbar cord, which includes motoneurons innervating the ischiocavernosus muscle, a sexually dimorphic perineal muscle. Adult females possess fewer motoneurons in the DLN, probably because of an absence of neurons innervating the ischiocavernosus muscle, which females lack. The effect of a single dose of testosterone propionate on day 2 of life was confined to a specific rostrocaudal region of the adult DLN in which it partially masculinized the female DLN. Masculinized females have more DLN neurons than control females. The direction of change induced in DLN neuron number by the neonatal hormone treatment is compatible with the hypothesis that androgens are involved with the sexually dimorphic development of the DLN. In another motor nucleus, the retrodorsolateral nucleus, a small sex difference in neuron number was found in one study, but was not replicated in a second experiment.     

Androgenic regulation of dendritic trees of motoneurons in the spinal nucleus of the bulbocavernosus: reconstruction after intracellular iontophoresis of horseradish peroxidase

Androgen-sensitive motoneurons in the spinal nucleus of the bulbocavernosus (SNB) in adult male rats were labeled after intracellular iontophoresis of horseradish peroxidase, after which they were fully reconstructed in three dimensions in order to measure their dendritic trees. Three groups of rats were compared: intact adult male rats and male rats castrated as adults and given Silastic tube implants containing either testosterone or nothing. In the high-androgen groups (intact males and testosterone-treated castrates), soma size and the diameter of the first-order dendrites were larger than in blank-treated castrates. Moreover, the terminal dendrites in all groups possessed growth cones, implying that the dendrites of these motoneurons are capable of growth in adulthood. However, there were no statistically significant group differences in the length, membrane surface area, or volume of the dendritic trees, or in the orientation or branching symmetry of dendrites. In general, there were positive correlations between the size of the motoneuronal soma and various measures of the size of the dendritic tree and between the diameter of individual stem (first-order) dendritic branches and the size of remainder of that dendrite. These data suggest that there may be a modest effect of androgen on the size of the dendritic trees of SNB motoneurons in adulthood, although the effect is much smaller than has previously been reported.     

Vasopressin cells in the bed nucleus of the stria terminalis of the rat: sex differences and the influence of androgens

A sex difference in the number of vasopressin-immunoreactive cells was found in the bed nucleus of the stria terminalis of the rat. The number of cells found in males exceeded the female corresponding value. A sharp decrease in the number of vasopressin-immunoreactive cells was noted 21 weeks after the castration of adult male rats. This decline could be reversed completely by a 5-week testosterone substitution therapy.     

Hormone-sensitive periods for the control of motoneuron number and soma size in the dorsolateral nucleus of the rat spinal cord

The dorsolateral nucleus (DLN) of the rat lumbosacral spinal cord is sexually dimorphic, with males having more and larger DLN motoneurons than do females. The development of this dimorphism depends on the presence of perinatal androgens. The present study sought to determine the periods in development during which the DLN is sensitive to the masculinizing effects of the androgen testosterone propionate (TP). The size and number of DLN motoneurons in neonatally ovariectomized female rats that were exposed to TP during either the late prenatal, early postnatal, or late postnatal period were compared to control males and females. Both late prenatal and early postnatal TP injections significantly increased DLN number by 48% and 50%, respectively, but the sensitive period for TP masculinization of soma size seems to be primarily postnatal, because prenatal TP injections had little or no effect on that measure. The sensitive period for TP masculinization of DLN neuron number is similar to that of the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB). However, the sensitive period for TP masculinization of DLN soma size appears to begin later than for the SNB.     

The functional development of descending inhibitory pathways in the dorsolateral funiculus of the newborn rat spinal cord

The postnatal development of descending inhibition in the spinal cord has been studied in the rat. Electrophysiological recordings were made in neonatal rat pups of the activity in single lumbar dorsal horn cells evoked by stimulation of the skin of the hindlimb. Descending inhibition was tested by observing the effect of stimulation of the dorsolateral funiculus (DLF) at thoracic level on the dorsal horn cell responses. In adults the DLF is known to contain descending axons from the brainstem which inhibit dorsal horn cell activity. Such inhibition was always observed in days 22-24 rat pups. At 18 days of age it was present but required higher-intensity stimulation to produce an effect. On day 12 only half the dorsal horn cells tested were inhibited by DLF stimulation and then only weakly. On day 9 no cells were inhibited. Application of horseradish peroxidase to DLF axons in the lumbar cord resulted in retrograde labelling of cells in the medulla, pons and midbrain. The labelling on day 6 was comparable to the adult. The results show that despite the early anatomical existence of a descending DLF pathway, there is no functional descending inhibition until days 10-12 of life. It is suggested that this is due to delayed maturation of crucial interneurones in the dorsal horn or to insufficient levels of 5-hydroxytryptamine or other neurochemicals in the descending DLF axon terminals.     

Observations on the morphology of a nucleus in the dorsolateral funiculus of the spinal cord of the guinea-pig, rabbit, ferret and cat

A nucleus was found in the dorsolateral funiculus of the spinal cord of the guinea-pig. The nucleus extended from upper cervical to lumbar segments of the cord and was similar in appearance to that previously described in the rat. The nucleus also extended into lumbar segments of the spinal cord in both the rabbit and the ferret although in these species there were not as many cells in the nucleus in thoracic and lumbar segments of the cord as in the guinea-pig. In the cat, the nucleus was confined to the upper two or three cervical segments of the spinal cord.     

Harmonal regulation of adult sympathetic neurons: the effects of castration on tyrosine hydroxylase activity

The effects of the hormone testosterone on neurotransmitter synthesis in peripheral sympathetic ganglia were examined in adult male Sprague-Dawley rats. Tyrosine hydroxylase (T-OH), the rate limiting enzyme in catecholamine biosynthesis was examined in the hypogastric (HG), coeliac (CG), and superior cervical ganglion (SCG) subsequent to castration. Initial studies indicated that 2 weeks after surgery, HG T-OH activity fell to approximately 30% of control. In order to more clearly define the pattern of testosterone effects, HG was examined 1, 2 and 4 weeks after surgery. T-OH activity was 67%, 50% and 11% of control at these 3 respective time points, and the observed alteration in T-OH activity appeared to parallel changes in the size of pelvic target organs. Similar hormonal effects did not occur in other peripheral sympathetic ganglia; T-OH activity was unchanged in SCG and CG when examined 1 month after castration. Enzyme activity was restored following replacement therapy with testosterone, whereas the neural metabolite 17-beta estradiol was without effect. The recovery in T-OH activity was associated with partial recovery of target organ size. These studies suggest that hormonal factors regulate neurotransmitter synthesizing enzymes in adult sympathetic neurons and may do so via consequences of alterations in target organs. These observations parallel similar events in the developing nervous system.     

Motoneuron development after deafferentation: II. Dorsal rhizotomy does doe block estrogen-supported growth in the dorsolateral nucleus (DLN)

The lumbar spinal cord of the rat contains two sexually dimorphic motor nuclei, the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN). Postnatally, SNB and DLN motoneurons grow substantially and reach their adult morphology by 7 weeks of age. The masculinization of SNB and DLN motoneuron dendrites depends upon steroid hormones. After early castration, the growth of SNB and DLN dendrites is markedly attenuated, but testosterone replacement restores this growth. In the SNB, initial dendritic growth is also supported in castrates treated with estrogen. By using castration and hormone replacement techniques, we examined the development of DLN motoneuron morphology in estrogen-treated castrated rats to determine if estrogen also supports the growth of DLN motoneurons. In addition, given that dorsal root ganglia may be a site of estrogen action, we tested the hypothesis that estrogen acts at primary afferents to support DLN dendritic growth. Thus, we attempted to block the potential trophic effect of estrogen by performing unilateral dorsal rhizotomies in estrogen-treated castrates. DLN motoneuron morphology was analyzed at 4 and 7 weeks of age by using cholera toxin horseradish peroxidase (BHRP) histochemistry. As found for SNB motoneurons, estrogen treatment transiently supported development. DLN motoneurons in estrogen-treated castrates developed normally through 4 weeks of age, but by 7 weeks, DLN motoneuron morphology in estrogen-treated castrates was no longer different from that in oil-treated castrates. Moreover, deafferentation via unilateral dorsal rhizotomy did not inhibit estrogen's ability to masculinize the early development of DLN motoneurons. Thus, the trophic effect of estrogen did not appear to act via the dorsal root ganglia to support the early postnatal development of DLN motoneurons.     

Distribution and steroid hormone regulation of aromatase mRNA expression in the forebrain of adult male and female rats: A cellular-level analysis using in situ hybridization

Many of the effects of gonadal steroid hormones in the male brain are due to the actions of the testosterone metabolite estradiol, which is synthesized by the actions of the P450 enzyme aromatase. Aromatase activity is present in regions of the preoptic area, hypothalamus, and limbic system. Levels of aromatase activity in the brain are highly dependent on gonadal steroid hormones in many brain regions, but not all. We examined the distribution of aromatase mRNA in adult male and female rat brains as well as the regulation of the levels of aromatase mRNA in the brains of males by gonadal steroid hormones using in situ hybridization. This method was performed using a ³⁵S-labelled cRNA probe, transcribed in vitro from the rat ovarian aromatase cDNA. In the adult male, many heavily labelled cells were found in the encapsulated bed nucleus of the stria terminalis (BNST), the medial preoptic nucleus (MPN), the ventromedial nucleus (VMN), the medial amygdala (mAMY), and the cortical amygdala (CoAMY). The regional distribution of aromatase mRNA was similar in females, but females tended to have a lower number of aromatase mRNA expressing cells in each region compared to males. Aromatase mRNA levels in the BNST, MPN, VMN, and mAMY tended to be lower in castrated males than in intact males, whereas aromatase mRNA levels were unaltered by castration in the CoAMY. The degree of reduction in mean levels of aromatase mRNA following castration does not simply account for the large changes measured in activity following castration. Examination of the entire population of individual cells expressing aromatase mRNA in castrated males suggests that aromatase mRNA may be regulated by steroid hormones differentially in specific populations of neurons within regions where activity is known to decrease following castration. © 1996 Wiley-Liss, Inc.     

Glucose regulation of synaptic transmission in the dorsolateral septal nucleus of the rat.

Intracellular recordings were made from neurons in the dorsolateral septal nucleus (DLSN) of rat brain slices. Lowering the concentration of extracellular glucose resulted in a concentration-dependent membrane hyperpolarization associated with a cessation of spontaneous firing. The amplitude of the excitatory postsynaptic potential (EPSP), inhibitory postsynaptic potential (IPSP), and late hyperpolarizing potential (LHP) evoked by a single stimulus applied to the fimbrial/fornix pathway was decreased when the concentration of glucose was reduced to 0-2 mM. Substitution of glucose with 2-deoxy-D-glucose (11 mM), an antimetabolite of glucose substrate, mimicked the effects of glucose depletion. Mannoheptulose (10-20 mM), a potent hexokinase blocker, and dinitrophenol (50 microM), a potent inhibitor of oxidative phosphorylation, produced both the hyperpolarization and inhibition of postsynaptic potentials, even in the presence of 11 mM glucose. The sulphonylureas, glibenclamide (10 microM) and tolbutamide (1 mM), did not antagonize the hyperpolarization and the inhibition of the postsynaptic potentials produced by glucose depletion. The amplitude of membrane depolarizations produced by pressure application of glutamate (10 mM) and the membrane hyperpolarizations produced by pressure application of either muscimol (1 mM) or baclofen (1 mM) were almost unchanged, even when glucose was reduced to 1-2 mM. These results indicate that intracellular glucose metabolism regulates the function of septal neurons, not only by changing the resting membrane potential, but also by presynaptically affecting neurotransmission between the hippocampal formation and the lateral septum.     

Long ascending projections to the midbrain from cells of lamina I and nucleus of the dorsolateral funiculus of the rat spinal cord

Small volumes (5-40 nl) of an aqueous solution of wheat-germ-agglutinin-conjugated horseradish peroxidase (WGA-HRP) were injected unilaterally into midbrain structures of 18 adult, albino rats. In 17 of these preparations cells of many types were found to be retrogradely labeled in cervical and lumbar spinal cord segments. The data reported here concern the number and location of labeled cells from injection sites in the midbrain that affected two distinct cell populations: neurons within the marginal layer (lamina I cells) and neurons of the nucleus of the dorsolateral funiculus (NDLF cells). In ten of the preparations, only nine of which are reported in detail here, a total of 1,831 labeled lamina I cells were identified. In the lumbar enlargement they reached a density of more than 60 cells/mm. Of these, 85% projected to medial portions of the caudal, contralateral midbrain. Injection sites that were centered in the caudal periaqueductal gray (PAG) and/or in the immediately adjacent region of nucleus cuneiformis labeled the largest numbers of lamina I cells. Cells of the NDLF were retrogradely labeled in all preparations in which lamina I cells were labeled but they were also observed in five cases in which lamina I cells were not labeled. A total of 1,914 NDLF cells were labeled from all injection sites. These cells were found to have essentially a bilateral distribution with 57% of the cells located in the contralateral DLF. Although there is substantial overlap between the terminal fields of lamina I and NDLF cells within the midbrain, NDLF cells had a more diffuse target area encompassing the reticular core of the midbrain and PAG, bilaterally, while the target area for lamina I cells was comparatively discrete, being largely restricted to the more medially situated midbrain structures, contralaterally. Whether the terminations of lamina I cells in and near the PAG are from collaterals of spinothalamic neurons originating in lamina I, or a subclass of lamina I neurons that project exclusively to the midbrain, is not known. It is significant, however, that lamina I cells, known to be activated by noxious stimuli to the skin, should project to a region of the brain stem from which analgesia can be produced by electrical stimulation or by local application of opiates.     

Motor nuclei of peroneal muscles in the cat spinal cord

The cat peroneal muscles have been used in numerous investigations dealing with the physiological properties of motor units, muscle spindles, and Golgi tendon organs. This report presents a study of the organization of peroneal motor pools in the cat spinal cord by means of retrograde axonal transport of horseradish peroxidase from individual muscles to the corresponding motoneurons. The motor nuclei of peroneus longus (PL), peroneus brevis (PB), and peroneus tertius (PT) muscles formed thin columns in the lateral part of the ventral horn in spinal segments L6-S1. In the transverse plane, the PT and PL nuclei occupied, respectively, dorsolateral and ventromedial positions, with PB nucleus in an intermediate position overlapping with the other two nuclei. Measurements of cell body diameters allowed identification of alpha and gamma subgroups in peroneal motoneuron populations. The average numbers of motoneurons were about 96 alpha and 60 gamma in PL, 75 alpha and 54 gamma in PB, and 34 alpha and 23 gamma in PT. Comparison with data from electrophysiological studies indicated that whole populations of motoneurons were labeled in each motor nucleus. The proportions of gamma motoneurons were the same, and cell bodies of gamma motoneurons had similar sizes in the three peroneal populations. In contrast, alpha motoneurons were significantly smaller in PB than in the two other pools, in keeping with the fact that PB contains a proportion of slow motor units larger than the two other muscles. In large samples of homonymous motoneurons, the numbers of first-order dendrites correlated linearly with motoneuron sizes.     

The size and dendritic structure of HRP-labeled gamma motoneurons in the cat spinal cord.

We report quantitative data obtained from 60 fully reconstructed dendritic trees belonging to eight gamma-motoneurons (gamma-MNs) and six additional gamma-MNs that were not completely reconstructed. The cells were labeled intracellularly with horseradish peroxidase (HRP). These data are compared to measurements from 79 reconstructed dendrites belonging to seven documented alpha-motoneurons (alpha-MNs), supplemented by a larger sample of alpha-MNs labeled intracellularly or by retrograde transport with HRP. As expected from earlier studies, the soma dimensions and total membrane area of gamma-MNs were smaller than those of alpha-MNs. Although gamma-MN dendrites were, on average, slightly but significantly longer than those of alpha-MNs, the former had, on average, smaller diameter stem dendrites, less membrane area, and less profuse branching, and they tended to branch closer to the soma and to terminate farther from the soma. These differences were evident even when subsets of dendrites with similar stem diameters were compared. Some of the anatomical distinctions suggest that gamma-MNs are qualitatively as well as quantitatively different from alpha-MNs, even though the distributions of many of the morphological variables examined showed no abrupt discontinuities between the two motoneuron groups.     

Alteration in axial motoneuronal morphology in the spinal cord injured spastic rat

Following spinal cord injury (SCI), exaggerated reflexes and muscle tone emerge that contribute to a general spastic syndrome in humans. At present, the underlying mechanisms involved with the development of spasticity following traumatic spinal cord injury, especially with regard to axial musculature, remains unclear. The purpose of the present study was to examine the temporal changes in sacrocaudal motoneuronal morphology following complete transection of the sacral spinal cord and to correlate these changes with the onset and progression of spasticity within the tail musculature. The spinal cords of rats were transected at the upper sacral (S(2)) level. Animals were behaviorally tested for the onset and progression of spasticity in the tail and at 1, 2, 4, or 12 weeks postinjury were sacrificed. At these time points, the animals demonstrated stage 1, 2, 3, or 4 spastic behavior, respectively. Sacrocaudal motoneurons innervating selected flexor muscles within the tail were retrogradely labeled with cholera toxin beta-subunit and neuronal morphology was analyzed using a combination of immunocytochemistry and standard microscopy. Initially over the first 2 weeks postinjury, a transient increase in the lengths of primary and secondary dendrites occurred. However, a progressive decrease in the overall number of dendritic branches was observed between 2 and 12 weeks postinjury, which parallels the time frame for the progressive increase in spastic behavior in the tail musculature. Following spinal cord injury, there is an alteration in the morphology of tail flexor motoneurons, which may be relevant to the development of spasticity within the tail.     

A system of rat spinal cord lamina 1 cells projecting through the contralateral dorsolateral funiculus

The aim of these experiments was to sample the properties of lamina I neurones with long ascending projections. Recordings have been made from 136 units at the LA/5 level, with ascending axons reaching C2. More than 80% of the units projected via the contralateral dorsolateral white matter and only 10% via the contralateral ventral quadrant. None projected via the dorsal columns. Receptive fields were typically 1–2 cm² and although a substantial number of units responded to a limited range of intense stim-uli, a greater number of units were fired by both low- and high-threshold stimulation. In contrast to cells of deeper laminae, the majority of units were excited following activation of descending pathways in the dorsolateral funiculus. The functional role of these units is not obvious, but the location of the ascending projection and the influence of descending pathways does not support the notion that the output of lamina 1 constitutes a simple “pain pathway”.