Extent of the ipsilateral representation in the ventral posterior medial nucleus of the monkey thalamus

Summary Single and multiunit mapping was used to determine the extent of the representation of ipsilateral structures in the ventral posterior medial (VPM) nucleus of the thalamus in cynomolgus monkeys. The extent of the VPM occupied by terminations of afferent fibers arising in the ipsilateral principal trigeminal nucleus was also determined by anterograde transport of horseradish peroxidase. Both methods indicate that most of the medial half of VPM is occupied by the ipsilateral representation. This is much larger than previously suspected. Units in the medial half of VPM have small, well localized receptive fields on the ipsilateral side of the lower lip, tongue and palate, in the ipsilateral cheek pouch and on the ipsilateral teeth. The representation is largest for the ipsilateral side of the tongue and the cheek pouch. Most units in the lateral half of VPM have small, contralateral receptive fields. Few units in VPM have bilateral receptive fields. VPM is clearly distinguishable by cytochrome oxidase (CO) staining. Anteroposteriorly elongated, CO-positive aggreations correspond to elongated aggregations of units with the same or closely similar receptive fields, especially in the medial, ipsilateral representation.Abbreviations CL Central lateral nucleus - CM Centre médian nucleus - DCN Dorsal cochlear nucleus - DIT Dorsal ipsilateral trigeminal tract - IO Inferior olivary nuclei - ML Medial lemniscus - MV Motor trigeminal nucleus - PRV Principal sensory trigeminal nucleus - SO Superior olivary nuclei - SPV Spinal trigeminal nucleus - Ves Vestibular nuclei - VMb Basal ventral medial nucleus - VPI Ventral posterior inferior nucleus - VPL Ventral posterior lateral nucleus - VPM Ventral posterior medial nucleus - IV Trochlear nucleus - VI Abducens nucleus     

Ultrastructure of the anterior ventral and anterior medial nuclei of the cat thalamus

Summary Electron microscopical studies of the thalamic AV-AM nuclei substantiated the presence of two main types of neurons, i.e. principal (or relay) cells and Golgi type II interneurons. Characteristic synaptic islands are found in abundance in the AV-AM. Four different types of synaptic terminals have been identified in these islands: RL-boutons = large axonal terminals with round synaptic vesicles; RS-boutons = small axonal terminals with round synaptic vesicles; F₁-boutons = small axonal profiles containing flattened synaptic vesicles, and F₂-profiles interpreted as presynaptic dendrite appendages, bearing pleomorphic vesicles, both belonging to the Golgi type II interneurons. — The synaptic relations were studied in normal preparations and after lesions in the mamillary body, limbic cortex and hippocampus. The specific afferents (RL-boutons) — originating from the medial mamillary nucleus — are presynaptic to both relay cell dendrites and presynaptic dendrite profiles of Golgi type II interneurons, which in turn are presynaptic to the same relay dendrites (synaptic triads). RS-boutons originate mainly from limbic cortex and hippocampus.     

Reactions of neurons of the posterior ventral nucleus of the thalamus of the rat during movements of the vibrissae

The reactions of neurons of the posterior ventral nucleus of the thalamus were investigated during movements of the vibrissae, accomplished independently by the animal, in experiments on rats utilizing a technique of partial curarization proposed by the author. Differences were identified in the pattern of the reactions of the thalamic neurons to deviation of a vibrissa by the experimenter from the pattern of the reactions of the same neurons to deviation of the vibrissa elicited by its hitting against a barrier during a sweep. A dependence of the response of the sensory neurons on whether or not the barrier was mobile during the period of the sweep of the vibrissae was also demonstrated. The hypothesis is advanced that at the thalamic level the analysis of the parameters of the stimulus is accomplished in connection with information regarding movements of the vibrissae.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 77, No. 2, pp. 31–35, February, 1991.     

Mechanical and thermal hypersensitivity develops following kainate lesion of the ventral posterior lateral thalamus in rats

Damage to the ventral-posterior lateral nucleus (VPL) of the thalamus or its afferent pathways can produce moderate to severe on-going pain and pain in response to normally innocuous stimuli (allodynia) and hypersensitivity to mildly noxious stimuli (hyperalgesia). The present study measured the responses to mechanical and thermal stimuli before and 2, 8, 24 and 48 h after a kainate-induced lesion of the VPL in male rats. Compared with control animals, hypersensitivity to mechanical stimulation of the hindpaw was apparent by 24 h post-lesion. At 48 h, the frequency of mechanical response increased from a baseline response frequency of 17+/-4.7 to 46+/-11.6%. Thermal withdrawal latencies 48 h after the lesion decreased from a baseline latency of 9.9+/-1.8 to 5.3+/-0.4 s. It is concluded that a neurotoxic lesion of the VPL results in a delayed onset of mechanical and thermal hyperalgesia. This study suggests a potential model for studying the basic mechanisms and potential therapies for central pain syndrome.     

Receptive-field properties of rat ventral posterior medial neurons before and after selective kainic acid lesions of the trigeminal brain stem complex

Single neurons were recorded from the ventral posteromedial thalamic nucleus (VPM) of urethan-anesthetized rats. Six of these animals were intact, 28 sustained kainic acid (KA) lesions of trigeminal nucleus principalis (PrV), and 9 received similar lesions of trigeminal subnucleus interpolaris (SpVi). Four animals sustained PrV lesions that were followed, at an interval of 1-3 mo, by KA injections into SpVi. Special attention was paid to the receptive-field characteristics of neurons that were sensitive to deflection of the mystacial vibrissae. In normal animals, we recorded a total of 167 VPM neurons, 85% (n = 142) of which were vibrissa sensitive. The remaining VPM cells were excited by either guard hair deflection (8.4%), indentation of the skin (0.6%), or deflection of either vibrissae or guard hairs (1.8%). Seven cells (4.2%) were unresponsive. The topography of the trigeminal representation in VPM was similar to that reported previously by Waite (59). Vibrissa-sensitive neurons in intact rats generally gave rapidly adapting responses (84.5%), and only 16.2% were directionally selective. The vast majority (80.3%) of the vibrissa-sensitive cells were activated by deflection of only one whisker (1.2 +/- 0.5, mean +/- SD); none were excited by deflection of more than four vibrissae. Injections of KA into SpVi of otherwise intact rats (n = 9) had no appreciable effect on the receptive-field characteristics of vibrissa-sensitive VPM neurons. Injections of KA into PrV markedly altered the receptive-field properties of VPM cells. Recordings were made from 45 VPM neurons over a period extending from 0 to 10 h after KA injections into PrV in five rats. Of these cells, 4.4% were excited by vibrissa deflection and the remainder were unresponsive. Additional recordings from SpVi and the superior colliculus of these same animals indicated that the neurotoxin probably did not damage interpolaris neurons or their axons. Recordings were made from 394 VPM cells in 22 rats that survived 1-6 days after KA lesions of PrV. These experiments demonstrated an increase in the number of thalamic cells that were responsive to peripheral stimulation over this period. By 6 days after the lesion (4 animals), 52.8% of the 73 VPM neurons we recorded were excited by somatosensory stimuli. Of these, 89.5% were activated by deflection of one or more mystacial vibrissae. The average number of whiskers that excited a given VPM cell in these rats was 6.3 +/- 2.0 (SD). Recordings were made from VPM in five rats that survived 30-90 days after KA injections in PrV.(ABSTRACT TRUNCATED AT 400 WORDS)     

Glutamate,aspartate and co-localization with calbindin in the medial thalamus An immunohistochemical study in the rat

Experimental Brain Research - ?Topographical and quantitative features of medial thalamic neurons in which aspartate (ASP) or glutamate (GLU) might act as neurotransmitters were investigated...     

Electron-autoradiographic analysis of projections of somatosensory cortical areas I and II in the posterior ventral nucleus of the thalamus

Differences in the organization of corticofugal fibers arising from somatosensory cortical areas I (S_I) and II (S_II) were detected by electron-microscopic autoradiography in the posterior ventral nucleus (NVP) of the thalamus. The distribution of corticofugal fibers from the corresponding zones of the two somatosensory cortical areas within NVP differs. Endings of both types of fibers form synaptic contacts chiefly with distal dendrites of relay cells of NVP and much less frequently with dendrites of Golgi type II interneurons. No direct convergence of fibers arising from the two somatosensory areas on single cells of NVP was observed.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 5, pp. 604–606, May, 1977.     

Differential effects of GDF5 on the medial and lateral rat ventral mesencephalon

Growth/differentiation factor 5 (GDF5) is a member of the transforming growth factor-beta (TGF-beta) superfamily that has potent neurotrophic and protective effects on dopaminergic neurones and is expressed in the developing rat substantia nigra (the ventral mesencephalon; VM). GDF5 has the potential to be used in the treatment of Parkinson's disease (PD), a neurodegenerative disorder characterised by the selective degeneration of nigrostriatal dopaminergic neurones. One therapy being explored for PD involves transplantation of fetal VM tissue into the striatum in order to replace lost dopaminergic neurones. The majority of transplantation studies have used transplants incorporating the whole VM. The principal location of dopaminergic neurones in the E14 rat VM is in the medial VM. In the present study, the effects of GDF5 on cultures prepared from medial, lateral and whole E14 rat VM tissue were compared. GDF5 treatment increased the number of dopaminergic neurones in whole and lateral, but not in medial, VM cultures, whereas it increased total cell number in medial, but not in whole or lateral, VM cultures. RT-PCR studies showed that the receptors for GDF5 were differentially expressed in E14 VM; the expression of BMPR-IB and Ror2 was low in medial but high in lateral VM tissue. This study suggests that GDF5 increases the number of dopaminergic neurones in whole VM cultures by acting on BMPR-IB and Ror2-expressing cells in the lateral VM.     

Temporal shaping of phasic neuronal responses by GABA- and non-GABA-mediated mechanisms in the somatosensory thalamus of the rat

Trapezoidal mechanical movement of whiskers was used to study the responses of 44 single thalamic ventral posteromedial (VPM) neurons to dynamic and static stimulus components in urethane-anesthetized rats. The effects of local administration of the GABA_A receptor antagonist, bicuculline, and the GABA_B receptor antagonist, 2-hydroxysaclofen, were tested to determine whether and to what extent the responses altered when GABA-mediated inhibitory synaptic transmission was blocked. Two classes of phasically responding neurons were identified, ON/OFF and movement-sensitive types. Bicuculline enhanced the magnitudes of the responses from both types by 2.5-fold and ON/OFF responses were converted to movement-sensitive ones in 17 (43%) of the 40 ON/OFF neurons. 2-hydroxysaclofen either had no effect or appeared to act like a GABA agonist. In 21 (48%) neurons, a significantly reduced responsiveness was observed during a 100-ms period following the ON and OFF responses. This discharge suppression was especially prominent during the plateau phase of the stimulus, and in some cases extended for several 100 ms following its onset. This suppression was overcome neither by the GABA receptor antagonists, nor by ejection of AMPA or glutamate at currents that otherwise produced vigorous excitation. These results suggest that one functional role for GABA_A-receptor-mediated synaptic inhibition in the somatosensory thalamus is the intramodal regulation of the form of expression of phasically responding neurons. Other thalamic inhibitory processes not mediated by GABA_A or GABA_B receptors that help to shape the expression of the responses of certain phasic neurons to maintained stimulation may exist. Overall, these mechanisms appear to mediate the precision of timing of thalamic neuronal firing in response to the rats tactile environment.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Interactions among the medial prefrontal cortex, hippocampus and midline thalamus in emotional and cognitive processing in the rat

The medial prefrontal cortex (mPFC) participates in several higher order functions including selective attention, visceromotor control, decision making and goal-directed behaviors. We discuss the role of the infralimbic cortex (IL) in visceromotor control and the prelimbic cortex (PL) in cognition and their interactions in goal-directed behaviors in the rat. The PL strongly interconnects with a relatively small group of structures that, like PL, subserve cognition, and together have been designated the 'PL circuit.' These structures primarily include the hippocampus, insular cortex, nucleus accumbens, basolateral nucleus of the amygdala, the mediodorsal and reuniens nuclei of the thalamus and the ventral tegmental area of the midbrain. Lesions of each of these structures, like those of PL, produce deficits in delayed response tasks and memory. The PL (and ventral anterior cingulate cortex) (AC) of rats is ideally positioned to integrate current and past information, including its affective qualities, and act on it through its projections to the ventral striatum/ventral pallidum. We further discuss the role of nucleus reuniens of thalamus as a major interface between the mPFC and the hippocampus, and as a prominent source of afferent limbic information to the mPFC and hippocampus. We suggest that the IL of rats is functionally homologous to the orbitomedial cortex of primates and the prelimbic (and ventral AC) cortex to the lateral/dorsolateral cortex of primates, and that the IL/PL complex of rats exerts significant control over emotional and cognitive aspects of goal-directed behavior.     

Steroid sensitive identified and unidentified neurons in the medial preoptic area of the rat

In view of the role played by the preoptic area and the glucocorticoids in adrenocortical regulation, the iontophoretic effects of cortisol on non-identified and identified preoptic neurons, which send their axons to the mediobasal hypothalamus, were investigated. More than half of the cells changed their rate or pattern of firing, as studied by autocorrelation, but few cells changed their pattern only. The iontophoretic effect persisted only few seconds beyond cessation of current. Twenty three percent of the studied cells were antidromically identified and most of them responded to the iontophoretic application of cortisol. The possible relation of these findings to the neuroendocrine regulation of adrenocortical secretion is discussed.     

Electrophysiological and anatomical demonstration of a bulbar relayed pathway towards the medial thalamus in the rat

In the rat cells antidromically activated by stimulation of the thalamic centrum medianum and centralis lateralis were searched for in the bulbopontine region which receives spinoreticular pathways. Antidromically activated cells were found in the nuclei gigantocellularis and pontis oralis and they possessed peripheral receptive fields that were large, bilateral and often responded to nociceptive stimuli. Injections of horseradish peroxidase or iron-dextran at the same thalamic level revealed retrogradely labelled cells in the same bulbopontine nuclei. Cells retrogradely labelled were also found in the mesencephalic reticular formation, the inferior colliculus and grisea centralis.     

Effect of the state of sleep and wakefulness on transmission of the afferent signal through the posterior ventral nucleus of the thalamus

The effect of the state of sleep and wakefulness on transmission of afferent stimuli and subsequent inhibitory processes in the posterior ventral nucleus of the thalamus was studied in chronic experiments on unanesthetized cats. In a drowsy state and in a state of superificial sleep stimulus transmission is reduced, whereas in an active state (during the arousal reaction, movement, eating, etc.) it is increased. In paradoxical sleep stimulus transmission is at the same level as in a state of quiet wakefulness. In a drowsy state and in the first phase of sleep marked fluctuation of transmission is observed. The level of stimulus transmission is most stable in active states. The intensity of the after-inhibition following transmission of the afferent signal depends on the level of anesthesia, of wakefulness, and of natural sleep. Processes following transmission of the afferent stimulus in the posterior ventral nucleus of the thalamus during barbiturate anesthesia differ radically from those in the unanesthetized animal. After-inhibition, so characteristic of anesthesia, is manifested in the drowsy state only to a slight degree, and in the waking state it is not exhibited at all.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 4, pp. 387–390, April, 1977.     

Neuron number decreases in the rat ventral, but not dorsal, medial prefrontal cortex between adolescence and adulthood

Neuroimaging studies have established that there are losses in the volume of gray matter in certain cortical regions between adolescence and adulthood, with changes in the prefrontal cortex being particularly dramatic. Previous work from our laboratory has demonstrated that cell death can occur as late as the fourth postnatal week in the rat cerebral cortex. The present study examined the possibility that neuronal loss may occur between adolescence and adulthood in the rat prefrontal cortex. Rats of both sexes were examined during adolescence (at day 35) and young adulthood (at day 90). The volume, neuronal number, and glial number of the medial prefrontal cortex (mPFC) were quantified using unbiased stereological techniques. Neurons were lost from the ventral, but not dorsal, mPFC between adolescence and adulthood, suggesting a late wave of apoptosis that was region-specific. This was accompanied by a decrease in the volume of the female ventral mPFC. In contrast to neuron number, the number of glial cells was stable in the ventral mPFC and increased between adolescence and adulthood in the dorsal mPFC. Sex-specific developmental changes in neuron number, glial number, and volume resulted in sex differences in adults that were not seen during adolescence. The loss of neurons at this time may make the peri-adolescent prefrontal cortex particularly susceptible to the influence of environmental factors.     

Mapping by laser photostimulation of connections between the thalamic reticular and ventral posterior lateral nuclei in the rat

We used laser scanning photostimulation through a focused UV laser of caged glutamate in an in vitro slice preparation through the rat's somatosensory thalamus to study topography and connectivity between the thalamic reticular nucleus and ventral posterior lateral nucleus. This enabled us to focally stimulate the soma or dendrites of reticular neurons. We were thus able to confirm and extend previous observations based mainly on neuroanatomical pathway tracing techniques: the projections from the thalamic reticular nucleus to the ventral posterior lateral nucleus have precise topography. The reticular zone, which we refer to as a "footprint," within which photostimulation evoked inhibitory postsynaptic currents (IPSCs) in relay cells, was relatively small and oval, with the long axis being parallel to the border between the thalamic reticular nucleus and ventral posterior lateral nucleus. These evoked IPSCs were large, and by using appropriate GABA antagonists, we were able to show both GABA(A) and GABA(B) components. This suggests that photostimulation strongly activated reticular neurons. Finally, we were able to activate a disynaptic relay cell-to-reticular-to- relay cell pathway by evoking IPSCs in relay cells from photostimulation of the region surrounding a recorded relay cell. This, too, suggests strong responses of relay cells, responses strong enough to evoke spiking in their postsynaptic reticular targets. The regions of photostimulation for these disynaptic responses were much larger than the above-mentioned reticular footprints, and this suggests that reticulothalamic axon arbors are less widespread than thalamoreticular arbors, that there is more convergence in thalamoreticular connections than in reticulothalamic connections, or both.     

Vestibular,auditory, and somatic input to the posterior thalamus of the cat

Summary The responses of 157 neural units in the magnocellular (mc) and parvocellular (pc) components of the medial geniculate nucleus (MG) and other nuclei of the posterior (PO) thalamic group were recorded and analyzed. Units were tested for a response to electrical stimulation of the vestibular nerve, natural auditory and electrical cochlear nerve stimulation, and natural stimulation of joint, muscle, and cutaneous receptors of the limbs, trunk, and neck (somatic stimulation). Only 45% of the units responded to these stimuli. Twenty-four percent of the responsive units were multimodal, responding to more than one stimulus. All multimodal units were activated by auditory stimuli. More units responding to vestibular stimulation were found in mcMG than in pcMG or other components of the PO group. Potentials evoked by vestibular nerve stimulation were recorded in all 3 regions with latencies of 5–25 msec. No evidence was found for a thalamic relay from vestibular nerve to cortex in the area investigated, since the recorded latency for activity from vestibular nerve stimulation was longer than the latency of responses recorded in the cortex. This region of the thalamus appears to be important for reception of auditory information and integration with vestibular and somatic modalities.This investigation was supported in part by USPHS Grant NS 11307     

Anatomic, intrinsic, and synaptic properties of dorsal and ventral division neurons in rat medial geniculate body.

Anatomic, intrinsic, and synaptic properties of dorsal and ventral division neurons in rat medial geniculate body. Presently little is known about what basic synaptic and cellular mechanisms are employed by thalamocortical neurons in the two main divisions of the auditory thalamus to elicit their distinct responses to sound. Using intracellular recording and labeling methods, we characterized anatomic features, membrane properties, and synaptic inputs of thalamocortical neurons in the dorsal (MGD) and ventral (MGV) divisions in brain slices of rat medial geniculate body. Quantitative analysis of dendritic morphology demonstrated that tufted neurons in both divisions had shorter dendrites, smaller dendritic tree areas, more profuse branching, and a greater dendritic polarization compared with stellate neurons, which were only found in MGD. Tufted neuron dendritic polarization was not as strong or consistent as earlier Golgi studies suggested. MGV and MGD cells had similar intrinsic properties except for an increased prevalence of a depolarizing sag potential in MGV neurons. The sag was the only intrinsic property correlated with cell morphology, seen only in tufted neurons in either division. Many MGV and MGD neurons received excitatory and inhibitory inferior colliculus (IC) inputs (designated IN/EX or EX/IN depending on excitation/inhibition sequence). However, a significant number only received excitatory inputs (EX/O) and a few only inhibitory (IN/O). Both MGV and MGD cells displayed similar proportions of response combinations, but suprathreshold EX/O responses only were observed in tufted neurons. Excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) had multiple distinguishable amplitude levels implying convergence. Excitatory inputs activated alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors the relative contributions of which were variable. For IN/EX cells with suprathreshold inputs, first-spike timing was independent of membrane potential unlike that of EX/O cells. Stimulation of corticothalamic (CT) and thalamic reticular nucleus (TRN) axons evoked a GABAA IPSP, EPSP, GABAB IPSP sequence in most neurons with both morphologies in both divisions. TRN IPSPs and CT EPSPs were graded in amplitude, again suggesting convergence. CT inputs activated AMPA and NMDA receptors. The NMDA component of both IC and CT inputs had an unusual voltage dependence with a detectable DL-2-amino-5-phosphonovaleric acid-sensitive component even below -70 mV. First-spike latencies of CT evoked action potentials were sensitive to membrane potential regardless of whether the TRN IPSP was present. Overall, our in vitro data indicate that reported regional differences in the in vivo responses of MGV and MGD cells to auditory stimuli are not well correlated with major differences in intrinsic membrane features or synaptic responses between cell types.     

Electrophysiological and morphological properties of identified crossed tecto-reticular neurons in the rat superior colliculus

Previously we classified randomly sampled neurons in the intermediate layer (SI) of the rat superior colliculus (SC) into six subclasses according to their firing responses to depolarizing current pulses and five subclasses based on their morphological properties in slice preparations. In the present study, we investigated properties of a major output cell group of the rat SC (PND 17-24), crossed tecto-reticular neurons (cTRNs), which project to the contralateral medial pontine reticular formation. The cTRNs were identified by retrograde labeling with a fluorescent tracer (n=112). We compared their properties with those of presumed interneurons (n=127). We found that a majority of cTRNs were regular spiking neurons with moderate firing frequency (73%) and were multipolar-shaped (66%). The cTRNs had larger membrane capacitance, larger soma size and lower input impedance than presumed interneurons. Electrical stimulation of the superficial gray layer induced oligosynaptic EPSPs in the cTRNs. When bicuculline was added to the extracellular solution, the EPSPs were markedly enhanced and bursting spike responses were induced. The bursting responses were suppressed by applying D-2-amino-5-phosphonovalerate. These results suggest that the cTRNs exhibit NMDA receptor-dependent bursting responses to visual inputs. These observations give insights into the neuronal mechanism of generating burst activity in cTRNs, which triggers orienting behaviors.