445
(GSI, ratio of gonad to body mass) have T and 11-KT levels that peak at the beginning
of the nesting season in May and June while reproductive females with a relatively
high GSI have well-developed eggs (~5 mm diameter) and low T and E 2 levels.
During the nesting period, “humming” type I males have signifi cantly higher circulating plasma levels of 11-KT than non-humming males (Genova et al. 2013 ). The
post-nesting period occurs during the fall months of September and October when
type I males and females exhibit a marked decrease in their GSI and in E 2 , T, and
11-KT plasma levels. The non-reproductive period occurs during the winter months
from December to February when type I males have low GSI with no sperm present
and low T and 11-KT plasma levels, whereas females have low GSI with ovaries
that contain undeveloped oocytes and low E 2 and T plasma levels.
The brief spike in E 2 levels that female midshipman exhibit approximately 30
days before the start of the breeding season led Sisneros et al. ( 2004b ) to hypothesize that E 2 or T was responsible for inducing the observed seasonal changes in
saccular afferent sensitivity (Sisneros and Bass 2003 ). Results from Sisneros et al.
( 2004a ) showed that ovariectomized non-reproductive females implanted with
either E 2 or T capsules to mimic pre-nesting steroid levels resulted in increased saccular sensitivity. Specifi cally, E 2 and T separately improved the phase-locking accuracy of saccular afferents and enhanced the encoding of the auditory afferents to
frequencies that corresponded to the dominant harmonic components of the male
advertisement call. The response profi les of the saccular afferents were shown to be
similar to the female reproductive auditory phenotype previous reported by Sisneros
and Bass ( 2003 ). Sisneros et al. ( 2004a ) also confi rmed the presence of estrogen
receptor alpha (ERα) in the sensory macula of the saccule, which provided further
evidence for direct effects of steroid hormones on the peripheral auditory system.
3 Context for Recent Studies on Catecholamines
and the Midshipman Model
While it is well established that steroid hormones such as estrogen drive seasonal
peripheral auditory plasticity in female Porichthys in order to better encode the
male’s mate call, neuromodulators downstream of steroids as well as central mechanisms are unexplored and little is known of the neural substrates that underlie the
motivation and coordinated behavioral response to auditory social signals. As discussed by Bhandiwad and Sisneros (this volume), how attention affects hearing and
perception is unexplored in fi shes, and the neurochemical components which underlie attention to sound may account for individual variability in behavioral assays.
Our studies focused on establishing if catecholamines are potential substrates for
modulation of auditory physiology and motivated auditory-driven behaviors (e.g.,
phonotaxis). Therefore, we fi rst aimed to characterize CA innervation of the central
and peripheral auditory system of midshipman . Secondly, we tested the hypotheses
that (1) innervation of the auditory system is seasonally plastic and (2) CA neurons
are activated in response to conspecifi c vocalizations.
Neuroanatomical Evidence for Catecholamines as Modulators of Audition…
(GSI, ratio of gonad to body mass) have T and 11-KT levels that peak at the beginning
of the nesting season in May and June while reproductive females with a relatively
high GSI have well-developed eggs (~5 mm diameter) and low T and E 2 levels.
During the nesting period, “humming” type I males have signifi cantly higher circulating plasma levels of 11-KT than non-humming males (Genova et al. 2013 ). The
post-nesting period occurs during the fall months of September and October when
type I males and females exhibit a marked decrease in their GSI and in E 2 , T, and
11-KT plasma levels. The non-reproductive period occurs during the winter months
from December to February when type I males have low GSI with no sperm present
and low T and 11-KT plasma levels, whereas females have low GSI with ovaries
that contain undeveloped oocytes and low E 2 and T plasma levels.
The brief spike in E 2 levels that female midshipman exhibit approximately 30
days before the start of the breeding season led Sisneros et al. ( 2004b ) to hypothesize that E 2 or T was responsible for inducing the observed seasonal changes in
saccular afferent sensitivity (Sisneros and Bass 2003 ). Results from Sisneros et al.
( 2004a ) showed that ovariectomized non-reproductive females implanted with
either E 2 or T capsules to mimic pre-nesting steroid levels resulted in increased saccular sensitivity. Specifi cally, E 2 and T separately improved the phase-locking accuracy of saccular afferents and enhanced the encoding of the auditory afferents to
frequencies that corresponded to the dominant harmonic components of the male
advertisement call. The response profi les of the saccular afferents were shown to be
similar to the female reproductive auditory phenotype previous reported by Sisneros
and Bass ( 2003 ). Sisneros et al. ( 2004a ) also confi rmed the presence of estrogen
receptor alpha (ERα) in the sensory macula of the saccule, which provided further
evidence for direct effects of steroid hormones on the peripheral auditory system.
3 Context for Recent Studies on Catecholamines
and the Midshipman Model
While it is well established that steroid hormones such as estrogen drive seasonal
peripheral auditory plasticity in female Porichthys in order to better encode the
male’s mate call, neuromodulators downstream of steroids as well as central mechanisms are unexplored and little is known of the neural substrates that underlie the
motivation and coordinated behavioral response to auditory social signals. As discussed by Bhandiwad and Sisneros (this volume), how attention affects hearing and
perception is unexplored in fi shes, and the neurochemical components which underlie attention to sound may account for individual variability in behavioral assays.
Our studies focused on establishing if catecholamines are potential substrates for
modulation of auditory physiology and motivated auditory-driven behaviors (e.g.,
phonotaxis). Therefore, we fi rst aimed to characterize CA innervation of the central
and peripheral auditory system of midshipman . Secondly, we tested the hypotheses
that (1) innervation of the auditory system is seasonally plastic and (2) CA neurons
are activated in response to conspecifi c vocalizations.
Neuroanatomical Evidence for Catecholamines as Modulators of Audition…