Dorsal column input to thalamic VL neurons: an intracellular study in the cat

Summary This study investigated the role of the ventral lateral (VL) nucleus of the thalamus as a lemniscal relay to motor cortex. Intracellular recordings were obtained from thalamic VL relay neurons in cats anesthetized with chloralose, following stimulation of the dorsal column nuclei. VL neurons were identified by their short-latency input from the cerebellar nuclei, their antidromic activation from motor cortex and their anatomical location. A total of 105 neurons was studied. The occurence of temporal facilitation to double volleys was also examined. It was found that 80/105 (75%) neurons responded with excitation and/or inhibition to stimulation of the dorsal column nuclei. The latencies of the postsynaptic responses ranged from 2.0 to 20 ms (median 10.0 ms). The latencies of nearly all responses (79/80) were > 3 ms and nearly all responses (45/47) which were tested for it, displayed temporal facilitation to double shock stimulation, consistent with polysynaptic transmission. Effective stimulation sites were found in the gracile and cuneate nuclei. Recording sites were located throughout VL, including the border region with the ventral posterior lateral nucleus (VPL). There was no obvious topographic relationship between location of recording site and latency or polarity (excitation versus inhibition) of the synaptic responses. This is consistent with dorsal column input diffusely distributed over VL. When the recording electrodes penetrated VPL, characteristics of the EPSPs were indicative of monosynaptic transmission (short latency, no temporal facilitation). This clear transition from VL to VPL suggests that it is not necessary to define, on physiological grounds, a separate border region between these two nuclei. The data provide evidence that dorsal column information reaches VL neurons polysynaptically, not monosynaptically. This indicates that VL is part of a long-latency, not short-latency path through the dorsal column nuclei to motor cortex.     

Characteristics of spinoreticular and spinothalamic neurons with renal input

Spinoreticular (SRT) and spinothalamic (STT) neurons were studied for responses to renal and somatic stimuli in 34 cats that were anesthetized with alpha-chloralose. SRT cells were antidromically activated from the medial medullary reticular formation near the gigantocellular tegmental field contralateral (35 cells), ipsilateral (15 cells), or both contralateral and ipsilateral (11 cells) to the recording site. Collision tests showed that activation from two electrodes resulted from stimulation of separate axonal branches and not from current spread. Twenty STT cells were activated from the spinothalamic tract just medial to the medial geniculate nucleus. SRT cells were located in laminae I, V, VII, and VIII of the T12-L2 segments. Most cells were located in lamina VII. STT cells were found in laminae I, V, and VII. The axons of 12 SRT cells were located in the ventrolateral or ventral quadrants of the upper cervical spinal cord. Antidromic conduction velocities of SRT cells averaged 48.7 +/- 3.7 m/s. No differences in conduction velocity were found between cells projecting to different reticular sites. In addition conduction velocity did not vary with the type of somatic or renal input. Antidromic conduction velocities of STT cells averaged 46.4 +/- 4.7 m/s. Renal nerve stimulation excited 58 and inhibited 3 SRT cells. All 20 STT cells were excited. Thirty SRT cells were excited only by A-delta input, 26 received both A-delta- and C-fiber inputs, and 2 cells received only C-fiber input. Ten STT cells received A-delta input only and 10 received both A-delta- and C-fiber inputs. All cells with renal input also received somatic input. Thirty-six SRT cells (59%) were classified as high threshold, 12 (20%) as wide dynamic range, and 10 (16%) as deep. Ten STT cells were classified as high threshold and 10 as wide dynamic range. Somatic receptive fields of STT cells were usually simple and invariably included the left flank region, although many of the fields extended to the left hindlimb or abdomen. Eighteen of the 20 were restricted to the ipsilateral side. In contrast, somatic receptive fields of SRT cells were primarily bilateral (71%). While all but two receptive fields included the left flank area, most extended to one or both hindlimbs, the abdomen, or the right flank. Inhibitory receptive fields were found for 33% of the SRT cells and 20% of the STT cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Convergence of cortical and thalamic input to direct and indirect pathway medium spiny neurons in the striatum

The major afferent innervation of the basal ganglia is derived from the cortex and the thalamus. These excitatory inputs mainly target the striatum where they innervate the principal type of striatal neuron, the medium-sized spiny neurons (MSNs), and are critical in the expression of basal ganglia function. The aim of this work was to test directly whether corticostriatal and thalamostriatal terminals make convergent synaptic contact with individual direct and indirect pathway MSNs. Individual MSNs were recorded in vivo and labelled by the juxtacellular method in the striatum of BAC transgenic mice in which green fluorescent protein reports the expression of dopamine D1 or D2 receptors. After recovery of the neurons, the tissue was immunolabelled for vesicular glutamate transporters type 1 and 2, as markers of cortical and thalamic terminals, respectively. Three of each class of MSNs were reconstructed in 3D and second-order dendrites selected for electron microscopic analysis. Our findings show that direct and indirect pathway MSNs, located in the matrix compartment of the striatum, receive convergent input from cortex and thalamus preferentially on their spines. There were no differences in the pattern of innervation of direct and indirect pathway MSNs, but the cortical input is more prominent in both and synaptic density is greater for direct pathway neurons. The 3D reconstructions revealed no morphological differences between direct and indirect MSNs. Overall, our findings demonstrate that direct and indirect pathway MSNs located in the matrix receive convergent cortical and thalamic input and suggest that both cortical and thalamic inputs are involved in the activation of MSNs.     

Responses of thalamic neurons to input from the male genitalia

There have been relatively few electrophysiological studies, in any species, describing the supraspinal processing of inputs from the male genital tract. The thalamus was the focus of the present study. In 11 urethan-anesthetized male rats, subregions of the thalamus were surveyed for neuronal responses to the search stimulus, bilateral electrical stimulation of the dorsal nerve of the penis (DNP). A total of 133 DNP-responsive neurons were found and further tested for degree of somatovisceral convergence from other peripheral structures. Histological reconstruction of the recording sites revealed that the penile-responsive neurons were distributed among various thalamic subregions. These thalamic subregions included the medial-dorsal nuclei and ventral and lateral thalamic subregions (majority of neurons responsive to both tactile and pinch stimulation of the penis) as well as intralaminar, posterior and reticular subregions (majority responsive to pinch only). Taken together, the data demonstrate the existence of thalamic neurons with inputs from the male genitalia with widespread somatovisceral convergence. These neurons likely contribute to the neural circuitries underlying various aspects of penile sensation associated with reproductive and nociceptive events.     

Classification of primate spinothalamic and somatosensory thalamic neurons based on cluster analysis

Data analyzed in this study were derived from the responses of 128 spinothalamic tract (STT) cells and 110 thalamic neurons recorded in 75 anesthetized monkeys. A k-means cluster analysis, a nonhierarchical clustering technique, was performed using the relative magnitudes of responses to a graded series of innocuous and noxious mechanical stimuli applied to the receptive field. For comparison, a parallel analysis was performed based on definitions of low-threshold (LT), wide dynamic range (WDR), and high-threshold (HT) cells used by our laboratory. For 128 STT cells, a classification scheme with three clusters was found statistically to be the best. This yielded groups of 22, 57, and 49 cells in clusters 1, 2, and 3, respectively. Cluster 1 cells were activated best by low-intensity mechanical stimuli, whereas cluster 3 cells were activated primarily by nociceptive stimuli. Cluster 2 cells had intermediate characteristics. When the classification scheme based on the cluster analysis was compared with the classification of the same neurons as LT, WDR, and HT cells, cluster 1 cells were divided into LT and WDR cells, whereas cluster 2 and 3 cells included WDR and HT cells. For 110 thalamic neurons, a classification scheme with five clusters was found statistically to be the best. Clusters 1-5 contained 25, 34, 17, 10, and 24 cells, respectively. Response characteristics of cells in each group indicated a gradual change in sensitivity to higher intensities of peripheral input from cluster 1 to 5. When this classification scheme was compared with the classification scheme previously used by our laboratory, cluster 1 cells belonged to the LT group, clusters 2 and 3 split into LT and WDR cells, and clusters 4 and 5 included WDR and HT cells. It is concluded that a classification scheme based on a cluster analysis of the responses of neurons to standardized stimuli may provide an objective and functionally meaningful way to categorize somatosensory neurons.     

Intracellular recordings from rat thalamic VL neurons: a study combined with intracellular staining

Summary Intracellular recordings from thalamic neurons receiving cerebellar inputs were performed under urethane anesthesia in the rat. A total of 64 neurons were recorded intracellularly with micropipettes filled with 4% biocytin solution (dissolved in 0.5 M K-acetate), and cerebellar-induced EPSPs (CN-EPSPs), the membrane resistance and firing properties were analyzed with intracellular current injections. The mean latency of CN-EPSPs was 1.9 ± 0.8 ms and the mean input resistance measured in 10 neurons was 17.6 ± 5.0 M. Thirty-two out of 35 stained neurons were analysed morphologically; 28 of these neurons were located in the VL, and 26 received CN-EPSPs. Their somata were round or polygonal in shape and the mean size was 22.5 × 15.2 m. They had radially extending spinous dendrites, and the mean radii of the dendritic fields were 214.7 m in the frontal and 171.4 m in the sagittal planes. These morphological features were similar to those observed in the sensory relay nucleus of the thalamus.     

Evidence that C1 and C2 propriospinal neurons mediate the inhibitory effects of viscerosomatic spinal afferent input on primate spinothalamic tract neurons.

1. Lumbosacral spinothalamic tract (STT) neurons can be inhibited by noxious pinch of the contralateral hindlimb or either forelimb and by electrical stimulation of cardiopulmonary sympathetic, splanchnic, and hypogastric afferents. A previous study found that spinal transections between C2 and C4 sometimes abolished the inhibitory effect of spinal afferent input and sometimes left it intact. This suggested that propriospinal neurons in the C1 and C2 segments might mediate this effect. To test whether neurons in the C1 and C2 segments were involved in producing this inhibitory effect, the magnitude of the reduction in neural activity was measured in the same STT neuron before and after spinal transection at C1 or between C3 and C7. 2. All neurons were antidromically activated from the contralateral thalamus and thoracic spinal cord. For us to accept a neuron for analysis, the characteristics of the somatic input and the latency and shape of the antidromatic spike produced by spinal cord stimulation had to be the same before and after the spinal transection. Also, spinal transection often causes a marked increase in spontaneous cell activity, which may affect the magnitude of an inhibitory response. To avoid this confounding problem, a cell was accepted for analysis only if it showed marked inhibition of high cell activity evoked by somatic pinch before spinal transection. For analysis 13 STT neurons met these criteria: 6 neurons were in monkeys with C1 transections, and 7 neurons were in animals with transections between C3 and C7.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative study of viscerosomatic input onto postsynaptic dorsal column and spinothalamic tract neurons in the primate.

The purpose of the present investigation was to examine, in the primate, the role of the postsynaptic dorsal column (PSDC) system and that of the spinothalamic tract (STT) in viscerosensory processing by comparing the responses of neurons in these pathways to colorectal distension (CRD). Experiments were done on four anesthetized male monkeys (Macaca fascicularis). Extracellular recordings were made from a total of 100 neurons randomly located in the L(6)-S(1) segments of the spinal cord. Most of these neurons had cutaneous receptive fields in the perineal area, on the hind limbs or on the rump. Forty-eight percent were PSDC neurons activated antidromically from the upper cervical dorsal column or the nucleus gracilis, 17% were STT neurons activated antidromically from the thalamus, and 35% were unidentified. Twenty-one PSDC neurons, located mostly near the central canal, were excited by CRD and three were inhibited. Twenty-four PSDC neurons, mostly located in the nucleus proprius, did not respond to CRD. Of the 17 STT neurons, 7 neurons were excited by CRD, 4 neurons were inhibited, and 6 neurons did not respond to CRD. Of the unidentified neurons, 23 were excited by CRD, 7 were inhibited, and 5 did not respond. The average responses of STT and PSDC neurons excited by CRD were comparable in magnitude and duration. These results suggest that the major role of the PSDC pathway in viscerosensory processing may be due to a quantitative rather than a qualitative neuronal dominance over the STT.     

Electrophysiological study of spinothalamic inputs to ventrolateral and adjacent thalamic nuclei of the cat.

1. Extracellular and intracellular methods were used to record from fibers and neurons in the ventral lateral (VL) and adjacent nuclei of the cat thalamus. The receptive fields of the recorded units were analyzed and the units tested for inputs from the medial lemniscus (ML) and spinothalamic tract (STT) by electrical stimulation of the dorsal columns (DC) and ventrolateral funiculus (VLF) at the C2-3 spinal level. 2. Thirty-eight STT fibers were isolated in the thalamus. Their conduction velocities ranged from 15 to 75 m/s (mode 36 m/s). Adequate stimuli were found for 23 of these fibers. Seventeen were low-threshold (LT), 3 were wide-dynamic-range (WDR), and 3 were high-threshold (HT) units. 3. Five STT fibers were intra-axonally injected. Three were sufficiently well filled for analysis of their terminal fields. An intermediate-velocity STT fiber (conduction velocity 38 m/s) had a 4.3-microns axon and a single large terminal field in the central lateral nucleus (CL). The other two STT fibers were smaller, with diameters of 2.5 and 2.3 microns, conduction velocities of 15 and 19 m/s, and terminal fields made up of a few small boutons at the borders of the ventral posterior lateral nucleus (VPL). 4. Of 319 neurons isolated, 14 out of 129 (10.8%) in VL, 14 out of 76 (18.4%) in the VPL or ventral posterior medial (VPM) nucleus, 27 out of 64 (42.2%) in the CL nucleus, and 5 out of 50 (10%) in the reticular nucleus (R) responded at latencies less than 50 ms to VLF stimuli. A train of three pulses was more effective in driving VLF-responding neurons in all these nuclei than a single pulse. VLF-responding cells were widely dispersed in VL, concentrated in a focus in CL, and distributed around the borders of VPL. Most of those in VL and a small number in CL could be antidromically activated by stimulation of motor cortex. 5. Latencies of presynaptic responses (STT fibers) to VLF stimulation were short and varied from 0.8 to 3.9 ms (mode 1.6 ms). Despite this, very few fast-responding neurons were found. These were six VPL neurons (2.5 to 4 ms), one VL neuron (3 ms), and four CL neurons (3-4 ms). The initial spike latencies of the majority of thalamic neurons responding to VLF stimulation appeared in two peaks, one between 6 and 8 ms and the other at 10-15 ms.(ABSTRACT TRUNCATED AT 400 WORDS)     

Spinal commissural neurons mediating vestibular input to neck motoneurons in the cat upper cervical spinal cord.

Spinal commissural neurons (CNs) activated di- or trisynaptically by stimulation of ipsilateral vestibular afferents were stained with intraaxonal injection of horseradish peroxidase in the cat upper cervical spinal cord. Stem axons of CNs in lamina VIII or VII, after crossing the midline, had ascending and/or descending main branches that gave off multiple axon collaterals to laminae IX and VIII over a few cervical segments. Terminal boutons appeared to make contact with proximal dendrites and somata of retrogradely-labelled neck motoneurons. Therefore, these CNs were regarded as mediating vestibular afferent input to contralateral neck motoneurons trisynaptically at the shortest.     

Anatomical analysis of ventrolateral thalamic input to primate motor cortex.

1. The origin and topographical organization of input to the arm area of the primate motor cortex from the ventrolateral thalamus were examined using the method of retrograde transport of horseradish peroxidase (HRP). 2. A thin, continuous slab of labeled neurons was found in the ventrolateral thalamus followingmultiple injections of HRP into the arm area of the motor cortex. The slab of labeled neurons was flanked, medially and laterally, by groups of unlabeled neurons. 3. The origin of ventrolateral thalamic input was more extensive than previously thought. Labeled neurons were found from A10.0 to A6.0 and occurred in three ventolateral thalamic subdivisions: ventralis lateralis pars oralis (VLo), ventralis lateralis pars caudalis (VLc), and ventralis posterior lateralis pars oralis (VPLo). For simplicity this region containing labeled neurons has been termed the ventrolateral thalamic (VL) arm area. 4. Injections of HRP into the somatic sensory cortex indicated that the thalamic regions which project to the somatic sensory cortex are separate from the VL arm area. 5. The distribution of labeled neurons following single injections of HRP into different regions of the motor cortex arm area indicated that the VL arm area is topographically organized, particularly its caudal part. Ventral regions of the VL arm area were labeled following HRP injections into motor cortex regions adjacent to the central sulcus where the representation of largely distal musculature is localized. Dorsal regions of the VL arm area were labeled following HRP injections into motor cortex regions more rostral to the central sulcus where the representation of more proximal musculature is localized. 6. A larger region of the VL arm area was labeled following HRP injections adjacent to the central sulcus than following the more rostral motor cortex injections. This suggests that, like the arm area of the motor cortex, more of the VL arm area is allotted to the representation of distal than proximal musculature. 7. Following very small cortical HRP injections, isolated labeled thalamic neurons were diffusely scattered throughout a 3-mm rostrocaudal extent of the VL arm area. In addition, a small focal cluster of labeled thalamic neurons was also seen. The labeled cluster was limited to 0.5 mm rostrocaudally and 300 mum in width. The focal distribution of labeled thalamic neurons suggests that aspects of a point to point organization may exist in the connection between VL and the motor cortex arm area.     

Responses of primate spinothalamic neurons to graded and to repeated noxious heat stimuli.

1. The responses of primate spinothalamic tract cells innervating the glabrous skin of the foot to noxious thermal stimuli have been examined. 2. Of the 41 cells studied, 98% responded to noxious thermal stimuli. Heating the cutaneous receptive field with a series of stimuli from 35 to 43, 47, and 50 degrees C produced a graded increase in discharge rate. The responses were characterized by an onset, which occurred after the temperature change had either slowed or stopped, an acceleration in the discharge up to a peak, and then an adaptation to a new base-line level. The time constants of adaptation were faster than those reported for C polymodal nociceptors. 3. No systematic differences were found in the responses to noxious thermal stimuli of cells with wide dynamic range receptive fields and of cells with narrow dynamic range, high-threshold receptive fields. There were also no differences in the responses of cells located in the marginal zone and of cells located in the neck of the dorsal horn. 4. The relationship between peak frequency and final skin temperature with a 30 s stimulus duration can best be described by a power function with an exponent of 2.1. An increase in the stimulus duration to 120 s resulted in an increase in the exponent of the power function to 3.2. 5. Repetition of the series of 30-s heat stimuli resulted in an increase in peak frequency, total impulse count, and background activity. Repetition of stimuli having a duration of 120 s produced an increase in the peak frequency at 43 and 45 degrees C, a smaller increase at 47 degrees C, and a decrease at 50 degrees C. Background activity was increased by the lower temperature stimuli, but was decreased following higher temperature stimuli. 6. In six additional cells, the skin was heated with three consecutive presentations at each temperature level (43, 45, 47, and 50 degrees C) for 30 s. No change was observed in the peak frequencies of the responses to successive stimuli of the same intensity. However, the exponent of the power function relating the average peak frequency for the six cells to changes in skin temperature was 3.9. This exponent was larger than that seen when two series of graded heat stimuli of 120 s duration were used, indicating more sensitization despite the fact the total time of exposure to noxious heat was less. 7. A role for both high-threshold and wide dynamic range spinothalamic cells in transmitting nociceptive information to the diencephalon is postulated.     

脊髓下丘脑和脊髓丘脑束神经元在内脏痛传导中的作用

脊髓下丘脑束在从脊髓向间脑和脑干的信息传递过程中起着重要作用.我们对脊髓下丘脑束是否参与了大鼠内脏痛信号传导过程的研究结果显示,在所有被检测的腰段和骶段脊髓下丘脑束和脊髓丘脑束神经元中,随着对结肠、直肠和(或)阴道的强制性扩张刺激强度的增加,三分之一以上神经元的放电频率逐级增加.在所检测的下位胸段脊髓神经元中,约二分之一的脊髓下丘脑束神经元可通过逐级扩张胆管被激活,且这些神经元的反应高度符合加速函数曲线.结果 提示,在应对内脏器官伤害性扩张的微小变化时,这些神经元的放电频率明显增加.同时表明,脊髓下丘脑束在从脊髓到大脑广泛区域伤害性内脏感觉信息的直接传递过程中起着重要作用.     

Urinary bladder and hindlimb afferent input inhibits activity of primate T2-T5 spinothalamic tract neurons

1. Extracellular recordings were made from 41 spinothalamic tract (STT) neurons on the left side of the T2-T5 spinal segments of 20 monkeys (Macaca fascicularis) anesthetized with alpha-chloralose. Manipulation of the left triceps-chest region and electrical stimulation of cardiopulmonary sympathetic afferent fibers excited these cells. 2. Isotonic urinary bladder distensions (UBD) to pressures between 20 and 80 cmH2O reduced the spontaneous activity in 33 of 41 cells. Cell activity was significantly reduced by UBD at 20 cmH2O. Distensions to 40, 60, and 80 cmH2O produced progressively greater reductions in spontaneous discharge. Activity was decreased throughout distension in 29 cells (tonic inhibition) and at the onset of distension in 3 neurons (phasic inhibition). In one cell, inhibition followed a brief excitation at the onset of distension (phasic excitation-tonic inhibition). Spontaneous bladder contractions also inhibited STT cell activity. 3. Inhibition by UBD was observed in STT cells characterized as wide dynamic range, high threshold, and high threshold inhibitory. No correlation existed between cell type or laminar location and inhibition by urinary bladder distension. Cells excited by cardiopulmonary sympathetic afferent A delta- and C-fibers had a significantly greater tendency to be inhibited by UBD (17 of 18) than cells activated by A delta- but not C-fibers (13 of 20). 4. Urinary bladder distension and pinch of the hindlimbs also reduced activity of STT cells excited by input from cardiopulmonary sympathetic afferents and from the proximal forelimb. 5. Urinary bladder distension to 40, 60, or 80 cmH2O produced a greater absolute but smaller relative reduction in the firing frequency of STT cells as spontaneous activity increased. Thus the magnitude of this inhibitory effect may depend on whether the inhibitory effect is measured as an absolute or relative change in cell activity. 6. Convergent inhibitory input from somatic regions also was observed. Noxious pinch of the hamstring region of the right hindlimb decreased activity in 32 of 39 cells. Left hindlimb pinch inhibited 21 of 38 cells, and 15 of 29 cells were inhibited by right triceps pinch. 7. Convergent inhibitory input from the hamstring region of the hindlimbs and from the urinary bladder to upper thoracic STT cells may be important for coding the intensity and location of noxious visceral and somatic stimuli and for organizing the appropriate sequence of motor responses when multiple noxious stimuli are present.     

Excitation of primate spinothalamic neurons by cutaneous C-fiber volleys.

1. The responses of spinothalamic tract cells in the lumbosacral spinal cords of anesthetized monkeys were examined following electrical stimulation of the sural nerve or the application of noxious thermal and mechanical stimuli to the skin on the lateral aspect of the foot. 2. The spinothalamic tract neurons were classified as wide dynamic range (WDR), high-threshold (HT), or low-threshold (LT) cells on the basis of their responses to mechanical stimuli. 3. All of the WDR and HT spinothalamic tract cells tested responded to volleys in A- and C-fibers. However, strong C-fiber responses were more common in HT than in WDR cells. 4. The responses atributed to C-fibers were graded with the size of the C-fiber volley. The latencies of the responses attributed to C-fibers indicated that the fastest afferents involved had a mean conduction velocity of 0.9 m/s. The responses remained after anodal blockade of conduction in A-fibers. 5. Temporal summation of the responses of spinothalamic tract cells was demonstrated both to brief trains of stimuli at 33 Hz and to single stimuli repeated at 1- to 2-s intervals. The latter phenomenon is often called "windup." 6. The responses of several spinothalamic tract cells to noxious heat pulses could still be elicited during anodal blockade of conduction in A-fibers. Similarly, it was possible to demonstrate an excitatory action of noxious mechanical stimuli despite interference with conduction in A-fibers by anodal current. 7. The cells investigated were located either in the marginal zone or in the layers of the dorsal horn equivalent to Rexed's laminae IV-VI in the cat. The cells were generally activated antidromically from the caudal part of the ventral posterior lateral nucleus of the thalamus.     

Responses of primate spinothalamic tract neurons to renal pelvic distension

1. Experiments were performed to examine responses of spinothalamic tract (STT) neurons to distension of the renal pelvis. Nineteen monkeys (Macaca fascicularis) were anesthetized with alpha-chloralose, paralyzed, and artificially ventilated. Fifty-four STT neurons in the T11-L2 segments were studied. Each cell was excited by renal nerve stimulation and had a somatic receptive field in the left flank and/or the abdomen. 2. Distension of the left renal pelvis to 50 mmHg for 20-30 s increased activity of 40 STT neurons. Two types of responses were observed. Six cells responded rapidly to the increase in renal pelvic pressure. Thereafter activity of these cells completely adapted. The other 34 cells also responded rapidly to the distension: however, the subsequent adaptation was not complete. Average activity before distension was 13 +/- 1 (SE) spikes/s. Distension increased activity to a peak of 42 +/- 3 spikes/s. Mean activity just before the end of the distension was 27 +/- 3 spikes/s. 3. The pelvic pressure-cell response relation was determined for 16 cells. Only one cell responded to a pressure of 20 mmHg. Three responded to 30 mmHg, and all others responded to 40 mmHg and higher. The average response threshold was 32 +/- 1 mmHg. Peak responses increased as distending pressure increased from 40-80 mmHg. Responses to a pressure of 100 mmHg were no greater than to 80 mmHg. Adapted levels of activity were also a function of distending pressure in the 40-80 mmHg range. 4. Probability of responses was unrelated to somatic input. However, cells with A delta- and C-fiber renal input were significantly more likely to respond to renal pelvic distension than cells with only A delta-renal input. Magnitude of responses to a pressure of 50 mmHg was not related to the type of renal input to the cells; however, among the cells tested at all pressures, cells with A delta- and C-fiber input had significantly greater responses to pressures of 80 and 100 mmHg. 5. Cells were studied in laminae I and IV-VII: responses were unrelated to laminar location. None of the 6 cells located in L2 responded to renal pelvic distension; 8 of 12 in L1 responded; 24 of 28 in T12 responded; and all 8 cells in T11 responded. 6. Stimulation of inhibitory receptive fields on the right hindlimb reduced activity of four cells to a significantly greater extent during pelvic distension than before pelvic distension.(ABSTRACT TRUNCATED AT 400 WORDS)     

Projection on the motor cortex of thalamic neurons with pallidal input in the monkey

Summary The cortical projection areas of thalamic neurons with basal ganglia and/or cerebellar inputs were studied electrophysiologically in unanesthetized monkeys. Thalamic neurons which receive inhibition from the pallidum were found to project to the motor cortex (area 4) as well as to premotor cortex. The neurons with pallidal input and motor cortical projection were located mainly in VLo. This result indicates that the basal ganglia innervate the motor cortex through the thalamus. Thus the basal ganglia can modify the cortical output for controlling movements directly through this pathway as compared with its influence through the prefrontal and premotor cortices.     

Serotonergic transmission in the periaqueductal gray matter in relation to aversive behaviour: morphological evidence for direct modulatory effects on identified output neurons

Intracellular recordings were made from 21 cells in the dorsolateral periaqueductal gray matter in coronal midbrain slices. In the majority (n=20) bath application of 5-hydroxytryptamine (30 or 150 mM) evoked either hyperpolarizing (n=11) or depolarizing (n=9) responses. Reconstructions of 11 neurons in the dorsolateral periaqueductal gray matter after filling with biocytin revealed a population of output neurons whose axons followed a dorsolateral trajectory towards the perimeter of the ipsilateral periaqueductal gray matter. In seven cells, the axon could be followed into the adjacent mesencephalic reticular formation. At the light microscopic level, immunostaining for 5-hydroxytryptamine revealed immunoreactive processes throughout the dorsolateral periaqueductal gray matter but no labelled somata or dendrites. Close associations (i.e. no discernible gap) were observed between serotonergic profiles and the somata and dendrites of biocytin-filled cells. At the ultrastructural level, serial sections through 21 appositions on to biocytin-filled dendrites in three slices revealed 19 true appositions (i.e. having closely parallel plasma membranes with no intervening glial cell profiles) with the biocytin-filled dendrite. Only four of the appositions (21%) showed evidence of synaptic specializations which included aggregations of synaptic vesicles, and some thickening of the apposing membrane. The dense reaction product in the biocytin-filled cells precluded identification of the ultrastructure of postsynaptic elements. However, examination of contacts between 5-hydroxytryptamine-immunoreactive profiles and unlabelled elements in material taken from the contralateral side of the periaqueductal gray matter (i.e. no biocytin present) or in material taken from perfusion-fixed whole brain, in which ultrastructural preservation was superior compared with slices, revealed a similar incidence (21% and 23%, respectively) of synaptic specializations.The data indicate that serotonergic transmission on to output neurons in the dorsolateral periaqueductal gray matter is largely mediated by non-junctional contacts, suggesting that the actions of 5-hydroxytryptamine on these cells are mediated predominantly by volume rather than wiring transmission.