Prospective comparison of three methods for detecting peri-operative neurocognitive disorders in older adults undergoing cardiac and non-cardiac surgery.

Postoperative neurocognitive disorders occur frequently in older adult patients. Neuropsychological assessment is the gold standard for diagnosis, but the resources required for routine use are significant. Instead, it is common for simplified and unvalidated tests to be used for trials and in clinical practice. We undertook a single-centre prospective observational study in elective surgical patients aged ≥ 65 years recruited between September 2019 and January 2021. Patients underwent neuropsychological assessment, the Modified Telephone Interview for Cognitive Status and Montreal Cognitive Assessment before surgery. Tests were repeated at approximately four to eight postoperative weeks. We included 105 patients and 28 (27%) were lost to follow-up. Pre-operative Modified Telephone Interview for Cognitive Status and cognitive domain scores were very weakly to moderately correlated (r = 0.09-0.41). Pre-operative Montreal Cognitive Assessment and cognitive domain scores were very weakly to weakly correlated (r = 0.17-0.37) Postoperative Modified Telephone Interview for Cognitive Status and cognitive domain scores were very weakly to weakly correlated (r = 0.09-0.36). Postoperative Montreal Cognitive Assessment score and cognitive domain scores were very weakly to weakly correlated (r = 0.07-0.36). Overall, there was limited agreement between tests. We conclude that the Modified Telephone Interview for Cognitive Status and Montreal Cognitive Assessment should not be used in isolation to diagnose postoperative neurocognitive disorders. There seems to be little to no pre-operative, postoperative or pre- to postoperative correlation between these tests and the neuropsychological assessment in older adults without pre-operative cognitive impairment.

Astrocytes and guidance of outgrowing corticospinal tract axons in the rat. An immunocytochemical study using anti-vimentin and anti-glial fibrillary acidic protein.

In the present investigation the role of astrocytes and their precursors in guidance of outgrowing corticospinal tract axons in the rat is studied. Antibodies against glial fibrillary acidic protein and vimentin are used to analyse immunogen expression of glial cells, whereas the postnatal outgrowth of corticospinal tract axons through the spinal cord was studied using anterogradely transported horseradish peroxidase. The first, leading corticospinal tract axons, being the objective of the present study, are characterized by dilatations at their distal ends, the growth cones. Growth cones of pioneer corticospinal tract axons are randomly distributed in the presumptive corticospinal tract area of the ventral most part of the dorsal funiculus. A dramatic change in glial cell labelling is found from the majority being vimentin immunoreactive and glial fibrillary acidic protein-negative at birth to almost all being the reverse at the end of the fourth postnatal week. From double labelling experiments it can be concluded that the vimentin-glial fibrillary acidic protein transition occurs within astrocyte precursor cells. The absence of glial fibrillary acidic protein-immunoreactive glial cells during the outgrowth period of pioneer corticospinal tract axons indicates that they cannot play a role in the guidance of outgrowing corticospinal tract pioneer axons. Vimentin-immunoreactive glial cells are present throughout the presumptive corticospinal tract area at the time of arrival of the leading corticospinal tract fibres. The vimentin-immunoreactive glial cells, which themselves are orientated perpendicular to the outgrowing corticospinal tract axons, are mainly arranged in longitudinal tiers parallel to the rostrocaudal axis. Electron microscopically, growth cones of pioneer corticospinal tract axons frequently exhibit protrusions into vimentin-immunoreactive glial cell processes, suggesting an adhesive type of contact. Therefore, in addition to a positional role, vimentin-immunoreactive glial cells probably play a chemical role in guidance of pioneer corticospinal tract axons. A prominent vimentin-immunoreactive glial septum was noted during corticospinal tract outgrowth in the midline raphe of the medulla oblongata and spinal cord whereas it is absent in the decussation area of corticospinal tract fibres. After the first postnatal week the major vimentin-immunoreactive glial barrier either completely disappears (medullary levels) or gradually reduces to a minor glial fibrillary acidic protein-immunoreactive one (spinal cord levels).(ABSTRACT TRUNCATED AT 400 WORDS)

Immunoelectron microscopic localization of cell adhesion molecule L1 in developing rat pyramidal tract.

The glycoprotein L1 is a cell adhesion molecule that has been proposed to function in the peripheral nervous system in axon fasciculation and onset of myelination. In this report we localize L1 during the development of a major central pathway: the pyramidal tract. The (sub)cellular localization of L1 was determined both by pre-embedding staining on Vibratome sections and by immunogold labelling on ultracryosections in developing rat pyramidal tract at the fifth cervical segment. On arrival at the fifth cervical segment, i.e. at postnatal day 1, growth cones of pioneer fibres did not exhibit L1-immunoreactivity. In the contact zone between pyramidal tract growth cones and glial processes no L1-immunoreactivity was observed. A clear L1-immunoreactivity was noted on small unmyelinated other axons situated in the entrance area of the pyramidal tract growth cones. Also on later arriving, i.e. between postnatal days 2 and 10, small unmyelinated fasciculating pyramidal tract axons L1 were present. It is our impression that L1 is localized in an irregular patchy way on the outer side of the axonal membrane. During the onset of myelination, i.e. between postnatal days 10 and 14, L1 could not be detected on axons ensheathed by oligodendrocytic processes. When myelination is largely completed, i.e. at postnatal day 21, the L1 antigen could be localized within the axoplasma of both unmyelinated and myelinated pyramidal tract axons. Furthermore, L1 could be observed occasionally on small unmyelinated pyramidal tract axons. Whereas compact myelin was always L1-negative, L1 was noted periaxonally between the axolemma and compact myelin and at (para)nodal regions at the contact zone between axolemma and oligodendrocytic processes. From these results it may be deduced that: (1) L1 is involved in fasciculation of outgrowing later arriving pyramidal tract fibres: (2) L1 is not involved in the onset of myelination in this central tract; (3) L1 might play an additional adhesive role in myelinated rat pyramidal tract.

Ultrastructural visualization of anterogradely transported horseradish peroxidase in developing corticospinal tract of rat.

Until now a satisfactory method for electron microscopic (EM) detection of anterogradely transported horseradish peroxidase (HRP) in developing neural tissue, using sensitive chromogen tetramethylbenzidine (TMB), has not been described. Use of the stabilizing agent ammoniumheptamolybdate (AHM), in combination with a modified prolonged osmication [4 hr at pH 5.0 in 0.1 M phosphate buffer (PB)] made possible visualization of HRP-TMB-(AHM) reaction product at the ultrastructural level in outgrowing corticospinal tract (CST) fibers of young postnatal rat. This reaction product appeared to be very distinctive and clearly detectable, making ultrastructural identification of HRP-labeled outgrowing CST fibers in rat spinal cord rather easy. In addition, the procedure described in this report preserves the ultrastructural details of the developing neural tissue.

Unmyelinated corticospinal axons in adult rat pyramidal tract. An electron microscopic tracer study.

The aim of the present study was to provide experimental ultrastructural evidence for a corticospinal component in the adult rat pyramidal tract (PT). For this purpose, the entire sensorimotor and frontal cortex of the left hemisphere was labelled using the anterograde tracer horseradish-peroxidase (HRP). Six months old rats were sacrificed 24 or 48 h after implantation of 6-8 HRP-gels. The detection of anterogradely transported HRP at the cervical as well as the lumbar intumescence was carried out as described earlier (J. Histochem. Cytochem., 35 [1987] 623-626). Our results demonstrate the occurrence of labelled myelinated as well as labelled unmyelinated axons within the adult rat PT at both spinal cord levels analyzed. This implicates that at least part of the unmyelinated profiles in the adult rat PT belong to fibres originating in the cortex and therefore must be interpreted as corticospinal axons. The findings are discussed in the light of their physiological significance.

An anterograde tracer study of the developing corticospinal tract in the rat: three components.

Light microscopic analysis of anterogradely transported wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) has been used to study the developing corticospinal tract (CST) in the rat. This study was carried out to examine the relationship between the site of injection within the cortex and the pattern of labelling of the developing CST in the spinal cord from postnatal day 1 (P1) through postnatal day 10 (P10). For this purpose the cortex was subdivided into 3 equal areas along the rostrocaudal axis: anterior, intermediate and posterior. After the operation the animals were allowed to survive for 24 h. The caudal extension of labelled CST axons originating in the anterior cortical area was restricted (L1 at P7 or P10) as compared with that of the CST fibres originating in the intermediate cortical area (S3 at P10). The axons of the posterior corticospinal (CS) neurones reach their most caudal extension in the spinal cord (T5) at P7 but then gradually disappear up till P14. Quantitative analysis of the amount of label along the length of the outgrowing CST fibres revealed the formation of a large stable peak at the level of the cervical enlargement after labelling of either the anterior or the intermediate cortical area. The formation of a second 'running' peak which moves caudally from mid-thoracic levels at P5 to mid-lumbar levels at P10 was only accomplished by labelling the intermediate cortical area and is probably caused by the accumulation of label in the growth cones at the distal ends of the outgrowing CST fibres. After labelling the posterior cortical area, no peaks could be detected, neither at the cervical nor at the lumbar intumescence. The major spinal grey termination field of the anterior CS neurones appeared to be the cervical intumescence, whereas the major spinal grey termination field of the intermediate CS neurones is the lumbar enlargement. By contrast, axons of posterior CS neurones never showed any outgrowth into the spinal grey matter at any level. Concluding, the developing CST in the rat consists of 3 components: the first having its originating neurones in the anterior part of the cortex and its termination field in the cervical intumescence; the second with its originating neurones in the intermediate part of the cortex and its termination field predominantly in the lumbar enlargement, and a third transient one, originating in the posterior cortex and gradually disappearing from spinal cord levels. Research using anterograde tracing techniques in combination with electron microscopy is necessary to further analyse these 3 different components.

Induction of c-fos expression in cervical spinal interneurons after kainate stimulation of the motor cortex in the rat.

The expression of the immediate-early gene c-fos was used as a marker of neuronal activity to investigate the cervical spinal interneuron populations involved in the corticomotoneuronal pathway. Adult rats received unilateral kainate injections in the forelimb area of the primary motor cortex. After a survival period of 90 min, during which the animals showed vehement twitching of the contralateral forelimb, the rats were perfused and their brains and cervical spinal cords processed for Fos-like immunoreactivity. In the cervical spinal cord Fos-like immunoreactive neurons were found bilaterally in the dorsal horn and in the intermediate zone, though contralaterally significantly more labelled nuclei were encountered in two different areas. One area closely resembles the corticospinal terminal field as demonstrated with anterograde horseradish-peroxidase tract-tracing and the other reflecting primary afferent and noxious sensory neurons in the dorsal horn. Thus by monitoring the evoked expression of the immediate-early gene c-fos, structural components of the rat motor system can be identified.

Differential cortico-motoneuron vulnerability after chronic mitochondrial inhibition in vitro and the role of glutamate receptors.

Chronic treatment of rat cortical slices with a relative low concentration of mitochondrial inhibitor malonate leads to cortical motoneuron (CMN) death. In the neurodegenerative disease amyotrophic lateral sclerosis (ALS) corticospinal neurons, CMNs projecting to the spinal cord, degenerate. In the present study we compared the effect of chronic mitochondrial inhibition on the survival of CMNs located in the dorsal cortical areas (including corticospinal neurons) with that on ventrally located CMNs (non-corticospinal neurons) in vitro. In the explant culture model used, the dorsally located CMNs were less vulnerable to a 2-week period of mitochondrial inhibition with malonate as compared to ventrally located CMNs. Treatment with 5 mM malonate resulted in 50% surviving CMNs in the dorsal part and only 16% in the ventral part. Neuroprotection of the CMNs could be achieved with co-administration of the non-NMDA antagonist CNQX, the NMDA antagonist MK-801, or the glutamate release inhibitor riluzole, suggesting that chronic energy shortage leads to excitotoxicity. In the dorsal cortical areas CNQX, MK-801, and riluzole had a neuroprotective effect on the CMNs, whereas in the ventral cortical areas only MK-801 was neuroprotective. The sensitivity to energy depletion and consequently excitotoxicity may be related to glutamate receptor density and subunit composition in various cortical areas, but also to the projection length and input of CMNs in vivo. The present investigation gives insight in mechanisms leading to excitotoxic cell death of CMNs and may therefore be important for the development of treatment strategies in protection and survival of cortical motoneurons in ALS.

Selective elimination of transient corticospinal projections in the rat cervical spinal cord gray matter.

In the present paper a description is given of the development of the rat corticospinal tract (CST) in the lower cervical spinal cord. This area contains, among other cells, the motoneurons innervating the distal forelimb muscles. HRP gels were implanted in the sensorimotor cortex of Wistar rats varying in age from postnatal day 0 (P0) to P60. After a survival period of 48 h, the rats were transcardially perfused, the spinal cords transversely sectioned at 30 microns and the sections reacted for HRP. Labelled CST axons in the dorsal funiculus were first detected at P2, and after a delay of 2 days the first fibres were found in the adjacent gray matter (P4). More labelled fibres were gradually added until maximal number and extension was reached at P10. By then the entire gray matter and large parts of the white matter were covered by labelled CST axons. From P10 onwards, the number of labelled CST fibres as well as their extension decreased. In the adult rat, some areas such as the lateral part of the ventral and dorsal horn and large parts of the ventral and lateral white matter ultimately became devoid of labelled CST axons. It is concluded that a massive overshoot occurs during the development of the terminal field of the rat CST. The results are discussed in conjunction with our previous findings on the development of the motoneurons innervating the rat distal forelimb muscles. The concurrent selective elimination of both CST axons and motoneuron dendrites is suggested to be correlated with progressively more mature, coordinated movements and with high digital skills especially.

Transient functional connections between the developing corticospinal tract and cervical spinal interneurons as demonstrated by c-fos immunohistochemistry.

Previous research on the rat corticospinal tract (CST) which develops mainly postnatally revealed that some CST axons grow transiently into the spinal gray matter and are subsequently eliminated. In the present study the question was addressed whether these fibres also form transient functional connections. Rats aged 14 and 60 days postnatally received unilateral injections of the potent glutamate agonist kainate into the cerebral motor cortex. After a survival period of 90 min. the rats were perfused and their brains and spinal cords processed for the immediate early gene c-fos by immunohistochemistry. Increased levels of c-fos as opposed to sham-operated animals was observed in several brain nuclei as well as in the cervical spinal cord. In the spinal gray one population of labelled interneurons in particular appeared to correlate well with the CST projection field. A decrease was noted in the number of c-fos positive neurons from postnatal day 14 to 60, suggesting that during development transient functional connections are formed between the CST and its target.

Collateralization of the cervical corticospinal tract in the rat.

Anterograde staining with Phaseolus vulgaris leucoagglutinin (PHA-L) revealed the spinal arborization pattern of corticospinal tract (CST) fibers in the cervical enlargement of the rat. Within the confines of the pyramidal tract local nets of small fibers are present in addition to the rather large CST fibers with varicosities. CST termination is primarily located in lamina IV and extends into lamina V and VI. Extensive collateralization of CST axons was found interconnecting neurons located both in different horizontal laminae and in subsequent spinal cord segments. This complex pattern of CST collateralization is suggested to add a coordinative role in motor control to this tract both through serial axo-dendritic contacts in the spinal gray and through axo-axonal contacts in the white as well as the gray matter.

Immunocytochemical localization of cell adhesion molecule L1 in developing rat pyramidal tract.

L1 is a representative of a family of carbohydrate neural cell adhesion molecules. The expression of L1 was studied during postnatal development of the rat pyramidal tract by immunohistology using polyclonal antibodies to L1 in spinal cord cervical intumescences. On postnatal day 1 (P1), L1 immunoreactivity was present in the entire dorsal funiculus, consisting of the ascending fasciculus gracilis and fasciculus cuneatus and the descending pyramidal tract. At that time the cervical pyramidal tract contains the first outgrowing corticospinal axons. At P4 both the fasciculus gracilis and the pyramidal tract are immunoreactive whereas the fasciculus cuneatus is negative. At P10 the pyramidal tract is intensely labelled whereas both ascending bundles are negatively stained. In the period between P4 and P10 the pyramidal tract is characterized by a massive outgrowth of corticospinal axons. During pyramidal tract myelination, between P10 and the end of the third postnatal week (P21), L1 immunoreactivity is progressively reduced. These observations suggest that L1 may play a prominent role in outgrowth, fasciculation and the onset of myelination of rat pyramidal tract axons. The differential L1 immunoreactivity of the pyramidal tract and the earlier developing ascending systems in rat dorsal funiculus indicate that this polyclonal antiserum is a useful differentiating marker for outgrowing fibre tracts.

Direct cortico-motoneuronal synaptic contacts are present in the adult rat cervical spinal cord and are first established at postnatal day 7.

In order to demonstrate direct cortico-motoneuronal synaptic contacts in the cervical spinal cord of the rat and to determine at which postnatal age these contacts are established, an electron microscopic study using double labelling was performed. Corticospinal axons were anterogradely labelled after horseradish peroxidase (HRP)-gel implantation into the cerebral motor cortex and motoneurons were retrogradely labelled after cholera toxin subunit B conjugated to HRP (CTB-HRP) injections into the distal forelimb flexor muscle. With the histochemical procedures used, both tracers yield similar needle-like crystalline deposits. Labelled axons, however, can be well differentiated from labelled motoneuronal dendrites and somata on morphological grounds. In adult rats, direct cortico-motoneuronal contacts were encountered. Experiments in developing postnatal rats demonstrated that these synapses are first present on postnatal day 7.

Neurogenesis in the basal forebrain in the Chinese hamster (cricetulus griseus). II. Site of neuron origin: morphogenesis of the ventricular ridges.

In the present study the morphogenesis of the ventricular ridges, i.e. the site of origin for neurons in the basal ganglia and various related basal forebrain structures, has been studied in the Chinese hamster with the aid of three-dimensional and graphical reconstructions. The first ridge appears at developmental stage 14 (E 12 1/2). It originates at the level of the torus hemisphaericus, thereby obscuring the basal part of the telodiencephalic boundary. Later on this ridge passes into the medial ventricular ridge. Subsequently, the lateral ventricular ridge arises at stage 16 (E 13 1/2). Initially, both ridges are completely separated by the sulcus subpallii intermedius. During further development, however, this limiting groove fades away, a process starting caudally and gradually proceeding in the rostral direction. Eventually, this process results in the formation of one single ventricular eminence at the second fetal stage (E 18). In the adult stage the ventricular eminence curves around the cerebral stem area. Thickening of the telencephalic walls and local coarctations have considerably reduced the lumen of the lateral ventricle. The preoptic region in the adult must be considered as a derivative of the diencephalic part of the medial ventricular ridge.

Postnatal development of the corticospinal tract in the rat. An ultrastructural anterograde HRP study.

Horseradish-peroxidase was used to anterogradely label and thus to trace the growth of corticospinal axons in rats ranging in age from one day to six months. Three to eight HRP-gels were implanted in the left cerebral hemisphere of the cortex. In each spinal cord three levels were studied, the cervical intumescence (C5), the mid-thoracic region (T5) and the lumbar enlargement (L3). The methodology employed for the electron microscopic visualization of HRP has been described previously (Joosten et al. 1987a). The outgrowth of labelled unmyelinated corticospinal tract axons in the rat spinal cord primarily occurs during the first ten postnatal days. The outgrowth of the main wave of these fibres is preceded by a number of pathfinding axons, characterized by dilatations at their distal ends, the growth cones. By contrast, later appearing unmyelinated axons, which presumably grow along the pathfinding axons, do not exhibit such growth cones. The first labelled pioneer axons can be observed in the cervical intumescence at postnatal day one (P1), in the mid-thoracic region at day three (P3) and in the lumbar enlargement at day five (P5). Prior to the entrance of the axons, the prospective corticospinal area or the pre-arrival zone is composed of fascicles consisting of unlabelled, unmyelinated fibres surrounded by lucent amorphous structures. During the outgrowth phase of the corticospinal fibres some myelinated axons could be observed within the outgrowth area even before day 14. These axons, however, were never labelled. These findings strongly suggest that the outgrowth area, which is generally denoted as the pyramidal tract, contains other axons besides the corticospinal fibres (and glial cells).(ABSTRACT TRUNCATED AT 250 WORDS)

On the development of the pyramidal tract in the rat. I. The morphology of the growth zone.

An electron microscopic study has been made of the tip of the growing pyramidal tract in the rat. This part of the developing bundle, designated as the growth-zone, has been examined at the levels of the medulla oblongata and the third spinal segment at embryonic day 20 and on the day of birth, respectively. The tip of the pyramidal tract contains, apart from axons, numerous larger profiles. An analysis of serial sections revealed that these represent either growth cones or preterminal periodic varicosities. In the growth cones of the corticospinal axons three zones can be distinguished: a proximal "tubular", an intermediate "vesicular-reticular" and a distal "fine-granular" zone. As distinct from the classical descriptions the corticospinal growth cones end in a single or, less frequently, in two more or less parallel filopodia. None of the growth cones analyzed in this study showed multiple filopodia radiating from the terminal expansion as observed at the end of growing axons in tissue cultures and in developing spinal fibre tracts of nonmammalian vertebrates. As regards the varicosities, most of these structures are characterized by a light cytoplasmic density. Others, however, contain a denser cytoplasm, closely resembling that of the vesiculo-reticular part of growth cones.

On the development of the pyramidal tract in the rat. II. An anterograde tracer study of the outgrowth of the corticospinal fibers.

An anterograde tracer study has been made of the developing corticospinal tract (CST) in the rat using wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Analysis of normal Rager stained material revealed that corticospinal axons reach upper cervical spinal cord levels at the day of birth (PO). Postnatal rats ranging in age from one (P1) to fourteen (P14) days received multiple WGA-HRP injections into the cortex of their left hemisphere and were allowed to survive for 24 h. The first labeled CST fibers caudally extend into the third thoracic spinal cord segment at P1; into the eighth thoracic segment at P3; into the first or second lumbar segment at P7 and into the second to third sacral segment at Pg. Thus the outgrowth of the leading 'pioneer' fibers of the CST is completed at P9 but later developing axons are continuously added even beyond P9. Quantitative analysis of the amount of label along the length of the outgrowing CST revealed a characteristic pattern of labeling varying with age. The most striking features of that pattern are: the formation of two standing peaks at the level of the cervical and lumbar enlargements respectively and the transient presence of a smaller running peak which moves caudally with the front of the outgrowing bundle. The standing peaks are ascribed to the branching of the axon terminals at both intumescences, whereas the running peak probably arises by the accumulation of tracer within the growth cones at the tips of the outgrowing CST axons. Factors such as the number of axons, the varying axon diameters, the branching collaterals, the presence of varicosities, the transport rate of the tracer, the uptake of the tracer at the injection site, which possibly may affect the amount of label present in both the entire bundle and in the individual axons are discussed. Current research is focused upon an analysis of the relation between the site of injection within the cortex and the pattern of labeling of the CST. A delay of two days was found between the arrival of the CST axons at a particular spinal cord level and their outgrowth into the adjacent spinal gray. However, combined HRP and electronmicroscopic experiments are necessary to determine the factors behind the maturation of the CST as well as the maturation of the spinal gray.