Evolution of the amniote basal ganglia

Recent findings indicate that the basal ganglia of amniotes, i.e. modern birds, reptiles and mammals, contain similar neuronal subpopulations, as defined by the transmitters these neurons use and their connections. These data suggest that the evolution of the basal ganglia has been much more conservative than once believed and that this region of the forebrain performs a similar motor role in birds, reptiles and mammals. The basal ganglia of birds and reptiles, however, differ from those of mammals in that they appear to have their major influence over motor functions by an output to the tectum via the pretectum. In contrast, the mammalian basal ganglia are thought to have their major influence over motor functions by an output to the motor cortex via the thalamus.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24712/1/0000133.pd

Reduced Performance of Prey Targeting in Pit Vipers with Contralaterally Occluded Infrared and Visual Senses

Both visual and infrared (IR) senses are utilized in prey targeting by pit vipers. Visual and IR inputs project to the contralateral optic tectum where they activate both multimodal and bimodal neurons. A series of ocular and pit organ occlusion experiments using the short-tailed pit viper (Gloydius brevicaudus) were conducted to investigate the role of visual and IR information during prey targeting. Compared with unoccluded controls, snakes with either both eyes or pit organs occluded performed more poorly in hunting prey although such subjects still captured prey on 75% of trials. Subjects with one eye and one pit occluded on the same side of the face performed as well as those with bilateral occlusion although these subjects showed a significant targeting angle bias toward the unoccluded side. Performance was significantly poorer when only a single eye or pit was available. Interestingly, when one eye and one pit organ were occluded on opposite sides of the face, performance was poorest, the snakes striking prey on no more than half the trials. These results indicate that, visual and infrared information are both effective in prey targeting in this species, although interference between the two modalities occurs if visual and IR information is restricted to opposite sides of the brain

Auditory sensitivity exhibits sexual dimorphism and seasonal plasticity in music frogs

Seasonal changes in the structure and function of the vertebrate brain have been described in many species, particularly in seasonal breeders. However, it remains unclear whether sexual dimorphism varies between breeding seasons for specific brain regions. Auditory event-related potential (ERP) changes were evaluated in the Emei music frog (Babina daunchina) to assess sexual dimorphism and seasonal variations in auditory sensitivity. An acoustic playback experiment using an oddball paradigm design was conducted, in which two conspecific call types were used as deviant stimuli with synthesized white noise as standard stimulus. ERP components were analyzed for the telencephalon and mesencephalon of both sexes in the non-reproductive and reproductive states. Results show that auditory sensitivity is modulated by reproductive status, implying that seasonal plasticity is involved in auditory perception. Moreover, the amplitude of the N1 ERP component (mean amplitudes during the interval occurring 30-130ms after stimulus onset) is higher in females for the telencephalon and higher in males for the mesencephalon, regardless of reproductive status and acoustic stimulus type. These results show that auditory ERP responses for specific brain regions exhibit sexual dimorphism in the absence of exogenous sexual stimulation during both the two reproductive states in the music frog

Mating signals indicating sexual receptiveness induce unique spatio-temporal EEG theta patterns in an anuran species.

Female mate choice is of importance for individual fitness as well as a determining factor in genetic diversity and speciation. Nevertheless relatively little is known about how females process information acquired from males during mate selection. In the Emei music frog, Babina daunchina, males normally call from hidden burrows and females in the reproductive stage prefer male calls produced from inside burrows compared with ones from outside burrows. The present study evaluated changes in electroencephalogram (EEG) power output in four frequency bands induced by male courtship vocalizations on both sides of the telencephalon and mesencephalon in females. The results show that (1) both the values of left hemispheric theta relative power and global lateralization in the theta band are modulated by the sexual attractiveness of the acoustic stimulus in the reproductive stage, suggesting the theta oscillation is closely correlated with processing information associated with mate choice; (2) mean relative power in the beta band is significantly greater in the mesencephalon than the left telencephalon, regardless of reproductive status or the biological significance of signals, indicating it is associated with processing acoustic features and (3) relative power in the delta and alpha bands are not affected by reproductive status or acoustic stimuli. The results imply that EEG power in the theta and beta bands reflect different information processing mechanisms related to vocal recognition and auditory perception in anurans

Effect of the Level of Anesthesia on the Auditory Brainstem Response in the Emei Music Frog (Babina daunchina).

Anesthesia is known to affect the auditory brainstem response (ABR) in mice, rats, birds and lizards. The present study investigated how the level of anesthesia affects ABR recordings in an amphibian species, Babina daunchina. To do this, we compared ABRs evoked by tone pip stimuli recorded from 35 frogs when Tricaine methane sulphonate (MS-222) anesthetic immersion times varied from 0, 5 and 10 minutes after anesthesia induction at sound frequencies between 0.5 and 6 kHz. ABR thresholds increased significantly with immersion time across the 0.5 kHz to 2.5 kHz frequency range, which is the most sensitive frequency range for hearing and the main frequency range of male calls. There were no significant differences for anesthetic levels across the 3 kHz to 6 kHz range. ABR latency was significantly longer in the 10 min group than in the 0 and 5 min groups at frequencies of 0.5, 1.0, 1.5, 2.5 kHz, while ABR latency did not differ across the 3 kHz to 4 kHz range and at 2.0 kHz. Taken together, these results show that the level of anesthesia affects the amplitude, threshold and latency of ABRs in frogs

The right thalamus may play an important role in anesthesia-awakening regulation in frogs

Background. Previous studies have shown that the mammalian thalamus is a key structure for anesthesia-induced unconsciousness and anesthesia-awakening regulation. However, both the dynamic characteristics and probable lateralization of thalamic functioning during anesthesia-awakening regulation are not fully understood, and little is known of the evolutionary basis of the role of the thalamus in anesthesia-awakening regulation. Methods. An amphibian species, the South African clawed frog (Xenopus laevis) was used in the present study. The frogs were immersed in triciane methanesulfonate (MS-222) for general anesthesia. Electroencephalogram (EEG) signals were recorded continuously from both sides of the telencephalon, diencephalon (thalamus) and mesencephalon during the pre-anesthesia stage, administration stage, recovery stage and post-anesthesia stage. EEG data was analyzed including calculation of approximate entropy (ApEn) and permutation entropy (PE). Results. Both ApEn and PE values differed significantly between anesthesia stages, with the highest values occurring during the awakening period and the lowest values during the anesthesia period. There was a significant correlation between the stage durations and ApEn or PE values during anesthesia-awakening cycle primarily for the right diencephalon (right thalamus). ApEn and PE values for females were significantly higher than those for males. Discussion. ApEn and PE measurements are suitable for estimating depth of anesthesia and complexity of amphibian brain activity. The right thalamus appears physiologically positioned to play an important role in anesthesia-awakening regulation in frogs indicating an early evolutionary origin of the role of the thalamus in arousal and consciousness in land vertebrates. Sex differences exist in the neural regulation of general anesthesia in frogs