Caudal autotomy and regeneration in lizards

Caudal autotomy, or the voluntary self-amputation of the tail, is an anti-predation strategy in lizards that depends on a complex array of environmental, individual, and species-specific characteristics. These factors affect both when and how often caudal autotomy is employed, as well as its overall rate of success. The potential costs of autotomy must be weighed against the benefits of this strategy. Many species have evolved specialized behavioral and physiological adaptations to minimize or compensate for any negative consequences. One of the most important steps following a successful autotomous escape involves regeneration of the lost limb. In some species, regeneration occurs rapidly; such swift regeneration illustrates the importance of an intact, functional tail in everyday experience. In lizards and other vertebrates, regeneration is a highly ordered process utilizing initial developmental programs as well as regeneration-specific mechanisms to produce the correct types and pattern of cells required to sufficiently restore the structure and function of the sacrificed tail. In this review, we discuss the behavioral and physiological features of self-amputation, with particular reference to the costs and benefits of autotomy and the basic mechanisms of regeneration. In the process, we identify how these behaviors could be used to explore the neural regulation of complex behavioral responses within a functional context.     

Timm-staining intensity is correlated with the density of Timm-positive presynaptic structures in the cerebral cortex of lizards

Summary In cortical areas of the lizard, Podarcis hispanica, Timm staining reveals a distinct pattern of lamination. At the electron-microscope level, virtually all of the reaction product is located in the synaptic vesicles of Timm-positive boutons. Using linear-regression analysis, the area density of Timm-positive bouton profiles as well as the numerical and volume density of stained vesicles were found to be closely correlated with the light-microscopic densitometric values obtained for each Timm-positive cortical zone. We discuss the possibility of estimating stereological electron-microscopic data parameters from densitometric measurements at the light-microscope level.     

Timm-staining intensity is correlated with the density of Timm-positive presynaptic structures in the cerebral cortex of lizards

In cortical areas of the lizard, Podarcis hispanica, Timm staining reveals a distinct pattern of lamination. At the electron-microscope level, virtually all of the reaction product is located in the synaptic vesicles of Timm-positive boutons. Using linear-regression analysis, the area density of Timm-positive bouton profiles as well as the numerical and volume density of stained vesicles were found to be closely correlated with the light-microscopic densitometric values obtained for each Timm-positive cortical zone. We discuss the possibility of estimating stereological electron-microscopic data parameters from densitometric measurements at the light-microscope level.     

Tail regeneration in the lizards Anguis fragilis and Lacerta dugesii

Rates of tail regeneration in the Madeira wall lizard ( Lacerta dugesii ) and the slow-worm ( Anguis fragilis ) were studied.
L. dugesii regenerates very rapidly, the new tail sometimes attaining a maximum rate of growth of 2'6 mm a day during the fifth week after autotomy. By the twelfth week 90% of the original tail length has been replaced. Average regeneration rates of samples of lizards were reduced after repeated autotomies, but our investigation of this problem was probably complicated by another factor, the amount of tail lost, and is inconclusive.
The tip of the regenerate grows more rapidly than the rest; no elongation occurs at its cranial aspect.
Anguis , even when kept at 27°C, regenerates its tail very slowly, the best performance observed being a new tail of 5 mm after 14 weeks. The longest natural regenerate seen (16 mm) may have taken several years to produce in the wild.
The histological features of regeneration in Anguis are basically similar to those in other lizards. The new osteoderms are formed entirely in the subepidermal tissues but have a regular relationship with the scales. Some nerve fibres are regenerated with the ependymal tube.
The scales on the lizard's regenerating tail develop in a different manner from those in the lizard embryo and show suggestive resemblances to mammalian hairs.     

Light microscopy of the medial wall of the cerebral cortex of the lizard Psammodromus algirus

The telencephalic medial wall of the lizard Psammodromus algirus was studied using Golgi and conventional light microscopic techniques. The area is formed by two different cytological fields—medial cortex and dorsomedial cortex. These two cortices possess three layers dorsoventrally: a superficial plexiform layer, a cellular layer, and a deep plexiform layer. The alveus, a deep fiber system, runs adjacent to the ependyma. Four classes of neurons are found in the cellular layer of the medial cortex on the basis of soma shape, dendritic pattern, and position in the layer: horizontal, double pyramidal, and candelabra cells. Solitary cells are present in the superficial and deep plexiform layers of the medial cortex. Those of the superficial plexiform layer are stellate cells. Horizontal and vertical cells are found in the deep plexiform layer. Double pyramidal cells are the most frequently impregnated in the cellular layer of the dorsomedial cortex. In addition, candelabra cells are present at the lateral end of the layer. Two cell types are found in the deep plexiform layer of the dorsomedial cortex: solitary pyramidal cells and, among the fibers of the alveus, horizontal cells. Ependymal tanycytes line the ventricular surface, and protoplasmic astrocytes are found in the plexiform layers of both medial and dorsomedial cortices.     

Morphine excitation in the cerebral cortex.

Microiontophoretic administrations of morphine to cholino-excitable neurones in the cerebral cortex of decerebrate cats evoked a weak excitation which became more prominent upon repeated administrations of the alkaloid. This effect was not antagonized by naloxone. Iontophoresis of methylatropine prevented the excitation induced with acetylcholine and morphine, leaving that caused by glutamate relatively unaltered. Similar applications of morphine to neurones which were not excited by test applications of acetylcholine did not result in excitation but elicited mainly a depression of glutamate-evoked firing. It is suggested that the muscarinic effect of morphine in the cortex may be related to the excitation and convulsions, but not the analgesia, which occurs upon systemic administrations of the narcotic.     

Intrinsic organization of the medial cerebral cortex of the lizard Lacerta pityusensis: A golgi study

The morphology of cells and the organization of axons were studied in Golgi-Colonnier and toluidine blue stained preparations from the medial cerebral cortex of the lizard Lacerta pityusensis. In the medial cortex, six strata were distinguished between the superficial glial membrane and the ependyma. Strata I and II formed the outer plexiform layer, stratum III formed the cellular layer, and strata IV go VI the inner plexiform layer. The outer plexiform layer contained smooth bipolar neurons; their dendrites were oriented anteroposteriorly and their axons were directed towards the posterior zone of the brain. Five neuronal types were observed in the cellular layer. The spinous pyramidal neurons had well-developed apical dendrites and poorly developed basal ones. Their axons entered the inner plexiform layer and gave off collaterals oriented anteroposteriorly. The small, sparsely spinous pyramidal neurons had poorly developed dendrites and their axons entered the inner plexiform layer. The spinous bitufted neurons had well-developed apical and basal dendritic tufts. Their axons gave off collaterals that reached the outer and inner plexiform layers of both the dorsomedial and dorsal cortices. The sparsely spinous horizontal neurons had dendrites restricted to the outer plexiform layer. Their axons entered the inner plexiform layer. The sparsely spinous, multipolar neurons had their soma close to stratum IV and their axons entered the outer plexiform layer. In stratum V of the inner plexiform layer were large, spiny polymorphic neurons; they had dendrites with long spines, and their axons reached the cellular layer. On the basis of these results, we have subdivided the medial cortex into two subregions: the superficial region, which contains the neurons of the cellular layer and their dendritic domains, and the deep region, strata V and VI, which contains the large, spiny polymorphic neurons. The neurons in the medial cortex of these lizards resembles those in the area dentata of mammals. On this basis, the superficial region may be compared to the dentate gyrus and the deep region to the hilar region of the hippocampus of mammals.     

Acetylcholinesterase in neurons of the rat cerebral cortex.

AChE-containing neurons have been demonstrated by electron-microscopical histochemistry in the neocortex of the rat. These cells are mainly located in layer VI. AChE activity is seen in the cisternae of the RER, in subsurface cisternae and in the dendritic membranes.     

Fluid compartmentation and electrolytes of cat cerebral cortex in vitro. I. Swelling and solute distribution in mature cerebral cortex

The distribution of indicator solutes (inulin, sucrose, raffinose, thiocyanate, chloride, and isethionate) and the swelling in slices of adult cat cerebral cortex incubated in vitro have been investigated for a variety of incubation media and conditions. Where appropriate, these data have been compared with analogous data obtained on cat cerebral cortex in vivo (Bourke et al., 1965) and with data previously reported for slices of rat cerebral cortex (Pappius and Elliott , 1956; Pappius et al., 1962) and guinea pig cerebral cortex (Varon and Mc Ilwain , 1961; Keesey et al., 1965) incubated in vitro under comparable conditions. In addition to substantial agreement of present data with previously reported in vitro data, a number of new findings have been added by the present study: (a) a component of slice swelling which is K⁺-dependent; (b) the association of slice swelling with presence of a diffusible, external anion (Cl^?) and its prevention by replacement with a relatively non-diffusible anion (isethionate^?); (c) variation of the size of slice chloride spaces as a direct function of slice swelling; (d) dependence of the size of slice fluid spaces accessible to inulin and sucrose upon time, during incubation, of solute addition and upon K⁺ concentration of the incubation medium; (e) indications of the dynamic and presumably metabolically-dependent nature of indicator solute distribution; and (f) the mobility of a portion of the fluid of swelling associated with changing the K⁺ concentration but not the tonicity of the medium during incubation. At least five operationally-defined fluid compartments may be inferred from the present data : (1) interstitial or extracellular space(s) readily accessible to all solutes and of a size which can be minimally estimated from direct determinations in viuo; (2) additional fluid space(s) accessible to most solutes, including inulin and sucrose, under apparently suboptimal conditions of slice metabolism in vitro; (3) fluid space(s) prone to swell under in vitro conditions and readily accessible in vitro to chloride and thiocyanate but not to inulin or sucrose; (4) fluid space(s) which swell reversibly in the presence of added external K⁺ (or Rb⁺) and are inaccessible to all usual indicator solutes; and (5) after exclusion of the foregoing, the remaining fluid presumably comprising most of the intracellular space(s). The data have been discussed in terms of the morphological complexity of cerebral cortex, in terms of applicability to studies of cortical electrolyte distribution, and in terms of the general problem of delineating cerebral interstitial spaces.     

Functional organization of the medial frontal cortex

The anterior cingulate cortex (ACC) and adjacent areas of the medial frontal cortex (MFC) have been implicated in monitoring behaviour and in detecting errors. Recent evidence, however, suggests that the ACC not only registers the occurrence of errors but also represents other aspects of the reinforcement history that are crucial for guiding behaviour. Other studies raise the possibility that dorsal MFC areas not only monitor behaviour but also actually control response selection, particularly when the task in hand is changing. Many decisions are made in social contexts and their chances of success depend on what other individuals are doing. Evaluation of other individuals is therefore crucial for effective action selection, and some ACC regions are implicated in this process.     

Monoamines and self-stimulation of the medial prefrontal cortex in the rat

The participation of noradrenaline (NE) and serotonine (5-HT) in self-stimulation (SS) of the medial prefrontal cortex (MPC) in the rat has been studied. Three groups of rats with bilateral electrodes implanted into the MPC were used in these experiments. In one of the groups, electrodes were also implanted into the locus coeruleus. In the first group, the rats received systemic injections of the following drugs: clonidine (alpha-agonist), phenoxybenzamine (alpha-antagonist), isoproterenol (beta-agonist) and propranolol (beta-antagonist). In the second group, p-chlorophenylalanine (a 5-HT synthesis inhibitor) was administered intragastrically and SS measured during the following 16 days. In these two groups of rats and previous to every SS session, spontaneous motor activity (SM) was measured as control for non specific effects of the drugs. In a third group of rats, lesions of the locus coeruleus were performed unilaterally and SS measured in both prefrontal cortex during the following 16 days post-lesion. SS contralateral to the lesioned side served as control for non-specific effects of the lesions. After all these treatments, SS of the MPC was not specifically affected. Our results suggest the non participation of NE and 5-HT terminals in the neural substrates underlying SS of the MPC.     

Auditory processing in primate cerebral cortex.

Auditory information is relayed from the ventral nucleus of the medial geniculate complex to a core of three primary or primary-like areas of auditory cortex that are cochleotopically organized and highly responsive to pure tones. Auditory information is then distributed from the core areas to a surrounding belt of about seven areas that are less precisely cochleotopic and generally more responsive to complex stimuli than tones. Recent studies indicate that the belt areas relay to the rostral and caudal divisions of a parabelt region at a third level of processing in the cortex lateral to the belt. The parabelt and belt regions have additional inputs from dorsal and magnocellular divisions of the medial geniculate complex and other parts of the thalamus. The belt and parabelt regions appear to be concerned with integrative and associative functions involved in pattern perception and object recognition. The parabelt fields connect with regions of temporal, parietal, and frontal cortex that mediate additional auditory functions, including space perception and auditory memory.     

Volition and conflict in human medial frontal cortex

Controversy surrounds the role of human medial frontal cortex in controlling actions. Although damage to this area leads to severe difficulties in spontaneously initiating actions, the precise mechanisms underlying such "volitional" deficits remain to be established. Previous studies have implicated the medial frontal cortex in conflict monitoring and the control of voluntary action, suggesting that these key processes are functionally related or share neural substrates. Here, we combine a novel behavioral paradigm with functional imaging of the oculomotor system to reveal, for the first time, a functional subdivision of the pre-supplementary motor area (pre-SMA) into anatomically distinct areas that respond exclusively to either volition or conflict. We also demonstrate that activity in the supplementary eye field (SEF) distinguishes between success and failure in changing voluntary action plans during conflict, suggesting a role for the SEF in implementing the resolution of conflicting actions. We propose a functional architecture of human medial frontal cortex that incorporates the generation of action plans and the resolution of conflict.     

Delayed maturation of the male cerebral cortex in rats.

45 male and female Wistar rats were given a single injection of 3H-thymidine (10 mu Ci/g body weight) on day 1, 7, 14 or 21. All animals survived until 60 days of age when they were perfused with 10% neutral formalin and the brains were removed and prepared for autoradiography. The sagittal section of the cortex (L980 micron) was 6.8% larger in the males (p less than 0.05) but the packing density of the cortical cells was 5.9% higher in the females (p less than 0.01), thus bringing the total number of cells to the male levels. The diameter of the female cortical cells was 3.8% smaller than those of the males (p less than 0.05). The greatest difference was among the smaller cells (3-9 micron). The rate of postnatal acquisition of cortical cells was indicated by the number of radioactive-labelled cells. Males had more labeled cells after each injection; it was most pronounced (32% difference) on day 7 (p less than 0.05). This may reflect a delayed acquisition rate of cells formed before birth, since more cells could be labeled by the postnatal injection.