Sensory and Hypothalamic Control of Lordosis Behavior in Female Rodents

When applied during the sustained lordosis response of female hamsters, gentle probing at points on the perineal surface elicited stereotyped rump and tail movements. The rump movements always served to rapidly center the vaginal opening beneath the continuing stimulation. Tail deflections were only elicited by stimulation applied above and lateral to the vaginal opening. The tail was deflected away from the side stimulated. These observations help to complete the description of the stimulus-response relations of the component reflexes which comprise the complete lordosis response in hamsters. The movements would serve to facilitate vaginal access during copulation and foster accurate targeting of penile thrusts to the vaginal opening. Puffs of air directed to the lateral flank surface triggered lordosis in some estrogen-progesterone treated, ovariectomized female hamsters. This stimulation covered only a small area of the flank, and exerted very little pressure on deep structures, indicating that the deflection of a few hairs within a small area of the flank is sufficient to trigger lordosis in some hamsters. Prior exposure to the ministrations of a sexually active male hamster facilitated the triggering of lordosis by unilaterally applied air puffs, and potentiated the intensity of the lordoses exhibited. The expression of this effect did not require the activation of rump displacement reflexes by perineal stimulation during the post-male test. Light brushing of flank hairs, on one or both flanks elicited lordosis as reliably as post-male, unilateral air puffs. Increasing the area or intensity of artificially applied stimulation triggered more intense lordosis responses. These observations help to define the minimal sensory stimulus required to trigger lordosis in hamsters, providing Information useful in the neurophysiological analysis of this hormone dependent reflex. In estrogen-replaced, ovariectomized rats, selective transections were used to interrupt, together or separately, the medial and lateral pathways by which efferent fibers from the ventromedial nucleus of the hypothalamus reach the lower brainstem. Transections interrupting both projections reduced or eliminated lordosis performance. Transections which intercepted all of the medially descending fibers, but spared the lateral pathway, did not reduce lordosis performance in mating or manual stimulation tests. The lateral pathway was interrupted at two different locations. The lateral pathway, as a whole, was not required for lordosis when the medial pathway was left intact. Also, no particular subset of fibers assuming a lateral trajectory from the VMN to the brainstem were required for the display of lordosis. However, the fibers running through the lateral brainstem do play some role in the expression of the reflex - their transection bilaterally did reduce lordosis performance. The failure of lordosis to occur in mating tests was not a result of a systematic increase in rejection behavior. The observation of intermittent lordosis responses, or increased lordosis, performance following additional estrogen and progesterone treatment revealed that these transected animals were still able to produce the motor behavior required for lordosis. The deficits seen were attributed to the interruption of fibers mediating the control of lordosis by the hypothalamus. This control of lordosis by the ventromedial nucleus can be described as a tonic, estrogen-dependent facilitation of supraspinal lordosis control mechanisms located more caudally in the brainstem. The laterally, rather than the medially, descending efferent fibers from the ventromedial nucleus may play a quantitatively more important role in the control of lordosis

Approach-avoidance analysis of rat diencephalon

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49985/1/901200206_ftp.pd

Cortical-hippocampal processing: prefrontal-hippocampal contributions to the spatiotemporal relationship of events

The hippocampus and prefrontal cortex play distinct roles in the generation and retrieval of episodic memory. The hippocampus is crucial for binding inputs across behavioral timescales, whereas the prefrontal cortex is found to influence retrieval. Spiking of hippocampal principal neurons contains environmental information, including information about the presence of specific objects and their spatial or temporal position relative to environmental and behavioral cues. Neural activity in the prefrontal cortex is found to map behavioral sequences that share commonalities in sensory input, movement, and reward valence. Here I conducted a series of four experiments to test the hypothesis that external inputs from cortex update cell assemblies that are organized within the hippocampus. I propose that cortical inputs coordinate with CA3 to rapidly integrate information at fine timescales. Extracellular tetrode recordings of neurons in the orbitofrontal cortex were performed in rats during a task where object valences were dictated by the spatial context in which they were located. Orbitofrontal ensembles, during object sampling, were found to organize all measured task elements in inverse rank relative to the rank previously observed in the hippocampus, whereby orbitofrontal ensembles displayed greater differentiation for object valence and its contextual identity than spatial position. Using the same task, a follow-up experiment assessed coordination between prefrontal and hippocampal networks by simultaneously recording medial prefrontal and hippocampal activity. The circuit was found to coordinate at theta frequencies, whereby hippocampal theta engaged prefrontal signals during contextual sampling, and the order of engagement reversed during object sampling. Two additional experiments investigated hippocampal temporal representations. First, hippocampal patterns were found to represent conjunctions of time and odor during a head-fixed delayed match-to-sample task. Lastly, I assessed the dependence of hippocampal firing patterns on intrinsic connectivity during the delay period versus active navigation of spatial routes, as rats performed a delayed-alternation T-maze. Stimulation of the ventral hippocampal commissure induced remapping of hippocampal activity during the delay period selectively. Despite temporal reorganization, different hippocampal populations emerged to predict temporal position. These results show hippocampal representations are guided by stable cortical signals, but also, coordination between cortical and intrinsic circuitry stabilizes flexible CA1 temporal representations

Design, implementation and validation of an exoskeletal robot for locomotion studies in rodents

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 214-226).Growing interest in robotic treatment of patients with neurological injury motivates the development of therapeutic robots for basic research into recovery. Though humans are the ultimate beneficiaries, basic research frequently involves rodent models of neurological injury, which motivates robotic devices that can interact with rats or mice. Currently, available apparatus for locomotion studies of rodents is built upon treadmills, which simplify the design and implementation but also restrict the scope of possible experiments. This is largely due to the treadmill's single-dimensional movement and the lack of accommodation for natural or voluntary movement of the animal. In order to open up new possibilities for locomotion studies in rodents, this work introduces newly developed apparatus for locomotion research in rodents. The key concept is to allow maximal freedom of voluntary movement of the animal while providing forceful interaction when necessary. Advantages and challenges of the proposed machine over other existing designs are discussed. Design and implementation issues are presented and discussed, emphasizing their impact on free, voluntary, movement of the animal. A live-animal experiment was conducted to verify the design principles. Unconstrained natural movement of the animal was compared with movement with the overground robot attached. The compact, overground design and backdrivable implementation of this robot allow novel experiments that involve open-space, free (or interactive) locomotion of the animal.by Yun Seong Song.Ph.D

An investigation into the function of single-neuron activity in the mesoaccumbens dopamine system of the rat

The mesoaccumbens dopamine system has been implicated in many basic psychological processes (e.g. "wanting" and "liking") and illnesses (e.g. addiction, depression, schizophrenia). However, the precise computational functions of nucleus accumbens and dopamine neurons within the system remain unknown. In this thesis, we test some of the current hypotheses regarding the function of this system using a behavioural neurophysiology approach in the rat. The first question we wanted to answer was whether nucleus accumbens neurons process reward-predictive stimuli (e.g. conditioned reinforcers) and reward delivery differently, since previous studies report equivocal findings. To do so, we trained thirsty rats to bar-press on a second-order schedule of saccharin reinforcement, within which the temporal pattern of rats' bar-pressing was reinforced by presentations of a conditioned reinforcer and primary reinforcer (reward). We found that nucleus accumbens neurons typically responded to these conditioned and primary reinforcers with opposite sign, which suggests they were processed differently. We were not sure whether responses to conditioned reinforcers encoded reward-prediction or facilitated a behavioural switch in the rat's behaviour. Indeed, since studies using a variety of experimental techniques have implicated the mesoaccumbens dopamine system in both reward prediction and behavioural switching, we sought to test whether neurons in the nucleus accumbens and dopamine-rich areas of the midbrain respond to outcome-associated stimuli to predict reward or switch behaviour. We found both sets of neurons predominantly did the former. Finally, to understand more about reward consummatory responses from both sets of neurons, we developed a rat behavioural task providing measures of reward "wanting" and "liking". In conclusion, on the basis of our data, the most parsimonious explanation for the function of the mesoaccumbens dopamine system is that it acts to modulate goal-seeking behaviour. Further research is required to identify the function of the interactions between nucleus accumbens and dopamine neurons during goal-seeking and goal consumption

Role of the Medial Septal Area in Regulating Prefrontal Theta Rhythm in Rats

Theta rhythms are electroencephalogram (EEG) waveforms between 4-12 Hz and are correlated with arousal, orientation, exploration, attention, learning and memory, motivational drives and emotions and movements. The last sixty years have been witness to a greatly increasing understanding of the underlying anatomical pathways and mechanisms necessary for theta rhythms. Today, it is well established that cells of the medial septal area (MSA) fire in a rhythmic bursting pattern to pace the theta rhythm in the hippocampus (HPC) and that lesioning the MSA abolishes theta rhythm in the HPC. However, comparatively little is known about the anatomy driving the theta rhythm of non-hippocampal areas, such as the prefrontal cortex (PFC). Therefore, this study examined whether the MSA also drives the theta rhythm in the PFC. Results indicated that selective infusions of the muscarinic receptor antagonist scopolamine into the MSA significantly decreased PFC theta power but had no effect on theta frequency. While this study has not been conducted before, these results coincide with other studies implicating the MSA as a widespread controller of theta power. Thus, it appears that the MSA affects PFC theta in the same manner as HPC theta with regards to both power and frequency