Comparison of anodal and cathodal lesions and metal deposition in eliciting postoperative locomotion in the rat

Anodal lesions made with stainless steel electrodes elicited more vigorous running in the first 8 postoperative hr than cathodal lesions. Vigorous dose dependent running also followed 1 or 5 μg injections of FeCl₃ and CuCl₂ but was less vigorous following H₂O or HCl injections. Injections of other transition metals and AlCl₃ were ineffective. Particularly active sites for both lesions and injections were the dorsomedial n and the posterior hypothalamic n, but running also followed anterior hypothalamic-preoptic and anterior lateral hypothalamic lesions. Midbrain lesions did not elicit running. Behavioral tests administered at 24 hr failed to reveal persistent deficits correlated with effective lesion placements for running, but increasing the lesion size in the caudal hypothalamus decreased postlesion running and increased the occurrence and severity of postlesion akinesia and somnolence. A zone of tissue inflammation surrounded sites of anodal cavitation and sites of FeCl₃ and CuCl₂ injections. The results suggest that the irritative action of metals deposited by injection or lesion produce postoperative running and tissue inflammation, possibly concurrently.     

The variability of the interaural line vs the stability of bregma in rat stereotaxic surgery.

A comparison of the accuracy of stereotaxic localization using the interaural line and the bregmoidal intersection as the zero referent was made in male rats ranging in weight from 161 to 782 g. As body weight increased so did head length such that the angle of the skull and the distance from the interaural line to both the incisors and bregma varied as a linear function of body weight. Consequently, an electrode placement could recede by up to 4 mm from a target as rats' size increased. If head angle was held constant interaural line values could be adjusted by using an appropriate regression formula. With head angle constant and bregma used as the zero referent, the placement variation was less than 0.5 mm and was not systematically affected by body weight. The results show that coordinates from avoilable stereotaxic atlases can be adjusted for use with adult rats of widely varying body size.     

Olfaction directs skilled forelimb reaching in the rat

Rats were trained to reach for food pellets, which varied in size from 20 to 300 mg, from one of 21 locations on a shelf located just outside a test cage. After a barrier was lifted, giving access to a food pellet, latency to contact the food was timed, number of reaches to contact the food were counted, the distance of each misplaced reach from the food was measured and the success or failure of each attempt was noted. Control rats walked along the front of the cage sniffing to locate the food. Once they located a food pellet, they inserted their nose between the bars of the cage, sniffed the food for one to three respiratory cycles, raised their snout slightly, and then inserted a forepaw to grasp the food. They seldom required more than three reaches to contact the food and on about half of all trials they were successful in grasping the food. They were more successful in grasping medium-sized food pellets. Performance was unchanged on all measures after vision was occluded with eye patches. Following olfactory bulb removal, however, the rats no longer sniffed to locate the food or sniffed the food prior to initiating a reach. Rather they systematically moved along the length of the cage inserting their snout between the bars at each possible food location and without sniffing reached for the food 'as if blind'. Latency, number of reaches to contact the food and the distance of misplaced reaches increased whereas success rate remained unchanged. Substantial additional impairments were not produced when the bulbectomized rats were given visual occlusion. The study demonstrates that rats locate food and direct reaching using olfaction. The results are discussed in terms of the sensory control of skilled limb use and their relevance to the evolution of the sensory guidance of limb use.     

The mating movements of male decorticate rats: evidence for subcortically generated movements by the male but regulation of approaches by the female

The study shows that although many features of copulation in decorticate male rats are normal, copulatory success is importantly dependent upon the control of approaches exerted by the normal female rat. Copulation by neonatally decorticated adult rats and normal adult rats was studied in cohabitation and videotaped tests. Seven of 10 decorticate rats and 6 of 6 normal rats sired pups in the cohabitation test. When initially paired with ovariectomized and primed female rats, in the videotaped tests, all normal rats, but only one decorticated rat, copulated. All decorticate rats made movements indicative of sexual interest including: treading on the female's back, passing over the female, and sniffing the female's genitals. After activating stimulation, 5 of 6 remaining decorticated males copulated. After one successful mount the remaining copulatory patterns proceeded relatively normally. Numbers of mounts, intromissions, ejaculations, postejaculatory songs, and the intromission and ejaculatory patterns were like those of control rats, although the decorticate rats had fewer mount bouts and showed abnormalities in the execution of movements. Precopulatory movements were notated, using the Eshkol-Wachmann system, and compared with copulatory movements. Non-copulatory and copulatory approaches were similar, except that clasping appeared to be the key movement involved in the transition of an approach movement into a copulatory movement. The analysis also showed that the females' movements of hopping, turning, and kicking were important for regulating the males' approaches, and were instrumental in the success achieved by the decorticated males. The study shows that although the cortex, insofar as it facilitates the appearance of certain movements and contributes to their efficiency, is involved in male sexual activity, in its absence well organized sexual activity is possible, although this is dependent, in part, upon the behaviour of the female.     

Contributions of cingulate cortex to two forms of spatial learning and memory

The contribution of anterior and posterior cingulate cortical areas to spatial learning and memory was examined in 4 experiments using the place-navigation task. Rats with complete bilateral cingulate cortex aspiration or aspiration of posterior cingulate cortex (area 29) alone could not swim directly to a hidden platform located in a fixed place. When animals with these lesions were tested for 40 d in a place-alternation task in which they received 16 daily trials with the platform placed in a new location each day, they did not show reliable improvement in place navigation. The inability to swim to changing locations or to a single location was not overcome by preoperative training in these tasks. Rats with anterior cingulate cortex aspirations showed a less severe impairment in both tasks and, with more training than is necessary for control rats, they acquired near-normal place-navigation accuracy. Rats with complete cingulate cortex aspiration were almost as accurate as control rats in learning to swim to a visible platform. The results imply that posterior cingulate areas play an essential role in the use of topographical information, probably by transmitting and elaborating information passing between the hippocampal system and neocortical association areas.     

Sparing of skilled forelimb reaching and corticospinal projections after neonatal motor cortex removal or hemidecortication in the rat: support for the Kennard doctrine

Skilled forelimb use in reaching for food was studied in rats with variously sized and placed unilateral cortical lesions given in adulthood or on the day of birth. Fluorescent retrograde labelling was used to document changes in corticospinal tracts. In free choice tests, preferential use of the limb ipsilateral to damage was induced by adult motor, but not parietal or occipital, cortex damage. Similar preference for the ipsilateral limb was induced by neonatal motor and parietal, but not occipital, cortex damage. In both adult and neonate groups success with the preferred limb decreased in proportion to the increase in lesion size. To force use of the non-preferred limb, a bracelet, which prevented reaching but not other movements, was attached to the forearm of the preferred forelimb. Success with the non-preferred limb was poorer than with the preferred limb and success again decreased in proportion to the increase in lesion size. Adult and neonatal rats were divided into 4 groups according to the extent of motor cortex damage. Across all lesion sizes the neonatal operates were significantly more successful than the adult operates and their reaching movements appeared more normal. Surprisingly, some rats with large adult motor cortex lesions or hemidecortications were able to reach. Slow-motion video analysis of reaching impairments in both adult and neonate groups showed that limb extension and food grasping were less impaired than limb retraction and adduction of the limb to the mouth. The results show that the integrity of a neocortical hemisphere is not essential for contralateral limb use in reaching, but contributes to successful use of the limb. Following neonatal lesions, facilitation may be promoted by the ipsilateral neocortex through an augmented ipsilateral corticofugal pathway.     

The effects of alcohol and atropine on EEG and behavior in the rabbit

Electroencephalographic (EEG) activity was recorded from hippocampus and neocortex of rabbits. It was found that movement, movement-related 6–12 Hz rhythmical slow actvity (RSA), and movement-related neocortical desynchronization were unaffected by intravenous atropine sulfate but depressed by ethyl alcohol (ethanol). Slower 4–8 Hz immobility-related RSA and immobility-related neocortical desynchronization produced by sensory stimulation (visual, auditory, tactle, vestibular) were relatively unaffected by ethanol even at high (0.1–0.2 g-%) blood alcohol levels, but were abolished by atropine sulfate. The results provide evidence for the idea of two pharmacologically separable cortical activating systems and suggest that ethanol has a greater effect on noncholinergic than cholinergic systems.     

Generators and topography of hippocampal theta (RSA) in the anaesthetized and freely moving rat.

Spontaneous and hypothalamically induced hippocampal rhythmical slow activity (RSA or theta) was studied acutely in rats anaesthetized with urethane or immobilized with D-tubocurarine. Systematic tracking of microelectrodes showed two foci of hippocampal RSA, one located in the basal part (stratum oriens) of CAl (mean amplitude 1 mV) and the other located in stratum moleculare of the dorsal blade of the fascia dentata (mean amplitude 2 mV). The hippocampal RSA recorded from the lower blade of the fascia dentata was always smaller than that found in the upper blade (mean amplitude 1 mV). The whole dorsal hippocampal extent within each generator zone was shown to be in synchrony, and the respective generator zones of both hippocampi were synchronous with one another. A null zone in stratum radiation was found interposed between the two generators and a zone of large amplitude fast activity (30-50 Hz) was localized to the hilus of the fascia dentata. Wave form analysis showed that the RSA recorded from the two generators was approximately 180 degrees out of phase. Amplitude and analysis of phase changes of RSA recorded in brain areas outside of the two generator zones suggested that such activity was due to physical spread from the two generators, with the possible exception of a restricted portion of CA3. The existence of the two generators, 180 degrees out of phase, was demonstrated in freely moving rats. Behavioural observations showed that the two generators were related systematically to concurrent motor behaviour. Preliminary observations suggest that, of the two generators, the one located in CAl may be the more variable.