Seasonal difference in TH-ir innervation of the cholinergic octavolateralis efferent nucleus (OE).

<p>(A, B) Transverse sections through the rostral OE showing TH-ir fibers and terminals on somata and dendrites (d) of OE neurons labeled by choline acetyltransferase (ChAT)-ir. Data in C and D are expressed as the percent area of ChAT-ir in the OE that is covered by TH-ir fibers (mean ± SE). Mean percent area TH-ir overlap of OE somata and dendrites for animal in A = 22.4% and 33.4%; B = 17% and 29.7%, respectively. *<i>p</i> = 0.01, *** <i>p</i> = 0.0001. Abbreviations: MLF, medial longitudinal fasciculus; VIIm, facial motor nucleus. Scale bar = 100 μm.</p

Seasonal differences in TH-ir area but not cell number in the dopaminergic periventricular posterior tuberculum (TPp).

<p>(A, B) Large, pear-shaped TH-ir neurons and thick processes are seen just dorsal and lateral to the paraventricular organ (PVO) and medial to the medial forebrain bundle (MFB) along the midline in transverse section through the diencephalon. Data in C are expressed as number of TH-ir neurons per section (mean ± SE). (D) TH-ir area including cells and processes are quantified per unit area (143,139 μm²). Mean TH-ir area for animal in A = 6205.1μm²; B = 2658.4 μm². **<i>p</i> = 0.001. Scale bar = 100 μm.</p

No seasonal differences in number of TH-ir cells in the noradrenergic locus coeruleus (LC).

<p>Examples of small numbers of clustered TH-ir neurons just lateral to the fourth ventricle (IV) characteristic of the LC in transverse sections through the isthmal brainstem in summer (A) and winter (B) animals. Mean ± SE for number of TH-ir cells/ section = 4.2 ± 0.37 (summer) and 4.7 ± 0.21 (winter). Scale bar = 100 μm.</p

Seasonal comparison of TH-ir fiber density in the auditory system.

<p>Arrows indicate direction of significant differences between reproductive (summer) and non-reproductive (winter) females.</p><p>TH-ir, tyrosine hydroxylase immunoreactivity.</p><p>*<i>P</i>-values represent results from 2-tailed independent groups t-test.</p><p>Seasonal comparison of TH-ir fiber density in the auditory system.</p

Seasonal differences in dopaminergic but not cholinergic innervation of the saccule, the main endorgan of hearing.

<p>(A, B) Transverse sections through the saccular epithelium. TH-ir and ChAT-ir puncta are largely concentrated at the base of hair cells and within the support cell layer. HC and SC labels point to DAPI-stained nuclei of individual hair cells and support cells, respectively. The rest of the hair cell is unlabeled and is a light purple background. Stereocillia (unlabeled) are located at the apical end of the hair cells. Quantification of numbers (C) and size (D) of putative TH-ir and ChAT-ir terminals (puncta) in the saccule (mean ± SE). Arrowhead in B indicates an example of a thick, varicose TH-ir fiber along the base of the SC layer that was excluded from the puncta analysis. Colors in the graphs match TH-ir and ChAT-ir in the micrographs. Mean number of puncta per image for animal in A = 41.4; B = 68.7. Mean area per punctum for animal A = 0.63 μm²; B = 0.78 μm². *<i>p</i> = 0.017, **<i>p</i> = 0.001. Scale bar = 25 μm.</p

Example micrographs showing no seasonal differences in TH-ir fiber density in transverse sections through (A, B) anterior tuberal hypothalamus (AT), (C, D) torus semicircularis (TS) and (D, E) ventral division of secondary octaval nucleus (SOv).

<p>Mean ± SE TH-ir density for summer vs. winter: AT (15.22% ± 0.74/ 11.68% ± 2.7); TS (16.30% ± 1.5/ 14.28% ± 1.0); SOv (4.12% ± 0.44/ 3.94% ± 0.25). Scale bar = 100 μm.</p

Seasonal differences in TH-ir fiber density in forebrain auditory nuclei.

<p>(A, B) central posterior nucleus of the thalamus (CP) and (D, E) lateral division of nucleus preglomerulosus (PGl). Left edge in A and B is midline of brain. Left edge in D and E is lateral edge of brain. Data in C and F are represented as percent area of the nucleus that contains TH-ir (mean ± SE). Mean TH-ir density for animal in A = 9.9%; B = 5.8%; D = 4.5%; E = 1.9%. *<i>p</i> = 0.03; *** <i>p</i> = 0.0003. Scale bar = 100 ¼m.</p

Seasonal differences in dopaminergic neuron number in the forebrain.

<p>(A, B) Clusters of small TH-ir cells (arrowheads) located in the lateral region of the anterior parvocellular preoptic nucleus (PPa). (D, E) Sparse numbers of TH-ir cells (arrowheads) in the anterior tuberal hypothalamus (AT). Data in C and D are expressed as number of TH-ir neurons per section (mean ± SE). Mean number of neurons per section for animal in A = 14; B = 32; D = 0; E = 0.6. **<i>p</i> = 0.001. Scale bar = 100 μm.</p

Seasonal comparison of catecholaminergic neuron number.

<p>Arrows indicate direction of significant differences between reproductive (summer) and non-reproductive (winter) females.</p><p>TH, tyrosine hydroxylase.</p><p>*<i>P</i>-values represent results from 2-tailed independent groups t-test.</p><p>^†Statistical difference is uncertain due to an unequal number of sections sampled between groups.</p><p>Seasonal comparison of catecholaminergic neuron number.</p

A representative series of line drawings illustrating rostro-caudal distribution of major tyrosine hydroxylase immunoreactive (TH-ir) cell populations (large dots), fibers (lines) and terminals (small dots) in the midshipman brain covering areas analyzed in the current study (adapted from [24]).

<p>Abbreviations: ac, anterior commissure; AT, anterior tuberal nucleus; CA, cerebral aqueduct; cc, cerebellar crest; Cm, molecular layer of the corpus of the cerebellum; Cg, granular layer of the corpus of the cerebellum; CP, central posterior nucleus of the thalamus; Df, diffuse nucleus of the hypothalamus; dl, dorsolateral division of the descending octaval nucleus; Dl, lateral zone of area dorsalis of the telencephalon; dm, dorsomedial division of the descending octaval nucleus; Dm, medial zone of area dorsalis of the telencephalon; G, nucleus glomerulosus; Ha, habenula; Hc, central periventricular hypothalamus; Hd, dorsal periventricular hypothalamus; Hv, ventral periventricular hypothalamus; iaf, internal arcuate fiber tract; IV, fourth ventricle; LC, locus coeruleus; ll, lateral lemniscus; MED, medial octavolateralis nucleus; MFB, medial forebrain bundle; MLF, medial longitudinal fasciculus; OB, olfactory bulb; OE, octavolateralis efferent nucleus; OT, optic tract; PAG, periaqueductal gray; Pe, periventricular cell layer of the torus semicircularis; PPa, anterior parvocellular preoptic nucleus; PGl, lateral division of nucleus preglomerulosus; Pit, pituitary; PTN, posterior tuberal nucleus; PTT, paratoral tegmentum; PVO, paraventricular organ; RF, reticular formation; SR, superior raphe; SV, saccus vasculosus; Te, midbrain tectum; TPp, periventricular posterior tuberculum; TS, torus semicircularis; Vc, central nucleus of area ventralis of the telencephalon; Vd, dorsal nucleus of area ventralis of the telencephalon; Vde, descending tract of the trigeminal nerve; VL, ventrolateral nucleus of the thalamus; VM, ventromedial nucleus of the thalamus; Vp, postcommissural nucleus of area ventralis of the telencephalon; Vs, supracommissural nucleus of area ventralis of the telencephalon; vT, ventral tuberal hypothalamus. Scale bar = 500 μm.</p