SUMMARY1. The response characteristics of lamina I neurones recorded extracellularly in the lumbrosacral enlargement of chloralose-anaesthetized cats were examined with peripheral nerve electrical stimulation, adequate mechanical and thermal stimulation of hind-limb skin, and algesic mechanical and chemical stimulation of musculotendinous structures, particularly the gastrocnemius-soleus (g.s.) muscle. Antidromic activation from an electrode array that spanned the contralateral thalamus was used to identify lamina I spinothalamic tract (lam.I-s.t.t.) neurones.2. Recordings were made from a total of 218 lumbosacral lam.I-s.t.t. neurones. Their mean central conduction latency was 90 1 ms (range 20-300 ms), corresponding to a mean conduction velocity of 3-7 m/s (range 1 1-16 7). Neurones responsive only to peripheral A6 fibre stimulation had significantly shorter central conduction latencies (mean = 62-8 ms) than those with both A8 and C fibre input (mean = 81-9 ms) and those with only C fibre input (mean = 134-6 ms). Ofthese 218 neurones, 103 (47 00) projected only to medial thalamus, 41 (19 %) only to lateral thalamus, and 56 (260%) to both; 18 (8 %) were classified as mid-thalamic projecting cells. About 100 of all cells had ongoing activity when first isolated.3. Ninety-three lam.I-s.t.t. neurones responded to stimulation of the sciatic nerve. The response characteristics of forty-seven of these were examined with the complete set of stimuli used. Twenty-four non-s.t.t. lamina I neurones were also characterized for comparison.4. Twenty-eight of the lam.I-s.t.t. neurones tested with the complete set of stimuli responded specifically to either cutaneous noxious (n = 19), cutaneous innocuous cold (n = 6) or algesic musculo-tendinous (n = 3) stimulation. Thirteen neurones responded to cutaneous noxious stimulation, and, in addition, to cold stimulation (n = 6), to deep stimulation (n = 4), or to both (n = 3). Six cells did not respond to any of the natural stimuli employed. All of the cold-specific and many of the multireceptive cold-sensitive neurones had ongoing discharge. The average central conduction latencies of cold-sensitive neurones (65-5 ms) and unresponsive neurones (48-7 ms) were shorter than that of nociceptive neurones (91-2 ms).5. Two response categories had distinct thalamic projection patterns. The majority of cold-specific neurones projected only to medial thalamus. Almost all multireceptive cold-sensitive neurones projected to both medial and lateral thalamus.

We present a systematic approach for detecting nonlinear components in heart rate variability (HRV). The analysis is based on twenty-three 48-h Holter recordings in healthy persons during sinus rhythm. Although many segments of 1,024 R-R intervals are stationary, only few stationary segments of 8,192–32,768 R-R intervals can be found using a test of Isliker and Kurths ( Int. J. Bifurcation Chaos 3:1573–1579, 1993.). By comparing the correlation integrals from these segments and corresponding surrogate data sets, we reject the null hypothesis that these time series are realization of linear processes. On the basis of a test statistic exploring the differences of consecutive R-R intervals, we reject the hypothesis that the R-R intervals represent a static transformation of a linear process using optimized surrogate data. Furthermore, time irreversibility of the heartbeat data is demonstrated. We interpret these results as a strong evidence for nonlinear components in HRV. Thus R-R intervals from healthy persons contain more information than can be extracted by linear analysis in the time and frequency domain.

SUMMARY1. In nembutal-anaesthetized cats, the responses of intradental Ad and C fibres to rapid cooling of the crown of canine teeth were studied.2. Single-unit recordings were obtained from a total of eighty-six intradental Ad and C fibres. The mean conduction velocity of Ad fibres was 13-9 m/s (n = 43; range: 3-6-26-0 m/s), that of C fibres was 1-3 m/s (n = 43; range: 05-2-2 m/s).3. In the intact tooth none of the identified Ad or C fibres showed any ongoing activity in the absence of intentional stimulation.4. 84% of the Ad fibres (thirty-six out of forty-three) and 88% of the C fibres (thirty-eight out of forty-three) were excited by cold stimulation of the canine tooth they were innervating.5. For all cold-sensitive Ad fibres the responses to rapid lowering of the tooth temperature were rather uniform. After an initial high-frequency discharge during the most rapid change in temperature, the discharge rate fell as the rate of change of temperature became smaller, and firing stopped completely when the temperature had reached a steady level. No firing occurred as the tooth temperature returned to its initial value. 6. A good linear correlation (r = 089) was found between the initial dynamic discharge of responding Ad fibres and the maximum rate of change of temperature achieved in a particular experiment.7. The response behaviour of C fibres to rapid cooling of the tooth was also rather uniform but different from that of Ad fibres. For C fibres no initial dynamic response phase was observed. After a mean latency of 7-3 s the fibres began to discharge regularly at a low rate at a time when the change of tooth temperature was already small.8. The firing rate of the C fibres had a weak linear correlation (r = 06) with the static tooth temperature achieved. No discharge was observed as the temperature returned to its initial value.9. For eleven cold-sensitive Ad and C fibres the receptive fields were determined by mechanical stimulation of the exposed pulp tissue. For Ad fibres the receptive * Present address: Department of Physiology, University of Helsinki, Siltavuorenpenger 20 J, SF-00170 Helsinki, Finland.PHY 391 E. JYVASJARVI AND K.-D. KNIFFKI fields were located at the pulp-dentine border, those for C fibres were located much deeper in the pulp and tended to have higher mechanical thresholds.10. When a human tooth was stimulated by a similar cold stimulus as used in the animal experiments, the sensation evoked and rated by the subjects using a fiftypoint categorical division procedure was described as a sharp, shooting pain being localized strictly to the tooth tested. Sensations other than pain were not perceived.11. Comparing the pain ratings of human subjects with the response characteristics of feline intradental Ad and C fibres to cold stimulation of a tooth, it is concluded that Ad fibres with the properties found in the cat are probably responsible for the cold-evoked dental pain sensation in man.

The double fluorescent retrograde labeling method was used to examine the distribution of spinothalamic tract (STT) cells that project to the medial and lateral thalamus in the cat. Injections of one fluorescent tracer (Fast Blue or Diamidino Yellow) were made throughout the lateral thalamus and injections of the other tracer were made in the medial thalamus at sites extrapolated from recording track coordinates. Survival times were successively extended (up to 5 weeks) in order to maximize labeling in both the cervical and lumbosacral spinal cord. On average, over 2,000 labeled contralateral STT cells were counted in serial sections from segments C5-7 and L5-S2. Numerical variability of the order of a factor of two was attributable to inherent differences between individual animals. The total number of cells labeled with fluorescent tracers was comparable to the number labeled with horseradish peroxidase in control cases, although there were significant differences between the laminar distributions of labeling produced by the two methods. Injections made anterior to the thalamus to control for labeling due to leakage or passing fibers did not produce substantial spinal labeling. The laminar distribution of fluorescent dye-labeled STT cells was consistent; about half (47%) were located in lamina I, 8% were in lamina V, 5% in lamina VI, 20% in lamina VII, and 20% in lamina VIII. The proportions of STT cells in laminae I and V were higher in cervical segments (57% and 12%, respectively) than in lumbosacral segments (38% and 6%). The dominant contribution of lamina I cells to the STT thus revealed by the fluorescent tracers is striking. The proportions of STT cells labeled from the medial and the lateral thalamus varied with segmental and laminar location and with injection placement. The majority (62%) of STT cells in most cases projected only to the medial thalamus, 25% projected only to the lateral thalamus, and 13% projected to both. The STT cell populations in laminae I, VII, and VIII each displayed this common projection pattern. In contrast, cells in laminae V and VI projected predominantly to the lateral thalamus. Twice as many STT cells in lamina I (19%) projected to both the medial and the lateral thalamus as from other laminae. A greater proportion of laminae V-VIII STT cells in segments L5-6 projected to the lateral thalamus, and in S1-2, more projected to the medial thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Cold stimuli of varying intensities were randomly applied to upper middle incisors of 12 healthy young subjects for a mean duration of 2 min by individually adapted thermodes the temperatures of which ranged from +30 degrees C to -30 degrees C. The subjects were asked to rate the magnitude of their pain sensations during application of the stimuli by means of a linear potentiometer according to a category scale. After each stimulus, they were asked to describe the quality of their pain sensations. Cold stimulation of the teeth evoked pain sensations were reproducible that in subsequent trials and could be graded according to stimulation intensity. Below certain individually different threshold thermode temperatures the onset of a stimulus was followed, after a short latency (1.6 +/- 1 sec), by a sharp and shooting pain sensation which immediately decreased after reaching its maximum value while the stimulus was still present. The mean maxima of the pain intensities were correlated to the thermode temperature. In general, this first pain component was followed by a second one (latency: 29.9 +/- 6.3 sec) with a lower threshold temperature, less of an increase in rate and lower magnitude. This was described as a dull, burning pain which was difficult to localize. The human pain ratings are compared to recordings of intradental nerve fibres in the cat and, under the assumption that the response behaviour of human pulpal nerve fibres is comparable to that of the cat, we hypothesize that the first pain component is evoked by intradental A delta fibres exhibiting their typical phasic response behaviour and firing during the initial steep temperature decrease. After some seconds, intradental temperature reached values sufficient to evoke C-fibre activity associated with the second pain component.