Oxytocin-immunoreactive Fibers Research Articles

Distribution of oxytocin-immunoreactive neuronal elements in the rat spinal cord

We investigated the distribution of oxytocin in rat spinal cord using immunocytochemistry and radioimmunoassay (RIA). Each segment of the spinal cord from cervical to coccygeal contained oxytocin-immunoreactive fibers. The Rexed laminae I and II of the dorsal horn showed moderate to intense immunoreactivity. A dense network was found around the central canal where some fibers apposed the ependyma. The autonomic centers of the spinal cord at the thoracolumbar and sacral segments were heavily innervated. Few fibers were found around the motoneurons. In the white matter, the immunoreactivity was localized mainly in the dorsal part of the lateral funiculus, in the pars funicularis of the nucleus intermediolateralis and in a longitudinal network of the lateral funiculus below the spinal cord surface. Some fibers from this network entered the pia mater. RIA measurements revealed that the cervical spinal cord had lower oxytocin content than that found in either the thoracic, lumbar, sacral or coccygeal region. Our results show that the distribution of oxytocin-immunoreactive fibers in the spinal cord correlates with anatomic locations related to nociceptive, autonomic and motor functions. We assume that oxytocin-containing axons play a role in secreting oxytocin directly into the liquor space of the spinal cord.

Characterization of the oxytocin system regulating affiliative behavior in female prairie voles

Oxytocin regulates partner preference formation and alloparental behavior in the socially monogamous prairie vole (Microtus ochrogaster) by activating oxytocin receptors in the nucleus accumbens of females. Mating facilitates partner preference formation, and oxytocin-immunoreactive fibers in the nucleus accumbens have been described in prairie voles. However, there has been no direct evidence of oxytocin release in the nucleus accumbens during sociosexual interactions, and the origin of the oxytocin fibers is unknown. Here we show for the first time that extracellular concentrations of oxytocin are increased in the nucleus accumbens of female prairie vole during unrestricted interactions with a male. We further show that the distribution of oxytocin-immunoreactive fibers in the nucleus accumbens is conserved in voles, mice and rats, despite remarkable species differences in oxytocin receptor binding in the region. Using a combination of site-specific and peripheral infusions of the retrograde tracer Fluorogold, we demonstrate that the nucleus accumbens oxytocin-immunoreactive fibers likely originate from paraventricular and supraoptic hypothalamic neurons. This distribution of retrogradely labeled neurons is consistent with the hypothesis that striatal oxytocin fibers arise from collaterals of magnocellular neurons of the neurohypophysial system. If correct, this may serve to coordinate peripheral and central release of oxytocin with appropriate behavioral responses associated with reproduction, including pair bonding after mating, and maternal responsiveness following parturition and during lactation.

Differential vasopressin and oxytocin innervation of the human parabrachial nucleus: no changes in Alzheimer's disease.

The distribution of vasopressin and oxytocin immunoreactive fibers was examined in the pontine parabrachial nucleus of the human brain using purified polyclonal antibodies. The results revealed a striking predominance of vasopressin in this brain region. No obvious density difference, either in vasopressin or in oxytocin innervation, was found between Alzheimer's disease patients and matched controls. The present study corroborates other reports that suggest that in Alzheimer's disease the vasopressin innervation in the caudal part of the human brain is not affected.

Oxytocin modulates the effects of galanin in carrageenan-induced hyperalgesia in rats

In the present study we have investigated the effects of galanin and/or oxytocin on carrageenan-induced hyperalgesia, the relationship between oxytocin and galanin-containing nerve fibers in the spinal cord and the influence of galanin on oxytocin secretion. Galanin (1 μg) given intrathecally (i.t.) decreased significantly the mechanical nociceptive threshold of the carrageenan-treated hindpaw, with no significant effect on thermal nociception. The decrease in the mechanonociceptive threshold exerted by galanin was modulated by oxytocin (1 μg, i.t.) administered simultaneously. There was a close relationship between galanin- and oxytocin-immunoreactive fibers in the dorsal horn of the thoracic spinal cord, although there was no evidence for colocalization. Galanin 0.1 and 1 μg given intracerebroventricularly or intraperitoneally significantly decreased the oxytocin level in plasma 60 min after injection. Taken together, these data indicate that galanin may contribute to mechanical hyperalgesia by inhibiting the release of oxytocin from nerve terminals in the spinal cord and that oxytocin may be a potential analgesic agent.

The intermediolateral cell column of the thoracic spinal cord is comprised of target-specific subnuclei: evidence from retrograde transport studies and immunohistochemistry

In this study we examined the hypothesis that the intermediolateral cell column (IML) of the thoracic spinal cord, the nucleus from which preganglionic sympathetic neurons originate, provides an anatomical substrate through which selective regulation of sympathetic nervous system targets is accomplished. Preganglionic sympathetic neurons of rats were retrogradely labeled by the simultaneous exposure of the cervical sympathetic trunk (CST) and the adrenal medulla to Fluoro-Gold and True blue, contrasting fluorescent dyes. Retrograde labeling from these sites revealed 2 populations of sympathetic preganglionic neurons in IML whose distribution overlapped between segments T1 and T4. In regions where these 2 groups of retrogradely labeled neurons overlapped, sympathoadrenal preganglionic (SAP) neurons occupied the most lateral aspect of the nucleus. It was also determined whether individual retrogradely labeled neurons within these two groups sent axon collaterals to both the CST and adrenal medulla. Diamidino yellow, a fluorescent retrograde tracer dye that labels only nuclei, was substituted for Fluoro-Gold and used in combination with True blue to simultaneously label preganglionic sympathetic neurons projecting to either the CST or adrenal medulla. No double-labeled cell bodies were observed in spinal cords of rats treated in this manner. Thus it appeared that the efferent projections of these 2 cell populations in IML were target-specific. Immunohistochemical analysis of the relationship between nerve fibers in the IML and preganglionic sympathetic neurons was also undertaken in an attempt to classify further these 2 populations of sympathetic preganglionic neurons. Equal proportions of identified CST and SAP neurons appeared to be apposed by varicosities immunoreactive for either somatostatin or serotonin. On the other hand, when the comparison was based on whether oxytocin-immunoreactive varicosities appeared to appose these 2 populations of retrogradely labeled sympathetic neurons, a highly significant difference was revealed. That is, oxytocin-immunoreactive fibers and terminals appeared to avoid SAP neurons. Thus these data support the hypothesis that an anatomical substrate exists in spinal cord IML whereby selective regulation of sympathetic nervous system targets may be mediated. Moreover, the lack of oxytocin-immunoreactive varicosities apposing SAP neurons in IML suggests that if the paraventricular nucleus innervates SAP neurons in IML, it does so via a population of neurons that do not use oxytocin as a neurotransmitter.

Sympathoadrenal preganglionic neurons: their distribution and relationship to chemically-coded fibers in the kitten intermediolateral cell column

The location of those sympathetic preganglionic neurons in the spinal cord that project to the adrenal medulla — the sympathoadrenal preganglionic (SAP) neurons — was studied by the method of retrograde axonal transport of the fluorescent dye Fast Blue. The distribution of chemically-coded fibers and their relationship to the SAP neurons was also investigated using the indirect immunofluorescence technique. In kittens, 5 of a 1% solution of Fast Blue was injected into the medulla of the left adrenal gland. After a survival period of 5 days, the spinal cords from C8 to L5 were sectioned and processed for the localization of enkephalin-, neurophysin-, oxytocin-, serotonin-, substance P- and somatostatin-like immunoreactivity. Retrogradely labeled neurons were found in the ipsilateral intermediolateral cell column (IML) (89.8% of all retrogradely labeled neurons) from T1 to L4, and in the contralateral IML (10.2%) from T1 to L4. The enkephalin, serotonin and substance P immunoreactive fibers appeared to surround both the retrogradely labeled and unlabeled IML neurons. The somatostatin immunoreactive fibers were observed only in proximity to the retrogradely labeled neurons. Only a sparse population of neurophysin and oxytocin immunoreactive fibers were observed in IML, and were not seen to be in apposition to the retrogradely labeled neurons.

The differential distribution and relationship of serotoninergic and peptidergic fibers to sympathoadrenal neurons in the intermediolateral cell column of the rat: A combined retrograde axonal transport and immunofluorescence study

The preganglionic sympathetic neurons in the intermediolateral cell column of the thoracic and upper lumbar segments of the spinal cord which innervate the chromaffin cells in the adrenal medulla, sympathoadrenal preganglionic neurons, were identified by the method of retrograde axonal transport of the fluorescent dyes Fast Blue and True Blue. In rats, Fast Blue or True Blue was injected into the medulla of the left adrenal gland. After a survival period of 5 days, the animals were perfusion fixed, the thoracic and lumbar spinal cord sectioned and processed for the immunofluorescent localization of met-enkephalin, neurophysin, oxytocin, serotonin, somatostatin and substance P immunoreactivity. Neuronal perikarya which were retrogradely-labeled with Fast Blue or True Blue were observed in the intermediolateral cell column from the T1 to the L2 spinal cord segments. The distribution of the sympathoadrenal neurons was determined by counting the number of retrogradely-labeled neurons per spinal cord segment. In the five animals used for quantifying the sympathoadrenal preganglionic neurons, the majority (72.3%) of the retrogradely-labeled neurons counted per spinal cord were located within the T7–T12 segments. The T9 segment contained the largest average number (20.1%) of retrogradely-labeled cells in a single segment. Met-enkephalin, serotonin and substance P immunoreactive fibers were prominent in the intermediolateral cell column, whereas oxytocin, neurophysin and somatostatin immunoreactive fibers were sparse. The met-enkephalin, serotonin and substance P fibers were seen surrounding both unlabeled and retrogradely-labeled neurons; somatostatin fibers appeared to preferentially contact retrogradely-labeled neurons; whereas, the neurophysin and oxytocin fibers were not found in proximity to retrogradely-labeled neurons. Met-enkephalin, neurophysin, oxytocin, somatostatin and substance P immunoreactivity were depleted in the intermediolateral cell column below the level of a spinal cord transection. Serotonin immunoreactivity was depleted in the intermediolateral cell column below the level of the transection for five to six segments, but sparse networks of immunoreactive fibers were observed in both the intermedio-lateral cell column and the ventral horn in more caudal segments. Met-enkephalin, serotonin, somatostatin and substance P immunoreactivity were decreased in both the contralateral and ipsilateral intermediolateral cell column below the level of a spinal cord hemisection, suggesting that both crossed and uncrossed descending pathways exist. Neurophysin and oxytocin immunoreactivity were depleted below the level of the hemisection in the ipsilateral intermediolateral cell column without noticeable decrease in the level of immunoreactivity in the contralateral intermediolateral cell column, suggesting that a decussation does not occur at the level of the spinal cord, but may exist above the level of the hemisection. The sympathoadrenal preganglionic neurons in the intermediolateral cell column of the thoracic and lumbar spinal cord were observed and quantified. The findings suggest that sympathoadrenal preganglionic neurons, as well as other neurons in the intermediolateral cell column, receive met-enkephalin, serotonin and substance P afferents; somatostatin afferents preferentially surround sympathoadrenal neurons; and neurophysin and oxytocin immunoreactive fibers do not appear to impinge upon sympathoadrenal preganglionic neurons.