Neuroscience
-
There are experimental evidences indicating that the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist ketamine impairs cognition and produces a series of schizophrenia-like symptoms in rodents (hyperactivity, stereotypies and ataxia). The present study was designed to investigate the effects of ketamine on rats' non-spatial and spatial recognition memory. ⋯ Pre- or post-training systemic administration of ketamine (0.3, 1 and 3 mg/kg; i.p.) in a dose-dependent manner disrupted animals' performance in both these recognition memory paradigms, suggesting that this compound affected pre- and post-training memory components. The current results indicate that the non-competitive NMDA antagonist ketamine may modulate either spatial or non-spatial recognition memory.
-
In the present study, we examined whether exposing rats to a high-dose regimen of manganese chloride (Mn) during the postnatal period would depress presynaptic dopamine functioning and alter nonassociative and associative behaviors. To this end, rats were given oral supplements of Mn (750 microg/day) on postnatal days (PD) 1-21. On PD 90, dopamine transporter (DAT) immunoreactivity and [3H]dopamine uptake were assayed in the striatum and nucleus accumbens, while in vivo microdialysis was used to measure dopamine efflux in the same brain regions. ⋯ Interestingly, acquisition of a fixed ratio task was impaired in Mn-exposed rats, suggesting a deficit in procedural learning. In sum, these results indicate that postnatal Mn exposure causes persistent declines in various indices of presynaptic dopaminergic functioning. Mn-induced alterations in striatal functioning may have long-term impact on associative and nonassociative behavior.
-
The inferior colliculus is a major relay nucleus in the ascending auditory pathways that receives multiple glutamatergic inputs. Vesicular glutamate transporters 1 and 2 (VGLUT1, VGLUT2) most often have complementary non-overlapping distributions and can be used to differentiate glutamatergic inputs. The present study therefore examined co-immunolabeling of VGLUT1 and VGLUT2 in three divisions of the rat inferior colliculus. ⋯ VGLUT2 immunolabeled terminals were numerous on the soma and proximal dendrites of many medium-to-large and large neurons in the central nucleus and medium to large neurons in the dorsal cortex. There were more VGLUT2 terminals than VGLUT1 in all divisions and more VGLUT2 terminals in dorsal and lateral cortices than in the central nucleus. This study shows that VGLUT1 and VGLUT2 differentiate complementary patterns of glutamatergic inputs into the central nucleus, lateral and dorsal cortex of the inferior colliculus with VGLUT1 endings predominantly on the dendrites and VGLUT2 on both dendrites and somas.
-
Afferents to the primary startle circuit are essential for the elicitation and modulation of the acoustic startle reflex (ASR). In the rat, cochlear root neurons (CRNs) comprise the first component of the acoustic startle circuit and play a crucial role in mediating the ASR. Nevertheless, the neurochemical pattern of their afferents remains unclear. ⋯ Other subunits, such as GluR1 and GluR4 of the AMPA GluRs, were observed in glial cells neighboring unlabeled CRN cell bodies. We further confirmed the existence of noradrenergic afferents onto CRNs from the locus coeruleus by combining tyrosine hydroxylase immunohistochemistry and tract-tracing experiments. Our results provide valuable information toward understanding how CRNs might integrate excitatory and inhibitory inputs, and hence how they could elicit and modulate the ASR.
-
Comparative Study
Sound localization behavior in ferrets: comparison of acoustic orientation and approach-to-target responses.
Auditory localization experiments typically either require subjects to judge the location of a sound source from a discrete set of response alternatives or involve measurements of the accuracy of orienting responses made toward the source location. To compare the results obtained by both methods, we trained ferrets by positive conditioning to stand on a platform at the center of a circular arena prior to stimulus presentation and then approach the source of a broadband noise burst delivered from 1 of 12 loudspeakers arranged at 30 degrees intervals in the horizontal plane. Animals were rewarded for making a correct choice. ⋯ However, the final head bearing progressively undershot the target with increasing eccentricity and rarely exceeded 60 degrees to each side of the midline. In contrast to the approach-to-target responses, the accuracy of the head orienting responses did not change much with stimulus duration, suggesting that the improvement in percent correct scores with longer stimuli was due, at least in part, to re-sampling of the acoustical stimulus after the initial head turn had been made. Nevertheless, for incorrect trials, head orienting responses were more closely correlated with the direction approached by the animals than with the actual target direction, implying that at least part of the neural circuitry for translating sensory spatial signals into motor commands is shared by these two behaviors.