Organization of sensory cortex in the East African hedgehog (Atelerix albiventris)

We investigated the organization of neocortex in the East African hedgehog (Atelerix albiventris) with microelectrode recordings from sensory areas that were later correlated with cytochrome oxidase patterns in sections of flattened cortex. The location of corticospinal projecting neurons was also examined and related to sensory areas by making small injections of wheat germ agglutinin-horseradish peroxidase into the spinal cord. Our goals were to determine how hedgehog cortex is organized, how much sensory areas overlap, and to compare results with recent findings in other insectivores. Evidence was found for three separate topographically organized somatosensory areas, two visual areas, and a caudolateral auditory area. A medial somatosensory area corresponded to S1, the primary somatosensory area, whereas two lateral areas partially encircled auditory cortex and corresponded to the parietal ventral area (PV) and the secondary somatosensory area (S2). Primary visual cortex (V1) was delineated by a caudomedial cytochrome oxidase dark oval, and a more lateral visual area between V1 and somatosensory cortex corresponded to V2, or area 18. Two patches of corticospinal projecting cells were found primarily overlapping S1 and S2. Some bimodal auditory and somatosensory responses were found in parts of PV and S2, but for the most part, areas had relatively sharp histochemically apparent and physiologically defined borders. The present results indicate that the caudal neocortex of hedgehogs has only a few sensory areas, corresponding to those commonly found in several other small-brained mammals. Hedgehog cortical organization differs significantly in somatotopy, number, and position of fields from that of closely related shrews and moles. Thus, clear specializations occur, even within the order Insectivora.

Pharmacological properties of blood pressure and heart rate control in suncus

Blood pressure and heart rate and responses to various physiological substances in suncus were characterized and compared with those in mice. The blood pressures of the two species were similar, but the heart rate of suncus (about 400 beat/min) was significantly lower than that of mice. Norepinephrine increased the blood pressure but decreased the heart rate in suncus. The latter was blocked by cervical vagotomy. Sensitivities to acetylcholine and isoproterenol were lower in suncus. These results suggest that regulation of blood pressure and heart rate in suncus is very unique and different from the well-defined system of the rodents.

Emetic responses of Sorex unguiculatus

We have shown previously that Suncus murinus, a species of the insectivore, can vomit in response to various emetogenic stimuli. In the present study we investigated whether or not Sorex unguiculatus, which belongs to different subfamily (Soricinae) of insectivore, vomits in response to emetogenic drugs. Subcutaneous injection of veratrine and oral administration of copper sulfate caused emesis in the animal. Histological study showed that bilateral structure of the area postrema was not important for the emetic reflex. Therefore, the capability of emesis may be common to the family of soricidae of the insectivore, and the Sorex unguiculatus is the smallest known mammal which can vomit.

The ear in subterranean insectivora and rodentia in comparison with ground-dwelling representatives. I. Sound conducting system of the middle ear

Compared to acoustically unspecialized mammals (soricids and murids), the middle ear of subterranean insectivores and rodents (twelve species of six families examined) was clearly distinguished and characterized by many common features: rather round and relatively larger eardrum without a pars flaccida; reduced gonial; loose or no connection between the malleus and the tympanic bone; reduced and straightened transversal part of the malleus; enlarged incus; increased and rather flat incudo-mallear joint; rather parallel position of the mallear manubrium and incudal crus longum in some species (and their fusion in bathyergids); reduced or even missing middle ear muscles. Convergent occurrence of these structural features in taxa of different origin and their generally derived character suggest that they cannot be categorized as degenerative. The form of the stapes can be considered as a non-adaptive trait; it was taxon specific yet remarkably polymorphous in some species and exhibited no convergent features among subterranean mammals. Structural retrogression resulting in a columella-like stapes was observed in some species lacking the stapedial artery. The stapedial base was relatively larger than in unspecialized mammals. The subterranean mammals did not exhibit conspicuously enlarged eardrums as would be required for sensitive tuning to low frequencies. It is, however, argued that while selective pressures in the subterranean ecotope promoted hearing of low frequencies, hearing sensitivity did not have to be enhanced.

Cisplatin-induced emesis in Suncus murinus

Emetic responses to cisplatin and participation of vagal innervation in emesis were studied in suncus. Intraperitoneal and intravenous administration of cisplatin caused dose-dependent emesis. ED50 values, latencies and frequencies were not significantly different between the two administrations. Cis-diaqodiammineplatinum (DAP), an active metabolite of cisplatin, also induced emesis, but with significantly shorter latency. Vagotomy completely abolished both types of vomiting. These results suggest that cisplatin is metabolized to DAP that subsequently causes emesis through stimulation of the vagus afferent.

Selective blockade of cytotoxic drug-induced emesis by 5-HT3 receptor antagonists in Suncus murinus

Antiemetic effects of serotonin 5-HT3 receptor antagonists (ICS205-930, zacopride, BRL43694, GR38032F) were investigated in Suncus murinus. Veratrine, nicotine, copper sulfate, cisplatin, cyclophosphamide and motion sickness were used as emetic stimuli. Serotonin 5-HT3 receptor antagonists did not inhibit emetic responses to veratrine, nicotine, copper sulfate and motion sickness. However, cisplatin- and cyclophosphamide-induced emesis was strongly blocked by them. Both subcutaneous and intravenous injections of 5-HT3 antagonists were effective. Serotonin 5-HT1 and 5-HT2 receptor antagonists were less effective. These results clearly indicate that a 5-HT3 receptor-mediated mechanism(s) is involved in the emesis caused by cancer chemotherapeutic agents and that 5-HT3 receptor antagonists are very effective as prophylactic drugs.

The relationship between body mass and rate of rewarming from hibernation and daily torpor in mammals

1. Rewarming rate from torpor and body mass were inversely related in 86 mammals ranging in body mass between 2 and 8500 g. 2. Most of the mammalian taxa investigated showed a similar change of rewarming rate with body mass. Only the insectivores showed a more pronounced increase in rewarming with a decrease in body mass than did the other taxa. The rates of rewarming of marsupials were similar to those of placentals. 3. At low air temperature (Ta), the rate of rewarming of marsupials was not related to body mass, although a strong relationship between the two variables was observed in the same species at high Ta. 4. The slopes relating rewarming rates and body mass of the mammalian groups and taxa analysed here were similar to those obtained earlier for mass-specific basal metabolic rate (BMR) and body mass in mammals, suggesting that the rate of rewarming and BMR are physiologically linked.

Synaptonemal complex analysis in Talpa occidentalis spermatocytes (Insectivora, Mammalia). II. Evolution of the X-chromosome self-pairing process

Zygotene and pachytene configurations of the X chromosome were studied in whole-mount, silver-stained preparations of spermatocytes from XY males from a population of Talpa occidentalis in which sex reversal has been described. The most striking finding in this study was a self-pairing conformation of the axial (differential) element of the X chromosome. This self-pairing was markedly constant in the site of initiation, which invariably involved the distal free end of the X and the region beyond the X-Y pairing segment, so that X-Y synapsis was never disturbed. In addition, self-pairing occurred later than autosomal synapsis and was accompanied by thickening of the axes, although this seemed to occur after the formation of an ordinary synaptonemal complex. The etiology of this phenomenon may be based on residual homology, possibly due to conservation of a primitive isochromosome throughout the karyotypic evolution of this species. However, the possible relationship between self-pairing and sex reversal remains obscure.

Deficiency of beta-adrenoceptor-mediated relaxation in suncus trachea

Characteristics of beta-adrenoceptor in the tracheal smooth muscle of Suncus murinus (suncus) were studied in comparison with those of rats and guinea pigs. Isoproterenol induced concentration-dependent relaxation of suncus trachea. However, the maximal relaxation was very small, and about 1000 times higher concentration was necessary compared to the case of the guinea pig. The order of the sensitivity to isoproterenol and the maximal relaxation was guinea pig much greater than rat greater than suncus. Tracheae from younger suncus were more sensitive to isoproterenol, but the maximal relaxation was not significantly different from the results using adult animals. Forskolin, a direct activator of adenylate cyclase, relaxed tracheae to similar extents in the three species. Though the affinity of specific [3H]dihydroalprenolol binding was not significantly different, the maximal number of binding sites was in the order of rat greater than guinea pig greater than suncus. However, the differences in density of the binding among the three species were not as great as differences in isoproterenol-induced relaxation. These results suggest that 1) beta-adrenoceptor-mediated relaxation of tracheal smooth muscle is not well-developed in the suncus and 2) the deficient relaxation is probably caused by insufficient coupling between adrenoceptors and adenylate cyclase.

Suncus murinus: a new experimental model in emesis research

Effects of various emetic and antiemetic drugs were studied using Suncus murinus for its potential use as an experimental model in emetic research. Subcutaneous injection of nicotine bitartrate (10-15 mg/kg), veratrine sulfate (0.5-1.0 mg/kg), emetine dihydrochloride (40-80 mg/kg) and oral administration of copper sulfate (20-100 mg/kg) caused dose-dependent emesis in suncus. The ED50 of nicotine, veratrine, emetine and copper sulfate were 7.9, 0.4, 47.6 and 21.4 mg/kg, respectively. However, subcutaneously injected apomorphine hydrochloride (0.1-100 mg/kg), digitoxin (0.5-1.0 mg/kg) and orally administered emetine dihydrochloride (10-80 mg/kg) did not induce the vomiting. Chlorpromazine and promethazine decreased the emetic effect of nicotine, veratrine and copper sulfate, but scopolamine hydrobromide was not effective. These results indicate that the Suncus murinus is sensitive to various emetic and antiemetic drugs and can be used as a new experimental animal model for the emesis. Emetic behavior of suncus was discussed in comparison with other animals.

A cineradiographic and electromyographic study of mastication in Tenrec ecaudatus

Regular chewing was studied in the specialized Malagasy insectivore Tenrec ecaudatus with the aid of precisely correlated electromyography of the main adductors, digastrics, and two hyoid muscles and cineradiography for which metallic markers were placed in the mandibles, tongue, and hyoid bone. During the power stroke the body of the mandible moves dorsally and medially. The medially directed component of movement at this time is greatly increased by simultaneous rotation of the mandible about its longitudinal axis. The highly mobile symphysis, spherical dentary condyle, loss of superficial masseter muscle and zygoma, and the simplified zalamnodont molars all appear to be related to the large amount of mandibular rotation that occurs during occlusion. The balancing side lateral pterygoid muscle (inferior head) apparently shifts the working side mandible laterally during the last part of opening and the first part of closing. The working side temporalis and the superficial masseter muscle are both responsible for the shift back to the midline. The temporalis is usually active to the same extent on the working and balancing sides during the power stroke. The level of activity (amplitude) of the temporalis and duration of the power stroke increase with harder foods. Whenever soft foods are chewed, the superficial masseter is only active on the working side; whenever foods of increasing hardness are chewed, its level of activity on the balancing side increases to approach that of the working side. Mandibular rotation is greatly reduced when hard foods are chewed.

Follicular development, ovulation, fertilization and fetal development in tenrecs (Tenrec ecaudatus)

Reproduction in female tenrecs was studied on Praslin Island (4 degrees 20'S, 55 degrees 45'E) in the Seychelles from November 1977 to September 1980. Dissection and histological examination of reproductive tracts revealed that each ovary is encapsulated in a bursa. Polyovular follicles were abundant and contained up to 5 oocytes. The occurrence of more implanted fetuses than corpora lutea (CL) indicated successful polyovuly in 25% of pregnancies. No antrum was observed during follicular growth at oestrus, and follicles were relatively small at maturation, reaching a maximum diameter of 570 microns. Ovulation involves a gentle extrusion of the granulosa and ovum into the periovarian space. Spermatozoa were abundant in the female reproductive tract including the periovarian space at oestrus. Spermatozoa penetrated the loosely-packed theca of mature follicles and were present in CL, indicating that intrafollicular fertilization may occur. The relatively small CL formed by eversion, reaching a maximum size after implantation. Fusion of up to four CL occurred in the ovaries of 41% of pregnant females. Polyovulation in the tenrec was confirmed by the occurrence of 10.4 +/- 0.5 (mean +/- s.e.m.) CL and 9.7 +/- 0.5 (mean +/- s.e.m.) implantations. Resorption occurred in 74% of 19 dissectable pregnancies, occurring in both uterine horns in 26% of pregnancies. Coefficients of variation in weights of fetuses in each litter were 10.0-26.8%, with the largest value corresponding to 273% variation in fetus weights. Litter size in the Seychelles tenrecs was smaller than in the same species in Madagascar (17.1 +/- 1.9 implantations) where the tenrec is native.

Seasonal changes in testosterone levels and androgen-dependent organs in male moles (Talpa europaea)

Seasonal changes in testicular and plasma testosterone levels and in androgen-dependent organs were determined in moles breeding at 53 degrees N. Although the testes contain up to 30 times more testosterone during spermatogenesis than during sexual quiescence, appreciable quantities of this hormone are present during late summer and early autumn. Annual spermatogenesis lasts for only 2 months, but in some moles spermatozoa remain in the epididymis for up to 3 months after the testes have begun to involute, and may therefore be available to inseminate females coming into a second oestrus.

Sweating on paws and palms: what is its function?

Man sweats on his palms and the soles of his feet in response to stress and exercise, but not in response to heat. Several functions have been proposed for this type of sweating: increasing friction between skin and substrate; increasing the toughness of the skin; and increasing tactile sensitivity. This study uses a comparative approach to evaluate the role of footpad sweating on increasing friction, utilizing a variety of mammals which possess sweat glands on their footpads (rat, tenrec, hyrax, and dog). We found that all of these animals sweat on their paws while running. Blocking this sweating with atropine sulfate dramatically decreased the coefficient of static friction between the paw and the tread of an inclined treadmill. A similar dose of atropine sulfate had no effect on the coefficient of static friction in a rabbit, and animal that possesses no sweat glands on its paws. We conclude that an important function of this type of sweating is to help prevent slipping between the paw and sthe substrate during running or climbing, and we postulate that the sweating observed in response to stress may play an important role in preparing an animal for fleeing from stressful situations.

Visual attention in the tree shrew: an ablation study of the striate and extrastriate visual cortex

Removal of the striate area in tree shrews results in increased distractibility, which prevents the animals from learning to discriminate form when hue is an irrelevant and distracting cue. Removal of the extrastriate visual cortex results in the reciprocal deficit: an increase in perseveration manifested by an inability to shift attention when irrelevant dimensions are made relevant.