Contribution of different somatosensory afferent input to subcortical somatosensory evoked potentials in humans

ObjectivesTo investigate the subcortical somatosensory evoked potentials (SEPs) to electrical stimulation of either muscle or cutaneous afferents.MethodsSEPs were recorded in 6 patients suffering from Parkinson’s disease (PD) who underwent electrode implantation in the pedunculopontine (PPTg) nucleus area. We compared SEPs recorded from the scalp and from the intracranial electrode contacts to electrical stimuli applied to: 1) median nerve at the wrist, 2) abductor pollicis brevis motor point, and 3) distal phalanx of the thumb. Also the high-frequency oscillations (HFOs) were analysed.ResultsAfter median nerve and pure cutaneous (distant phalanx of the thumb) stimulation, a P1-N1 complex was recorded by the intracranial lead, while the scalp electrodes recorded the short-latency far-field responses (P14 and N18). On the contrary, motor point stimulation did not evoke any low-frequency component in the PPTg traces, nor the N18 potential on the scalp. HFOs were recorded to stimulation of all modalities by the PPTg electrode contacts.ConclusionsStimulus processing within the cuneate nucleus depends on modality, since only the cutaneous input activates the complex intranuclear network possibly generating the scalp N18 potential.SignificanceOur results shed light on the subcortical processing of the somatosensory input of different modalities.     

Localization of motor and verbal fluency effects in subthalamic DBS for Parkinson's disease

IntroductionSubthalamic nucleus deep brain stimulation (STN DBS) improves cardinal motor symptoms of Parkinson's disease (PD) but can worsen verbal fluency (VF). An optimal site of stimulation for overall motor improvement has been previously identified using an atlas-independent, fully individualized, field-modeling approach. This study examines if cardinal motor components (bradykinesia, tremor, and rigidity) share this identified optimal improvement site and if there is co-localization with a site that worsens VF.MethodsAn atlas-independent, field-modeling approach was used to identify sites of maximal STN DBS effect on overall and cardinal motor symptoms and VF in 60 patients. Anatomic coordinates were referenced to the STN midpoint. Symptom severity was assessed with the MDS-UPDRS part III and established VF scales.ResultsSites for improved bradykinesia and rigidity co-localized with each other and the overall part III site (0.09 mm lateral, 0.93 mm posterior, 1.75 mm dorsal). The optimal site for tremor was posterior to this site (0.10 mm lateral, 1.40 mm posterior, 1.93 mm dorsal). Semantic and phonemic VF sites were indistinguishable and co-localized medial to the motor sites (0.32 mm medial, 1.18 mm posterior, 1.74 mm dorsal).ConclusionThis study identifies statistically distinct, maximally effective stimulation sites for tremor improvement, VF worsening, and overall and other cardinal motor improvements in STN DBS. Current electrode sizes and voltage settings stimulate all of these sites simultaneously. However, future targeted lead placement and focused directional stimulation may avoid VF worsening while maintaining motor improvements in STN DBS.     

丘脑底核电刺激治疗苍白球毁损术后的帕金森病(12例报告)

目的探讨帕金森病(Parkinson's disease,PD)苍白球腹后部毁损术(posteroventral pallidotomy,PVP)后再行丘脑底核(subthalamic nucleus,STN)脑深部电刺激术(deep brain stimulation,DBS)的可行性、术中电生理学特点和治疗结果。方法应用MR和微电极记录技术进行靶点定位,对12例单侧PVP术后症状再次加重的PD患者实施STN-DBS手术,其中4例行毁损灶对侧的STN-DBS,8例行双侧STN-DBS。结果STN-DBS对本组12例PD患者症状有不同程度的改善,双侧STN-DBS的效果尤为明显,术后3个月的UPDRS运动及ADL评分较术前明显减少(P<0．05或0．01),美多巴的用量明显减少(P<0．01),无明显术后并发症。术中电生理记录显示毁损灶同侧的细胞放电明显低于正常情况。结论曾行单侧PVP的PD患者如面临二次手术,可以选择DBS手术,以双侧STN的DBS效果最好,可减少药物用量。     

Ultrastructural detection of neuronally transported choleragenoid by postembedding immunocytochemistry in freeze-substituted Lowicryl HM20™ embedded tissue

Choleragenoid (cholera toxin B-fragment; CTB) is an anterograde, retrograde and transganglionic neuronal tracer. We describe a method for detecting CTB-labeled neuronal cell bodies, neurites and boutons at the ultrastructural level, using postembedding immunogold techniques on freeze-substituted Lowicryl HM20™ embedded nervous tissue. Primary afferents and motoneurons were labeled by injection of CTB in the dorsal ramus of the C2 spinal nerve of the rat. Following fixation with paraformaldehyde (4%) and glutaraldehyde (0.25%), tissue sections from the spinal cord C2 segment were freeze-substituted and embedded in Lowicryl HM20™ and subsequently processed with postembedding immunocytochemistry for CTB and glutamate. Immunogold particles indicating CTB immunoreactivity were found over primary afferents and motoneurons. In primary afferents in the central cervical nucleus (CCN) and motor nuclei, immunogold labeling was seen in boutons over vesicle-containing axoplasm and to a lesser extent over axoplasm devoid of vesicles, but not over mitochondria or axolemma. In motoneurons, immunogold particles were seen over the Golgi apparatus in the soma and over lysosomes in both soma and dendrites. Quantification of glutamate-like immunoreactivity in 20 CTB-labeled and 20 CTB-negative boutons in the neuropil was found similar, indicating that CTB does not interfere with the immunocytochemical detection of neuronal epitopes such as the transmitter substance glutamate.     

Monolateral hypoplasia of the motor vagal nuclei in a case of sudden infant death syndrome

During the development of motor vagal nuclei (MVN), the neuroblasts of the myeloencephalic basal plate migrate in the dorsolateral direction to form the dorsal motor vagal nucleus (DMVN) and ventrolaterally to form the ventral motor vagal nucleus (VMVN). Those neuroblasts that remain close to the median sulcus will form the hypoglossal nucleus. In support of the congenital origin of the alteration of the MVN in sudden infant death syndrome (SIDS), we report the case of an 8‐month‐old female child who was found dead in her cot. The neuropathological assessment revealed that the medullary triangle of the 4th ventricle floor was asymmetric, owing to the presence of three prominences to the left side of the median sulcus. The medial prominence corresponded to the hypoglossal nucleus, which showed a marked increase in the number of large neurons; the intermediate prominence corresponded to the DMVN whose large neurons were reduced and were recognizable mainly at the level of the medial fringe; the lateral prominence corresponded to the solitary nucleus. The left solitary tract showed a reduction of the transverse diameter. Also, the left VMVN showed marked reduction in the number of neurons. Inflammatory and astrocytic reactions were absent. We suggest that in SIDS cases the hypocellularity of the MVN and the increased number of neurons of the hypoglossal nucleus are intimately related, indicating a congenital alteration due to incomplete migration of the vagal neuroblasts with abnormality of the autonomic cardio‐respiratory control.     

Extracellular characteristics of putative cholinergic neurons in the rat laterodorsal tegmental nucleus

The extracellular electrophysiological properties of neurons in the laterodorsal tegmental nucleus (LDT), a major source of cholinergic afferents to the thalamus, were studied in chloral hydrate-anesthetized rats. A combination of antidromic activation from the thalamus and histological verification of recording sites was used to correlate the identity of extracellular recordings in the rat LDT with cholinergic neurons in that region. All neurons antidromically activated by stimulation of the anteroventral thalamus were histologically verified to be within clusters of cholinergic (NADPH-d-positive) cells in the LDT or in the adjacent nucleus locus coeruleus (LC). The thalamically projecting LDT neurons had a homogeneous neurophysiological profile consisting of long duration action potentials (mean = 2.5 ms), slow conduction velocities (mean = 0.78 m/s), and lengthy chronaxie values (mean = 0.725 ms). The appearance and axonal characteristics of these neurons resembled those of noradrenergic LC neurons, but the two populations exhibited substantially different spontaneous activity patterns and sensory responsiveness. These characteristics may be useful in the preliminary identification of putative cholinergic neurons in vivo, and thereby provide a foundation for exploring the neuropharmacology, afferent modulation, sensory responsiveness and behavioral correlates of the brainstem cholinergic system.     

Dopaminergic transmission in the hypothalamic arcuate nucleus to produce acupuncture analgesia in correlation with the pituitary gland

Acupuncture analgesia (AA) caused by low frequency stimulation of the acupuncture point (AP) was abolished by hypophysectomy and adrenalectomy. Termination of the AA producing pathway from the AP to the pituitary gland was in the medial hypothalamic arcuate nucleus (M-HARN). The origin of the descending pain inhibitory system associated with AA was in the posterior HARN (P-HARN). AA in the hypophysectomized rats, and enhanced neuronal activity in the P-HARN that were abolished during acupuncture stimulation, were both restored by intraperitoneal microinjection of 0.5 mg/kg morphine or 0.1 micrograms beta-endorphin into the P-HARN during acupuncture stimulation. Of the analgesia produced by dopamine or beta-endorphin injected into the P-HARN, that caused by beta-endorphin disappeared after denervation of the M-HARN. The P-HARN neurons that responded to acupuncture stimulation also responded to iontophoretic dopamine, but not to iontophoretic morphine nor ultramicroinjected beta-endorphin. The transmission between the M-HARN and P-HARN may be dopaminergic, and beta-endorphin might presynaptically modulate this transmission. Reduction of sodium ions may have been the reason for abolition of AA after adrenalectomy.     

Loss of basal forebrain P75(NTR) immunoreactivity in subjects with mild cognitive impairment and Alzheimer's disease.

The long-held belief that degeneration of the cholinergic basal forebrain was central to Alzheimer's disease (AD) pathogenesis and occurred early in the disease process has been questioned recently. In this regard, changes in some cholinergic basal forebrain (CBF) markers (e.g. the high affinity trkA receptor) but not others (e.g., cortical choline acetyltransferase [ChAT] activity, the number of ChAT and vesicular acetylcholine transporter-immunoreactive neurons) suggest specific phenotypic changes, but not frank neuronal degeneration, early in the disease process. The present study examined the expression of the low affinity p75 neurotrophin receptor (p75(NTR)), an excellent marker of CBF neurons, in postmortem tissue derived from clinically well-characterized individuals who have been classified as having no cognitive impairment (NCI), mild cognitive impairment (MCI), and mild AD. Relative to NCI individuals, a significant and similar reduction in the number of nucleus basalis p75(NTR)-immunoreactive neurons was seen in individuals with MCI (38%) and mild AD (43%). The number of p75(NTR)-immunoreactive nucleus basalis neurons was significantly correlated with performance on the Mini-Mental State Exam, a Global Cognitive Test score, as well as some individual tests of working memory and attention. These data, together with previous reports, support the concept that phenotypic changes, but not frank neuronal degeneration, occur early in cognitive decline. Although there was no difference in p75(NTR) CBF cell reduction between MCI and AD, it remains to be determined whether these findings lend support to the hypothesis that MCI is a prodromal stage of AD.     

Endogenous vasopressin and baroreflex mechanisms

This article reviews the anatomical and functional evidence for ascending pathways from specific brain regions to the PVN and SON which could influence AVP release. The majority of evidence favours the main projection being from a region in the caudal VLM which may coincide with the noradrenergic neurons of the A₁ cell group. However, the transmitter(s) involved have yet to be identified, and whether the pathway is excitatory and/or inhibitory remains to be fully resolved.Anatomical and functional evidence is reviewed for descending projections from the SON and PVN to specific brain regions involved in cardiovascular control, and their possible involvement in baroreflex mechanisms is discussed. However, there is little unequivocal evidence that AVP is the main neurotransmitter utilized by descending projections from PVN to NTS and DMX. While, in some situations, circulating endogenous AVP exerts cardiovascular effects, details of its putative influences on baroreflex mechanisms are lacking.     

Organization of the trigeminal and facial motor nuclei in the hagfish, Eptatretus burgeri: a retrograde HRP study

We studied the trigeminal and facial motor nuclei of the hagfish by the retrograde HRP method. We distinguished 4 components in a single column of the motor nuclei of the trigeminal nerve and the facial nerve, viz., the pars magnocellularis of the trigeminal motor nucleus (mVm), the anterior part of the pars parvocellularis of the trigeminal motor nucleus (mVp1), the posterior part of the pars parvocellularis of the trigeminal motor nucleus (mVp2) and the facial motor nucleus (mVII). Although in Nissl preparations only the mVm could be distinguished from the rest of the nucleus, the boundaries of the other 3 components were clearly demarcated in HRP preparations. Intramuscular injections into two representative antagonistic jaw muscles revealed that there was no apparent topological organization of the neurons pertaining to the opening and closing muscles in the mVm and mVp1, but both antagonistic muscles were innervated bilaterally. Although the hagfish does possess a cartilaginous jaw, the organization pattern of the motor nuclei of the jaw muscles seems to be the most primitive of all living vertebrates.