Medullary swallowing-related neurons in the anesthetized cat

Swallowing-related neurons (SRNs) were recorded systematically in the medulla oblongata of urethane-anesthetized cats. The SRNs received orthodromic inputs from the superior laryngeal nerve (SLN) and showed transient changes in their activity synchronous with swallowing. These neurons could be divided into three types. Type I SRNs are sensory-relay neurons from the SLN in the nucleus of the tractus solitarius (NTS), type II are interneurons located diffusely in the parvocellular reticular formation ventral to the NTS, which received oligosynaptic inputs from the SLN, and type III are motoneurons in the nucleus ambiguus. Some type II neurons still showed the swallowing activity after the animals were paralysed, which suggests that they could be involved in the generation of swallowing outputs.     

Reactions of red-nucleus neurons in the alert cat to cutaneous stimulation

Responses of the red nucleus (RN) neurones to cutaneous stimulation were studied in unanaesthetized chronic cats by means of microelectrode technique. It was revealed that the reactions were predominantly excitatory and the RN neurons had larger receptive fields covering one half of the body or all the limbs of the animal. The somatotopic principle of the cutaneous representation in RN was shown. The destruction of the cerebellar nuclei and sensorimotor cortex caused the lowering of the background activity of the RN neurones, changed their responses to cutaneous stimulation, as well as the narrowing and redistribution of the peripheral receptive fields. With all the changes described, the somatotopic character of the cutaneous representation in RN as preserved, though a large majority of RN neurones (52,8%) did not show this somatotopic distribution. The cerebellum is the main collector in transferring the cutaneous impulsation to the RN. In awake cats there were predominantly involved spinocerebellar pathways, activated by the flexor reflex afferents. The participation of the sensorimotor cortex in the reaction under study is revealed by the phenomenon of sprouting of the corticorubral axon terminals from the dendritic portions to the neuronal somata of RN.     

Development of intrinsic electrophysiological properties in neurons from the gustatory region of rat nucleus of solitary tract

There is no current understanding of the nature or time course of maturation of intrinsic electrophysiological properties for neurons in the gustatory region of the nucleus of the solitary tract (NST). Therefore, we used whole cell recordings in an in vitro slice preparation of the rat brainstem to characterize development of resting membrane, action potential and repetitive discharge properties of cells in gustatory NST at postnatal days 5, 10, 15, 20, and 30, and adult ages. Neurons were filled with Biocytin to verify location and characterize morphology. Membranes from younger neurons demonstrated a steeper current-voltage relation or higher input resistance, and a longer time constant than mature cells. Action potentials in younger cells had a slower rate of rise and were longer in duration. The afterhyperpolarization that typically follows the spike discharge usually had one phase in younger neurons, but was characterized by two or more phases in an increasing proportion of older cells. The repetitive discharge frequency in response to a range of depolarizing current pulses increased during development, and frequency/current plots were steeper in older compared with younger neurons. However, in all age groups there was clear accommodation of the discharge frequency. The greatest changes in resting membrane, action potential, and discharge properties were observed between P5 and P15, and mature values were generally reached by P20. At each postnatal age, neurons could be categorized in four neuron groups, based on the discharge pattern in response to a hyperpolarizing/depolarizing current protocol. Anatomical reconstructions indicated that although cells increased in overall dendritic expanse during development, neurons became less complex as illustrated by decreases in number of dendritic branch points, and in number and density of spines. The timing of major developmental differences in intrinsic electrical characteristics observed here is associated with a period of previously reported maturational changes in extracellular taste responses to number and concentration of chemical stimuli. However, further alterations in extracellular taste responses proceed after apparent maturation of intrinsic neural properties.     

Vestibular nucleus neurons, projecting to the "gastric" area of the solitary tract nucleus

OBJECTIVES: To describe the natural recovery of visuospatial neglect in stroke patients and the distribution of errors made on cancellation tests using a standardised neuropsychological test battery. METHOD: A prospective study of acute (< seven days) patients with right hemispheric stroke. Patients identified with visuospatial neglect were followed up for three months with monthly clinical and neuropsychological testing RESULTS: There were 66 patients with acute right hemispheric stroke assessed of whom 27 (40.9%) had evidence of visuospatial neglect. Patients with neglect, on admission, had a mean behavioural inattention test (BIT) score of 56.3, range 10-126 (normal>129). Three of the subtests identified errors being made in both the right and left hemispaces. During follow up, recovery occurred across both hemispaces, maximal in the right hemispace. Recovery from visuospatial neglect was associated with improvement in function as assessed by the Barthel score. At the end of the study period only six (31.5%) patients had persisting evidence of neglect. On admission the best predictor of recovery of visuospatial neglect was the line cancellation test (Spearman's rank correlation r=-0.4217, p=0.028). CONCLUSION: The demonstration of errors in both hemispaces has implications for the theory that neglect is a lateralised attentional problem and is important to recognise in planning the rehabilitation of stroke patients.     

Electrophysiological and morphological properties of neurons acutely isolated from the rostral gustatory zone of the rat nucleus of the solitary tract

The biophysical and morphological characteristics of acutely isolated neurons from the rostral nucleus of the solitary tract (rNST) were investigated under current clamp conditions and compared with the results obtained from neurons recorded in brain slices. The passive membrane properties of the isolated neurons were similar to rNST neurons in brain slices and the neurons maintained their morphological characteristics although their dendritic tree was truncated. The isolated neurons also retained their characteristic repetitive firing properties. In addition we also noted developmental changes in the intrinsic membrane properties of the isolated neurons, such as a shortening in action potential duration, decrease in membrane time constant and input resistance, that occurred when these parameters were compared in neurons isolated from young (5-10 days) and older animals. These enzymatically dispersed neurons therefore retained both the membrane properties and morphology observed in the intact brainstem and in vitro brain slice preparation. The use of this isolated neuron preparation provides a basis for further study of rNST neurobiology.     

Intracellular recordings in response to monaural and binaural stimulation of neurons in the inferior colliculus of the cat

The inferior colliculus (IC) is a major auditory structure that integrates synaptic inputs from ascending, descending, and intrinsic sources. Intracellular recording in situ allows direct examination of synaptic inputs to the IC in response to acoustic stimulation. Using this technique and monaural or binaural stimulation, responses in the IC that reflect input from a lower center can be distinguished from responses that reflect synaptic integration within the IC. Our results indicate that many IC neurons receive synaptic inputs from multiple sources. Few, if any, IC neurons acted as simple relay cells. Responses often displayed complex interactions between excitatory and inhibitory sources, such that different synaptic mechanisms could underlie similar response patterns. Thus, it may be an oversimplification to classify the responses of IC neurons as simply excitatory or inhibitory, as is done in many studies. In addition, inhibition and intrinsic membrane properties appeared to play key roles in creating de novo temporal response patterns in the IC.     

Effects of systemic morphine on lamina I spinothalamic tract neurons in the cat

Lamina I spinothalamic tract (STT) neurons are an integral component of the central representation of pain and temperature and thus their sensitivity to various analgesics needs to be examined. In the present study, the effects of successive, cumulative doses (0.125-2.0 mg/kg) of intravenous morphine sulfate on the quantitative stimulus-response properties of nociceptive lamina I STT cells have been tested in the intact, barbiturate-anesthetized cat. Both nociceptive-specific (n = 7) and multireceptive (heat, pinch and cold sensitive; n = 7) lamina I STT cells were inhibited in a dose-dependent manner. Parallel dose-dependent effects on responses to noxious heat and pinch were generally observed that reduced ongoing discharge levels and the slopes of the stimulus-response functions. However, non-STT lamina I cells (n = 5) differed significantly; the responses of one multireceptive (heat, pinch and cold-sensitive) cell and the responses to pinch of 3 of 4 wide dynamic range cells were not inhibited. In addition, two-thirds of the nociceptive lamina I STT cells showed enhanced responses at the lowest dose of morphine (0.125 mg/kg). These results contrast with the varied effects of morphine reported for superficial dorsal horn cells with uncharacterized projections and they support the role of lamina I STT cells in pain. Furthermore, these observations are consistent with previous findings indicating that lamina I STT neurons are a distinct subpopulation of lamina I cells. These results support previous evidence that opiatergic modulation of sensory activity in lamina I is functionally organized.     

Tetanic stimulation induces short-term potentiation of inhibitory synaptic activity in the rostral nucleus of the solitary tract

Whole cell recordings from neurons in the rostral nucleus of the solitary tract (rNST) were made to explore the effect of high-frequency tetanic stimulation on inhibitory postsynaptic potentials (IPSPs). IPSPs were elicited in the rNST by local electrical stimulation after pharmacological blockade of excitatory synaptic transmission. Tetanic stimulation at frequencies of 10-30 Hz resulted in sustained hyperpolarizing IPSPs that had a mean amplitude of -68 mV. The hyperpolarization resulted in a decrease in neuronal input resistance and was blocked by the gamma-aminobutyric acid-A (GABAA) antagonist bicuculline. For most of the neurons (n = 87/102), tetanic stimulation resulted in a maximum hyperpolarization immediately after initiation of the tetanic stimulation, but for some neurons the maximum was achieved after three or more consecutive shock stimuli in the tetanic train of stimuli. When the extracellular Ca2+ concentration was reduced, the maximum IPSP amplitude was reached after several consecutive shock stimuli in the tetanic train for all neurons. Tetanic stimulation at frequencies of 30 Hz and higher resulted in IPSPs that were not sustained but decayed to a more positive level of hyperpolarization. In some neurons the decay was sufficient to become depolarizing and resulted in a biphasic IPSP. It was possible to evoke this biphasic IPSP in all the neurons tested if the cells were hyperpolarized to -75 to -85 mV. The ionic mechanism of the depolarizing IPSPs was examined and was found to be due to an elevation of the extracellular K+ concentration and accumulation of intracellular Cl-. Tetanic stimulation increased the mean 80-ms decay time constant of a single shock-evoked IPSP up to 8 s. The length of the IPSP decay time constant was dependent on the duration and frequency of the tetanic stimulation as well as the extracellular Ca2+ concentration. Afferent sensory input to the rNST consists of trains of relatively high-frequency spike discharges similar to the tetanic stimulation frequencies used to elicit the IPSPs in the brain slices. Thus the short-term changes in inhibitory synaptic activity in the slice preparation probably occur in vivo and may play a key role in taste processing by facilitating synaptic integration.     

Cardiovascular responses to gastric hypo-osmolar stimulation in anesthetized dogs

We compared the cardiovascular response to the gastric infusion of distilled water (DI) with that to the gastric infusion of 0.9% saline (SI) and gastric ballooning with 37 degrees C water (BA) through a gastric fistula in splenectomized mongrel dogs (n = 7). DI, and SI amounting to 5% of body wt and the same volume of water were infused in approximately 20 s through the tube and responses in mean arterial pressure (MAP), CVP, heart rate (HR), and intra-esophageal pressure (EP) were monitored continuously. After DI, SI, and BA, the measured variables showed significant increases and attained maximal increases at about 2 min after the treatments. After DI, the maximum elevation in MAP was 21.3 +/- 1.9 mmHg and 2 times higher than in SI and BA. The corresponding value in CVP was 5.0 +/- 0.3 mmHg and 2-3 times higher than with SI and BA, and HR increased by 26.1 +/- 3.0 beats/min showing 3 to 6 times larger increases compared with SI and BA. These gastro-cardiovascular reflexes were abolished after subdiaphragmatic truncal vagotomy. These findings suggest that both the mechanical and osmotic stimuli to the stomach induce cardiovascular reflexes and that the vagus is involved in the reflex.     

Response diversity of pontine and deep cerebellar nuclear neurons to air puff stimulation of the eye in the alert cat

The discharge of antidromically identified brainstem and cerebellar nuclear neurons involved in the corneal reflex was recorded in the alert cat during corneal air puffs. Eye movements were measured with the search coil technique. Recorded sensory, motor, reticular formation and cerebellar nuclear neurons showed a wide diversity in latencies and patterns of response to air puff stimulation. This diversity suggests that each part of the circuit may contribute different properties to information processing for the corneal reflex, for sustained eyelid closure and, possibly, for the classical conditioning of the nictitating membrane response.     

Spinal cord segments mediating tonic sympathetic nerve discharge to the kidney in the anesthetized cat

According to anatomical data, preganglionic neurons projecting to the kidney via sympathetic ganglia occupy a wide range of adjacent segments in the thoracolumbar spinal cord, from Th7 to L2. Since, however, the majority of preganglionic neurons is silent at resting states, the active segments indeed transmitting sympathetic activity, at rest, may be different. In the present experiments, the spontaneous sympathetic activity was recorded before and after the sympathetic trunk and white rami (WR) Th8-L3 were cut in a sequential manner. The step-by-step changes in the power of renal nerve discharge were estimated and used for mapping tonic renal outflow to the spinal cord. We found that powerful activity comprising 70-95% of the power of control recordings remained after eliminating the input from Th1-Th12, indicating that thoracic spinal cord including segments that contain the largest number of cells projecting to renal postganglionic neurons contributes relatively weakly to tonic renal nerve activity. It appeared that resting sympathetic nerve discharge was predominantly maintained by the caudalmost division of the renal preganglionic neuron population since the largest decrease in nerve power occurred after severing WR Th13, L1, and L2. These findings suggest that the 'active segmental map' of preganglionic neurons controlling a certain organ at rest does not necessarily match the distribution of the total population of neurons projecting to the same effector.     

The effect of activation of central adrenergic receptors by clonidine on the excitability of the solitary tract neurons in cats

The effect of i.v. administered clonidine (10-15 mug/kg) on the evoked potential recorded in the dosal part of medulla oblongata, during carotid sinus nerve stimulation, was studied in chloralose-urethane anaesthetized cats. Clonidine influenced the amplitude and configuration of the evoked potential and the changes were parallel to the blood pressure depressor response. However, the blood pressure drops, evoked by i.v. infusion of papaverine, did not influence the potential. It is concluded that the synaptic transmission from the carotid sinus nerve to the second order neurons in the solatary tract area can be modulated by the clonidine-induced activation of central adrenergic receptors.     

A cholecystokinin-B receptor antagonist potentiates GABAergic and glycinergic inhibition in the nucleus of the solitary tract of the rat

In both rodent and primate in vivo models, cholecystokininB (CCKB) antagonists such as PD134,308 have anxiolytic effects that may involve the potentiation of GABAergic transmission. We have investigated this interaction using exogenous application of GABA and whole cell patch recording techniques in neurons of the nucleus of the solitary tract (NTS) in brainstem slice preparations. In the presence of PD143,308 the magnitude of the GABA-evoked decrease in membrane input resistance was enhanced by 41.2 +/- 3.1% and the duration of the response was prolonged by 34.8 +/- 2.2%. Also, PD134, 308 potentiated glycine-evoked decreases in membrane input resistance, increasing the amplitude of the response by 62.8 +/- 4. 85 and prolonging the duration of the response by 23.5 +/- 3.6%. The effect of PD134,308 persisted in the presence of tetrodotoxin, after reversal of the transmembrane gradient of chloride ions and under conditions of exaggerated GABAA receptor desensitization. Our results demonstrate that at least part of the functional link between PD134,308 and the GABAA response occurs postsynaptically.     

The N-methyl-D-aspartate receptor pathway is involved in hypoxia-induced c-Fos protein expression in the rat nucleus of the solitary tract

In chloroplast photosystem II, the extrinsic polypeptide of 33 kDa is involved in the stabilization the Mn cluster in charge of water splitting and in the fulfilment of the Ca(2+)-cofactor requirement for oxygen evolution. The conformational analysis of the purified 33 kDa extrinsic polypeptide was carried out using FTIR spectroscopy with its self-deconvolution and second derivative resolution enhancement as well as curve-fitting procedures. The FTIR spectroscopic results showed that the isolated polypeptide is characterized by a major proportion beta-sheet conformation (36%) with 27% alpha-helix, 24% turn, and 13% beta-antiparallel structures.     

Odorant response properties of convergent olfactory receptor neurons

Information about odorant stimuli is thought to be represented in spatial and temporal patterns of activity across neurons in the olfactory epithelium and the olfactory bulb (OB). Previous studies suggest that olfactory receptor neurons (ORNs) distributed in the nasal cavity project to localized regions in the glomerular layer of the OB. However, the functional significance of this convergence is not yet known, and in no studies have the odorant response properties of individual ORNs projecting to defined OB regions been measured directly. We have retrogradely labeled mouse ORNs connecting to different glomeruli in the dorsal OB and tested single cells for responses to odorants using fura-2 calcium imaging. ORNs that project to clusters of dorsomedial (DM) glomeruli exhibit different odorant response profiles from those that project to dorsolateral (DL) glomeruli. DL-projecting ORNs showed responses to compounds with widely different structures, including carvone, eugenol, cinnamaldehyde, and acetophenone. In contrast, DM-projecting neurons exhibited responses to a more structurally restricted set of compounds and responded preferentially to organic acids. These data demonstrate that ORN afferents segregate by odorant responsiveness and that the homogeneity of ORN and glomerular input varies with different OB regions. The data also demonstrate that a subpopulation of ORNs projecting to DM glomeruli is functionally similar.     

Response properties of corticotectal and corticostriatal neurons in the posterior lateral suprasylvian cortex of the cat

Lateral suprasylvian cortex (LS) is an important source of visual projections to both the striatum and superior colliculus. Although these two LS efferent systems are likely to be involved in different aspects of visual processing, little is known about their functional properties. In the present experiments, 86 neurons in halothane-anesthetized, paralyzed cats were recorded along the posterior aspects of the medial and lateral banks of LS (PMLS and PLLS). Neurons were selected for analysis on the basis of antidromic activation from electrodes chronically implanted in the superior colliculus and caudate nucleus. The segregated nature of corticostriatal and corticotectal neurons was apparent; in no instance could a neuron be antidromically activated from both the superior colliculus and the caudate nucleus. Many common features were revealed between corticotectal and corticostriatal neurons; the majority of neurons in both populations were binocular and contralaterally dominant, showed similar responses to stationary flashed light, and expressed within-field spatial summation and surround inhibition. However, a number of information-processing features distinguished between corticotectal and corticostriatal neurons; the former were generally tuned to lower velocities than were the latter, and, for a given eccentricity in visual space, corticotectal neurons had smaller receptive fields than did corticostriatal neurons. Moreover, most corticotectal neurons displayed a marked preference for movements toward temporal visual space, whereas corticostriatal neurons revealed no specialization for a particular direction of movement. In addition, whereas corticotectal neurons were selective for receding stimuli, corticostriatal neurons were selective for approaching stimuli. The presence of these two corticofugal pathways is discussed in relation to their presumptive functional roles in the facilitation of attentive and orientation behaviors.     

A morphological study of cat dorsal spinocerebellar tract neurons after intracellular injection of horseradish peroxidase

This work represents an attempt to elucidate structural features of electrophysiologically characterized, individual cat dorsal spinocerebellar tract (DSCT) neurons by using intracellular application of horseradish peroxidase (HRP). Intracellular recordings and HRP injections were made in DSCT neurons of the Clarke's column in cat lumbar (L3) spinal cord. The units were identified by antidromic invasion following electrical stimulation of the ipsilateral dorsolateral funiculus at C1. In addition, sensory inputs to the DSCT neurons were determined by natural (adequate) stimuli applied to the hind limb with intact innervation. The morphological analysis is based on data obtained from 19 well-stained electrophysiologically identified neurons located in Clarke's column. Thirteen of these units received excitatory sensory inputs from muscle receptors, two were activated by cutaneous afferents only, and four had a convergent (muscle + cutaneous) input. The DSCT--muscle cells were equivalent to the large Clarke cells (class C of Leowy, '70). Their dendrites were oriented primarily in the rostro--caudal direction (up to 2500 micron) and appeared generally smooth except for some branchlets. In four of these cells, the axon was traced into the lateral funiculus. In light microscopic analysis there was no evidence that axon collaterals arose from these axons during the initial trajectory through the spinal grey matter. The four DSCT--convergent neurons were similar in shape to the DSCT--muscle units although they appeared to have somewhat smaller cell bodies. Of the two DSCT--cutaneous neurons one was found to be of the B type, with the dendritic tree having fewer branches and oriented mainly in the medio--lateral direction. The other cell, however, turned out to be similar in appearance to the C type Clarke neurons.     

Response properties of neurons in the inferior colliculus of the monaurally deafened ferret to acoustic stimulation of the intact ear

Response properties of neurons in the central nucleus of the inferior colliculus (ICC) were investigated after unilateral cochlear removal at various ages during infancy. Nineteen ferrets had the right cochlea surgically ablated, either in adulthood or on postnatal day (P) 5, 25, or 40, 3-18 mo before recording. Adult ablations were made on the same day as ("acute," n = 3), or 2-3 mo before ("chronic," n = 3), recording. Two ferrets were left binaurally intact. Single-unit (n = 702) and multiunit (n = 1,819) recordings were made in the ICC of barbiturate-anesthetized ferrets ipsilateral (all ages) or contralateral (P5 and acute adult only) to the intact ear. In binaurally intact animals, tonal stimulation of the contralateral ear evoked excitatory activity at the majority (94%) of recording loci, whereas stimulation of the ipsilateral ear evoked activity at only 33% of recording loci. In acutely ablated animals, the majority of contralateral (90%) and ipsilateral (70%) loci were excited by tonal stimulation of the intact ear. In chronically ablated animals, 80-90% of loci were excited by ipsilateral stimulation. Single-unit thresholds were generally higher for low-best frequency (BF) than for high-BF units, and higher in the ipsilateral than in the contralateral ICC. Analysis of covariance showed highly significant differences between all of the ipsilateral and contralateral groups, but no effects of age at ablation or survival time following ablation, other than that the group ablated at P25 had higher mean ipsilateral thresholds than the groups ablated at P5 or, acutely, in adulthood. Cochlear ablation at P5, 25, or 40 resulted in a significant increase in dynamic ranges of ipsilateral ICC unit rate-intensity functions relative to acutely ablated animals. Dynamic ranges of units in the contralateral ICC of P5-ablated ferrets were also significantly increased compared with those of acutely ablated animals. Cochlear ablation at P5, 25, or 40 resulted in a significant increase in single-unit spontaneous discharge rates in the ICC ipsilateral but not contralateral (P5 only) to the intact ear. These data show that unilateral cochlear removal in adult ferrets leads to a rapid and dramatic increase in the proportion of neurons in the ICC ipsilateral to the intact ear that is excited by acoustic stimulation of that ear. In addition, the data confirm that, in ferrets, cochlear removal in infancy leads to a further increase in responsiveness of individual neurons in the ipsilateral ICC. Finally, the data show that responses in the ICC contralateral to the intact ear are largely but not completely unchanged by unilateral cochlear removal.     

Cholinergic responsiveness of neurons in the ventroposterior thalamus of the anesthetized rat

Acetylcholine has been implicated as an important neurotransmitter in the mechanisms of thalamic activation. Cholinergic mechanisms are thought to directly underlie the high level of excitability observed in thalamic relay neurons during waking and rapid eye movement sleep. We sought to determine if the cholinergic responsiveness of neurons in the ventroposterior nuclei of the thalamus in rat is consistent with this view. Neurons in the chloral hydrate-anesthetized rat were studied with extracellular recording and microiontophoretic application of cholinergic agents. In most cases (63% of 63 cells), the ejection of the agonist, carbachol, had no observable effect on spontaneous activity. Facilitation (25%), inhibition (8%) and inhibition followed by facilitation (3%) were also observed. Carbachol ejections that by themselves were ineffective in altering spontaneous activity proved capable, in 93% of 28 cells, of antagonizing the uniformly facilitatory responses produced by glutamate ejection. The putative M1-selective, cholinergic agonist, McN-A-343, was also ineffective alone in altering spontaneous activity in the majority of cases (74% of 27 cells) and produced only inhibitory responses in the remaining seven neurons studied. Interacting applications of McN-A-343 and glutamate resulted, in all cases, in antagonism of glutamate facilitation (N = 12). The various responses to applied cholinergic agonists were all capable of being antagonized by muscarinic receptor-blocking agents. Both the high proportion of inhibitory responses and the antagonism of glutamate facilitatory responses suggest that ventroposterior neurons in the rat differ from other thalamocortical relay neurons in the rat and cat with regard to cholinergic responsiveness. Additionally, the lack of predominantly facilitatory responding renders it unlikely that cholinergic mechanisms directly underlie increases in excitability of ventroposterior neurons observed during waking and rapid eye movement sleep.