Since the time of the introduction of the spontaneously hypertensive rat (SHR) into medical research, several neuropharmacological studies have been performed on these animals which have been unrelated to their cardiovascular systems. A few of these studies have indicated possible abnormalities in the dopaminergic systems of SHR. Therefore the present study was undertaken to examine more closely the sensitivity of SHR to stimulation of their dopamine (DA) receptors.

Long-Evans rats were raised from birth to eight weeks of age at 5°C, 20°C and 30°C. Blood was taken from animals two to eight weeks of age and assayed for growth hormone and thyroid stimulating hormone. The 30°C reared rats were found to have the longest ear, tail and hind limbs, followed by the 20°C reared rats. The 5°C rats were found to have the shortest ear, tail and hind limb. The 30°C and 5°C reared rats were found to have similar masses at the termination of the experiment. The 20°C reared rats had the smallest mass. Differences in size between the three groups when compared on a weekly basis were not found to be related to weekly obtained serum levels of growth hormone and thyroid stimulating hormone. Food consumption was greatest for the 5°C reared rats followed by the 20°C reared rats. The 5°C reared rats were found to have the lowest routine metabolic rate in the 5°C chamber. The 20°C reared rats were found to have the lowest routine metabolic rate in both the 20°c and 30°C chamber. When 30°C and 20°C reared rats were put in the 5°C chamber with the 5°C reared rats, they initially lost mass, however after three weeks in the 5°C chamber they began to gain mass. The 30°C reared rats gained mass at a greater rate than did the 20°C reared rats. The 5°C reared rats continued to gain mass throughout this period. While in the 5°C chamber the total food consumption of the 20°c reared rats was the greatest, whereas the 5°C and 30°C reared rats consumed similar amounts of food.

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Merging the senses is key to perception, yet how we achieve this remains unclear. New research finds multimodality even in primary sensory areas, but its role is not understood. We address this question by using in vivo 2-photon calcium imaging in awake mice to test several hypotheses about the possible functions primary somatosensory cortex (S1) may subserve in integrating auditory and tactile sensory input. We first test whether S1 encodes pure auditory stimulus identity by training a linear classifier to decode different sounds from S1 activity. We find that decoder accuracy is slightly-but-significantly above chance, suggesting that S1 weakly encodes sounds. We then ask whether S1 encodes specific audio-tactile feature conjunctions by testing decoder performance for distinct combinations of simultaneously-presented auditory and tactile stimuli. We find that accuracy was within chance levels, indicating that sound-evoked suppression of whisker responses is auditory-stimulus non-specific. Subsequently, we test whether passive experience is sufficient to induce either a) Hebbian-like reactivation of tactile stimulus representations by correlated auditory stimuli or b) enhanced mixed selectivity. We find that passive experience results in neither effect. We also find S1’s auditory and audio-tactile encoding properties to be stable in the face of reinforcement conditioning. As part of a separate project, we also present results that reinforcement conditioning enhances encoding of time and temporal surprise in primary somatosensory cortex.

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