Spinal projection neurons to the laterodorsal pontine tegmental nucleus: relationship to preganglionic neurons and nitric oxide synthase.

The region of the rat sacral parasympathetic nucleus (SPN) contains distinct subpopulations of neurons that project supraspinally or are preganglionic neurons. Some preganglionic neurons in the SPN serve as the motor outflow for urinary bladder contraction; other neurons in the SPN project to regions of the rostral pons that subserve micturition reflexes. Previous studies utilizing immunohistochemistry or staining for nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) have demonstrated that numerous neurons in the SPN contain nitric oxide synthase (NOS), the enzyme for nitric oxide synthesis. Thus, the objectives of this study were to determine 1) the distribution of neurons in the region of the SPN that project to the laterodorsal tegmentum (LDT) of the pons, 2) whether spinal neurons projecting to a peripheral autonomic ganglion also project to the LDT, and 3) whether NOS or NADPH-d is present in LDT projection neurons. Preganglionic neurons were identified by injecting the retrograde tracer fluorogold (FG) into the major pelvic ganglion (MPG). Supraspinally projecting neurons were identified by injecting the retrograde tracer fast blue (FB) into the LDT. Numerous FB-labeled neurons were present in the ipsi- and contralateral SPN and were immediately dorsal to FG-labeled preganglionic neurons. Neurons containing both tracers were not observed. Approximately 20% of preganglionic neurons, but no LDT projection neurons, were reactive for NOS and NADPH-d. These data suggest that the region of the SPN is a site for distinct subpopulations of neurons that project to the LDT and to the MPG and that NOS is contained in some preganglionic neurons, but is not a marker for LDT projection neurons.

Nitric oxide nerves in the uterus are parasympathetic, sensory, and contain neuropeptides.

Nitric oxide (NO) is synthesized in neurons and is a potent relaxor of vascular and nonvascular smooth muscle. The uterus contains abundant NO-synthesizing nerves which could be autonomic and/or sensory. This study was undertaken to determine: 1) the source(s) of NO-synthesizing nerves in the rat uterus and 2) what other neuropeptides or transmitter markers might coexist with NO in these nerves. Retrograde axonal tracing, utilizing Fluorogold injected into the uterine cervix, was employed for identifying sources of uterine-projecting neurons. NO-synthesizing nerves were visualized by staining for nicotinamide adenine dinucleotide phosphate (reduced)-diaphorase (NADPH-d) and immunostaining with an antibody against neuronal/type I NO synthase (NOS). NADPH-d-positive perikarya and terminal fibers were NOS-immunoreactive (-I). Some NOS-I/NADPH-d-positive nerves in the uterus are parasympathetic and originate from neurons in the pelvic paracervical ganglia (PG) and some are sensory and originate from neurons in thoracic, lumbar, and sacral dorsal root ganglia. No evidence for NOS-I/NADPH-d-positive sympathetic nerves in the uterus was obtained. Furthermore, double immunostaining revealed that in parasympathetic neurons, NOS-I/NADPH-d-reactivity coexists with vasoactive intestinal polypeptide, neuropeptide Y, and acetylcholinesterase and in sensory nerves, NOS-I/NADPH-d-reactivity coexists with calcitonin gene-related peptide and substance P. In addition, tyrosine hydroxylase(TH)-I neurons of the PG do not contain NOS-I/NADPH-d-reactivity, but some TH-I neurons are apposed by NOS-I varicosities. These results suggest NO-synthesizing nerves in the uterus are autonomic and sensory, and could play significant roles, possibly in conjunction with other putative transmitter agents, in the control of uterine myometrium and vasculature.

NADPH-diaphorase-positive nerves and the role of nitric oxide in CGRP relaxation of uterine contraction.

We previously demonstrated calcitonin gene-related peptide (CGRP) immunoreactivity in sensory nerves in the rat uterus and that CGRP inhibits stimulated uterine contraction in vitro. The present study was undertaken to: 1) examine possible roles nitric oxide (NO) may have in the inhibitory action of CGRP on uterine contraction and 2) identify sites where NO may be synthesized. The relaxing effect of CGRP on SP-stimulated uterine contraction was established in vitro on uterine horns from diethylstilbestrol-treated rats. These experiments were repeated with or without an arginine analog [NG-monomethyl-L-arginine (L-NMMA)] that inhibits NO formation. The localization of the synthetic enzyme for NO production, NO synthase, was accomplished by histochemically staining for NADPH-diaphorase. Calcitonin gene-related peptide (10(-7) M) significantly reduced SP (10(-5) or 10(-6) M)-stimulated uterine contraction. The L-NMMA (10(-3) M) blocked the relaxing action of CGRP on SP-stimulated uterine contraction. The L-NMMA alone had no effect on SP-stimulated uterine contraction. NADPH-diaphorase-positive nerve fibers were located in the myometrium, endometrium, and adjacent to the vasculature. These data demonstrate that: 1) L-NMMA suppresses the relaxant effect of CGRP on myometrial activity and 2) NADPH-diaphorase (indicative of NO synthase) is localized in uterine nerve fibers. These data suggest that the inhibitory action of CGRP may be dependent on NO formation and that the enzyme necessary for NO production is present in nerves in areas optimal to affect myometrial activity.

Light- and electron-microscopic study of synaptic connections in the paracervical ganglion of the female rat: special reference to calcitonin gene-related peptide-, galanin- and tachykinin (substance P and neurokinin A)-immunoreactive nerve fibers and terminals.

Nerve fibers and varicosities in the pelvic paracervical ganglia (PG) are immunoreactive for the neuropeptides calcitonin gene-related peptide, galanin, and the tachykinins substance P and neurokinin A. Many of these fibers and varicosities are capsaicin-sensitive, originate in dorsal root ganglia and, thus, are considered to be primary afferent fibers. Numerous immunoreactive varicosities are pericellular to principal neurons in the PG. The present study examines the ultrastructure of calcitonin gene-related peptide-, galanin-, substance P-, and neurokinin A-immunoreactive nerve fibers and varicosities in the ganglia to determine their relationships to principal neurons and their synaptic connectivity. Paracervical ganglia of female rats were processed for light-microscopic immunohistochemistry using antisera against synapsin I, as a nerve terminal marker, and microtubule-associated protein-2 to define soma and dendrites. The rationale for performing this co-immunohistochemical analysis was to reveal the relationship between nerve endings and principal neurons. Synapsin I endings were predominantly axosomatic with fewer being axodendritic. Other ganglia were processed for electron-microscopic immunohistochemistry using both standard immunogold and peroxidase-anti-peroxidase procedures. Unmyelinated fibers and varicosities immunoreactive for calcitonin gene-related peptide, galanin, and the tachykinins were routinely observed in the interstitium between neuron somas. Numerous immunoreactive axon profiles were present in small groups that were ensheathed by Schwann cells. Immunoreactive fibers and varicosities were also observed within the satellite-cell sheath of the neuron soma and often intimately associated with the membrane of the soma, somal protrusions, or with the proximal part of a dendrite. Membrane specializations, indicative of synaptic contacts, between the fibers and the principal neurons were observed. It is suggested that these peptide-immunoreactive sensory fibers and varicosities are involved in regulation of activity in the PG.

CGRP-immunoreactive primary afferent nerve fibers in the rat urinary bladder: effects of dorsal rhizotomy and MK-801.

A transection lesion of the suprasacral spinal cord results in a decreased density of calcitonin gene-related peptide (CGRP)-immunoreactive (I) primary afferent nerve fibers in the rat urinary bladder. The fiber density can be restored by postsurgical treatment with the N-methyl-D-aspartate receptor antagonist MK-801. We are attempting to determine the level of the primary afferent neuron at which MK-801 might have a restorative effect on CGRP immunostaining. Thus, the purpose of this study was to determine if MK-801 had a similar restorative effect on immunostaining for CGRP in bladder nerves after a direct lesion of the sacral afferent system, i.e., rhizotomy of the L6 and S1 dorsal roots. To assess the effect of the lesion, the mean length and number of bladder CGRP-I nerve fibers, as well as the number of CGRP-I perikarya in the L6 and S1 dorsal root ganglia (DRG), were measured following bilateral L6 and S1 dorsal rhizotomies. Both the mean length and the numbers of CGRP-I bladder fibers were significantly decreased by the lesion. However, the number of CGRP-I primary afferent perikarya in the L6 and S1 DRG was unchanged from control values. Rats which received rhizotomies and subsequent treatment with MK-801 did not exhibit restoration of the density of CGRP-I bladder fibers nor an alteration in the number of CGRP-I primary afferent perikarya. These data suggest that MK-801-induced restoration of bladder CGRP-I primary afferent nerve fibers may rely on an intact central process.

Distribution of NADPH-diaphorase-positive nerves in the uterine cervix and neurons in dorsal root and paracervical ganglia of the female rat.

Nitric oxide synthase (NOS) was selectively stained in nerve fibers of the uterine cervix and neurons of the paracervical (PG) and dorsal root ganglia (DRG) by NADPH diaphorase histochemistry. In the cervix, numerous NADPH-diaphorase-positive nerve fibers were observed in the myometrium, endometrium and around arteries. In addition, a subpopulation of neurons within ganglia that innervate the cervix, i.e., the PG and DRG, were NADPH-diaphorase positive; thus the fibers in the cervix could be sensory and/or autonomic. NADPH-diaphorase/NOS localization identifies sites where nitric oxide (NO) can be synthesized. Since NO relaxes vascular and nonvascular smooth muscle, the prevalence and anatomical localization of NADPH-diaphorase-positive fibers suggest that they could influence functions of the uterine cervix.

Origin and distribution of NADPH-diaphorase-positive neurons and fibers innervating the urinary bladder of the rat.

Nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry was utilized to localize nitric oxide synthase (NOS), and thus sites where nitric oxide (NO) can be synthesized, within peripheral nervous system perikarya and fibers. Recent studies suggest that NO relaxes vascular and non-vascular smooth muscle. In this study, the origin and distribution of NADPH-diaphorase perikarya and fibers in the rat urinary bladder were examined. Results suggest that a small number of NADPH-diaphorase-positive perikarya are present within the bladder wall and within adjacent small ganglia. In addition, NADPH-diaphorase-positive nerve fibers were observed in the adventitial and muscular layers, subjacent to the urothelium and as perivascular fibers. After injection of the retrograde tracer fluorogold (FG) into the bladder wall, numerous FG-labeled perikarya in the major pelvic ganglia and the T13-L2, L6 and S1 dorsal root ganglia were NADPH-diaphorase positive. However, none of the FG-labeled perikarya in the inferior mesenteric ganglia were NADPH-diaphorase positive. The prevalence of NADPH-diaphorase-positive perikarya and fibers suggests that NO may serve a role in bladder function.

CGRP immunoreactivity and NADPH-diaphorase in afferent nerves of the rat penis.

Calcitonin gene-related peptide (CGRP)-immunoreactive afferent nerve fibers are abundant in the rat penis. In addition, NADPH-diaphorase, which stains for nitric oxide synthase, has been localized within both autonomic and sensory dorsal root ganglia (DRG) and may be part of an important biochemical pathway involved in penile tumescence. The purpose of this study was: 1) to examine the circuitry of afferent nerves that are CGRP immunoreactive from the L6 DRG, 2) to examine the possibility that there are NADPH-diaphorase-positive afferent fibers from the L6 DRG to the rat penis, and 3) to examine the localization and colocalization of CGRP and NADPH-diaphorase within L6 DRG afferent perikarya. Calcitonin gene-related peptide immunostaining in the penis was eliminated following a bilateral transection of the pudendal nerves, but was unchanged following a bilateral transection of the pelvic splanchnic or hypogastric nerves. The NADPH-diaphorase staining was not altered by any of the nerve transections. Injection of the retrograde axonal tracer fluorogold (FG) into the dorsum penis labeled perikarya in the L6 DRG. Although the majority of FG-labeled perikarya contained neither CGRP nor NADPH-diaphorase, small subpopulations of perikarya contained either CGRP immunoreactivity, NADPH-diaphorase, or both. A unilateral pudendal nerve transection virtually eliminated (> 99%) FG labeling in the ipsilateral L6 DRG. These data suggest that NADPH-diaphorase and CGRP are present, either together or separately, within a subpopulation of penile afferent perikarya. In addition, CGRP-immunoreactive afferent nerve fibers reach the penis primarily via the pudendal nerves. Finally, NADPH-diaphorase-positive penile afferents may be another important source of nitric oxide (NO) for penile tumescence.

Coexistence of calcitonin gene-related peptide and galanin immunoreactivity in female rat pelvic and lumbosacral dorsal root ganglia.

Coexistence of immunoreactivity for calcitonin gene-related peptide (CGRP) and galanin (GAL) was examined in varicose nerve endings in female rat pelvic paracervical ganglia (PG) and in perikarya of lumbosacral dorsal root ganglia (DRG). Varicose peptide-containing nerves were closely adjacent to somata of neurons in the PG, certain somata being virtually surrounded by immunoreactive varicosities. Some nerve endings were immunoreactive for either CGRP or GAL; in others, immunoreactivity for CGRP and GAL coexisted. Likewise, many perikarya in DRG were CGRP immunoreactive, fewer were GAL immunoreactive, and in some immunoreactivity for CGRP and GAL coexisted. The results suggest there are subpopulations of neuropeptide-containing sensory nerve endings in the PG; some contain CGRP, some contain GAL, and in some CGRP and GAL coexist. These substances contained in sensory nerve endings could have important roles in pelvic ganglionic functions.

Effects of spinal cord transection and MK-801 on CGRP immunostaining in the rat urinary bladder.

Numerous studies have demonstrated that lesions in the CNS can alter the density of sensory nerve processes in peripheral organs. In the present study, rat spinal cords were transected at the second lumbar segmental level and the density of calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers in the urinary bladder was examined. Additional rats had spinal cord transections followed by 12 days of treatment with the N-methyl-D-aspartate receptor antagonist, MK-801. In the bladders of control rats, CGRP-immunoreactive fibers were present as thick nerve trunks, perivascular plexi, and a fine meshwork of varicose nerve fibers. Twelve days following a spinal cord transection, the density of CGRP-immunoreactive nerve fibers was markedly reduced; occasional fibers appeared primarily as nonvaricose fine fibers. In bladders from rats receiving a spinal cord transection and MK-801 treatment, CGRP-immunoreactive fibers were abundantly distributed throughout the detrusor muscle; these fibers exhibited numerous varicosities as well as some enlarged terminal varicosities. These data demonstrate that (i) an upper motor neuron-type lesion markedly decreases the density of CGRP-immunoreactive peripheral afferent nerve processes and (ii) following a spinal cord transection, MK-801 appears to enhance the density of CGRP immunostaining in the bladder.

Galanin and calcitonin gene-related peptide immunoreactivity in nerves of the rat uterus: localization, colocalization, and effects on uterine contractility.

Immunoreactivity to the neuropeptides galanin (GAL) and calcitonin gene-related peptide (CGRP) was examined in nerves in the rat uterus as a prelude to studying their effects on uterine contractility. With immunocytochemical techniques, GAL immunoreactivity (GAL-I) and CGRP-I were localized in myometrial nerves throughout the uterine horns and cervix, with nerves immunoreactive for CGRP being more numerous. Immunocytochemical double-labeling studies revealed GAL coexists with CGRP in a subpopulation of CGRP-I nerve fibers, i.e., GAL-I was not present in all CGRP-I nerves. Effects of these neuropeptides on uterine contractility were examined on in vitro preparations of uterine horns from diethylstilbestrol-treated rats. GAL (10(-5) to 10(-8) M) stimulated uterine contraction in a dose-related manner. CGRP had no effect on basal uterine tension, but CGRP (10(-7) M) reduced GAL-stimulated (10(-7) M) uterine contraction by 92.5%. These results demonstrate that GAL- and CGRP-I are present in, and coexist in, some uterine nerves, presumably afferent nerves. GAL and CGRP could be released from afferent fibers in an "efferent fashion" and influence uterine contractility, GAL having a contractile effect and CGRP having a relaxing effect.

Acute and chronic ethanol alter somatosensory-evoked potentials in conscious rats.

This study examined the effects of acute and chronic ethanol on cortical somatosensory-evoked potentials (SEPs) of laboratory rats. Evoked potentials were recorded following stimulation of the left hindpaw before and after injection of either saline or ethanol. Animals were then chronically exposed to ethanol in vapor inhalation chambers for five weeks. Recordings of SEPs before and after acute ethanol injection were then obtained 24 h and again seven days after withdrawal from ethanol exposure. The results indicate that acute ethanol produced a dose-dependent reduction in SEP amplitude, but did not alter peak latencies. Chronic ethanol exposure and withdrawal resulted in a significant increase in preinjection baseline response amplitudes when measured at 24 h after withdrawal, but not at seven days, and this treatment did not alter response latency or the effects of acute ethanol administration.

Intraspinal sprouting of calcitonin gene-related peptide containing primary afferents after deafferentation in the rat.

The occurrence of sprouting in the spinal cord in response to denervation has been a subject of debate. To test for sprouting of primary afferent fibers after denervation, rats were unilaterally deafferented for 35 days (chronic side) by dorsal rhizotomies performed from T2 to T8 and T10 to L5, thus isolating or sparing the T9 root. The contralateral T9 root was spared by a similar surgery 5 days (acute side) prior to sacrifice. The survival time on the chronic side presumably allows intraspinal sprouting of T9 primary afferents to occur whereas the time on the acute side does not. To test for sprouting of primary afferents, it is necessary to identify these nerve processes. Calcitonin gene-related peptide (CGRP) immunoreactivity has been localized to a subpopulation of primary afferent nerve processes and their terminals within the dorsal horn. Therefore, immunohistochemical methods were used to determine the distribution of CGRP immunoreactivity in laminae I and II on both sides of the spinal cord. Using image analysis, there was an increase of 153 to 704% in the density of CGRP immunoreaction product on the chronic side compared to the acute side in the spared segment. This difference is statistically significant. Furthermore, the increased density on the chronic side extended two segments cranial and two segments caudal to the spared root segment. No difference was found in the laminar distribution between sides. These data support the hypothesis of primary afferent sprouting following spinal cord denervation.

Parathyroid hormone-related protein inhibits stimulated uterine contraction in vitro.

The effect of parathyroid hormone-related protein (PTHrP) fragments 1-34, 38-64, and 67-86 on acetylcholine-stimulated rat uterine contraction was examined in vitro. In addition, the possibility that PTHrP-(38-64) or (67-86) influenced relaxation caused by PTHrP-(1-34) was also investigated. Contraction of uterine horns was stimulated with 10(-6) or 10(-5) M acetylcholine. PTHrP-(1-34) reduced the magnitude of acetylcholine-stimulated uterine contraction. This effect was dose related over a concentration range of 10(-9)-10(-6) M. Neither PTHrP-(38-64) or PTHrP-(67-86) at concentrations of 10(-8)-10(-6) M affected uterine contraction stimulated by 10(-6) M acetylcholine. These fragments did not affect the relaxation caused by 10(-7) M PTHrP-(1-34). These results demonstrate that (1) PTHrP-(1-34) at 10(-6) M influences contraction of the rat myometrium and (2) the muscle relaxant activity of PTHrP is associated with the first 34 N-terminal amino acids.

Projection of nodose ganglion cells to the upper cervical spinal cord in the rat.

Afferent fibers mediating pain from myocardial ischemia classically are believed to travel in sympathetic nerves to enter the thoracic spinal cord. After sympathectomies, angina pectoris still may radiate to the neck and inferior jaw. Sensory fibers from those regions are thought to enter the central nervous system through upper spinal cord segments. We postulated that axons from nodose ganglion cells might project to cervical cord segments. The purpose of this study was to determine the density and pathway of vagal afferent innervation to the upper cervical spinal cord. Following an injection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the upper cervical spinal cord, approximately 5.8% of cells in the nodose ganglion contained reaction product. Cervical vagotomy did not diminish the density of WGA-HRP labeled cells in the nodose ganglion. However, a spinal cord hemisection cranial to the injection site eliminated labeling of nodose cells. These data indicate that a portion of vagal afferent neurons project from the nodose ganglion to the upper cervical spinal cord. In addition, vagal afferent fibers reach the spinal cord via a central route rather than through dorsal root ganglia.

Effects of MK-801 on rat primary afferent neurons and fibers.

Recent evidence suggests that glutamate and its N-methyl-D-aspartate (NMDA) receptor may participate in regulating neurite morphology and peptide expression. A previous study from this laboratory showed that treatment with the NMDA receptor antagonist, MK-801, induced an apparent increase in the density of calcitonin gene-related peptide (CGRP)-immunoreactive primary afferent fibers in the dorsal spinal cord of the rat. The present study was undertaken to extend this work by: 1) quantifying the MK-801-induced increase in CGRP immunostaining in the dorsal grey commissure/medial dorsal horn region and 2) examining the effect of MK-801 on the number of CGRP-immunoreactive primary afferent cell bodies in lumbar dorsal root ganglia. Following 7 days of MK-801 treatment, a significant increase (p less than 0.001) in CGRP immunostaining was observed in the dorsal grey commissure/medial dorsal horn. However, after MK-801 treatment, no significant difference was noted in the numbers of CGRP-immunoreactive primary afferent cell bodies in dorsal root ganglia. These data suggest that MK-801 produces significant alterations in the intraspinal projection of CGRP-immunoreactive fibers without inducing immunocytochemically detectable CGRP within a new population of primary afferent neurons.

Substance P and calcitonin gene-related peptide immunoreactivity in nerves of the rat uterus: localization, colocalization and effects on uterine contractility.

Immunoreactivity to the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) was examined in nerves in the rat uterus as a prelude to studying their effects on uterine contractility. With immunocytochemical techniques, SP immunoreactivity (SP-I) and CGRP-I were localized in myometrial nerves throughout the uterine horns, with nerves immunoreactive for CGRP being the more numerous. Immunocytochemical double labeling studies revealed SP coexisted with CGRP in a subpopulation of CGRP-I nerve fibers, i.e., SP-I was not present in all CGRP-I nerves. Effects of these neuropeptides on uterine contractility were examined on in vitro preparations of uterine horns from diethylstilbestrol-treated rats. SP (10(-4) to 10(-8) M) stimulated uterine contraction in a dose-related manner. CGRP(1-37) and CGRP(8-37) had no effect on basal uterine tension. While CGRP(1-37) (10(-7) M) reduced SP-stimulated (10(-5) M) uterine contraction by 56%, CGRP(8-37) had no effect on SP-stimulated uterine contraction. However, CGRP(8-37) (10(-6) M) significantly reduced the ability of CGRP(1-37) (10(-7) M) to inhibit SP-stimulated uterine contraction. These results demonstrate that SP- and CGRP-I are present in, and coexist in some uterine nerves, presumably afferent nerves. The first 7 amino acids are necessary for the inhibitory effect of CGRP(1-37) on stimulated uterine contraction. In addition, CGRP(8-37) acted as an antagonist to this inhibitory action. SP and CGRP could be coreleased from afferent fibers in an "efferent fashion" and influence uterine contractility. SP having a contractile effect and CGRP having a relaxing effect.

Origin of galanin-immunoreactive nerve fibers in the rat paracervical autonomic ganglia and uterine cervix.

Retrograde axonal tracing with fluorogold in conjunction with immunohistochemistry was used to examine the source of galanin-immunoreactive nerve fibers in the paracervical ganglia and uterine cervix of the female rat. Immunohistochemistry revealed galanin-immunoreactive neuron somata in lumbosacral dorsal root ganglia and around the central canal of the lumbosacral spinal cord (lamina X). Injection of fluorogold into the paracervical ganglia resulted in labelled cells in dorsal root ganglia and the sacral parasympathetic nucleus of the spinal cord; but fluorogold-labelled, galanin-immunoreactive cells were found only in dorsal root ganglia. Injection of the tracer in the cervix resulted in labelled cells in the paracervical ganglia and dorsal root ganglia; however, fluorogold-labelled, galanin-immunoreactive cells were again evident only in dorsal root ganglia. It is suggested that the galanin-immunoreactive nerve fibers and varicosities in the paracervical ganglia and uterine cervix are sensory fibers from spinal dorsal root ganglia. The galanin-immunoreactive varicosities in the ganglia could play a role in the modulation of pelvic visceral activity, while those in the musculature of the cervix could influence contractility.

Effects of ethanol exposure on myelination and axon numbers in the L2 dorsal root of the neonatal rat.

Previous studies have demonstrated that exposure to ethanol during development delays the rate at which axons in certain central nervous system tracts acquire myelin. This delay appears to be related to an alteration in oligodendrocyte function and not to an aberrancy in axon size or number. The present study was designed to determine if alterations similar to those observed in the central nervous system also occur in peripheral nerves, specifically the L2 dorsal root. Dams were fed either an ethanol-containing or control liquid diet 2 weeks prior to pregnancy and throughout gestation. The pups born to the pregnant dams were artificially reared from postnatal day (PD) 4 to PD 10 on a similar ethanol-containing or control diet. The pups were sacrificed on PD 10, L2 dorsal roots removed and processed for electron microscopy. The numbers of axons in various states of myelination were quantified. No difference was observed in the number of unmyelinated axons in the L2 dorsal roots from ethanol-exposed and control pups. In roots from ethanol-exposed pups, there was a significant decrease in the number of axons possessing myelin arranged in compact lamellae, but a significant increase in the number of axons surrounded by myelin lamellae in which the Schwann cell cytoplasm had not yet been extruded (noncompact). However, when the number of axons possessing noncompact myelin and a compact myelin sheath were summed, no significant difference was observed. These data suggest that the delay in myelination following ethanol exposure may be a ubiquitous phenomenon throughout the nervous system.