PubMed Health⌕ Search

Biomedical subjects

P O Gerrits

Publications and source records attributed to P O Gerrits.

At least 19 recordsLinked to original sources
PubMed2000

Retroambiguus projections to the cutaneus trunci motoneurons may form a pathway in the central control of mating.

Our laboratory has proposed that the nucleus retroambiguus (NRA) generates the specific motor performance displayed by female cats during mating and that it uses direct pathways to the motoneurons of the lower limb muscles involved in this activity. In the hamster a similar NRA-projection system could generate the typical female mating posture, which is characterized by lordosis of the back as well as elevation of the tail. The present study attempted to determine whether this elevation of the tail is also part of the NRA-mating control system. The basic assumption was that elevation of the tail is a function of the cutaneous trunci muscle (CTM), which was verified by bilateral tetanic stimulation of the lateral thoracic nerves innervating the CTM. It resulted in upward movement of the tail to a position similar to the tail-up position during the lordosis posture. Retrograde tracing results showed that CTM motoneurons are located in the ventral and ventrolateral part of the C(7)-C(8) ventral horn, those innervating the tail region ventrolateral to those innervating the axillary region. Anterograde tracing studies showed that NRA fibers terminate bilaterally in both parts of the CTM motoneuronal cell groups. Electron microscopical studies revealed that labeled NRA terminals make monosynaptic contacts with retrogradely labeled dendrites of CTM motoneurons. Almost all of these terminal profiles had asymmetric synapses and contained spherical vesicles, which suggests an excitatory function. The observation that 15% of the labeled NRA terminals make more than one synaptic contact with a retrogradely labeled CTM motoneuronal dendrite within the same section indicates how powerful the NRA-CTM projection is. The results indicate that during mating the NRA not only could generate the lordosis posture but also the elevation of the tail.

Animals↗
PubMed1999

Estrogen receptor-alpha-immunoreactive neurons in the mesencephalon, pons and medulla oblongata of the female golden hamster.

Recent studies have revealed brainstem-spinal pathways involved in the generation of receptive behavior in hamster and cat, and the enormous influence of estrogen on these pathways. The present study gives an overview of the location of estrogen receptor-alpha-immunoreactive neurons (ER-alpha-IR) in the brainstem of the female hamster. In the mesencephalon, ER-alpha-IR cells were found in the arcuate and peripeduncular nuclei as well as throughout the rostrocaudal extent of the periaqueductal gray (PAG), and the laterally adjoining tegmentum. In the caudal brainstem, groups of ER-alpha-IR cells were present in the ventrolateral parabrachial nucleus, the solitary nucleus, and in contrast to the cat, in the nucleus retroambiguus. No ER-alpha-IR cells were found in any other part of the brainstem. The functional implications of these findings are discussed.

Animals↗
PubMed1999

[Characteristics of pedigree cat breeding in the Netherlands: breeds, population increase and litter size].

A survey of the Dutch Cat Fancy was carried out to determine reproductive, patterns of pedigree cats. The data of the present study were obtained by questioning the pedigree registers of the cat clubs participating in the foundation 'Overleg Platform van de Nederlandse Cat Fancy'. The Dutch Cat Fancy registers 34 different cat breeds. From 1992 up to 1996 a total of 25.985 litters were registered. Over this period the number of litters increased from 4989 to 5313. Litters from Longhair and Exotic Shorthair cats comprised the biggest group and accounted for 55% of the total number of litters. However, over this period, the number of Longhair and Exotic Shorthair litters decreased by 9%. Litters from British Shorthair, Birman, Maine Coon and Norwegian Forrest Cat increased in number as did litters from small breeds such as Ragdoll, Bengal and Sphynx. Litters from Abyssinian, Siamese, Oriental Shorthair cats remained relatively the same. The average litter size of the total cat population, based on pedigree certificates, was calculated at 3.3 kittens per litter. For different breeds litter size varied from 2.7 (Longhair and Exotic Shorthair) to 4.3 (Burmese and Maine Coon). Taking into account an average age of 14 years, the total Dutch pedigree cat population was estimated at 240,000 viz. about 10% of the total cat population.

Animals↗
PubMed1999

Descending projections from the nucleus retroambiguus to the iliopsoas motoneuronal cell groups in the female golden hamster: possible role in reproductive behavior.

In the cat, the nucleus retroambiguus (NRA) projects to expiratory motoneurons in the brainstem and spinal cord. Recently, it has been demonstrated that the NRA sends fibers to a specific set of motoneurons in the lumbosacral cord, which pathway is thought to play a crucial role in mating behavior. The question is whether such projections exist in the hamster, because the female of this species displays a very distinctive receptive behavior. In the hamster, lumbosacral cord injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) combined with hemisection 1 or 2 segments rostral to injection sites in three of the five cases demonstrated retrogradely labeled neurons in the NRA at levels 1.0-2.25 mm caudal to the obex, contralateral to the injection sites. Injections of WGA-HRP into the NRA and adjoining reticular formation revealed that NRA fibers crossed the midline in the caudal medulla and descended in the contralateral lateral and ventrolateral funiculi to terminate bilaterally, but mainly contralaterally, in the motoneuronal cell groups of the abdominal wall and iliopsoas muscles. NRA projections to levels caudal to lumbar segment 5 were virtually absent. Electron microscopic examination revealed that, of the 162 labeled NRA terminal profiles found in the ultrathin sections, 144 (89%) made monosynaptic contacts with retrogradely labeled dendrites of iliopsoas motoneurons. These NRA terminals formed asymmetrical synapses and contained spherical vesicles indicative of an excitatory function. The results indicate that, in the hamster, direct contralateral NRA projections exist to iliopsoas motoneurons. A concept is discussed in which this pathway plays a crucial role in mating behavior.

Animals↗
PubMed1998

[Organization of the Dutch Cat Fancy].

The present study of the foundation 'Overleg Platform van de Nederlandse Cat Fancy' describes the organization and structure of the Dutch Cat Fancy, and is subdivided into three parts. The first part presents a survey of the number of cat clubs, date of their establishment, number of members, associated breed clubs and participation in the foundation 'Overleg Platform van de Nederlandse Cat Fancy'. The second part describes the basic organization of Dutch cat clubs, including their membership, cattery registration, breed registration, exhibitions and judges, cat magazines, health care and welfare, and breed clubs. The third part focuses attention on other organizational forms such as clubs for a particular breed, seen within the Dutch Cat Fancy.

Animal Welfare↗
PubMed1997

The lumbar cord location of the motoneurons innervating psoas and iliacus muscles: a single and double labeling study in the female Syrian golden hamster.

The spinal cord location of the motoneurons innervating the psoas and iliacus muscles was determined in the golden hamster. The results of single and double labeling studies, using the retrograde tracers horseradish peroxidase (HRP) and cholera toxin B-subunit (CTB), showed that both psoas and iliacus motoneurons were present ventrolaterally in the ventral horn in the caudal L1 to rostral L5 lumbar spinal segments with their motoneurons intermingled in one cell group. Further retrograde tracing studies demonstrated abdominal muscle motoneurons ventrolaterally in the ventral horn of the L1 and upper L2 segments. Double labeling experiments revealed that at these levels (caudal L1 and rostral L2), the abdominal muscle motoneurons were located dorsomedial to the psoas and iliacus motoneurons.

Abdominal Muscles↗
PubMed1997

Motoneuronal location of the external urethral and anal sphincters: a single and double labeling study in the male and female golden hamster.

The location of external urethral (EUS) and anal sphincter (EAS) motoneurons was investigated in the golden hamster using the retrograde tracers horseradish peroxidase and cholera toxin B-subunit. Single and double labeling studies revealed that the motoneurons of the EUS and EAS were present in the same nucleus (nucleus of Onuf) ventrolaterally in the ventral horn of the caudal first sacral segment and throughout the second sacral segment. Within Onuf's nucleus the EAS motoneurons were located dorsomedial to the EUS motoneurons, which were located at the border of the gray and white matter. This location is similar to that in cat, dog, monkey and man, but differs from that in rat, Mongolian gerbil and domestic pig.

Anal Canal↗
PubMed1996

Pontine and medullary projections to the nucleus retroambiguus: a wheat germ agglutinin-horseradish peroxidase and autoradiographic tracing study in the cat.

The nucleus retroambiguus (NRA) in the caudal medulla oblongata plays a role in expiration, vocalization, vomiting, and possibly lordosis. The present study tried to determine which structures, in turn, control the NRA. One cell group is the periaqueductal gray (PAG), which is considered to be the final integrator of defensive and aggressive behaviors, micturition, vocalization, and lordosis. Structures rostral to the PAG seem to bypass the NRA. With respect to the existence of cell groups caudal to the PAG projecting to the NRA, the situation is less clear. Therefore, in five adult female cats, injections of wheat germ agglutinin-horseradish peroxidase were centered on the NRA, and the resulting retrogradely labeled neurons were plotted. In the areas containing retrogradely labeled cells, the anterograde autoradiographic tracer [3H]-leucine was injected in 66 cats. The combined results demonstrated that NRA afferents not only originate from the PAG but also from specific cell groups in the pontine and medullary lateral tegmental field, i.e., the ventrolateral parabrachial nucleus, the nucleus Kölliker-Fuse, the retrotrapezoid nucleus, and the ventrolateral part of the medulla caudal to the facial nucleus including the Bötzinger and pre-Bötzinger complex and the periambigual region. Afferents also originate from the solitary nucleus and two cell groups in the ventral part of the medullary medial tegmental field, one at the level of facial nucleus and one just rostral to the hypoglossal nucleus. It can be concluded that many respiratory-related cell groups have direct access to the NRA. The cell groups in the medial tegmental field, which have not yet been found to play an important role in respiration, might serve as relay for certain limbic system cell groups to reach the NRA in the context of specific emotional behavior.

Afferent Pathways↗
PubMed1996

The effect of gonadectomy on the clinical course of chronic experimental allergic encephalomyelitis.

Experimental allergic encephalomyelitis (EAE) is an animal model for the human neurological disease multiple sclerosis (MS). Upon immunization with guinea pig spinal cord under a low dose of Cyclosporin A, male Lewis rats develop a severe chronic (relapsing) course of EAE (CR-EAE). By contrast, female Lewis rats develop a more mitigated course of EAE: only half of the female rats develop relapses. To further analyze factors determining this sexual dimorphism in the course of EAE, in the present study male and female Lewis rats were gonadectomized before induction of CR-EAE. Now both male and female rats all developed a severe chronic course of EAE, showing extensive pathological changes in the CNS. In the female sham-gonadectomy (control) group only one third of the rats developed relapses. These female rats only showed mild pathological changes in the CNS. In the male sham-gonadectomy (control) group all rats developed relapses of EAE and showed extensive pathological changes in the CNS. From these data we conclude that the presence of the ovaries (partially) protects female rats against relapses of EAE and CNS injury. Presence or absence of the testes apparently makes no difference on the course of EAE. We propose that sex hormones produced in the ovaries protect female rats against relapses of EAE and underlying CNS injury.

Animals↗
PubMed1995

Glycol methacrylate embedding of alginate-polylysine microencapsulated pancreatic islets.

A method for processing and embedding alginate-polylysine microencapsulated pancreatic tissue in glycol methacrylate resin (GMA) is described. Fixation in 4% phosphate buffered formaldehyde, processing in ascending concentrations of glycol methacrylate monomer and embedding in Technovit 7100 results in well preserved morphological details of hydrogels, hydrogel-cell interfaces, and encapsulated pancreatic tissue. Routine staining with Loeffler's methylene blue, hematoxylin and eosin, and Romanovsky-Giemsa gave excellent images of the GMA embedded alginate polylysine membrane and tissues allowing cells on the outside of the capsule to be analyzed effectively as part of the foreign body reaction against the capsule membrane.

Alginates↗
PubMed1995

Effects of storing initiated 2-hydroxyethyl methacrylate solutions for embedding tissues for light microscopy: some practical implications.

The effects of storing 2-hydroxyethyl methacrylate (HEMA) solutions for embedding tissues for light microscopy were studied using three commercially available HEMA embedding kits: Technovit 7100, Technovit 8100, and JB-4. These HEMA solutions were examined at various times of storage over a period of one year using a panel of physicochemical techniques including gas chromatography, titration, viscosimetry, determination of the maximum polymerization temperature and the time required to reach the maximum temperature, and detection of degradation products of HEMA monomers by histochemical procedures. The quality of the resin blocks was examined by the observation of mini-folds in sections. Data obtained from these tests showed that the release of by-products as a result of the degradation of the HEMA monomer during storage of HEMA solutions does not occur. Development of cross-linking agents by transesterification of HEMA monomer was not detected either. Gradual decrease of the inhibitor concentration during storage proved to be the main cause of the reduction of shelf-life of HEMA solutions. Inconsistent tissue infiltration after storage may be due to decreased rates of tissue penetration as a result of HEMA chain lengthening. Guidelines for safe and economical handling of HEMA mixtures are given.

Methacrylates↗
PubMed1994

In vitro NMR micro imaging of the spinal cord of chronic relapsing EAE rats.

Chronic relapsing experimental allergic encephalomyelitis (Cr-EAE) was induced in Lewis rats with an emulsion of guinea pig spinal cord tissue in complete Freund's adjuvant enriched with Mycobacterium tuberculosis H37 RA. The sensitized rats developed Cr-EAE showing two to three relapses during the first 40 days. In vitro transverse T2-weighted spin echo images of the spinal cord of Cr-EAE rats, sacrificed at the clinical height (hind leg paralysis and urinary incontinence) of the third bout and their controls, were compared with the corresponding histopathology. Lesions extended over the entire spinal cord, however, the larger lesions were predominantly present in the cervical and upper thoracic regions. In the white matter only areas of demyelination and large perivascular demyelination were discernable on the MR images. Size and shape of these lesions correlated well with the morphological characteristics revealed by histopathology. Plaques in the ventrolateral funiculus were generally located peripherally, while plaques in the dorsal funiculus were mainly present in the medial part. The NMR images, however, could not distinguish between demyelination, remyelination, inflammation, and oedema. Also lesions in the gray matter could not be distinguished with MR imaging techniques. However, if lesions were localized at the interface of the gray and white matter the boundary between the gray and white matter was less well defined.

Animals↗
PubMed1993

A new subdivision of the rat midbrain periaqueductal gray based on its myeloarchitecture.

A new subdivision of the periaqueductal gray (PAG) based on its myelin content is described. Using a methacrylate-resin embedding technique for high resolution light microscopy, a myeloarchitectonic map of the normal rat PAG was made. Six main columns were distinguished. Column I is the central thin subependymal layer, in which myelinated axons are virtually absent. This layer is surrounded by column II with many rostrocaudally oriented fibers. Lateral and dorsolateral to column II lies column III, which contains rostrocaudally as well as tangentially oriented fibers. Column III is divided into a ventral and a dorsal part by column IV. This column is located in the dorsolateral part of the PAG and contains very few, mostly tangentially oriented fibers. Column V is located ventrally and contains a mixture of rostrocaudally and tangentially oriented fibers. Column VI is only present in the most caudal part of the PAG and contains mainly tangential fibers.

Animals↗
PubMed1992

The effects of glycol methacrylate as a dehydrating agent on the dimensional changes of liver tissue.

The dimensional changes of liver sections during the course of processing with glycol methacrylate (GMA) or with ethanol are described. Tissue processing with ethanol served as a control. During prolonged processing steps (24 h each), linear shrinkage of tissue specimens dehydrated with GMA at room temperature was 13.2%. Subsequent infiltration with GMA resulted in trivial swelling, and polymerization in slight shrinkage (2.3%). In comparison, processing with cold GMA resulted in shrinkage during dehydration (about 10.8%), a slight swelling in pure GMA, followed by shrinkage during polymerization (2.2%). Short routine processing schedules resulted in similar shrinkage/swelling patterns, although precise values differed slightly. In all experiments, ethanolic dehydration resulted in smaller dimensional tissue changes than did GMA dehydration. The dimensional changes of tissue sections during stretching on water, mounting and drying compensated for the major part of the shrinkage manifested during processing.

Animals↗
PubMed1992

Staining sections of water-miscible resins. 2. Effects of staining-reagent lipophilicity on the staining of glycol-methacrylate-embedded tissues.

Glycol methacrylate (GMA) sections of animal tissues were stained with a group of twenty-seven reagents of very varied chemical characteristics. The artefactual background staining of the resin was found to be dependent on the hydrophilic/lipophilic character of the staining reagent, as estimated from the logarithm of its octanol-water partition coefficient (log P). Intense background staining occurred with lipophilic stains, whose log P greater than 2. In keeping with this, use of GMA semi-permeable membranes for enzyme histochemistry failed to give staining when using a lipophilic substrate, probably because the substrate was trapped in the membrane. An analysis of other routine histochemical stains--in terms of the probable occurrence of high resin background staining and low tissue sensitivity--is made. A numerical guide is provided to help avoid artefacts resulting from hydrophobic and size effects. Note: small, hydrophilic reagents (log P less than 0; molecular weight less than 550 Da) are least likely to show either type of artefact. Conversely, reagents which are lipophilic, or/and of intermediate size (log P greater than 2; 550 less than ionic weight less than 1000 Da), give strong background staining.

Animals↗
PubMed1991

Glycol methacrylate embedding in diagnostic pathology. A standardized method for processing and embedding human tissue biopsy specimens.

A standardized "low-cost" processing and embedding procedure is described for the preparation of semithin glycol methacrylate (GMA) sections of human tissue biopsy specimens for use in routine diagnostic pathology. The method is highly reliable and reproducible and is based on many years of experience in fundamental GMA research. The procedure combines the application of new, less toxic, plasticizers and the preparation of high-quality GMA mixtures. Microwave irradiation was used to improve staining qualities and to reduce staining times. An improved reticulin staining procedure is presented as well.

Biopsy↗
PubMed1990

A numerical procedure for choosing effective, low toxicity plasticizers for glycol methacrylate embedding.

A numerical method for selecting low toxicity plasticizers for glycol methacrylate (GMA) embedding mixtures is described. It involves use of various numerical parameters, namely; molecular weight, melting point, solubility parameter, and toxicity data. On the basis of these parameters, nine plasticizers were selected. Their effects on microtomy and tissue processing, and also their influence on tissue morphology and staining, were investigated. For tissue processed at low temperatures into GMA, using ethanol dehydration, the following compounds were as satisfactory as 2-butoxyethanol whilst being less toxic: 2-isopropoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, 2-(n-butoxyethoxy)ethanol. However for tissues processed using the plasticizer as dehydrating agent, the optimum plasticizers were 2-isopropoxyethanol, 2-(2-methoxyethoxy)ethanol and 2-(2-ethoxyethoxy)ethanol. It is possible to give a numerical specification of the preferred plasticizers, and for the first procedure this is: a solubility parameter in the range 21-26 J0.5 cm-1.5 or higher, a melting point well below 0 degree C, and a rat oral LD50 greater than 12.52 mmol kg-1. It was also possible to analyse the differential effects of the dehydrating agents on histochemical and enzyme histochemical staining on a numerical basis, using a structure-activity relations approach.

Animals↗