Identification of the midbrain locomotor region and its relation to descending locomotor pathways in the Atlantic stingray, Dasyatis sabina.

The midbrain locomotor region (MLR) in the Atlantic stingray, Dasyatis sabina, was identified and characterized. Stimulation (50-100 microA, 60 Hz) of the midbrain in decerebrated, paralyzed animals was used to elicit locomotion monitored as alternating activity in nerves innervating an antagonist pair of elevator and depressor muscles. Effective sites for evoking locomotion in the midbrain included parts of several nuclei: the caudal portion of the interstitial nucleus of the medial longitudinal fasciculus and the caudomedial parts of the cuneiform and subcuneiform nuclei. This region did not include the red nucleus, any parts of the optic tectum or the medial or lateral mesencephalic nuclei. Electrical stimulation in the MLR evokes locomotion in either the ipsi- or contralateral pectoral fin, whereas stimulation in the medullary reticular formation evokes locomotion only in the contralateral fin. Lesion experiments were performed to identify the location of descending pathways from the midbrain to the medullary reticular formation. To abolish locomotion evoked by electrical stimulation in the MLR, the medial reticular formation in the rostral medulla had to be lesioned bilaterally, or the ipsilateral medial medullary reticular formation and fibers projecting from the MLR to the contralateral midbrain had to be disrupted. Injections of HRP into the magnocellular/gigantocellular reticular formation confirmed that this area received bilateral projections from the MLR. The MLR of the Atlantic stingray appears to be similar to the lateral component of the mammalian MLR and to the MLR in other non-mammalian vertebrates.

Changes in substance P and 5-HT binding in the spinal cord dorsal horn and lamina 10 after dorsolateral funiculus lesions.

The present study was undertaken to determine whether changes in receptor binding of substance P (SP) and 5-hydroxytryptamine (5-HT) occur in lumbar spinal cord laminae 2, 3, 4 and 10 following interruption of descending SP and 5-HT input. These transmitters and spinal cord regions have been implicated in nociceptive and visceral functions. Quantitative receptor binding autoradiography was used to assess the binding of 2 nM [3H]SP and 2 nM [3H]5-HT to lumbar spinal cord sections taken from normal rats and rats with unilateral thoracic dorsolateral funiculus (DLF) lesions. Postoperative survival times ranged from 1 to 28 days. Substance P binding was above normal in laminae 2 and 3 ipsilateral to the lesion and in contralateral lamina 2 at 1 day postoperatively (DPO), and declined thereafter, reaching below normal levels by 28 DPO. Substance P binding in lamina 10 was significantly above normal at 7 and 14 DPO, but not at 1 or 28 DPO. Binding of 5-HT was above normal at 7 DPO in lamina 2 ipsilateral to the lesion, lamina 3 contralaterally, and lamina 10 bilaterally. These increases were not sustained, however, and at 28 DPO 5-HT binding was significantly below normal in laminae 2-4 bilaterally. The bilateral effects seen in the present study are consistent with the bilaterality of descending thoracic DLF projections demonstrated by the Fink-Heimer method.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of 5-HT1 binding sites in cat spinal cord.

Quantitative analysis of high affinity [3H]5-HT binding to 5-HT1 receptors in the cervical, thoracic, lumbar, and sacral spinal cord of the cat revealed specific binding throughout the grey matter, with the highest levels of binding in laminae II and III, and the lowest levels in laminae I and VII. Relatively high levels were also observed in the thoracic intermediolateral cell column. There were no significant differences in the degree of binding between various segmental levels. Comparison of these data with published maps of 5-HT immunoreactivity reveals--with the exception of lamina I--a close correspondence between the degree of immunoreactivity and the degree of 5-HT binding. These results suggest that 5-HT plays an important role in a variety of spinal cord sensory, motor and autonomic functions.

Anesthetic blockade of the dorsolateral funiculus enhances evoked activity of spinal cord dorsal horn neurons.

1. A previous study of cat lumbar dorsal horn neurons found reduced responsiveness to A-fiber stimulation 1.5-12 h after thoracic dorsolateral funiculus (DLF) lesions. The present study was undertaken to determine whether this was due to the loss of descending activity or to factors specifically associated with injury by examining the response properties of dorsal horn cells before and during lidocaine blockade of the ipsilateral DLF. Electric shocks applied to the dorsal columns were used to search for dorsal horn cells. Noxious and nonnoxious cutaneous mechanical stimuli and graded electrical stimuli applied to the tibial nerve were used to activate peripheral afferent fibers. Cells were classed as low threshold (LT), high threshold (HT), or multireceptive (MR), according to their responses to natural stimuli. Baseline data were collected from a total of 58 cells. Twelve of these were further studied after lidocaine injection of the DLF. All cells examined with lidocaine were in dorsal horn laminae III-V. 2. All cells responded to activation of tibial nerve A fibers. However, the median threshold for the HT and MR cells (200 microA) was significantly higher than that of the LT cells (75 microA). Some cells in each class were also activated by C fibers (10, 70, and 64% of the LT, HT, and MR cells, respectively). 3. For the cells that were further characterized by lidocaine blockade of the DLF, all LT cells (n = 3) responded only to A-fiber stimulation, and all HT (n = 3) and MR cells (n = 6) responded to both A- and C-fiber stimulation. 4. For LT cells, responses evoked by mechanical and electrical stimuli were unaltered by lidocaine blockade. 5. HT and MR cells showed enhanced responses to electrical stimulation of C fibers during DLF blockade. There was no consistent effect of the blockade on A-fiber-evoked responses. 6. Two of three HT and four of six MR cells studied with lidocaine had spontaneous activity, which exhibited a small but significant increase during DLF blockade. 7. Receptive fields for noxious stimulation expanded in two of six MR cells during DLF blockade. Two of three HT cells developed responses to tactile stimuli during the blockade. 8. In two additional cells (1 HT and 1 MR), spontaneous activity and responses to C-fiber input increased after the DLF was cut.(ABSTRACT TRUNCATED AT 400 WORDS)

Nociceptive neurons of the raccoon lateral thalamus.

1. Responses to noxious mechanical and thermal stimuli were examined in 48 thalamic neurons in barbiturate or chloralose-anesthetized raccoons, with special attention to neurons whose peripheral receptive fields (RFs) included glabrous skin of the forepaw. Recording loci were in the core of the ventrobasal complex (VB; n = 32), its ventral or dorsal border (n = 5), or the medial division of the posterior nuclear group (POm; n = 11). 2. Twenty-one VB neurons and 7 POm neurons were classed as wide dynamic range (WDR), whereas 2 VB neurons and 4 POm neurons were classed as nociceptive specific (NS). Response properties of 14 light touch (LT) neurons located in VB were also examined. 3. WDR and NS neurons were not segregated, but rather were intermixed along the ventral and dorsal borders of VB, as well as in POm, and WDR and LT neurons were intermixed in the core of VB. Within the VB core, both LT and WDR neurons were somatotopically organized. 4. All WDR neurons had larger high-threshold than low-threshold RFs, and this difference was greater for POm neurons than for VB neurons. RF areas of LT neurons and low-threshold RF areas of WDR neurons were comparable to those previously reported for raccoon VB units. 5. Out of 25 WDR cells tested, 20 had heat thresholds > 53 degrees C; the range of thresholds in the remaining 5 was 49-53 degrees C. Four out of five NS neurons tested had heat thresholds > 53 degrees C; the threshold of the fifth was 51 degrees C. Of the six neurons with heat thresholds < or = 53 degrees C, two each were in the core of VB, along the border of VB, and in POm. 6. Sensitization to heat after a mild heat injury to the glabrous RF (53 degrees C for 90 s, or 55 degrees C for 30 s) occurred in 8 out of 16 neurons tested, and persisted for up to 2 h. Median thresholds decreased from > 53 degrees C before injury to 47 degrees C after injury, and responses to suprathreshold stimuli were enhanced. There was a significantly greater likelihood (P = 0.02) for sensitization to occur in POm neurons (6/7) than in VB neurons (2/9). 7. It is suggested that a small proportion of neurons located in VB and POm contribute to the sensation of heat pain. Furthermore, sensitization of these neurons may contribute to heat hyperalgesia after an injury to glabrous skin.