3 years Natural Transformation

[Ghoul]

Effects of testosterone on spatial learning and memory in adult male rats - PMC

A male advantage over females for spatial tasks has been well documented in both humans and rodents, but it remains unclear how the activational effects of testosterone influence spatial ability in males. In a series of experiments, we tested how ...

pmc.ncbi.nlm.nih.gov

"A male advantage over females for spatial tasks has been well documented in both humans and rodents, but it remains unclear how the activational effects of testosterone influence spatial ability in males. In a series of experiments, we tested how injections of testosterone influenced the spatial working and reference memory of castrated male rats. In the eight-arm radial maze, testosterone injections (0.500 mg/rat) reduced the number of working memory errors during the early blocks of testing but had no effect on the number of reference memory errors relative to the castrated control group. In a reference memory version of the Morris water maze, injections of a wide range of testosterone doses (0.0625-1.000 mg/rat) reduced path lengths to the hidden platform, indicative of improved spatial learning. This improved learning was independent of testosterone dose, with all treatment groups showing better performance than the castrated control males. Furthermore, this effect was only observed when rats were given testosterone injections starting seven days prior to water maze testing and not when injections were given only on the testing days. We also observed that certain doses of testosterone (0.250 and 1.000 mg/rat) increased perseverative behavior in a reversal-learning task. Finally, testosterone did not have a clear effect on spatial working memory in the Morris water maze, although intermediate doses seemed to optimize performance. Overall, the results indicate that testosterone can have positive activational effects on spatial learning and memory, but the duration of testosterone replacement and the nature of the spatial task modify these effects."

Key thing in this study was keeping testosterone in the physiological range.

They note earlier studies, and since this study in 2012 more recent studies have continued to demonstrate, supraphysiological test levels impair learning ability.

What caught my attention was this study (and the references here are very comprehensive if anyone wants to dig further into this topic), showing that modafinil removed the spatial learning penalty caused by supraphysiological levels of test.

https://farmaciajournal.com/wp-content/uploads/2017-02-art-19-Belaran_Karimian_275-283.pdf

 

[malfeasance]

What is the reference range for a rat?

They go up to 1mg daily (7 a week). Since humans are about 6 a day, are rats so high as 1mg a day, being such small creatures?

The researchers appear unconvinced about the nature of supraphysological doses causing a loss of spatial memory.

"In contrast to the results from our Experiment 2A, one previous study in which rats were injected with testosterone only on the days of testing showed a testosterone-induced enhancement of reference memory in the Morris water maze (Khalil et al., 2005). This difference may have been due to the supra-physiological dose of testosterone that was used (2.5 mg/rat), but another study using very high doses of testosterone (20-120 mg/kg) failed to find any effects of testosterone on performance in the Morris water maze (Naghdi et al., 2005b). Clearly more experiments are needed in the high dose range to clarify these differences, but the results of our study and some others indicate that testosterone can cause a small enhancement of spatial reference memory relative to hypogonadal individuals.

Although a wide range of testosterone doses was used in Experiment 2B (0.0625-1.000 mg/rat), the effects of testosterone on path lengths during testing day 2 were independent of dose. This suggests that there may be a low threshold for the ability of testosterone to restore spatial reference memory in hypogonadal males. This may explain why some studies with eugonadal men have failed to demonstrate a correlation between circulating testosterone levels and spatial ability (Fonda et al., 2005; Matousek and Sherwin, 2010; Puts et al., 2010). Similar to our results, some studies of aged men with relatively low testosterone levels have shown that testosterone replacement can improve spatial ability (Cherrier et al., 2001; Cherrier et al., 2005; Janowsky et al., 1994). The results of Experiment 2B do not indicate that there is an optimal dose of testosterone for spatial reference memory. This differs from our findings for spatial working memory in the water maze (Experiment 3) in which an apparent curvilinear relationship between testosterone and performance was noted. This highlights the fact that the effects of testosterone on spatial working and reference memory seem to differ.

Small, but statistically significant, effects of testosterone on spatial memory retention were observed during the probe trials in Experiment 2A. Specifically, the 0.250 mg T and 1.000 mg T groups had better memory retention than did the Control group. No significant differences in memory retention were observed in Experiment 2B, although a relatively low level of retention in the 0.500 mg T group was observed in both experiments. These results indicate that testosterone may have a small dose-dependent effect on retention of spatial reference memories."