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E J Neafsey

Publications and source records attributed to E J Neafsey.

At least 37 records · Page 2Linked to original sources
PubMed1992

Novel S-adenosylmethionine-dependent indole-N-methylation of beta-carbolines in brain particulate fractions.

Guinea pig brain S-adenosylmethionine (SAM)-dependent N-methyltransferase activity toward physiologically relevant beta-carboline (BC) substrates was examined with reverse-phase HPLC and radiochemical detection. Representative BCs, norharman and harmine, were enzymatically methylated on the 2[beta]-nitrogen by [3H]CH3-SAM in undialyzed homogenates to yield 2[beta]-methylated BCs and subsequently on the 9[indole]-nitrogen to generate 2,9-dimethylated BC products. This may be the first account of mammalian indole N-methyl transfer. There was no HPLC evidence for 9-methyl BC or (from carbon methylation) 2,6-dimethyl BC products. Capillary gas chromatography-mass spectrometry analysis confirmed the structures of the 2,9-dimethyl and 2-methyl products of norharman. The 2[beta]- and 9[indole]-N-methylation activities were mainly in the nuclear fractions and were negligible in undialyzed cytosol. This differs from the cytosolic SAM-dependent N-methylations reported with other azaheterocyclics, including 1,2,3,4-tetrahydro-BCs. The involvement of a single enzyme was suggested because the two N-methyl transfers with BC substrate had similar subcellular activity patterns, regional brain distributions, and Km and Vmax values. Sequential N-methylation of various BCs that have been observed in vivo may be a unique route to centrally retained N2,N9-dimethylated beta-carbolinium ions. Because they resemble the synthetic parkinsonian toxicant, N-methyl-4-phenylpyridinium, with respect to structure and neurotoxic activity, such "bioactivated" carbolinium ions could be endogenous causative factors in Parkinson's disease.

Animals↗
PubMed1991

Heterotopic neocortical transplants. An anatomical and electrophysiological analysis of host projections to occipital cortical grafts placed into sensorimotor cortical lesions made in newborn rats.

Plates of presumptive occipital neocortex obtained from fetal rats at 14-16 days gestation were grafted into the cerebral hemisphere of newborn rats. The transplants were placed heterotopically into sensorimotor cortical lesion cavities made immediately prior to grafting. At maturity, some of the transplants were injected with the retrograde fluorescent tracers Fast Blue and Diamidino yellow. In other animals, single-unit activity in the transplants or in normal cortex was recorded using standard electrophysiological techniques. Histologically, host projections to the transplants were demonstrated by the presence of retrogradely labeled neurons in the host primary and secondary somatosensory cortices as well as several thalamic areas including the anteroventral, anteromedial, ventrobasal, mediodorsal and central medial nuclei. Additional labeling was found in the claustrum, lateral hypothalamus, zona incerta and basal forebrain. Electrophysiologically, transplant single-unit activity was evoked in 43/69 (62%) neurons by thalamic stimulation, but only 1/69 transplant neurons responded to electrical stimulation of the contralateral forepaw. In further work, volumetric measurements showed that the transplants did not ameliorate the thalamic atrophy found after neocortical lesions. These results are compared to previous studies involving the homotopic placement of sensorimotor cortical grafts.

Animals↗
PubMed1990

Dopamine uptake inhibitory capacities of beta-carboline and 3,4-dihydro-beta-carboline analogs of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) oxidation products.

Potentially endogenous beta-carboline and 3,4-dihydro-beta-carboline alkaloidal compounds were compared, generally as 2-methylated (quaternary) and normethylated pairs, to the neurotoxin, 1-methyl-4-phenyl-dihydropyridinium ion (MPP+), with respect to inhibition of [3H]dopamine uptake into rat striatal synaptosomal preparations. Although less potent than MPP+, several compounds displayed IC50 values for inhibition in the moderate range (12-24 microM). Notably, quaternization generally did not improve inhibitory potency, and the 3,4-dihydro-compounds often were more effective inhibitors than their heteroaromatic analogs. The partially competitive nature of inhibition by one of the more effective pairs, 2-methyl-harmine and harmine, was consistent with uptake of the beta-carbolines by the synaptosomal dopamine uptake system, as was the fact that the accumulation of 2-[14C]methyl-harmine was significantly reduced by low Na+ media and by nomifensine, a potent inhibitor of the dopamine transporter. When viewed with reports that certain 2-methyl-beta-carbolines show MPP+-like toxicity in vitro and in vivo, these studies support the proposal that a mammalian beta-carbolinium compound may be taken up by nigrostriatal neurons and provoke the neuronal degeneration underlying Parkinson's disease.

1-Methyl-4-phenylpyridinium↗
PubMed1990

Hippocampal input to a "visceral motor" corticobulbar pathway: an anatomical and electrophysiological study in the rat.

The hippocampus has previously been shown to influence cardiovascular function, and this effect appears to be mediated by the connection the hippocampus has with the infralimbic area of the medial frontal cortex (MFC), a region which projects directly to the nucleus of the solitary tract (NTS) in the dorsal medulla. In the present study, anatomical and electrophysiological techniques were utilized to determine the degree of convergence of hippocampal input to the MFC on neurons in the MFC which project to the NTS. Injections of the anterograde and retrograde neuroanatomical tracer wheat-germ agglutinin-horseradish peroxidase (WGA-HRP) into the NTS retrogradely labelled cells in the infralimbic and prelimbic regions of the MFC. Injections of WGA-HRP into the ventral hippocampus anterogradely labelled terminals in the MFC which, at the light microscopic level, closely overlapped the origin of the descending projection from the MFC to the brainstem. Electron microscopic analysis revealed that anterogradely labelled terminals make synaptic contact primarily on dendritic processes in the neuropil adjacent to retrogradely labelled cells. In addition, anterogradely labelled terminals did, in some cases, make synaptic contact on the somas of retrogradely labelled cells. Electrical stimulation of the NTS antidromically activated cells in the infralimbic and prelimbic areas of the MFC. The average latency of antidromic activation was 30 msec, corresponding to a conduction velocity of approximately 0.7 m/s. Electrical stimulation of the ventral hippocampus orthodromically activated cells in the MFC. With an appropriate delay between the hippocampal and NTS stimuli, the orthodromic and antidromic potentials could be made to collide. The results of this study establish a structural as well as functional link between the hippocampus and NTS-projection neurons in the MFC.

Animals↗
PubMed1990

Mitochondrial respiratory inhibition by N-methylated beta-carboline derivatives structurally resembling N-methyl-4-phenylpyridine.

Mitochondrial accumulation and respiratory inhibition are critical steps in the actions of N-methyl-4-phenylpyridinium ion (MPP+), the toxic metabolite of the parkinsonism-inducing agent, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. We examined the respiratory characteristics of 2-methylated beta-carbolines (2-Me beta Cs) and 2-methylated 3,4-dihydro-beta-carbolines (2-MeDH beta Cs), which encompass the MPP+ structure. As indoleamine derivatives, they could have endogenous roles in idiopathic parkinsonism. With rat liver mitochondria, the order for inhibition of NAD(+)-linked O2 consumption (6-min preincubations) was as follows: MPP+ = 2-methylharmine greater than 2-methylharmol = 2-methylharmaline much greater than 2-methylharmalol greater than 2-methylnorharman greater than 6-OH-2-methylharmalan much greater than 2-methylharman. Similar to MPP+, 2-MeDH beta C/2-Me beta C inhibition was potentiated by tetraphenylboron and reversed by dinitrophenol, consistent with the involvement of cationic forms. However, the participation of neutral forms was indicated by the 2-MeDH beta C/2-Me beta C inhibitory time courses, which were unlike MPP+. The neutral forms probably arise via indolic nitrogen deprotonation because the characteristics of a cationic beta-carboline that cannot N-deprotonate, 2,9-dimethylnorharman, mirrored MPP+ rather than 2-Me beta Cs. Succinate-supported respiration was also significantly blocked by 2-MeDH beta Cs/2-Me beta Cs, but results with tetraphenylboron and 2,9-dimethylnorharman indicated that cationic forms were less important than in the inhibition of NAD(+)-linked respiration. We suggest that the relatively potent inhibition by certain 2-MeDH beta Cs/2-Me beta Cs involves neutral forms for passive mitochondrial entry and cationic as well as neutral forms that act at several respiratory sites. Respiratory inhibition could reasonably underlie the reported neurotoxicity of 2-Me beta Cs.

1-Methyl-4-phenylpyridinium↗
PubMed1989

Striatal dopaminergic toxicity following intranigral injection in rats of 2-methyl-norharman, a beta-carbolinium analog of N-methyl-4-phenylpyridinium ion (MPP+).

Methylated beta-carboline compounds are mammalian indole metabolites that we have proposed to be endogenous neurotoxins due to their structural similarity to MPP+, the active oxidized product of the dopaminergic toxin, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Several laboratories have demonstrated that MPP+ administration into the substantia nigra or median forebrain bundle of rats results in extensive depletion of striatal dopamine and its metabolites. We now report that three weeks after intranigral injection of the beta-carboline, 2-methyl-norharman, striatal dopamine, DOPAC, and homovanillic acid (HVA) concentrations ipsilateral to the injection are reduced 41-64% compared to vehicle-injected controls; in individual animals dopamine depletions of 96% were achieved. In addition, at the 2-methyl-norharman injection site in the substantia nigra, large lesions and gliosis were apparent under light microscopic examination. This is the first direct demonstration that a 2-methyl-beta-carbolinium ion is neurotoxic. It lends further validity to the hypothesis that MPP+-like beta-carbolines may be endogenous causative agents in Parkinson's disease.

1-Methyl-4-phenylpyridinium↗
PubMed1989

Fetal cortical transplants into neonatal rats respond to thalamic and peripheral stimulation in the adult. An electrophysiological study of single-unit activity.

Plates of presumptive sensorimotor neocortex obtained from fetal rats at 14-16 days gestation were grafted into the cerebral hemisphere of 0- to 1-day-old newborn rats. The transplants were placed into small lesion cavities in the sensorimotor cortical area made immediately prior to grafting. At 4-5 months of age, single-unit activity in the transplants (TP) or normal cortex (NCX) was recorded under ketamine HCl anesthesia using standard electrophysiological techniques. Over 90% of cells in both the transplants (n = 63) and normal cortex (n = 39) responded to ventral thalamic stimulation. Their average response latencies were similar (11.48 +/- 0.56 ms in TP. 12.77 +/- 1.20 ms in NCX, mean +/- S.E.M., no significant difference), as were their average responses of slightly more than 1 spike per thalamic stimulus (1.24 +/- 0.08 in TP, 1.07 +/- 0.01 in NCX, no significant difference). In addition, 64% (30/47) of transplant cells and 44% (14/32) of normal cells also responded to electrical stimulation of the contralateral forepaw, and here also the latencies were similar (16.11 +/- 0.67 ms in TP, 14.30 +/- 0.78 ms in NCX). The spontaneous neuronal activity observed within the transplants was also comparable to that seen in normal cortex, as measured by comparison of spontaneous interspike interval (ISI) histograms (median ISI of 84.5 for TP and 80.5 for NCX) and comparison of the burst index (% of intervals less than 5 ms, 14.7% for TP and 10.5% for NCX). These results are compared to those found in several recent studies where fetal cortex is grafted into adult hosts.

Animals↗
PubMed1989

Organization of cerebral cortico-olivary projections in the rat.

Injection of wheatgerm agglutinin-conjugated horseradish peroxidase into electrophysiologically identified portions of the rodent sensorimotor and medial frontal cortex revealed anterograde-labeled projections to the inferior olivary complex. Forelimb motor cortical and supplementary motor cortical regions were found to project predominantly to the principal olive while forelimb sensory cortex fibers distributed mainly within the dorsal accessory olive. Forelimb cortical fibers (both sensory and motor) terminated more rostrally and medially in the medial and dorsal accessory olives than did hindlimb projections. Medial frontal cortex projected to the beta subnucleus, the rostral medial accessory olive (especially the ventral aspect), and to the ventrolateral outgrowth of the dorsal cap. These findings indicate a more extensive origin for cortico-olivary projections than previously described for rats or cats and they demonstrate a rather precise topography for olivary projections from various cortical regions.

Animals↗
PubMed1988

Cardiovascular and respiratory responses to electrical and chemical stimulation of the hippocampus in anesthetized and awake rats.

Electrical (30-60-s trains of 0.25-ms pulses at 25 Hz, currents 10-150 microA) and chemical (microinjections of 0.1-0.5 microliters of a 1.0 M glutamate solution) stimulation of the hippocampal formation in the anesthetized and the awake rat evokes marked decreases in heart rate, blood pressure and slower, deeper, more regular respirations. Artificial ventilation (2 ml/breath; 100 breaths/min) has no effect on the cardiovascular responses, indicating that these effects are not secondary to respiratory changes. Administration of methyl atropine (0.4 mg/kg) eliminates the bradycardia response and attenuates or obliterates the blood pressure response but does not alter the respiratory response. This suggests that the cardiovascular responses are mediated partially by the vagus nerve and partially by sympathetic influences. Ablation of the medial frontal cortex, a visceral motor region which projects directly to the nucleus of the solitary tract and which receives a heavy direct projection from the CA1 and subicular cell fields of the ventral hippocampus, markedly attenuates or eliminates the cardiovascular and respiratory responses to stimulation of the ventral but not the dorsal hippocampus. The possibility that the medial frontal cortex may be a relay by which the hippocampus influences cardiovascular responses, including those observed during stress, is discussed.

Animals↗
PubMed1987

Remodeling of dorsal column nuclear efferents to the basilar pontine gray after cortical ablations in newborn rats.

In view of previous reports documenting corticopontine remodeling in response to neonatal cerebral cortical lesions, we examined possible alterations of ascending pontine afferents from the dorsal column nuclei after the same types of neonatal lesion. Two anterograde tracing techniques, autoradiography and the Fink-Heimer silver degeneration method, were combined to facilitate a topographic analysis. The distribution patterns of cuneo- and gracilopontine terminations appeared expanded in response to neonatal sensorimotor cortical lesions, as compared to non-lesioned animals.

Animals↗
PubMed1987

The rat medial frontal cortex projects directly to autonomic regions of the brainstem.

Pressure injections of the anterograde tracer wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) into the infralimbic (IL) and prelimbic (PL) regions of the medial frontal cortex of the rat produced anterograde, terminal-like labeling in the lateral dorsal tegmental nucleus (LDTg) of the dorsal pons and the ventral, ventrolateral, intermediate, medial and commissural subnuclei of the nucleus of the solitary nucleus (NTS) in the dorsomedial medulla. Injections involving IL resulted in heavier labeling than the labeling seen after PL injections only. The LDTg has been described as the pontine micturition center, involved in the micturition reflex. The possible role that the projections to the LDTg may play in fluid homeostasis is discussed. The labeled NTS subnuclei receive visceral afferent inputs from the heart, baroreceptors, lungs and gut. The direct cortical projections to these areas may be involved in mediating the bradycardia, depressor responses, and changes in respiratory and gastric activity which are seen after electrical stimulation of the rat medial frontal cortex. The present data support the concept that the infralimbic and prelimbic cortices function as a "visceral motor" cortex, involved in control of a variety of autonomic functions.

Afferent Pathways↗
PubMed1986

A study of forelimb movements evoked by intracortical microstimulation after hemicerebellectomy in newborn, young and adult rats.

Microstimulation of the cerebral motor cortex in normal adult rats evokes low-threshold contralateral and high-threshold ipsilateral forelimb movements. The present study examined the effects of hemicerebellar ablation at different postnatal ages on the current threshold values needed to evoke forelimb movements by intracortical stimulation. Animals that received hemicerebellar lesions at various ages were electrophysiologically tested 4-6 months postoperatively. In all groups, including non-lesion control animals, forelimb movements contralateral to the stimulating electrode were evoked at threshold values of 7-11 microA. Ipsilateral forelimb movements for control animals as well as those receiving cerebellar lesions at 45 or 120 days of age showed significantly higher mean threshold current values, ranging from 38 to 45 microA. In contrast, the mean threshold current values for ipsilateral forelimb movements in adult animals sustaining hemicerebellar lesions at 2, 10 or 21 days of age were significantly lowered, ranging from 16 to 22 microA. Secondary lesions of spared cerebellar tissue or callosal fibers in adult animals that had sustained hemicerebellectomy at two days of age had no effect on the current intensities needed to evoke forelimb responses. In comparison, lesions of the cerebral cortex contralateral to the stimulated cortex increased the threshold for ipsilateral movements and medullary pyramidal lesions ipsilateral to the stimulated cortex both reduced the number of responses and increased the threshold current intensities needed to evoke them. These data indicate that hemicerebellectomy within 3 weeks of age can induce electrophysiological alterations in the responses mediated by the corticospinal tract. These results support previous suggestions of the cerebral cortical involvement in compensation for neonatal cerebellar lesions.

Animals↗
PubMed1986

A chronic unit study of the sensory properties of neurons in the forelimb areas of rat sensorimotor cortex.

The sensory properties of neurons in the several forelimb areas of rat sensorimotor cortex were examined using the technique of extracellular single-unit recording in the awake, head-restrained rat. Cells with peripheral receptive fields were tested for the amount and modality of sensory input during joint manipulation and brushing and tapping of limbs, face and trunk. Input-output correlations were made on the basis of the results of receptive field mapping and intracortical microstimulation in the same electrode penetration. It was found that neurons (n = 117) in the rostral forelimb area receive virtually no sensory input while 30% of neurons (n = 114) in the caudal forelimb primary motor area do receive such input. The inputs to caudal forelimb motor area neurons were primarily (83%) from single joints; along perpendicular electrode penetrations the same joint that activated a cortical cell also moved when microstimulation was delivered along the same electrode penetration. In the granular and dysgranular zones of somatic sensory forelimb cortex, 70% of neurons (n = 82) were responsive to peripheral sensory inputs, with most of the cells in the granular cortex responsive to cutaneous inputs while cells in the dysgranular cortex were more responsive to deep inputs. The lack of sensory inputs to the rostral forelimb motor area is consistent with the proposal that this region may be a part of the supplementary motor area of the rat.

Afferent Pathways↗
PubMed1986

Topography of corticopontine remodelling after cortical lesions in newborn rats.

Autoradiographic and axonal degeneration staining techniques were combined in individual animals to study the distribution of corticopontine fibers. In normal animals, forelimb and hindlimb motor cortical projections terminated somatotopically within the ipsilateral pontine nuclei. Sparse crossed projections also displayed a somatotopic pattern. After unilateral sensorimotor cortical lesions in newborn rats, an increase in the crossed corticopontine fibers arising from the opposite unablated motor cortex was observed at maturity. These fibers distributed in a topographic pattern similar to the normal ipsilateral corticopontine pattern; forelimb motor cortical projections terminated rostral to hindlimb motor cortical fibers. The specific distribution of the anomalous fibers suggests that they constitute a functional pathway.

Animals↗
PubMed1986

The topographical organization of neurons in the rat medial frontal, insular and olfactory cortex projecting to the solitary nucleus, olfactory bulb, periaqueductal gray and superior colliculus.

In 19 rats two different retrograde tracers (Fast Blue, Diamidino Yellow, Rhodamine-labeled latex microspheres, or wheat germ agglutinin conjugated with HRP) were injected into the solitary nucleus (NTS) and either the olfactory bulb (OB), periaqueductal gray (PAG) or superior colliculus (SC). The pattern of retrogradely labeled neurons in the medial frontal, insular and olfactory cortices was examined to determine the topographical organization of the cell populations projecting to these subcortical targets and the extent to which they overlapped. In the medial frontal cortex (MFC) SC projections originated most dorsally, while NTS and OB projections originated most ventrally and exhibited slight overlap. PAG projections originated from virtually the entire MFC and overlapped with cells projecting to the OB, NTS and SC. These results are consistent with the role of dorsal MFC as the rat's frontal eye field and the ventral MFC as a visceral motor area. Laterally, in the insular cortex there was virtually complete overlap between cells projecting to the NTS and PAG. The extensive overlap of PAG projections with NTS projections medially and laterally and with SC projections medially suggests the PAG is involved in a variety of brain visceral and somatic functions. In the piriform cortex there was overlap between cells projecting to the OB and cells projecting to the SC; the cells projecting to the SC were located in the endopiriform nucleus, and may provide a substrate for orienting responses to odors.

Animals↗
PubMed1986

The medial frontal cortex and gastric motility: microstimulation results and their possible significance for the overall pattern of organization of rat frontal and parietal cortex.

Bilateral intracortical microstimulation (60-90 strains of 0.5 ms pulses at 10 Hz, currents below 50 microA) of medial frontal infralimbic and prelimbic cortical areas in ketamine-anesthetized rats produces clear and consistent decreases in ongoing gastric motility. The majority of responses consists of reductions in gastric tone, reductions in the amplitude of gastric contractions, or combined reductions in tone and amplitude. Bilateral section of the vagus nerves eliminates most of the responses, suggesting that the responses are mediated by this nerve. The effective cortical stimulation zone (the 'visceral motor' cortex) largely overlaps the source of the recently described direct projection from medial frontal cortex to the nucleus of the solitary tract; this pathway may be involved in producing the effect. Connections of this cortex with the limbic system suggest it may be involved in producing physiological responses to stress. The topographical, medial to lateral sequence of cortical functional areas revealed by these and other experiments (visceral motor, frontal eye fields, somatic motor, somatic sensory, visceral sensory) is discussed, as well as the possible implications of this pattern to the question of cortical evolutionary development.

Animals↗