Projections of visceral and somatic primary afferents to the sacral spinal cord of the domestic fowl revealed by transganglionic transport of horseradish peroxidase

A comparative assessment of age-related nicotinamide adenine dinucleotide phosphate-diaphorase positivity in the spinal cord and medulla oblongata of pigeons, rats, and mice

Nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase (N-d) positive neurons have been extensively studied across various animals, and N-d neurodegenerative neurites have been detected in some aged animal models. However, detailed knowledge on N-d positivity and aging-related alterations in the spinal cord and medulla oblongata of pigeons is limited. In this study, we investigated N-d positivity and age-related changes in the pigeon's spinal cord and medulla oblongata and compared them to those in rats and mice. Pigeons, had more N-d neurons in the dorsal horn, around the central canal, and in the column of Terni in the thoracic and lumbar segments, with scattered neurons found in the ventral horn of the spinal segments. N-d neurons were also present in the white matter of the spinal cord. Morphometric analysis revealed that the size of N-d soma in the lumbosacral, cervical, and thoracic regions was substantially altered in aged pigeons compared to young birds. Furthermore, the lumbar to sacral segments underwent significant morphological alterations. The main findings of this study were the presence of age-related N-d positive bodies (ANB) in aged pigeons, predominantly in the external cuneate nucleus (CuE) and occasionally in the gracilis and CuEs. ANBs were also identified in the gracile nuclei and spinal cord in the aged rats and mice, whereas in aged rats, ANBs were detected in the CuE spinal nucleus. Immunohistochemistry showed that the age-related alterations occurred in the cell types and neuropeptides in old animals. The results suggest weak inflammatory response and neuronal dysfunction in the spinal cord in aged pigeons. Our results suggested that the ANB could be a potential aging marker for the central nervous system.

Neural pathways mediating control of reproductive behavior in male Japanese quail

The sexually dimorphic medial preoptic nucleus (POM) in Japanese quail has for many years been the focus of intensive investigations into its role in reproductive behavior. The present study delineates a sequence of descending pathways that finally reach sacral levels of the spinal cord housing motor neurons innervating cloacal muscles involved in reproductive behavior. We first retrogradely labeled the motor neurons innervating the large cloacal sphincter muscle (mSC) that forms part of the foam gland complex (Seiwert and Adkins-Regan [1998] Brain Behav Evol 52:61-80) and then putative premotor nuclei in the brainstem, one of which was nucleus retroambigualis (RAm) in the caudal medulla. Anterograde tracing from RAm defined a bulbospinal pathway, terminations of which overlapped the distribution of mSC motor neurons and their extensive dorsally directed dendrites. Descending input to RAm arose from an extensive dorsomedial nucleus of the intercollicular complex (DM-ICo), electrical stimulation of which drove vocalizations. POM neurons were retrogradely labeled by injections of tracer into DM-ICo, but POM projections largely surrounded DM, rather than penetrated it. Thus, although a POM projection to ICo was shown, a POM projection to DM must be inferred. Nevertheless, the sequence of projections in the male quail from POM to cloacal motor neurons strongly resembles that in rats, cats, and monkeys for the control of reproductive behavior, as largely defined by Holstege et al. ([1997], Neuroscience 80:587-598).

Central projections of thoracic splanchnic and somatic nerves and the location of sympathetic preganglionic neurons in Xenopus laevis

The central and peripheral organization of thoracic visceral and somatic nervous elements was studied by applying dextran amines to the proximal cut ends of the thoracic splanchnic and somatic nerves in Xenopus laevis. Many labeled dorsal root ganglion cells of visceral afferents, and all somatic afferents, were located in a single ganglion of one spinal segment, and the two types of cells were distributed topographically within the ganglion. The labeled sympathetic preganglionic neurons were located predominantly in the same area of the thoracic spinal gray as in other frogs and in mammals. The labeled visceral afferents projected to Lissauer's tract and the dorsal funiculus. The visceral fibers of the tract ascended to the level of the subcerebellar area, supplying collateral branches to the lateral one-third of the dorsal horn and to the area of brainstem nuclei, including lateral cervical and descending trigeminal nucleus, and descended to the filum terminale. The visceral fibers of the dorsal funiculus were distributed to the dorsal column nucleus and the solitary tract. A similar longitudinal projection was also seen in the somatic afferents. The dual central pathway of thoracic primary afferents in the anuran spinal cord is a property held in common with mammals, but the widespread rostrocaudal projection through Lissauer's tract may be a characteristic of the anuran central nervous system. In frogs, the direct transmission of primary afferent information to an extremely wide area of the central nervous system may be important for prompt assessment of environmental factors and control of body functions.

Excitatory synaptic currents in lumbosacral parasympathetic preganglionic neurons evoked by stimulation of the dorsal commissure

Excitatory pathways from the dorsal commissure (DCM) to L(6)-S(1) parasympathetic preganglionic neurons (PGN) were examined using whole-cell patch-clamp recording techniques in spinal cord slices from neonatal rats. PGN were identified by retrograde axonal transport of a fluorescent dye injected into the intraperitoneal space. Excitatory postsynaptic currents (EPSCs) were evoked in PGN by stimulation of DCM in the presence of bicuculline methiodide (10 microM) and strychnine (1 microM) to block inhibitory pathways. Electrical stimulation of DCM evoked two types of inward currents. In the majority of PGN (n = 66), currents (mean amplitude, 47.9 +/- 4.7 pA) occurred at a short and relatively constant latency (3.8 +/- 0.1 ms) and presumably represent monosynaptic EPSCs (Type 1). However, in other neurons (n = 20), a different type of EPSC (Type 2) was noted, consisting of a fast monosynaptic component followed by a prolonged inward current with superimposed fast transients presumably representing excitatory inputs mediated by polysynaptic pathways. Type 1 EPSCs were pharmacologically dissected into two components. A fast component was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 5 microM) and a slowly decaying component was blocked by 2-amino-5-phosphonovalerate (APV, 50 microM). The fast component of Type 1 EPSCs had a linear current-voltage relationship and reversed at a membrane potential of -7.6 +/- 1.3 mV (n = 5). The fast component of Type 2 EPSCs was also blocked by 5 microM CNQX and the remaining slower component was blocked by 50 microM APV. When the DCM was stimulated in the presence of 50 microM APV, the time to peak and decay time constant in Type 1 EPSCs were 1.9 +/- 0.2 and 4.1 +/- 0.8 ms, respectively. Examination of the NMDA receptor-mediated component of the EPSCs in the presence of 5 microM CNQX revealed a current-voltage relationship that had a region of negative slope conductance (from -20 to -80 mV), which was abolished in Mg(2+)-free external solution. The time to peak and decay time constant of this component were 14.2 +/- 2.0 and 91.0 +/- 12.4 ms, respectively. Type 1 EPSCs in some PGN responded in an all-or-none manner and presumably represented unitary synaptic responses; whereas Type 2 EPSCs always exhibited a graded stimulus intensity-response relationship. Paired-pulse facilitation (50-ms interstimulus intervals; 141 +/- 5.6% increase, n = 8) of EPSCs was observed. These results indicate that PGN receive monosynaptic and polysynaptic glutamatergic excitatory inputs from neurons and/or axonal pathways in the DCM.

Ontogeny of PACAP immunoreactivity in extrinsic and intrinsic innervation of chicken gut

An immunohistochemical study was conducted on the ontogeny of pituitary adenylate cyclase-activating polypeptide-27 (PACAP) immunoreactive elements within the extrinsic and intrinsic nerve supply of the chicken embryo gut. The first PACAP-immunoreactivity was detected in the extrinsic nerve supply at E 4 within the pharyngeal region and the primary sympathetic chain. At E 5.5 it appeared in the vagus nerve, the spinal cord, the secondary sympathetic chain, some perivascular plexuses and the Remak ganglion. In the intrinsic nerve supply, the first PACAP-immunoreactive elements were shown at E 4.5-E 5 in the mesenchymal bud of the proventriculus/gizzard. Then they gradually appeared also cranially and caudally both in myenteric and submucous plexuses.

Spinal coadministration of ketamine reduces the development of tolerance to visceral as well as somatic antinociception during spinal morphine infusion

This study was designed to investigate the effects of ketamine, an N-methyl-D-aspartate receptor antagonist, on the development of tolerance to morphine and morphine antinociception during intrathecal infusion. Two intrathecal catheters were implanted in the subarachnoid space in male rats under pentobarbital anesthesia. One catheter was used for the intrathecal infusion with the following solutions: morphine 1 microg x kg(-1) x hr(-1)(M1) and 5 microg x kg(-1) x hr(-1) (M5);ketamine 250 microg x kg(-1) x hr(-1) (K250); morphine plus ketamine, 1 microg x kg(-1) x hr(-1) plus 250 microg x kg(-1) x hr(-1) (M1 + K250) and 5 microg x kg(-1) x hr(-1) + 250 microg x kg(-1) x hr(-1) (M5 + K250); or saline. The other catheter was used for morphine challenge tests. The responses to noxious somatic and visceral stimuli were measured by tail flick (TF) and colorectal distension (CD) tests, respectively. Measurements were performed once a day for 7 days. Challenge tests with intrathecal morphine were performed to assess the magnitude of tolerance on Day 5 and Day 7. The antinociceptive effect was evaluated by using the percent of maximal possible effect (%MPE). Morphine infusion produced significant increases in %MPEs in TF and CD tests, while the saline and K250 infusions did not show any changes. The M1 + K250 infusion significantly increased the %MPEs in TF and CD tests, although the M1 and K250 infusions alone showed no changes. M5 + K250 enhanced the increases of %MPEs in TF and CD tests compared with the M5 infusion alone. In the challenge tests, the M1 + K250 infusion showed no significant decrease in %MPEs and TF and CD tests. The M5 + K250 infusion significantly inhibited those decreases in %MPEs, although the M5 infusion showed significant decreases in TF and CD tests. We concluded that ketamine attenuated the development of morphine tolerance to antinociceptive effects and increased the somatic and visceral antinociception of morphine.

IMPLICATIONS

Intrathecally coinfused ketamine attenuated morphine tolerance to somatic and visceral antinociception and increased morphine antinociception at the spinal level. These results suggest that a combination of morphine with ketamine may have an advantage in long-term use of opioids for controlling visceral as well as somatic pain.

Projections of ankle joint afferents to the spinal cord and brainstem of the chicken (Gallus g. domesticus)

The projections of the ankle joint capsule afferents were studied by transganglionic transport of horseradish peroxidase injected directly into the ankle joint. The number and size of the labelled dorsal root ganglion cells were measured from synsacral nerves 2-9. In the dorsal root ganglia, all sizes of sensory neurones were labelled, and the largest number of labelled cells was in ganglia 5-7. The extensive sympathetic innervation of the ankle joint was identified by the large number of cell bodies labelled in the sympathetic ganglia of the paravertebral chain. Labelled afferent fibres projected to the spinal cord from the 2nd to the 8th synsacral nerves, with the rostral projection mainly via Lissauer's tract and the dorsal funiculus. Terminal labelling in the dorsal horn was identified in laminae I-III and VI, with a slight projection to V. Two areas of dense labelling, which did not correspond with the largest number of labelled dorsal root ganglion cells, were identified. A rostral area with the highest density of label was observed at the level of synsacral nerves 3-4 and a second slightly less dense area between synsacral nerves 7-8. In the caudal medulla, diffuse terminal labelling was observed in the nucleus gracilis et cuneatus, nucleus of the tractus solitarius, and the nucleus cuneatus externus. These results are discussed in a comparative context to identify similarities and differences between different primary afferent projections in birds and mammals and to highlight the possible functional significance of the avian articular afferent projection.

Central projections of primary afferents from the interosseous nerve in the pigeon

The interosseous nerve in the pigeon's leg innervates a string of Herbst corpuscles. Because Herbst corpuscles are vibration-sensitive, this study, using neuronal tracing methods, was expected to show the central representation of vibration sense. After application of a mixture of free and lectin-conjugated horseradish peroxidase to the interosseous nerve, labeled cell bodies of sensory and postganglionic neurons were mainly located in the dorsal root ganglia and paravertebral sympathetic ganglia L3/L4. In spinal segments L3/L4 fibers and terminals were mainly distributed at the lateral border of the head of the dorsal horn. In more cranial or caudal segments terminal fields were at intermediate parts of laminae I/II and laminae IV/V. Some labeled fibers entered the dorsal horn from medial to terminate in lamina IV. Primary afferents of the interosseous nerve projected directly to the gracile nucleus in the brainstem and distributed all along its rostrocaudal extent. Because the main terminal fields in the spinal cord are typical for the projection of small afferent fibers, vibration information seems to reach the brainstem via the dorsal column primary afferents.

Projection patterns of primary sensory neurons studied by transganglionic methods: somatotopy and target-related organization

The anatomical organization of the centrally projecting branches of different peripheral sensory nerves was not possible to investigate efficiently until the development of the axonal tracing methods. Horseradish peroxidase applied peripherally could be visualized in central projection areas provided a sensitive histochemical method was used; this created the basis for transganglionic tracing from the periphery. This has permitted the investigation of large-scale projections from peripheral sensory nerves. The use of conjugates of horseradish peroxidase and lectins with affinities for different populations of primary sensory neurons, as well as the use of different postoperative survival times, has offered the possibility for selective visualization of projections from subsets of primary sensory neurons. For detailed studies of single afferent fiber projections, a combined physiological-anatomical approach using single-unit recording followed by intraaxonal application of horseradish peroxidase, has become the method of choice. This chapter will focus on results which have been achieved by transganglionic tracing methods, in regard to the organization of the central projections of peripheral sensory nerves.

Sympathetic and sensory neurons projecting into the cervical sympathetic trunk in the chicken

The cell bodies of the sensory and sympathetic pre- and postganglionic neurons projecting into the cervical sympathetic trunk were retrogradely labeled with horseradish peroxidase in the chicken. Preganglionic neurons were located in the spinal segments T1-T6 (maximum T2), postganglionic neurons in the paravertebral ganglia T1-T3 (maximum T1) and sensory neurons in the dorsal root ganglia T1-T4 (maximum T1). Labeled preganglionic neurons were widely distributed across the intermediate gray matter and lateral funiculus, but the majority of them were located in the intermediomedial area dorsolateral to the central canal. The short and long axis diameters of labeled preganglionic neurons in this area decreased caudally. From the data of the present study, it is estimated that about 4190 preganglionic, about 450 postganglionic and about 390 sensory neurons project into the cervical sympathetic trunk cranial to the paravertebral ganglion T1 in the chicken.

Somatotopic organization of hindlimb skin sensory inputs to the dorsal horn of hatchling chicks (Gallus g. domesticus)

The somatotopic organization of skin sensory nerve projections to the lumbosacral dorsal horn of hatchling chickens was determined with the aid of transganglionic transport of horseradish peroxidase (HRP) processed with tetramethylbenzidine histochemistry. A total of eight hindlimb nerves were studied, five of which were purely cutaneous. When combined, the innervation fields of these nerves covered most of the hindlimb surface, allowing a nearly complete somatotopic map of the hindlimb to be generated. This report describes a novel pattern of cutaneous nerve projections to the dorsal horn. Unlike other vertebrates, cutaneous nerves of chickens formed two separate, somatotopically organized projections across the mediolateral axis of the dorsal horn; when serially reconstructed and superimposed, these projections produced two nonoverlapping somatotopic maps of the skin surface lying side by side. Each of these separate maps was nearly identical to the other in overall topology. These two separate maps appear to represent distinct modalities of sensory information, as projections composing the medial map were preferentially labeled by choleragenoid-HRP, whereas those composing the lateral map were preferentially labeled by wheat germ agglutinin-HRP. In mammals, these HRP ligands selectively label the central projections of myelinated and unmyelinated cutaneous afferents, respectively. The present study, therefore, strongly supports the cytoarchitectonic findings of Brinkman and Martin (Brain Res. 56:43-62, '73) that lamina III lies medial, rather than ventral, to lamina II in the chicken dorsal horn. Further, the present studies also suggest that laminae II and III of chickens are homologous to the homonymous laminae in the dorsal horn of mammals.

Demonstration of reversible membrane internalization after exocytosis in the rat neurohypophysis

Isolated rat neurohypophysis was stimulated electrically in media containing fluid phase markers such as carboxyfluorescein and choline. After the markers in the extracellular space were washed out, release of the markers trapped in the tissue was evoked by stimulation. Both the uptake and the release of fluid phase markers were not observed in a Mn2+-containing medium. These results provide direct evidence that internalized vesicles have the function to fuse with plasma membrane in response to Ca2+ entry during electrical stimulation.