Neural mechanisms of female sexual behavior in the rat; comparison with male ejaculatory control.

The sequential organization of sexual behavior of the female rat is described, eventually leading to the lordotic posture, shown during mating. A complex set of signals: olfactory, cutaneous sensory as well as genitosensory, is guiding the female to this specific posture, eventually. Genitosensory signals converge in the lumbosacral levels of the spinal cord, from where they are dispersed to a series of supraspinal brain areas, in the brainstem, thalamus, hypothalamus and limbic system. The similarity with the neural activation patterns observed in the male rat is remarkable. In a number of brain areas, however: the midbrain periaqueductal gray, the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl) and the medial preoptic-lateral septum regions, specific male-female differences have been observed. Especially the VMHvl is an intriguing area, as it has been shown that the same neurons may be involved in 'opposite behavior' like aggression and the induction of lordosis. The motor mechanisms controlling the lordosis posture in the rat as well as in some other mammals are discussed, as well as some aspects of the reward mechanisms contributing to female sex. We conclude that we have collected a great amount of neurophysiological knowledge over the last 20 years, but that the unresolved questions are still numerous. In this field, there is still much to explore.

Spumiform basement membrane aberrations in the microvasculature of the midbrain periaqueductal gray region in hamster: rostro-caudal pathogenesis?

Spumiform basement membrane degeneration (sbmd) is a specific kind of aberration present in the capillaries of the midbrain periaqueductal gray (PAG) region of the senescent hamster. These capillaries, separated by the ependymal cell layer, are bordering the Sylvian cerebral aqueduct. The aqueduct, connecting the 3rd and 4th ventricle, may be crucial for local homeostatic as well as general autonomic functions of the PAG. Local pressure effects of the flowing and pulsating cerebrospinal fluid on the PAG-vasculature are probably different for the rostral 'entrance' and the caudal 'exit' of the aqueduct. In view of the different functions of the various divisions of the PAG, the frequency and extent of the aberrations in the rostral, intermediate and caudal dl/vlPAG-microvasculature could shed some light on the causal factors involved in the regional distribution of the particular microvascular aberrations found in the PAG during aging. In the present study we investigated the ultrastructure of capillaries in dorsal and ventral subdivisions of anterior and posterior regions of the PAG of young and old female Syrian hamsters. Sbmds were classified into four stages of spumiform severity and for each stage the frequency was determined in the rostral PAG, at two levels in the intermediate PAG and in a dorsal and a ventral part of the caudal PAG. Results of our quantitative studies showed that in aged hamster PAG various stages of sbmd were present in 91.6 ± 0.6% of all capillaries. No clear evidence was found for regional differentiation between rostral, intermediate and caudal parts of the PAG. Next to sbmd, capillary split basement membrane (sbm) and vacuolization were common features at all five PAG locations. 84.3 ± 2.3% of all screened PAG capillaries displayed sbm. In agreement with our previous findings, several other types of microvascular aberrations were observed in addition to general aspects of aging and some ependymal structural peculiarities. We conclude that the presence of various forms of sbmds in the PAG of senescent hamsters is a phenomenon that appears to be specific to the PAG region, but causal factors for this type of capillary degeneration remain unclear. Sbmds in the PAG may have serious consequences not only for blood-brain barrier functioning, but also for vascular perfusion and blood supply with eventually serious consequences for adequate regulation of the autonomic and motor control functions of the PAG region.

'Last-minute' donations influence actuarial prediction in an anatomical body donation program.

BACKGROUND: At some American and European universities the dissection program is threatened by a shortage of anatomical specimens. In contrast, the annual numbers of registrations at the University Medical Center Groningen (UMCG) in the Netherlands increased substantially in recent years. Uncontrolled body registrations and an increasing number of incoming bodies urge institutes to halt registration. This is usually carried out on an ad hoc basis because to date no analyses were available to predict the consequences of such a stop, resulting in uncertainty about the number of incoming bodies or a shortage. METHODS: The UMCG holds a database consisting of two different data sets: registered potential body donors and records of deceased body donors. This database currently consists of 2357 potential body donors and 1363 deceased body donors. These data were incorporated in an actuarial predictive model. FINDINGS: A substantial number (on average 29%) of the persons registered between 2003-2008 died within 1 year after registration and seemed to have made a 'last-minute' donation decision. Last-minute registrations are significantly more likely to be males than females (n=155 vs. n=85, p<0.01%). This new information markedly influenced final modeling. In coherence with standard models of mortality, it was possible to construct a prediction for the incoming bodies for the coming years. CONCLUSIONS: The present study provides the first method to reliably model the number of incoming deceased donors of a body donation program for 5 years based on actuarial predictions, and to orchestrate these numbers by partial donor registration stops.

Columnar organization of estrogen receptor-alpha immunoreactive neurons in the periaqueductal gray projecting to the nucleus para-retroambiguus in the caudal brainstem of the female golden hamster.

In the hamster brainstem estrogen receptor-alpha-immunoreactive neurons (ER-alpha-IR) are present in the nucleus para-retroambiguus (NPRA), located in the caudal ventrolateral medulla (CVLM) ventrolaterally to the nucleus retroambiguus (NRA). NPRA neurons project mainly to the thoracic and upper lumbar cord and are probably involved in the autonomic adaptations during the estrous cycle. The periaqueductal gray (PAG), projecting to the CVLM, also contains ER-alpha-IR neurons. This raises the questions: how are these projections organized and are ER-alpha-IR neurons in PAG and NPRA linked directly? Combined retro- and anterograde tracing techniques, using wheat germ agglutinin-horseradish peroxidase (WGA-HRP), were carried out to demonstrate neuronal relationships between PAG and NPRA and/or NRA. Finally, a double-label immunostaining was performed in ovariectomized hamsters combining anti-ER-alpha antibody immunocytochemistry with cholera toxin B injections into the CVLM, to differentiate between ER-alpha-IR projections from the PAG to either NRA or NPRA. The experiments showed that retrograde labeling from the NRA mainly occurred in the rostral and intermediate ipsilateral PAG, while injections involving both NRA and NPRA resulted in numerous labeled neurons in the ipsilateral rostral, intermediate and especially the caudal PAG. The anterograde tracing studies confirmed these projections: from the rostral PAG almost exclusively to the NRA and from the caudal PAG to the NPRA, while the intermediate lateral PAG projects to both NPRA and NRA. Our double-immunostudies revealed that ER-alpha-IR projections descend only towards the NPRA and mainly originate from the ipsilateral caudal PAG. Retrogradely labeled ER-alpha-IR neurons in the PAG were observed in two separate columns, laterally and ventrolaterally in the caudal half of the PAG. The results provide evidence for the existence of differentiated PAG-CVLM projections to NRA and NPRA, respectively, originating from discrete longitudinal "PAG-columns." Only the projection to the NPRA is estrogen receptive, supporting the hypothesis that the NPRA is involved in the adaptive changes in autonomic control during successive phases of the estrous cycle.

Estrous cycle-dependent neural plasticity in the caudal brainstem in the female golden hamster: ultrastructural and immunocytochemical studies of axo-dendritic relationships and dynamic remodeling.

UNLABELLED: During the short four-day estrous cycle of the female hamster various behavioral (lordosis, vocalization and aggression) and autonomic adaptations occur. Presumably, these changes are under ovarian control. Recently, we described a distinct estrogen receptor-alpha immunoreactive (ER-alpha-IR) cell group, now called nucleus para-retroambiguus (NPRA), in the caudal ventrolateral medulla (Gerrits et al., 2008). Neurons of this group project to the ipsilateral intermediolateral cell column in the thoracic and upper lumbar cord. Clearly, the NPRA is part of an estrogen-sensitive neuronal network and the same applies to the region containing the commissural part of the solitary tract nucleus (NTScom) and the A2 group, here called NTScom/A2. Estrogen is known to modulate neuronal ultrastructure in various brain areas and spinal cord, but not in the caudal brainstem. Because we assumed that the NPRA plays a role in estrous cycle related adaptations, we hypothesized the occurrence of plasticity in this nucleus. In the present study we examined morphological changes of axo-dendritic relationships in NPRA and NTScom/A2 in estrous, diestrous and ovariectomized (OVX) hamsters, using immuno-electron microscopy and the 1D5 anti-ER-alpha antibody. Ultrastructural analysis revealed that the ratio "axon terminals surface/dendrite surface" was significantly increased in both the NPRA and NTScom/A2 during the estrous phase compared to the OVX and diestrous conditions. Remodeling of axon terminals due to axonal sprouting into large terminal fields filled up with pleomorphic vesicles resulted in contacts with more dendrites, and was the main cause for the "axonal terminal-dendritic-ratio" shift. IN CONCLUSION: Estrous cycle-induced axonal and dendritic plasticity is present in the NPRA, and in the NTScom/A2 group. Our findings support our hypothesis that estrogen-sensitive neuronal networks in the caudal brainstem display structural plasticity, probably to modulate steroid hormone dependent behaviors or autonomic adaptations.

The nucleus para-retroambiguus: a new group of estrogen receptive cells in the caudal ventrolateral medulla of the female golden hamster.

Receptive female hamsters display very rigid lordotic postures. Estradiol facilitates this behavior via activation of estrogen receptors. In the hamster brainstem estrogen receptor-alpha-immunoreactive neurons (ER-alpha-IR) are present in various brainstem regions including nucleus retroambiguus (NRA) in the caudal ventrolateral medulla (CVLM) and nucleus of the solitary tract. ER-alpha-IR neurons in the CVLM project to the thoracic and upper lumbar cord. However, A1 neurons in this region do not project to the spinal cord, in contrast to overlapping C1 neurons. The question now arises: are ER-alpha-IR cells in the CVLM part of the A1/C1 group, or do they belong to the NRA or do they compose a separate cluster. A study in ovariectomized female hamsters using a combination of double immunostaining and retrograde tracing techniques and measurement of soma diameters was carried out. The results showed that A1/C1 neurons in the CVLM are almost never ER-alpha-positive; neurons inside or bordering the NRA can be divided in two different types: large multipolar and small; the large NRA-neurons, projecting caudally, are neither tyrosine hydroxylase- (TH) nor ER-alpha-IR; the small neurons, bordering the NRA and projecting caudally, are ER-alpha-IR but not TH-IR. From the available evidence and the present findings it can be concluded that the group of small ER-alpha-IR neurons in the CVLM has to be considered as a distinct entity, probably involved in the autonomic physiological changes concurring with successive phases of the estrous cycle. Because the location is closely related to the NRA itself the nucleus is called nucleus para-retroambiguus, abbreviated (NPRA).

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.

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.

[Characteristics of pedigree cat breeding in the Netherlands: breeds, population increase and litter size]. / Karakteristieken van de Nederlandse raskattenfokkerij: rassen, populatie-grootte en nestomvang.

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.

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.

[Organization of the Dutch Cat Fancy]. / Organisatie van de nederlandse 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.

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.

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.

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.

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.

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.

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.

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.

Single fibre action potentials in skeletal muscle related to recording distances.

Single muscle fibre action potentials (SFAPs) are considered to be functions of a bioelectrical source and electrical conductivity parameters of the medium. In most model studies SFAPs are computed as a convolution of the bioelectrical source with a transfer function. Calculated peak-to-peak amplitudes of SFAPs decrease with increasing recording distances. In this paper an experimental validation of model results is presented. Experiments were carried out on the m. extensor digitorum longus (EDL) of the rat. Using a method including fluorescent labelling of the active fibre, the distance between the active fibre and the recording electrode was derived. With another method, the decline of the peak-to-peak amplitude of SFAPs detected along a multi-electrode was obtained. With both experimental methods, in general peak-to-peak amplitudes of SFAPs decreased with increasing recording distances, as was found in model results with present volume conduction theory. However, this behaviour was not found in all experiments. The rate of decline of the peak-to-peak amplitudes with recording distance was always less than in models.