Taste stimuli: a behavioral categorization.

The selective patterns of generalization to various chemicals, obtained in rats after radiation-induced gustatory-avoidance conditioning against single chemicals, were used to evaluate qualitative similarities among taste stimuli. DL-Alanine, glycine, and sodium saccharin were classed together, but not with D-glucose or potassium chloride. Groupings such as these may serve as a basis for determining the dimensions along which taste quality is represented.

Taste stimuli: quality coding time.

Rats conditioned to avoid drinking 300 millimolar NaCl recognized and rejected this solution within 250 to 600 milliseconds of onset of stimulus, a period containing the phasic portion of the peripheral neural response. They generalized to 500 millimolar NaCl but not to 500 millimolar sucrose. Rejection was based on quality identification neurally encoded within this brief period.

Licking behavior: evidence of hypoglossal oscillator.

Action potentials and slow waves were recorded from the hypoglossal nucleus of rats during licking of water from a drinking tube. Periods of licking and of rhythmic neural activity were usually highly correlated, as were their frequencies. Neural activity sometimes continued after cessation of licking; at other times, it stopped during a short interruption of licking and resumed in rhythm with licking. These observations are consistent with an oscillatory model of the control of licking.

Modulation of the excitability of avian peripheral nerves by vitamin D: relation to calbindin-D28k, calcium status and lipid composition.

Calbindin-D28k (CaBP), previously localized in some of the cell bodies of ganglia of the avian intestinal (Remark's) nerve, was shown to be vitamin D-dependent. In the present studies, the effect of vitamin D3 on electrophysiological properties of this nerve was examined in vitro. Electrical stimulation of the nerve yielded a compound action potential with two primary components, Peaks I and II. Peak II, suppressed by hexamethonium bromide or Ca(2+)-free buffer, is synaptically mediated. The transit time between the two peaks was unaffected by vitamin D3. The apparent conduction velocity, defined as [(activation time + transit time)/nerve length], was increased by vitamin D-deficiency and decreased by vitamin D3 repletion, the latter decrease due entirely to an increase in activation time. Activation time after vitamin D-repletion was correlated with an increase in CaBP and plasma Ca2+ levels. However, normalization of plasma Ca2+ by supplementation of vitamin D-deficient diets with excess calcium (2.5 and 4.0%) also resulted in an increase in activation time, without affecting neuronal CaBP levels. Vitamin D3 also decreased the conduction velocity and increased CaBP of the vagus nerve and, by lipid analysis, was shown to increase and decrease its phosphatidylcholine and phosphatidylethanolamine content, respectively, and to decrease its phospholipid/cholesterol ratio. Modulation of peripheral nerve activity by vitamin D3 is related to calcium status and perhaps to changes in lipid composition. The functional role of CaBP in the behaviour of this complex nerve remains unknown.

A dorsal spinal neural network in cat. III. Dynamic nonlinear analysis of responses to random stimulation of single type 1 cutaneous input fibers.

The input/output characteristics of a subset of dorsal horn neurons in laminae 3 and 4 [( L3,4:SA1,X], see INTRODUCTION; output cells) of cat have previously been examined in the resting unperturbed condition using single or paired input pulses introduced once every three seconds on single slowly adapting type 1 (SA1) cutaneous mechanoreceptor afferent fibers (1, 27, 28). The present study extends this description to the dynamic condition by use of a random-stimulation method developed for the characterization of multiport pulse-input/pulse-output nonlinear systems. A total of 58 SA1 receptor input channels to 29 [L3,4:SA1,X] network output cells were tested individually in 15 spinal cats with several random train stimuli of differing mean input rates [5, 10, 20, 30, 50 pulses per second (pps)]. Simultaneous stimulation of two input channels with independent random trains was performed in 16 units. In each case, zero-, first-, and second-order descriptions of network behavior were obtained; the second-order characteristics of interest were expressed in the form of excitability functions, which are directly comparable with those obtained from condition-test results. Preliminary testing with multiple input pulses suggested that, in addition to the strong second-order effects previously identified, third- and higher-order nonlinearities and effects with long time constants could generate significant rate effects. Nonetheless, first-order response characteristics obtained in the dynamic condition at the lowest mean input rate used (5 pps) were in each case qualitatively identical, though slightly smaller in magnitude, to the poststimulus time histograms (PST) obtained in the unperturbed condition. Second-order excitability functions were generally, but not always, similar to condition-test results in the eight cases in which comparisons were made. Furthermore, use of a complete second-order characterization to predict the output response to a different random input in five cases resulted in an average correlation with the observed output that was a 50% improvement over the linear model predictions. These results indicate strong second-order and weaker higher-order nonlinearities in the [L3,4:SA1,X] network. Three classes of channel-specific second-order excitability characteristics were identified into which the previous descriptions (28) can be incorporated. The general pattern was initial facilitation followed by inhibition. This was observed for both the early and late response components in about half the channels (class I).(ABSTRACT TRUNCATED AT 400 WORDS)

A dorsal spinal neural network in cat. I. Responses to single impulses in single type I cutaneous input fibers.

1. We have studied some properties of a sacral dorsal spinal gray matter network. the lamina 4:type 1 afferent fiber network (L4:T1 network) in 24 adult cats that were anesthetized with urethan and the spinal cord transected at the thoracolumbar junction. 2. The network in the first sacral segment is composed of a subgroup of lamina 4 cells as principal neurons that are connected to type 1 afferent fibers emerging from the skin, the manipulable input channels. Other primary afferent fibers and axons of central cells of other segments may also be input elements. Cells of the substantia gelatinosa (SG) and of the marginal layer constitute the intrinsic neurons. We monitored the output of the network by unit recording of the lamina 4 cell's impulse activity. 3. We activated the network by single impulses delivered via single type 1 afferent fibers. We stimulated fibers individually by focused electrical stimulation and monitored the selectivity of the stimulus by a computer-averaging procedure. The basic stimulus paradigm (each stimulus trial) consisted of 100 single impulses delivered 1 impulse/3 s. For nine networks, each of the accessible type 1 fibers was used as an input channel. 4. The typical pattern of response to the 100 impulses was composed of: a) an early discharge lasting for 5 ms after the input impulse invades the central arbor of the type 1 fiber, b) a late discharge of variable duration terminated by c) a postresponse reduction in ongoing discharge rate. Early-only and late-only discharges were occasionally observed. We conclude that the response pattern reflects the specific neuronal and synaptic configuration that is engaged by each input channel. 5. Across input channels, the early discharge was characterized by: a) a bimodal distribution of low- and high-probability responses, reflecting two predominating groups of type 1 input channels, one believed to be weakly coupled and the other strongly coupled to the principal neuron; b) relatively little multiple discharge; c) modal response during the first 2 ms of the discharge; d) response produced via a monosynaptic connection of the type 1 fiber with the lamina 4 neuron and average synaptic delay of 0.53 +/- 0.01 ms (mean +/- SE, n = 100); e) in general, a stable response throughout the 5-min stimulus trial, although an occasional habituating response was noted. 6. The late discharge was characterized by: a) a multiple discharge and a wide response jitter; b) mean duration approximately 29 ms; c) in general, high-probability response; d) a tendency for the response to wane during the course of the stimulus trial. 7. We observed no relationship between the magnitude of the early or late response and the level of ongoing discharge when considered across input channels. However, for a given input channel over time, the output response was often highly correlated with the level of ongoing discharge. The effect was best described by a log-log relationship...

Lateral cervical nucleus in the cat: functional organization and characteristics.

1. The lateral cervical nucleus (LCN) was investigated with extracellular recordings in the anesthetized cat. A total of 556 LCN units were characterized; the locations of most of these were histologically verified. Half of these had receptive fields on the rostral third of the ipsilateral body surface including the face; 14% had fields on the thorax or abdomen, 33% had fields on the hindlimb or tail, and about 3% had receptive fields larger than one limb. 2. The LCN was observed to be somatotopically organized in experiments using angled microelectrode penetrations. Hindlimb units were dorsolateral, forelimb units ventromedial, and face units most medial within the LCN. In regions where LCN cells were present only in the medial portion of the dorsolateral funiculus, they were all forelimb units. 3. A special subpopulation (17%) of cells were clustered most ventromedially in the LCN. These units had large or disjoint receptive fields, and/or responded to deep, visceral, or noxious stimulation. A third of these did not project in the medial lemniscus (ML); many were synaptically activated by stimulation of the ML. Those that did project in the ML had significantly longer latencies than all other LCN units. It is suggested that this subpopulation contains local LCN interneurons. 4. The specific mechanoreceptor inputs were identified for each of 121 projecting LCN units. Receptor inputs were uniform across each receptive field; that is, each unit that responded to a given receptor type was observed to respond to receptors of that type throughout its receptive field. Input from large-fiber-diameter, velocity-sensitive mechanoreceptors was predominant. The absence of input from slowly adapting type I and II receptors and from joint receptors was confirmed. A significant number of units (17.3%) could be driven by only one receptor type. The LCN sample profile agrees closely with the receptor representation in the hindlimb portion of the spinocervical tract. It is concluded that these data that anatomic specification of convergence occurs in the LCN with respect to receptor connectivity, and that this specification originates in lamina IV of the dorsal horn. 5. Stimulation of the dorsal column nuclei synaptically excited 23% of the LCN units tested. In two cases it was possible to demonstrate, by collision, that this occurred via collaterals of spinocervical tract axons. It is concluded that some spinocervical axons have collaterals terminating in the rostral parts of the dorsal column nuclei.

Parametric studies of dorsal horn neurons responding to tactile stimulation.

Dorsal horn neurons responding to tactile input were recorded in segments L3-S2 of unanesthetized, low-spinal cats. Single units were characterized with regard to receptive field (RF) location, RF size and shape, spontaneous discharge rate, central delay, and convergence of four tactile afferent types. 1. RF size increased from the toes to the calf region. 2. Length-width ratio increased from the toes to the calf and declined from the calf to the hip. 3. The relation between RF size and position on the limb was independent of segmental and laminar location of the neurons. 4. RF size was positively correlated with spontaneous discharge rate. 5. The relation between RF size and shape and RF position can be interpreted in terms of regional variations in the magnitude of the gradient of representation in the dorsal horn somatotopic map. 6. Central delay was negatively correlated with both RF size and rate of ongoing discharge. 7. There were no statistically significant differences among the laminae with respect to central delay, RF size or shape, ongoing discharge, or convergence combinations of the four tactile afferent systems. 8. Data presented were at variance with Wall's laminar cascading model for laminae IV-VI. Our results suggest that the model should be modified, at least to emphasize monosynaptic tactile input to all three of these laminae.

Recent studies on the biological actions of vitamin D on intestinal transport and the electrophysiology of peripheral nerve and cardiac muscle.

Vitamin D, with parathyroid hormone and calcitonin, is an essential factor in the homeostatic regulation of systemic calcium in most vertebrate species. Targets for this aspect of vitamin D action, through its biologically active metabolites, are primarily the intestine, kidney and bone. Each of these tissues or organs are stimulated by 1,25(OH)2D3 to increase the transport calcium into the extracellular fluid compartment when plasma calcium levels are below normal and/or when there is a greater need for calcium to meet the requirements of physiological processes, such as growth, gestation and lactation. During such periods, the efficiency of the absorption of calcium from the intestine increases, the resorption of calcium salts from bone is stimulated, and the efficiency of the reabsorption of filtered calcium by the renal tubule is increased. In addition to the homeostatic function of vitamin D, there is an increasing amount of evidence that vitamin D has important effects on tissues and organs other than those concerned with calcium homeostasis. With regard to the intestinal epithelial system, the genomic effect of 1,25(OH)2D3 was shown several years ago when the de novo synthesis of a specific vitamin D-induced calcium-binding protein (CaBP, calbindin-D) was demonstrated. In our view, this appears to be an essential factor in the well-documented enhancement of calcium absorption by vitamin D. The function of calbindin-D, a high affinity calcium-binding protein, in the absorptive process is not precisely known but currently considered to act as an intracellular facilitator of the diffusion of calcium from the microvillar pole of the enterocyte to the basal-lateral membrane. There is evidence that vitamin D influences another step in the absorptive process. This step appears to be associated with the entrance of luminal calcium into the enterocyte, the first step in the transepithelial transport process. This response appears to occur relatively early (1 h or less) after 1,25(OH)2D3 is given to vitamin D-deficient animals, whereas the de novo synthesis of transport proteins has a much longer lag time (about 4 h). The in vitro absorption studies of Nemere et al (1984) and the in vivo experiments of our group (Wasserman et al, 1982) accentuate this point. However, the more rapid reaction, i.e., the possible modification of the permeability properties of the brush border membrane, does not result in a substantive increase in overall calcium absorption unless the enterocyte had been "primed" by previous exposure to vitamin D. The "priming" reaction might represent the synthesis of CaBP or some other intracellular component.(ABSTRACT TRUNCATED AT 400 WORDS)