Contribution of supraspinal and spinal structures to the responses of dorsal spinal cord blood flow to innocuous cutaneous brushing in rats

Responses of dorsal spinal cord blood flow (SCBF) to innocuous mechanical cutaneous stimulation were investigated in anesthetized central nervous system intact (CNS-intact) and C2 spinalized rats. SCBF was recorded at the L4-L6 level with a laser Doppler flowmeter. SCBF increased with brushing of the ipsilateral proximal hindlimb and hindpaw, and there were no significant differences in the magnitudes of the responses in CNS-intact and spinalized animals. Brushing of the lower back had no effect on SCBF at the L4-L6 level in either cohort. Brushing stimulation produced no significant changes in systemic arterial blood pressure. The responses of SCBF to brushing in CNS-intact animals were diminished by pretreatment with phenoxybenzamine, an alpha-adrenoceptor blocking agent, but no such effects were seen in spinalized animals. These results indicate that innocuous mechanical cutaneous input can produce a segmentally-organized increase in regional SCBF, and that the responses are modulated, in part at least, by alpha-adrenergic receptors via supraspinal structures.     

Bulbar pathway for contralateral lingual nerve-evoked reflex vasodilatation in cat palate

We investigated the brain-stem pathway(s) by which electrical stimulation of the central cut end of the lingual nerve (LN) evokes parasympathetic reflex vasodilatation in the palate contralateral to the stimulated side. This occurs in artificially ventilated, cervically vagosympathectomized cats deeply anesthetized with alpha-chloralose and urethane. For this purpose, we made microinjections within the brain stem to produce nonselective, reversible local anesthesia (lidocaine) or soma-selective, irreversible neurotoxic damage (kainic acid). Local anesthesia of the trigeminal spinal nucleus (Vsp) ipsilateral to the stimulated side produced by microinjection of lidocaine (2%; 1 microl/site) reversibly and significantly reduced the LN stimulus-evoked palatal blood flow (PBF) increases. PBF increases ipsilateral and contralateral to the stimulated nerve were equally affected. In contrast, microinjection of lidocaine into the Vsp contralateral to the stimulated side did not affect these responses. Microinjection of kainic acid (10 mM/site; 1 microl) into the Vsp ipsilateral to the stimulated side led to a bilateral irreversible reduction in reflex vasodilatation in the palate. Microinjection of lidocaine into either superior salivatory nucleus (SSN) attenuated the PBF increase only on the side ipsilateral to the microinjection site. Hexamethonium (1.0 mg/kg iv) significantly reduced the vasodilator responses to electrical stimulation of Vsp by blocking ganglionic transmission on both sides. The simplest interpretation of these results is that the LN-evoked parasympathetic reflex vasodilatation in the contralateral palate depends on activation of a pathway originating from the Vsp ipsilateral to the stimulated nerve and crossing to the contralateral SSN.     

Enhancement of electrically evoked startle-like responses by tetanic stimulation of the superior colliculus

Single-pulse unilateral electrical stimulation of either the amygdala or the inferior colliculus elicited startle-like responses in chloral hydrate anesthetized rats. EMG responses to intracranial stimulation were recorded from the anterior biceps femoris muscles. The EMG responses were generally enhanced following unilateral tetanic stimulation of the deep layers of the superior colliculus, but the enhancement was stronger for amygdala sites than inferior colliculus sites. The enhancement of EMG responses to ipsilateral amygdala stimulation was much larger than that for contralateral amygdala stimulation and that for ipsilateral inferior colliculus stimulation. The enhancement of EMG responses to contralateral inferior colliculus stimulation was not significant. The present study provides a motor-output model for studying plasticity in the neural pathways mediating startle facilitation.     

Crossed responses found in human trapezius muscles are not H‐reflexes

Introduction: We sought to confirm the presence of crossed short‐latency reflexes in trapezius. Methods: Mmax and Hmax were measured in the ipsilateral trapezius in 10 subjects by percutaneous electrical stimulation of the accessory nerve and the cervical nerves of C3/4 respectively. Repeated stimulation of the C3/4 cervical nerves was performed during 3 different tasks (relaxation, contraction of ipsilateral side, contraction of contralateral side). Results: Ipsilaterally, responses increased significantly with an increase in the prestimulus electromyogram (EMG) and decreased significantly with a decrease in prestimulus EMG. Contralateral potentials increased significantly with contraction of the trapezius ipsilateral to the stimulus compared with contraction of the muscle in which they were recorded and decreased significantly with increasing distance from the ipsilateral side. Conclusions: We found ipsilateral and contralateral responses consistent with previous findings. However, we conclude that the contralateral response in trapezius is not a crossed reflex. Muscle Nerve 49 :362–369, 2014     

Unilateral subcutaneous bee venom but not formalin injection causes contralateral hypersensitized wind-up and after-discharge of the spinal withdrawal reflex in anesthetized spinal rats

This study aimed to investigate the effect of tonic nociception on spinal withdrawal reflexes including (1) long lasting spontaneous responses elicited by subcutaneous (s.c.) administration of formalin (2.5%, 50 microl) and bee venom (BV, 0.2 mg/50 microl) into the hind paw and (2) corresponding ipsilateral (primary) and contralateral (secondary) hypersensitivity to noxious pinch and repetitive supra-threshold (1.5 x T) electrical stimuli at different frequencies (3 Hz: wind-up; 20 Hz: after-discharge) in anesthetized spinal rats. Spinal withdrawal reflexes were studied by simultaneously assessing single motor units (SMUs) electromyographic (EMG) activities from the bilateral medial gastrocnemius (MG) muscles. Subcutaneous formalin-induced persistent spontaneous SMU EMG responses were in typical biphasic manner with an apparent silent period (about 13-18 min), but in contrast, BV elicited monophasic long lasting (about 1 h) SMU EMG responses without any resting state. The mechanically and electrically evoked responsiveness of SMUs were enhanced significantly by ipsilateral BV injection, whereas enhanced electrically, but not mechanically, evoked responses (including wind-up and after-discharge) were found at the non-injection site of the contralateral hind paw. However, s.c. administration of formalin was only able to establish ipsilateral hypersensitivity of the SMUs to repeated electrical, not mechanical, stimulation. Neither mechanically nor electrically evoked contralateral hypersensitivity of the SMUs was found during the ipsilateral formalin-induced nociception. For pharmacological intervention, intrathecal administration of the non-N-methyl-d-aspartate (non-NMDA) receptor antagonist CNQX (40 nmol/10 microl), but not the non-competitive NMDA receptor antagonist MK-801 (40 nmol/10 microl), significantly depressed BV-induced contralateral hypersensitivity of the SMUs to repeated 3 Hz (wind-up) and 20 Hz (after-discharge) frequencies of electrical stimulation. Using the extracellular SMU recording technique, we found that s.c. administration of formalin and BV shows a significant difference in long lasting spontaneous firing of SMUs. This is consistent with previous observations in animal behavioral studies. Additionally, contralateral electrically evoked hypersensitivity of the SMUs was found only following BV injection, not in the formalin test. The maintenance and development of BV-induced contralateral hypersensitivity of the spinal withdrawal reflex to noxious electrical stimulation indeed depend on different central pharmacological receptors. The spinal non-NMDA, but not the NMDA, receptors may play important role in BV-induced contralateral central hyperexcitability and sensitization.     

The cutaneous contribution to the hamstring flexor reflex in the rat: an electrophysiological and anatomical study

The location and properties of the cutaneous receptive fields responsible for detecting the flexor withdrawal reflex in the posterior head of biceps femoris (pBF) and semitendinosus (ST) components of the hamstring muscle have been examined in unanaesthetized decerebrate rats, spinalized at T10-T11. Single alpha-motoneurone efferents were recorded from the nerve to pBF and the principal head of ST and their responses to ipsi- and contralateral hindlimb skin stimulation investigated. The efferents to both muscles characteristically had a low or absent background discharge and they all had mechanoreceptive fields on the ipsilateral foot. The mechanical threshold of these fields was high with no response to light touch or brush. Fifty-four percent of these units also had a smaller and weaker contralateral mechanoreceptive field. The only apparent difference between ST and pBF efferents was that more ST efferents had contralateral fields than pBF units. Noxious, hot and cold thermal stimuli applied to the ipsilateral foot activated 56% of the efferents. Mustard oil, a chemical irritant, produced a long-lasting flexor response when applied to the ipsilateral foot. The responses of these efferents to stimulation of A beta, A delta and C cutaneous afferents in the sural nerve were also studied. Short latency reflexes were elicited in all efferents by A beta inputs, longer latency reflexes were elicited in 64% by A delta inputs and very long latency responses with long afterdischarges were found in 73% of the units to C inputs. Retrograde labelling of the hamstring motoneurones with WGA-HRP indicated that they lay in ventrolateral lamina IX extending from the caudal portion of the third lumbar segment to the junction of the 5th and 6th lumbar segments. Transganglionic labelling of small diameter primary afferent terminals in the dorsal horn of cutaneous nerves innervating the foot revealed that the longitudinal distribution corresponded closely with that of the hamstring motor nucleus. The flex-or reflex in the spinal rat provides a useful model therefore, for studying how the input in nociceptive afferents is processed and transformed within the spinal cord, to produce appropriate outputs.     

The critical importance of stimulus intensity in intraoperative monitoring for partial dorsal rhizotomy

During partial lumbosacral dorsal rhizotomy (PDR), intraoperative dorsal rootlet stimulation (drs) evokes motor responses, presumed to be reflexes, which are used to select rootlets for section. However, dr stimuli may also costimulate ventral root (vr) and evoke an M rather than a reflex response, the two being distinguishable only by comparison of response latencies after drs at two separate sites. In 15 consecutive spastic cerebral palsy patients undergoing PDR, we asked whether reflex and M responses were distinguishable on the basis of stimulus intensity (SI). For soleus H reflexes evoked by percutaneous tibial nerve stimulation, the SI for reflex afferents was usually subthreshold for exciting motor fibers. Similarly, for nerve roots, reflexes were evoked by drs at SIs generally less than that for M responses evoked by vr stimulation (vrs). In contrast, M responses evoked by drs required SIs that were on average 20 times greater. Finally, costimulation of contralateral vr after ipsilateral vrs occurred at SIs shown to evoke M responses after drs. We conclude that: (1) reflex and M responses evoked by drs are distinguishable on the basis of the required SI; and (2) drs employing SIs greater than that required for vrs evokes M rather than reflex responses due to costimulation of ipsilateral and contralateral vr. © 1996 John Wiley & Sons, Inc.     

Conditioned cortical slow potential responses in urethane anesthetized rats

Cortical slow potential (SP) responses to tone or light stimuli preceding medial forebrain bundle (MFB) stimulation were recorded in urethane anesthetized rats. In the first study, rats were implanted with Ag-AgCl electrodes for recording frontal cortex SPs as well as monopolar electrodes for MFB stimulation. Following recovery, optimum stimulation parameters for SP conditioning were determined for each rat during self-stimulation sessions. These animals were then subjected to extensive associative conditioning in the unanesthetized state. Trials were presented at variable intervals and a 2-sec tone preceded a single 0.5 sec train of MFB stimulation. Negative SP responses developed with training and responses of similar waveform and amplitude were observed in the same animals under urethane anesthesia. Other rats were implanted with MFB stimulating electrodes and, after recovery, stimulation parameters were determined as above but the animals were not subjected to the conditioning procedure prior to urethane administration. Under urethane anesthesia, Ag-AgCl electrodes were placed on the dura over frontal cortex for recording SP responses during pseudoconditioning, conditioning, extinction and retraining trials, using either light or tone stimuli. Negative bilateral SP responses to the tone or light were minimal or nonexistent during pseudoconditioning, developed gradually with pairing, diminished markedly during extinction and returned to maximum amplitude with retraining. The SP responses also reflected discrimination between reinforced and nonreinforced tone and light stimuli as well as reversal conditioning. Furthermore, turning off a light could also serve as the conditioned stimulus for SP response generation. Cortical slow potential responses can be conditioned in urethane anesthetized rats. Therefore, it may be possible to apply additional neurophysiological techniques in these animals to investigate event-related slow potential mechanisms.     

Antagonizing effects of haloperidol and bicuculline on inhibition of neurons of the substantia nigra,pars compacta

In rats anesthetized with urethane, effects of intravenously administered haloperidol (HAL; 0.1 mg/kg) and bicuculline (BCL; 0.2 mg/kg) were tested on inhibition of neuronal discharges of the substantia nigra, pars compacta (SNC), induced by single-shock stimulation of the sciatic nerve (SC). In two-thirds of the SNC neurons tested these two drugs antagonized the SC-induced inhibition, independent of the side of stimulation. In the remaining cases the effects of HAL and BCL were asymmetric. With HAL the inhibition from the contralateral SC was antagonized, whereas that from the ipsilateral SC was not antagonized or sometimes slightly potentiated. The asymmetric effect of BCL occurred in the opposite direction to that of HAL.     

Long-lasting modification of reflexes after neonatal nerve injury in the rat

The reflex activity of motoneurones to the extensor digitorum longus (EDL) muscle following sciatic nerve crush during the first 5 days after birth (neonatal crush) or in the adult (adult crush) was studied 3-6 months later, when the axons had reinnervated their target muscles. Electromyograms (EMG) and muscle tension were recorded from the EDL muscle (a physiological flexor) on the injured and uninjured sides. Reflex responses were evoked by stimulation of the common peroneal (CP), the tibial (T) and the sural (S) nerves, ipsilateral and contralateral to the side of injury. In animals which had sustained a neonatal crush, stimulation of branches of the injured sciatic nerve elicited ipsilateral reflex responses that were about 3 times larger than those recorded from the uninjured side or in normal animals. Stimulation of the CP nerve on the uninjured side invariably elicited a contralateral reflex response from the reinnervated muscles, while stimulation of the CP nerve on the injured side either failed to produce a response or produced a very weak reflex response from the control muscles. Reflexes recorded from the reinnervated muscles by stimulation of the tibial and sural branches of the uninjured sciatic nerve were 3-7 times greater than those recorded from the uninjured side or in normal animals. The reflex responses obtained from reinnervated muscles of animals with nerve injury in adulthood were similar to those obtained from control, unoperated adult rats. These results indicate that sciatic nerve injury during a critical development period leads to a permanent enhancement of reflex responses from reinnervated fast flexor muscles not seen after similar injury in adults.     

Ipsi- and contralateral exteroceptive EMG modulation in uni- and bilaterally activated thenar muscles.

OBJECTIVE: The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-delta fibers. The exact underlying neural pathway, however, is unknown. This study was undertaken to investigate whether the neural circuitry mediating CSPs is wired unilaterally or whether there is evidence of influence from or upon the contralateral side. METHODS: Fifteen healthy subjects underwent bilateral CSP testing following unilateral nociceptive digit II stimulation. Surface electromyographic (EMG) recordings were obtained bilaterally from thenar muscles following unilateral recurrent nociceptive digit II stimulation while activating the ipsilateral or the contralateral or both thenar muscles against resistance. RESULTS: Nociceptive digit II stimulation evoked consistent CSPs in ipsilateral thenar muscles during voluntary contraction, while there was no consistent influence on EMG activity in contralateral thenar muscles at rest. Furthermore, nociceptive digit II stimulation did neither consistently affect EMG activity in ipsilateral thenar muscles at rest nor in contralateral thenar muscles during voluntary contraction. Finally, there was no significant difference between any CSP parameters obtained during unilateral versus bilateral muscle contraction. Occasional late excitatory EMG activity in relaxed or contracted thenar muscles resembled startle reflexes, which seem to contribute to the post-inhibition EMG-rebound. CONCLUSIONS: The present findings are consistent with unilateral wiring of the spinal circuitry mediating CSPs. SIGNIFICANCE: The essential lack of a crossed inhibitory influence of nociceptive digit II stimulation underscores the utility of CSP testing in the assessment of the A-delta fiber system in healthy subjects and patients with various pathologies.     

Response of brainstem trigeminal neurons to electrical stimulation of the dura

The extracellular response of medullary trigeminal neurons to electrical stimulation of the dura was studied in anesthetized cats. Fifty-six medullary trigeminal units were excited by stimulation sites near major dural vessels with an average latency of 11.0 ms. Many units also responded to infraorbital nerve shock and had cutaneous receptive fields that included the ipsilateral periorbital region. These cutaneous responses were either wide dynamic range or nociceptive specific in type. Electrical stimulation of the midbrain periaqueductal gray region suppressed the response of medullary trigeminal units to either dural stimulation or infraorbital nerve shock. Medullary trigeminal neurons that receive convergent inputs from dura and facial skin may provide a physiological substrate for the cutaneous referral of dural sensation.     

Expression of c-fos protein in rat brain elicited by electrical stimulation of the pontine parabrachial nucleus.

The expression of Fos, the protein product of the primary response gene c-fos, was used metabolically to map the short-term (1 hr) effects of urethane and sodium pentobarbital anesthesia in rat. Subsequently, urethane-anesthetized rats were used to study the integrated response to electrical stimulation (1-1.5 hr) of the pontine parabrachial nucleus (PBN), an important center for relay of autonomic information in the brain. Immunohistochemistry was used to localize Fos-like immunoreactivity (FLI) in the brain. To approximate amounts of FLI in the conscious animal, rats were killed immediately after attaining surgical anesthesia with sodium pentobarbital (50 mg/kg) or urethane (1.2-1.7 gm/kg). No FLI was found in the brains of these rats. In rats killed 1 hr after anesthesia with sodium pentobarbital, FLI was found only in the habenulae. After 1 h of urethane anesthesia, low levels of FLI were found in the following areas: nucleus of the tractus solitarius (NTS); caudal and rostral ventrolateral medulla (VLM); lateral PBN; ventromedial, paraventricular, and supraoptic nuclei (SON) of the hypothalamus; medial preoptic area; central nucleus of the amygdala (ACE); endopiriform cortex; insular cortex; piriform cortex; and islands of Calleja. Electrical stimulation of the PBN (10 sec on, 10 sec off; 15-50 microA at 20 Hz for 60-90 min) in rats anesthetized with urethane led to increases in mean arterial pressure (10-30 mm Hg) and to ipsilateral increases of FLI in the lateral PBN, dorsal division of SON, ACE, endopiriform nucleus, insular cortex, piriform cortex, and islands of Calleja. In two animals, ipsilateral increases were found in the ventromedial hypothalamus and medial amygdaloid nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Crossed and uncrossed central effects of muscle spindle afferents from the lateral pterygoid muscle of the guinea pig

Physiological evidence is presented for the presence of stretch reflexes in the lateral pterygoid (Pt) muscle of the guinea pig. The central reflex effects of excitation of Pt stretch reflex afferents were also investigated. Passive lateral jaw displacement, which resulted in stretch of the Pt muscle on the side of jaw movement and stretch of the zygomatico-mandibularis (Z) muscle on the side contralateral to the movement, evoked increased EMG activity in these muscles. Stimulation of the trigeminal mesencephalic nucleus (mes V) evoked monosynaptic reflexes in both the Pt and Z nerves. Tonic stretch of the Pt muscle facilitated the monosynaptic reflex in the Pt nerve evoked by stimulation of mes V. Tonic vibration of the Pt muscle facilitated the mes V evoked monosynaptic reflex in the nerves to the ipsilateral Pt and contralateral Z muscles. Conversely, tonic vibration of the Z muscle facilitated the monosynaptic reflex evolved by mes V stimulation in the contralateral Pt and ipsilateral Z nerve. The results support the view that muscle spindles exist in the Pt and Z muscles and that there is a monosynaptic stretch reflex for both the Pt and Z muscles with cell bodies located in the mes V nucleus. It was also shown that the ipsilateral Pt muscle and the contralateral Z muscle act as synergists in the production of lateral jaw movements and that the organization of the stretch reflexes originating from the Pt and Z muscles support their synergistic action.     

Anesthetic-dependent excitability changes in the hypothalamic ventromedial nucleus of the rat

In acute experiments in rats anesthetized with urethane, the field potentials, population spike, and unit activity evoked in the hypothalamic ventromedial nucleus (HVM) by amygdaloid stimulation are significantly increased with respect to control when preceded by a conditioning volley at 20- to 100-ms intervals. Under pentobarbital anesthesia, in contrast, the evoked responses were inhibited by the conditioning stimulus for similar interstimulus intervals. In unanesthetized animals chronically implanted with stimulating and recording electrodes, a facilitation of responses by a conditioning stimulus was observed when they were awake or anesthetized with urethane. When the same animals were anesthetized with pentobarbital the HVM evoked response was inhibited by a conditioning pulse. Frequency facilitation and post-tetanic potentiation of HVM responses were markedly enhanced under urethane, whereas in pentobarbital-anesthetized animals inhibition predominated. Picrotoxin reversed the inhibition under pentobarbital to facilitation. These results suggest that the HVM neuron population is under both excitatory and inhibitory influences from the amygdala, the former being predominant in awake and urethane-anesthetized animals and the latter being expressed under pentobarbital anesthesia and is probably mediated by γ-aminobutyric acid.     

Contralateral intramuscular acupuncture-like electrical stimulation differentially changes the short-latency responses to muscle stretch

Measurements were made from the human first dorsal interosseous and extensor digitorum communis muscles of the surface electromyographic activity reflexly produced by brief stretch of the muscle. For the first dorsal interosseous muscle, reflex EMG activity was also produced by electrical stimulation of the ulnar nerve at the wrist. The procedures were carried out before, during, and after 25 min of nonspecific, low-frequency electrical stimulation to the contralateral arm delivered through intramuscular electrodes. Control stimulation was delivered subcutaneously. The EMG recorded during a maintained contraction was rectified, filtered, and averaged. Two reflex components (M1 and M2) of the EMG response to muscle stretch or ulnar nerve stimulation were investigated. During nonspecific intramuscular stimulation to the contralateral arm, M1 responses of the extensor digitorum communis were depressed, initially by 37%. The effect began to fade during stimulation but extended beyond it. Reflex responses were elicited alternately by brief stretch of the first dorsal interosseus muscle and by electrical stimulation of the ulnar nerve in the same experiment. Nonspecific intramuscular stimulation to the contralateral arm depressed the M1 response to stretch, but had no effect on the M1 response to electrical stimulation. It is concluded that nonspecific intramuscular electrical stimulation reduces the amplitude of the M1 component of the response to brief stretch of contralateral muscle, either through depression of fusimotor activity or inhibition of oligosynaptic pathways that contribute to the early reflex response.     

Vestibular influence on tongue activity

The vestibular system was electrically stimulated in cats anesthetized with ketamine. Peripheral stimulation by an electrode positioned in the vestibule evoked torsional contralateral eye deviations and an electromyogram (EMG) response in a contralateral dorsal neck extensor. Consistently associated with this well documented vestibular pattern was an EMG response in tongue protrusive muscles, at a latency of 13 +/- 5 (means +/- SD) ms. Stimulation in a specific part of the rostroventral lateral vestibular nucleus elicited the same combination of responses: torsional contralateral eye deviations, dorsal neck EMG, and tongue EMG at a latency of 14 +/- 3 ms. Possible tongue activation by current spread to peripheral and central neural structures was examined in detail. Cerebellar, V, VII, cochlear, IX, X, and XII nerve influences were considered. On the basis of combined evidence, it was concluded that the vestibular system does influence tongue activity.     

Expression of Fos in rat central nervous system elicited by afferent stimulation of the femoral nerve

To investigate the distribution of Fos-like immunoreactivity (FLI)_in the central nervous system of urethane anesthetized rats after activation of a somatosympathetic reflex pathway, the cut central end of the right femoral nerve of 17 male Wistar rats was stimulated electrically for 1 h at parameters such that increases in heart rate and arterial pressure were elicited. Sections of brain and spinal cord were incubated in anti-Fos antibody and the presence of FLI was detected using the ABC immunoperoxidase method. In the spinal cord FLI was present in the ipsilateral lumbar spinal cord (laminae 1 and 2, 4–6 and 10) and contralateral intermediolateral nucleus in the thoracic spinal cord. In the hindbrain, FLI was present in the contralateral rostral ventrolateral medulla and bilaterally in the cochlear nucleus, external cuneate nucleus, locus coeruleus and lateral parabrachial nucleus. In the midbrain, label appeared in the Edinger-Westphal nucleus and peripenduncular nucleus on both sides. In the forebrain, FLI appeared bilaterally in the central nucleus of the amygdala, para- and periventricular hypothalamus, supraoptic nucleus, paraventricular thalamus, reuniens nucleus, subfornical organ and bed nucleus of the stria terminalis. These results define the central nervous system pathways of somatosymphathetic reflexes and demonstrate that areas in the forebrain not previously known to be activated by somatosympathetic reflexes, but previously implicated in mediating the defense reaction, are activated by these reflexes.     

Noxious and innocuous mechanical cutaneous stimulation increase the sympathetic efferent nerve activity innervating the interscapular brown adipose tissue in anesthetized rats

Effects of pinching and brushing of the various segmental skin areas (face, ear, neck, forelimb, chest, abdomen, hindlimb) on the activities of the sympathetic efferent nerve innervating the interscapular brown adipose tissue (IBAT) and contributing to its thermogenesis were examined in anesthetized rats. Pinching the face, ear, neck, or forelimb produced significant reflex increases in the efferent nerve activities, whereas pinching the chest, abdomen, or hindlimb did not produce any significant responses. In the case of brushing stimulation, only the stimulation of the ear produced significant increases. These results demonstrated that cutaneous mechanical stimulations at cranial, cervical, and upper thoracic segments were effective in producing reflex increases in the activities of the IBAT sympathetic nerve and that noxious stimulation was more dominant for eliciting the reflex responses.     

Single-unit study of lateral line cells in the optic tectum of Xenopus laevis: evidence for bimodal lateral line/optic units

Responses of single units in the Xenopus tectum to stimulation of the contralateral anterior lateral line nerve (cALLN) and optic nerve were studied. Cells responded to cALLN stimulation with a phasic burst of spikes that was repeatable between trials; latencies ranged from 4 to 23 msec. The most excitable cells were located in layer 6 of the ventrolateral tectum. Cells responding to stimulation of the ipsilateral ALLN were far less numerous and robust, and showed latencies 3-10 msec greater than those of contralateral responses. Tectal cell responses to cALLN nerve stimulation grew progressively to saturation with stimulus voltage and paralleled the growth of the ALLN compound action potential; cells responded to stimulation of either supra- or infraorbital branches of cALLN. These observations indicate convergence of primary lateral line afferents in the medulla and/or tectum. Lateral line tectal cells showed strong habituation at interstimulus times less than 8-20 seconds. Experiments on bimodal cells revealed facilitatory and inhibitory interactions between optic and lateral line inputs. Some cells responded to stimulation of either lateral line or optic nerves, with combined stimulation producing responses exceeding the sum of responses to separate nerve stimulation. In other cells the response to optic nerve stimulation was markedly increased by lateral line nerve stimulation, despite the absence of response to lateral line nerve stimulation alone. Facilitation was also evident in cells that responded only to combined stimulation of lateral line and optic nerves. Some cells exhibited an early (5-10 msec) and late (20-40 msec) response to optic nerve stimulation; lateral line nerve stimulation, despite eliciting no response itself, produced strong facilitation of the early but almost complete suppression of the late optic nerve response.