Cranial manipulation affects cholinergic pathway gene expression in aged rats

CONTEXT

Age-dependent dementia is a devastating disorder afflicting a growing older population. Although pharmacological agents improve symptoms of dementia, age-related comorbidities combined with adverse effects often outweigh their clinical benefits. Therefore, nonpharmacological therapies are being investigated as an alternative. In a previous pilot study, aged rats demonstrated improved spatial memory after osteopathic cranial manipulative medicine (OCMM) treatment.

OBJECTIVES

In this continuation of the pilot study, we examine the effect of OCMM on gene expression to elicit possible explanations for the improvement in spatial memory.

METHODS

OCMM was performed on six of 12 elderly rats every day for 7 days. Rats were then euthanized to obtain the brain tissue, from which RNA samples were extracted. RNA from three treated and three controls were of sufficient quality for sequencing. These samples were sequenced utilizing next-generation sequencing from Illumina NextSeq. The Cufflinks software suite was utilized to assemble transcriptomes and quantify the RNA expression level for each sample.

RESULTS

Transcriptome analysis revealed that OCMM significantly affected the expression of 36 genes in the neuronal pathway (false discovery rate [FDR] <0.004). The top five neuronal genes with the largest-fold change were part of the cholinergic neurotransmission mechanism, which is known to affect cognitive function. In addition, 39.9% of 426 significant differentially expressed (SDE) genes (FDR<0.004) have been previously implicated in neurological disorders. Overall, changes in SDE genes combined with their role in central nervous system signaling pathways suggest a connection to previously reported OCMM-induced behavioral and biochemical changes in aged rats.

CONCLUSIONS

Results from this pilot study provide sufficient evidence to support a more extensive study with a larger sample size. Further investigation in this direction will provide a better understanding of the molecular mechanisms of OCMM and its potential in clinical applications. With clinical validation, OCMM could represent a much-needed low-risk adjunct treatment for age-related dementia including Alzheimer's disease.

A glutamate concentration-biased allosteric modulator potentiates NMDA-induced ion influx in neurons

Precisely controlled synaptic glutamate concentration is essential for the normal function of the N-methyl D-aspartate (NMDA) receptors. Atypical fluctuations in synaptic glutamate homeostasis lead to aberrant NMDA receptor activity that results in the pathogenesis of neurological and psychiatric disorders. Therefore, glutamate concentration-dependent NMDA receptor modulators would be clinically useful agents with fewer on-target adverse effects. In the present study, we have characterized a novel compound (CNS4) that potentiates NMDA receptor currents based on glutamate concentration. This compound alters glutamate potency and exhibits no voltage-dependent effect. Patch-clamp electrophysiology recordings confirmed agonist concentration-dependent changes in maximum inducible currents. Dynamic Ca2+ and Na+ imaging assays using rat brain cortical, striatal and cerebellar neurons revealed CNS4 potentiated ion influx through native NMDA receptor activity. Overall, CNS4 is novel in chemical structure, mechanism of action and agonist concentration-biased allosteric modulatory effect. This compound or its future analogs will serve as useful candidates to develop drug-like compounds for the treatment of treatment-resistant schizophrenia and major depression disorders associated with hypoglutamatergic neurotransmission.

Intracellular potassium depletion enhances apoptosis induced by staurosporine in cultured trigeminal satellite glial cells

PURPOSE

Satellite glial cells (SGC) surrounding neurons in sensory ganglia can buffer extracellular potassium, regulating the excitability of injured neurons and possibly influencing a shift from acute to neuropathic pain. SGC apoptosis may be a key component in this process. This work evaluated induction or enhancement of apoptosis in cultured trigeminal SGC following changes in intracellular potassium [K]ic.

MATERIALS AND METHODS

We developed SGC primary cultures from rat trigeminal ganglia (TG). Purity of our cultures was confirmed using immunofluorescence and western blot analysis for the presence of the specific marker of SGC, glutamine synthetase (GS). SGC [K]ic was depleted using hypo-osmotic shock and 4 mM bumetanide plus 10 mM ouabain. [K]ic was measured using the K⁺ fluorescent indicator potassium benzofuran isophthalate (PBFI-AM).

RESULTS

SGC tested positive for GS and hypo-osmotic shock induced a significant decrease in [K]ic at every evaluated time. Cells were then incubated for 5 h with either 2 mM staurosporine (STS) or 20 ng/ml of TNF-α and evaluated for early apoptosis and late apoptosis/necrosis by flow cytometry using annexin V and propidium iodide. A significant increase in early apoptosis, from 16 to 38%, was detected in SGC with depleted [K]ic after incubation with STS. In contrast, TNF-α did not increase early apoptosis in normal or [K]ic depleted SGC.

CONCLUSION

Hypo-osmotic shock induced a decrease in intracellular potassium in cultured trigeminal SGC and this enhanced apoptosis induced by STS that is associated with the mitochondrial pathway. These results suggest that K⁺ dysregulation may underlie apoptosis in trigeminal SGC.

Mechanoceutics Alters Alzheimer's Disease Phenotypes in Transgenic Rats: A Pilot Study

Current advancements in neurovascular biology relates a mechanoceutics treatment, known as cranial osteopathic manipulation (COM), Alzheimer's disease (AD). COM could be used as an evidence-based treatment strategy to improve the symptoms of AD if molecular mechanisms, which currently remain unclear, are elucidated. In the present pilot study, using transgenic rats, we have identified COM mediated changes in behavioral and biochemical parameters associated with AD phenotypes. We expect these changes may have functional implications that might account for improved clinical outcomes of COM treatment. Further investigations on COM will be helpful to establish an adjunct treatment for AD.

Effect of Osteopathic Cranial Manipulative Medicine on an Aged Rat Model of Alzheimer Disease

CONTEXT

In the aging brain, reduction in the pulsation of cerebral vasculature and fluid circulation causes impairment in the fluid exchange between different compartments and lays a foundation for the neuroinflammation that results in Alzheimer disease (AD). The knowledge that lymphatic vessels in the central nervous system play a role in the clearance of brain-derived metabolic waste products opens an unprecedented capability to increase the clearance of macromolecules such as amyloid β proteins. However, currently there is no pharmacologic mechanism available to increase fluid circulation in the aging brain.

OBJECTIVE

To demonstrate the influence of an osteopathic cranial manipulative medicine (OCMM) technique, specifically, compression of the fourth ventricle, on spatial memory and changes in substrates associated with mechanisms of metabolic waste clearance in the central nervous system using the naturally aged rat model of AD.

RESULTS

Significant improvement was found in spatial memory in 6 rats after 7 days of OCMM sessions. Live animal positron emission tomographic imaging and immunoassays revealed that OCMM reduced amyloid β levels, activated astrocytes, and improved neurotransmission in the aged rat brains.

CONCLUSION

These findings demonstrate the molecular mechanism of OCMM in aged rats. This study and further investigations will help physicians promote OCMM as an evidence-based adjunctive treatment for patients with AD.

Ligand binding domain interface: A tipping point for pharmacological agents binding with GluN1/2A subunit containing NMDA receptors

N-methyl D-aspartate (NMDA) receptors play a crucial role in normal brain function, pathogenesis of neurodegenerative and psychiatric disorders. Functional tetra-heteromeric NMDA receptor contains two obligatory GluN1 subunits and two identical or different non-GluN1 subunits that evolve from six different genes including four GluN2 (A-D) and two GluN3 (A-B) subunits. Since NMDA receptors confer varied physiological properties and spatiotemporal distributions in the brain, pharmacological agents that target NMDA receptors with specific GluN2 subunits have significant potential for therapeutic applications. In the present work, by using electrophysiology techniques, we have studied the role of ligand binding domain (LBD) interactions in determining the effect of well-characterized pharmacological agents including agonists, competitive antagonists, channel blockers and an allosteric modulator. Remarkably, point mutations at the distal end (site-II&III) of GluN1 LBD interface increased memantine potency up to sevenfold when co-expressed with wild type GluN2A receptors but exhibit no effect on Mg²⁺ activity. Conversely, mutations at the proximal end (site-I) of the LBD interface did not affect the memantine but altered Zn²⁺ and Mg²⁺ potency towards opposite directions. These results indicate that GluN1/2A LBD interface interactions play a key role in determining channel function. Further, subtle changes in LBD interaction can be readily translated to the downstream extracellular vestibule of channel pore to adopt a conformation that may affect memantine, Zn²⁺ and Mg²⁺ binding. Further studies on NMDA receptor LBD to transmembrane domain signal propagation mechanisms will help develop GluN2 subunit selective biomolecules that can be used for the treatment of neurological and psychiatric disorders.

Positive Modulatory Interactions of NMDA Receptor GluN1/2B Ligand Binding Domains Attenuate Antagonists Activity

N-methyl D-aspartate receptors (NMDAR) play crucial role in normal brain function and pathogenesis of neurodegenerative and psychiatric disorders. Functional tetra-heteromeric NMDAR contains two obligatory GluN1 subunits and two identical or different non-GluN1 subunits that include six different gene products; four GluN2 (A–D) and two GluN3 (A–B) subunits. The heterogeneity of subunit combination facilities the distinct function of NMDARs. All GluN subunits contain an extracellular N-terminal Domain (NTD) and ligand binding domain (LBD), transmembrane domain (TMD) and an intracellular C-terminal domain (CTD). Interaction between the GluN1 and co-assembling GluN2/3 subunits through the LBD has been proven crucial for defining receptor deactivation mechanisms that are unique for each combination of NMDAR. Modulating the LBD interactions has great therapeutic potential. In the present work, by amino acid point mutations and electrophysiology techniques, we have studied the role of LBD interactions in determining the effect of well-characterized pharmacological agents including agonists, competitive antagonists, and allosteric modulators. The results reveal that agonists (glycine and glutamate) potency was altered based on mutant amino acid sidechain chemistry and/or mutation site. Most antagonists inhibited mutant receptors with higher potency; interestingly, clinically used NMDAR channel blocker memantine was about three-fold more potent on mutated receptors (N521A, N521D, and K531A) than wild type receptors. These results provide novel insights on the clinical pharmacology of memantine, which is used for the treatment of mild to moderate Alzheimer's disease. In addition, these findings demonstrate the central role of LBD interactions that can be exploited to develop novel NMDAR based therapeutics.

Immunohistochemical Changes in the Mouse Striatum Induced by the Pyrethroid Insecticide Permethrin

Epidemiological studies have linked insecticide exposure and Parkinson's disease. In addition, some insecticides produce damage or physiological disruption within the dopaminergic nigrostriatal pathway of non-humans. This study employed immunohistochemical analysis in striatum of the C57BL/6 mouse to clarify tissue changes suggested by previous pharmacological studies of the pyrethroid insecticide permethrin. Dopamine transporter, tyrosine hydroxylase, and glial fibrillary acidic protein immunoreactivities were examined in caudate-putamen to distinguish changes in amount of dopamine transporter immunoreactive protein from degeneration or other damage to dopaminergic neuropil. Weight-matched pairs of pesticide-treated and vehicle-control mice were dosed and sacrificed on the same days. Permethrin at 0.8, 1.5 and 3.0 mg/kg were the low doses and at 200 mg/kg the high dose. Brains from matched pairs of mice were processed on the same slides using the avidin-biotin technique. Four fields were morphometrically located in each of the serial sections of caudateputamen, digitally photographed, and immunopositive image pixels were counted and compared between members of matched pairs of permethrin-treated and vehicle-control mice. For low doses, only 3.0 mg/kg produced a significant decrease in dopamine transporter immunostaining. The high dose of permethrin did not produce a significant change in dopamine transporter or tyrosine hydroxylase immunostaining, but resulted in a significant increase in glial fibrillary acidic protein immunostaining. These data suggest that a low dose of permethrin can reduce the amount of dopamine transporter immunoreactive protein in the caudate-putamen. They also suggest that previously reported reductions in dopamine uptake of striatal synaptosomes of high-dose mice may be due to nondegenerative tissue damage within this region as opposed to reductions of dopamine transporter protein or death of nigrostriatal terminals. These data provide further evidence that insecticides can affect the primary neurodegenerative substrate of Parkinson's disease.

Occupational health outcomes for workers in the agriculture, forestry and fishing sector: implications for immigrant workers in the southeastern US

BACKGROUND

Workers in the Agriculture, Forestry, and Fisheries (AgFF) sector experience exposures directly related to the work itself, as well as the physical environment in which the work occurs. Health outcomes vary from immediate to delayed, and from acute to chronic.

METHODS

We reviewed existing literature on the health outcomes of work in the AgFF sector and identified areas where further research is needed to understand the impact of these exposures on immigrant Latino workers in the southeastern US.

RESULTS

Outcomes related to specific body systems (e.g., musculoskeletal, respiratory) as well as particular exposure sources (e.g., pesticides, noise) were reviewed. The most extensive evidence exists for agriculture, with a particular focus on chemical exposures. Little research in the southeastern US has examined health outcomes of exposures of immigrant workers in forestry or fisheries.

CONCLUSION

As the AgFF labor force includes a growing number of Latino immigrants, more research is needed to characterize a broad range of exposures and health outcomes experienced by this population, particularly in forestry and fisheries.

Consequences of manganese administration for striatal dopamine and motor behavior in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-exposed C57BL/6 mice

Environmental compounds may be important contributors to Parkinson's disease etiology. Epidemiological and experimental evidence for the facilitation of parkinsonism by manganese is equivocal. This work addressed methodological concerns in the few studies of manganese modulation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced toxicity in C57BL/6 mice. Male, retired breeder mice received 0 or 100 mg/kg of manganese chloride (MnCl₂; subcutaneously on days 1, 4 and 7) and 0 or 20 mg/kg of MPTP (intraperitoneally on day 8) and survived up to day 15 or 22. On the day of sacrificing, horizontal (grid crossing) and vertical (rearing) open field movement, swimming, grip strength and grip fatigue were examined. Striata were analyzed for dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) using high-performance liquid chromatography. MPTP produced a main effect decrease in striatal dopamine (48.8%) and DOPAC (38.1%), but there was no main effect of MnCl₂ or MnCl₂ x MPTP interaction. However, modulatory interactions were observed between the effects of MnCl₂ and MPTP for grid crossing, rearing and grip strength. Interestingly, these interactions reduced the severity of behavioral deficits attributable to either of these compounds alone. For rearing and grip strength, the MnCl₂ x MPTP interaction was dependent upon survival time. The mechanistic nature of the MnCl₂ x MPTP interaction upon these behaviors, in the absence of such an interaction for striatal dopamine and DOPAC, remains to be clarified.

Congenital infection of mice with Toxoplasma gondii induces minimal change in behavior and no change in neurotransmitter concentrations

We examined the effect of maternal Toxoplasma gondii infection on behavior and the neurotransmitter concentrations of congenitally infected CD-1 mice at 4 and 8 wk of age when latent tissue cysts would be present in their brains. Because of sex-associated behavioral changes that develop during aging, infected female mice were compared with control females and infected male mice were compared with control males. Only the short memory behavior (distance between goal box and first hole investigated) of male mice congenitally infected with T. gondii was significantly different (P < 0.05) from that of uninfected control males at both 4 and 8 wk by using the Barnes maze test. The other parameters examined in the latter test, i.e., functional observational battery tests, virtual cliff, visual placement, and activity tests, were not significantly different (P > 0.05) at 4 and 8 wk. Concentrations of neurotransmitters and their metabolites (dopamine; 3,4-dihydroxyphenylacetic acid; homovanillic acid; norepinephrine; epinephrine; 3-methoxy-4-hydroxyphenylglycol; serotonin; and 5-hydroxyindoleacetic acid) in the frontal cortex and striatum were not different (P > 0.05) between infected and control mice at 8 wk of age. The exact mechanism for the observed effect on short-term memory in male mice is not known, and further investigation may help elucidate the molecular mechanisms associated with the proposed link between behavioral changes and T. gondii infection in animals. We were not able, however, to confirm the widely held belief that changes in neurotransmitters result from chronic T. gondii infection of the brain.

Pyrethroid and organophosphate insecticide exposure in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson’s disease: an immunohistochemical analysis of tyrosine hydroxylase and glial fibrillary acidic protein in dorsolateral striatum

The pyrethroid insecticide permethrin and the organophosphate insecticide chlorpyrifos can experimentally produce Parkinson’s disease (PD)-associated changes in the dopaminergic nigrostriatal pathway, short of frank degeneration, although at doses considerably higher than from a likely environmental exposure. The ability of permethrin (200 mg/kg), chlorpyrifos (50 mg/kg), or combined permethrin + chlorpyrifos to facilitate nigrostriatal damage in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg) C57BL/6 mouse model of PD was investigated in three separate experiments. Tyrosine hydroxylase (TH) and glial fibrillary acidic protein (GFAP) immunohistochemistry assessed nigrostriatal degeneration or nigrostriatal damage more subtle than frank degeneration. Four fields in the dorsolateral caudate-putamen were examined at two rostrocaudal locations. The dopaminergic neurotoxin MPTP decreased striatal TH immunopositive neuropil and increased GFAP immunopositive neuropil. Neither permethrin nor chlorpyrifos, alone or in combination, altered the effects of MPTP upon TH or GFAP immunostaining. Permethrin alone increased striatal GFAP immunopositive neuropil but not when combined with chlorpyrifos treatment. Therefore, combined administration of the two insecticides appeared to protect against an increase in a neuropathological indicator of striatal damage seen with permethrin treatment alone. Differences compared with analysis of entire striatum emphasize the value of varying the topographic focus used to assess nigrostriatal degeneration in studies of insecticides in PD.

Basal Ganglia accumulation and motor assessment following manganese chloride exposure in the C57BL/6 mouse

Equivocal clinical evidence for involvement of manganese in development of Parkinson's disease necessitates experimental studies on this issue. The aged, 1-methyl-4-phenyl-1,2,3,6-tetrahyropyridine-treated C57BL/6 mouse is one of the most common models for Parkinson's disease. However, there is little information on brain bioaccumulation of manganese, and little or no information on clinical/behavioral manifestations of manganese neurotoxicity, in this strain. Male C57BL/6 retired breeder mice were given a single subcutaneous injection of either 0, 50, or 100 mg/kg of MnCl(2) (single-dose regimen) or three injections of either of these doses over 7 days (multiple-dose regimen). Behavioral assessment was performed 24 h after final injection, followed by sacrifice, and body weight was recorded each day. There was a 105% increase in striatal manganese concentration 1 day after a single 100 mg/kg injection, and 421% and 647% increases, respectively, 1 day after multiple doses of 50 or 100 mg/kg of MnCl(2). One day after a single injection, there were respective 30.9% and 38.9% decreases in horizontal movement (grid crossing) for the 50 and 100 mg/kg doses and a 43.2% decrease for the multiple dose of 100 mg/kg. There was no significant main effect of dose level on rearing, swimming, grip strength, or grip fatigue. Unlike previous work with the C57BL/6 strain using smaller intraperitoneal doses, this study established dosing regimens that produced significant increases in basal ganglia manganese concentration reminiscent of brain increases in the CD-1 mouse following subcutaneous doses close to our lowest. A decrease in locomotor behavior, significant but not severe in this study, has been reported following manganese exposure in other mouse strains. These data, particularly the significant increase in basal ganglia manganese concentration, provide guidance for designing studies of the potential role of manganese in Parkinson's disease using the most common animal model for the disorder.

Pharmacological properties of the MPTP analog trans-1-methyl-4-[4-dimethylaminophenylethenyl]-1,2,3,6-tetrahydropyridine and its pyridinium metabolite in mouse brain synaptosomes: a potential visual marker for substrates of MPTP-induced neurotoxicity

1. The tetrahydropyridine trans-1-methyl-4-[4-dimethylaminophenylethenyl]-1,2,3,6-tetrahydropyridine (t-THP), like MPTP, can undergo monoamine oxidase (MAO)-mediated conversion to a dihydropyridinium intermediate and subsequent metabolism to a pyridinium species. t-THP is also a better substrate for MAO B than MAO A. In contrast to the metabolism of MPTP, the pyridinium ion derived from t-THP is highly fluorescent. This endows t-THP with potential as an in vivo visual probe for localizing the substrates of MPTP-like neurotoxicity. As a prelude to in vivo labeling studies, we examined the metabolism and uptake kinetics of t-THP and its metabolites in mouse striatal and cortical synaptosomes. 2. T-THP was found to induce a concentration-dependent and saturable fluorescence within striatal and cortical synaptosomes that was also MAO-dependent. Like MPP+, the fluorescent pyridinium ion t-P+, derived from t-THP, inhibited the uptake and facilitated the release of monoamines from synaptosomes in a concentration-dependent fashion. The ion did not rely on sodium-dependent membrane transporters for its concentration-dependent uptake into synaptosomes, although it may have an irreversible affinity for the dopamine transporter. 3. These data suggest that t-THP could be appropriate for use as a visual marker for microenvironments where MPTP-like compounds are taken up and converted to potentially neurotoxic pyridinium species. Such a marker could be employed to address some of the issues regarding the selectivity of MPTP-induced neurotoxicity.

The 2001 Carl J. Norden Distinguished Teacher Award. Teaching the basic sciences to veterinary students: science or art or both? One teacher's journey into self-examination

Veterinary faculty do not often get the chance to reflect on their own teaching practices. Recent circumstances dictated that the author perform such a self-analysis. This article represents the fruits of that reflection process. A personal philosophy of teaching is presented, along with impressions of the student experience. Using these as a guide, ideas are presented about the package of material that should be delivered to the students, how that package should be delivered, and some special tools to aid delivery. A personal wish list of items that might lead to a better teaching experience is also included. Although the teaching game plan presented here is unlikely to be the best strategy, it is hoped that it may provide some helpful hints for other instructors of veterinary medicine or, at least, stimulate further thinking about how the teaching and learning experience can be improved for both teacher and student.

Rapid shifts in receptive fields of cells in trigeminal subnucleus interpolaris following infraorbital nerve transection in adult rats

Transection of the infraorbital nerve in adult rats results in an array of chronic functional anomalies in trigeminal brainstem subnucleus interpolaris, including changes in normal receptive field organization. This work examined whether long-term maintenance of acute modifications, such as unmasking or strengthening of normally ineffective inputs to interpolaris cells, might contribute to the previously described chronic abnormalities. Using glass micropipettes, extracellular isolation of 37 interpolaris cells, with infraorbital receptive fields, was maintained following intraorbital transection of the infraorbital nerve. Receptive fields and dynamic response properties were characterized immediately before and after the cut and throughout the post-transection isolation period. Orthodromic latencies to trigeminal ganglion shocks and antidromic activation from thalamus or cerebellum were also examined. Of the 37 cells, 21.6% exhibited receptive field shifts to non-infraorbital regions after cutting the infraorbital nerve. Using the normal probability of observing an interpolaris cell with more than one trigeminal division in its receptive field, the probability of observing this shift by chance was 0.0013. No such changes were observed for 12 control cells, recorded for durations equal to or greater than total recording times for the shifting cells, with the nerve intact. The representation of local circuit, thalamic-projecting and cerebellar-projecting cells was similar in the total sample; however, all neurons exhibiting transection-induced receptive field shifts were projection neurons. In comparing the sample of cells that exhibited receptive field shifts with those that did not, prior to infraorbital nerve cut, there was no difference in mean latencies and thresholds for activation from the stimulating electrodes or in mean depth at which the cells were isolated. In addition, no difference was evident in receptive field size, effective receptor surface, dynamic response characteristics or spontaneous activity. These data suggest that maintenance of acute receptive field changes, following infraorbital nerve cut, may contribute to some types of chronic functional alterations observed after such damage.

Structure-function relationships in rat brainstem subnucleus interpolaris. XI. Effects of chronic whisker trimming from birth

Whisker trimming from birth reduces activity and alters receptive fields (RFs) in the barrel cortex and thalamus. To assess whether or not this reflects deprivation effects on trigeminal (V) first- and second-order neurons, 59 primary afferents and 343 cells in V brainstem subnucleus interpolaris (SpVi) were studied in rats whose whiskers were trimmed daily for 6-9 weeks from birth. Deprivation did not effect brainstem somatotopy or primary afferent RFs. However, many SpVi cells had abnormal RFs and higher-order inputs, resembling the changes caused by infraorbital nerve injury. For example, in controls, only 3% of whisker-sensitive local circuit neurons responded to more than one whisker, whereas 35% of the deprived and 41% of the infraorbital nerve cut samples had multiwhisker. RFs. Deprived rats also had higher than normal incidences of cells with split or absent RFs, RFs spanning more than one V division, intermodality convergence, and directional or high-velocity sensitivity. Because these changes mimic those caused by nerve section, deprivation may underlie some nerve injury effects on V brainstem RF size and character. Insofar as cytochrome oxidase, anterograde labeling, and unit recordings revealed normal topography in deprived primary afferents and SpVi cells, RF changes in SpVi cells may reflect altered SpVi circuitry. To test this hypothesis, we assessed the morphology of 32 similarly deprived V primary afferents. In SpVi, deprived fibers had normal numbers of collaterals with normal shapes, transverse arbor areas, and topography. However, the total number of boutons per collateral was significantly reduced. Thus, deprivation effects on V higher-order RFs reflect quantitative changes in V afferent terminals.

Functional properties of cells in rat trigeminal subnucleus interpolaris following local serotonergic deafferentation

We have previously demonstrated increases in serotonin (5-HT) content and immunoreactivity within spinal trigeminal subnucleus interpolaris (SpVi) that are correlated with the functional changes observed in this subnucleus following adult infraorbital nerve (ION) transection. To assess the possible functional significance of this change, we have examined the influence of 5-HT afference upon the normal response properties of cells in SpVi. We employed local depletion of the transmitter, using 5,7-dihydroxtryptamine (5,7-DHT), in combination with extracellular single-cell recording. Chromatographic methods revealed a 97.6% depletion of 5-HT 24 hr after neurotoxin injection. Immunocytochemical procedures revealed depletion of 5-HT throughout SpVi. Physiological recordings were made from 403 SpVi cells in 5,7-DHT-injected rats and 387 cells in vehicle-injected rats. All recordings were made 19-27 hr after injection. Horseradish peroxidase (HRP) deposits from the recording electrode were used to mark recording tracks. 5-HT depletion did not influence receptive field (RF) location, size, or continuity, or the dynamic response characteristics of SpVi cells. It did, however, (1) alter the probability that certain types of somatosensory receptor surfaces would activate local-circuit neurons, and (2) influence the rate of firing of spontaneously active SpVi cells. There was a significant increase in the proportion of vibrissa-sensitive cells with infraorbital RF components, and a concurrent decrease in the proportion of guard-hair-sensitive cells. It therefore appears that 5-HT input to SpVi is necessary for some mechanoreceptive features of the normal functional organization of this area. These functional changes were interesting in that they were opposite to those found following adult ION transection, which increases 5-HT within SpVi. Thus, changes in 5-HT central afference to SpVi that follow ION damage may be responsible for at least one type of functional change observed following this peripheral lesion.

Neonatal infraorbital nerve damage and the development of eating behavior in the rat

It has been previously shown that bilateral infraorbital nerve (ION) transection in adult rats has little effect upon body weight regulation or eating behavior. However, in neonatal mouse, unilateral ION cut produces a profound decrease in body weight, beginning around the time of weaning. To help clarify the role of the ION in the development and sensorimotor control of eating solid food in rodents, the present experiment examined the effects of unilateral, neonatal ION transection in rats, upon body weight regulation and post-weaning eating behaviors. Comparison of normal and lesioned groups of rats, up to postnatal day (PND) 61, revealed no significant difference in mean adjusted (for sex) body weight. In addition, no significant differences were detected between the groups on post-weaning (PND 26 to PND 61) measures of mean adjusted (for weight) food intake, responsiveness to food, biting ability or inefficiency of mandibulation. At the end of the experiment, the effectiveness of the lesion was histologically evaluated. A significant 48.5% mean reduction in the cross-sectional area of the ophthalmic-maxillary portion of the trigeminal ganglion was observed on the lesioned side, relative to the intact side. There appears to be a differential influence of unilateral, neonatal ION cut upon eating in rat and mouse.

Structure-function relationships in rat brainstem subnucleus interpolaris. X. Mechanisms underlying enlarged spared whisker projections after infraorbital nerve injury at birth

Prior studies indicate that the central projections of noninfraorbital vibrissae occupy greater than normal transverse areas in the rat trigeminal brainstem complex after infraorbital nerve section at birth. Here, we assessed the development of this phenomenon and possible underlying mechanisms. Cytochrome oxidase patches representing spared supraorbital (SO) or posteroorbital (PO) whiskers in the trigeminal subnucleus interpolaris (SpVi) were not reliably larger than those on the control side 24 hr after the infraorbital lesion. By 72 hr, SO and PO patches were 91% and 28% larger than those on the control side. Reliable increases were also observed on postnatal day 5 (PND5), PND7, and PND10 for the SO (59%, 65%, 66%) and PO (23%, 44%, 51%) patches. To test the hypothesis that central reorganization reflects the maintenance of peripheral supernumerary axons, myelinated and unmyelinated axons in SO vibrissa follicles were counted at PND0, PND7, PND17, and PND60. A corollary hypothesis, that peripheral regeneration errors result in both SO and surviving infraorbital axons, contributing to central SO patches, was tested with retrograde double-labeling methods. Both hypotheses were rejected. Thus, enlargement of SO patches is not due to either the maintenance of an immature peripheral innervation pattern, or regeneration of infraorbital axons into SO follicles. To determine if the enlargement of SO and PO patches produced by infraorbital nerve section is due to an activity-dependent competitive disadvantage imposed upon infraorbital afferents, TTX or bupivicaine was applied to the intact infraorbital nerve over the first 5-9 postnatal days. Brainstem maps developed normally and SO and PO patch areas were unaffected. Thus, impulse activity-based mechanisms do not appear to contribute to injury-induced patch enlargement. To test the hypothesis that patch enlargement is due to central collateral reorganization, intra-axonal recording and staining methods were applied to control and spared-whisker primary afferents in adult rats. Total bouton or collateral numbers did not differ in SpVi; however, arbor areas were reliably larger in experimental (14,879 +/- 350 microns 2) versus control (5527 +/- 1811 microns 2) fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

Time course of serotonergic afferent plasticity within rat spinal trigeminal nucleus following infraorbital nerve transection

High-performance liquid chromatography with electrochemical detection (HPLC-ED) and immunocytochemistry were used to examine the time course of serotonergic afferent plasticity within trigeminal subnucleus interpolaris (SpVi) following infraorbital nerve (ION) transection in adult rats. Biochemical analysis was also performed in trigeminal subnucleus caudalis (SpVc) to examine the possibility of transient lesion-induced changes in this region. No significant changes in serotonin (5-HT) or 5-hydroxyindoleacetic acid (5-HIAA) concentration, or in density of 5-HT-immunoreactive (5-HTIR) axonal varicosities were observed in either subnucleus on the lesioned side, up to 51 days following ION cut. However, at 76-79 days post-lesion, a significant increase in 5-HT concentration was again demonstrated within SpVi.

Orofacial pain sensitivity in adult rats following neonatal infraorbital nerve transection

A modification of the formalin test was used to assess orofacial pain sensitivity in adult rats that received infraorbital nerve transection at birth. Normal and neonatally lesioned adult animals received an injection of either 5% formalin or saline vehicle into the whiskerpad and the duration of whiskerpad rubbing was observed for 45 min. Normal rats given formalin exhibited the previously reported biphasic pattern of rubbing. Neonatally lesioned rats given formalin did not exhibit this pattern, and were indistinguishable from either of the saline control groups.

Chronic functional consequences of adult infraorbital nerve transection for rat trigeminal subnucleus interpolaris

In adult rats, transection of the infraorbital nerve and subsequent regeneration have been shown to result in altered somatotopic organization and changes in response properties of primary afferents within the trigeminal ganglion. The present study examined how these changes affect the postsynaptic targets of these neurons within subnucleus interpolaris of the trigeminal brainstem. Extracellular recordings were made from 330 cells in normal rats and 424 cells in rats surviving 57-290 days after transection of the infraorbital nerve in adulthood. Adult infraorbital nerve transection resulted in significant functional reorganization within subnucleus interpolaris. Relative to normal rats, the major changes can be summarized as follows: (1) a decrease in the dorsoventral extent of infraorbital representation; (2) a disruption of inter- and intradivisional somatotopic organization; (3) an increase in the proportion of cells with no discernible receptive field; (4) an increase in receptive field size for cells with infraorbital receptive field components; (5) the appearance of a significant proportion of cells with discontinuous receptive fields; (6) an increase in the proportion of cells exhibiting interdivisional convergence; (7) significant changes in the types of receptor surfaces activating local-circuit neurons with infraorbital receptive field components; (8) the appearance of a significant proportion of cells exhibiting convergence of different receptor surfaces; (9) significant changes in the dynamic response characteristics of cells with infraorbital receptive field components; and (10) an increase in the proportion of spontaneously active infraorbital-responsive cells. The changes observed were quite similar to those reported in adult subnucleus interpolaris following neonatal infraorbital nerve transection. The majority of changes observed in both studies can be most parsimoniously explained by alterations of primary afferents. However, central mechanisms may be more likely substrates for others. Regardless of the mechanism, the mature rodent trigeminal system appears capable of considerable functional reorganization following peripheral nerve damage.

Numbers of axons innervating mystacial vibrissa follicles in newborn and adult rats

Electron-microscopic techniques were used to determine the numbers of axons in the deep vibrissal nerves innervating the C1 and C4 follicles in newborn and adult rats. All counts were made from thin sections taken after the nerve had entered the follicle capsule (FC). In newborn animals, the nerves supplying the C1 (n = 10) and C4 (n = 10) follicles contained an average (means +/- standard deviation) of 355.0 +/- 40.0 and 233.9 +/- 19.2 axons, respectively. In the adult animals (n = 10 for C1 and n = 9 for C4), the respective values were 314.4 +/- 26.2 and 233.3 +/- 34.4 axons. There were no significant differences between the values for the counts from the neonates and adults for either follicle (p greater than 0.01, independent t tests). In the vibrissal nerves of neonates, both degenerating axons and occasional growth cones were visible. Such profiles were not observed in the nerves taken from adults.

Trigeminal projections to contralateral dorsal horn originate in midline hairy skin

The present study tested the hypothesis that the trigeminal (V) primary afferent projection to the contralateral dorsal horn originates in midline hairy skin. A prior study (Jacquin et al., 1990) showed that this crossed projection is heaviest to ophthalmic regions of medullary and cervical dorsal horns, and that it does not arise from V ganglion cells that innervate cornea, nasal mucosa, or cerebral dura mater. Here, retrograde double-labeling methods were used to show that many ophthalmic ganglion cells that innervate midline hairy skin via the supraorbital nerve project to the contralateral medullary and upper cervical dorsal horns. Diamidino yellow injections into the right dorsal horn labeled an average of 104 cells in the left V ganglion. Of these contralaterally projecting ganglion cells, an average of 45% were also labeled by horseradish peroxidase (HRP) injections into the left supraorbital nerve, and 25% were also labeled by HRP injections into the midline opthalmic hairy skin. However, only 2% were labeled by HRP injections restricted to left supraorbital vibrissae follicle nerves. Almost all of the double-labeled cells were located in the dorsal one-half of the V ganglion, and they did not differ in size from single-labeled cells. On the basis of these and prior data, we conclude that a high percentage of contralaterally projecting V ganglion cells originate in midline hairy skin. It is also likely that the contralaterally projecting V ganglion cells serve a low-threshold mechanoreceptive function, given the relatively large ganglion cells and axons giving rise to this pathway and their central terminations in dorsal horn laminae III-V.

Biochemical and anatomical consequences of adult infraorbital nerve transection for serotonergic afferents within rat trigeminal subnuclei interpolaris and caudalis

Immunocytochemistry and high-performance liquid chromatography with electrochemical detection (HPLC-ED) were used, more than 76 days after infraorbital nerve (ION) transection, to examine the distribution and density of serotonin-immunoreactive (5-HTIR) axons, as well as serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content, within the infraorbital (IO) regions of subnuclei caudalis (SpVc) and interpolaris (SpVi). In SpVi, increases in 5-HT concentration and in density of 5-HTIR axonal varicosities were observed on the lesioned side. No changes were seen in SpVc.

Topography of the facial musculature within the facial (VII) motor nucleus of the neonatal rat

WGA-HRP, HRP and fluorescent tracers were used to determine the representation of the facial muscles in the facial motor nuclear complex (FMNC) of the newborn rat. Tracer injections of the superficial cervical and anterior mandibular portions of platysma, the orbicularis oculi muscle, the nasolabial musculature and the posterior auricular musculature revealed an adult-like topographic organization across FMNC subnuclei. Tracer delivery to individual vibrissa follicle loci of the whiskerpad also demonstrated an adult-like musculotopic organization within the lateral subnucleus.

Structure-function relationships in the rat brainstem subnucleus interpolaris: VI. Cervical convergence in cells deafferented at birth and a potential primary afferent substrate

Possible substrates for peripheral injury-induced receptive field (RF) changes were assessed in the trigeminal (V) subnucleus interpolaris (SpVi). In adult rats with infraorbital nerve section at birth, 449 cells were studied ipsilateral to the lesion by using electrophysiological methods. Of these, 33 (7.4%) had RFs that included facial vibrissae, guard hairs, and skin, as well as ipsilateral regions normally innervated by cervical primary afferents (ear, neck, shoulder, arm, forepaw). Such non-V convergence was never seen in 373 normal SpVi cells or in 641 V ganglion cells ipsilateral to the lesion. SpVi cells with cervical RFs discharged to V ganglion shocks and their latencies (1.6 +/- 0.7 ms, mean +/- s.d.) did not differ from normal (1.4 +/- 0.5). Most (71%) projected to the thalamus. None were nociceptive-biased, and many had unusually discontinuous RFs (48%). Possible pathways by which cervical inputs might reach SpVi neurons were investigated in additional anatomical and electrophysiological experiments. Eight SpVi cells with cervical RFs were intracellularly labeled with HRP. Although all had dendrites that were polarized toward SpVi regions containing spared mandibular and/or ophthalmic primary afferents, none had dendrites which extended out of SpVi. In other neonatally nerve-damaged adults, WGA-HRP was injected bilaterally into forepaw, arm, and shoulder regions. Transganglionic transport was restricted to normal targets. However, WGA-HRP injections into SpVi retrogradely labeled a total of 46 +/- 20 (mean +/- s.d.) cells in ipsilateral C1-3 dorsal root ganglia, and 24 +/- 8 cells in C4-8 ganglia. In controls, labeled cells were seen only in C1-3 ganglia (32 +/- 9). The distribution and number of labeled cells in the somatosensory cortex did not differ in experimental and control cases. No labeled cells were visible in the dorsal column nuclei of either the normal or experimental rats. Thus, retrograde labeling studies suggest that a cervical primary afferent projection to SpVi is a potential substrate for cervical convergence expressed in neonatally deafferented SpVi cells.

Physiological and anatomical consequences of infraorbital nerve transection in the trigeminal ganglion and trigeminal spinal tract of the adult rat

Single-unit recording and retrograde tracing techniques were used to assess the receptive field properties, topography, and projections of rat trigeminal primary afferent neurons subsequent to transection of the infraorbital (IO) nerve in adulthood. Four hundred and fifty-eight units were recorded in the trigeminal ganglion ipsilateral to nerve section. Of these, 66.6% had IO receptive fields. Thirty percent responded to innocuous stimulation of vibrissae, 39.1% to guard hair deflection, 8.2% to gentle indentation or stretch of the skin, and 22.3% to noxious stimuli (compared to 77.2% vibrissa, 12.0% guard hair, 4.5% skin, and 6.3% noxious in normal animals). An additional 15 units were driven by a stimulating electrode placed on the IO nerve proximal to the site of the lesion but had no receptive field. Of the cells with vibrissa receptive fields, 33.3% were slowly adapting type I (SAI), 6.6% were slowly adapting type II (SAII), 32.2% were low velocity rapidly adapting (RA-LV), 20.0% were high velocity rapidly adapting (RA-HV), and 7.7% were nociceptive (NX, in normal animals 43.8% were SAI, 10.3% SAII, 27.6% RA-LV, 16.8% RA-HV, and 1.5% NX). A number of cells had receptive field properties not seen in normal animals. The single-unit recordings indicated that the topography of mandibular and ophthalmic representations in the ganglion were essentially normal, while the organization of the maxillary region of the ganglion was slightly abnormal. The ganglion physiology experiments were augmented by records from primary afferents in the trigeminal spinal tract (TrV). Eighty-one (72.2%) of the 112 fibers recorded in the TrV of normal rats had IO receptive fields. Of these, 73.2% responded to innocuous vibrissal stimulation, 14.6% to guard hair deflection, 8.5% to gentle indentation of the skin, and 2.5% to noxious stimuli. Of the 61 vibrissa units, 37.8% were SAI, 19.7% SAII, 37.8% RA-LV, 3.3% RA-HV, and 1.6% NX. In adult-lesioned animals, 81 (61.3%) of the recorded fibers had IO receptive fields. Of this number, 38.2% responded to vibrissae, 29.6% to guard hairs, 16.0% to skin, and 19.7% to noxious simuli. Of the vibrissa-sensitive units, 16.1% were SAI, 3.2% were SAII, 45.2% were RA-LV, 35.5% were RA-HV, and 3.2% NX. As in the ganglion recording studies, a number of abnormal receptive fields were documented.(ABSTRACT TRUNCATED AT 400 WORDS)

Anatomical consequences of neonatal infraorbital nerve transection upon the trigeminal ganglion and vibrissa follicle nerves in the adult rat

A large body of experimental literature has demonstrated that neonatal infraorbital nerve damage in rodents produces anatomical and/or functional alterations of the normal whisker representation in central trigeminal structures. Less is known about the organization of primary afferent components of the trigeminal system following this manipulation. Such information provides an important basis for interpreting the central changes observed following damage of infraorbital nerve fibers at birth. We have therefore examined the composition and order of peripheral innervation in the pathway from the trigeminal ganglion to the vibrissa follicles in adult rats subjected to unilateral neonatal infraorbital nerve transection. Electron microscopy was used to determine the number and diameter of myelinated and unmyelinated fibers in vibrissa follicle nerves of these animals. Wheat germ agglutinin-horseradish peroxidase and fluorescent retrograde tracers were employed to examine the number and diameter, as well as the topographic organization and branching, of ganglion cells innervating the vibrissae in these rats. The data presented below indicate that neonatal infraorbital nerve transection has the following consequences within the adult trigeminal nerve and ganglion: 1) an alteration of the gross morphology of vibrissal nerves, 2) a significant reduction in the average number (85.4%) and diameter (32.6%) of myelinated, but not unmyelinated, follicle nerve axons, 3) a significant decrease in the average number (36.8%) of trigeminal ganglion cells innervating vibrissa follicles, 4) no significant change in the distribution of ganglion cell diameters, 5) an increase in peripheral branching (1.8-fold) of these ganglion cell axons, and 6) an alteration of somatotopic order within the trigeminal ganglion. Taken together, these data indicate that neonatal infraorbital nerve transection produces a profound reorganization of the primary afferent component of the trigeminal neuraxis.

Renewed growth of identified brainstem axons into fetal cortical transplants in adult rat

Transplantation of fetal neocortex into the site of trigeminal brainstem injury induces regeneration of trigeminal primary afferent axons in adult rats. Renewed growth of injured primary afferent fibers into donor cortex can be extensive, though the innervation pattern does not resemble that normally seen in either brainstem or somatosensory cortex. Examination of the structural and functional characteristics of individual regenerate axon collaterals suggests that their morphology is determined by both intrinsic and postsynaptic target factors. Marked topographic alterations, however, question the utility of fetal cortical transplantation procedures in effecting functional recovery from brainstem injury.

Effects of altered visual input upon the development of the visual and somatosensory representations in the hamster's superior colliculus

The right superior colliculus and right eye were ablated in hamsters within 12 h of birth and the visual and somatosensory representations in the remaining (left) superior colliculus were evaluated using standard single unit recording and receptive field mapping techniques when the animals reached adulthood (at least 3 months of age). In a number of the hamsters used for recording, injections of [3H]leucine were made into the left eye 6-10 days prior to the terminal experiment. This was done to insure that the neonatal lesions did, in fact, produce the extensive recrossing of retinal fibers demonstrated by others who have employed this preparation. All of the hamsters which received [3H]leucine injections prior to the recording experiment exhibited a markedly expanded ipsilateral retinocollicular projection and retinal axons which recrossed the midline at the level of the tectum. The recording experiments showed further that this projection resulted in a visual map which was generally mirror symmetric to that in normal hamsters. There were, however, numerous irregularities and discontinuities in this representation and, in a few hamsters, it appeared almost completely disorganized. There were also a number of abnormalities in the somatosensory representation in the deep tectal laminae of the neonatally brain damaged hamsters. There was a substantial increase in the number of cells with receptive fields that extended onto the ipsilateral side of the body, neurons with split receptive fields were recorded and there were changes in the magnification of different portions of the body surface. These alterations did not, however, change the organization of the somatosensory map in a manner which brought it into alignment with the visual representation in the superficial laminae. Nevertheless, additional recording experiments in animals subjected to enucleation of both eyes and ablation of the superficial laminae of one superior colliculus did indicate that the existence of the aberrant retinal projection was a necessary condition for the somatosensory abnormalities which we observed. Additional anterograde and retrograde tracing experiments demonstrated only one abnormality in the organization of the somatosensory afferent input to the remaining colliculus. In 75% of the brain damaged hamsters, there was a weak crossed projection from the sensorimotor cortex that was never observed in normal animals. Ablation of this cortex at the time of the recording experiment did not, however, reduce the incidence of abnormal somatosensory receptive fields in these hamsters.

The structural and functional characteristics of tectospinal neurons in the golden hamster

Intracellular recording and horseradish peroxidase (HRP) injection techniques were used to delineate the structural and functional characteristics of the superior collicular cells in the hamster, which could be antidromically activated from the first cervical segment of the spinal cord. Thirty-one such neurons were characterized, filled with HRP, and recovered. Complete physiological data were obtained from another 21 tectospinal cells for which anatomical data were sufficient only to define the laminar location of the cell body from which recordings were made. Of the total sample of 52 cells, 7.7% had their somata in the stratum griseum intermediale (SGI), 50% were in the stratum album intermedium (SAI), 36.5% were in the stratum griseum profundum (SGP), and 5.8% were in the stratum album profundum (SAP). The tectospinal cells were fairly uniform morphologically. They had large (27.7 +/- 5.5 microns diameter) cell bodies, which gave rise to an average of 6.7 +/- 1.2 primary dendrites. These were generally smooth and extended up to 500 microns away from the cell body. In many cases, they ascended out of the deep laminae into the stratum opticum (SO) and/or stratum griseum superficiale (SGS). The axons of TS cells averaged 3.4 +/- 0.8 microns in diameter, and they generally coursed radially to the SAP where they curved around the periaqueductal gray and entered the predorsal bundle. These axons often gave rise to collaterals that arborized in the deep laminae of the ipsilateral superior colliculus and subjacent reticular formation. The tectospinal cells were also fairly uniform physiologically. Their average conduction latency was 2.0 +/- 2.3 ms, and this variable had a strong negative correlation (-.81) with axon diameter for the recovered cells. Most (63.5%) of the TS cells were exclusively somatosensory and gave rapidly adapting responses to deflection of vibrissae and/or guard hairs; 7.7% were bimodal (visual-somatosensory); 11.5% had complex (Rhoades et al., '83) somatosensory receptive fields; 1.9% were discharged only by a noxious pinch, and 15.4% were unresponsive. A common feature of all bimodal tectospinal neurons was dendrites that extended at least as far dorsally as the SO. Whereas there were no other clear-cut correlations between the structural and functional characteristics of these tectal neurons, we did note that all of the cells with complex somatosensory receptive fields received inhibitory input from axons that either originated from, or passed through, the contralateral superior colliculus.

Reorganization of the peripheral projections of the trigeminal ganglion following neonatal transection of the infraorbital nerve

Two different anatomical techniques were used to obtain evidence that transection of the infraorbital (IO) nerve on the day of birth would result in reorganization of the peripheral projections of the trigeminal nerve. In 14 of 19 neonatally nerve-damaged adult rats, injection of horseradish peroxidase (HRP) directly into the IO nerve, proximal to the point of the neonatal transection, resulted in labeled cells in the ophthalmic-maxillary portion of the ganglion and labeled fibers in mandibular sensory nerves. In an additional 28 neonatally nerve-damaged adult rats, double-labeling techniques were employed to document the reorganization suggested by the HRP tracing experiments. In these experiments, one fluorescent tracer, diamidino yellow (DY), was injected directly into the regenerate IO nerve, proximal to the point of the neonatal transection; a second tracer, true blue (TB), was deposited into peripheral ophthalmic and/or mandibular fields. These combinations of injections invariably resulted in the demonstration of a small number (46-401) of double-labeled cells that were located in the ophthalmic-maxillary part of the ganglion. Identical combinations of injections in normal adult rats and the intact sides of nerve-damaged animals never produced more than 6 double-labeled cells per ganglion. In two additional series of experiments, sequential double-labeling techniques were employed to demonstrate that the multiply projecting ganglion cells probably arose in at least two ways: (1) development of non-IO projections by ganglion cells that contributed axons to the IO nerve at the time of the lesion; (2) elaboration of IO axon branches by primary afferent neurons that had non-IO projections at the time of the lesion. A final two-stage double-labeling experiment demonstrated that approximately 75% of the ganglion cells that projected to the whisker pad at birth, and survived transection of the IO nerve on the first postnatal day, regenerated axons into this trigeminal branch.

Functional consequences of neonatal infraorbital nerve section in rat trigeminal ganglion

Standard single-unit recording and stimulation techniques were used to assess the topographic organization, receptive field properties, and projections of cells (n = 297) in the ophthalmic-maxillary part of the trigeminal ganglion in 6 normal adult rats and 15 adults with unilateral infraorbital nerve section at birth (cells recorded ipsilateral to lesion: n = 641; cells recorded on the intact side: n = 223). Stimulating electrodes were placed on the central portion of the regenerate infraorbital nerve and in the trigeminal brain stem subnucleus caudalis in 6 nerve-damaged rats and at equivalent points in 5 normal animals. Data from the normal rats and the intact side of the nerve-damaged animals were identical and were considered together. Of these cells, 73.5% had infraorbital receptive fields. Of these, 77.2% were discharged by vibrissa stimulation (43.8% slow-adapt type I, 10.3% slow-adapt type II, 27.6% low-velocity sensitive rapid adapt, 16.8% high-velocity sensitive rapid adapt, and 1.5% noxious-biased), while the rest responded best to guard hair deflection (12.0%), gentle skin indentation (4.5%), or a strong pinch or deep pressure (6.3%). In stereotaxically matched penetrations in ganglia ipsilateral to the neonatal infraorbital nerve lesions, only 40.6% of the cells had infraorbital receptive fields. Of these, only 37.7% responded to vibrissa stimulation (29.8% slow-adapt type I, 1.2% slow-adapt type II, 2.2% low-velocity sensitive rapid adapt, 32.9% high-velocity sensitive rapid adapt, 33.9% noxious). Other infraorbital cells responded best to guard hair deflection (11.9%), gentle skin indentation (10.8%), or a strong pinch or deep pressure (39.6%). An additional 30 cells did not have a detectable receptive field and were identified only by infraorbital and brain-stem shocks. We also recorded cells with unusual infraorbital receptive fields: 9 units responded to more than 1 vibrissa, 4 were activated by both vibrissa and guard hair deflection, 10 had unusually large skin or deep receptive fields, 1 had a split receptive field, and 7 were discharged only by deep pressure to the region of the nerve section. Seven cells with infraorbital receptive fields were not driven by infraorbital shocks, and 2 were not activated by brain-stem shocks. In normal rats, all cells with infraorbital receptive fields were driven by both electrodes. The percentages of receptive field types for noninfraorbital cells were unchanged in ganglia ipsilateral to the damaged nerve.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural and functional characteristics of commissural neurons in the superior colliculus of the hamster

Intracellular recording and horseradish peroxidase (HRP) injection techniques were employed to delineate the structural and functional properties of superior collicular (SC) neurons in the hamster that were antidromically activated by electrical stimulation of the contralateral tectum. A total of 39 such cells were completely characterized, injected, and recovered. In ten of these, the axonal filling allowed us to reconstruct at least a portion of the terminal arborization in the SC contralateral to the labelled cell. Two of the recovered neurons were located in the stratum griseum superficiale (SGS), three were in the stratum opticum (SO), ten were in the stratum griseum intermediale (SGI), 11 were in the stratum album intermedium (SAI), 11 were in the stratum griseum profundum (SGP) and two were located in the stratum album profundum (SAP). The recovered cells were highly varied in both their morphological and their physiological characteristics. Somal areas ranged between 74 microns2 and 364 microns2, and the sample of recovered neurons included horizontal cells, narrow field vertical cells, and a variety of other multipolar neurons. Over one-third (38.5%) of the recovered cells were unresponsive, 2.6% were exclusively visual, 33.3% responded only to innocuous cutaneous stimuli, 10.2% were bimodal, 7.7% were specifically nociceptive, and 7.7% had complex (Rhoades, Mooney, and Jacquin: J. Neurosci. 3:1342-1354, '83) somatosensory receptive fields. We observed no clear-cut correlations between the structural and functional characteristics of these neurons. The conduction latencies of the commissural SC neurons ranged between 0.8 and 14.0 ms. The most rapidly conducting cells were located in the SGP and SAP. Conduction latency had a significant negative correlation with soma area. Labelled axons, in many cases, had at least one terminal arbor in a portion of the SC that was mirror symmetric with the location of the cell from which it originated. In several cases, however, commissural axons gave off a number of collaterals across the mediolateral extent of the tectum. commissural axonal terminations were visible only in the laminae ventral to the SO. Several commissural SC neurons also had extensive ipsilateral axon collaterals. Both the ipsilateral and commissural axon branches of these cells gave off en passant and terminal swellings.

Topographic organization of peripheral trigeminal ganglionic projections in newborn rats

Retrograde transport of fluorescent tracers (true blue and diamidino yellow) was employed to delineate the topography of the peripheral projections of trigeminal ganglion cells in newborn (less than 12 h of age) rats. Identical injections were made in adult animals for comparison. In neonates, both inter- and intradivisional topography of ganglionic projections were adult-like. Neurons which innervated mandibular fields were located posterolaterally while cells with ophthalmic or maxillary projections were restricted to the anteromedial and central parts of the ganglion, respectively. An adult-like topographic representation of the mystacial vibrissae follicles was also evident in the neonates.

The structural and functional characteristics of striate cortical neurons that innervate the superior colliculus and lateral posterior nucleus in hamster

Intracellular recording and horseradish peroxidase injection techniques were used to structurally and functionally characterize the striate cortical neurons in hamster that projected to the superior colliculus and/or lateral posterior nucleus of the thalamus. With two exceptions, the receptive field properties and morphological characteristics of the neurons antidromically activated from the colliculus and lateral posterior nucleus were quite similar. Striate corticotectal and striate cortico-lateral posterior neurons generally had non-oriented receptive fields which gave either "on-off' or no responses to flashed stimuli. Only a small number (less than 5%) were orientation selective, but about one-third were directionally selective. Most of the cells preferred movement with an upward component. Most striate corticotectal and cortico-lateral posterior cells responded to a wide range of stimulus velocities and exhibited little spatial summation. With the possible exception of two cells, all the projection neurons we recovered were large lamina V pyramidal cells whose apical dendrites extended to and branched extensively in layer I. All had extensive (in some cases over 1 mm) tangential axon collaterals, primarily in layers V and/or VI. The electrophysiological experiments also demonstrated that some (50% of a sample of 20 cells) corticotectal neurons also sent an axon collateral to the lateral posterior nucleus. Finally, our recordings showed that many (56% of a sample of 27 neurons) cells which could be antidromically activated from the lateral posterior nucleus, but not the superior colliculus had response latencies which exceeded those of almost all the cells which could be antidromically activated from the tectum. Retrograde transport of diamidino yellow and true blue confirmed the electrophysiological result that individual cortical neurons projected to both the superior colliculus and lateral posterior nucleus. These experiments showed that 20% of the striate cortical cells that projected into colliculus also sent an axon collateral to the lateral posterior nucleus.

Grasping in the pigeon (Columba livia): final common path mechanisms

A combination of cinematographic and denervation procedures were used to analyse the mechanisms involved in the adjustment of gape size during grasping in the pigeon. Gape size was found to vary directly with seed size and to reflect the operation of two variables, jaw opening velocity and jaw opening duration. Effects upon duration are mediated, indirectly, by the effect of seed size upon head height, which, in turn, controls the velocity of head descent. The data suggest that the control of gape during grasping may involve two different effector systems (jaw muscles, neck muscles). Analysis of the displacement of individual jaws (maxilla, mandible) during grasping indicates that both opener muscles take part in the control of gape. Denervation experiments (motor nerve section) identified these opener motoneurons as contributors to the final common path for the opening phase of grasping. A comparison of the kinematics of pecking/grasping in pigeons and reaching/grasping in humans reveals a number of similarities in the topography and spatiotemporal organization of these behaviors.

Correlations between the structural and functional characteristics of neurons in the superficial laminae and the hamster's superior colliculus

Intracellular recording, receptive field mapping, and horseradish peroxidase (HRP) injection techniques were used to determine the structural and functional characteristics of neurons in the superficial laminae (stratum griseum superficiale and stratum opticum) of the hamster's superior colliculus (SC). Fifty-nine neurons (from 38 different hamsters) were successfully characterized, injected with HRP, and recovered. Of these, 8 were marginal cells, 14 had stellate morphology, 10 had narrow, vertically oriented dendritic trees, 12 had wide, vertically oriented dendritic arbors, and 8 were horizontal cells. Seven neurons had somatodendritic morphologies which did not fall into any of these groups. Overall, the distribution of receptive field properties for these cells matched that obtained in previous extracellular recordings from the superficial SC laminae in this species (Chalupa, L.M., and R.W. Rhoades (1977) J. Physiol. (Lond.) 270: 595-626; Chalupa, L.M. and R.W. Rhoades (1978) J. Physiol. (Lond.) 274: 571-592). There were significant correlations between receptive field properties and morphology. Sixty-four percent of the stellate cells and 75% of the marginal cells were directionally selective. Only 17% of the other cell types exhibited this response property. In addition, only 36% of the stellate cells and 25% of the marginal neurons were discharged by stationary, flashed spots. Eighty-one percent of the other recovered cells gave reliable responses to such stimuli. Stellate and marginal cells could also be differentiated from the other cell types on the basis of speed selectivity. Only 29% of the stellate and 13% of the marginal cells responded to stimulus speeds in excess of 20 degrees/sec.(ABSTRACT TRUNCATED AT 250 WORDS)

Extensive recrossing of retinotectal axons after neonatal unilateral superior collicular lesions in hamster

Anterograde transport methods were used to examine the ipsilateral retinocollicular projections of adult hamsters subjected to ablation of one superior colliculus (SC) on the day of birth. In many of these animals ipsilateral retino-SC axons were not limited to the medial part of the remaining tectum as previously reported but encompassed the entire rostrocaudal and mediolateral extents of this SC. A common pattern was the existence of a dense patch of label contiguous with the midline, a more lateral region of diffuse labeling, a second dense lateral patch and diffuse labeling which extended to the lateral boundary of the tectum. The dense patches of label were usually aligned into rostrocaudally oriented bands. Additional experiments in which one optic tract was sectioned a week prior to the eye injection showed that the reorganization was primarily due to axons which recrossed the midline at the level of the midbrain. However, the uncrossed retinotectal projection was also abnormally dense in the animals subjected to neonatal SC lesions. Dense patches of label in the caudal half of the tectum were only observed when recrossing fibers were labeled. In a final set of experiments, both the ipsilateral and contralateral projections were labeled with different tracers in individual hamsters. These experiments showed a clear tendency for fibers from the two eyes to segregate in the remaining SC. This segregation was, however, incomplete, even in regions where labeling from each eye was quite dense.

Representation of whisker follicle intrinsic musculature in the facial motor nucleus of the rat

Retrograde transport of wheatgerm-agglutinin horseradish peroxidase (WGA-HRP) and fluorescent tracers (true blue-TB, nuclear yellow-NY, and diamidino yellow-DY) from isolated whisker follicles was used to define the somatotopic organization of the facial (VII) motoneurons which innervate the intrinsic follicle muscles. Motoneurons supplying these muscles were restricted almost completely to the lateral (Martin and Lodge, '77) facial subnucleus and the motoneurons which innervated a given follicle were distributed over the entire length of this subnucleus. Cells projecting to dorsal (A-row) follicles were located in the most lateral part of the lateral subnucleus, while those supplying ventral (E-row) follicles were restricted to the medial part of the subnucleus. Injections of different tracers into rostral and caudal follicles within a given row revealed no somatotopic representation of the rostrocaudal axis of the whiskerpad. Additional control experiments demonstrated that some of the labelling obtained with WGA-HRP resulted from spread of this tracer to extrinsic muscles. This was not the case with the fluorescent tracers. The results of the control experiments suggested further that a significant percentage of the motoneurons in the lateral facial subnucleus innervate only intrinsic follicle muscles.

Dendrites of deep layer, somatosensory superior collicular neurons extend into the superficial laminae

Intracellular recording and horseradish peroxidase (HRP) injection techniques were used to delineate the structural and functional properties of superior collicular (SC) neurons in hamsters. Of 34 cells recovered from the deep laminae (those ventral to the stratum opticum--SO), 26 were exclusively somatosensory and 10 of these extended dendrites into the superficial layers, the stratum griseum superficiale (SGS) and SO. In 2 instances, dendrites extended only to the SO, but in 8 others they reached the SGS. Three of the latter cells had dendrites which terminated just beneath the pial surface. These findings show that an anatomical substrate for communication from superficial to deep layer cells exists in the hamster SC, but that such communication may not necessarily be reflected in the response of deep layer neurons.

Afferents to the trigeminal and facial motor nuclei in pigeon (Columba livia L.): central connections of jaw motoneurons

Trigeminal and facial motor nuclei innervating the pigeon's jaw muscles were identified using a combination of microstimulation and EMG recording and HRP injections were made iontophoretically. The trigeminal motor nucleus receives an ipsilateral projection from sensory neurons in the trigeminal mesencephalic nucleus which forms the afferent limb of the monosynaptic stretch reflex of the jaw-closers. Both the trigeminal and facial motor nuclei receive bilateral projections from interneurons in the intertrigeminal area and the lateral (parvocellular) reticular formation of the pons and medulla. These neurons serve as premotor elements in the control of jaw movements, mediating ascending, descending and internuclear connections. The similarity of inputs to the trigeminal and facial nuclei may reflect their common function as jaw motoneurons in this species.